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 we are developing 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 currently planned experiments the changes in temperature arising from the flow of energy from a heme group is studied. The heating step might also be effected by means of an infrared pulse. Specifically, the system proposed as a test bed for this technology are Mb, Hb and Cyt-C derivatives having different ligands. After optical excitation, the ligand may dissociate. The energy of dissociation can go directly to heating the immediate surroundings but the energy retained as internal vibrational energy is bottlenecked. Some energy may be released or consumed in protein structural changes associated with ligand dissociation. The released thermal energy is used to excite mainly low frequency modes of the surroundings. There are not yet answers to how the energy released at the heme flows through the protein which ultimately heats the surrounding H2O. For example, is the protein measurably isotropic or anisotropic in regard to its thermal diffusivity? Does energy bottleneck in specific global structural regions of the protein? Can we find a quantitative theoretical description of the initially created hot spectra? These questions can be addressed directly by probing the IR spectra of transitions in the H2O and the protein that have known temperature dependence.