Kinetics of the post-column complexation reaction of Cu(II) with N-formylmethionyl chemoattractant and chemotactic peptides Original Research Article

The N-formylmethionyl peptides comprise an important class of peptides that activate neutrophils to attack microbial invaders. The post-column reaction of Cu(II) with peptides following their separation leads to electroactive complexes that are detectable with electrochemical detection. The need to minimize post-column band spreading puts constraints on the time allowed for the complexation reaction to occur. For most peptides, the reaction rate is rapid, however, for peptides without a free terminal amine the reaction rate is slower. In order for this detection scheme to be sensitive to so-called N-blocked peptides, the rate law and the influence of buffers need to be understood. The kinetics of the complexation of Cu(II) with several N-blocked chemoattractant and chemotactic peptides are similar. One N-blocked peptide, N-f-MLF, has been studied in detail. Two parallel paths have been found for the complexation reaction. The reaction at the amide terminus is first order in [peptide] and [OH−]. The reaction at the carboxylate terminus is first order in [peptide], [Cu(II)], and total carbonate at constant pH. The response of the rate as pH is changed reveals that bicarbonate ion is the active species.