Multimodal imaging using MALDI MSI, ATR/FTIR and Raman imaging to study light- and SO2-induced degradation in parchment

In-depth understanding of molecular mechanisms of parchment degradation is essential for its preservation and can contribute further to the conservation of cultural heritage. In this proof-of-concept study, a multimodal imaging workflow for a comprehensive characterization of structural and chemical alterations in sheep parchment exposed to light and sulfur dioxide (SO 2 ), beyond established surface and bulk analysis was developed. For this, vibrational spectroscopy imaging (VSI), ATR/FTIR and Raman spectroscopic imaging (RSI) were combined with proteomic and lipidomic studies using MALDI mass spectrometry imaging (MSI). Spectroscopy revealed protein destabilization, progressing from native helical conformations to β-sheets, culminating in disordered structures. The spatially resolved approach allowed the assessment of the conformational transitions in a gradient from sample surfaces into deeper central layers of the material. MALDI MSI gave the first comprehensive overview of different collagens and extracellular matrix (ECM) proteins in parchment. Moreover, it highlighted different degradation patterns for collagens, dermal glycoproteins, and proteoglycans, including fibronectin and biglycan, resolving and further explaining the loss of hierarchical integrity proposed by spectroscopic measurements in detail. Despite parchment's low lipid content, lipidomic MALDI MSI identified a variety of lipid species and related oxidation products, including dicarboxylic acids and oxysterols, showing strong dependence on the type of environmental stress and exposed parchment side. This study presents the first spatially resolved approach to localize protein and lipid degradation markers across the layered, fibrous parchment structure. Therefore, the integrated analytical approach provides unprecedented molecular insights into the degradation behavior of parchment and, additionally, offers promising potential for damage assessment of further cultural heritage.