MECHANISM OF PROTON-TRANSFER IN PROTEINS .2. RELATIONSHIP BETWEEN LOCAL PROPERTIES OF SOLVENT AND RATE OF EXCITED-STATE PROTON-TRANSFER FOR2-NAPHTHOL DERIVATIVES BOUND TO SELECTED SITES OF PROTEINS

Centres of gravity (CGs) of the fluorescence bands of protonated and d eprotonated forms of 2-naphthol derivatives (NSOH), bound to proteins, were determined at various experimental conditions. CGs are correlate d with the solvent relaxation time around fluorophores. The variation in the rate of excited state proton transfer (ESPT) for NSOH groups bo und to proteins can be explained in terms of the solvent polarizabilit y and the solvent relaxation rate with respect to a moving proton. Fro m a comparison of the fluorescence decay data with the results of stea dy state measurements, the probability of geminal recombination in the ESPT reaction is estimated. This probability is negligible for one of our samples and 0.3-0.4 for two other samples. The mechanism of this effect is discussed briefly.