Analytical pyrolysis of proteins in samples from artistic and archaeological objects

Abstract

The paper presents a study of proteins found in artistic and archaeological objects based on analytical pyrolysis. Proteins (mainly egg yolk and/or egg white, casein, animal glue and collagen) have been extensively used as paint binders, adhesives and varnishes in mural and easel paintings, and they can be found in archaeological findings, such as bones and skin tissues. In order to overcome limitations of wet chemical methods arising from the reduced solubility of aged proteins in samples of cultural heritage, a combination of analytical pyrolysis techniques was used to characterise reference materials, paint reconstructions and samples from different historical periods (2nd century BC-20th century AD) and geographical origins, which were collected from paintings and archaeological findings. In particular evolved gas analysis mass spectrometry (EGA/MS), pyrolysis coupled with gas chromatography/mass spectrometry (Py/GC/MS) and double shot pyrolysis/gas chromatography/mass spectrometry (DSP/GC/MS) were used. This analytical approach allowed us to characterise and differentiate the proteinaceous media, investigate their thermal behaviour and evidence changes occurring with ageing. Data clearly indicate that egg, casein and animal glue can be identified and distinguished in a sample of unknown composition using each of the analytical pyrolysis techniques used. With time though differences tend to disappear to the extent that extremely degraded samples present pyrolytic profiles extremely similar to each other, irrespective of the nature of the proteins present. The data also indicate that proteins tend to become more thermally stable with ageing, suggesting that extensive intramolecular and intermolecular aggregation, and/or covalent cross-linking occur with time

Evolved Gas Analysis‐Mass Spectrometry to Identify the Earliest Organic Binder in Aegean Style Wall Paintings

“…[6] 80 %ofthe fragments studied from Te lKabri were part of this group. It has been demonstrated that during aging,p roteinaceous materials become highly thermally stable [20,21] and show very little solubility,c hallenging GC-MS and MS proteomics-based approaches that require an extraction of the proteinaceous material from the matrix. It has been demonstrated that during aging,p roteinaceous materials become highly thermally stable [20,21] and show very little solubility,c hallenging GC-MS and MS proteomics-based approaches that require an extraction of the proteinaceous material from the matrix.…”

“…Thestudy of ancient paintings is asignificant challenge for the analytical chemist. [22][23][24] Evolved gas analysis mass spectrometry (EGA-MS) instead is based on analytical pyrolysis and yields temperature-resolved mass spectrometric information on the gaseous products evolved from samples upon progressive heating.T hough highly degraded samples yield pyrolytic profiles of proteinaceous materials without specificity,h indering the identification of the binder, [20] the technique has the advantage of giving rapid indications regarding the presence of organic media without the need for any sample work-up. [22][23][24] Evolved gas analysis mass spectrometry (EGA-MS) instead is based on analytical pyrolysis and yields temperature-resolved mass spectrometric information on the gaseous products evolved from samples upon progressive heating.T hough highly degraded samples yield pyrolytic profiles of proteinaceous materials without specificity,h indering the identification of the binder, [20] the technique has the advantage of giving rapid indications regarding the presence of organic media without the need for any sample work-up.…”

“…Thea verage mass spectra in the range 400-450 8 8Co fb oth samples (Figure 3c)a re dominated by fragment ions (m/z 67, 91, 107,117, 131) corresponding to nitrogen-and oxygen-containing aromatic compounds (i.e. [20] Thetemperature range in which the evolution of aromatic compounds occurs,aswell as the absence of fragmented ions ascribed to diketopiperazines,r esulting from the cyclisation [20] Thetemperature range in which the evolution of aromatic compounds occurs,aswell as the absence of fragmented ions ascribed to diketopiperazines,r esulting from the cyclisation …”

“…Theaverage mass spectrum in this temperature range (290-310 8 8C) of both samples (Figure 3b), shows the presence of fragmented ions ascribable to hexadecanenitrile and octadecanonitrile (m/z 194, 208, 222, 236). [20] The formation of hexadecanenitrile and octadecanonitrile has been related to the pyrolysis of the products of ac hemical interaction of carbonyl moieties of egg lipids and the primary amine group of Lysand Arg in egg proteins. [20] The formation of hexadecanenitrile and octadecanonitrile has been related to the pyrolysis of the products of ac hemical interaction of carbonyl moieties of egg lipids and the primary amine group of Lysand Arg in egg proteins.…”

Onsite advanced biocleaning system for historical wall paintings using new agar-gauze bacteria gel

“…A few micrograms of the sample mixed with 2 ll of hexamethyl-disilazane (HMDS) was placed in a quartz tube. The detailed working conditions are published elsewhere (Andreotti et al 2009;Lluveras et al 2010;Rampazzi et al 2012;Orsini et al 2017).…”