Glycosidic moiety changes the spectroscopic properties of dl-α-tocopherol in DMSO/water solution and in organic solvents

Abstract

In this study we estimated how conjugation with a sugar moiety influences the spectral properties of tocopherol and relate the spectroscopic properties of glycosides to solvent properties such as viscosity and polarity.Spectroscopic properties (absorption, fluorescence, fluorescence anisotropy and fluorescence lifetime) of three dl-α-tocopheryl glycosides (dl-α-tocopheryl orthoacetate derivative and glycosides of dl-α-tocopherol model compounds: 2,2,5,7,8-pentamethyl-6-chromanol and Trolox) were studied in DMSO/water solution. In all investigated compounds dissolved in DMSO/water mixture the absorption and emission maxima were blue-shifted. The fluorescence lifetimes were longer compared with those obtained for the parent compounds, except for the Trolox glucoside, in which it was shorter. The observed effect is connected with an increase in the electronic energy in the ground state due to electron rearrangement in the chromanol system caused by interaction with the sugar moiety. The extent of the spectral shift is related to the sugar moiety substituted at the phenolic oxygen rather than to substitution at the 2a position in the chromanol ring.The fluorescent properties of dl-α-tocopheryl glucoside in organic solvents were measured. The Stokes shift was related to the orientational polarizability of the solvents. The study of viscosity suggested two different mechanisms explaining the results observed in a low- and high-viscosity environment. The results indicated the fundamental role of interactions between the chromophore and sugar moiety in a low-viscosity environment. The results obtained at high values of viscosity are discussed in terms of a frictional boundary solvent–solute interaction model.