PRIN 2008

2010 - 2012
Title: 
Physico-chemical and modeling methods for the study of proteins in oxalate patina and paintings.
Principal Investigator: 
Emilia Bramanti
Project type: 
National

Abstract

Protein-based paint media derive from animal sources and include glues (collagen from tissue), glair and ‘tempera' (egg white and egg yolk respectively) and milk (a
mixture of globular proteins, casein and sugars). These binding media with pigments have been used for the execution of paintings and polychromy, as varnish and
for the conservation of paintings. Assessing the chemical composition and the state of conservation associated with aging of these proteinaceous media in the
presence or not of common pigments is pivotal for elucidating the origin of an unknown work and for the design of optimum conservation/restoration plans. There is
little doubt that proteins are targets for radicals and other oxidants in the environment. The chemistry of reaction of a large number of different radicals with amino
acids, peptides, and proteins has been elucidated in vivo, but extensive difficulties are associated with the analysis of proteins in art materials and these include the
low concentration of organic material relative to inorganic pigments and other compounds, the chemical complexity of organic materials which are rarely pure, often
degraded and deteriorated, and their chemical reactivity, which may be poorly understood. Moreover, no data are reported on the role of proteins on the oxalate film
formation, found both in paints and in marble operas, though an interesting correlation has been found between protein content and oxalic acid recovery in several
samples.
Thus, the development of novel physico-chemical methodologies and modelling approaches for the characterization of protein components in paints and their
degradation products due to aging and photo-oxidative processes, as well as for the study of the origin of oxalate films, is crucial. Furthermore, the
identification/determination/characterization of stable portions of proteins during aging/degradation processes is fundamental for the production of specific
antibodies and the development of immunological procedures for in-situ immunostaining. This suggests the need of conservative extraction procedure, alternative to
hydrolysis, followed by suitable separation and purification methods.
The IPCF unit has all expertise in thermoanalytical, analytical and modelling methods required to achieve these goals.
In this project the IPCF unit (UR3) will investigate reference samples of proteins typically found in paints as binders (egg proteins, caseins and collagen), in mixture
or not with metals and pigments, and their degradation products after photo-oxidative/aging process in solid state and in solutions. Real samples provided by UR1
and UR2 will be characterized. We aim to optimize analytical methods and procedures in thermogravimetry (TG), thermomechanical analysis (TMA), differential
scanning calorimetry (DSC), liquid chromatography (LC), infrared spectroscopy (FTIR) and modelling approaches. In particular, the UR3 milestones in this project
will include:
1)Study of the mechanism of formation of oxalate films in works of art: development and testing of theoretical models. Experimental design on aminoacid and protein
solutions and dried protein films. Analysis of real samples.
2)Effects of ageing and degradation, due to exposure to light, thermal cycles, oxygen, NOx or other pollutant gases, of lysozyme, ovalbumin, caseins, collagen, in
mixture or not with metals (copper, mercury), pigment model (azurite and cinnabar), and/or sugars, and or inorganic compounds (gypsum and calcium carbonate).
Study of the role of metals, inorganic constituents and sugars in cross-linking processes that occur during degradation, transformation and oxidative processes of the
protein matrix.
3)Development of mild extraction methods for the proteins of interest coupled to methods in liquid chromatography focused on the identification of peptide/polypeptide portions newly exposed during protein denaturation/aging. These degradation markers will be purified and designed for proteomic analysis (UR2) and antibody production for immunochemical methods (UR1).