Solvatochromism of (-)-Epigallocatechin 3-O-Gallate (EGCG) Fluorescence: Dependence on Solvent Protonicity

TL;DR

This study investigates how the fluorescence of EGCG varies with solvent protonicity, revealing its potential to differentiate environments based on protonic properties, which aids in understanding its interactions in biological systems.

Contribution

It demonstrates the dependence of EGCG fluorescence intensity on solvent protonicity and introduces its use for probing EGCG interactions in different environments.

Findings

FI inversely correlates with solvent Kap

HCl decreases FI, NaOH increases FI in water

NaOH causes slow transient FI changes

Abstract

Health benefits of EGCG are well established; however, the mechanisms of EGCG action are not completely understood. In our previous study we discovered solvatochromism of EGCG fluorescence and described the dependence of fluorescence maxima on solvent polarity. We also noted that fluorescence intensity (FI) depends on solvent. The goal of this study was to gain insights into how the protonic properties of the environment affect FI. We demonstrate that 1) FI of EGCG inversely correlates with the autoprotolysis constant (Kap) of the solvents, 2) HCl decreases, and NaOH increases FI of EGCG in water, and 3) NaOH evokes slow (~10 min time scale) transient changes in FI of EGCG. We conclude that EGCG fluorescence depends on Kap, i.e. protonicity of the environment, that is useful for differentiating EGCG in protic aqueous environment at physiological pH~7.0{\div}7.4, where EGCG fluorescence is substantially quenched, from EGCG in aprotic environments, where EGCG fluorescence significantly increases. Thus, this property of EGCG fluorescence is useful for investigation of specific EGCG interactions within more aprotic protein binding sites.