Caractérisation de composés hybrides organique-inorganique à base de cuivre rencontrés en peinture (étude de leur formation et transformation)

Cette thèse, financée par la Fondation des Sciences du Patrimoine, Patrima, a pour but la compréhension du mécanisme chimique responsable du brunissement de certains pigments verts à base de cuivre, sous forme de complexes organométalliques, utilisés en peinture de l'Antiquité à la Renaissance. Il s'agit du vert de gris et du résinate de cuivre . La variation chromatique de ces pigments engendre une perte de lisibilité de l'œuvre et pose un important problème de conservation. La détermination des réactions impliquées dans l'altération est fondamentale pour définir une méthodologie d'intervention. Afin de clarifier le mécanisme responsable du changement de couleur il est nécessaire d'étudier d'une part la géométrie du centre métallique et d'autre part la nature des liaisons cuivre-ligand. Dans ce but une stratégie multianalytique a été développée. Elle est basée sur la reconstitution des composés utilisés par les artistes et de ceux qui peuvent se former dans les couches picturales, et sur leur caractérisation, avant et après un vieillissement accéléré (thermique oupar exposition à la lumière). La synthèse des ces systèmes modèles a permis d'évaluer l'influence de plusieurs paramètres (solvant, pH, température et temps de réaction) sur la structure des complexes. Les produits de départ et les composés de dégradation ont été analysés par différentes techniques. L'étude des morphologies et la répartition chimique du cuivre au sein des systèmes est réalisée par MEB -EDS. La structure moléculaire a été caractérisée par IRTF diffraction des rayons X, spectroscopie d'absorption des rayons X et par résonance paramagnétique électronique. La caractérisation des produits de dégradation présents dans la phase organique est effectuée par chromatographie en phase gazeuse couplée à la spectrométrie de masse. En parallèle l'étude de leurs propriétés optiques a été réalisée par spectroscopie UV-visible. Les données collectées sont comparées à celles obtenues, par les mêmes méthodes analytiques, sur des échantillons de couches picturales prélevés sur des œuvres peintes plus ou moins altérées. Ce travail comparatif a permis à la fois de mieux comprendre les mécanismes de formation et de transformation au cours du vieillissement de ces systèmes hybrides organique-inorganique, d'évaluer quels paramètres ont plus d'influence sur l'altération et de valider ou d'invalider certaines hypothèses proposées concernant les changements des propriétés optiques observées.This thesis, funded by Patrima, Foundation for Cultural Heritage Sciences, aims to understand the chemical mechanisms responsible for the darkening of some green copper organometallic pigments (Verdigris and copper resinate) widely used in paintings from Antiquity to the Renaissance. The color variation of these pigments involves a loss of legibility of the artwork and is a major conservation issue. The determination of the reactions involved in the alteration is fundamental to define an intervention methodology. In order to clarify the discoloration process it is necessary to get information on the geometry of the copper cluster and the nature of the copper-ligand bonds. With this aim, a multi-analytical methodology has been developed, based on the reconstitution of ancient pigment and of the compounds that can be formed in the paint layer. These model systems have been characterized before and after an accelerated ageing (by heat or light). Their synthesis has permitted to evaluate the influence of several parameters (solvent, pH, temperature and reaction time) on the resulting structure. The original materials and their degradation products have been analyzed by different techniques. The study of the morphology and chemical distribution of copper in the system was performed by SEM-EDS. The molecular structure was characterized by FTIR, XRD spectroscopy, X-ray absorption and EPR (Electronic Paramagnetic Resonance). The characterization of organic degradation products has been carried out by gas chromatography coupled to mass spectrometry. At the same time a study of optical properties has been performed by UV-visible spectroscopy. The data collected are compared to those obtained, by the same analytical methods, on samples of paint layers taken from ancient paintings. This comparative work has permitted to better understand the mechanisms of formation and transformation of these organic-inorganic systems, to assess which parameters influence the alteration, and to validate or invalidate some preliminary hypothesis about the chromatic changes.CERGY PONTOISE-Bib. electronique (951279901) / SudocSudocFranceF

Les chancis des peintures de chevalet : étude des traitements de restauration actuels et proposition d’une alternative innovante

Les chancis de vernis et de couches picturales des peintures de chevalet à l’huile sont des altérations récurrentes induites principalement par l’humidité. L’article expose un état de l’art sur la restauration des peintures chancies à partir de substances transparentes filmogènes ou de solvants sous forme vapeur ou liquide. Pour les chancis de vernis, l’analyse par nanotomographie à contraste de phase de prélèvements restaurés selon des pratiques actuelles (application d’un solvant suivi d’un vernissage) démontre leur manque d’efficacité et surtout de durabilité. Trouver une solution pérenne constitue un enjeu de taille pour la restauration et la conservation des œuvres chancies. L’emploi du perfluoropolyéther développé dans le cadre de ce projet a été testé sur des échantillons modèles. Les analyses par spectrocolorimétrie et microtomographie X en absorption mettent en évidence son efficacité et sa réversibilité à l’échelle macroscopique et microscopique.The blanching of the varnish and paint layers in easel paintings executed in oils is a recurrent alteration mainly caused by humidity. This paper is a review of the restoration of blanched paintings using transparent film-forming substances or liquid or vaporous solvents. For the blanched varnish layers, analysis by phase-contrast nanotomography of samples restored by current practices (application of a solvent followed by varnishing) showed their ineffectiveness and, above all, their lack of durability. Finding a long-standing solution represents a serious challenge for the restoration and conservation of blanched paintings. The use of perfluoropolyether (PFPE), developed in the course of this investigation, was tested on selected samples. Spectrocolorimetry and X-ray microtomography demonstrated its effectiveness and reversibility on a macroscopic and microscopic scale

1,4-Disubstituted-[1,2,3]triazolyl-Containing Analogues of MT-II: Design, Synthesis, Conformational Analysis, and Biological Activity

Side chain-to-side chain cyclizations represent a strategy to select a family of bioactive conformations by reducing the entropy and enhancing the stabilization of functional ligand-induced receptor conformations. This structural manipulation contributes to increased target specificity, enhanced biological potency, improved pharmacokinetic properties, increased functional potency, and lowered metabolic susceptibility. The CuI-catalyzed azide–alkyne 1,3-dipolar Huisgen’s cycloaddition, the prototypic click reaction, presents a promising opportunity to develop a new paradigm for an orthogonal bioorganic and intramolecular side chain-to-side chain cyclization. In fact, the proteolytic stable 1,4- or 4,1-disubstituted [1,2,3]triazolyl moiety is isosteric with the peptide bond and can function as a surrogate of the classical side chain-to-side chain lactam forming bridge. Herein we report the design, synthesis, conformational analysis, and functional biological activity of a series of i-to-i+5 1,4- and 4,1-disubstituted [1,2,3]triazole-bridged cyclopeptides derived from MT-II, the homodetic Asp5 to Lys10 side chain-to-side chain bridged heptapeptide, an extensively studied agonist of melanocortin receptors

Hirao Cross-Coupling Reaction as an Efficient Tool to Build Non-natural C2-Phosphonylated Sugars

International audienceAbstract A range of C2-phosphonylated sugars have been accessed through a palladium-catalyzed Hirao cross-coupling on 2-iodoglycals using trialkylphosphites as phosphorylating reagents. The developed conditions led to the creation of an unnatural C–P bond on sugars and proved to be compatible with diversely protected glycals (acetyl-, benzyl-, PMB-protected) as well as with unprotected substrates. Several monosaccharides and one disaccharide have been synthesized by applying this methodology. Deprotection conditions are also described

Copper(II) SBA-15: A reusable catalyst for azide–alkyne cycloaddition

International audienceThe azide-alkyne cycloaddition reaction was investigated under catalytic conditions involving a copper (II) loaded silica based mesoporous material. Cu(II) SBA-15 demonstrated a high catalytic effect in 1,4-triazoles synthesis in organic. No additives such as a base or a reductant are required. Quantitative yields were obtained and a mere filtration of the mesoporous material which retains copper (II) allows the recovery of the catalyst. In addition, up to 5 times recycling of the catalyst was achieved without loss of the activity affording 1,4-triazoles in a yield up to 98%

Synthesis of ribavirin 2'-Me-C-nucleoside analogues Full Research Paper Open Access

Abstract An efficient synthetic pathway leading to two carbonated analogues of ribavirin is described. The key-steps in the synthesis of these ribosyltriazoles bearing a quaternary carbon atom in the 2'-position are an indium-mediated alkynylation and a 1,3-dipolar cyclization. 755 Figure 1: Targeted compounds

Low Fluorinated Oligoamides for Use as Wood Protective Coating

New highly hydrophobic fluorinated oligoamides were synthesized and studied as materials for the protection of non-varnishable wooden artifacts. The new oligoamides were designed to achieve the best performance (including high chemical affinity to the wood material) and the lowest environmental impact. In order to minimize the risk of bioaccumulation, short perfluoroalkyl side chains were reacted with oligoethylene L-tartaramide (ET), oligoethylene adipamide-L-tartaramide (ETA), oligoethylene succinamide-L-tartaramide (EST), oligoethylene succinamide (ES), and oligodiethylenetriamino-L-tartaramide (DT). Favorable reaction conditions were also adopted to obtain low molecular weight compounds characterized by non-film-forming properties and solubility or dispersibility in environmentally friendly organic solvents. Their behavior in terms of modification of the wood surface characteristics, such as wettability, moisture absorption, and color, was analyzed using a specific diagnostic protocol to rapidly obtain preliminary, but reliable, results for optimizing a future synthesis of new and tailored protectives. The influence of different monomer units on the reactivity, solubility, and hydrophobic properties of different oligoamides was compared showing ESF (contact angle 138.2°) and DF (132.2°) as the most effective products. The study of stability to photochemical degradation confirms ESF as promising protective agents for artefacts of historical and artistic interest in place of long-chain perfluoroalkyl substances (PFAS), products currently subject to restrictions on use

Partially perfluorinated derivatives as powerful tool for the restoration of blanching easel paintings

Perfluorinated oligoamides/amines were prepared and characterized. They were evaluated then for easel painting restoration by filling pores resulting of the blanching. They were used on prepared mock-ups analysed by FEG-SEM for morphological changes and by spectro-colorimetry analysis for the restoration. Compared to DG6G900 , the new partially perfluorinated products DSTF and DSF are recommended as restoration products for blanching easel paintings

Synthesis of ribavirin 2’-Me-C-nucleoside analogues

International audienceAn efficient synthetic pathway leading to two carbonated analogues of ribavirin is described. The key-steps in the synthesis of these ribosyltriazoles bearing a quaternary carbon atom in the 2'-position are an indium-mediated alkynylation and a 1,3-dipolar cyclization