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Electrostatic interactions effect in the aminolysis of some β ‐lactams in the presence of poly(ethyleneimine):structure‐reactivity
Author(s) -
Arcelli Antonio,
Porzi Gianni,
Rinaldi Samuele,
Sandri Monica
Publication year - 2008
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1301
Subject(s) - aminolysis , chemistry , ethyleneimine , reactivity (psychology) , computational chemistry , polymer chemistry , organic chemistry , catalysis , polymer , medicine , alternative medicine , pathology
The 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 K 1 between polyelelectrolyte and β‐ lactam and the first order rate constant of the reactive complex decomposition k cat were calculated. The substituent effect at C‐6′ or C‐7′ position of β ‐lactam on the aminolysis rate does not correlate with the σ I 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.