Vibrational Energy Transfer and Heat Conduction in a Protein

Abstract

The normal modes of myoglobin, their lifetimes, the speed of sound, and mean free path are calculated to determine the coefficient of thermal conductivity and thermal diffusivity for the protein. A propensity is found for frequency differences of pairs of normal modes localized to nearby regions of the protein to be several hundred cm-1. As a result, the anharmonic decay rate of higher frequency, localized normal modes, calculated by perturbation theory, is typically nearly independent of temperature, consistent with results of pump−probe studies on myoglobin. The thermal diffusivity of myoglobin at 300 K is calculated to be 14 Å2 ps-1, the same as the value for water. The thermal conductivity at 300 K is found to be 2.0 mW cm-1 K-1, about one-third the value for water.