Kinetic Study of CO2 Hydration by Small-Molecule Catalysts with A Second Coordination Sphere that Mimic the Effect of the Thr-199 Residue of Carbonic Anhydrase

Abstract

Zinc complexes were synthesized as catalysts that mimic the ability of carbonic anhydrase (CA) for the CO2 hydration reaction (H2O + CO2 → H+ + HCO3-). For these complexes, a tris(2-pyridylmethyl)amine (TPA) ligand mimicking only the active site, and a 6-((bis(pyridin-2-ylmethyl)amino)methyl)pyridin-2-ol (TPA-OH) ligand mimicking the hydrogen-bonding network of the secondary coordination sphere of CA were used. Potentiometric pH titration was used to determine the deprotonation ability of the Zn complexes, and their pKa values were found to be 8.0 and 6.8, respectively. Stopped-flow spectrophotometry was used to confirm the CO2 hydration rate. The rate constants were measured to be 648.4 and 730.6 M-1s-1, respectively. The low pKa value was attributed to the hydrogen-bonding network of the secondary coordination sphere of the catalyst that mimics the behavior of CA, and this was found to increase the CO2 hydration rate of the catalyst.

Highly Hydrophilic ZIF-8 as a Carbonic Anhydrase Mimetic Catalyst for Promoting CO2 Absorption

“…These results demonstrate that, compared with ZIF-8, ZIF-8-TA has a faster catalytic rate for HCO 3 – production and release but a slower catalytic rate for H 2 O deprotonation. Because previous research has shown that the HCO 3 – production and release rates play a dominant role in the CA-mimetic enzyme-catalyzed CO 2 hydration reaction, ,,, ZIF-8-TA is expected to have higher catalytic performance in CO 2 hydration, which is consistent with the experimental results.…”

“…In the deprotonation step, the H 2 O molecule can be directly deprotonated over ZIF-8, while it must overcome a barrier (TS2′ = 6.42 kcal/mol) before deprotonation over ZIF-8-TA. These results demonstrate that, compared with ZIF-8, Because previous research has shown that the HCO 3 − production and release rates play a dominant role in the CAmimetic enzyme-catalyzed CO 2 hydration reaction, 7,30,45,46 ZIF-8-TA is expected to have higher catalytic performance in CO 2 hydration, which is consistent with the experimental results.…”

“…A more weakly bound OH − has a stronger nucleophilicity, thereby making it easier to react with CO 2 to produce HCO 3 − , while a more weakly bound HCO 3 − can be more easily released from Zn 2+ . 7,45,46 Therefore, the electron-donating effect of TA on Zn 2+ improves the catalytic rate of ZIF-8-TA for HCO 3 − production and release. Through Multiwfn combined with the IGMH, we can illustrate the weak interaction between catalyst and reactants.…”

Amino Acid-Mediated Synthesis of the ZIF-8 Nanozyme That Reproduces Both the Zinc-Coordinated Active Center and Hydrophobic Pocket of Natural Carbonic Anhydrase

“…Biomimetic nanozymes are catalysts that mimic natural enzyme catalytic structures and functions, mainly including polypeptide metal complexes, small molecule metal complexes, , and nanomaterials. − Compared with natural enzymes, nanozymes not only have similar catalytic activity but also have the advantages of easy synthesis and high stability . Till now, several biomimetic CA analogues have been synthesized. ,− The zinc complex of 1,4,7,10-tetraazacyclododecane is considered one of the most representative functional models of biomimetic CA .…”

“…16−19 As an enzymatic catalyzer, CA is sensitive to external environments and high temperature and pH will reduce its stability and catalytic efficiency and even inactivate it. 20,21 Biomimetic nanozymes are catalysts that mimic natural enzyme catalytic structures and functions, mainly including polypeptide metal complexes, 22 small molecule metal complexes, 23,24 and nanomaterials. 25−29 Compared with natural enzymes, nanozymes not only have similar catalytic activity but also have the advantages of easy synthesis and high stability.…”