Archaeological biophysics: structural study of ancient collagen in archaeological skin and bone samples.

Abstract

The present work is based on the study of a series of ancient remains coming from different archaeological contexts, such as mummified skin and fossilized bones, focusing the attention on their state of preservation. The mummified skin samples belong to the Egyptian collection of the Museum of Anthropology and Ethnography of the University of Turin and to the Roccapelago anthropological findings while the bone samples come from Central Anatolia and Friuli (Italy). Previous works showed that the state of preservation of these ancient materials is, in such way, correlated to the mechanism of transformation or degrade of the constituent biological macromolecules. The main component of skin and bone is represented by type I collagen. Collagen is a fibrous protein that shows an incredible survival capability during time and in extreme environmental conditions. Dehydration mechanism and glycation reactions are the main factors that influence the structural modifications of the collagen secondary structure. In vitro experiments of controlled dehydration-rehydration and glycation with different types of sugar of a pure type I collagen in its native conformation were carried out. The consequent collagen structural modifications were studied by means of Fourier Transformed Infrared Spectroscopy and Circular Dichroism Spectroscopy. The revealed modifications of the collagen secondary structure can provide information about the aging mechanism of this protein. Simultaneously, several analyses were performed on the archaeological samples by means of FTIR Spectroscopy, Scanning Electron Microscopy and histological analyses. The great amount of results was interpreted in the lights of the results obtained from the in vitro experiments. Thus, it was possible to assess a degree of preservation to the archaeological remains in relation to the aging of the samples, the different types of mummification, natural or anthropogenic and to the different burial environmental conditions for fossilised bone. Furthermore collateral study of experimental archaeology about Egyptian embalming agents and their evolution during historical time, and funeral practices of cremation and their influence on the colour and microstructure of charred bones were performed.