Studies on spin-trapped radicals in γ-irradiated aqueous solutions of cis-4-chloro-L-proline and cis-4-hydroxy-L-proline by high-performance liquid chromatography and ESR spectroscopy

Aqueous solutions of cis-4-chloro-L-proline and cis-4-hydroxy-L-proline were γ irradiated in the presence of a spin trap, 2-methyl-2-nitrosopropane. Stable spin adducts produced in the γ-irradiated solutions were analyzed by high-performance liquid chromatography and ESR spectroscopy. The following spin adducts were found and identified: t-BuN(O)-*CH(COO-)-CH2-*CHCl-CH2NH3+ (I) and t-BuN(O)-*CHCH2NH2+-*CH(COO-)CH2 (II) from cis-4-chloro-L-proline (γ irradiated in the presence of sodium formate); t-BuN(O)-*CH(COO-)CH2-*CH(OH)CH2NH3+ (III) and t-BuN(O)-*CHNH2+-*CH(COO-)CH2-*CHOH (IV) from cis-4-hydroxy-L-proline. Each of spin adducts II and IV was found as a pair of diastereomeric radicals, which revealed mutually different hyperfine splitting constants. The diastereoisomers of spin adduct II were individually separared, and their preferential conformations were considered on the basis of their hyperfine structures. The ESR spectra of the spin adducts from L-proline and trans-4-hydroxy-L-proline in their γ-irradiated aqueous systems, which have been reported previously (Suzuki et al., ref 1), were reexamined and assigned by computer simulations and by taking account of the results from cis-4-chloro-L-proline and cis-4-hydroxy-L-proline