TSC study of the dielectric relaxations of human-bone collagen

Differential scanning calorimetry (DSC) and thermally stimulated current (T SC) were used to characterize human-bone collagen. DSC glass-transition and denaturation temperatures of the collagen in a dehydrated state were 90 an d 215 degrees C, respectively. By TSC, the main relaxation mode, labeled a and located around 90 degrees C, could be attributed to the dielectric mani festation of the glass transition. The corresponding molecular movements ar e cooperative with a compensation temperature close to the denaturation tem perature. At low temperatures and in a hydrated state, a second mode labele d beta(2) was observed at -110 degrees C. Dehydration shifted this mode to higher temperatures, revealing a weak mode labeled gamma at -150 degrees C. This gamma mode was attributed to motions of aliphatic side chains. An ana lysis of low-temperature elementary spectra allowed us to assign the beta(2 ) mode to structural water movements and revealed an additional compensatio n phenomenon in the temperature range (-80 to -50 degrees C). Because the c ompensation temperature of this mode was close to the collagen glass-transi tion temperature, the corresponding mode beta(1) was attributed to polar si de-chain motions, precursors of a collagen glass transition. Finally, aroun d ambient temperature, three sharp peaks were attributed to hydrogen bonds breaking. (C) 2000 John Wiley & Sons, Inc.