Fluorescence line narrowing and site selectivity are observed for red edge excitations (≈300 nm) of tryptophan in alcohol glasses and proteins at cryogenic temperature (2-200 K). Structured and broad fluorescence bands are observed. Both components are excitation wavelength dependent. These two spectral features are assigned to emission from 1Lb and an exciplex version of 1La (designated 1Laexc) respectively. The latter can be populated either through barrier crossing from 1Lb or directly via highly excited vibrational levels of 1Laexc. The barrier separating 1Lb and 1Laexc appears to be on the order of a few hundred cal/mole suggesting that in solution at ambient temperatures the 1Laexc state should dominate the emission process. Influence of protein relaxation upon the 1Laexc emission is not apparent until T>100 K. A model incorporating the conformational substate description of proteins and the rotamer model for tryptophan is developed and discussed in terms of the presented results.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry