15N CIDNP during reaction of the oxoperoxonitrate–CO2 adduct with bovine albumin and L-tyrosine derivatives

Abstract

During the reaction of the oxoperoxonitrate–CO₂ adduct with bovine albumin (ALB), the ¹⁵N NMR signals of nitrated tyrosyl residues in ALB (3-NO₂-ALB) appear as emission indicating the nitration reaction to be a radical mechanism. The nuclear polarisations are built up by radical pairs [ALB˙ ˙NO₂]^F generated by free radical encounters of nitrogen dioxide ˙NO₂ and phenoxyl type radicals ALB˙ formed by hydrogen abstraction from the phenolic residues in ALB. Analogous effects are observed during reaction with valyltyrosylvaline (Val-Tyr-Val) and N-acetyl-L-tyrosine (Tyrac). During nitration of Val-Tyr-Val and Tyrac with nitric acid, identical ¹⁵N CIDNP effects are observed in the nitration products. The reactions are inhibited in the presence of sodium azide or sulfamic acid indicating a nitrous acid catalysed reaction. A comparison of the ¹⁵N CIDNP intensities reveals that the radical reaction with the oxoperoxonitrate–CO₂ adduct is the main, if not the only nitration reaction.