Reduction, oxidation, and addition reactions between free radicals and flavins

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Abstract
Flavins and reduced flavins were reacted with a variety of free radicals produced in dilute aqueous solution at pH 7 .+-. 0.1 by radiation chemical methods. The radical .cntdot.CH2C(CH3)2OH and the aliphatic .beta., .gamma. and .delta. radicals of ethanol, 2-propanol and 1-butanol added to the radical form of FAD (FH.cntdot.) to yield products that could not be reoxidized to flavin by oxygen. The first radical also added to FAD, but with a much lower efficiency. In contrast, the .alpha.-carbon radicals .cntdot.CH(OH)CH2OH, CH3.ovrhdot.CHOH and (CH3)2.ovrhdot.COH appeared to undergo 2 reactions: .**GRAPHIC**. The formate radical anion .cntdot.CO2- reacted similarly, producing stoichiometric 2-electron reduction of riboflavin and lumiflavin as well as FAD. While eaq- also seemed capable of this, it reacted irreversibly with FADH2, which makes it a poor reagent for producing the dihydroflavin. The dihydro form of FAD was reoxidized to FAD by the species RS.cntdot. and .cntdot.Br2-. In contrast to FAD, the alloxazine lumichrome underwent only 1-electron reduction and oxidation by .cntdot.CO2- and .cntdot.Br2-, respectively.