A comparative study of magnetic field effects on the dynamics of geminate and random radical pair processes in micelles

Article abstract of DOI:10.1021/ja00065a036

Magnetic field effects on the dynamics of random radical-radical reactions in micellar systems are reported for the self-reaction of benzyl radicals in sodium dodecyl sulfate (SDS) and cetyltrimethylammonium chloride (CTAC) micelles. The self-reaction rate constants (2k₁) determined using laser flash photolysis techniques are reduced by 44% (SDS) and 35% (CTAC) by application of moderate fields. One-half of the maximum magnetic field effect can be achieved with as little as 200 and 120 G in SDS and CTAC micelles, respectively. The results are discussed in terms of a single kinetic model where 75% of random encounters lead to micellized triplet radical pairs where micellar escape and intersystem crossing are competitive processes. The implications of these observations in biological chemistry are briefly discussed. The benzyl radicals were produced from dibenzyl ketone. In short time scales the geminate radical pairs involve benzyl and phenylacetyl radical pairs. The dynamics of this widely studied system were examined in detail. For example, for the SDS system, it is estimated that phenylacetyl exit occurs with a rate constant of ～6.6 × 10⁶ s^-1 (compared with 1.4 × 10⁶ s^-1 reported for benzyl), and geminate reaction with K_gem = 1.2 × 10⁷ s^-1. Of the initial benzyl-phenylacetyl geminate radical pairs, approximately 23% decarbonylate, 31 % separate, and 46% undergo geminate reaction.