Influence of the microenvironment dynamics of tryptophan on its fluorescence parameters at different temperatures

The temperature dependences of the fast and slow fluorescence decay components of aqueous solution of tryptophan molecules after freezing to -170°C - 20°C under actinic light and in the dark were investigated. A model of the direct and reverse electronic transitions from an excited state to the ground state and to the state with charge transfer for a tryptophan molecule was used to perform quantitative analysis. Three main spectral regions of tryptophan fluorescence are shown, they differ in the behavior of the temperature dependences depicted for the rates of transition from the excited state of tryptophan to the state with charge transfer. It has been shown that the dynamics of the hydrogen bonded system plays a key role in this transition. The system of hydrogen bonding determines the nonlinear nature in tryptophan fluorescence in the selected spectral regions. The non-linear behavior of the fluorescence lifetime and fluorescence spectra with temperature change is determined by the type of the interaction of tryptophan with water and ice. It has been found that temperature rearrangements play a critical role in hydrogen bonding structure of H₂O ₂ that surrounds a tryptophan molecule in the excited state.

tryptophan, Fluorescence decay kinetics, temperature dependence, hydrogen bonds, molecular dynamics