High pH and Temperature Tolerant Molecular Mimics of Carbonic Anhydrase Towards Long-Term Carbonate Production in Enzymatic Construction Material

We recently applied carbonic anhydrase (CA) for the rapid catalytic conversion of carbon dioxide to enable the self-healing properties of concrete and in the development of a carbon-negative concrete replacement named Enzymatic Construction Material (ECM). Here, we explore the stability and carbonate generation ability of model molecular mimics of carbonic anhydrase under high pH and elevated temperatures relevant to long-term durability in cementitious and concrete-like materials. Molecular mimics include Zn2+-based organometallic complexes with an aromatic ligand tris(2-pyridylmethyl)amine, TPA, and with an aliphatic ligand cyclen, 1,4,7,10-tetraazacyclododecane. The Zn(TPA) and Zn(cyclen) complexes are stable in aqueous environments at standard pressures ranging from neutral to pH 13 and temperatures up to 120 °C, where CA is inactive. Under the temperature and pH conditions studied, organometallic degradation pathways do not involve the decomposition of either organic ligand, but rather dissociation of the complex that is reversible upon neutralization in the case of Zn(TPA). Zn(cyclen) is stable at high temperatures at pH 12 and above, resembling cementitious conditions for over 365 days with no signs of degradation. Separately, alkaline calcium-containing solutions with either 25 nM CA or 5 mM Zn(cyclen) catalyst demonstrated accelerated pH decreases compared to catalyst-free controls upon sparging with carbon dioxide because of the conversion of CO2 and H2O to HCO3– and H+. Notably, the inclusion of sub-molar concentrations of detergents, such as sodium dodecyl sulfate, in carbonate production reactions demonstrated no change in the reactivity of control solutions or those with the Zn(cyclen) catalyst, but severely attenuated the conversion in CA-containing solutions concomitant with CA denaturation and loss of enzymatic activity.