Mechanism of proton transfer in proteins II. Relationship between local properties of solvent and rate of excited state proton transfer for 2-naphthol derivatives bound to selected sites of proteins

Abstract Centres of gravity (CGs) of the fluorescence bands of protonated and deprotonated forms of 2-naphthol derivatives (NSOH), bound to proteins, were determined at various experimental conditions. CGs are correlated with the solvent relaxation time around fluorophores. The variation in the rate of excited state proton transfer (ESPT) for NSOH groups bound to proteins can be explained in terms of the solvent polarizability and the solvent relaxation rate with respect to a moving proton. From a comparison of the fluorescence decay data with the results of steady 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.