Science Journal of Chemistry 2013; 1(5): 56-66 Published online November 20, 2013 (http://www.sciencepublishinggroup.com/j/sjc) doi: 10.11648/j.sjc.20130105.12 Metal-based Antimicrobial agents: Synthesis, Characterization and Biological studies of Mannich base derivatives of Benzimidazole and their Metal complexes Misbah ur Rehman 1 , Muhammad Imran 2, * , Muhammad Arif 2 , Muhammad Farooq 3 1 Institute of Chemical Sciences, Gomal University, D. I. Khan, KPK, Pakistan 2 Institute of Chemical Sciences, Bahauddin Zakariya University, Multan, Pakistan 3 Department of Chemistry, Govt. College, Gujranwala, Pakistan Email address: imran345@hotmail.com (M. Imran) To cite this article: Misbah ur Rehman, Muhammad Imran, Muhammad Arif, Muhammad Farooq. Metal-based Antimicrobial Agents: Synthesis, Characterization and Biological Studies of Mannich Base Derivatives of Benzimidazole and Their Metal Complexes. Science Journal of Chemistry. Vol. 1, No. 5, 2013, pp. 56-66. doi: 10.11648/j.sjc.20130105.12 Abstract: Novel Mannich base derivatives of Benzimidazole were prepared through the condensation reaction of benzimidazole derivative with formaldehyde and primary and/ secondary amine. Zinc(II), copper(II), nickel(II) and cobalt(II) complexes of Mannich bases have also been synthesized. All the compounds were fully characterized by, elemental analyses, magnetic moment determination, molar conductivity measurement, thermogravimetric analysis, spectral and analytical data. Experimental results showed that metal complexes act as bi-dentate ligands towards divalent metal ions via azomethine-N and deprotonated-O while suggesting an octahedral geometry. All the compounds were screened for in-vitro antibacterial and antifungal activity against various bacterial and fungal strains. Almost all the compounds showed good potent activity against microorganisms. It was also seen that compounds with complexed form were more active as compared to un-complexed form. The prepared compounds were also screened for their cytotoxicity and results showed that only Ni(II) complexes exhibit some cytotoxicity while all other compounds were almost inactive. Keywords: Mannich Bases, Benzimidazole, Metal Complexes, Biological Activity, Cytotoxicity 1. Introduction The benzimidazoles contain a phenyl ring fused to an imidazole ring. Benzimidazole and their derivatives have diverse applications in coordination chemistry, photophysics, photochemistry and bioinorganic chemistry.[1-4] Over the past few decades, Mannich base reactions of benzimidazole have been the guiding tent for the synthetic chemists because of their widespread pharmaceutical importance i.e. antibacterial, anthelmintic[5], antifungal[6], anti-inflamatory[7], antiviral[8] and analgesic[9] properties. The compounds with azomethine group in its structure are known as Schiff bases, which are synthesized by the condensation reaction of primary amines and active carbonyl groups.[10] Schiff bases of benzimidazole have been reported with remarkable antibacterial[11], antimicrobial[12] and antiproliferative[13] activities. In addition to their biological importance, benzimidazoles form stable complexes with various transition metals.[14] Transition metal complexes of 2-substituted benzimidazole and benzimidazole-based mixed ligands have been reported with mono-, bi- and tri dentate coordination behavior.[15-19] The worthwhile biological activities of Mannich and Schiff bases have been guiding for the synthesis of novel Mannich and Schiff bases in a single molecule. The main objective of present communication is to provide a comprehensive account of N-Mannich type bases of benzimidazole, their chelating behavior and to highlight their potential in evolving better antimicrobial drugs. A total of 6 Mannich and Schiff bases and 24 metal(II) complexes have been prepared in this study and well characterized by their physical, spectral and analytical data. The synthesized compounds were further evaluated for their antimicrobial properties against various pathogens using MIC method.