Interactions between inorganic pigments and proteinaceous binders in reference paint reconstructions

TitleInteractions between inorganic pigments and proteinaceous binders in reference paint reconstructions
Publication TypeJournal Article
Year of Publication2013
AuthorsDuce, C, Bramanti, E, Ghezzi, L, Bernazzani, L, Bonaduce, I, Colombini, MP, Spepi, A, Biagi, S, Tiné, MR
JournalDalton Transactions
ISSN14779226 (ISSN)
KeywordsArticle, Artificial light, Binders, Calcium Carbonate, Calorimetry, Casein, Caseins, chemistry, Chromatography, coloring agent, Coloring Agents, Differential Scanning, Differential scanning calorimetry, Ferric Compounds, ferric ion, ferric oxide, Fourier Transform Infrared, Fourier transform infrared spectroscopy, Gel, gel chromatography, Hydrophobic interactions, Infrared spectroscopy, Inorganic pigments, Intermolecular interactions, Lead, lead oxide, metabolism, Ovalbumin, oxide, Oxides, Paint, Protein molecules, protein secondary structure, Protein Structure, Proteinaceous binders, Proteins, Random coil, Secondary, Side-chains, Spectroscopy, Thermogravimetric analysis, Thermogravimetry

The degradation of the proteinaceous binders, ovalbumin (OVA) and casein, and their interactions with azurite (Cu3(CO3) 2(OH)2), calcium carbonate (CaCO3), hematite (Fe2O3) and red lead (Pb3O4) pigments were studied. A multi-analytical approach based on Thermogravimetric Analysis (TG), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR) and Size Exclusion Chromatography (SEC) was used. The research was carried out on a set of paint reconstructions, which were analysed before and after artificial light ageing. We highlighted that in most cases the inorganic pigments interact with both proteins by decreasing their thermal stability and their intermolecular $\beta$-sheet content, and that ageing induces aggregation. We hypothesized that pigments intercalate between protein molecules, producing a partial disruption to the protein-protein intermolecular interaction. In the case of casein, these phenomena continued during ageing. In fact, we observed a complete disappearance of intermolecular $\beta$-sheets and an increase in intramolecular $\beta$-sheets and random coil during ageing. This result is in agreement with the structural properties of casein, whose aggregation is known to be induced by hydrophobic interactions. On the other hand, in aged OVA paint replicas, we observed the formation of new intermolecular $\beta$-sheets and an increase in thermostability. In addition FTIR showed oxidation of the side chains of the aged OVA/hematite sample and aged casein pigment samples, and SEC highlighted hydrolysis phenomena in aged carbonate, azurite and red lead/OVA complexes and in aged casein/calcium carbonate and casein/azurite samples. © 2013 This journal is The Royal Society of Chemistry.