A Study of the Temperature Dependence of Tryptophan Fluorescence Lifetime in the Range of –170 to +20°С in Various Solvents

The temperature dependences (–170...+20°C) of the fluorescence lifetime of tryptophan molecules in an aqueous solution, in solutions of glycerol (50 and 75% by volume), dimethyl sulfoxide (50 and 75% by volume) and in 1 M aqueous solution of trehalose were studied. In this temperature range, the fluorescence kinetics at room temperature in all samples were best approximated by three exponents with characteristic times of τ 1 ~ 3 ns, τ 2 ~ 4 ns, and τ 3 ~ 15 ns. The temperature dependences of the fluorescence lifetime of the fastest and medium components in the temperature range from –60 to 10°C were found to be directed in opposite directions (in antiphase). To explain these temperature dependences, a new model of the nature of multicomponent fluorescence was proposed, which considered the transition of the tryptophan molecule from the excited state to the charge-transfer state, the reverse transition to the excited state, as well as the radiative and nonradiative transitions of the charge-transfer state to the ground state. The results we obtained can serve as a basis for the interpretation of the experimental dependences of the lifetime of tryptophan fluorescence on the temperature in proteins.