Solvent dependence of oxygen isotope effects on the decarboxylation of 4-pyridylacetic acid

Article abstract of DOI:10.1021/ja00161a038

Oxygen isotope effects on the decarboxylation of 4-pyridylacetic acid have been measured by the remote-label technique. The isotope effect varies from k¹⁶/k¹⁸ = 0.995 per oxygen in 25% dioxane to 1.003 in 75% dioxane. The isotope effect reflects three contributions: An inverse isotope effect of 0.98-0.99 due to the change in carbon-oxygen bond order on going from ground state to transition state, an effect of 1.01-1.02 due to desolvation of the carboxyl group, and an effect of approximately 1.01 due to the acid-base equilibrium of the carboxyl group. Thus, oxygen isotope effects on decarboxylation should be a useful probe for carboxyl desolvation in enzymatic decarboxylations.