Collagen‐based proteinaceous binder‐pigment interaction study under UV ageing conditions by MALDI‐TOF‐MS and principal component analysis

Abstract

This study focuses on acquiring information on the degradation process of proteinaceous binders due to ultra violet (UV) radiation and possible interactions owing to the presence of historical mineral pigments. With this aim, three different paint model samples were prepared according to medieval recipes, using rabbit glue as proteinaceus binders. One of these model samples contained only the binder, and the other two were prepared by mixing each of the pigments (cinnabar or azurite) with the binder (glue tempera model samples). The model samples were studied by applying Principal Component Analysis (PCA) to their mass spectra obtained with Matrix-Assisted Laser Desorption/Ionization-Time of Flight Mass Spectrometry (MALDI-TOF-MS). The complementary use of Fourier Transform Infrared Spectroscopy to study conformational changes of secondary structure of the proteinaceous binder is also proposed. Ageing effects on the model samples after up to 3000 h of UV irradiation were periodically analyzed by the proposed approach. PCA on MS data proved capable of identifying significant changes in the model samples, and the results suggested different aging behavior based on the pigment present. This research represents the first attempt to use this approach (PCA on MALDI-TOF-MS data) in the field of Cultural Heritage and demonstrates the potential benefits in the study of proteinaceous artistic materials for purposes of conservation and restoration.

Fourier transform infrared spectroscopic study of rabbit glue/inorganic pigments mixtures in fresh and aged reference paint reconstructions

“…However, their intercalation among collagen fibers gives a global lower thermal stability. We can hypothesize that the pigment salts and oxides located between beta sheets or between helices interfere with the mutual interaction of collagen fibers, thus inducing a destabilization of the protein structure [13,39,41,42].…”

“…Infrared spectroscopy is also a fundamental tool to investigate the degradation and ageing of organic materials in Cultural Heritage. Among these, proteinaceous paint binders are particularly complex, given their composition and structure [1,[13][14][15].…”

Multi-technique chemical characterisation of a 12–13th-century painted Crucifix

“…A comparison was also carried out with the peptides of various protein-based materials commonly found in paintings (i.e., egg yolk, egg white, animal glue, casein) as reported in literature [21,22,24,28,31,32] and with an internal database obtained from the analysis of standard samples. It is worth noting that proteinaceous binders are subjected to ageing processes accelerated by the occurrence of some catalytic pigments [27,44,45]. The most likely modifications of proteinaceous materials are oxidation, deamidation, loss of water, and, in some cases, hydrolytic degradation leading to protein truncation.…”

“…Py-GC/MS is particularly suitable for the analysis of synthetic polymers [12][13][14][15] or polymeric fractions of natural resins [16][17][18][19], whereas MALDI-TOF-MS has recently been shown to be efficient in fast and complete identification of historic paint binders. In fact, since a decade the use of new mass spectrometric techniques based on soft ionization, such as MALDI [20][21][22][23][24][25][26][27] or Electrospray Ionization (ESI) [25][26][27][28][29][30][31][32][33][34][35][36] for investigation of organic materials as present in polychrome artefacts or archaeological finds has significantly increased. In particular, MALDI-MS offers a series of advantages such as direct analysis of complex mixtures with reduced sample pretreatment, short analysis times, relatively easy interpretation of results, and high sensitivity, fundamental in the study of paintings with very limited sample amounts.…”

Vibrational Spectroscopies and Chemometry for Nondestructive Identification and Differentiation of Painting Binders

“…These are obvious problems for the analysis of samples of historical interest [4,11,12]. Spectroscopic techniques have the potential to overcome these limitations, as they allow nondestructive and contactless measurements, giving molecular information on complex macromolecules, and could be performed in situ by means of portable devices.…”