Pulse radiolysis studies of intermolecular charge transfers involving tryptophan and three-electronbonded intermediates derived from methionine

摘要

The oxidation processes of the radiation-generated, three-electronbonded intermediates AcMet_2 [S;S]~+ and AcMet [S;Br] were investigated by pulse radiolysis via their reactions with tryptophan (TrpH). These intermediates were derived from N-acetyl-methionine amide (N-AcMetNH_2) and N-acetylmethionine methyl ester (N-AcMetOMe). The bimolecular rate constant k of the reaction between each intermediate and L-tryptophan (TrpH) was measured. For N-AcMetNH_2, k for the reaction of AcMet_2 [S;S]~+ with TrpH were 3.4 9 10~8 and 2.2 9 10~8 dm~3 mol~(-1) s~(-1) at pH = 1 and 4.5, respectively. For N-AcMetOMe, k for the reaction of AcMet_2 [S;S]~+ with TrpH were 4.0 × 10~8 and 2.~8 × 10~8 dm~3 mol~(-1) s~(-1) at pH 1 and 4.5, respectively. The rate constants for the intermolecular transformation of Met [S;Br] into TrpH~+ or Trp were also estimated. For N-AcMetNH_2, k for the reaction of AcMet_2 [S;Br] with TrpH were 2.6 × 10~8 and 3.3 × 10~8 dm~3 mol~(-1) s~(-1) at pH 1 and 4.5, respectively. Related mechanisms were discussed.