Synthesis, Characterization, and Biological Studies of Binuclear Copper(II) Complexes of (2E)-2-(2-Hydroxy-3-Methoxybenzylidene)-4N-Substituted Hydrazinecarbothioamides
Four novel binuclear copper(II) complexes [1–4] of (2E)-2-(2-hydroxy-3-methoxybenzylidene)-4N-substituted hydrazinecarbothioamides, (OH)(OCH3)C6H4CH=NNHC(S)NHR, where R？=？H (L1), Me (L2), Et (L3), or Ph (L4), have been synthesized and characterized. The FT-IR spectral data suggested the attachment of copper(II) ion to ligand moiety through the azomethine nitrogen, thioketonic sulphur, and phenolic-O. The spectroscopic characterization indicates the dissociation of dimeric complex into mononuclear [Cu(L)Cl] units in polar solvents like DMSO, where L is monoanionic thiosemicarbazone. The DNA binding properties of the complexes with calf thymus (CT) DNA were studied by spectroscopic titration. The complexes show binding affinity to CT DNA with binding constant ( ) values in the order of 106 M？1. The ligands and their metal complexes were tested for antibacterial and antifungal activities by agar disc diffusion method. Except for complex 4, all complexes showed considerable activity almost equal to the activity of ciprofloxacin. These complexes did not show any effect on Gram-negative bacteria, whereas they showed moderate activity for Gram-positive strains. 1. Introduction Thiosemicarbazones have been emerged as an important class of sulphur and nitrogen containing ligands in the last few decades [1–6] due to their variety of biological activities, such as antitumor [7], antifungal [8, 9], antibacterial [9, 10], and antiviral [11] activities. The biological activity of these compounds depends upon the starting materials and their reaction conditions [12], also related to molecular conformation in particular, which can also be significantly affected by the presence of intra- and intermolecular hydrogen bonding. Thiosemicarbazones usually act as chelating ligands for metal ions, bonding through sulphur (=S) and azomethine (=N–) groups, although in some cases they behave as mono dentate ligands where they bind through sulphur (=S) only [13]. The structural investigations of 2-hydroxy-3-methoxy benzaldehyde thiosemicarbazone (L1) [14] and its copper(II) [15] and molybdenum(VI) [16–18] complexes were reported, but the structural studies on thiosemicarbazone ligands obtained from substituted thiosemicarbazides and their complexes are worthy to be reported. Therefore, in continuation of ongoing study on thiosemicarbazones and their metal complexes [13, 19–22], we report herein the synthesis, characterization, and biological studies on copper(II) complexes of (2E)-2-(2-hydroxy-3-methoxybenzylidene)-4N-substituted hydrazinecarbothioamides. 2. Experimental
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