Solid state complexation of natural organic dyes with Al(III): electronic and vibrational spectroscopies
Résumé
Used in antiquity as pigments in painting, lakes are coloured organic-inorganic hybrid materials [1]. They were prepared by addition of natural organic dyes to a white mineral substrate involving a complexation of colouring molecules with a metallic cation such as Al(III). Knowledge of correlations between the organic and inorganic constituents is required to control the colour and the stability of the pigment. This work concerns the solid state complexation of aluminium with quercetin. This chromophore is used as a model for the phenolic compounds extracted from immature fruits of Rhamnus catharticus L. employed for Stil de grain lake or “jaune d’Avignon” [2,3] . The characterization of the synthesised powder materials was performed by UV-Visible, IR and Raman spectroscopy which makes it possible to correlate the experimental parameters of lake preparation with the physicochemical properties of corresponding aluminium complexes in solution [4]. Lastly, the comparison of quercetin with historic model lake shows that they are composed of an aluminium complex encapsulated into an amorphous matrix of aluminium hydroxide. For all the lakes the intensity color comes from the dilution of the different complex into the inorganic support.
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