Magnetic, Structural and Computational Studies on Transition Metal Complexes of a Neurotransmitter, Histamine

Abstract

In this study, the transition metal complexes of histamine (His) prepared with oxalate (Ox), that is, [Cu(His)(Ox)(H<inf>2</inf>O)], [Zn(His)(Ox)(H <inf>2</inf>O)] (or [Zn(His)(Ox)]·(H<inf>2</inf>O)), [Cd(His)(Ox)(H <inf>2</inf>O)<inf>2</inf>] and [Co(His)(Ox)(H<inf>2</inf>O)], are investigated experimentally and computationally as part of ongoing studies on the mode of complexation, the tautomeric form and non-covalent interactions of histamine in supramolecular structures. The structural properties of prepared complexes are experimentally studied by X-ray diffraction (XRD) technique and Fourier transform infrared (FT-IR) spectroscopy and computationally by density functional theory (DFT). The magnetic properties of the complexes are investigated by electron paramagnetic resonance (EPR) technique. The [Cu(His)(Ox)(H<inf>2</inf>O)] complex has a supramolecular structure constructed by two different non-covalent interactions as hydrogen bond and C-H⋯π interactions. EPR studies on [Cu(His)(Ox)(H<inf>2</inf>O)], Cu 2+-doped [Zn(His)(Ox)(H<inf>2</inf>O)] and [Cd(His)(Ox)(H <inf>2</inf>O)<inf>2</inf>] complexes show that the paramagnetic centers have axially symmetric g values. It is also found that the ground state of the unpaired electrons in the complexes is dominantly d<inf>x2-y2</inf> and unpaired electrons' life time is spent over this orbital. © 2011 Elsevier B.V. All rights reserved.