title: Interactions between inorganic pigments and proteinaceous binders in reference paint reconstructions.
abstract: The degradation of the proteinaceous binders, ovalbumin (OVA) and casein, and their interactions with azurite (Cu(3)(CO(3))(2)(OH)(2)), calcium carbonate (CaCO(3)), hematite (Fe(2)O(3)) and red lead (Pb(3)O(4)) 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 β-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 β-sheets and an increase in intramolecular β-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 β-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.
authors.affiliation: Dipartimento di Chimica e Chimica Industriale, Via Risorgimento 35, 56127 Pisa, Italy.
authors.forename: Celia
authors.initials: C
authors.lastname: Duce
authors.forename: Emilia
authors.initials: E
authors.lastname: Bramanti
authors.forename: Lisa
authors.initials: L
authors.lastname: Ghezzi
authors.forename: Luca
authors.initials: L
authors.lastname: Bernazzani
authors.forename: Ilaria
authors.initials: I
authors.lastname: Bonaduce
authors.forename: Maria Perla
authors.initials: MP
authors.lastname: Colombini
authors.forename: Alessio
authors.initials: A
authors.lastname: Spepi
authors.forename: Simona
authors.initials: S
authors.lastname: Biagi
authors.forename: Maria Rosaria
authors.initials: MR
authors.lastname: Tine
mesh_terms: D002119:Calcium Carbonate / Q000737:chemistry; D002152:Calorimetry, Differential Scanning; D002364:Caseins / Q000737:chemistry* / Q000378:metabolism; D002850:Chromatography, Gel; D004396:Coloring Agents / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry; D007854:Lead / Q000737:chemistry; D010047:Ovalbumin / Q000737:chemistry* / Q000378:metabolism; D010087:Oxides / Q000737:chemistry; D010150:Paint / Q000032:analysis*; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared; D013818:Thermogravimetry
chemical_list: D002364:Caseins; D004396:Coloring Agents; D005290:Ferric Compounds; D010087:Oxides; C000499:ferric oxide; D007854:Lead; C047365:lead oxide; D010047:Ovalbumin; D002119:Calcium Carbonate