Caged CO(2) for the direct observation of CO(2)-consuming reactions.

CO(2)-consuming reactions, in particular carboxylations, play important roles in technical processes and in nature. Their kinetic behavior and the reaction mechanisms of carboxylating enzymes are difficult to study because CO(2) is inconvenient to handle as a gas, exists in equilibrium with bicarbonate in aqueous solution, and typically yields products that show no significant spectroscopic differences from the reactants in the UV/Vis range. Here we demonstrate the utility of 3-nitrophenylacetic acid and related compounds (caged CO(2)) in conjunction with infrared spectroscopy as widely applicable tools for the investigation of such reactions, permitting convenient measurement of the kinetics of CO(2) consumption. The use of isotopically labeled caged CO(2) provides a tool for the assignment of infrared absorption bands, thus aiding insight into reaction intermediates and mechanisms.