Reactions of lumiflavin and lumiflavin radicals with .cntdot.CO2- and alcohol radicals

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Abstract
The kinetics of reaction of oxidized lumiflavin (Fo) with the radicals .cntdot.CO2-, CH3.ovrhdot.CHOH, and (CH3)2.ovrhdot.COH were investigated at pH 7 and 24 .+-. 1.degree. C by the pulse radiolysis technique. The radicals react with lumiflavin with 2nd-order rate constants of 36 .+-. 4, 26 .+-. 3, and 20 .+-. 3 in units of 108 M-1 S-1, respectively. These rate constants are close to the diffusion limit. The main product in each case was the lumiflavin semiquinone radical FH.cntdot.. Long pulses (.apprx. 100 .mu.s) were used to show that the reaction FH.cntdot. + .cntdot.AH(.alpha.) .fwdarw. FH- + A(.alpha.) + H+ [.cntdot.AH(.alpha.) = .cntdot.CO2-, CH3.ovrhdot.CHOH, or (CH3)2.ovrhdot.COH] proceeded for all 3 types of .cntdot.AH(.alpha.) radical with 2nd-order rate constants of 17 (+4, -3), 9 (+5, -3), and 9 (+4, -3), respectively, in the above units. The .beta.-carbon radical .cntdot.CH2CH(OH)CH3 added to .cntdot.FH, forming an alkylated flavin, while the .cntdot.CH2CH2OH radical appeared to be capable of addition or H atom donation to .cntdot.FH.