LOW FREQUENCY MODES & THEIR ROLE IN EQUILIBRATION

振动跃迁对温度（频率）很敏感

Vibrational transitions are sensitive to temperature (frequency shifts and bandwidth changes) so it is proposed to develop transient IR methods to study heat transport in proteins and other structures in aqueous solutions. In particular, the IR spectrum of water is modified by heating which breaks hydrogen bonds and the proposed methods can measure changes of ca. 0.02 C. In recent experiments the changes in temperature arising from the flow of energy from a heme group was studied. The rise times of the heating signal in deoxyhemoglobin (Hb) and deoxymyoglobin (Mb) solutions were studied in detail to investigate the energy transport mechanisms in heme proteins. The kinetics of this increase of transmission is fitted to a model that consists of a fast and a slow component. The fast component is best fitted by a Gaussian rise function with time constants of 7.5 1 1.5 and 8.5 1 1.5 ps for Mb solution and Hb solutions, respectively. The slow component (ca. 20 ps), with 40% of the total amplitude, was attributed to energy transfer from heme to water through the protein via a classical diffusion process based on agreement between the measured time and that calculated with classical diffusion theory. The fast component, almost identical for both Hb and Mb, could not be described by classical diffusion theory and is suggested to proceed through collecti ve motions of the protein. Experiments on myoglobin (Mb) were also performed to investigate the flow of energy from heme after excitation into different electronic states of the heme. Distinct absorption and bleaching features could be ascribed to vibrationally "hot" heme within the Mb that relaxed with a time constant of 2 to 5 ps.