EPR study on stable magnesium complexes of the phenoxyl radicals derived from a vitamin E model and its deuterated derivatives

The phenoxyl radical 1asterisk inside a circle sign, generated by the reaction of a vitamin E model, 2,2,5,7,8-pentamethylchroman-6-ol (1H), with 2,2-bis(4-tert-octylphenyl)-1-picrylhydrazyl (DOPPHasterisk inside a circle sign), was significantly stabilized by complex formation with Mg²⁺ in deaerated acetonitrile at 298 K. The assignments of the hyperfine coupling constants (hfc) obtained by computer simulations of the observed EPR spectrum of the Mg²⁺ complex of 1asterisk inside a circle sign (Mg ²⁺-1asterisk inside a circle sign), were carried out using three deuterated isotopomers of 1asterisk inside a circle sign, i.e., 5-CD ₃-1asterisk inside a circle sign, 7-CD₃-1asterisk inside a circle sign, and 8-CD₃-1asterisk inside a circle sign, where a methyl group at the C5, C7, or C8 position is replaced by a CD₃ group, respectively. The decreased spin density of the benzene ring in the Mg²⁺-1asterisk inside a circle sign complex indicates that delocalization of the unpaired electron in 1asterisk inside a circle sign into Mg²⁺ by complexation between Mg²⁺ and 1asterisk inside a circle sign results in the enhanced stability of 1asterisk inside a circle sign in the presence of Mg²⁺.