MODE-SELECTIVE ENERGY LOCALIZATION DURING PHOTOEXCITATION OF DEOXYHEMOGLOBIN AND HEME MODEL COMPLEXES

Vibrational energy redistribution may be important in regulating the function of hemes and related macrocycles. Transient resonance Raman experiments reveal a non-Boltzmann vibrational energy distribution among the heme normal modes of photoexcited deoxyhemoglobin. Within 10 ns excitation pulses, v4 exhibits flux-dependent anti-Stokes peak position, Stokes and anti-Stokes linewidths, and anti-Stokes:Stokes ratios corresponding to temperatures as high as 600 K. Other modes, most notably v7, do not behave in this manner. Spectra of protoporphyrin IX-2-methyl-imidazole obtained under the same conditions indicate that specific heme-protein interactions cannot be entirely responsible for this behavior.