Electrostatic interactions effect in the aminolysis of some β‐lactams in the presence of poly(ethyleneimine):structure‐reactivity

Abstract

AbstractThe aminolysis reaction of a series of β‐lactams in the presence of poly(ethyleneimine) (PEI) at 30°C and pH = 8.40 has been studied. The substrates investigated follow a pseudo first order rate, except two β‐lactams which show a two step consecutive reaction. Increasing the polyelectrolyte concentration, Michaelis–Menten type kinetics are been observed and for four substrates a more complex rate behaviour was verified owing to the polyelectrolyte inhibition effect. Both the binding constant K1 between polyelelectrolyte and β‐lactam and the first order rate constant of the reactive complex decomposition kcat were calculated. The substituent effect at C‐6′ or C‐7′ position of β‐lactam on the aminolysis rate does not correlate with the σI value (Taft plot). Most probably, steric and electronic effects are important, but the electrostatic ones are determining factors for the relevant acceleration attributable to both the binding phenomena and the increased reactivity of the substrate–polyelectrolyte complex. The comparison between poly(ethyleneimine) and Human Serum Albumin (HSA) is also discussed. Copyright © 2007 John Wiley & Sons, Ltd.