New dinuclear copper(II) and zinc(II) complexes for the investigation of sugar–metal ion interactions

Abstract

We have studied the binding interactions of biologically important carbohydrates ( d-glucose, d-xylose and d-mannose) with the newly synthesized five-coordinate dinuclear copper(II) complex, [Cu 2(hpnbpda)(μ-OAc)] ( 1) and zinc(II) complex, [Zn 2(hpnbpda)(μ-OAc)] ( 2) [H 3hpnbpda = N, N′-bis(2-pyridylmethyl)-2-hydroxy-1,3-propanediamine- N, N′-diacetic acid] in aqueous alkaline solution. The complexes 1 and 2 are fully characterized both in solid and solution using different analytical techniques. A geometrical optimization was made of the ligand H 3hpnbpda and the complexes 1 and 2 by molecular mechanics (MM+) method in order to establish the stable conformations. All carbohydrates bind to the metal complexes in a 1:1 molar ratio. The binding events have been investigated by a combined approach of FTIR, UV–vis and 13C NMR spectroscopic techniques. UV–vis spectra indicate a significant blue shift of the absorption maximum of complex 1 during carbohydrate coordination highlighting the sugar binding ability of complex 1. The apparent binding constants of the substrate-bound copper(II) complexes have been determined from the UV–vis titration experiments. The binding ability and mode of binding of these sugar substrates with complex 2 are indicated by their characteristic coordination induced shift (CIS) values in 13C NMR spectra for carbon atoms C1, C2, and C3 of sugar substrates.