Hidden mysteries in ancient Egyptian paintings from the Theban Necropolis observed by in-situ XRF mapping.

The material study of ancient Egyptian paintings began with the advent of Egyptology during the 19th century. By the 1930s, a lot had already been sampled and described. The limited palette for example has been analysed from actual painted surfaces but also from pigments and painting tools retrieved on site. However, most of these studies took place in museums while the painted surfaces, preserved in funerary chapels and temples, remained somewhat estranged from this primary physical understanding. The artistic process has been also reconstructed, mainly from the information presented by unfinished monuments, showing surfaces at different stages of completion. A lot of this modern and theoretical reconstruction is, however, based on the usual archaeological guessing game that aims at filling the remaining blanks. Our interdisciplinary project has decided to experiment on-site with state-of-the-art portable analysis tools, avoiding any physical sampling, to see if our knowledge of the work of the ancient Egyptian painters and draughtsmen could be taken at a further stage, while based on physical quantification that could be seen as a stronger and more reliable foundation for a redefined scientific hypothesis. The use of XRF mapping has, for instance, been applied to a known case of correction by surface repaint, something that is supposedly rare in the ancient Egyptian formal artistic process, while another fully unexpected one was discovered during the analytic exploration of a royal representation. In both cases, the precise and readable imaging of the physical composition of the painted surface offers a renewed visual approach based of chemistry, that can be shared through a multi- and interdisciplinary approach. However, this also leads to a more complex description of pigment mixtures that could have multiple meanings, where the practical often leads towards the symbolic, and from there hopefully to a renewed definition of the use of colours in complex sets of ancient Egyptian representations. At this stage, though the progress in this on-site material assessment of ancient works of art definitely means astonishing progress, one humbly has to face the fact that these ancient treasures shall still retain part of their defining mysteries.

Stressing the differences in alizarin and purpurin dyes through UV-visible light absorption and 1H-NMR spectroscopies.

Three anthraquinone-based chromophores (9,10-anthraquinone, alizarin, purpurin) are compared from the point of view of their experimental and computed NMR and UV-visible light absorption spectra. Using a hybrid (explicit/implicit) solvent model, each proton chemical shift can be reproduced with an error of less than 7%, even when such protons are engaged in inter-molecular hydrogen bonds with the solvent or when the analyzed sample contains a significant amount of impurities, for instance, 9,10-anthraquinone in purpurin. All the steady-state UV-visible absorption spectra feature a significant vibrational progression in the first absorption band. The shape of the corresponding computed spectra, including vibronic couplings obtained with the adiabatic Hessian approach and the Franck-Condon and Herzberg-Teller approximation of the transition dipole, are in excellent agreement with the experimental ones. The importance and the nature of the vibronic couplings are different for the three molecules, even if they only differ by the number of hydroxyl groups.

Connecting Rheological Properties and Molecular Dynamics of Egg-Tempera Paints based on Egg Yolk.

Egg-tempera painting is a pictorial technique widely used in the Middle Ages, although poorly studied in its physico-chemical aspects until now. Here we show how NMR relaxometry and rheology can be combined to probe egg-tempera paints and shed new light on their structure and behavior. Based on recipes of the 15th century, model formulations with egg yolk and green earth have been reproduced to characterize the physicochemical properties of this paint at the mesoscopic and macroscopic scales. The rheological measurements highlight a synergetic effect between green earth and egg yolk, induced by the interactions between them and the structural organisation of the system. 1 H NMR relaxometry emphasizes the presence and the structure of a network formed by the yolk and the pigment.

Zn-doped mesoporous hydroxyapatites and their antimicrobial properties.

Recently, zinc-based materials have gained immense attention as antimicrobial agents. In this study, zinc-doped mesoporous hydroxyapatites (HAps) with various Zn contents were prepared by co-precipitation using a phosphoprotein as the porous template. The use of the phosphoprotein as the porous template resulted in the formation of zinc-doped mesoporous HAps (mHAps) with large pores and specific surface area (182 m2 g-1), as indicated by the nitrogen adsorption/desorption measurements. The formation of the zinc-doped HAps was confirmed by various analytical techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The biomaterials prepared in this study were used as antimicrobial agents against gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria. The Zn2%-mHAp sample showed the maximum bacterial inhibitory concentrations of 50 ± 5% and 77 ± 5% for the Gram-positive and Gram-negative bacteria, respectively. The antibacterial activity of the mHAp samples depended strongly on their Zn2+ content. Thus, the use of a biotemplate and Zn2+ ions is an efficient approach for the formation of novel HAp-based biomaterials with promising antibacterial properties. This synthesis approach will pave a new pathway for the functionalization of other materials for different biomedical applications.

Green earth pigments dispersions: Water dynamics at the interfaces.

HYPOTHESIS: The objective is to elucidate the multiscale dynamics of water within natural mixtures of minerals, green earth pigments that are mainly composed of phyllosilicates containing large amount of iron. In particular, the interaction of water with the different kinds of surfaces has to be probed. One issue is to examine the influence of surface type, basal or edge, on the dispersion quality. EXPERIMENT: The study was carried out using 1H variable field NMR relaxometry on various green earth pigment dispersions and concentrations. To analyse the data, a new analytical model was developed for natural phyllosilicates containing large amount of paramagnetic centres. FINDING: The proposed theoretical framework is able to fit the experimental data for various samples using few parameters. It allows to determining water diffusion and residence times in complex phyllosilicate dispersions. Furthermore, it makes it possible to differentiate the contribution of the basal and edge surfaces and their respective surface area in interaction with water. Moreover, NMR relaxation profile reveals to be highly sensitive to the structural aspect of the phyllosilicates and to the accessibility of water to iron, hence allowing to discriminate clearly between two very similar phyllosilicates (glauconite and celadonite) that are difficult to distinguish by standard structural methods.

Green Earth pigments aqueous dispersions: NMR relaxation rates dataset.

The data presented here are related to the research paper entitled "Green Earth pigments dispersions: water dynamics at the interfaces". The nuclear magnetic resonance (NMR) relaxometry data are provided for various aqueous Green Earth (GE) pigments dispersions with volume fraction spanning approximately from 0.1 to 0.5. For two of them (Cyprus GE and Bohemian GE), the NMR relaxation profiles from 10 kHz to 30 MHz (1H frequency) is given for several temperatures spanning from 293 to 318K. In addition, the X-ray diffraction pattern is provided for France GE (Kremer pigments) for the identification of the main mineral component. The nitrogen gas isotherms are provided for Cyprus GE and Bohemian GE.

Amino hydroxyapatite/chitosan hybrids reticulated with glutaraldehyde at different pH values and their use for diclofenac removal.

Diclofenac sodium (DS) is an emergent pollutant, and among the methods investigated for its removal, adsorption is the most widely utilized technique. Hydroxyapatite and chitosan are biomaterials often used for adsorption. However, both biomaterials are limited due to their low chemical stability in an acidic medium; furthermore, pure hydroxyapatite interacts poorly with diclofenac. In this work, hydroxyapatite was organofunctionalized with 3-aminopropyltrimethoxysilane and further used to obtain amino hydroxyapatite /chitosan hybrids by crosslinking with glutaraldehyde at pH 3, 4, 5, and 6. X-ray diffraction patterns indicated the preservation of the hydroxyapatite phase under all pH conditions. Based on the control reaction of the amino hydroxyapatite with glutaraldehyde and its further reduction in sodium borohydride, the formation of CN moieties was highlighted as the main interaction mechanism between the aldehyde and amino groups. Therefore, crosslinking with glutaraldehyde was evaluated by infrared, Raman spectroscopy, and 13C NMR techniques; the results suggested contributions of imine formation and hydrogen bonding. The hybrid obtained at pH 3 exhibited an enhanced adsorption capacity of 125 mg g-1 at 15 min. The synergy between amino hydroxyapatite and chitosan crosslinked by glutaraldehyde was demonstrated.

The degradation of organic compounds impacts the crystallization of clay minerals and vice versa.

Expanding our capabilities to unambiguously identify ancient traces of life in ancient rocks requires laboratory experiments to better constrain the evolution of biomolecules during advanced fossilization processes. Here, we submitted RNA to hydrothermal conditions in the presence of a gel of Al-smectite stoichiometry at 200 °C for 20 days. NMR and STXM-XANES investigations revealed that the organic fraction of the residues is no longer RNA, nor the quite homogeneous aromatic-rich residue obtained in the absence of clays, but rather consists of particles of various chemical composition including amide-rich compounds. Rather than the pure clays obtained in the absence of RNA, electron microscopy (SEM and TEM) and diffraction (XRD) data showed that the mineralogy of the experimental residues includes amorphous silica and aluminosilicates mixed together with nanoscales phosphates and clay minerals. In addition to the influence of clay minerals on the degradation of organic compounds, these results evidence the influence of the presence of organic compounds on the nature of the mineral assemblage, highlighting the importance of fine-scale mineralogical investigations when discussing the nature/origin of organo-mineral microstructures found in ancient rocks.

Confinement and Time Immemorial: Prebiotic Synthesis of Nucleotides on a Porous Mineral Nanoreactor.

We report the successful one-pot synthesis of adenosine mono-, di-, and triphosphate in the confined space of a mordenite zeolite. This is also the first report of ATP synthesized onto a porous mineral surface. The results revealed a plausible prebiotic route to ribonucleotides and highlighted the contribution of microporous minerals in the origins of life.

The Photochemistry on Space Station (PSS) Experiment: Organic Matter under Mars-like Surface UV Radiation Conditions in Low Earth Orbit.

The search for organic molecules at the surface of Mars is a top priority of the Mars Science Laboratory (NASA) and ExoMars 2020 (ESA) space missions. Their main goal is to search for past and/or present molecular compounds related to a potential prebiotic chemistry and/or a biological activity on the Red Planet. A key step to interpret their data is to characterize the preservation or the evolution of organic matter in the martian environmental conditions. Several laboratory experiments have been developed especially concerning the influence of ultraviolet (UV) radiation. However, the experimental UV sources do not perfectly reproduce the solar UV radiation reaching the surface of Mars. For this reason, the International Space Station (ISS) can be advantageously used to expose the same samples studied in the laboratory to UV radiation representative of martian conditions. Those laboratory simulations can be completed by experiments in low Earth orbit (LEO) outside the ISS. Our study was part of the Photochemistry on the Space Station experiment on board the EXPOSE-R2 facility that was kept outside the ISS from October 2014 to February 2016. Chrysene, adenine, and glycine, pure or deposited on an iron-rich amorphous mineral phase, were exposed to solar UV. The total duration of exposure to UV radiation is estimated to be in the 1250-1420 h range. Each sample was characterized prior to and after the flight by Fourier transform infrared (FTIR) spectroscopy. These measurements showed that all exposed samples were partially degraded. Their quantum efficiencies of photodecomposition were calculated in the 200-250 nm wavelength range. They range from 10-4 to 10-6 molecules·photon-1 for pure organic samples and from 10-2 to 10-5 molecules·photon-1 for organic samples shielded by the mineral phase. These results highlight that none of the tested organics are stable under LEO solar UV radiation conditions. The presence of an iron-rich mineral phase increases their degradation.

A new durable pigment with hydrophobic surface based on natural nanotubes and indigo: Interactions and stability.

Covering with polyorganosilane (POS) was proved as an effective way to enhance the chemical and thermal stability of clay/dye hybrid pigments. But the photostability and interactions with clay minerals, dyes and POS layer has never been reported. In order to investigate above issues, new organic-inorganic hybrid pigments based on halloysite (Hal) and indigo (In) were prepared by grinding method. X-ray diffraction, transmission electron microscopy, thermogravimetry, Fourier transform infrared spectroscopy were applied to characterize the structure of In-Hal (without POS layer) and In-Hal-POS (with POS layer) pigments. Solid state nuclear magnetic resonance (NMR) was employed to reveal the interactions between Hal, In and POS. Reflection spectra and CIE 1976 color space system were used to evaluate the color parameters and color changes of pigments. Thermal stability, chemical resistance to ethanol, 1 mol·L-1 HCl and 1 mol⋅L-1 NaOH, and light fastness to visible light were tested. Indigo molecules dispersed on the surface of Hal nanotubes. POS layer homogeneously covered on the surface of hybrid pigments, without changing the crystal structure and morphology of Hal. Covering with POS layer seldomly affect the color of hybrid pigments. However, In-Hal-POS exhibited better stability than In-Hal, due to hydrophobic surface which can prevent indigo molecules from chemical reactions and degradation. A new route was proposed to prepare organic-inorganic hybrid pigments, ignoring the interaction between dye molecules and substrates.

Author Correction: Proton irradiation: a key to the challenge of N-glycosidic bond formation in a prebiotic context.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Thiabendazole/bentonites hybrids as controlled release systems.

Clay minerals are commonly used in pharmaceutical products as excipients and active agents. New drug vehicles based on clay minerals have been developed. In this work, sodium (BentNa), calcium (BentCa) and magnesium (BentMg) exchanged bentonites were used for the sorption of thiabendazole (TBZ), and their potential use as controlled release systems was evaluated. Pristine bentonite and exchanged bentonites were characterized by X-ray diffraction, infrared spectroscopy, thermogravimetry and transmission electron microscopy (TEM), and the influence of the different parameters such as pH, contact time and initial concentration of the drug was investigated. The maximum adsorption reached after 45 min period with 2000 mg L-1 of thiabendazole to BentNa and after 105 min with 1300 mg L-1 to BentCa and BentMg, respectively. The maximum adsorbed quantities of thiabendazole were 164.4; 152.3 and 133.3 mg g-1 for BentNa, BentCa and BentMg, respectively. The emission profiles obtained for the bentonite/drug hybrids were similar when simulated body fluids were used and these emission profiles were fitted according to the Korsmeyer-Peppas kinetic model.

One Step up the Ladder of Prebiotic Complexity: Formation of Nonrandom Linear Polypeptides from Binary Systems of Amino Acids on Silica.

Evidence for the formation of linear oligopeptides with nonrandom sequences from mixtures of amino acids coadsorbed on silica and submitted to a simple thermal activation is presented. The amino acid couples (glutamic acid+leucine) and (aspartic acid+valine) were deposited on a fumed silica and submitted to a single heating step at moderate temperature. The evolution of the systems was characterized by X-ray diffraction, infrared spectroscopy, thermosgravimetric analysis, HPLC, and electrospray ionization mass spectrometry (ESI-MS). Evidence for the formation of amide bonds was found in all systems studied. While the products of single amino acids activation on silica could be considered as evolutionary dead ends, (glutamic acid+leucine) and, at to some extent, (aspartic acid+valine) gave rise to the high yield formation of linear peptides up to the hexamers. Oligopeptides of such length have not been observed before in surface polymerization scenarios (unless the amino acids had been deposited by chemical vapor deposition, which is not realistic in a prebiotic environment). Furthermore, not all possible amino acid sequences were present in the activation products, which is indicative of polymerization selectivity. These results are promising for origins of life studies because they suggest the emergence of nonrandom biopolymers in a simple prebiotic scenario.

Dual role of layered double hydroxide nanocomposites on antibacterial activity and degradation of tetracycline and oxytetracyline.

The antibiotic intercalation inside the layered double hydroxide (LDH) layers was usually considered for water decontamination but rarely for drug delivery. Here, tetracycline (TCH) and oxytetracycline (OXY) were immobilized in Zn2Al-Cl LDH following two methods: co-precipitation and anionic exchange. The interfacial concentration of antibiotic varies from 0.04 to 0.5 depending the method of immobilization. The antibiotics are not intercalated in the interlayer space allowing their release in 10 Hours. The antibacterial activity against both E. coli and S. epidermidis revealed that the loaded antibiotics are still active but less efficient compared to the free ones. After exposition to UV light or to high temperature storage (30, 60 and 120 °C), their antibacterial activity significantly decreases due to their degradation especially when antibiotic is loaded on material by co-precipitation. These results are promise to reduce antibiotic contamination in waters.

Going through the wine fining: Intimate dialogue between organics and clays.

Wine chemistry inspires and challenges with its complexity and intriguing composition. In this context, the composites based on the use of a model protein, a polyphenol of interest and montmorillonite in a model hydroalcoholic solution have been studied. A set of experimental characterization techniques highlighted the interactions between the organic and the inorganic parts in the composite. The amount of the organic part was determined by ultraviolet-visible (UV-VIS) and thermal analysis. X-ray diffraction (XRD) and transmission electronic microscopy (TEM) informed about the stacking/exfoliation of the layers in the composites. Vibrational and nuclear magnetic resonance spectroscopies methods stressed on the formation of a complex between the protein and the polyphenol before adsorption on the clay mineral. The mobility/rigidity of the organic parts were determined by fluorescence time resolved spectroscopy. Changes in the secondary structure of the protein occured upon complexation with polyphenol on clay mineral due to strong interactions. Although not representating faithfully enological conditions, these results highlight the range and nature of mechanisms possibly involved in wine fining.

Potential Role of Inorganic Confined Environments in Prebiotic Phosphorylation.

A concise outlook on the potential role of confinement in phosphorylation and phosphate condensation pertaining to prebiotic chemistry is presented. Inorganic confinement is a relatively uncharted domain in studies concerning prebiotic chemistry, and even more so in terms of experimentation. However, molecular crowding within confined dimensions is central to the functioning of contemporary biology. There are numerous advantages to confined environments and an attempt to highlight this fact, within this article, has been undertaken, keeping in context the limitations of aqueous phase chemistry in phosphorylation and, to a certain extent, traditional approaches in prebiotic chemistry.

Proton irradiation: a key to the challenge of N-glycosidic bond formation in a prebiotic context.

The formation of nucleosides in abiotic conditions is a major hurdle in origin-of-life studies. We have determined the pathway of a general reaction leading to the one-pot synthesis of ribo- and 2'-deoxy-ribonucleosides from sugars and purine nucleobases under proton irradiation in the presence of a chondrite meteorite. These conditions simulate the presumptive conditions in space or on an early Earth fluxed by slow protons from the solar wind, potentially mimicking a plausible prebiotic scenario. The reaction (i) requires neither pre-activated precursors nor intermediate purification/concentration steps, (ii) is based on a defined radical mechanism, and (iii) is characterized by stereoselectivity, regioselectivity and (poly)glycosylation. The yield is enhanced by formamide and meteorite relative to the control reaction.

Mesoporous calcium phosphate using casein as a template: Application to bovine serum albumin sorption.

Mesoporous hydroxyapatites were synthesized at room temperature using casein as a template, and key experimental factors, such as casein concentration, pH and extraction of casein in the final solids by washing and thermal treatment, were systematically investigated. The X-Ray Diffraction (XRD) patterns confirmed the synthesis of well-crystallized hydroxyapatite. The N2 adsorption/desorption isotherms were in agreement with the formation of mesoporous hydroxyapatite with a maximum surface area of 106m2g-1. Infrared spectroscopy and thermogravimetry analysis were performed to investigate the extraction of casein in water in the post-synthesis stage. Pure mesoporous hydroxyapatite exhibited good BSA adsorption capacity higher than the one obtained for conventional hydroxyapatite.

Adsorption and photophysical properties of fluorescent dyes over montmorillonite and saponite modified by surfactant.

In the present study, the adsorption capacities of two intercalated smectites, CTAB-saponite and CTAB-montmorillonite with a cationic surfactant, were investigated with three fluorescent dyes namely Rhodamine 640 perchlorate rhodamine (Rho), sulforhodamine B (SR) and Kiton red 620 (KR). The adsorption isotherms fit well with the non-linear Langmuir isotherm model and the maximum adsorption capacities of all the composites are determined. The photophysical properties such as anisotropy and fluorescence lifetime of all the fluorescent dyes over the clay materials are determined. The set of experimental data based on X-Ray diffraction (XRD), transmission electron microscopy (TEM), Thermal analysis (TG-DTA) and fluorescence measurements allow highlighting the presence or the absence of interactions between the dyes and the modified clay minerals.