Studies on the reactivity of malondialdehyde. I. Effects of acid concentration and solvent composition on deuterium exchange reactions |
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Authors: | Noemi Chuaqui-Offermanns Claudio A Chuaqui |
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Institution: | Medical Biophysics Branch, Whiteshell Nuclear Research Establishment, Atomic Energy of Canada Limited Research Company, Pinawa, Manibota, ROE 1L0 Canada |
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Abstract: | The rates of deuterium exchange reactions of malondialdehyde (MDA) and deuterated malondialdehyde (MDAd) have been studied as a function of acidity and the content of dimethyl sulfoxide (DMSO) in binary mixtures with D2O . MDA incorporates deuterium from D2O solutions in a first-order reaction with a rate constant (kobs) that depends on the acid concentration. From this dependence, a catalytic constant, kcat, can be derived (kcatMDA = 2.25 × 105M?s?1). Similar kinetic behavior was found for MDAd in H2O solutions, and in this case, kcatMDA = 1.56 × 105M?1s?1. Results from reactions of MDA and MDAd in identical H2OD2O mixtures show that primary and secondary isotope effects are small (kH/kD = 1.13) and that solvent isotope effects cause most of the differences found between reactions in D2O and H2O. Reactions in binary DMSOd6D2O mixtures show a six-fold rate increase as the proportion of DMSOd6 increases from 50% to 90%. These results also illustrate the relatively high reactivity of MDA at pH values well above its pKa and the importance of medium composition on its reaction rate. |
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Keywords: | malondialdehyde reactivity isotope exchange isotope effects |
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