Optimization of poly(N-isopropylacrylamide) as an artificial amidase

Poly(N-isopropylacrylamide) microgel (NMG) has been developed by adding various functional groups to control surface charges, hydrophobicity, pKa and protein adsorption capacity. Here, we developed and optimized NMG anchored with three types of functional groups as a polymeric catalyst to hydrolyze amide bonds under optimized mild conditions. Various optimization strategies were evaluated for efficient hydrolysis activity on a p-nitroaniline-based substrate by using a colorimetric assay. Based on the results, we propose a mechanism to hydrolyze amide bonds and determine the theoretical average distance, using NMG bearing functional group of 1-vinylimidazole as the study model. The hydrolysis of amide bonds was inhibited by a transition-state protease inhibitor, which also confirmed the proposed reaction model for NMG. These results provide an insight into the strategies developed to functionalize hydrogels through an enzyme-mimic approach for future robust bio- and chemical conversions as well as therapeutic utilities.