The Spectral Properties of (-)-Epigallocatechin 3-O-Gallate (EGCG) Fluorescence in Different Solvents: Dependence on Solvent Polarity

Abstract

(-)-Epigallocatechin 3-O-gallate (EGCG) a molecule found in green tea and known for a plethora of bioactive properties is an inhibitor of heat shock protein 90 (HSP90), a protein of interest as a target for cancer and neuroprotection. Determination of the spectral properties of EGCG fluorescence in environments similar to those of binding sites found in proteins provides an important tool to directly study protein-EGCG interactions. The goal of this study is to examine the spectral properties of EGCG fluorescence in an aqueous buffer (AB) at pH=7.0, acetonitrile (AN) (a polar aprotic solvent), dimethylsulfoxide (DMSO) (a polar aprotic solvent), and ethanol (EtOH) (a polar protic solvent). We demonstrate that EGCG is a highly fluorescent molecule when excited at approximately 275 nm with emission maxima between 350 and 400 nm depending on solvent. Another smaller excitation peak was found when EGCG is excited at approximately 235 nm with maximum emission between 340 and 400 nm. We found that the fluorescence intensity (FI) of EGCG in AB at pH=7.0 is significantly quenched, and that it is about 85 times higher in an aprotic solvent DMSO. The Stokes shifts of EGCG fluorescence were determined by solvent polarity. In addition, while the emission maxima of EGCG fluorescence in AB, DMSO, and EtOH follow the Lippert-Mataga equation, its fluorescence in AN points to non-specific solvent effects on EGCG fluorescence. We conclude that significant solvent-dependent changes in both fluorescence intensity and fluorescence emission shifts can be effectively used to distinguish EGCG in aqueous solutions from EGCG in environments of different polarity, and, thus, can be used to study specific EGCG binding to protein binding sites where the environment is often different from aqueous in terms of polarity.

Optimization of Ultrasound-Assisted Extraction Condition for Phenolic Compounds, Antioxidant Activity, and Epigallocatechin Gallate in Lipid-Extracted Microalgae

“…When the separated peak was identified according to RT and spectrum obtained from DAD in comparison with standard compounds (Figure 7), it was quantified as epigallocatechin gallate (EGCG), a type of catechin (also known as epigallocatechin-3-gallate) consisting of epigallocatechin and gallic acid. Figure 8 shows the chemical structure of EGCG (C22H18O11) with a maximum absorbance of 275 nm and was shown to have maximum absorbance of the same range as the results of previous studies [32].…”

Comparative studies on extracts from Hericium erinaceus by different polarity reagents to gain higher antioxidant activities

“…The active ingredients in H. erinaceus can not be 100% extracted by a single reagent. Furthermore, different bioactive molecules have different solubilities in various solvents (11). Therefore, it is essential to evaluate the antioxidant activities of extracts produced by multiple representative solvents with different polarities.…”

Formulation of Niosomal Gel Containing Green Tea Extract (Camellia Sinensis L. Kuntze) Using Thin-Layer Hydration

“…First, a calibration curve of standard solution containing standard EGCG in ethanol was prepared at concentrations of 7,8,10,15,20, and 24 ppm to give A (absorbance) of 0.2-0.8 at λ max =275 nm [11]. EGCG concentration in the crude extract of green tea was determined using the calibration curve.…”

“…The size and distribution of the particles were determined using a PSA, lamellarity was determined using a TEM, efficiency of encapsulation was determined using a UV-Vis spectrophotometer, and zeta potential was determined using the Zetasizer [11,[15][16][17][18].…”