Nontoxic Pigments Research Articles

Insight into the Antioxidant Activity of 1,8-Dihydroxynaphthalene Allomelanin Nanoparticles.

Melanins are stable and non-toxic pigments with great potential as chemopreventive agents against oxidative stress for medical and cosmetic applications. Allomelanin is a class of nitrogen-free melanin often found in fungi. The artificial allomelanin obtained by the polymerization of 1,8-dihydroxynaphthalene (DHN), poly-DHN (PDHN), has been recently indicated as a better radical quencher than polydopamine (PDA), a melanin model obtained by the polymerization of dopamine (DA); however, the chemical mechanisms underlying this difference are unclear. Here we investigate, by experimental and theoretical methods, the ability of PDHN nanoparticles (PDHN-NP), in comparison to PDA-NP, to trap alkylperoxyl (ROO•) and hydroperoxyl (HOO•) radicals that are involved in the propagation of peroxidation in real conditions. Our results demonstrate that PDHN-NP present a higher antioxidant efficiency with respect to PDA-NP against ROO• in water at pH 7.4 and against mixed ROO• and HOO• in acetonitrile, showing catalytic cross-termination activity. The antioxidant capacity of PDHN-NP in water is 0.8 mmol/g (ROO• radicals quenched by 1 g of PDHN-NP), with a rate constant of 3 × 105 M-1 s-1 for each reactive moiety. Quantum-mechanical calculations revealed that, thanks to the formation of a H-bond network, the quinones in PDHN-NP have a high affinity for H-atoms, thus justifying the high reactivity of PDHN-NP with HOO• observed experimentally.

The structural characterization and color stabilization of the pigment protein-phycoerythrin glycosylated with oligochitosan

Phycoerythrin (PE) is a kind of natural and nontoxic pigment protein with a distinctive phycobilin, and this pigment is easy to be destroyed in the process of food application, which makes its stability weak and application limited. In this work, PE was extracted by freeze-thaw method from Porphyra haitanensis, and the transglutaminase (10 U g−1 protein) was used to catalyze the glycosylation reaction between PE and oligochitosan with molar ratios of 1:1 to 4:1 (oligochitosan/PE) to obtain the oligochitosan-modified phycoerythrin complexes (OMPC). The glycosylation of oligochitosan to PE was proven by the polyacrylamide gel electrophoresis and was evidenced by the glucosamine and free amino analysis. When the molar ratio of oligochitosan to PE was 3:1, the glucosamine content of OMPC was the highest, which was 31.403 ± 0.004 mg g−1 protein. The OMPC samples were studied by infrared spectrum, fluorescence spectrum, and scanning electron microscopy. The results showed that the secondary structure and tertiary structure of glycosylated products changed, and a compact polymer appeared. In addition, compared with untreated PE, the surface hydrophobicity and emulsifying activity of OMPC decreased, while the solubility, emulsifying stability, thermal stability, photostability, and pH stability were significantly improved. This study reveals an innovative method to stabilize PE by a glycosylation approach, which will advance PE usage as a natural colorant in food applications.

Pigment produced from Arcopilus aureus isolated from grapevines: Promising natural yellow colorants for the food industry

Interest in the use of natural non-toxic pigments by the food industry has grown. Some filamentous fungi are producers of natural pigments that are more stable at temperature and pH than other pigments also classified as natural, such as those produced by plants. Production potential of natural pigments by endophytic fungi from grapevines was evaluated. Arcopilus aureus was selected as a potential source for a yellow pigment, which was characterized and tested for stability to variations in temperature and pH. Components, cochlioquinol II and riboflavin, were detected, which has not previously been reported in A. aureus. The pigment was stable and showed increased absorption at lower / acidic pH. These results provide information on the potential of this fungus and a yellow pigment for the first time, which can be used for further development and industrial application.

Chronic electrical stimulation of peripheral nerves via deep-red light transduced by an implanted organic photocapacitor.

Implantable devices for the wireless modulation of neural tissue need to be designed for reliability, safety and reduced invasiveness. Here we report chronic electrical stimulation of the sciatic nerve in rats by an implanted organic electrolytic photocapacitor that transduces deep-red light into electrical signals. The photocapacitor relies on commercially available semiconducting non-toxic pigments and is integrated in a conformable 0.1-mm3 thin-film cuff. In freely moving rats, fixation of the cuff around the sciatic nerve, 10 mm below the surface of the skin, allowed stimulation (via 50-1,000-μs pulses of deep-red light at wavelengths of 638 nm or 660 nm) of the nerve for over 100 days. The robustness, biocompatibility, low volume and high-performance characteristics of organic electrolytic photocapacitors may facilitate the wireless chronic stimulation of peripheral nerves.

Biosynthesis and preparation of phycoerythrobilin in recombinant Escherichia coli

Phycoerythrobilin (PEB) is a special pigment in red algae and cyanobacteria that plays an important role in capturing light energy. As a natural non-toxic pigment with antioxidant properties, PEB is widely used in food and cosmetics industries. At present, the presence of other pigments in red algae and cyanobacteria, such as chlorophyll and phycocyanobilin, makes the preparation of PEB complicated and costly. In this study, the PEB synthesizing enzyme genes of hox1 from Synechocystis sp. PCC6803 and pebS from Nostoc sp. PCC 7120 were co-expressed in Escherichia coli to produce recombinant PEB. In addition, single-factor and response surface methods were used to enhance the yield of recombinant PEB. Under the conditions of lactose concentration at 4 mmol L−1, induction temperature at 27 °C, OD600 nm of 0.9, and induction time at 14 h, the concentration of PEB reached 20.37 mg L−1. In addition, a high-purity (purity > 70%) PEB was obtained through chloroform extraction, and the purified product was verified in UV spectrometry, high-performance liquid chromatography, and mass spectrometry.

Preparation and application of rare earth sulfides

Rare earth sulfides are a new type of functional materials with complex crystal structures, which show unique optical, electrical and magnetic properties. They are widely used in many fields, such as non-toxic pigments and energy storage, and have perspective application in photocatalytic, thermoelectric power generation, permanent magnet and other fields. Based on our group’s work in these fields, this review systematically summarizes the research progress and milestone on synthetic methodology, crystal structure modification and composite construction of rare earth sulfide in recent years. The performance enhancement strategies of rare earth sulfide in inorganic pigment, energy storage and photocatalysis are comprehensively sorted out. The structure-activity relationship of rare-earth sulfide is discussed and their positive prospects are proposed. Finally, this review summarizes the existing problems in current research and puts forward the prospects for its research direction.

Role of chelating compounds towards thermal resistance property of industrial grade goethite

PurposeThe iron oxide-based goethite (FeOOH) is proven to be an alternative replacement for carcinogenic chrome-based pigments. Because of its low heat stability, it tends to lose water of hydration and turns red as temperature ascends beyond 240ºC. Thus, the purpose of this paper is to increase the heat stability temperature of industrial grade (IG) goethite pigment. For this, the IG goethite pigment was surface treated with sequestrant. The properties of untreated and treated IG goethite were compared.Design/methodology/approachThree different compounds (sodium hexametaphosphate, calcium disodium ethylene diamine tetra-acetate salt, sodium gluconate) were used into the IG goethite at different concentration level. The experiments were conducted by varying the temperature and exposure time of treated and untreated samples. The total colour difference value (DE) was compared for the treated and untreated samples.FindingsThe surface treatment of IG goethite showed significant enhancement in heat stability property. From X-ray diffraction results it was confirmed that with surface treatment, there was no phase change of IG goethite even at 300ºC. Fourier transform infrared analysis states that with surface treatment when there is gradual increase in temperature from 260ºC the % transmittance of the OH (hydroxyl) deformation region band is delayed due to sequestering effect. Also, based on the total colour DE, the colour tone of surface treated IG goethite was not perceptible by human eyes even at 280ºC.Research limitations/implicationsBy increasing the heat stability of IG goethite, it will have increased spectrum of end usage in the high temperature coating segment. Coil coating is one of the biggest potential markets for this pigment. The increased heat stability will provide manufacturers with the option of an economical and non-toxic pigment in coil coatings and also in other sectors such as plastics, powder coatings and high temperature coatings.Practical implicationsThe outcome of this study has been commercially implemented to produce heat stable goethite pigments in an industrial plant. The surface treated IG goethite pigments can be used in high-performance coil, powder and high temperature coatings.Originality/valueThe method for enhanced heat stability property of IG goethite by surface treatment with sequestrants is novel and could find numerous applications in high-performance coatings.

Preparation and Research of Solvent-Free Epoxy Coating for Drinking Water Tank

By compounding E42 and E51 epoxy resin, blending modified polyamide curing agent and modified fatty amine curing agent, optimizing glycidyl ether reactive diluent system, using safe non-toxic pigment filler and grading wear resistance filling and optimization auxiliaries system, the developed coating sanitary index meets the requirements of “Sanitary Standard for Drinking Water”, and the wear resistance (cs17, 1000g/1000r, mg) is 64.4mg. The coatings passed 6J impact resistance test and is resistant to bending 1.5° without cracks. The coatings also have excellent resistance to medium corrosion and salt spray.

Bis-naphthopyrone pigments protect filamentous ascomycetes from a wide range of predators

It is thought that fungi protect themselves from predation by the production of compounds that are toxic to soil-dwelling animals. Here, we show that a nontoxic pigment, the bis-naphthopyrone aurofusarin, protects Fusarium fungi from a wide range of animal predators. We find that springtails (primitive hexapods), woodlice (crustaceans), and mealworms (insects) prefer feeding on fungi with disrupted aurofusarin synthesis, and mealworms and springtails are repelled by wheat flour amended with the fungal bis-naphthopyrones aurofusarin, viomellein, or xanthomegnin. Predation stimulates aurofusarin synthesis in several Fusarium species and viomellein synthesis in Aspergillus ochraceus. Aurofusarin displays low toxicity in mealworms, springtails, isopods, Drosophila, and insect cells, contradicting the common view that fungal defence metabolites are toxic. Our results indicate that bis-naphthopyrones are defence compounds that protect filamentous ascomycetes from predators through a mechanism that does not involve toxicity.

Enhanced Electrical Conduction in Anatase TaON via Soft Chemical Lithium Insertion toward Electronics Application

Metal oxynitride semiconductors with the d0 or d10 electron configuration are promising materials for nontoxic pigments and photocatalysts, but their electrical properties have scarcely been studied. Anatase TaON (δ-TaON) is a metastable polymorph of TaON, and its epitaxial thin films show good semiconducting properties such as a wide tunability of electrical conductivity and a rather high electron mobility comparable to that of anatase TiO2. However, the density of carrier electrons (ne) provided by anion vacancies is limited to ∼1 × 1020 cm–3, so establishing a method for carrier doping of anatase TaON remains a critical issue for its use in electronics applications. In this report, we used soft chemical insertion of Li into interstitial sites of anatase TaON epitaxial thin films by using an n-butyllithium solution, and the resulting material showed a higher ne (3.5 × 1020 cm–3) than anion-deficient anatase TaON films. Additionally, the Li-inserted anatase TaON showed an enhanced Hall mobility (μH) of o...

Valorization of Vanillyl Alcohol by Pigments: Prussian Blue Analogue as a Highly-Effective Heterogeneous Catalyst for Aerobic Oxidation of Vanillyl Alcohol to Vanillin

Prussian blue analogues (PBA), a class of metal-coordinated frameworks, are proposed in this study for aerobic oxidation of a lignin model compound, vanillyl alcohol (VAL), to the valuable product, vanillin (VN). While different metals and hexacyano-metalates are used to prepare various PBAs, the prototype PBA (Fe3[Fe(CN)6]2 abbreviated as “FeFe”) exhibited the highest catalytic activity towards VAL conversion to VN. The kinetics of VAL conversion is determined and the production of VN is also analyzed using the pseudo first order rate law. In addition, FeFe exhibits the highest catalytic activity to convert VAL to VN with the highest production and selectivity compared to the reported heterogeneous catalysts. FeFe can be also re-used to catalyze conversion of VAL to VN without significant activity loss. These features indicate that FeFe, as an easy-to-obtain and non-toxic pigment, is a promising catalyst for aerobic oxidation of VAL.

Anticorrosive Performance of New Epoxy-Amine Coatings Based on Zinc Phosphate Tetrahydrate as a Nontoxic Pigment for Carbon Steel in NaCl Medium

Epoxy resin is known to react with a hardener such as polyamine to form a thermoset 3D polymer net with an outstanding physical and mechanical properties. They are widely used in coating and adhesives. In this study, we present a new epoxy resin material useful for making an anticorrosive formulation for carbon steel. The epoxy resin presented in this study is diglycidyl ether 4, $$4^{\prime }$$ -dihydroxy diphenyl sulfone (DGEDDS). It was prepared in a two-step process that involves reacting epichlorohydrin with 4, $$4^{\prime }$$ dihydroxy diphenyl sulfone then with sodium hydroxide. The structural elucidation of DGEDDS was carried out with Fourier transform infrared. The anticorrosive formulation DGEDDS–MDA–ZPH was prepared from DGEDDS and the hardener 4, $$4^{\prime }$$ -methylene dianiline (MDA) in the presence of the anticorrosion pigment zinc phosphate tetrahydrate (ZPH). Another standard formulation (DGEDDS–MDA) was prepared without ZPH. The physicochemical and anticorrosive performance of the coated carbon steel was evaluated using electrochemical impedance spectroscopy (EIS). The coated surface was subjected to morphological characterization by SEM before and after immersion in the corrosive medium and exposing it to the UV radiation. The value of the polarization resistance ( $$R_{\mathrm{p}}$$ ) obtained by the EIS method for the standard coating DGEDDS–MDA and epoxy composite coating DGEDDS–MDA–ZPH was 31898 and 72611 $$\Omega \,\hbox {cm}^{2}$$ during the 1 h of immersion in 3 wt% NaCl, respectively. After aging by exposing the coatings for a 2000 h to UV radiation the values were dropped to 2596 and 5189 $$\Omega \,\hbox {cm}^{2}$$ , respectively. The values show the high stability and resistance of the epoxy resin coating to electrolytes and UV radiation. The coating even showed higher stability in the presence of ZPH pigment. As shown in the results, the tricomponent composite showed an outstanding stability in protecting carbon steel form corrosion in an aggressive marine environment where UV is very intense and the humidity and salts are very high.

Synthesis, characterization and thermal performance of Fe/N co-doped MgTiO3 as a novel high near-infrared reflective pigment

To obtain cool materials as inorganic and nontoxic pigments with high near-infrared reflectance, nano-powder of Fe/N co-doped MgTiO3 (FNM), were synthesized by the sol-gel method. The substitution of Fe/N changed the color from white to dark-red due to the point defect equilibrium theory, while the band gap decreased from 2.11ev to 1.89ev. Ammonolysis reaction can promote the particle dispersion and increase the particle size. Furthermore, the FNM pigments exhibit high NIR reflectance (>65%) and the NIR solar reflectance (>53.51%) in the range of 700–2500nm. After the prepared pigments (N-doped Mg1−xFexTiO3+δ, x=0.3) and conventional brown pigments used as building roof materials, the temperature difference of coatings could reach 2.4°C (the inner surface temperature of substrate plates) and 2.0°C (the interior temperature of the two boxes), respectively. Moreover, the surface temperature distribution of the coatings was recorded by infrared images and the difference (ΔT) varied at 0–12°C. According to the maximum value of coatings (x=0.3), energy savings would reduce annual emissions of 1379.35t carbon dioxide, 41.65t nitrogen oxides and 34.30t sulfur oxides. Owing to the wide range of color and good chemical stability, which meets reflectance of solar radiation energy and cooling energy needs, these FNM materials are considered as novel color pigments.

Potential use of natural pigments on laccase-based TTI Prototype: Substrate specificities and variations in Arrhenius activation energy

Non-toxic dyes and natural pigments were examined as potential substrates for a laccase-based time temperature integrator (TTI) prototype. Five compounds such as bromothymol blue (D1), methyl orange (D2), laccaic acid (P1), a pigment from bokbunja (Rubus coreanus) fruit (P2), and Gardenia blue pigment (P3) were all catalyzed, resulting in significant changes in color. CIE-Lab and ΔE appeared to have the most linear dependency on reaction time. Reaction rate constants, k, were estimated at 10–37°C with the coefficients of determination, R2, being the lowest at 0.94. The Arrhenius activation energies, Ea, were 42.6 66.1 kJ/mol depending on the substrate. The results show that alterations in Ea of this TTI is a very important finding in that Ea of the laccase-based TTI could be modulated with substrates to assess time-temperature history accurately and that a wide range of color compounds offer an opportunity for color-coded TTI to assure color blind individuals food safety.

Chemistry and applications of oxynitride perovskites

Oxynitride perovskites of early transition metals and rare earth or alkaline earth elements have been reported in the last decade as non-toxic pigments, colossal magnetoresistive materials, high permittivity dielectrics and photocatalysts. Nitride and oxide may occupy the same sites in the perovskite structure, forming solid solutions with ratios that are adjusted by synthesis. The valence states of cations, the bond covalency and the energy of the electronic states can be tuned by the introduction of nitrogen as a consequence of its lower electronegativity, higher electronic polarisability and higher formal anion charge relative to oxygen. This feature article will discuss the influence of the above factors on the crystal chemistry and properties of this group of materials that have emerged as a result of the development of new and controlled synthetic methodologies.

The anticorrosive performance of zinc-free non-toxic pigment for paints

The objective of this research was to study the efficiency of calcium aluminium phosphosilicate hydrate (PSh), as anticorrosive pigment for paints in simulated aggressive environments. This compound is zinc-free and the phosphate content is less than 30% by weight. Alkyd and epoxy paints, of the solvent-borne type, containing 30% by volume (v/v) of the pigment, were formulated. The pigment volume concentration was fixed at 42.3%. Standardised accelerated salt spray exposure and electrochemical tests were used to assess the protective performance of the coatings. Analysis and interpretation of the experimental data showed that PSh inhibits corrosion of painted steel panels exposed to aggressive environments. Zinc phosphate (ZP), a traditional anticorrosive pigment, was used as reference in all the essays.

Disturbance in hemoglobin metabolism and in vivo antimalarial activity of azole antimycotics

Plasmodium parasites degrade host hemoglobin to obtain free amino acids, essential for protein synthesis. During this event, free toxic heme moieties crystallize spontaneously to produce a non-toxic pigment called hemozoin or ß-hematin. In this context, a group of azole antimycotics, clotrimazole (CTZ), ketoconazole (KTZ) and fluconazole (FCZ), were investigated for their abilities to inhibit ß-hematin synthesis (IßHS) and hemoglobin proteolysis (IHbP) in vitro. The ß-hematin synthesis was recorded by spectrophotometry at 405 nm and the hemoglobin proteolysis was determined by SDS-PAGE 12.5%, followed by densitometric analysis. Compounds were also assayed in vivo in a malaria murine model. CTZ and KTZ exhibited the maximal effects inhibiting both biochemical events, showing inhibition of β-hematin synthesis (IC50 values of 12.4 ± 0.9 µM and 14.4 ± 1.4 µM respectively) and inhibition of hemoglobin proteolysis (80.1 ± 2.0% and 55.3 ± 3.6%, respectively). There is a broad correlation to the in vivo results, especially CTZ, which reduced the parasitemia (%P) of infected-mice at 4th day post-infection significantly compared to non-treated controls (12.4 ± 3.0% compared to 26.6 ± 3.7%, p = 0.014) and prolonged the survival days post-infection. The results indicated that the inhibition of the hemoglobin metabolism by the azole antimycotics could be responsible for their antimalarial effect.

Novel nontoxic nanopigments based on zirconia and rare earth mixed oxides

AbstractThis paper embodies the result of the investigations carried out on the synthesis of zirconia‐ rare earth mixed oxide pigments: ZrCe1‐xYxO4‐δ and ZrCe1‐xPrxO4‐δ by the solution combustion method and their characterization by X‐ray powder diffraction, transmission electron microscopy, energy dispersive spectrometric analysis, thermal analysis, reflectance spectral data and surface area measurements. The synthesized nano pigments possess low a and high b and exhibit yellow color when doped with Y and changes from yellow to orange‐red color when doped with Pr, with increase in x values. These pigments show maximum reflectance of 90% when the wavelength is above 550 nm. Due to the homogeneity of the phase formed and resistance to water, acids and alkali, the rare earth mixed oxides developed are found to be promising candidates as nontoxic pigments. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of Doping Elements on Residual Oxygen/Nitrogen Contents in Red Pigment of Tantalum Nitrides (Ta<sub>3</sub>N<sub>5</sub>)

Tantalum nitride (Ta3N5) is a nontoxic red pigment that is being developed as a substitute for Cd-related pigments Ta3N5 is produced by the nitridation and heat treatment of amorphous Tantalum precursors. Doping elements were added in the precursor manufacturing stage to improve the red color tone of tantalum nitride. Grain growth was observed in nitrides that formed second phases, such growth led to an increase in the average grain size comprared to undoped nitrides, and the colors declined as the oxygen content increased. Nitrides that did not form second phases in response to doping elements remained a single-phase Ta3N5 and exhibited an excellent red color with a high nitrogen content. We determined that a change in the oxygen/nitrogen contents affected the color manifestation, which depended on the amount by which doping was increased.

Structural and Spectroscopic Study of a New Pink Chromium‐Free Er2(Ti,Zr)2O7 Ceramic Pigment

Transition metal ions are usually incorporated as chromophores into pyrochlore structures in order to develop colored compounds. However, due to the high toxicity of some of them (Cr, Ni, Co, Cd …), other nontoxic species such as lanthanide ions have been studied in order to produce environment‐friendly pigments. This paper describes the structural and spectroscopic study of a pink pigment based on the Er2Ti2−xZrxO7 system synthesized by a sol–gel route. A previous research on the Er2Ti2O7 system revealed that this compound exhibits a pink coloration only in its defect fluorite‐type structure. At high temperature (800°C), an atomic rearrangement into a pyrochlore network significantly reduces its coloration. The stabilization of the fluorite phase in Er2Ti2O7 through substitution of Ti(IV) with larger Zr(IV) ions is studied in this work. The analysis by differential thermal analysis and thermogravimetric analysis, X‐ray powder diffraction, and Raman techniques indicates that the introduction of Zr(IV) species successfully avoids the undesired fluorite‐to‐pyrochlore transition. The colorimetric study concludes that the optimal composition corresponds to the Er2Ti0.6Zr1.4O7 stoichiometry, which gives an intense pink coloration independently of the thermal treatment. This study introduces a novel nontoxic pigment suitable for industrial applications at both low‐ and high‐temperature ceramic technologies.