Electronic States of Epigallocatechin-3-Gallate in Water and in 1,2-dipalmitoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (Sodium Salt) Liposomes

In this work, the spectroscopy of epigallocatechin-3-gallate (EGCG) and EGCG bonded to 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) (DPPG) lipid is studied both experimentally by combining high-resolution vacuum ultraviolet (VUV) photo-absorption measurements in the 4.0-9.0 eV energy range and by theoretical calculations using density functional theory (DFT) methodology. There is a good agreement between the experimental and theoretical data, and the inclusion of the solvent both implicitly and explicitly further improves this agreement. For all experimentally measured absorption bands observed in the VUV spectra of EGCG in water, assignments to the calculated electronic transitions are provided. The calculations reveal that the spectrum of DPPG-EGCG has an intense peak around 150 nm, which is in accordance with experimental data, and it is assigned to an electron transfer transition from resorcinol-pyrogallol groups to different smaller groups of the EGCG molecule. Finally, the increase in absorbance observed experimentally in the DPPG-EGCG spectrum can be associated with the interaction between the molecules.