Carbon-centered radicals add reversibly to histidine--implications.

Carbon-centered radicals of alcohols commonly used as hydroxyl radical scavengers (MeOH, EtOH, i-PrOH and t-BuOH) add reversibly to histidine with equilibrium constants up to 3 × 10(3) M(-1) and rate constants on the order of 10(9) M(-1) s(-1). Similar equilibria may compromise determinations of one-electron (radical) electrode potentials.