We investigated the complex formation between various underivatized carbohydrates and the binuclear copper(II) complex 1, Cu(2)(bpdpo). A combined approach of UV/vis and CD spectroscopic investigations shows a large discrimination ability of 1 for structurally closely related monosaccharides in alkaline solution. The dominating form of the binuclear copper(II) complex consists of a [Cu(2)L(-)(H)(OH)(2)](+) species between pH 11 and 13, as determined from pH-dependent spectrophotometric titration experiments. The binding strengths of the 1:1 sugar-1 complexes, derived from the biologically important monosaccharides d-mannose (3) and d-glucose (5), is about 1.5 orders of magnitude different at pH 12.40. Moreover, a blue- or a red-shift of the absorption maximum of 1 accompanies the sugar binding and highlights the ability of 1 to discriminate carbohydrates. This phenomenon is due to the number of hydroxyl groups of the particular monosaccharide involved in chelation to the binuclear metal complex.

In an effort to develop biomimetic glycosyl transfer catalysts, a polymerization protocol was developed that is applicable to the synthesis of crosslinked microgels via UV-initiated free radical polymerization of miniemulsions at ambient temperature and below. The catalytic activity of the microgels derived from butyl acrylate, EGDMA, and a catalyst-precursor ligand was established using the hydrolysis of 4-methylumbelliferyl β-d-galactopyranoside as a model reaction. The microgel-catalyzed hydrolysis was up to 3 × 10-fold accelerated over the background reaction and notably 38-fold faster than the hydrolysis catalyzed by its low molecular weight analog. Dynamic light scattering analysis demonstrated mean hydrodynamic diameters of the particles between 210 and 280 nm and chemical stability of the particles in aqueous solution between pH 1 and 13. A bell-shaped correlation between catalytic proficiency and material rigidity was observed that peaks at 40 mol % of crosslinking content of the microgel.

No abstract

A dormant macromolecular catalyst was prepared by polymerization of an aqueous styrene-butyl acrylate miniemulsion in the presence of a new polymerizable pentadentate ligand. The catalyst was activated by binding Cu(II) ions to the ligand site and then explored for its ability to hydrolyze glycosidic bonds in alkaline solution. The performance was correlated to the catalytic activity shown by low molecular weight analogs. A turnover rate of up to 43 × 10(-4) min(-1) was previously observed for cleavage of the glycosidic bond in selected p-nitrophenylglycosides with a binuclear, low molecular weight catalyst; by contrast, the same reaction is more than 1 order of magnitude faster and has a turnover rate of up to 380 × 10(-4) min(-1) when using the prepared macromolecular catalyst. The catalyzed hydrolysis is about 10(5)-fold accelerated over the uncatalyzed background reaction under the provided conditions, while a significant discrimination of the α- and β-glycosidic bond or of the galacto- and gluco-configuration in the sugar moiety in the glycoside substrates is not observed.