Imidazole catalyses in aqueous systems. X. Enzyme-like catalytic hydrolyses of phenyl esters by polymers containing imidazole and other anionic functions

Seiji Shinkai, Toyoki Kunitake

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6 Citations (Scopus)

Abstract

The catalytic hydrolysis of p-acetoxybenzoic acid (ABA) and 3-acetoxy-N-trimethylanilinium iodide (ANTI+) was carried out mainly at 30°C and pH 8.0 in 1.0-M aqueous KCl. The polymer catalysts used were water-soluble terpolymers of acrylamide, N[p-(4(5)-imidazolyl)benzyl]acrylamide (PI unit), and N-phenyl-methacrylamide derivatives with anionic functional groups such as sulfonate (BS unit), carboxylate (BA unit), hydroxyl (NP unit), and hydroxamate groups (HA unit). Michaelis—Menten kinetics were observed for all the catalysts; the reaction constants were Km=14.5—200 mM and kcat=0.004—0.026 min−1 for the imidazole catalysis. The Km value for ANTI+ decreases with increase in the content of BS and BA units in the polymers. On the other hand, the value of Km for ABA triples during the same increase: this establishes that the electrostatic interaction contributes to the substrate binding in addition to the hydrophobic interaction. The plot of Kcat vs. the BA content in the PI—BA polymers gave a maximum at ca. 30-mol % BA unit, whereas the Kact value for PI—BS polymer increased monotonously. These trends suggest the existence of cooperative action between the imidazole and carboxylate functions, but not between imidazole and sulfonate. The plots of logkcat vs. pKa of the anionic functional groups gave good linear relationships, and the general-basic contribution of the anionic functional groups is proposed. The catalytic behavior of the PI—HA polymer features the burst alkali consumption due to the HA unit. A novel scheme involving the acyl transfer from HA unit to PI unit, which is a model of α-chymotripsin, is suggested.

Original languageEnglish
Pages (from-to)387-396
Number of pages10
JournalPolymer Journal
Volume7
Issue number3
DOIs
Publication statusPublished - May 1975

All Science Journal Classification (ASJC) codes

  • Polymers and Plastics
  • Materials Chemistry

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