SYNTHESIS, CHARACTERIZATION AND ANTIMICROBIAL ACTIVITY OF SCHIFF BASE DERIVED FROM 4-BROMOANILINE AND ACETOPHENONE AND IT’S COBALT (II) COMPLEX.

 

For decades, the chemistry of metal complexes has fascinated and inspired Chemists across the globe. There is an increasing Academic, biochemical and commercial interest on the metal complexes of inorganic chelating Ligands (Archana 2013; Bagihalli Gwaram et al., 2012). This has brought the emergence of related fields like, organometallic Chemistry, homogeneous catalysis and heterogeneous catalysis. Among the chelating Ligands, Schiff base ligands have attracted the attention of many chemists due to their ease of synthesis and complexation. From 1842 to 1915, Schiff bases, named after Hugo Schiff as the compounds having a formula RHC=NR’ where R is an aryl group and R’ is either an alkyl or aryl group (Layer, 1963). Schiff base ligands contained azomethine group (-RC=N) which are formed from the condensation of a primary amine with an active carbonyl compound in an organic solvent media.

Compounds containing imines bases have found extensive application in organic synthesis. In the last decade Schiff base ligands have received more attention mainly because of their wide applications in the field of catalysis, antimicrobial and antifungal activities (Lamani, 2009).

Schiff base play an important role in inorganic chemistry as they can easily form stable complexes with most transition metal ions (Hamil, 2009). The development of the field of chemistry has increased the interest in Schiff base complexes, since it has been recognized that many of these complexes may serve as models for biological important species (Wahab and Sarrag.2004).

 In biological processes, Inorganic compounds play critical roles and it has been established that many organic compounds used in medicines are activated or bio¬¬-transformed by metal ion metabolism (Mishra., 2013). Schiff bases are classified as organic ligand derived from the condensation reactions of primary or secondary amines and corresponding aldehyde or ketones (Kumar,. 2009). Schiff base are considered a very important class of organic ligands possessing diverse applications. Copious transition metal complexes with polydentate Schiff bases containing Nitrogen, Oxygen or Sulphur donor atoms contribute immensely in biological systems (Malik, 2011: Alias, 2014). These complexes exhibit applications in clinical, analytical and industrial processes (Mounika,.2010). And are used as model molecules for biological oxygen carrier systems (Caballa, 2007).

Schiff bases are compounds containing C=N group. They are often synthesized from amine and aldehydes of ketone. They have gained importance due to their applications in many pharmacological activities like antibacterial antifungal and antiviral activities etc. Schiff bases are one of the important compounds with wide range of biological activities and industrial applications (Zemede et al., 2015). Complexes of metal (II) ion containing Schiff bases possess remarkable properties as catalyst in various biological systems (Zoubi, 2013; Abu-dief and Mohammed, 2015; Maity, 2019) anti-bacterial and antifungal activities (Jameel et al., 2014), antiviral activities (Kajal et al., 2013) anti-inflammatory (Jesmin et al., 2014). They also possess wide application in analytical chemistry, agrochemical and pharmaceutical fields (Bitu et al., 2019). The advances in inorganic chemistry provides better opportunities to use the metal complexes as therapeutic agents. They contributed a lot in the development of metal-based drugs with promising pharmacological application and may offer unique therapeutic opportunities, for instance, the clinical application of chemotherapeutic agents for cancer treatment, such as cisplatin (Rafique et al., 2010).

Schiff bases with aryl substituent are more stable and readily synthesized, compared to those containing alkyl substituents that are relatively unstable. The antimicrobial drugs occupy a unique niche in the history of medicine, considering the increased incidences of severe opportunistic bacterial infections in immunological deficient patients together with the development of resistance among pathogenic gram- positive and gram-negative bacteria (Song et al., 2013).

Schiff bases have also been seen to exhibit a broad range of biological activities which includes antibacterial, antifungal, anti-proliferative, anti-inflammatory, antiviral, antipyretic activities etc. But this work focuses on its antibacterial activities. 

Schiff bases have been pointed to as promising antibacterial agents. For example, N- (salicylidene)-2-hydroxyaniline is effective against Mycobacterium tuberculosis H37Rv. The synthesis and antimicrobial activity of a series of Schiff bases derived from the condensation of 5-chloro-salicylaldehyde and primary amines has recently been reported. The 5-chloro-salicylaldehyde-Shiff base derivatives were most active against at least one of the evaluated bacterial species.

Schiff bases with a 2,4-dichloro-5-fluorophenyl moiety have been demonstrated to inhibit the growth of fungi of clinical interest, such as mentagrophytes. Piperonyl-derived Schiff bases were active against some fungi at micro molar concentrations. (Cleiton et al., 2011), Some Schiff base of Copper (II) complexes with phenanthroline and bipyridyl shows better antifungal activity to control the fungal diseases in humans and plants.

Transition metal or element is a chemical element in the d-block of the periodic table. Since they are metals, they are lustrous and have good thermal and electrical conductivity. They form compounds in any of two or more different oxidation states and bind to a variety of ligands to form coordination complexes that are often colored. They form many useful alloys and are often employed as catalysts in elemental form or in compounds such as coordination complexes and oxides. Most are strongly paramagnetic because of their unpaired d-electrons, as are many of their compounds. All of the elements that are ferromagnetic near room temperature are transition metals (iron, cobalt and nickel) or inner transition metals (gadolinium). 

In coordination chemistry, a ligand (from a Latin word ligare) is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand’s electron pairs often through Lewis bases (Burdge., et al., 2020). The nature of metal-ligand bonding can range from covalent to ionic. Furthermore, the metal-ligand bond order can range from one to three. Ligands are viewed as Lewis bases, although rare cases are known to involve Lewis acidic “ligands” (Cotton et al., 1999).

Metals and metalloids are bound to ligands in almost all circumstances, although gaseous “naked” metal ions can be generated in a high vacuum. Ligands in a complex dictate the reactivity of the central atom, including ligand substitution rates, the reactivity of ligands themselves and redox. Ligand selection requires critical considerations in many practical areas, including bioinorganic and medicinal chemistry, homogenous catalysis and environmental chemistry. Ligands are hence classified in many ways including; charge, size, the identity of the coordinating atom(s), and the number of electrons donated to the central metal ion or atom (its denticity). The size of a ligand is indicated by its cone angle, that is, it is a measure of the steric bulk of a ligand in a transition metal coordination complex. In other words, it is defined as the solid angle formed with the metal at the vertex of the cone and the outermost edge of the van der Waals spheres of the ligand atoms at the perimeter of the base of the cone (Miessler et al., 2013).

In general, ligands are viewed as electron pair donors and the metals as electron pair acceptors, i.e., respectively, Lewis bases and Lewis acids. Also, according to molecular orbital theory, the HOMO (Highest Occupied Molecular Orbital) of the ligand should have an energy that overlaps with the LUMO (Lowest Unoccupied Molecular Orbital) of the metal preferential.

The aim of this research work is to synthesized and characterize a Schiff base derived from 4-bromoaniline and acetophenone and its Co (II) complex as a potential antimicrobial agent.

The increasing incidence of bacterial resistance especially in developing countries of West Africa such as Nigeria has become alarming. Hence, the need to develop efficient and effective antibacterial agents to face the challenges of resistant bacteria. This project work is also an attempt to explore the great possibilities of developing new, efficient and effective antibacterial agents.