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

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 (k cat/K M × k non) 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.

Antimicrobial Activity of Microgels with an Immobilized Copper(II) Complex Linked to Cross-Linking and Composition

“…As all microgels are subject to 20 dialysis cycles for purification prior to use in antimicrobial assays, residual hydrophobes, salts, sugar counterions, and unreacted monomers of the synthesis are thereby quantitatively removed. The resulting microgels contain 0.5 mol % of immobilized Cu­(II) complex in an aqueous CAPS buffer solution with SDS surfactant. ,,,, …”

“…The resulting microgels contain 0.5 mol % of immobilized Cu(II) complex in an aqueous CAPS buffer solution with SDS surfactant. 14,15,21,22,27 Most notably, the microgel Cu 2 L P 60% (Table 1, entry 4) shows a 617-fold higher antimicrobial activity than its low molecular weight analogue, the binuclear copper(II) complex Cu 2 bpdpo (Table 1, entry 8). Based on the known stability constant of the complex (K a = 10 17 M −2 ) 19 and the concentration of the immobilized VBbpdpo (3) ligand (8.75 × 10 −4 M), a concentration of 0.013 μg/mL of free Cu(II) ions leaching from the complex was calculated.…”

“…The procedure saturates the metal complex core during material synthesis and prevents metal ion leakage and interference with the polymerization reaction. The resulting microgels have a size between 204 nm (5% cross-linked) and 270 nm (80% cross-linked) …”

“…The resulting microgels have a size between 204 nm (5% cross-linked) and 270 nm (80% cross-linked). 21 When exploring the substrate scope of the developed microgel catalysts, a surprisingly efficient catalytic hydrolysis of 4-methylumbelliferyl N-acetyl-β-D-glucosaminide (4) was noted (Chart 2). 22 Model substrate 4 has the same amino sugar moiety and β-glycosidic linkage as N-acetylmuramic acid (5) and N-acetylglucosamine (6) (Chart 2), which are building blocks in the peptidoglycan layer of the bacterial cell wall of Gram-positive bacteria.…”

Structure–Activity-Relationship Studies to Elucidate Sources of Antibacterial Activity of Modular Polyacrylate Microgels

“… , Then, copper­(II) acetate is added to the prepolymerization mixture to transform the ligand in situ into copper­(II) complexes, followed by addition of an excess of coordinating counter ions, such as mannose, to prevent the copper­(II) ions from interfering with the radical polymerization. − Ultrasheering of the monomer mixture in an aqueous buffer-surfactant system yields in the presence of stabilizing hydrophobes defined droplets, which are captured as particles by free-radical polymerization under UV light. , The resulting microgels are spherical particles with predefined hydrodynamic diameters between 150 and 280 nm (Figure ). , An optimal antimicrobial activity was observed for microgels with a cross-linking content of 60 mol % …”