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12 pages, 3111 KiB

Open AccessArticle

Surface Characterization of Modified Electrodes Based on 4-(Azulen-1-yl)-2,6-bis((E)-2-(thiophen-2-yl)vinyl)pyridine

by Irinela Chilibon, Adina-Maria Păun, Cristina Vasiliu, Elena Diacu, Raluca Isopescu and Eleonora-Mihaela Ungureanu

Symmetry 2022, 14(12), 2506; https://doi.org/10.3390/sym14122506 - 27 Nov 2022

Viewed by 991

Abstract

Sensitive electrodes based on complexing azulene polymer films were prepared by electrochemical deposition on glassy carbon electrodes. The characterization of 4-(azulen-1-yl)-2,6-bis((E)-2-(thiophen-2-yl)vinyl)pyridine (M) and its polymerization were performed by voltammetric methods on glassy carbon disk working electrodes in millimolar solutions of acetonitrile [...] Read more.

Sensitive electrodes based on complexing azulene polymer films were prepared by electrochemical deposition on glassy carbon electrodes. The characterization of 4-(azulen-1-yl)-2,6-bis((E)-2-(thiophen-2-yl)vinyl)pyridine (M) and its polymerization were performed by voltammetric methods on glassy carbon disk working electrodes in millimolar solutions of acetonitrile in the presence of 0.1 M tetrabutylammonium perchlorate (TBAP). The films containing complexing (thiophen-2-yl)vinyl symmetrically substituted pyridine fragments were deposited either by scanning or by controlled potential electrolysis (CPE). Investigation and morphological characterization of samples by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Atomic Force Microscopy (AFM), Fourier Transform IR Spectroscopy (FTIR), and fluorescence showed particular features of the CMEs obtained at variable potentials and charges and suggested the conservation the complexing units in the films. The characterization methods for chemically modified electrodes (CMEs) were chosen depending on the desired uses of this monomer for heavy metal sensors or optical applications, respectively. Full article

(This article belongs to the Special Issue Electrochemical Behavior of the Nonbenzenoid Aromatic Hydrocarbon Azulene and Its Derivatives)

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15 pages, 3849 KiB

Open AccessFeature PaperArticle

Properties Assessment by Quantum Mechanical Calculations for Azulenes Substituted with Thiophen– or Furan–Vinyl–Pyridine

by Oana Ciocirlan, Eleonora-Mihaela Ungureanu, Alina-Alexandra Vasile (Corbei) and Amalia Stefaniu

Symmetry 2022, 14(2), 354; https://doi.org/10.3390/sym14020354 - 10 Feb 2022

Cited by 1 | Viewed by 1387

Abstract

In this paper, azulenes substituted with thiophen– or furan–vinyl–pyridine are reported as heavy metal ligands in systems based on chemically modified electrodes. We undertook a computational study of their structures using density functional theory (DFT). Based on these computations, we obtained properties and [...] Read more.

In this paper, azulenes substituted with thiophen– or furan–vinyl–pyridine are reported as heavy metal ligands in systems based on chemically modified electrodes. We undertook a computational study of their structures using density functional theory (DFT). Based on these computations, we obtained properties and key molecular descriptors related to chemical reactivity and electrochemical behavior. We investigated the correlation between some quantum parameters associated with the chemical reactivity and the complexing properties of the modified electrodes based on these ligands. The best correlations for the parameters were retained. We showed that the linear correlation between DFT-computed HOMO/LUMO energies and experimental redox potentials is very good. Full article

(This article belongs to the Special Issue Electrochemical Behavior of the Nonbenzenoid Aromatic Hydrocarbon Azulene and Its Derivatives)

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13 pages, 3840 KiB

Open AccessArticle

Polyazulene Based Materials for Heavy Metal Ions Detection. 4. Search for Conditions for Thiophen-Vinyl-Pyridine-Azulene Based CMEs Preparation

by Eleonora-Mihaela Ungureanu, Veronica Anăstăsoaie, Magdalena-Rodica Bujduveanu, Alina-Giorgiana Brotea, Raluca Isopescu and Gabriela Stanciu

Symmetry 2022, 14(2), 225; https://doi.org/10.3390/sym14020225 - 24 Jan 2022

Cited by 1 | Viewed by 1774

Abstract

The present work is connected to the study of electrode conditioning issues for the chemically modified electrodes (CMEs) prepared based on 2,6-bis((E)-2-(thiophen-2-yl)vinyl)-4-(5-isopropyl- 3,8-dimethylazulen-1-yl) pyridine (L). L is irreversibly electrooxidized to polymers leading to L-CMEs. The recognition experiments are the final [...] Read more.

The present work is connected to the study of electrode conditioning issues for the chemically modified electrodes (CMEs) prepared based on 2,6-bis((E)-2-(thiophen-2-yl)vinyl)-4-(5-isopropyl- 3,8-dimethylazulen-1-yl) pyridine (L). L is irreversibly electrooxidized to polymers leading to L-CMEs. The recognition experiments are the final test of chosen parameters (electropolymerization potential and charge in controlled potential electrolysis (CPE), anodic limit of the overoxidation cycles (OC), number of OC, anodic limit of the equilibration cycles (EC), number of EC, pH of the buffer solutions for HMs accumulation, complexation time, potential and time of reduction). The evidence of film deposition resulted by the change of ferrocene symmetrical signal characteristics on bare electrode in ferrocene solution was the simplest way to prove the formation of L-CMEs. However, finding the best electrode equilibration conditions turned out to be a source of increasing the analytical performance for the CMEs, especially those dedicated to the detection of Pb. The paper underlines the importance of understanding the role of each varied parameter, and of carrying out a systematic study of each possible variable. Optimum conditions for Pb ions analysis, using this new thiophen-vinyl-pyridine-azulene based CMEs, have been established, in order to get the best conditions for its detection in water. Full article

(This article belongs to the Special Issue Electrochemical Behavior of the Nonbenzenoid Aromatic Hydrocarbon Azulene and Its Derivatives)

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18 pages, 3747 KiB

Open AccessArticle

Surface Characterization of New Azulene-Based CMEs for Sensing

by Veronica Anăstăsoaie, Cristian Omocea, Laura-Bianca Enache, Liana Anicăi, Eleonora-Mihaela Ungureanu, Jacobus (Koos) Frederick van Staden and Marius Enăchescu

Symmetry 2021, 13(12), 2292; https://doi.org/10.3390/sym13122292 - 2 Dec 2021

Cited by 4 | Viewed by 1645

Abstract

Films of 2-(azulen-1-yldiazenyl)-5-phenyl-1,3,4-thiadiazole (T) were successfully deposited on glassy carbon surfaces to prepare chemically modified electrodes (CMEs). Their surface characterization was analyzed by electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). This complexing monomer has been [...] Read more.

Films of 2-(azulen-1-yldiazenyl)-5-phenyl-1,3,4-thiadiazole (T) were successfully deposited on glassy carbon surfaces to prepare chemically modified electrodes (CMEs). Their surface characterization was analyzed by electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). This complexing monomer has been deposited through direct electropolymerization in conditions established during the electrochemical characterization of T performed by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and rotating disk electrode voltammetry (RDE). These methods put in evidence the high degree of asymmetry of oxidation and reduction curves, which is due to the irreversible processes occurring at opposite potentials. The film formation was confirmed by ferrocene redox assay probe. The properties of the electrodes modified with T (T-CMEs) were investigated for sensing heavy metal (HM) ions in water solutions, with promising results for Pb(II) among Cd(II), Cu(II), and Hg(II) ions. Full article

(This article belongs to the Special Issue Electrochemical Behavior of the Nonbenzenoid Aromatic Hydrocarbon Azulene and Its Derivatives)

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17 pages, 3378 KiB

Open AccessArticle

Polyazulene-Based Materials for Heavy Metal Ion Detection. 3. (E)-5-((6-t-Butyl-4,8-dimethylazulen-1-yl) diazenyl)-1H-tetrazole-Based Modified Electrodes

by Laura-Bianca Enache, Veronica Anăstăsoaie, Cecilia Lete, Alina Giorgiana Brotea, Ovidiu-Teodor Matica, Cristina-Andreea Amarandei, Jérémy Brandel, Eleonora-Mihaela Ungureanu and Marius Enăchescu

Symmetry 2021, 13(9), 1642; https://doi.org/10.3390/sym13091642 - 7 Sep 2021

Cited by 4 | Viewed by 1702

Abstract

A recently synthesized azulene-tetrazole molecular receptor is proposed in this paper to continue the series of azulene substituted compounds that have been developed to build polyazulene-based materials for heavy metal (HM) ion detection. This study focuses on characterization of (E)-5-((6-t-butyl-4,8-dimethylazulen-1-yl) diazenyl)-1H-tetrazole [...] Read more.

A recently synthesized azulene-tetrazole molecular receptor is proposed in this paper to continue the series of azulene substituted compounds that have been developed to build polyazulene-based materials for heavy metal (HM) ion detection. This study focuses on characterization of (E)-5-((6-t-butyl-4,8-dimethylazulen-1-yl) diazenyl)-1H-tetrazole (L) by electrochemical techniques in view of its use for designing electrochemical sensors for HM ion complexation. The character of redox processes was proved by cyclic, differential pulse, and rotating disk electrode voltammetry. An in-depth thermodynamic study of the complexation properties of the free ligand with Pb(II) and Cd(II) from aqueous solutions was performed, and the stoichiometry and stability constant values were determined. Chemically modified electrodes (CMEs) based on L (L-CMEs) prepared by controlled potential electrolysis (CPE) at different applied potentials and charges were characterized by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Their surface morphology was examined by scanning electron microscopy (SEM). The complexing properties of L-CMEs were investigated towards the detection of HM ions by anodic stripping and compared to the stability constants of the complexes in solution. Voltametric curves showed well-defined peaks for Pb (II), Cd (II), Cu (II) and Hg (II), but the responses differ from each other and vary depending on the ion concentrations in the accumulation solutions. The best results were obtained for Pb(II) and Cd(II) ions. The results obtained for Pb(II) are promising and can be used for its analysis in water solutions (detection limit of about 10⁻⁹ M). Full article

(This article belongs to the Special Issue Electrochemical Behavior of the Nonbenzenoid Aromatic Hydrocarbon Azulene and Its Derivatives)

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19 pages, 2675 KiB

Open AccessArticle

Evaluation of (Z)-5-(Azulen-1-ylmethylene)-2-thioxothiazolidin-4-ones Properties Using Quantum Mechanical Calculations

by Alina-Alexandra Vasile (Corbei), Eleonora-Mihaela Ungureanu, Gabriela Stanciu, Mihaela Cristea and Amalia Stefaniu

Symmetry 2021, 13(8), 1462; https://doi.org/10.3390/sym13081462 - 10 Aug 2021

Cited by 2 | Viewed by 1686

Abstract

Derivatives of (Z)-5-(azulen-1-ylmethylene)-2-thioxothiazolidin-4-one are reported as heavy metal (HM) ligands in heterogeneous systems based on chemically modified electrodes. Their ability to coordinate HMs ions has recently been shown to be very selective. In this context, an additional computer-assisted study of their structure was [...] Read more.

Derivatives of (Z)-5-(azulen-1-ylmethylene)-2-thioxothiazolidin-4-one are reported as heavy metal (HM) ligands in heterogeneous systems based on chemically modified electrodes. Their ability to coordinate HMs ions has recently been shown to be very selective. In this context, an additional computer-assisted study of their structure was performed using density functional theory (DFT) to achieve a complex structural analysis. Specific molecular descriptors and properties related to their reactivity and electrochemical behaviour were calculated. The correlation between certain quantum parameters associated with the general chemical reactivity and the complexing properties of the modified electrodes based on these ligands was carried out to facilitate the design of molecular sensors. Good linear correlations between DFT-calculated HOMO/LUMO energies and experimental redox potentials were found. A good agreement between the chemical shifts predicted by the DFT method and those determined experimentally from NMR data for these ligands demonstrated the accuracy of the calculations to assess the structural data. Such a computational approach can be used to evaluate other properties, such as electrochemical properties for similar azulene derivatives. Full article

(This article belongs to the Special Issue Electrochemical Behavior of the Nonbenzenoid Aromatic Hydrocarbon Azulene and Its Derivatives)

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8 pages, 1842 KiB

Open AccessArticle

1-Vinylazulenes with Oxazolonic Ring-Potential Ligands for Metal Ion Detectors; Synthesis and Products Properties

by Mihaela Cristea, Liviu Bîrzan, Florea Dumitrascu, Cristian Enache, Victorita Tecuceanu, Anamaria Hanganu, Constantin Drăghici, Călin Deleanu, Alina Nicolescu, Maria Maganu and Alexandru C. Razus

Symmetry 2021, 13(7), 1209; https://doi.org/10.3390/sym13071209 - 6 Jul 2021

Cited by 6 | Viewed by 2200

Abstract

As a continuation of research on 1-vinylazulenes synthesis, on their physico–chemical properties as well as on their use as colorimetric and electrochemical materials for the detection of heavy metals ions, new compounds, 4-(azulen-1-ylmethylene)-2-phenyloxazol-5(4H)-ones, are reported. The exceptional structure of azulene moiety with symmetrical [...] Read more.

As a continuation of research on 1-vinylazulenes synthesis, on their physico–chemical properties as well as on their use as colorimetric and electrochemical materials for the detection of heavy metals ions, new compounds, 4-(azulen-1-ylmethylene)-2-phenyloxazol-5(4H)-ones, are reported. The exceptional structure of azulene moiety with symmetrical electron distribution only with respect to the x-axis gives some special chemical and physical properties to compounds in which it is inserted. Various azulene-1-carbaldehydes and hippuric acids are condensed with good yields in Erlenmeyer—Plöchl reaction conditions. The obtained 1-vinylzulenes were characterized and their UV-Vis and NMR spectra were briefly discussed. Full article

(This article belongs to the Special Issue Electrochemical Behavior of the Nonbenzenoid Aromatic Hydrocarbon Azulene and Its Derivatives)

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11 pages, 3672 KiB

Open AccessArticle

Recognition of Heavy Metal Ions by Using E-5-((5-Isopropyl-3,8-Dimethylazulen-1-yl) Dyazenyl)-1H-Tetrazole Modified Electrodes

by Adina-Maria Păun, Ovidiu-Teodor Matica, Veronica Anăstăsoaie, Laura-Bianca Enache, Elena Diacu and Eleonora-Mihaela Ungureanu

Symmetry 2021, 13(4), 644; https://doi.org/10.3390/sym13040644 - 11 Apr 2021

Cited by 7 | Viewed by 1402

Abstract

Chemically modified electrodes (CMEs) based on polymeric films of E-5-((5-isopropyl-3,8-dimethylazulen-1-yl) diazenyl)-1H-tetrazole (L) deposited on the surface of the glassy carbon electrode have been used for the recognition of heavy metal (Me) ions. The electrochemical study of L was done by three [...] Read more.

Chemically modified electrodes (CMEs) based on polymeric films of E-5-((5-isopropyl-3,8-dimethylazulen-1-yl) diazenyl)-1H-tetrazole (L) deposited on the surface of the glassy carbon electrode have been used for the recognition of heavy metal (Me) ions. The electrochemical study of L was done by three methods: differential pulse voltammetry (DPV), cyclic voltammetry (CV), and rotating disk electrode voltammetry (RDE). The CV, DPV, and RDE studies for L were performed at different concentrations in 0.1 M tetrabutylammonium perchlorate solutions in acetonitrile. The polymeric films were formed by successive cycling or by controlled potential electrolysis (CPE). The film formation was proven by recording the CV curves of the CMEs in ferrocene solution. The CMEs prepared at different charges or potentials were used for detection of heavy metal ions. Synthetic samples of heavy metal ions (Cd(II), Pb(II), Cu(II), Hg(II)) of concentrations between 10⁻⁸ and 10⁻⁴ M were analyzed. The most intense signal was obtained for Pb(II) ion (detection limit of about 10⁻⁸ M). Pb(II) ion can be detected by these CMEs in waters at such concentrations. The ability of the ligand L to form complexes with Pb(II) and Hg(II) ions was also tested by UV-Vis spectrometry. The obtained results showed the formation of Me(II)L₂ complexes. Full article

(This article belongs to the Special Issue Electrochemical Behavior of the Nonbenzenoid Aromatic Hydrocarbon Azulene and Its Derivatives)

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12 pages, 2949 KiB

Open AccessEditor’s ChoiceArticle

Electrochemical Comparison on New (Z)-5-(Azulen-1-Ylmethylene)-2-Thioxo-Thiazolidin-4-Ones

by Eleonora-Mihaela Ungureanu, Mariana Popescu (Apostoiu), Georgiana-Luiza Tatu (Arnold), Liviu Birzan, Raluca Isopescu, Gabriela Stanciu and George-Octavian Buica

Symmetry 2021, 13(4), 588; https://doi.org/10.3390/sym13040588 - 2 Apr 2021

Cited by 7 | Viewed by 1945

Abstract

Three (Z)-5-(azulen-1-ylmethylene)-2-thioxo-thiazolidin-4-ones are electrochemically characterized by cyclic voltammetry, differential pulse voltammetry, and rotating disk electrode voltammetry. The electrochemical investigations revealed that the redox potential is influenced by the number and position of the alkyl groups, and the possible oxidation mechanism is proposed. These [...] Read more.

Three (Z)-5-(azulen-1-ylmethylene)-2-thioxo-thiazolidin-4-ones are electrochemically characterized by cyclic voltammetry, differential pulse voltammetry, and rotating disk electrode voltammetry. The electrochemical investigations revealed that the redox potential is influenced by the number and position of the alkyl groups, and the possible oxidation mechanism is proposed. These compounds, after their immobilization on glassy carbon electrodes during oxidative electropolymerization, were examined as complexing ligands for heavy metal ions from aqueous solutions through adsorptive stripping voltammetry. Full article

(This article belongs to the Special Issue Electrochemical Behavior of the Nonbenzenoid Aromatic Hydrocarbon Azulene and Its Derivatives)

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Review

Jump to: Research

21 pages, 4208 KiB

Open AccessEditor’s ChoiceReview

Azulene Moiety as Electron Reservoir in Positively Charged Systems; A Short Survey

by Alexandru C. Razus

Symmetry 2021, 13(4), 526; https://doi.org/10.3390/sym13040526 - 24 Mar 2021

Cited by 14 | Viewed by 3714

Abstract

The non-alternant aromatic azulene, an isomer of alternant naphthalene, differs from the latter in peculiar properties. The large polarization of the π-electron system over the seven and five rings gives to azulene electrophile property a pronounced tendency to donate electrons to an acceptor, [...] Read more.

The non-alternant aromatic azulene, an isomer of alternant naphthalene, differs from the latter in peculiar properties. The large polarization of the π-electron system over the seven and five rings gives to azulene electrophile property a pronounced tendency to donate electrons to an acceptor, substituted at azulene 1 position. This paper presents cases in which azulene transfers electrons to a suitable acceptor as methylium ions, positive charged heteroaromatics and examples of neutral molecules that can accept electrons. The proposed product synthesis was outlined and the expected electron transfer was highlighted by analyzing the NMR, UV-Vis spectra and the pK_R⁺ values. Full article

(This article belongs to the Special Issue Electrochemical Behavior of the Nonbenzenoid Aromatic Hydrocarbon Azulene and Its Derivatives)

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