Characterization of Degradation-Induced Molecular Modifications in Parchment - A Combined Spectroscopic and Chemometric Approach,

Abstract

Key words: Parchment degradation, Raman, ATR-FTIR, band deconvolution, feature identification From its first introduction within Late Antiquity, parchment functioned as primary writing support for scrolls and manuscripts until the introduction of paper production at the end of Medieval times. Being produced from the dermal layer of animal skins, it comprises and is structured to a high extent by different types of the fibrous protein collagen. The raw material of animal skins and different treatment approaches within the complex manufacturing process can influence the material already during its preparation. Additionally, environmental stress, e.g., caused by UV light, moisture, or pollutants, at moderate levels during everyday handling and at extremer levels resulting from damaging events, likely played an essential role in further inducing changes over centuries [1]. Therefore, detailed knowledge of chemical modifications of collagen and their impact on the degradation behavior of parchment is essential for damage assessment and conservation. The presented approach focuses on the artificial aging with relative humidity and UV light - two parameters known for degrading parchment - and the subsequent non-destructive analysis of various traditionally prepared sheep parchments [1]. One set of samples is exposed to UV light at 155 W/m2 for one month, equaling yearly natural outdoor conditions. In comparison, another set of samples is aged at 80 %RH for one week. Fourier-transform infrared spectroscopy in attenuated total reflection mode (ATR-FTIR) and Raman spectroscopy are applied to study molecular changes of parchment components (collagen, water, and lipids). In addition to the commonly used amide bands (amide I, II, and III), spectral regions of interest in the IR spectra were 3600-3000 cm-1, containing amide A and B bands as well as OH-stretching bands, and 3000-2800 cm 1, including CH-stretching vibrations resulting from proteins and lipids [3]. They were complemented by the analysis of the fingerprint region between 1400 and 400 cm-1 in the Raman spectra, containing bands resulting from structurally important features, like proline, hydroxyproline, other amino acids (e.g. tyrosine), and disulfide bridges. Detailed band deconvolution and fitting combined with subsequent factor analysis on mixed data - to reduce the high number of resulting spectral features - revealed different changes in several overlapping bands depending on the applied aging conditions. [1] Maor, Y., Shor, P., Aizenshtat, Z., Parchment browning and the Dead Sea Scrolls – Part I: Artificial aging, Polymer Degradation and Stability. 2020, 176, 109109-109124. [2] Research Project of the Austrian Science Fund (FWF-Projekt Nr. 29892, coordinator Prof. Dr. H. Miklas) [3] Olsztyńska-Janus, S., Pietruszka, A., Kiełbowicz, Z., Czarnecki MA. ATR-IR study of skin components: Lipids, proteins and water. Part I: Temperature effect. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy. 2017, 188, 37-49.