Imprinted polymeric nanoparticles as artificial enzymes for ester hydrolysis at room temperature and pH 7

Abstract

Replication of the extraordinary catalysis of enzymes in synthetic systems is a long-standing goal of scientists. Here we report a synthetic mimic of carbonic anhydrase capable of hydrolyzing nonactivated alkyl esters at room temperature and neutral pH, while more reactive aryl esters stay intact in the same solution. This type of catalysis normally occurs only in enzymes but becomes possible with synthetic catalysts when a basic group is placed accurately near a zinc-bound water molecule to activate the latter for the nucleophilic attack on the ester substrate. Basicity and charge character of the proton acceptor determine the catalytic mechanism and its window of operation, as well as the type of esters to be hydrolyzed. The distance between the catalytic groups dictates the rate of hydrolysis for the benchmarking p -nitrophenyl ester, with a change by a single bond length impacting the rate more than changing the basicity of the active site base by20 orders of magnitude. • Hydrolysis of alkyl ester at room temperature and pH 7 • Enzyme-like catalytic proficiency • Selective transformation of less reactive esters over more reactive ones • Biomimetic cooperative catalysis Enzymes are characterized by their extraordinary catalytic efficiency and specificity but tend to denature easily under adverse conditions. If synthetic catalysts having similar catalytic capabilities but greater stability can be rationally designed and made, many fields of research and technology will benefit. This report describes synthetic enzymes that rival their biological counterparts in catalytic proficiency. As crosslinked polymeric nanoparticles, they become more active at higher temperatures and can potentially function under conditions totally impossible for natural biocatalysts. Their ability to selectively hydrolyze nonactivated esters under ambient conditions may facilitate chemical recycling of hydrolyzable plastics such as polyester and polycarbonate. Natural esterases hydrolyze esters under physiological pHs, but chemists often have to use strongly acidic or basic conditions for the same hydrolysis. We report synthetic nanoparticle catalysts that hydrolyze nonactivated alkyl esters at room temperature and neutral pH, with enzyme-like catalytic mechanisms and exquisite substrate selectivity. Unlike natural enzymes that denature easily at elevated temperatures, the synthetic catalysts become more active at higher temperatures.