Enzyme-like catalysis by polymers: disulphide cleavage effected by hydrophobically alkylated polyethyleneimine derivatives acting via a complexation step

Abstract

Polyethyleneimine, benzylated to the extent of 10% of its nitrogen atoms, cleaves the disulphide link of Ellman's reagent. The reaction exhibits a binding step, characteristic of the action of enzymes, followed by a bond-forming step between sulphur and nitrogen. The polymer molecule (M_W 240 000) possesses from 1 to 2 amino groups in 800 which are rapidly sulphenylated by the substrate as deduced from tritration and kinetic equilibrium techniques; this is consistent with ca. 1–2% of the benzyl groups providing a binding site close to a reactive amine. The benzyl polymer exhibits a remarkable 10⁶-fold catalytic enhancement over the corresponding efficiency of a simple amine nucleophile of similar pK_a. The cleavage reaction, namely reaction of bound substrate with adjacent amine, possesses a first-order rate constant with an effective molarity of 26M compared with the corresponding intermolecular process.