Exploring new water soluble bridged dicopper(II) assemblies: Synthesis, structure, spectroscopic characterization, properties, and their interactions with d-glucosamine

Abstract

Three new water soluble dimetallic copper(II) complexes, [Cu(H2O)5][Cu2(cpdp)(µ-O2As(CH3)2)]2Br2·13.83H2O·0.67CH3OH (1), [Cu2(Hcpdp)(µ-SO4)]·5H2O (2) and [Cu2(cpdp)(µ-pz)]·16H2O (3) (H3cpdp = N,N′-Bis[2-carboxybenzomethyl]-N,N′-Bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol; (CH3)2AsO2− = cacodylate; SO42− = sulfate; pz− = pyrazolate) have been successfully synthesized and characterized for the investigation of coordination/binding aspects with biologically significant monosaccharide, d-glucosamine. Preparation of 1, 2 and 3 has been achieved by carrying out reaction of H3cpdp with stoichiometric quantities of CuCl2·2H2O/NaO2As(CH3)2·3H2O, CuSO4·5H2O and CuCl2·2H2O/1H-pyrazole, respectively, in the presence of NaOH in MeOH/H2O at ambient temperature. Diverse analytical methods, for example, microanalysis, FTIR, UV–Vis and mass spectral techniques, including single crystal X-ray crystallography, have been utilized to characterize these complexes. Temperature dependant (2–300 K) magnetic susceptibility measurements reveal the presence of antiferromagnetic interactions between the copper(II) centers in 1 and 2. Thermogravimetric analysis of 1–3 indicates that they are stable on average up to ~ 214 °C. We have employed the UV–Vis spectroscopic technique to study the 1:1 interactions of the complexes with d-glucosamine in alkaline aqueous solution. The UV–Vis titration spectra clearly indicate the binding-induced steady decrease of the absorption intensities of 1–3, with a substantial blue shift of absorption maxima of the complexes upon addition of increasing amounts of d-glucosamine. The binding constant values between the complexes and d-glucosamine have been evaluated from the experimentally obtained UV–Vis titration data. Fukui functions at the metal sites, including HOMOs and LUMOs in 1–3 have been calculated by DFT method to forecast the possible metal centers engaged in the binding process with d-glucosamine. To the best of our knowledge, to date, neither the substrate interaction nor the mode of interaction with respect to d-glucosamine using any metal complex of any nuclearity has been documented in the literature.