Ligand centered radical pathway in catechol oxidase activity with a trinuclear zinc-based model: Synthesis, structural characterization and luminescence properties

A new trinuclear zinc(II) complex, [Zn-3(L)(NCS)(2)](NO3)(2)-CH3OH center dot H2O (I), of a (N,O)-donor compartmental Schiff base ligand (H2L = N,N'-bis(3-methoxysalicylidene)-1,3-diamino-2-propanol), has been synthesized in crystalline phase. The zinc(II) complex has been characterized by elemental analysis, IR spectroscopy, UV-Vis spectroscopy, powder X-ray diffraction study (PXRD), H-1 NMR, EI mass spectrometry and thermogravimetric analysis. PXRD revealed that 1 crystallizes in P - 1 space group with a = 9.218 angstrom, b = 10.849 angstrom, c = 18.339 angstrom, with unit cell volume is 2179.713 (angstrom)(3). Fluorescence spectra in methanolic solution reflect that intensity of emission for 1 is much higher compared to H2L and both the compounds exhibit good fluorescence properties. The complex 1 exhibits significant catalytic activities of biological relevance, viz. catechol oxidase. In methanol, it efficiently catalyzes the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to corresponding quinone via formation of a dinuclear species as [Zn-2(1)(3,5-DTBC)]. Electron Paramagnetic Resonance (EPR) experiment suggests generation of radicals in the presence of 3,5-DTBC and it may be proposed that the radical pathway is probably responsible for conversion of 3,5-DTBC to 3,5-DTBQ promoted by complex of redox-innocent Zn(II) ion. (C) 2015 Elsevier B.V. All rights reserved.