Research

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11 pages, 896 KiB

Open AccessArticle

Azaphilones Pigments from the Fungus Penicillium hirayamae

by Coralie Pavesi, Victor Flon, Grégory Genta-Jouve, Elodie Pramil, Alexandre Escargueil, Adeel Nasir, Tristan Montier, Xavier Franck and Soizic Prado

Colorants 2023, 2(1), 31-41; https://doi.org/10.3390/colorants2010003 - 25 Jan 2023

Cited by 1 | Viewed by 1352

Abstract

The use of fungal pigments as dyes is attractive for various industries. Fungal pigments arise a strong interest because they are suitable for large-scale industrial production and have none of the drawbacks of synthetic pigments. Their advantages over synthetic or vegetal dyes mark [...] Read more.

The use of fungal pigments as dyes is attractive for various industries. Fungal pigments arise a strong interest because they are suitable for large-scale industrial production and have none of the drawbacks of synthetic pigments. Their advantages over synthetic or vegetal dyes mark them as a prime target. Azaphilones are fungal polyketides pigments bearing a highly oxygenated pyranoquinone bicyclic core produced by numerous species of ascomyceteous and basidiomyceteous fungi. In order to find new azaphilones dyes, the fungal strain Penicillium hirayamae U., a known producer of azaphilone but, chemically, barely studied so far, was investigated by molecular networking and led to the isolation of three new azaphilones, penazaphilone J-L, along with the known penazaphilone D, isochromophilone VI, and sclerketide E. Their structures were determined based on extensive NMR and the absolute configurations by ECD. All compounds were evaluated for their cytotoxic activity against human cell lines and human pathogenic-resistant strains. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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12 pages, 5118 KiB

Open AccessArticle

Exploring the Colors of Copper-Containing Pigments, Copper (II) Oxide and Malachite, and Their Origins in Ceramic Glazes

by Iris Peng, Katie Hills-Kimball, Isabela Miñana Lovelace, Junyu Wang, Matthew Rios, Ou Chen and Li-Qiong Wang

Colorants 2022, 1(4), 376-387; https://doi.org/10.3390/colorants1040023 - 26 Sep 2022

Cited by 2 | Viewed by 2614

Abstract

The colors of copper-containing pigments, copper (II) oxide and malachite, and their origins in ceramic glazes were systematically examined over a wide firing temperature range using a suite of analytical and spectroscopy techniques including SEM, UV-Vis FORS, XRD, FTIR, and EPR to gain [...] Read more.

The colors of copper-containing pigments, copper (II) oxide and malachite, and their origins in ceramic glazes were systematically examined over a wide firing temperature range using a suite of analytical and spectroscopy techniques including SEM, UV-Vis FORS, XRD, FTIR, and EPR to gain new insight into the structural and chemical transformations of the glaze during firing. The two colorants investigated were black copper (II) oxide (CuO) nanopowder and blue-green basic copper carbonate, or malachite (Cu₂CO₃(OH)₂), both of which produce a final light blue color following firing. Additionally, silicon carbide (SiC) was used to locally reduce CuO to simulate firing glazes in a reductive environment and produce a final red color. At lower temperatures, malachite was found to decompose to form CuO at 550 °C, elucidating the reason that two different copper colorants could be used interchangeably to form the same “Robin’s Egg Blue” color. At 850 °C, a glaze sintering process occurred, resulting in the distribution of Cu²⁺ in a square planar geometry and an observed blue color. This structural change occurred at temperatures lower than the glaze’s melting point, indicating that complete vitrification of the glaze is not required for glaze coloration. Conversely, the reduction in Cu²⁺ to Cu⁺ through the addition of SiC did not occur until the glaze was fired above the melting temperature (1000 °C), signifying that high temperatures are required for the redox reaction to occur. This study sheds light on intermediate colorant-glaze interactions that are beneficial for understanding and predicting glaze coloring upon exposure to varying temperatures, and the results from this study can be applied to better-controlled glaze production for artists and a deeper appreciation of ceramic glaze chemistry and aesthetics. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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13 pages, 1602 KiB

Open AccessArticle

Can X-ray Diffraction Distinguish Natural from Anthropogenic Hematite? Replication of the Conversion of Natural Goethite in Both Furnace and Campfire

by Jules C. Picuri, Julia M. Natoli, Sophia E. Shaw, Shruthi P. Shyam, Stephen R. VanHoesen, Zhenyu Lin and Walter J. Bowyer

Colorants 2022, 1(3), 363-375; https://doi.org/10.3390/colorants1030022 - 06 Sep 2022

Cited by 1 | Viewed by 1433

Abstract

Hematite, the mineral that gives color to bright red iron ochres, occurs naturally, but there is much evidence that early humans sometimes artificially produced hematite by heating a related mineral, goethite, in wood fires. This represents an important cognitive and technological advance in [...] Read more.

Hematite, the mineral that gives color to bright red iron ochres, occurs naturally, but there is much evidence that early humans sometimes artificially produced hematite by heating a related mineral, goethite, in wood fires. This represents an important cognitive and technological advance in early human prehistory. Thus, there is a need to distinguish natural hematite from hematite generated by heating goethite in a wood fire. Measuring the line widths of powder X-ray diffraction (XRD) in hematite has been explored, and synthetic goethite heated in a modern furnace has been used as a model system for studying this process. We now show that to be an inappropriate model. Although chemically identical, natural goethite is physically different from and much more variable than goethite produced in a laboratory. Furthermore, by replicating the process using Stone Age technology, we show that heating goethite in a wood fire complicates the interpretation of XRD line widths of the resulting hematite. We conclude that strategies other than powder XRD are necessary to draw conclusions about the ancient processing of iron ochres. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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9 pages, 2277 KiB

Open AccessArticle

Substituent Control of Near-Infrared Absorption of Triphenylamine Radical Cation

by Masafumi Yano, Mai Sasaoka, Kohei Tamada, Misaki Nakai, Tatsuo Yajima, Koichi Mitsudo and Yukiyasu Kashiwagi

Colorants 2022, 1(3), 354-362; https://doi.org/10.3390/colorants1030021 - 01 Aug 2022

Cited by 1 | Viewed by 2333

Abstract

Five triphenyltriphenylamines with various substituents were investigated as precursors for near-infrared absorbing materials. Cyclic voltammetry (CV) studies showed that they all give stable radical cations in solution. The radical cations obtained by one-electron chemical oxidation of these compounds show strong absorption in the [...] Read more.

Five triphenyltriphenylamines with various substituents were investigated as precursors for near-infrared absorbing materials. Cyclic voltammetry (CV) studies showed that they all give stable radical cations in solution. The radical cations obtained by one-electron chemical oxidation of these compounds show strong absorption in the near-infrared region, and the position of the absorption is strongly influenced by the substituent. DFT (density functional theory) calculations suggest that the introduction of stronger electron-donating substituents would result in a smaller HOMO–SOMO energy gap and thus a larger long wavelength shift, which is consistent with the experimental results. On the other hand, strong electron-withdrawing substituents increase the HOMO–SOMO energy gap, resulting in a short wavelength shift. The position of the near-infrared absorption peak of the triphenylamine radical cation can be controlled to the longer or shorter wavelength direction depending on the substituent. A molecular design of near-infrared absorbing dyes utilizing the electronic effects of substituents is described. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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7 pages, 2384 KiB

Open AccessArticle

Synthesis and Color Evaluation of Tb⁴⁺-Doped Na₂ZrO₃ for Inorganic Yellow Pigments

by Ryohei Oka, Tomoyo Nouchi and Toshiyuki Masui

Colorants 2022, 1(3), 347-353; https://doi.org/10.3390/colorants1030020 - 01 Aug 2022

Cited by 1 | Viewed by 1713

Abstract

Tb⁴⁺-doped sodium zirconate samples, Na₂Zr_1−xTb_xO₃, were synthesized as novel environmentally friendly inorganic yellow pigments by a conventional solid-state reaction method. Their crystal structures, optical properties, and colors were characterized. A single-phase form [...] Read more.

Tb⁴⁺-doped sodium zirconate samples, Na₂Zr_1−xTb_xO₃, were synthesized as novel environmentally friendly inorganic yellow pigments by a conventional solid-state reaction method. Their crystal structures, optical properties, and colors were characterized. A single-phase form was obtained for the samples in the x range of x ≤ 0.18, while impurity phases were detected for the sample with x = 0.20. All samples showed strong optical absorption in the blue light region, due to the charge transfer transition between O²⁻ and Tb⁴⁺. As a result, the sample color became yellow, which is the complementary color of blue, and the color became more vivid with increasing Tb⁴⁺ content in the single-phase region. Among the samples, Na₂Zr₀.₈₂Tb₀.₁₈O₃ was the optimal composition, with the highest yellowness (b* = +67.2) and pure yellow hue (h° = 90.1). Although the b* value was lower than commercial yellow pigments such as BiVO₄ and ZrSiO₄:Pr, this sample had a purer yellow hue. Since Na₂Zr_0.82Tb_0.18O₃ is composed of non-toxic elements, it could be a new environmentally friendly inorganic yellow pigment. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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9 pages, 2294 KiB

Open AccessArticle

Photonics of Halogenated Zinc(II) and Cadmium(II) Dipyrromethene Complexes

by Iuliia Aksenova, Elena Bocharnikova and Maria Ashmarina

Colorants 2022, 1(3), 298-306; https://doi.org/10.3390/colorants1030018 - 09 Jul 2022

Viewed by 1279

Abstract

This article compares spectroscopic properties of the series of dipyrromethene dyes, namely their complexes of boron (III), zinc(II) and cadmium(II) with the halogenated ligands of the same structure. Absorption and emission spectra, lifetimes of long-lived emission and quantum yields of luminescence were studied [...] Read more.

This article compares spectroscopic properties of the series of dipyrromethene dyes, namely their complexes of boron (III), zinc(II) and cadmium(II) with the halogenated ligands of the same structure. Absorption and emission spectra, lifetimes of long-lived emission and quantum yields of luminescence were studied as the functions of molecular structure of dipyrromethene complexes. The role of the position and nature of a substituent in a ligand, polarity of a solvent and temperature of media were also investigated. The studies demonstrate that replacing the central atom boron(III) by zinc(II) decreases the fluorescence quantum yield, indicating the increased role of non-radiative processes in excitation energy deactivations such as intersystem crossings. In addition, according to the heavy atom effect, the efficiency of intersystem crossings in halogen-substituted zinc(II) and cadmium(II) dipyrromethene complexes is higher than in the corresponding boron fluoride dipyrromethenes (BODIPY), which leads to increase in phosphorescence at low temperatures (frozen solutions). The obtained results make it possible to carry out further investigations of potential sensory properties that are required for systematic use of halogenated dipyrromethene complexes for the creation of modern optical oxygen sensors and singlet oxygen photosensitizers for photodynamic therapy or photocatalytic oxidative reactions. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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18 pages, 38547 KiB

Open AccessArticle

Chemoinformatics Analysis of the Colour Fastness Properties of Acid and Direct Dyes in Textile Coloration

by Jianhua Ran, Victoria G. Pryazhnikova and Felix Y. Telegin

Colorants 2022, 1(3), 280-297; https://doi.org/10.3390/colorants1030017 - 05 Jul 2022

Cited by 3 | Viewed by 1823

Abstract

The efficiency of chemoinformatics methods based on a fragment approach for the analysis of relationships between the chemical structure of textile dyes and colour fastness of the dyeings have been shown by examining a large set of properties, including the light fastness of [...] Read more.

The efficiency of chemoinformatics methods based on a fragment approach for the analysis of relationships between the chemical structure of textile dyes and colour fastness of the dyeings have been shown by examining a large set of properties, including the light fastness of acid dyes on wool and polyamide fibres, the sensitivity of acid dyes on wool to oxygen bleaching, the wash fastness of acid dyes on wool, the adsorption of direct dyes on cotton, and the photodegradation of azo dyes in solution. An analysis of the developed regression models depicted the contribution of ten substructural molecular fragments for each indicator of the colour fastness properties of acid and direct azo dyes on textile materials. The similarity of several individual multi-atomic fragments for acid and direct azo dyes was found for wool, polyamide, and cotton fibres, which indicates the coinciding mechanisms of the physicochemical processes that accompany the destruction of dyes while testing the light fastness and sensitivity of the dyeings to oxygen bleaching, as well as their adsorption/desorption with the wash fastness and dyeability of wool and cotton. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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20 pages, 7327 KiB

Open AccessArticle

Preliminary in Silico Studies of the Interactions of Certain Genotoxic Azo Dyes with Different Double-Stranded DNA Conformations

by Erman Salih İstifli

Colorants 2022, 1(2), 236-255; https://doi.org/10.3390/colorants1020015 - 14 Jun 2022

Cited by 2 | Viewed by 1912

Abstract

Organic azo dyes, which are widely used in industrial, health and cosmetic fields, pose genotoxic risks due to their chemical structures; however, the molecular details of the undesirable effects of these dyes on DNA have been poorly or insufficiently clarified. In this computational [...] Read more.

Organic azo dyes, which are widely used in industrial, health and cosmetic fields, pose genotoxic risks due to their chemical structures; however, the molecular details of the undesirable effects of these dyes on DNA have been poorly or insufficiently clarified. In this computational molecular docking study, the DNA binding modes and binding affinities of 14 azo dyes, previously determined to show DNA clastogenicity, were characterized using 2 different double-stranded DNA (dsDNA) conformations (an intact dsDNA and dsDNA with an intercalation gap). In this study, it was determined that 10 out of the 14 genotoxic azo dyes were strong dsDNA minor groove binders, while the remaining ones formed tight binding complexes with dsDNA through intercalation or threading intercalation modes. The azo, nitro, hydroxyl, ammonium, sulfonate, naphthalene, methoxyphenyl, bromine, nitrophenyl, imidazole, amino-phenylethanol and chloro-nitrophenyl groups were found to play primary role in the most favorable binding conformations of these dyes on dsDNA with an affinity ranging from −6.35 kcal/mol to −9.42 kcal/mol. It was determined that dsDNA sequences containing GT dinucleotides are frequently preferred in binding by these dyes, and that rings and polar groups are important features for tight binding with dsDNA. It was concluded that these dyes may be banned, or non-genotoxic congeners should be manufactured with appropriate molecular optimization for the genetic health of the human population and for future generations. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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10 pages, 2251 KiB

Open AccessArticle

Near-Infrared Absorbing Molecule Based on Triphenylamine Radical Cation with Extended Homoaryl π-System

by Masafumi Yano, Kohei Tamada, Misaki Nakai, Koichi Mitsudo and Yukiyasu Kashiwagi

Colorants 2022, 1(2), 226-235; https://doi.org/10.3390/colorants1020014 - 02 Jun 2022

Cited by 3 | Viewed by 2695

Abstract

Four triphenylamines with extended π-systems were synthesized. Cyclic voltammetry (CV) measurements showed that they gave radical cations, which are stable in solution. Radical cations obtained upon one electron chemical oxidation showed strong absorption in the near-infrared region. The radical cations of the naphthalene-substituted [...] Read more.

Four triphenylamines with extended π-systems were synthesized. Cyclic voltammetry (CV) measurements showed that they gave radical cations, which are stable in solution. Radical cations obtained upon one electron chemical oxidation showed strong absorption in the near-infrared region. The radical cations of the naphthalene-substituted derivatives show a maximum absorption wavelength above 1000 nm and are classified as NIR-II dyes. Molecular design rules of novel near-infrared absorbing dyes are described. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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18 pages, 4645 KiB

Open AccessArticle

Following the Light: Use of Multimodal Imaging and Fiber Optic Spectroscopy to Evaluate Aging in Daylight Fluorescent Artists’ Pigments

by Fiona Beckett and Aaron Shugar

Colorants 2022, 1(2), 208-225; https://doi.org/10.3390/colorants1020013 - 23 May 2022

Viewed by 2644

Abstract

Daylight fluorescent artists’ colors have been well established as fugitive. Upon exposure to light, these vibrant colors can fade and exhibit color shifts. Artwork containing these fluorescent colorants presents complex challenges for art conservators faced with conserving these inherently problematic materials. This paper [...] Read more.

Daylight fluorescent artists’ colors have been well established as fugitive. Upon exposure to light, these vibrant colors can fade and exhibit color shifts. Artwork containing these fluorescent colorants presents complex challenges for art conservators faced with conserving these inherently problematic materials. This paper examined nine fluorescent colorants obtained from Kremer Pigmente, referred to the previous literature and research, and attempted to quantify the visual and photographic observations of fading and color changes. It provides additional information that could be useful in considering conservation documentation and treatment. Fiber optic spectroscopy using ultraviolet and visible light sources was used to measure the spectral shifts of the colorants before and after exposure to light. The fluorescent colors exhibited alterations in intensity coupled with primary peak shifts in the spectrum corresponding to the optical fading and color shifts. Multimodal imaging was executed to analyze the pigments in different regions of the spectrum before and after aging, which has not been documented before with these fluorescent colorants. Imaging in various regions of the spectrum indicated differences in absorption and reflectance between the pigments as captured by a modified camera. The results were compared to recently published research including the identification of the dyes present in the Kremer line of pigments. Multimodal imaging and fiber optic spectroscopy provided valuable information for future documentation and conservation of artworks containing these colorants. Specifically, these non-invasive techniques provide a method to document and identify the spectral changes between the aged and unaged pigment, graph and predict the direction of overall color change, and provide useful data for establishing future conservation treatment protocols. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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15 pages, 14786 KiB

Open AccessArticle

Comparison of the In Vitro Photodynamic Activity of the C1α and C1β Anomers of a Glucosylated Boron Dipyrromethene

by Junlong Xiong, Ka-Wing Yeung, Clarence T. T. Wong, Wing-Ping Fong and Dennis K. P. Ng

Colorants 2022, 1(2), 193-207; https://doi.org/10.3390/colorants1020012 - 02 May 2022

Cited by 4 | Viewed by 1783

Abstract

Photodynamic therapy (PDT) is an established treatment modality for a range of superficial and localized cancers. There has been tremendous interest in the development of advanced photosensitizers that exhibit superior photophysical properties, high tumor selectivity, and improved pharmacokinetics. Glucose is one of the [...] Read more.

Photodynamic therapy (PDT) is an established treatment modality for a range of superficial and localized cancers. There has been tremendous interest in the development of advanced photosensitizers that exhibit superior photophysical properties, high tumor selectivity, and improved pharmacokinetics. Glucose is one of the well-studied targeting moieties that can deliver various therapeutic agents to cancer cells selectively via the Warburg effect. However, the use of glucosylated photosensitizers for targeted PDT has remained little studied and to the best of our knowledge, the PDT effect of the positional isomers of these conjugates has never been compared. We report herein the preparation and photophysical properties of the C1α and C1β anomers of a glucosylated boron dipyrromethene-based photosensitizer. The cellular uptake and photocytotoxicity of both anomers were also studied and compared using A549 human lung carcinoma cells and HEK293 human embryonic kidney cells. Interestingly, the cellular uptake of the C1α anomer was approximately 2-fold higher than that of the C1β anomer regardless of the cell type and incubation time. The uptake pathway of both anomers was also studied. It was found that they were internalized through energy-dependent receptor/protein-mediated endocytosis rather than the well-known glucose transporters and sodium-driven glucose symporters. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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17 pages, 4478 KiB

Open AccessArticle

Nanoencapsulation of Red Bell Pepper Carotenoids: Comparison of Encapsulating Agents in an Emulsion Based System

by Nicolly de Lima Petito, Julia Marim Devens, Deborah Quintanilha Falcão, Fábio Moyses Lins Dantas, Thaís Souza Passos and Katia Gomes de Lima Araujo

Colorants 2022, 1(2), 132-148; https://doi.org/10.3390/colorants1020009 - 01 Apr 2022

Cited by 8 | Viewed by 2503

Abstract

Red bell pepper extract rich in carotenoids was (RBPE) encapsulated with four different encapsulating agents: calcium caseinate (ECC), bovine gelatin (EBG), whey proteins isolate (EWPI), and concentrate (EWPC), aiming to investigate the most effective material to coat and enable the water dispersibility of [...] Read more.

Red bell pepper extract rich in carotenoids was (RBPE) encapsulated with four different encapsulating agents: calcium caseinate (ECC), bovine gelatin (EBG), whey proteins isolate (EWPI), and concentrate (EWPC), aiming to investigate the most effective material to coat and enable the water dispersibility of pigments. Formulations were obtained by the oil in water (O/W) emulsification technique, followed by freeze-drying. Samples were analyzed by encapsulation efficiency, high-performance liquid chromatography (HPLC), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), atomic force microscopy (AFM), thermogravimetric analysis (TGA), dispersion stability, and CIELab. Nanoformulations showed a carotenoid encapsulation efficiency of 54.0% (ECC), 57.6% (EWPI), 56.6 % (EWPC), 64.0 % (EBG). Recovered carotenoid profiles from nanoformulations showed similarity to the RBPE, indicating the efficiency of the encapsulation process. Average particle sizes of approximately 109 nm (ECC), 71 nm (EWPI), 64 nm (EWPC), and 173 nm (EBG) were obtained. AFM revealed that all formulations exhibited spherical forms and a heterogeneous distribution profile. Regarding TGA, formulations presented similar thermal behaviors to and lower decomposition speeds than RBPE, suggesting improved thermal stability. Powder formulations were easily dispersed in water (8 mg/mL) and presented intense color and stability to sedimentation for 48 h. Results indicated that all formulations and the chosen technique efficiently increased carotenoid dispersibility in water, indicating their potential to be applied as natural food pigments. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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11 pages, 6016 KiB

Open AccessArticle

Improving the Dyeing of Polypropylene by Surface Fluorination

by Masanari Namie, Jae-Ho Kim and Susumu Yonezawa

Colorants 2022, 1(2), 121-131; https://doi.org/10.3390/colorants1020008 - 29 Mar 2022

Cited by 3 | Viewed by 3037

Abstract

The surface of polypropylene (PP) was modified with fluorine gas at 25 °C and 10–380 Torr for 1 h. The surface roughness of the fluorinated PP samples was approximately two times larger than that (5 nm) of the untreated sample. The results of [...] Read more.

The surface of polypropylene (PP) was modified with fluorine gas at 25 °C and 10–380 Torr for 1 h. The surface roughness of the fluorinated PP samples was approximately two times larger than that (5 nm) of the untreated sample. The results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy showed that the bonds (e.g., -C-C- and -CH_x) derived from raw PP decreased and were converted into fluorinated bonds (e.g., -CF_x) after surface fluorination. These fluorinated bonds showed higher electronegativity according to the zeta potential results. Fluorinated PP could be stained with the methylene blue basic dye because of the increased surface roughness and the negatively charged surface. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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Review

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11 pages, 1081 KiB

Open AccessReview

Tackling Colorants Sustainability Combining Disruptive Science and Sustainable Leadership: A Review Article

by Valentina Lorenzon and Greta Faccio

Colorants 2022, 1(4), 400-410; https://doi.org/10.3390/colorants1040025 - 26 Nov 2022

Viewed by 1693

Abstract

Many pigments and dyes are not only valuable molecules in manufacturing, but also environmental pollutants. Stemming from the observation of the slow pace of change taking place to counter the ‘fast fashion’ phenomenon and its environmental consequences, this critical review highlights the importance [...] Read more.

Many pigments and dyes are not only valuable molecules in manufacturing, but also environmental pollutants. Stemming from the observation of the slow pace of change taking place to counter the ‘fast fashion’ phenomenon and its environmental consequences, this critical review highlights the importance not only of biotechnological approaches but also of a sustainable leadership to achieve a future-proof fashion industry. Science has been producing sustainable alternatives to counter the issue of dyes, but this is not enough. A change in the business attitude and leadership approach of the organizations that operate in the industry is needed. Only through the successful combination of new technologies and forward-looking decision-making will it be possible to alter the status quo and deal with the multiple environmental challenges that businesses are and will be facing. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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40 pages, 9659 KiB

Open AccessReview

The Modernity of Ancient Pigments: A Historical Approach

by Mary Virginia Orna and Marco Fontani

Colorants 2022, 1(3), 307-346; https://doi.org/10.3390/colorants1030019 - 13 Jul 2022

Cited by 3 | Viewed by 6683

Abstract

Naturally occurring and synthetic ancient pigments have a history of use spanning thousands of years. Curiously, some of their newly discovered properties make them excellent candidates for semiconductors, anticounterfeiting agents and so much more. In this paper, we will review their ancient roots [...] Read more.

Naturally occurring and synthetic ancient pigments have a history of use spanning thousands of years. Curiously, some of their newly discovered properties make them excellent candidates for semiconductors, anticounterfeiting agents and so much more. In this paper, we will review their ancient roots in art and modern emergence as 21st century workhorses. You can never judge a pigment by its color alone! Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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24 pages, 2006 KiB

Open AccessReview

Isorhodopsin: An Undervalued Visual Pigment Analog

by Willem J. de Grip and Johan Lugtenburg

Colorants 2022, 1(3), 256-279; https://doi.org/10.3390/colorants1030016 - 23 Jun 2022

Cited by 1 | Viewed by 1952

Abstract

Rhodopsin, the first visual pigment identified in the animal retina, was shown to be a photosensitive membrane protein containing covalently bound retinal in the 11-cis configuration, as a chromophore. Upon photoexcitation the chromophore isomerizes in femtoseconds to all-trans, which drives [...] Read more.

Rhodopsin, the first visual pigment identified in the animal retina, was shown to be a photosensitive membrane protein containing covalently bound retinal in the 11-cis configuration, as a chromophore. Upon photoexcitation the chromophore isomerizes in femtoseconds to all-trans, which drives the protein into the active state. Soon thereafter, another geometric isomer—9-cis retinal—was also shown to stably incorporate into the binding pocket, generating a slightly blue-shifted photosensitive protein. This pigment, coined isorhodopsin, was less photosensitive, but could also reach the active state. However, 9-cis retinal was not detected as a chromophore in any of the many animal visual pigments studied, and isorhodopsin was passed over as an exotic and little-relevant rhodopsin analog. Consequently, few in-depth studies of its photochemistry and activation mechanism have been performed. In this review, we aim to illustrate that it is unfortunate that isorhodopsin has received little attention in the visual research and literature. Elementary differences in photoexcitation of rhodopsin and isorhodopsin have already been reported. Further in-depth studies of the photochemical properties and pathways of isorhodopsin would be quite enlightening for the initial steps in vision, as well as being beneficial for biotechnological applications of retinal proteins. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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28 pages, 3664 KiB

Open AccessReview

The First Century of Successful Applications of Pinacyanol: Some Noteworthy Results

by Serghey A. Shapovalov

Colorants 2022, 1(2), 165-192; https://doi.org/10.3390/colorants1020011 - 17 Apr 2022

Cited by 3 | Viewed by 2592

Abstract

The most important results obtained during the first century of pinacyanol (PIN) application in fundamental and applied research are summarized. The main usages of PIN during the century are described. The structural, protolytic, and thermodynamic properties of the dye in different systems (aqueous [...] Read more.

The most important results obtained during the first century of pinacyanol (PIN) application in fundamental and applied research are summarized. The main usages of PIN during the century are described. The structural, protolytic, and thermodynamic properties of the dye in different systems (aqueous and aqueous–organic solutions, premicellar and micellar surfactant systems, and salt-containing solutions) have been analyzed. Quantitative characteristics of intermolecular interactions are considered. Self-association and dissimilar association of PIN with the participation of other dyes, organic ions and molecules, and metal complex compounds under 5 × 10⁻⁷–8 × 10⁻⁵ mol/L concentrations of PIN are discussed. The analyzed data indicate that at present, as before, the scientific interest in this dye is very high. Full article

(This article belongs to the Special Issue Colorants: Ancient and Modern)

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