Photophysics of tryptophan: global analysis of the fluorescence decay surface as a function of pH temperature quencher concentration excitation and emission wavelengths timing calibration and de

摘要

The fluorescence decay surface of tryptophan measured over a very wide pH range (1.35 to 12.38) was analyzed in a single global analysis. It is clear that the decay components remain the same over the whole pH range. This is also confirmed by the decay- associated emission spectra. At low pH the decays are biexponential and both decay components contribute to the fluorescence up to pH 11. From about pH 7.5 onwards a third component has to be taken into account which becomes the only component at pH $GRT 11. The decay times decrease at low pH due to quenching by H$-3$/O$+$PLU$/. At pH $GRT 11 the decay times decline due to quenching by OH$+$MIN$/. Decays collected at different temperatures at neutral pH indicate that the short decay time is independent of temperature, both in H$-2$/O and D$- 2$/O solution. Both decay times increase by a factor of two when H$-2$/O is replaced by D$-2$/O as solvent. The decay times and their normalized pre-exponential terms at neutral pH in H$-2$/O solution are constant as a function of excitation wavelength (from 250 to 295 nm). This indicates that the absorption spectra associated with the two ground-state species overlap completely and that the contribution of both species to the total absorption remains constant over the whole absorption spectrum.