The influence of colouring materials and artificial ageing on the occurrence of nonspecific peptides in protein binders
Abstrakt
The aim of this work was to identify the influence of selected pigments and artificial ageing on the occurrence of nonspecific peptides in protein binders used in artworks. For this purpose, two groups of pigments - inorganic (cadmium yellow, chalk, and ochre) and organic (indigo, carmine, and madder lake) were selected. The model samples containing protein binders (casein binder, gelatine, yolk and whole egg binder) mixed with the indicated pigments in final concentration of 1 % were exposed to the conditions causing accelerated ageing (UV light, higher temperature and relative humidity).
The samples were analysed using two mass spectrometry techniques - LC-ESI-Q-TOF MS (Liquid Chromatography-Electrospray Ionization-Quadrupole-Time of Flight Mass Spectrometry) and MALDI-TOF MS (Matrix-Assisted Laser Desorption/Ionization-Time of Flight Mass Spectrometry). The results from LC-ESI-Q-TOF MS were searched for sites where nonspecific cleavage of proteins occurred and for types and the number of modifications. MALDI-TOF MS data were subjected to the Principal Component Analysis (PCA).
Beside amino acid modifications and spatial conformations another way of protein binder deterioration was described in this paper. It was found that pigments can influence the number of nonspecific peptide fragments and may thus led to binder degradation, or have a stabilizing effect. The data obtained from artificial ageing show that ageing may also affect the occurrence of nonspecific peptides and, that this effect strongly depends on the presence of the specific pigment or dye.