Bicarbonate Inhibition of Carbonic Anhydrase Mimics Hinders Catalytic Efficiency: Elucidating the Mechanism and Gaining Insight toward Improving Speed and Efficiency

Carbonic anhydrase (CA) mimics are often studied with a focus on the hydration of CO2 for atmospheric carbon capture. Consequently, the reverse reaction (dehydration of HCO3–) has received minimal attention, so much so that the rate-limiting step of the dehydration reaction in CA mimics is currently unknown. The rate-limiting step of the hydration reaction is reported to be the bicarbonate-bound intermediate step, and thus is susceptible to product inhibition. It is not, however, clear if this inhibition is a consequence of an increase in the rate of the competing dehydration reaction or resulting from the strong affinity of bicarbonate to the mimic. To address this, insight into the dehydration reaction kinetics is needed. We therefore report the most comprehensive study of a CA mimic to date. The dehydration profile of the fastest small-molecule CA mimic, ZnL1S, was characterized, and consequently evidence for the rate-limiting step for the dehydration reaction was seen to be the bicarbonate-bound inter...