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Special Issue "Chiroptical Techniques"

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A special issue of Molecules (ISSN 1420-3049).

Deadline for manuscript submissions: closed (15 December 2011)

Special Issue Editor

Guest Editor
Prof. Dr. Stig Allenmark (Website)

Department of Chemistry and Molecular Biology, Goteborg University, SE-41296 Goteborg, Sweden
Phone: +46 31 932315
Fax: +46 317723840
Interests: enantioselectivity in chromatography and in catalytic reactions; chiroptical methods for solving stereochemical problems

Special Issue Information

Dear Colleagues,

As we all know, chirality plays a cruical role in the chemistry of living systems, since the macromolecules involved in the life processes are chiral. Therefore, proteins are often able to discriminate between enantiomers, which, among other things, has consequences for chiral compounds with pharmacological activity, where the enantiomers may show large differences in uptake, action, and metabolization. As a result, chiroptical techniques for studies and characterization of optically active compounds have become of great importance and today a multitude of methods based on the use of chiral light exist. Some of these can be coupled to enantioselective chromatographic separation techniques and used for detection, others can be used together with results from theoretical calculations of spectra for the determination of absolute configuration or -conformation. Of great interest here is the use of infrared radiation to study vibrational optical activity (VOA) and particularly the use of vibrational CD (VCD), since here the number of useful optically active transitions is larger than in electronic CD (ECD). Ab initio calculations of VCD spectra are also easier to perform. Thus, the variety of chiroptical techniques available or under development today has catalyzed stereochemical research and the instrumentation is continuously improved.

This Special Issue on Chiroptical Techniques is intended to attract researchers dealing with optically active compounds who want to contribute their latest results to the forum of Molecules. It is my hope that a good deal of interesting papers will be submitted that will reflect the potential and rapid development of the use of chiroptical techniques for studies in the chemical and associated fields.

Dr. Stig Allenmark
Guest Editor

Keywords

  • optical activity
  • circular birefringence
  • polarimetry
  • electric and magnetic transition moments
  • optical rotation
  • optical rotatory dispersion (ORD)
  • Cotton effect
  • anisotropic refraction
  • anisotropic absorption
  • circular dichroism (CD) spectroscopy
  • rotational strength
  • circularly polarised light (cpl)
  • dissymmetry factor
  • fluorescence detected CD (FDCD)
  • anisotropic emission
  • circular polarization of emission (CPE)
  • circularly polarized luminescence (CPL)
  • sector rules
  • octant rule
  • absolute conformation
  • absolute configuration
  • induced CD
  • solid-state CD
  • coupled HPLC-CD
  • exciton coupling
  • exciton chirality
  • bisignate CD curves
  • couplets
  • time-resolved CD (TRCD)
  • CD of anisotropic phases
  • vibrational optical activity (VOA)
  • Raman optical activity (ROA)
  • vibrational circular dichroism (VCD)
  • theoretical calculation of CD-spectra

Published Papers (5 papers)

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Research

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Open AccessArticle Synthesis of Stable and Soluble One-Handed Helical Homopoly(substituted acetylene)s without the Coexistence of Any Other Chiral Moieties via Two-Step Polymer Reactions in Membrane State: Molecular Design of the Starting Monomer
Molecules 2012, 17(1), 433-451; doi:10.3390/molecules17010433
Received: 15 December 2011 / Revised: 28 December 2011 / Accepted: 30 December 2011 / Published: 4 January 2012
Cited by 4 | PDF Full-text (1651 KB)
Abstract
A soluble and stable one-handed helical poly(substituted phenylacetylene) without the coexistence of any other chiral moieties was successfully synthesized by asymmetric-induced polymerization of a chiral monomer followed by two-step polymer reactions in membrane state: (1) removing the chiral groups (desubstitution); [...] Read more.
A soluble and stable one-handed helical poly(substituted phenylacetylene) without the coexistence of any other chiral moieties was successfully synthesized by asymmetric-induced polymerization of a chiral monomer followed by two-step polymer reactions in membrane state: (1) removing the chiral groups (desubstitution); and (2) introduction of achiral long alkyl groups at the same position as the desubstitution to enhance the solubility of the resulting one-handed helical polymer (resubstitution). The starting chiral monomer should have four characteristic substituents: (i) a chiral group bonded to an easily hydrolyzed spacer group; (ii) two hydroxyl groups; (iii) a long rigid hydrophobic spacer between the chiral group and the polymerizing group; (iv) a long achiral group near the chiral group. As spacer group a carbonate ester was selected. The two hydroxyl groups formed intramolecular hydrogen bonds stabilizing a one-handed helical structure in solution before and after the two-step polymer reactions in membrane state. The rigid long hydrophobic spacer, a phenylethynylphenyl group, enhanced the solubility of the starting polymer, and realized effective chiral induction from the chiral side groups to the main chain in the asymmetric-induced polymerization. The long alkyl group near the chiral group avoided shrinkage of the membrane and kept the reactivity of resubstitution in membrane state after removing the chiral groups. The g value (g = ([θ]/3,300)/ε) for the CD signal assigned to the main chain in the obtained final polymer was almost the same as that of the starting polymer in spite of the absence of any other chiral moieties. Moreover, since the one-handed helical structure was maintained by the intramolecular hydrogen bonds in a solution, direct observation of the one-handed helicity of the final homopolymer has been realized in CD for the solution for the first time. Full article
(This article belongs to the Special Issue Chiroptical Techniques)
Open AccessArticle Chiroptical Measurement of Chiral Aggregates at Liquid-Liquid Interface in Centrifugal Liquid Membrane Cell by Mueller Matrix and Conventional Circular Dichroism Methods
Molecules 2011, 16(5), 3636-3647; doi:10.3390/molecules16053636
Received: 21 March 2011 / Revised: 18 April 2011 / Accepted: 19 April 2011 / Published: 29 April 2011
Cited by 8 | PDF Full-text (304 KB)
Abstract
The centrifugal liquid membrane (CLM) cell has been utilized for chiroptical studies of liquid-liquid interfaces with a conventional circular dichroism (CD) spectropolarimeter. These studies required the characterization of optical properties of the rotating cylindrical CLM glass cell, which was used under the [...] Read more.
The centrifugal liquid membrane (CLM) cell has been utilized for chiroptical studies of liquid-liquid interfaces with a conventional circular dichroism (CD) spectropolarimeter. These studies required the characterization of optical properties of the rotating cylindrical CLM glass cell, which was used under the high speed rotation. In the present study, we have measured the circular and linear dichroism (CD and LD) spectra and the circular and linear birefringence (CB and LB) spectra of the CLM cell itself as well as those of porphyrine aggregates formed at the liquid-liquid interface in the CLM cell, applying Mueller matrix measurement method. From the results, it was confirmed that the CLM-CD spectra of the interfacial porphyrin aggregates observed by a conventional CD spectropolarimeter should be correct irrespective of LD and LB signals in the CLM cell. Full article
(This article belongs to the Special Issue Chiroptical Techniques)

Review

Jump to: Research

Open AccessReview Chiroptical Switches: Applications in Sensing and Catalysis
Molecules 2012, 17(2), 1247-1277; doi:10.3390/molecules17021247
Received: 28 December 2011 / Revised: 18 January 2012 / Accepted: 20 January 2012 / Published: 31 January 2012
Cited by 26 | PDF Full-text (2616 KB)
Abstract
Chiroptical switches have found application in the detection of a multitude of different analytes with a high level of sensitivity and in asymmetric catalysis to offer switchable stereoselectivity. A wide range of scaffolds have been employed that respond to metals, small molecules, [...] Read more.
Chiroptical switches have found application in the detection of a multitude of different analytes with a high level of sensitivity and in asymmetric catalysis to offer switchable stereoselectivity. A wide range of scaffolds have been employed that respond to metals, small molecules, anions and other analytes. Not only have chiroptical systems been used to detect the presence of analytes, but also other properties such as oxidation state and other physical phenomena that influence helicity and conformation of molecules and materials. Moreover, the tunable responses of many such chiroptical switches enable them to be used in the controlled production of either enantiomer or diastereomer at will in many important organic reactions from a single chiral catalyst through selective use of a low-cost inducer: Co-catalysts (guests), metal ions, counter ions or anions, redox agents or electrochemical potential, solvents, mechanical forces, temperature or electromagnetic radiation. Full article
(This article belongs to the Special Issue Chiroptical Techniques)
Figures

Open AccessReview Two-Photon Polarization Dependent Spectroscopy in Chirality: A Novel Experimental-Theoretical Approach to Study Optically Active Systems
Molecules 2011, 16(4), 3315-3337; doi:10.3390/molecules16043315
Received: 2 March 2011 / Revised: 7 April 2011 / Accepted: 12 April 2011 / Published: 18 April 2011
Cited by 14 | PDF Full-text (1267 KB)
Abstract
Many phenomena, including life itself and its biochemical foundations are fundamentally rooted in chirality. Combinatorial methodologies for catalyst discovery and optimization remain an invaluable tool for gaining access to enantiomerically pure compounds in the development of pharmaceuticals, agrochemicals, and flavors. Some exotic [...] Read more.
Many phenomena, including life itself and its biochemical foundations are fundamentally rooted in chirality. Combinatorial methodologies for catalyst discovery and optimization remain an invaluable tool for gaining access to enantiomerically pure compounds in the development of pharmaceuticals, agrochemicals, and flavors. Some exotic metamaterials exhibiting negative refractive index at optical frequencies are based on chiral structures. Chiroptical activity is commonly quantified in terms of circular dichroism (CD) and optical rotatory dispersion (ORD). However, the linear nature of these effects limits their application in the far and near-UV region in highly absorbing and scattering biological systems. In order to surmount this barrier, in recent years we made important advancements on a novel non linear, low-scatter, long-wavelength CD approach called two-photon absorption circular dichroism (TPACD). Herein we present a descriptive analysis of the optics principles behind the experimental measurement of TPACD, i.e., the double L-scan technique, and its significance using pulsed lasers. We also make an instructive examination and discuss the reliability of our theoretical-computational approach, which uses modern analytical response theory, within a Time-Dependent Density Functional Theory (TD-DFT) approach. In order to illustrate the potential of this novel spectroscopic tool, we first present the experimental and theoretical results obtained in C2-symmetric, axially chiral R-(+)-1,1'-bi(2-naphthol), R-BINOL, a molecule studied at the beginning of our investigation in this field. Next, we reveal some preliminary results obtained for (R)-3,3′-diphenyl-2,2′-bi-1-naphthol, R-VANOL, and (R)-2,2′-diphenyl-3,3′-(4-biphenanthrol), R-VAPOL. This family of optically active compounds has been proven to be a suitable model for the structure-property relationship study of TPACD, because its members are highly conjugated yet photo-stable, and easily derivatized at the 5- and 6-positions. With the publication of these outcomes we hope to motivate more members of the scientist community to engage in state-of-the-art TPACD spectroscopy. Full article
(This article belongs to the Special Issue Chiroptical Techniques)
Open AccessReview Synthesis and Conformation of Substituted Chiral Binaphthyl-Azobenzene Cyclic Dyads with Chiroptical Switching Capabilities
Molecules 2011, 16(2), 1603-1624; doi:10.3390/molecules16021603
Received: 10 January 2011 / Revised: 2 February 2011 / Accepted: 11 February 2011 / Published: 14 February 2011
Cited by 9 | PDF Full-text (1115 KB)
Abstract
Optically active binaphthyl-azobenezene cyclic dyads were synthesized to develop a photochromic switching molecule. Azobenezene moieties were cis-trans isomerized by photoirradiation. As a reflection of the structural change, the specific optical rotation and circular dichroism underwent significant shifts. Under certain conditions, [...] Read more.
Optically active binaphthyl-azobenezene cyclic dyads were synthesized to develop a photochromic switching molecule. Azobenezene moieties were cis-trans isomerized by photoirradiation. As a reflection of the structural change, the specific optical rotation and circular dichroism underwent significant shifts. Under certain conditions, the positive-negative and zero-positive (or zero-negative) signals were reversed. Optical rotation may potentially be applied in noise-cancelling nondestructive photoswiches. The conformations were studied by experimental and theoretical methods. The results revealed that the helical chirality, (P) or (M), of the cis-azobenzene moiety was induced by intramolecular axial chirality. The twist direction depended on the axial chirality as well as the azobenzene linkage position to the binaphthyls, but was independent of the identity of substituted groups. 2,2’-Linked-(R)-binaphthyl was found to induce cis-(P)-azobenzene, whereas symmetrically 7,7’-linked-(R)-binaphthyl was found to induce cis-(M)-azobenzene. Full article
(This article belongs to the Special Issue Chiroptical Techniques)

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