Isomerization superoxide radical

The reactions of TTHA (Mn -triethylenetetraminehexaacetate) complexes with H02-02 radicals were studied (pH 2.5-9.S), and a mechanism was suggested that involves the formation of a transient Mn tthaH( 02 f complex. At low pH, this complex is protonated, with the release of H2O2. At higher pH, the dismutation of 02 from the equilibrium complex (Mn TTHA(02 f Mn TTHA + Os") is competitive with protonation. At low pH, the results indicate that there is a rapid first-order process that may be an isomerization from end-bound to side-bound of the attached superoxide radical. In contrast, the kinetics of the dismutation of superoxide radical by Escherichia coh MnSOD (manganese superoxide dismutase) were measured and shown to fit a mechanism involving the rapid reduction of Mn SOD by superoxide followed by both the direct reoxidation of Mn SOD by superoxide and the formation of a Mn SOD(02 ) complex. The differences in the mechanisms are discussed. 

An alternate mechanism to that proposed above by McAdam et al. (26, 27) has been postulated by Fee et al. (29) (Scheme III). In this mechanism, the interaction of MnSOD with 02 was suggested to involve equiUbria and, instead of a mechanism involving dual reoxidation pathways separated by a conformational change, an isomerization of the superoxide radical from an end-... 

For 12 and 13 type dyes with various counterions in nonpolar media, electron transfers via singlet and triplet states were distinguished by flash photolysis. The rate constant for electron transfer from the first excited singlet state of 02 in methanol to benzoquinone and other suitable acceptors is = (1-3) X 10 ° M secr. Electron transfer, involving the triplet state of T2-T4, was performed with benzoquinone and ascorbic acid in alcohols. ESR results with various cyanine dyes were interpreted by electron transfer involving the superoxide radical anion. Electron transfer competes with delayed fluorescence and trans—Kis isomerization when induced by energy transfer from triplet anthracene to 13 dyes. Charge-transfer states were reported for cyanine-oxonol ion pairs. 

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