Abstract
The reaction between the ruthenium nitrosyl complexes trans-[RuII(NO)L1L2]n+, where L1=(NH3)4 and L2=imN, nic, 4-pic and P(OEt)3 or L1/L2=Hedta, with superoxide (O2−) have been probed in aqueous medium at (25±0.1)°C by UV–Vis, DPV and EPR spectroscopies. The reaction involves one electron transfer from O2− to trans-[RuII(NO)L1L2]n+ yielding trans-[RuII(H2O)L1L2]n+ and nitric oxide (NO) as main reaction products. Using cytochrome c as a probe for superoxide and a competitive kinetic approach, the apparent bimolecular rate constant for the reaction between trans-[RuII(NO)L1L2]n+ and O2− have been determined to be in the range of (6.3±0.5)×103 (L1=(NH3)4; L2=4-pic) to (5.8±0.2)×106 (L1=(NH3)4; L2=P(OEt)3)M−1s−1. For L1=(NH3)4 and L2=P(OEt)3 the peroxynitrite formation as a by-product of O2− and NO reaction was detected using tyrosine as a probe monitoring the formation of 3-nitro-tyrosine by HPLC-DAD. These nitrosyl compounds can be activated by superoxide, thus holding radical scavenger potential in vivo, besides being useful to modulate the local NO levels.
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