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Colorants, Volume 1, Issue 1 (March 2022) – 7 articles

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30 pages, 9410 KiB  
Review
Melanin-Binding Colorants: Updating Molecular Modeling, Staining and Labeling Mechanisms, and Biomedical Perspectives
by Juan C. Stockert, Jesús Espada and Alfonso Blázquez-Castro
Colorants 2022, 1(1), 91-120; https://0-doi-org.brum.beds.ac.uk/10.3390/colorants1010007 - 24 Feb 2022
Cited by 2 | Viewed by 3365
Abstract
Melanin and melanoma tumors are two fields of increasing interest in biomedical research. Melanins are ubiquitous biopigments with adaptive value and multiple functions, and occur in the malignant melanoma. Although several chemical structures have been proposed for eumelanin, molecular modeling and orbitals indicate [...] Read more.
Melanin and melanoma tumors are two fields of increasing interest in biomedical research. Melanins are ubiquitous biopigments with adaptive value and multiple functions, and occur in the malignant melanoma. Although several chemical structures have been proposed for eumelanin, molecular modeling and orbitals indicate that a planar or spiral benzoquinone-porphycene polymer would be the model that better explains the broad-band light and ultrasound absorption, electric conductivity, and graphite-like organization shown by X-ray crystallography and electron microscopy. Lysosomes and melanosomes are selectively labeled by vital probes, and melanin also binds to metal cations, colorants, and drugs, with important consequences in pharmacology, pathology, and melanoma therapy. In addition to traditional and recent oncologic treatments, photodynamic, photothermal, and ultrasound protocols represent novel modalities for melanoma therapy. Since eumelanin is practically the ideal photothermal and ultrasound sensitizer, the vibrational decay from photo-excited electrons after NIR irradiation, or the electrochemical production of ROS and radicals after ultrasound absorption, induce an efficient heating or oxidative response, resulting in the damage and death of tumor cells. This allows repetitive treatments due to the remaining melanin contained in tumoral melanophages. Given that evolution and prognosis of the advanced melanoma is still a concern, new biophysical procedures based on melanin properties can now be developed and applied. Full article
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33 pages, 10111 KiB  
Article
Stability of Rhodamine Lactone Cycle in Solutions: Chain–Ring Tautomerism, Acid–Base Equilibria, Interaction with Lewis Acids, and Fluorescence
by Olena M. Obukhova, Nikolay O. Mchedlov-Petrossyan, Natalya A. Vodolazkaya, Leonid D. Patsenker and Andrey O. Doroshenko
Colorants 2022, 1(1), 58-90; https://0-doi-org.brum.beds.ac.uk/10.3390/colorants1010006 - 24 Feb 2022
Cited by 3 | Viewed by 3320
Abstract
The equilibrium between different tautomers that can be colored or colorless is an important feature for rhodamine dyes. Presently, this phenomenon is mostly discussed for rhodamine B. Herein, we studied the tautomerism and acid–base dissociation (HR+ ⇄ R + H+) [...] Read more.
The equilibrium between different tautomers that can be colored or colorless is an important feature for rhodamine dyes. Presently, this phenomenon is mostly discussed for rhodamine B. Herein, we studied the tautomerism and acid–base dissociation (HR+ ⇄ R + H+) of a set of rhodamines in organic media. Form R is an equilibrium mixture of the colored zwitterion R± and colorless lactone R0. Absorption spectra in 90 mass% aqueous acetone reflects the correlation between the dyes structure and the equilibrium constant, KT = [R0]/[R±]. Increase in the pKa value on transferring from water to organic solvents confirms the highly polar character of the R± tautomer. To reveal the role of the solvent nature, the tautomerism of an asymmetrical rhodamine, 2-(12-(diethyliminio)-2,3,5,6,7,12-hexahydro-1H-chromeno[2,3-f]pyrido[3,2,1-ij]quinolin-9-yl)benzoate, was examined in 14 media. This chain–ring tautomerism is an intramolecular acid–base reaction; the central carbon atom acts as a Lewis acid. The interaction with other Lewis acids, Li+, Ca2+, Mg2+, and La3+, results in rupture of lactone cycle. In polar solvents, lactones undergo photocleavage resulting in formation of highly fluorescent R±, whereas the blue fluorescence and abnormally high Stokes shift in low-polar media may be explained either by another photoreaction or by spiroconjugation and charge transfer in the exited state. Full article
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20 pages, 1894 KiB  
Systematic Review
Pigment Coloration Research Published in the Science Citation Index Expanded from 1990 to 2020: A Systematic Review and Bibliometric Analysis
by Mohammad Tajul Islam, Mohammad Sahariar Farhan, Farzana Faiza, A. F. M. Fahad Halim and Afsana Al Sharmin
Colorants 2022, 1(1), 38-57; https://0-doi-org.brum.beds.ac.uk/10.3390/colorants1010005 - 14 Feb 2022
Cited by 10 | Viewed by 5768
Abstract
A systematic review and bibliometric study were undertaken utilizing the Science Citation Index Expanded database from 1990 to 2020 to obtain insights into the trajectory of pigment coloration research. The study focused on the publication performance in terms of the yearly production and [...] Read more.
A systematic review and bibliometric study were undertaken utilizing the Science Citation Index Expanded database from 1990 to 2020 to obtain insights into the trajectory of pigment coloration research. The study focused on the publication performance in terms of the yearly production and citations, as well as mainstream journals, categories of the Web of Sciences, leading nations, well-known institutions, and research trends. The survey found that the yearly output of scholarly publications on pigment coloration research climbed gradually throughout the first quarter of the study period and then increased substantially in the latter five years. The present research emphasis and future trends were examined after summarizing the paper title and abstract analyses, author keyword analysis, and the most regularly used keywords derived from words in KeyWords Plus. To expand its reach in numerous application areas, pigment coloration research will continue to focus on improving pigment qualities. Full article
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18 pages, 3316 KiB  
Article
Concentration-Dependent Association of Flavylium Chloride with Differential Hydroxy Moieties in Ethanol
by Anthony Pagan, Jong I. Lee and Jeonghee Kang
Colorants 2022, 1(1), 20-37; https://0-doi-org.brum.beds.ac.uk/10.3390/colorants1010004 - 23 Dec 2021
Cited by 1 | Viewed by 3073
Abstract
Flavylium ions (6a6e) were synthesized using Aldol condensation to compare the spectroscopic properties caused by the different numbers and locations of hydroxy groups on the flavylium cations (AH+). Without the addition of acid, increasing the concentration [...] Read more.
Flavylium ions (6a6e) were synthesized using Aldol condensation to compare the spectroscopic properties caused by the different numbers and locations of hydroxy groups on the flavylium cations (AH+). Without the addition of acid, increasing the concentration of flavylium ions to 10 mM in ethanol led to the following observation. The flavylium ions with the least number of OH groups (6a and 6b) showed a change in peak at higher concentrations, whereas 6c and 6d did not show the same degree of change in their 1H-NMR signals. This suggests an equilibrium that shifts the isomers B, CE, and Cz more towards the flavylium ion with more OH groups even at low concentrations. One possibility for the cause of this shift is that the flavylium ions become more stable through aggregation. In addition to the NMR results, the UV measurements confirmed that isomers with fewer OH groups showed a more dramatic shift towards the flavylium ion at higher concentrations. Using modeling data at DFT//B3LYP/6311**G(d) level, the self-association was investigated to show that the hydrogen bonding of OH groups is the main player but cannot stabilize entirely without the presence of the chloride ion in the complex. Full article
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15 pages, 4433 KiB  
Article
Cation–Anionic Interactions of Dyes in Aqueous Solutions: Bromocresol Purple in the Processes of Dissimilar Association
by Serghey A. Shapovalov
Colorants 2022, 1(1), 5-19; https://0-doi-org.brum.beds.ac.uk/10.3390/colorants1010003 - 22 Dec 2021
Viewed by 2532
Abstract
The interaction between single- or double-charged anions of bromocresol purple (BP) and cyanine cations (quinaldine blue, QB, or quinaldine red, QR) at concentrations of dyes 5.0·10−7–4.0·10−5 mol/L has been investigated by vis-spectroscopy. The thermodynamic constants of dissimilar associations (K [...] Read more.
The interaction between single- or double-charged anions of bromocresol purple (BP) and cyanine cations (quinaldine blue, QB, or quinaldine red, QR) at concentrations of dyes 5.0·10−7–4.0·10−5 mol/L has been investigated by vis-spectroscopy. The thermodynamic constants of dissimilar associations (Kas) have been studied. Comparison of the values of lg Kas shows that QB associates of BP are more stable (6.61 ± 0.07) than QR associates (4.84 ± 0.06); a similar phenomenon is observed for associates of the BP2 anion. Semi-empirical calculations (PM3 method) are in agreement with the vis-spectroscopy data and indicate that the association of dye into an associate is possible. The standard enthalpies of formation of associates (ΔfHo) and energy diagrams have been determined. The ΔfHo data indicate that the formation of an associate between dye ions is an energetically favourable process. The gain in energy significantly exceeds the systematic error of semi-empirical calculations and increases from 157 kJ/mol (associate ”BP + QB+”) to 729 kJ/mol (associate “BP2− + QR+”). The most probable structures of dissimilar associates are presented. The study of the dissimilar association develops the concept of intermolecular interactions in solutions. Full article
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2 pages, 172 KiB  
Editorial
Publisher’s Note to Launch Colorants—A Scientific Journal of Dyes, Pigments and Color Chemistry
by Shu-Kun Lin
Colorants 2022, 1(1), 3-4; https://0-doi-org.brum.beds.ac.uk/10.3390/colorants1010002 - 17 Sep 2021
Cited by 1 | Viewed by 2296
Abstract
On 11 May 2010, the code ISSN 2079-6447 was obtained for Colorants following an application to the ISSN Center in Paris [...] Full article
3 pages, 467 KiB  
Editorial
Colorants: A New Journal Bringing Colour to Life
by Anthony Harriman
Colorants 2022, 1(1), 1-2; https://0-doi-org.brum.beds.ac.uk/10.3390/colorants1010001 - 14 Sep 2021
Cited by 2 | Viewed by 1806
Abstract
Colorant: A substance which is used to impart colour to another material! [...] Full article
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