Singlet-state information on proteins from triplet-state data

摘要

The inherent resolution of protein phosphorescence spectra and the long lifetime of the triplet state lead to unique information on the structure as well as the slow rotational and conformational dynamics of proteins. However, protein triplet states are populated through singlet excitation, so that initial phosphorescence intensities are determined by prior occurrences at the excited singlet level. The relative intensities of the tryptophan components within protein phosphorescence spectra, when coupled with time-dependent triplet-state measurements, are a source of information on singlet transfer between residues. While anomalous phosphorescence decay times derive from triplet interactions, the relative intensities of the anomalous components in time-dependent measurements reflect quenching and excitation exchange at the singlet level. Time-dependent phosphorescence measurements can be employed to distinguish between singlet quenching mechanisms involving enhanced spin- orbit coupling and energy or electron transfer.