Imidazole Catalyses in Aqueous Systems. I. The Enzyme-like Catalysis in the Hydrolysis of a Phenyl Ester by Imidazole-Containing Copolymers

Toyoki Kunitake, Fumiko Shimada, Chuji Aso

Research output: Contribution to journalArticle

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Abstract

Hydrolyses of 3-nitro-4-acetoxybenzoic acid catalyzed by copolymers of 1-vinyl-2-methylimidazole with 1-vinylpyrrolidone (copolymer A) and with acrylamide (copolymer B) were studied at 30° and mostly at pH 8.0 in 1.0 M aqueous KCl. The rate of the catalytic hydrolysis could be described by Michaelis-Menten kinetics, showing substrate saturation phenomena at high substrate concentrations, as in enzymatic reactions. Copolymer A of low (<20%) imidazole contents showed the same kinetic pattern, independent of the copolymer composition, and gave Km (dissociation constants of the catalyst-substrate complex) of 9.3 mM and k3 (first-order rate constant of the pseudo-intramolecular product formation) of 0.038 min-1. Copolymer B gave Km of 63 mM and k3 of 0.11 min-1. When, however, copolymer A contained higher amounts of the imidazole unit, the kinetic pattern was not the simple Michaelis-Menten type and the over-all catalytic efficiency decreased, suggesting the presence of the catalytic site of a differing nature. The substrate binding was attributed to hydrophobic interaction, since the electrostatic interaction between catalyst and substrate was found negligible. The kinetic characteristics of copolymer A were reasonably explained by assuming the loop formation of the polymer segment surrounding the substrate molecule. Finally, probable reasons for the relatively small k3 value for copolymer A were discussed, taking the nature of the catalytic site into consideration.

Original languageEnglish
Pages (from-to)2716-2723
Number of pages8
JournalJournal of the American Chemical Society
Volume91
Issue number10
DOIs
Publication statusPublished - May 1969

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Catalysis
Hydrolysis
Esters
Copolymers
Enzymes
Catalytic Domain
Substrates
Acrylamide
Kinetics
Static Electricity
Hydrophobic and Hydrophilic Interactions
Polymers
Acids
imidazole
Catalysts
Coulomb interactions
Rate constants
Molecules
Chemical analysis

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Imidazole Catalyses in Aqueous Systems. I. The Enzyme-like Catalysis in the Hydrolysis of a Phenyl Ester by Imidazole-Containing Copolymers. / Kunitake, Toyoki; Shimada, Fumiko; Aso, Chuji.

In: Journal of the American Chemical Society, Vol. 91, No. 10, 05.1969, p. 2716-2723.

Research output: Contribution to journalArticle

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abstract = "Hydrolyses of 3-nitro-4-acetoxybenzoic acid catalyzed by copolymers of 1-vinyl-2-methylimidazole with 1-vinylpyrrolidone (copolymer A) and with acrylamide (copolymer B) were studied at 30° and mostly at pH 8.0 in 1.0 M aqueous KCl. The rate of the catalytic hydrolysis could be described by Michaelis-Menten kinetics, showing substrate saturation phenomena at high substrate concentrations, as in enzymatic reactions. Copolymer A of low (<20{\%}) imidazole contents showed the same kinetic pattern, independent of the copolymer composition, and gave Km (dissociation constants of the catalyst-substrate complex) of 9.3 mM and k3 (first-order rate constant of the pseudo-intramolecular product formation) of 0.038 min-1. Copolymer B gave Km of 63 mM and k3 of 0.11 min-1. When, however, copolymer A contained higher amounts of the imidazole unit, the kinetic pattern was not the simple Michaelis-Menten type and the over-all catalytic efficiency decreased, suggesting the presence of the catalytic site of a differing nature. The substrate binding was attributed to hydrophobic interaction, since the electrostatic interaction between catalyst and substrate was found negligible. The kinetic characteristics of copolymer A were reasonably explained by assuming the loop formation of the polymer segment surrounding the substrate molecule. Finally, probable reasons for the relatively small k3 value for copolymer A were discussed, taking the nature of the catalytic site into consideration.",
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