Red Pigment Research Articles

Ketocarotenoid production in tomato triggers metabolic reprogramming and cellular adaptation: The quest for homeostasis.

Plants are sessile and therefore have developed an extraordinary capacity to adapt to external signals. Here, the focus is on the plasticity of the plant cell to respond to new intracellular cues. Ketocarotenoids are high-value natural red pigments with potent antioxidant activity. In the present study, system-level analyses have revealed that the heterologous biosynthesis of ketocarotenoids in tomato initiated a series of cellular and metabolic mechanisms to cope with the formation of metabolites that are non-endogenous to the plant. The broad multilevel changes were linked to, among others, (i) the remodelling of the plastidial membrane, where the synthesis and storage of ketocarotenoids occurs; (ii) the recruiting of core metabolic pathways for the generation of metabolite precursors and energy; and (iii) redox control. The involvement of the metabolites as regulators of cellular processes shown here reinforces their pivotal role suggested in the remodelled 'central dogma' concept. Furthermore, the role of metabolic reprogramming to ensure cellular homeostasis is proposed.

Co-production of pigment and high value-added bacterial nanocellulose from Suaeda salsa biomass with improved efficiency of enzymatic saccharification and fermentation

This study evaluated the co-production of pigment and bacterial nanocellulose (BNC) from S. salsa biomass. The extraction of the beet red pigment reduced the salts and flavonoids contents by 82.7%–100%, promoting the efficiencies of enzymatic saccharification of the biomass and the fermentation of BNC from the hydrolysate. SEM analysis revealed that the extraction process disrupted the lignocellulosic fiber structure, and the chemical analysis revealed the lessened cellulase inhibitors, consequently facilitating enzymatic saccharification for 10.4 times. BNC producing strains were found to be hyper-sensitive to NaCl stress, produced up to 400.4% more BNC from the hydrolysate after the extraction. The fermentation results of BNC indicated that the LDU-A strain yielded 2.116 g/L and 0.539 g/L in ES-M and NES-M, respectively. In comparison to the control, the yield in ES-M increased by approximately 20.0%, while the enhancement in NES-M was more significant, reaching 292.6%. After conducting a comprehensive characterization of BNC derived from S. salsa through Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and Thermogravimetric Analysis (TGA), the average fiber diameter distribution of these four BNC materials ranges from 22.23 to 33.03 nanometers, with a crystallinity range of 77%–90%. Additionally, they exhibit a consistent trend during the thermal degradation process, further emphasizing their stability in high-temperature environments and similar thermal properties. Our study found an efficient co-production approach of pigment and BNC from S. salsa biomass. Pigment extraction made biomass more physically and chemically digestible to cellulase, and significantly improved BNC productivity and quality.

Integrated analysis of the metabolome and transcriptome provides insights into anthocyanin biosynthesis of cashew apple

The cashew apple remains an underutilized agricultural product despite its abundance as a by-product of cashew nut production. Anthocyanins are water-soluble pigments responsible for red, purple, and blue hues in plant tissues and have various health-promoting properties. To investigate the anthocyanin biosynthesis in cashew apples, fruits with varying peel colors from three cultivars were subjected to integrative analyses with metabolomics and transcriptomics. Through a UPLC-ESI-MS/MS-based targeted metabolomics analysis, a total of 26 distinct anthocyanin compounds were identified in the fruits of the three cashew cultivars. Subsequent quantification revealed that Pelargonidin-3-O-galactoside, Petunidin-3-O-arabinoside, and Cyanidin-3-O-galactoside were the primary contributors responsible for the red pigmentation in cashew apple peels. Following transcriptomic analysis showed that the expression levels of anthocyanin biosynthetic genes were predominantly higher in the red cashew apples as compared to the other two cultivars. Moreover, correlation analysis revealed that eight potential transcription factors implicated in the regulation of anthocyanin biosynthesis. Among these, four transcription factors exhibited positive correlations with both anthocyanin contents and anthocyanin biosynthetic gene expression, while the remaining four transcription factors displayed negative correlations. These findings provide a comprehensive understanding of the molecular basis of anthocyanin biosynthesis in cashew apple peels.

Eumelanin Detection in Melanized Focal Changes but Not in Red Focal Changes on Atlantic Salmon (Salmo salar) Fillets

Superficial discolored spots on Atlantic salmon (Salmo salar) fillets are a serious quality problem for commercial seafood farming. Previous reports have proposed that the black spots (called melanized focal changes (MFCs)) may be melanin, but no convincing evidence has been reported. In this study, we performed chemical characterization of MFCs and of red pigment (called red focal changes (RFCs)) from salmon fillets using alkaline hydrogen peroxide oxidation and hydroiodic acid hydrolysis. This revealed that the MFCs contain 3,4-dihydroxyphenylalanine (DOPA)-derived eumelanin, whereas the RFCs contain only trace amounts of eumelanin. Therefore, it is probable that the black color of the MFCs can be explained by the presence of eumelanin from accumulated melanomacrophages. For the red pigment, we could not find a significant signature of either eumelanin or pheomelanin; the red color is probably predominantly hemorrhagic in nature. However, we found that the level of pigmentation in RFCs increased together with some melanogenic metabolites. Comparison with a “mimicking experiment”, in which a mixture of a salmon homogenate + DOPA was oxidized with tyrosinase, suggested that the RFCs include conjugations of DOPAquinone and/or DOPAchrome with salmon muscle tissue proteins. In short, the results suggest that melanogenic metabolites in MFCs and RFCs derive from different chemical pathways, which would agree with the two different colorations deriving from distinct cellular origins, namely melanomacrophages and red blood cells, respectively.

Astaxanthin alleviates PM2.5-induced cardiomyocyte injury via inhibiting ferroptosis

BackgroundLong-term exposure of humans to air pollution is associated with an increasing risk of cardiovascular diseases (CVDs). Astaxanthin (AST), a naturally occurring red carotenoid pigment, was proved to have multiple health benefits. However, whether or not AST also exerts a protective effect on fine particulate matter (PM2.5)-induced cardiomyocyte damage and its underlying mechanisms remain unclear.MethodsIn vitro experiments, the H9C2 cells were subjected to pretreatment with varying concentrations of AST, and then cardiomyocyte injury model induced by PM2.5 was established. The cell viability and the ferroptosis-related proteins expression were measured in different groups. In vivo experiments, the rats were pretreated with different concentrations of AST for 21 days. Subsequently, a rat model of myocardial PM2.5 injury was established by intratracheal instillation every other day for 1 week. The effects of AST on myocardial tissue injury caused by PM2.5 indicating by histological, serum, and protein analyses were examined.ResultsAST significantly ameliorated PM2.5-induced myocardial tissue injury, inflammatory cell infiltration, the release of inflammatory factors, and cardiomyocyte H9C2 cell damage. Mechanistically, AST pretreatment increased the expression of SLC7A11, GPX4 and down-regulated the expression of TfR1, FTL and FTH1 in vitro and in vivo.ConclusionsOur study suggest that ferroptosis plays a significant role in the pathogenesis of cardiomyocyte injury induced by PM2.5. AST may serve as a potential therapeutic agent for mitigating cardiomyocyte injury caused by PM2.5 through the inhibition of ferroptosis.

Analysis of a pigment grinding muller from Lacapelle Livron (Tarn and Garonne, France): A tool to prepare cinnabar in a medieval painter workshop or a scriptorium?

A hemispherical stone has been discovered in a 19th century ruined barn at the village of Lacapelle Livron (Tarn and Garonne, France). Its morphology and its mirror polished flat surface showing numerous picketing marks allow to propose a grinding function. Optical microscopic observation shows that numerous striations and depressions present on the main flattened surface are resulting from a grinding action on a hard material. Further investigation with SEM-EDS analysis revealed high quantity of cinnabar pigment spreaded on the whole working flat surface and minor traces on other sides, indicating that the stone have been used as a muller to process pigment. Minor incidental traces of orpiment and calcite and an undetermined black organic residue analysed on a smaller flattened side are probably in relation with a second step of pigment processing. Additionally, many vegetal micro-fragments and micro-fibres have been observed in relation with the main working surface and red pigment. Identification of cotton among this fibre material is suggesting a late medieval or renaissance dating. Other observations and analysis put also in evidence iron striated and lined residues on the stone surfaces which could have resulted from the contact metal tool (i.e., knife) used to pick pigment, and from a handle or from the storage in a box. At last, comparison of the artefact can be done with historical pigment mullers from 18th–19th century and representation of painting workshop between the 15th and 17th century can help to propose different possible contexts of usage of this tool.

Modulation by Neuropeptides with Overlapping Targets Results in Functional Overlap in Oscillatory Circuit Activation.

Neuromodulation lends flexibility to neural circuit operation but the general notion that different neuromodulators sculpt neural circuit activity into distinct and characteristic patterns is complicated by interindividual variability. In addition, some neuromodulators converge onto the same signaling pathways, with similar effects on neurons and synapses. We compared the effects of three neuropeptides on the rhythmic pyloric circuit in the stomatogastric ganglion of male crabs, Cancer borealis Proctolin (PROC), crustacean cardioactive peptide (CCAP), and red pigment concentrating hormone (RPCH) activate the same modulatory inward current, I MI, and have convergent actions on synapses. However, while PROC targets all four neuron types in the core pyloric circuit, CCAP and RPCH target the same subset of only two neurons. After removal of spontaneous neuromodulator release, none of the neuropeptides restored the control cycle frequency, but all restored the relative timing between neuron types. Consequently, differences between neuropeptide effects were mainly found in the spiking activity of different neuron types. We performed statistical comparisons using the Euclidean distance in the multidimensional space of normalized output attributes to obtain a single measure of difference between modulatory states. Across preparations, the circuit output in PROC was distinguishable from CCAP and RPCH, but CCAP and RPCH were not distinguishable from each other. However, we argue that even between PROC and the other two neuropeptides, population data overlapped enough to prevent reliable identification of individual output patterns as characteristic for a specific neuropeptide. We confirmed this notion by showing that blind classifications by machine learning algorithms were only moderately successful.Significance Statement It is commonly assumed that distinct behaviors or circuit activities can be elicited by different neuromodulators. Yet it is unknown to what extent these characteristic actions remain distinct across individuals. We use a well-studied circuit model of neuromodulation to examine the effects of three neuropeptides, each known to produce a distinct activity pattern in controlled studies. We find that, when compared across individuals, the three peptides elicit activity patterns that are either statistically indistinguishable or show too much overlap to be labeled characteristic. We ascribe this to interindividual variability and overlapping subcellular actions of the modulators. Because both factors are common in all neural circuits, these findings have broad significance for understanding chemical neuromodulatory actions while considering interindividual variability.

Thermal synthesis of red phosphate pigments based on the composition of natural ore

ABSTRACT The red phosphate pigments without harmful metals were prepared by heating a mixture of iron oxalate and sodium dihydrogen phosphate or potassium dihydrogen phosphate or ammonium dihydrogen phosphate in P/Fe = 1/1 at 300–700°C. In the samples, iron was oxidised to trivalent, causing the red colour. The red colour of the samples was affected by the different cations and heating temperatures. Samples prepared using NaH2PO4 and KH2PO4 exhibited a relatively strong red colour when heated to 600°C and 700°C, with a* values above 30. The samples were red after treatment with acid and base solvents, among which the samples prepared with NaH2PO4 showed high acid and base resistance.

Recycling of hazardous jarosite residues based on hydrothermal crystal transformation

Jarosite [MeFe3(SO4)2(OH)6] is a typical non-ferrous smelting slag produced in the process of iron removal from hydrometallurgical solution, which contains a large number of valuable and toxic metal elements. Treating the complex and hazardous jarosite residue in an economically and environmentally sound way has always been an urgent problem. A novel one-step hydrothermal treatment method was proposed in this paper for recycling of jarosite residues. It can be seen from the XRD and TEM results that jarosite residues could be completely transformed into hematite crystal particles under hydrothermal conditions at temperature above 220℃. Meanwhile, other valuable metal components (such as nickel sulfate hexahydrate) entrained in the residue will be dissolved in the aqueous solution, which can be reused in the hydrometallurgical process. Through phase composition analysis of the hydrothermal process, it is concluded that jarosite was firstly pyrolyzed to generate Fe3+. The obtained Fe3+ was then hydrolyzed to Fe (OH)3, which was transformed into Fe2O3 through dehydration condensation and directional arrangement. Further roasting the hematite particles, the obtained product contained 62.57 % of Fe, but only 0.21 % of S and 0.04 % of As, which meets the requirements of raw materials for iron making. In addition, compared with the current international standard ISO 1248:2006 (E), the obtained hematite particles with nanometer size and single crystal structure can be used as iron oxide red pigment. Overall, the one-step hydrothermal treatment of jarosite residues followed by reduction roasting not only realizes the economic recycling of the metal resources, but also solves the stacking problem of those hazardous residues.

Sintesis Pigmen Merah Hematit (α-Fe2O3) dari Pasir Besi dengan Metode Kopresipitasi dan Hidrotermal: A Review

The purified natural iron sand contains magnetic dioxide particles to produce ferric ions (Fe3+) which can be used as precursors for the synthesis of the red pigment hematite. Hematite red pigment synthesis was carried out by coprecipitation method with NaOH precipitating agent and hydrothermal.The optimum pH of the hematite red pigment synthesis reaction using the coprecipitation method is pH 6. At pH 6 it will produce a hematite red pigment with higher brightness. By the hydrothermal method Fe3O4 added 50 mL HCl (12,063 M) in a beaker. The filtrates are added boric acid with varying concentrations of 0.1 M; 0.3 m; 0.5 M and 1.0 M at a volume ratio of 1:1. Gradually the solution is supplemented with NH4OH 6 M until a solution with a pH of 8 is obtained at a constant temperature of 70oC. The formed precipitate is put in the microwave for 10 minutes with a pressure of 90P. The characterization was carried out using XRD to see the crystal structure of the product and UV-Vis to see the absorption wavelength.und is the anatase phase.

Comparative characteristics of ancient red pigments used to decorate Thracian sacred sites (4th–3rd centuries BC)

The mineral composition and geochemical features of red pigments from paints and plasters used in the color decoration of the Shushmanets, Dolno Lukovo, Maglizh tombs, the eschars from tumulus 21 and 31 from Sboryanovo National Reserve (Bulgaria) and the Documaci Tomb (Romania) are compared. The results show that red ochre pigment (mainly hematite) was applied in the decoration of all objects, and only in the Maglizh Tomb a red cinnabar pigment was used – separately or in a mixture with red ochre. Regardless of the territorial remoteness of the tombs Dolno Lukovo, Maglizh, Documaci and the eschars, the red ochres used in them contain As, Cu, Zn and inclusion of minerals jarosite, plumbojarosite and native gold. Such mineral and geochemical features are characteristic of the oxidation zones of Au-Pb-Zn deposits. The most likely source of the red ochre is the well-developed oxidation zone of Au-Pb-Zn deposits in the Eastern Rhodopes. A characteristic feature of the red ochre from the Shushmanets Tomb is the lack of heavy metals but the hematite of the ochre contains inclusions of magnetite. A probable source for mining of this pigment was non-economic magnetite-hematite ore deposits hosted in the in the neighborly exposed chlorite-sericite schists.

Four new Pyrenula species from primary forests in the Guianas, South America, and their ascospore development


 
 
 Four new species of the genus Pyrenula (Pyrenulaceae, Pyrenulales, lichenized Ascomycetes) are presented. They originate from primary forests in the Guianas: Pyrenula cubica Sipman, with cubical central lumina in the ascospores; Pyr­enula flavida Sipman, with a yellow-pigmented thallus; P. rubromarginata Sipman, with red pigment on the excipulum and not on the thallus; and P. submicromma Sipman, like P. micromma but with submuriform instead of bacillar ascospores. In addition, a description for P. atropurpurea is provided, and P. subvariabilis is reduced to synonymy of P. infrastroidea. Special attention was paid to the development of the ascospores. Two different development types are recognized. The phylogenetic significance of these types is unclear.
 
 

Use, symbolism, and access to red pigments based on hematite and cinnabar between 400 B.C. and A.D. 1450 in Huanchaco, a pre-Hispanic maritime community on the North Coast of Peru

Use, symbolism, and access to red pigments based on hematite and cinnabar between 400 B.C. and A.D. 1450 in Huanchaco, a pre-Hispanic maritime community on the North Coast of Peru

Dissociation of ferriheme from oxidized heme proteins and re-reduction of ferriheme to ferroheme are crucial for the formation of zinc protoporphyrin IX in nitrite/nitrate-free dry-cured meat products.

Zinc protoporphyrin IX (ZnPP) is the dominant red pigment in nitrate/nitrite-free dry-cured meat products such as Parma ham, and it is considered to be a potential alternative to nitrite/nitrate for reddening dry-cured meat products. Ferroheme and ferriheme dissociated from heme proteins in meat were proposed as substrates to form ZnPP. To elucidate their specific formation mechanism, nitric oxide, carbon monoxide, and azide were used to stable heme in heme proteins. The exogenous hemoglobin derivatives bound with these ligands showed lower heme dissociation compared with exogenous oxyhemoglobin and did not contribute to ZnPP formation. Meanwhile, azide inhibited almost all ZnPP formation by binding to ferriheme, indicating ferriheme dissociation from oxidized heme proteins, predominantly for ZnPP formation. Free ferriheme could not be converted to ZnPP unless it was reduced to ferroheme. Overall, ferriheme dissociated from oxidized heme proteins was the dominant substrate for conversion to ZnPP after re-reduction to ferroheme.

The indigenous microbial diversity involved in the spontaneous fermentation of red dragon fruit (Hylocereus polyrhizus) identified by means of molecular tools

Red dragon fruit (RDF) is well-known for its high nutritional content, especially the red pigment betacyanins that possess high antioxidant activity. Natural fermentation is an ancient yet outstanding technique that relies on the autochthonous microbiota from fruits and vegetables surfaces to preserve and improve the nutritional values and quality of the food product. The present study was to evaluate and identify the indigenous microbial community (bacteria and fungi) that are involved in the natural fermentation of RDF. Results revealed a total of twenty bacterial pure cultures and nine fungal pure cultures were successfully isolated from fermented red dragon fruit drink (FRDFD). For the first time, the PCR amplification of 16S rRNA and ITS regions and sequence analysis suggested nine genera of bacteria and three genera of fungi (Aureobasidium pullulans, Clavispora opuntiae, and Talaromyces aurantiacus) present in the FRDFD. Four dominant (≥10 % isolates) bacteria species identified from FRDFD were Klebsiella pneumonia, Brevibacillus parabrevis, Bacillus tequilensis and Bacillus subtilis. The carbohydrate fermentation test showed that all the indigenous microbes identified were able to serve as useful starter culture by fermenting sucrose and glucose, thereby producing acid to lower the pH of FRDFD to around pH 4 for better betacyanins stability. The present study provides a more comprehensive understanding of the indigenous microbial community that serves as the starter culture in the fermentation of RDF. Besides, this study provides a useful guide for future research to be conducted on studying the rare bacterial strains (such as B. tequilensis) identified from the FRDFD for their potential bioactivities and applications in medical treatment and functional foods industries.

Red pigment from isolated Serratia marcescens SEM: Structure, antimicrobial and antioxidant activity

Pigments from microbial sources are likely to be suitable alternatives to synthetic pigments. Not only do natural pigments have the potential to increase product marketability, but they also exhibit valuable biological activities as antioxidants and antimicrobial agents. Recently, microbial prodigiosin (PG) has received a lot of attention due to its many beneficial applications. PG is a natural red dye. It is an alkaloid secondary metabolite with a unique tertiary structure produced by Serratia marcescens. The purpose of our study was to isolate indigenous strains of S. marcescens and identify it, extraction the red pigment from culturable bacteria to confirm its structure, evaluate its antimicrobial activity against a series of pathogenic microbes (Staphylococcus aureus NRRL B-313 and Bacillus subtilus NRC, Escherichia coli NRC B-3703, Pseudomonas aeruginosa NRC B-32, Candida albicans ATCC1023 and Aspergillus niger NRC) by well diffusion assay and antioxidant activities by DPPH assay. The isolate was identified by morphological characteristics and 16S rRNA sequencing as S. marcescens SEM, with accession number OM757735.1. PG from S. marcescens was first confirmed its purity by UV absorption spectrum, FTIR and GC-MS spectrophotometer. PG possess effective antimicrobial activity against tested pathogens, with MIC 1.0 ± 0.15, 5.0 ± 0.25, 16.5 ± 0.87, 16.5 ± 0.92 and 3.3 ± 0.17 μg/mL against B. cereus, St. aureus, E. coli, P. aurgenosa, and C. albicans, respectively. Also, PG possess highly antioxidant activity 97.2% at the concentration of 400 μg/ml after 120 min in dark, this activity increased gradually with increasing concentrations and time of incubation in dark,with IC50 (250 μg/ml at 30 min; 225 μg/ml at 60 min; 200 μg/ml at 90 min; 125 μg/ml at 120 min).

Growth, morphology, and formation of cinnabarin in Pycnoporus cinnabarinus in relation to different irradiation spectra

BackgroundThe demand for natural pigments in general, and for fungi-derived pigments in particular, is constantly rising. Wood-decomposing fungi represent a promising source for natural pigments and they are usually easy to cultivate in pure culture. One of them, i.e., Pycnoporus cinnabarinus, offers a highly interesting spectrum of bioactivity, partly due to the formation of the orange–red pigment cinnabarin. However, apart from a few studies addressing its diverse potential biotechnological applications, there is still a large gap of knowledge concerning the influence of light on the formation of cinnabarin. The aim of this work was to investigate the effect of different irradiations on the cinnabarin content, the growth, and the morphology of three different P. cinnabarinus strains. We used highly standardized irradiation conditions and cultivation techniques in combination with newly developed methods for the extraction and direct quantification of cinnabarin.ResultsRed, green, blue, and UV-A irradiation (mean irradiance Ee = 1.5 ± 0.18 W m−2) had considerable effects on the growth and colony appearance of all three P. cinnabarinus strains tested. The cinnabarin content determined was, thus, dependent on the irradiation wavelength applied, allowing strain-specific thresholds to be defined. Irradiation with wavelengths below this strain-specific threshold corresponded to a lower cinnabarin content, at least at the intensity applied. The orange–red pigment appeared by light microscopy as incrusted extracellular plaques present on the hyphal walls. Highly efficient vegetative propagation occurred by arthroconidia, and we observed the tendency that this asexual reproduction was (i) most frequent in the dark but (ii) never occurred under UV-A exposure.Conclusion This study highlights a differential photo-dependence of growth, morphology, and cinnabarin formation in P. cinnabarinus. This confirms that it is advisable to consider the wavelength of the light used in future biotechnological productions of natural pigments.Graphical abstract

A multi-analytical approach to identify ancient pigments used in pottery towers excavated from the Han Dynasty tombs

In 2013, several tombs were discovered and excavated in Southeastern Beijing, China, yielding various burial products. Among these were pottery towers, a representative artifact of the Han Dynasty rarely found in the area. Many studies on architectural aspects, such as construction type and construction situation, have been conducted based on the excavated pottery towers, but only a few have examined their raw materials or pigments. In this study, black, white, and red pigments were identified as carbon black, calcite, and cinnabar, respectively, through a multi-analysis approach. The manufacturing method of the pigment was established based on the crystal form and particle size of the pigment, by factoring in the pigment characteristics, which cannot be distinguished by component analysis and crystal structure analysis. We recommend that a continuous database be prepared and used in the future, not only for an interpretation of ancient pigments but also to identify the factors to be considered (physical characteristics, such as pigment particle size among others) when estimating the manufacturing process and conservation treatment.

Plant-based red colouration of shell beads 15,000 years ago in Kebara Cave, Mount Carmel (Israel).

Decorating the living space, objects, body and clothes with colour is a widespread human practice. While the habitual use of red mineral pigments (such as iron-oxide, e.g., ochre) by anatomically modern humans started in Africa about 140,000 years ago, the earliest documentation of the use of organic plant or animal-based red pigments is known from only 6,000 years ago. Here, we report the oldest reliable evidence of organic red pigment use 15,000 years ago by the first sedentary hunter-gatherers in the Levant. SEM-EDS and Raman Spectroscopy analyses of 10 red-stained shell beads enabled us to detect and describe the use of a colourant made of Rubiaceae plants roots (Rubia spp., Asperula spp., Gallium spp.) to colour personal adornments from the Early Natufian of Kebara cave, Mount Carmel, Israel. This adds a previously unknown behavioural aspect of Natufian societies, namely a well-established tradition of non-dietary plant processing at the beginning of the sedentary lifestyle. Through a combined multidisciplinary approach, our study broadens the perspectives on the ornamental practices and the chaînes opératoires of pigmenting materials during a crucial period in human history.

The effects of chlorine-containing species on cinnabar: A density functional theory investigation into the surface adsorption reactivity of mercury sulfide

First-principles computations can be used to noninvasively probe semiconductor surfaces and describe mechanisms and transformations that occur on those surfaces. One such material of interest is the chalcogenide mercury sulfide (HgS), also known as cinnabar. Cinnabar (α-HgS) and its synthetic counterpart (vermilion) have been used as bright red pigments since antiquity and are important sulfide materials in the field of art conservation. However, it has been known since Roman times that these pigments can darken when exposed to light. It has been hypothesized that Cl2 and other chlorine-containing materials are involved in the photodegradation of cinnabar surfaces. Here we use first-principles density functional theory (DFT) to probe the adsorption reactivity of Cl-containing adsorbates on HgS surfaces, as DFT yields information at the atomistic level and can link changes in surface structure to changes in electronic states. Specifically, we model single adsorbates interacting with corrugated and flat HgS surfaces to probe the initial step in the photodegradation mechanism. This allows us to not only assess the strength of adsorption and any corresponding adsorbate dissociations, but also link these adsorption and dissociation events to key changes in the electronic band structure that may act as spectroscopic identifiers in the degradation pathway of chalcogenide semiconductors that contain photoreactive metals.