Relaxation processes on a picosecond time scale in hemoglobin and poly(L-alanine) observed by millimeter-wave spectroscopy

Broadband measurements of the millimeter-wave and far-ir absorption (10–10⁴ GHz) of lyophilized hemoglobin are reported. Additionally, the absorption of poly(L -alanine) and crystalline L -alanine at 70 GHz was measured for comparison. All measurements were extended over the temperature range from liquid helium to room temperature. For the millimeter range, this was attained by using the novel oversized-cavity technique. It was found that the millimeter-wave absorption of the materials increased nearly exponentially with temperature and increased as ν^1.2–ν² with frequency. The far-ir absorption of hemoglobin showed broadbands with almost no temperature dependence. The frequency and temperature dependence of the millimeter-wave absorption is quantitatively described as due to three distinct relaxation processes on a picosecond time scale occurring in asymmetric double-well potentials. These processes are most probably assigned to the NH ?OC hydrogen bonds of the peptide backbone.