Issue 0, 1971

The uncatalysed and metal-ion catalysed decarboxylation of 3-oxoglutaric acid: a model for an enzyme system

Abstract

The uncatalysed decarboxylation of 3-oxoglutaric acid, HO2C·CH2·CO·CH2·CO2H CH3·CO·CH2·CO2H + CO2 has been studied at 42°. The rate constants for the un-ionised acid, the monoanion, and the dianion are 12 × 10–3 min–1, 45 × 10–3 min–1, and 2·75 × 10–3 min–1 respectively. Because of the higher reactivity of the monoanion, the pH-rate profile for the uncatalysed decarboxylation is bell-shaped with a rate maximum at pH 3·5 (l= 0·1M). The enhanced reactivity of the monoanion appears to be due to intramolecular hydrogen bonding between the carbonyl group and the un-ionised carboxy-group. The practical ionisation constants of 3-oxoglutaric acid are pK1= 3·23 and pK2= 4·27 at 0·01M. The decarboxylation of 3-oxoglutaric acid, unlike that of acetoacetic acid, is catalysed by transition-metal ions, so that in the presence of metal ions there is a rapid loss of one molecular equivalent of carbon dioxide followed by a slower loss of a second molecular equivalent in the uncatalysed reaction. The catalytic effects of copper(II), nickel(II), and manganese(II) have been studied in some detail. It has been found that 2,2′-bipyridyl which is capable of π-bonding with the metal ions enhances the catalytic activity of manganese(II) by a factor of 10 while the effect with copper(II) and nickel(II) is less marked (ca. 2 times). The possible significance of these effects in the action of the metal-activated decarboxylases is discussed, as manganese(II) is the biologically important metal ion in the enzymatic reactions.

Article information

Article type
Paper

J. Chem. Soc. A, 1971, 3639-3647

The uncatalysed and metal-ion catalysed decarboxylation of 3-oxoglutaric acid: a model for an enzyme system

R. W. Hay and K. N. Leong, J. Chem. Soc. A, 1971, 3639 DOI: 10.1039/J19710003639

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Spotlight

Advertisements