Design and synthesis of new water-soluble dinuclear manganese(II) complexes as monosaccharide binding models

Abstract

The present article describes the design, synthesis, physicochemical characterization and monosaccharide binding events of two new water-soluble dinuclear manganese(II) complexes [Mn2(phpda)(µ-Cl)]·2H2O (1) and [Mn2(phpda)(µ-OAc)]·2H2O (2) of carboxylate and pyridyl-functionalized multidentate ligand, H3phpda (H3phpda = N,N′-bis[2-pyridylmethyl]-2-hydroxy-1,3-propanediamine-N,N′-dipropionic acid). FTIR, UV–Vis, ESI-MS, microanalysis, molar conductivity, cyclic voltammetry and room-temperature magnetic data establish their compositions. Structural features of 1 and 2 obtained from theoretical calculations indicate a self-assembled and well-packed array with average Mn···Mn separation of 2.952 Å. Both 1 and 2 have been studied towards 1:1 binding interactions with biologically important monosaccharides, such as d-glucose, d-xylose and d-glucosamine by employing UV–Vis spectroscopy and DFT computation. The binding constant values of monosaccharide-bound manganese(II) complexes evaluated from UV–Vis titration data are 2.145 x 103 M−1, 2.156 x 103 M−1, 2.652 x 103 M−1, 1.388 x 103 M−1, 1.793 x 103 M−1 and 2.146 x 103 M−1 for 1/d-glucose, 1/d-xylose, 1/d-glucosamine, 2/d-glucose, 2/d-xylose and 2/d-glucosamine assemblies, respectively. The possible metal centers engaged in the binding events have been ascertained by calculating the Fukui functions (fk+) on the manganese sites, including HOMOs and LUMOs. A comparative assessment of sugar-binding properties, in particular, suggests that the order of binding ability of monosaccharides with 1 and 2 is found to be d-glucosamine > d-xylose > d-glucose.