Specific features of the temperature dependence of tryptophan fluorescence lifetime in the temperature range of −170–20 °C

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Chemistry., 2020-04, Vol.393, p.112435, Article 112435
• Main Authors: Knox, Peter P., Gorokhov, Vladimir V., Korvatovsky, Boris N., Grishanova, Nadezhda P., Goryachev, Sergey N., Paschenko, Vladimir Z.
• Format: Article
• Language: English
• Subjects: Charge transfer state; Excited state; Fluorescence kinetics; Fluorescence lifetime; Forms; Protein conformation; Rotamer; Temperature dependence; Tryptophan
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2020.112435

[Display omitted] •The temperature dependence of Trp fluorescence lifetime in solutions was studied.•A model was suggested of Trp molecules transition from the excited state to the CTS.•Reversal transition from the CTS to the excited state of Trp is considered.•Formation of the quasi-conductive band in the system of hydrogen bonds is considered. The temperature dependence of tryptophan fluorescence lifetime in an aqueous solution, aqueous solutions of glycerol (50 and 75 %, v/v) and dimethyl sulfoxide (DMSO) (50 and 75 %), and 1 M aqueous trehalose solution was studied in the range of –170 to +20 °C. In this temperature range, the fluorescence kinetics in all samples is best approximated by three exponential terms with characteristic times τ1 ∼ 3 ns, τ2 ∼ 4 ns, and τ3 ∼ 15 ns at room temperature. Temperature dependences of fluorescence lifetimes for the fastest and medium components exhibited antisymbatic (antiphase) behavior in the temperature range of –60 to 10 °C. To explain this behavior, a model was suggested that takes into account the tryptophan (Trp) molecule transition from the excited state to the state with separated charges – charge transfer state (CTS), the transitions back to the excited state, and the radiative transitions of the CTS to the ground state. Mathematically, this model is equivalent to the model that we have suggested earlier in [Gorokhov et al. (2018) Biochemistry (Moscow), 82, 1615–1623] to describe the transitions between different rotamer forms of tryptophan. The obtained results can be used for interpreting the experimental temperature curves of tryptophan fluorescence lifetime in proteins.