Title

Modulating the Catalytic Performance of an Immobilized Catalyst with Matrix Effects - A Critical Evaluation

Document Type

Article

Publication Date

2018

Keywords

glycosides, hydrolysis, macromolecular catalyst, matrix effects, polyacrylate microgels

Abstract

Microgels with embedded binuclear copper(II) complex were prepared in the presence of galactose and mannose as biomimetic catalysts for the hydrolysis of glycosidic bonds. The study was designed to elucidate matrix effects responsible for the high catalytic proficiency (kcat/KM × knon) of the microgels that reaches up to 1.7 × 106 upon hydrolysis of 4-methylumbelliferyl-β-d-mannopyranoside. The experimental results reveal differences of sugar coordination to the binuclear copper(II) complex in coordination sites, binding strength, overall geometry, and binding energies that differ by 7.1 kcal/mol and are based on experiments using UV–Vis spectroscopy and isothermal titration calorimetry. Accompanying computational analyses, based on density functional theory (DFT) at the B3LYP/m6-31G(d) level of theory, further support the experimental results of sugar coordination by suggesting plausible binding sites of sugar coordination and providing additional insight into the cause of substrate discrimination during microgel-catalyzed glycoside hydrolyses. Subsequent kinetic analyses correlate the catalytic proficiency of the microgels with contributions of the metal complex core, the surrounding cross-linked matrix, and strongly binding mannose; however, the data reveal minor contributions of a templating effect to the overall catalytic performance of the water-dispersed microgel catalysts.

Comments

The authors thank Peter Pulay for advice and access to PQSmol and Feng Wang for critical reading of the manuscript. Support of this research to S.S. from the National Science Foundation (CHE-1305543) and the Arkansas Biosciences Institute is gratefully acknowledged.

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