Abstract
Complementary vibrational spectroscopic techniques – infrared, Raman and inelastic neutron scattering (INS) – were applied to the study of human bone burned under controlled conditions (400 to 1000 °C). This is an innovative way of tackling bone diagenesis upon burning, aiming at a quantitative evaluation of heat-induced dimensional changes allowing a reliable estimation of pre-burning skeletal dimensions. INS results allowed the concomitant observation of the hydroxyl libration (OHlibration), hydroxyl stretching (ν(OH)) and (OHlibration + ν(OH)) combination modes, leading to an unambiguous assignment of these INS features to bioapatite and confirming hydroxylation of bone’s inorganic matrix. The OHlib, ν(OH) and ν4(PO43−) bands were identified as spectral biomarkers, which displayed clear quantitative relationships with temperature revealing heat-induced changes in bone’s H-bonding pattern during the burning process. These results will enable the routine use of FTIR-ATR (Fourier Transform Infrared-Attenuated Total Reflectance) for the analysis of burned skeletal remains, which will be of the utmost significance in forensic, bioanthropological and archaeological contexts.
Highlights
Bone is a biphasic material comprising a protein component within an inorganic matrix of hydroxyapatite (Ca10(PO4)6OHx, HAp), the hydroxyl and phosphate groups being partly substituted by carbonate[1,2]
Previous studies have attempted to tackle this issue by infrared spectroscopy[4,5,9,10,11,31,32,33,34,35], an approach based on the intrinsic properties of bone was firstly followed by the authors through the application of inelastic neutron scattering (INS) spectroscopy to human bones burned under controlled conditions[36]
The process of bone combustion comprises several stages (Fig. 1)[12,42]: (i) dehydration – breakage of hydroxyl bonds and water removal; (ii) decomposition of the organic components; (iii) inversion – carbonate loss upon heating; (iv) fusion – changes in crystallinity usually accompanied by an increase in crystal size, and OH− and PO43− rearrangement within the pores left by the water and organic components
Summary
Bone is a biphasic material comprising a protein component (mostly collagen I) within an inorganic matrix of hydroxyapatite (Ca10(PO4)6OHx, HAp), the hydroxyl and phosphate groups being partly substituted by carbonate (respectively A- and B-type carbonates)[1,2]. Unlike optical techniques – Raman and FTIR6,8–11,24,32,37,38 – only a limited number of INS studies of bone have been carried out successfully in the last decade[36,39,40,41] These allowed detection of distinctive features such as changes in carbonate and water content, chemical substitutions at the hydroxyl sites and heat-elicited variations, revealing even minor differences in bone composition and being able to relate these to external factors affecting the skeletal samples (burning and/or other environmental events). INS is an extremely useful technique for probing a hydrogenous material such as bone, the intensity of each vibrational transition being expressed, for a given atom, by the dynamic structure factor
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