The DFT local reactivity descriptors of α-tocopherol.

The calculations of local reactivity descriptors, the electron donor Fukui function f(-)(r), the average local ionization energy Ī(r), the Fukui function dual descriptor f((2))(r), and the electron acceptor Fukui function f(+)(r) for α-tocopherol, the main biologically active form of vitamin E for antioxidant reactions in phospholipid membranes, is presented. The calculations are performed at B3LYP/6-311++G** level of theory in the gas-phase. The obtained results indicate that the most preferred sites for donating electron in a reaction with radical or oxidizing molecule are associated mostly with π electrons above and below the aromatic part of the α-tocopherol chromanol ring. The most reactive sites for accepting electrons are associated with the leaving H(9) atom in the extension of the phenolic OH bond on the α-tocopherol chromanol ring plane, in the place where the formation of H-bond of the precursor complex between approaching reactive oxygen radical and phenolic OH group of α-tocopherol could be expected. The separated reactive sites in α-tocopherol suggest that the proton and electron, along with the hydrogen atom transfer (HAT) process, could also be transferred to different proton and electron acceptors as in bidirectional proton coupled electron transfer (PCET) reactions. The results presented in this paper suggest that large charge redistribution and significant π-π interactions may be expected in antioxidant reactions of α-tocopherol.