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ABSTRACT:
Monobasic tridentate Schiff base hydrazone (pyrazine-2-carboxylic acid (phenyl-thiophen-2-yl-methylene)-hydrazide, HL) derived from condensation of pyrazine carboxylic acid hydrazide and 2-benzoyl thiophene reacted with transition metal (II) nitrates to form complexes of ML2 type [where M = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)]. Schiff base hydrazone and metal complexes were characterized by spectroscopic techniques (IR, NMR, mass, electronic and ESR), molar conductance and room temperature magnetic successptibility measurements. On the basis of various physicochemical studies, octahedral geometry was proposed for Mn(II), Co(II), Ni(II), Zn(II) complexes and distorted octahedral geometry for Cu(II) complex. Schiff base hydrazone coordinated to metal ion through carbonyl oxygen, azomethine nitrogen and sulfur of thiophene ring. Schiff base and metal complexes have been evaluated for antimicrobial activities against various bacteria (Bacillus subtilis, Micrococcus luteus, Pseudomonas aeruginosa, Pseudomonas mendocina) and various fungi (Verticillum dahliae, Cladosporium herbarium, Trichophyton soudanense) at different concentrations i.e. 25, 50, 100, 200 µg/mL. The hydrazone ligand was found to be biologically active and a marked enrichment was observed in antimicrobial activity on coordination with metal ions.
KEYWORDS: Tridentate, Hydrazone, 2-benzoyl thiophene and Antimicrobial activity
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INTRODUCTION:
Schiff bases containing nitrogen, oxygen and sulphur donor atoms act as effective chelating agents and have developed rapidly due to their structural varieties, applications in catalysis [1], pharmacology and biological systems[2]. Schiff base hydrazones are of particular interest due to presence of -NH-N=CH- group in their molecule with an additional donor site like C=O, which determine the versatility and flexibility of these compounds[3]. Schiff base hydrazones exhibit keto-enol tautomerism and can coordinate in netural, monoanionic, dianionic or trianionic forms to the metal ions which have coordination number of six and seven. Schiff base hydrazones show anticonvulsant[4-5], anti-inflammatory[6], antimicrobial[7-9], antimalarial[10], antituberculosis[11] and anti-HIV properties. Aroylhydrazone Schiff bases also have in vitro bacteriostatic properties against various microorganisms .
Such hydrazide derived compounds are potent inhibitors of DNA synthesis in variety of cultured human and rodent cells[13,14] and their metal complexes are known to provide useful models for the elucidation of mechanism of enzyme inhibition and also produce significant inhibition of tumor growth. Recently, we have synthesized and characterized some transition metal (II) complexes of Schiff base hydrazones and their in vitro antibacterial activity was also investigated[15]. So in continuation of...