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-alpha-tocopheryl
glycosides (dl-alpha-tocopheryl orthoacetate derivative and
glycosides of
dl-alpha-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-alpha-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.
