Fig. 2
From: Fossilization transforms vertebrate hard tissue proteins into N-heterocyclic polymers
Aligned Raman spectra of decalcified modern, matured, and fossil organic material. All spectra were obtained in aqueous solution, 500–1800 cm−1, 20 s exposure time, 4 accumulations. These spectra are based on a total of 12 specimens with soft tissue preservation used for high-resolution point measurements, while Raman spectra for an additional 12 specimens without soft tissue preservation can be found in Supplementary Fig. 9; a total of additional 29 specimens was used for experimental maturation. a Teeth and enamel scales. b Bones. c Eggshells. Differences in the color of the sampled material are represented in the icons on the right. Brown spectral band: advanced glycoxidation and lipoxidation end products (AGEs), oxidative crosslinks; yellow spectral bands: peptide amides. AGE bands increase in intensity relative to amide I bands (dotted lines) with age and artificial maturation. Protein degradation and deamidation over time are represented by a decrease in the band intensities identified as amide III and amide I. Details on experimentally matured reference tissues at different temperatures (autoxidation) on the right of the spectra show that oxidative, brown discoloration already occurs at low temperatures. The color scale associated with temperatures and incubation times for the maturation experiments range from red (relatively high temperatures) to blue (low temperatures). The scale bar equals 500 μm
