Conformations and electronic structures of oxidized and reduced isoalloxazine

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Abstract
The conformations of oxidized and reduced isoalloxazine [model for the cofactor of flavoenzymes] were examined by a molecular orbital method. PRDDO (partial retention of diatomic differential overlap). The angle .theta. of fold about the N.cntdot..cntdot..cntdot.N line of the central ring is zero for the planar oxidized form, but a bend of .theta. = 10.degree. requires only 2 kcal/mol. The reduced form is nonplanar (.theta. .apprx. 15.degree.), and the barrier for reversal of this bend is 4 kcal/mol, comparable with that in simple amines. Molecular properties and reactivity are interpreted in terms of charge and orbital distributions, and localized molecular orbitals were derived by the method of Boys.