Factors Affecting the Formation of 2:1 Host:Guest Inclusion Complexes of 2-[(R-Phenyl)amine]-1,4-naphthalenediones (PAN) in β- and γ-Cyclodextrins

The molecular hosts cyclodextrins form inclusion complexes with a wide variety of guests, resulting in complexes with various host:guest stoichiometries. In the case of a series of 19 1,4-naphthoquinolines as guests with either β- or γ-cyclodextrin studied using electrospray mass spectroscopy, in most cases only 1:1 complexes were observed, with 2:1 host:guest complexes observed in just 6 out of 38 host:guest combinations. It is shown that these higher-order complexes were observed only in the case of small (or no) electronically withdrawing substituents, and were much less likely in the case of the larger γ-cyclodextrin host. The size and electronic properties of the substituents involved shows that both steric and electronic factors must be taken into account in predicting which cyclodextrin host:guest stoichiometries will be stable enough to form (or once formed, be robust enough to be observed in the ESI-MS experiments). It is clear that the prediction of host-guest stoichiometry for a specific host-guest pair is complicated, and involves a subtle interplay of both electronic and steric factors. However, there are definite trends, which can be used to help predict host:guest stoichiometry for a given host-guest pair.


Introduction
Cyclodextrins (CDs), the cyclic oligomers of glucopyranose, are by far the most commonly used organic host compounds for the inclusion of organic guest molecules [1][2][3]. The inclusion of guest molecules into cyclodextrin host cavities results in significant changes to the guest properties, including solubility [4], spectroscopic properties [5] and stability [6]. These effects of cyclodextrin inclusion have been utilized in a wide variety of research and commercial applications [1][2][3], including in chromatography [7], trace analysis [8], drug delivery [9], guest stabilization [6], food science [6] and industrial applications [10].
However, it remains challenging to predict the stoichiometry of cyclodextrin host:guest inclusion complexes. In a broad sense, consideration of the size of the guest will to some extent help to predict this stoichiometry, as guests that are small relative to the native cyclodextrin host cavity diameter will tend to form 1:2 CD:guest complexes [11]; those that are similar in size to the CD cavity will form 1:1 complexes [12]; and those that are significantly larger (or in particular significantly longer) than fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely β-and γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely β-and γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely β-and γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely β-and γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely β-and γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes. We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely β-and γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely β-and γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes. We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely β-and γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. Guest R1 (meta) R2 (para) 1:1 β-CD 2:1 β-CD 1:1 γ-CD 2:1 γ-CD Molecules 2016, 21, 1568 3 of 13 fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely β-and γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes. We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely β-and γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. Guest R1 (meta) R2 (para) 1:1 β-CD 2:1 β-CD 1:1 γ-CD 2: Molecules 2016, 21, 1568 3 of 13 fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. Guest R1 (meta) R2 (para) 1:1 β-CD 2:1 β-CD 1:1 γ-CD 2: Molecules 2016, 21, 1568 3 of 13 fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely β-and γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others.
Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes. We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely β-and γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. Guest R1 (meta) R2 (para) 1:1 β-CD 2:1 β-CD 1:1 γ-CD 2:

Me H
Molecules 2016, 21, 1568 3 of 13 fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. Guest R1 (meta) R2 (para) 1:1 β-CD 2:1 β-CD 1:1 γ-CD 2: Molecules 2016, 21, 1568 3 of 13 fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. Guest R1 (meta) R2 (para) 1:1 β-CD 2:1 β-CD 1:1 γ-CD 2: Molecules 2016, 21, 1568 3 of 13 fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. Guest R1 (meta) R2 (para) 1:1 β-CD 2:1 β-CD 1:1 γ-CD 2: 21,1568 fascinated by the observed persistence of 2:1 complexes in the case of certain derivative gue their rather unusual behaviour under ESI conditions, and the reasons why some substitut derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in assure the formation and observation of only the most stable multi-cyclodextrin adduct ion the Wen group used protected CDs [32], many unexpected reactions took place, for dealkylation or sharing of guests between cyclodextrin hosts. For this reason we prefe suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, wh an appropriate cavity size for these guests. Furthermore, we decided to perform m modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observin significant differences justifying the stability of some of these complexes and the absence o Overall, our interest in unusual, uncommon or simply strange structures, proposed structures observed under ESI conditions, was undertaken to rationalise the observed co using the thermodynamic calculations via molecular modelling (MM+ in particular as a firs develop a hypothesis for their formation and in particular to explain the unusual stability in of some of these complexes. We present herein the comparison of the data obtained from the mass spectrometry o PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corres data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelli experimental and calculated data and results will be discussed in the following Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the s experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization e observed the complex ions), and were only observed at a relatively high excess of CD. A discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely β-and γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others.
Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes. We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely β-and γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely β-and γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others.
Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes. We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely β-and γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed.

H Et
Molecules 2016, 21, 1568 3 of 13 fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. Guest R1 (meta) R2 (para) 1:1 β-CD 2:1 β-CD 1:1 γ-CD 2:1 γ-CD fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely β-and γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes. We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely β-and γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed.  fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely β-and γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes. We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely β-and γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed.

H Me
Molecules 2016, 21, 1568 3 of 13 fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. Guest R1 (meta) R2 (para) 1:1 β-CD 2:1 β-CD 1:1 γ-CD 2:1 γ-CD fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. Guest R1 (meta) R2 (para) 1:1 β-CD 2:1 β-CD 1:1 γ-CD 2:1 γ-CD fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. Guest R1 (meta) R2 (para) 1:1 β-CD 2:1 β-CD 1:1 γ-CD 2:1 γ-CD 21,1568 fascinated by the observed persistence of 2:1 complexes in the case of certain derivative gue their rather unusual behaviour under ESI conditions, and the reasons why some substitut derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in assure the formation and observation of only the most stable multi-cyclodextrin adduct ion the Wen group used protected CDs [32], many unexpected reactions took place, for dealkylation or sharing of guests between cyclodextrin hosts. For this reason we prefe suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, wh an appropriate cavity size for these guests. Furthermore, we decided to perform m modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observin significant differences justifying the stability of some of these complexes and the absence o Overall, our interest in unusual, uncommon or simply strange structures, proposed structures observed under ESI conditions, was undertaken to rationalise the observed co using the thermodynamic calculations via molecular modelling (MM+ in particular as a firs develop a hypothesis for their formation and in particular to explain the unusual stability in of some of these complexes. We present herein the comparison of the data obtained from the mass spectrometry o PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corres data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelli experimental and calculated data and results will be discussed in the following Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the s experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization e observed the complex ions), and were only observed at a relatively high excess of CD. A discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest host:guest complexes were observed.  fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. Guest R1 (meta) R2 (para) 1:1 β-CD 2:1 β-CD 1:1 γ-CD 2:1 γ-CD fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely β-and γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others.
Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes. We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely β-and γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed.   fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. Guest R1 (meta) R2 (para) 1:1 β-CD 2:1 β-CD 1:1 γ-CD 2:1 γ-CD fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely β-and γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others.
Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes. We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely β-and γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed.   fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely β-and γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes. We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely β-and γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed.   fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely β-and γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes. We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely β-and γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. Guest R1 (meta) R2 (para) 1:1 β-CD 2:1 β-CD 1:1 γ-CD 2: fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed. fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed.
fascinated by the observed persistence of 2:1 complexes in the case of certain derivative guests, and their rather unusual behaviour under ESI conditions, and the reasons why some substituted PAN derivatives showed 2:1 complexation in the ESI-MS results, but the majority did not. In order to follow this trend we used in our ESI experiments the condition of excess of cyclodextrin in order to assure the formation and observation of only the most stable multi-cyclodextrin adduct ions. When the Wen group used protected CDs [32], many unexpected reactions took place, for example dealkylation or sharing of guests between cyclodextrin hosts. For this reason we preferred, as suggested by Kobetic [33], using the "native" CDs of differing size, namely βand γ-CD, which have an appropriate cavity size for these guests. Furthermore, we decided to perform molecular modelling studies of the 1:1 and 2:1 host:guest complexes, with the goal of observing some significant differences justifying the stability of some of these complexes and the absence of others. Overall, our interest in unusual, uncommon or simply strange structures, proposed for ion structures observed under ESI conditions, was undertaken to rationalise the observed complexes using the thermodynamic calculations via molecular modelling (MM+ in particular as a first step) to develop a hypothesis for their formation and in particular to explain the unusual stability in solution of some of these complexes.
We present herein the comparison of the data obtained from the mass spectrometry of the 19 PAN dyes (shown in Figure 1 and Table 1) and two CDs, namely βand γ-CD, and the corresponding data of calculated energies for 1:1 and 2:1 complexes obtained via molecular modelling. The experimental and calculated data and results will be discussed in the following sections. Surprisingly, the 1:1 complexes between PAN and CD are not easily formed under the standard experimental conditions for ESI/PI (methanol, drop of formic acid, optimized ionization energy to observed the complex ions), and were only observed at a relatively high excess of CD. As will be discussed below, under such excess CD conditions, 1:1 and in the case of some host-guest pairs 2:1 host:guest complexes were observed.

Electrospray Ionization Mass Spectroscopy (ESI-MS) Studies
ESI-MS experiments were performed for all 19 guests in both β-and γ-CD; the results of these experiments in terms of the observation of host:guest inclusion complexes, and their stoichiometry, are presented in Table 1. Representative ESI-MS spectra for the host β-CD itself, as well as the two  Considering the shape of the PAN guests, as shown in Figure 1, it is most likely that the phenyl ring of the aniline moiety is being included in the 1:1 complexes, due to the large steric hindrance caused by the two carbonyls on the quinone moiety. In other words, K1 is expected to be larger than K1'. This preference of inclusion of the anilino moiety over the quinone end is also supported by our molecular mechanics calculations, as will be discussed in Section 3.2.
It is observed that the formation of 2:1 complexes is more likely with β-CD (occurs with four PAN derivative guests) than with γ-CD (occurs only with two PAN derivative guests). This makes sense, considering the relative size of these two hosts: γ-CD is much larger than β-CD, so there is more likely to be unfavourable steric interaction between the two hosts in the case of γ-CD, making the encapsulation of the guest by a second host less likely. Furthermore, the cavity of γ-CD is larger than that of β-CD, making it more likely that the guest can be completely encapsulated within a single host cavity. The reason why only certain guests are encapsulated by β-and γ-CD will be discussed in Section 3.3, by considering the electronic properties of these different guests. In all six cases in which 2:1 host:guest inclusion complexes were observed, 1:1 complexes were also observed to varying relative concentrations. This indicates a stepwise equilibrium formation of these 2:1 complexes, as follows: with equilibrium binding constants K 1 and K 2 for Equilibria 1 and 2, respectively. The magnitude of the binding (formation) constants K 1 and K 2 cannot be determined from ESI-MS experiments, only the presence (or absence) of these complexes. The ESI-MS experiments provide direct and unequivocal determination of not only the formation of inclusion complexes but also the varying host:guest ratios (stoichiometries) observed. However, no experimental information is provided by this technique on the nature of these complexes (nor the magnitude of the binding constants, as discussed above), for example the specific orientation in which all or part of the PAN guest fits inside the CD cavity. In the case of PAN, as shown in Figure 1, it is possible to form 1:1 complexes by inclusion by the CD of either the anilino or quinone moiety ends. Complexation of either of these anilino or quinine complexes by a second host CD would then result in the same 2:1 complex formed. This results in a somewhat complex mechanism for the stepwise formation of the 2:1 complexes from initial 1:1 complexes as proposed above, due to the possibility of two different 1:1 intermediate complexes. This full set of equilibria is illustrated in Figure 3; in this case two different 1:1 binding constants, K 1 and K 1 ' (as indicated by Equilibrium 1 above), are needed, for the formation of anilino or quinone complexes, respectively, and also two pairs of 2:1 binding constants, K 2 and K 2 ' (as indicted by Equilibrium 2), for the addition of the second host CD to either the anilino or quinone 1:1 complexes, respectively.

Molecular Modeling Studies
Molecular modeling calculations were performed for all 19 PAN derivatives as guests encapsulated in the β-CD, to estimate the stabilization energy obtained by complexation (which provides an indication of the relative binding constants). Both modes of encapsulation for 1:1 inclusion were examined and compared, i.e., encapsulation of the anilino moiety (anilino complex) vs. encapsulation of the quinone moiety (quinone complex). Table 2 lists the results of the molecular modeling calculations for the stability of each of the two types of 1:1 complex with β-CD for each of the 19 guests, in terms of ΔE, the difference in energy between the complex and the free host and guest. Also listed is the value of ΔE for the formation of the 2:1 complex, in which both ends of the guest PAN are encapsulated by a β-CD host. Table 2. Molecular modeling calculations for the energy stabilization upon complexation (ΔE, in kcal/mol) for the inclusion of the 19 PAN derivatives, as 1:1 (anilino encapsulation), 1:1 (quinone encapsulation), or 2:1 (both ends encapsulated) complexes. Considering the shape of the PAN guests, as shown in Figure 1, it is most likely that the phenyl ring of the aniline moiety is being included in the 1:1 complexes, due to the large steric hindrance caused by the two carbonyls on the quinone moiety. In other words, K 1 is expected to be larger than K 1 '. This preference of inclusion of the anilino moiety over the quinone end is also supported by our molecular mechanics calculations, as will be discussed in Section 2.2.

ΔE ΔE ΔE
It is observed that the formation of 2:1 complexes is more likely with β-CD (occurs with four PAN derivative guests) than with γ-CD (occurs only with two PAN derivative guests). This makes sense, considering the relative size of these two hosts: γ-CD is much larger than β-CD, so there is more likely to be unfavourable steric interaction between the two hosts in the case of γ-CD, making the encapsulation of the guest by a second host less likely. Furthermore, the cavity of γ-CD is larger It should be mentioned that in the ESI-MS experiments, only complexes which survive the ionization process are observed. Thus, there is a small possibility that 2:1 complexes form in most cases (especially considering the experimental conditions of a large excess of cyclodextrin), but that such complexes fall apart under MS-ESI conditions for all but a few of the PAN derivatives, resulting in only 1:1 complexes, either anilino (most likely), quinone, or both, being observed in the ESI experiments. This possibility is depicted in Figure 5. . Hypothesis for the lack of observed 2:1 complexes in the case of most PAN derivatives: loss of one CD host to form 1:1 complexes, either anilino or quinone (consistent with the overall scheme shown in Figure 3).
derivative, and the effect of the specific substituents, has a major effect on determining the resulting host-guest stoichiometry, as does the size of the host CD cavity. Molecular modeling studies showed that 1:1 complexation most likely involves encapsulation of the aniline rather than the quinone moiety, and indicated large stabilization upon 2:1 complexation. Consideration of the Hammett parameters of the substituents showed that 2:1 host-guest complexes formed only with PAN derivatives with small substituents with negative σ m or σ p values, i.e., for guests with electron donating substituents. This trend indicates that higher electron density on the aromatic ring encourages complexation by 2 host molecules. However, larger alkyl substituents with negative σ m and σ p parameters did not yield 2:1 complexes, even for the larger γ-CD host, showing that steric effects in terms of guest size are also highly important. It is clear that the prediction of host-guest stoichiometry for a specific host-guest pair is complicated, and involves a subtle interplay of both electronic and steric factors. However, as demonstrated in this paper, there are trends in terms of the electronic nature of the guest and the size of both the guest and host, which can be used to help predict the expected host:guest stoichiometry for a given host-guest pair.