The synthesis, characterization and preliminary antimicrobial studies of some novel Schiff base ligands; N,N^/ - Bis(2-hydroxybenzylidene)-1,4-phenylenediimine(M) and N,N^/ - Bis(4-dimethylaminobenzylidene)-1,4-phenylenediimine (N) were undertaken. It was prepared by the condensation reaction of 1,4-phenylenediamine with 4-dimethylaminobenzadehyde and 2-hydroxybenzaldehde .Their Co(II), Mn(VII), Mo(VII) metal complexes were synthesized by coupling them respectively with the individual formed ligands. These ligands and their complexes were characterized on the basis of their melting point, stoichiometry, electronic spectra, infrared spectra and antimicrobial their antimicrobial properties. Spectrophotometric analysis gave the stoichiometry to be 1:1 metals to ligand mole ratio for the Co(II) and Mn(VII) complexes of theN,N^/ - Bis(2-hydroxybenzylidene)-1,4-phenylenediimine(M) ligand and a 1:2 metal to ligand mole ratio for its Mo(VII) complex. Secondly its N,N^/ - Bis(4-dimethylaminobenzylidene)-1,4-phenylenediimine (N) ligand gave a 2:3 metal to ligand mole ratio for its Co(II) complex, a 1:4 ratio for its Mn(VII), and a 1:1 ratio for Mo(VII) complexes. Based on their spectral studies the ligandN,N^/Bis(2-hydroxybenzylidene)-1,4-phenylenediimine(M) was observed to be bidentate through the participation of the oxygen from their hydroxyl endand N,N^/ - Bis(4-dimethylaminobenzylidene)-1,4-phenylenediimine (N) was bidentatethrough the participation of their imine nitrogen end. The ligand and its complexes were tested against Candida albicans , Escherichia coli,Salmonellatyphi, Enterococcus feacalis and Staphylococcus aureus with dimethylformamide (DMF) as the control. These screening were performed at different concentrations by the agar-well diffusion method and the gram negative organism showed activitythat the metal complexes are more potent than the parent Schiff base ligand.

TABLE OF CONTENTS

i. Title page

ii. Certification

iii. Dedication

iv. Acknowledgement

v. Abstracts

vi. Table of contents

vii. List of tables

viii. List of figures

CHAPTER ONE; INTRODUCTION

1.1 Schiff base

1.2 Schiff base metal complexes

1.3 Application of Schiff bases

1.3.1 Biological importance of Schiff bases

1.3.2 Antibacterial activities

1.3.3 Antifungal activities

1.3.4 Enzymatic Activities

1.4 Stoichiometry

1.4.1 Uses of stoichiometry

1.4.2 Stoichiometry complexation reactions

1.5 Aim and objective of the research

CHAPTER TWO

Literature review

CHAPTER THREE; EXPERIMENTAL, MATERIALS & METHOD

3.1 Materials /Apparatus

3.2 Reagents

3.3 Methods

3.3.1 Preparation of a Schiff base ligand

3.3.1a Synthesis ofN,N^/Bis (2-hydroxylbenzylidene- 1,4-phenylenediimine and)- M

3.3.1b Synthesis of N,N^/Bis(4-dimethylbenzylidene-1,4-phenylenediimine) -N

3.3.2 Preparation of complexes

3.3.2a Synthesis ofN,N^/Bis (2-hydroxylbenzylidene-1,4-phenylenediimine)- Co(II)complexes

3.3.2b Synthesis ofN,N^/Bis (2-hydroxylbenzylidene- 1,4-phenylenediimine )- Mn(VII) complexes

3.3.2c Synthesis ofN,N^/Bis (2-hydroxylbenzylidene- 1,4-phenylenediimine )- Mo(VII) complexes

3.3.2.dSynthesis of N,N^/Bis (4-dimethylbenzylidene-1,4-phenylenediimine)-Co(II) complexes

3.3.2e Synthesis of N,N^/Bis (4-dimethylbenzylidene-1,4-phenylenediimine)-Mn(VII) complexes

3.3.2f Synthesis of N,N^/Bis (4-dimethylbenzadehyde-1,4-phenylenediamine)Mo(VII) complexes

3.4 Stoichiometry of the complexes

3.5 Characterization of the Schiff base ligands and their complexes

3.5.1 Melting/decomposition point

3.5.2 Electronic Spectra

3.5.3 Infrared spectroscopy

3.5.4 Antimicrobial Analysis

CHAPTER FOUR; RESULT AND DISCUSSION

4.1 Physical properties

4.2 Solubility assay of the ligands and their complexes

4.3 Stoichiometry of the complex

4.4 Reaction Scheme

4.4.1 The reaction scheme between 1,4-phenylenediamine and 2-hydroxylbenzadehyde (M)

4.4.2 The reaction scheme between 1,4-phenylenediamine and 4-Dimethylaminobenzadehyde (N)

4.5 Electronic Spectra

4.5.1 N,N^/Bis(2-hydroxylbenzylidene-1,4-phenylenediimine)-M and their CoM, MnM, Mo₂M complexes

4.5.2 N,N^/Bis(4-dimethylaminobenzylidene- 1,4-phenylenediimine)-N and their CoN, MnN, Mo₂N complexes

4.6Infrared Spectra

4.8 Proposed Structures

4.9 Antimicrobial properties

CHAPTER FIVE

Conclusions and Recommendations

REFERENCE

APPENDIX

CHAPTER ONE

INTRODUCTION

1.1 SCHIFF BASES

Schiff bases are condensation products of primary amines with carbonyl compounds and they were first reported by Schiff (Cimerman et. al., 2000). The common structural feature of these compounds is the azomethine group with a general formula RHC=N-R1, where R and R1 are alkyl, aryl, cyclo alkyl or heterocyclic groups which may be variously substituted. The common structural feature of these compounds is the azomethine group with a general formula RHC=N-R1, where R and R1 are alkyl, aryl, cyclo alkyl or heterocyclic groups which may be variously substituted. These compounds are also known as anils, imines or azomethines. Several studies (Singh et. al., 1975, Perry et. al., 1988, Elmali et. al., 2000, Patel et. al., 1999, Valcarcel et. al., 1994, Spichiger et. al., 1998,Lawrence et. al., 1976)showed that the presence of a lone pair of electrons in an sp2 hybridized orbital of nitrogen atom of the azomethine group is of considerable chemical and biological importance.

R¹,R² and/or R³= alkyl or arynl

Fig.1. General structure of Schiff bases (Silva da. et al.,2011)

A Schiff base is a nitrogen analog of an aldehyde or ketone in which the C=O group is replaced by C=N-R group. It is usually formed by condensation of an aldehyde or ketone with a primary amine.The formation of a schiff base from an aldehydes or ketone is a reversible reaction and generally takes place under acid or base catalysis, or upon heating.

Fig 2: formation of Schiff base upon heating

Schiff bases are generally bidentate (1), tridentate (2), tetradentate (3) or polydentate (4) ligands capable of forming very stable complexes with transition metals. They can only act as coordinating ligands if they bear a functional group, usually the hydroxyl, sufficiently near the site of condensation in such a way that a five or six membered ring can be formed when reacting with a metal ion.

Fig.3.Some classes of Schiff base ligands

Schiff bases derived from aromatic amines and aromatic aldehydes have a wide variety of applications in many fields, eg., biological, inorganic and analytical chemistry (Cimerman et. al.,2000 and Elmali et. al.,2000). Applications of many new analytical devices require the presence of organic reagents as essential compounds of the measuring system.

1.2 SCHIFF BASE METAL COMPLEXES

Transition metal complexes with Schiff bases have expanded enormously and embraced wide and diversified subjects comprising vast areas of organometallic compounds and various aspects of bio-coordination chemistry (Anacona et. al., 1999). The design and synthesis of symmetrical Schiff bases derived from the 1:2 step wise condensation of carbonyl compounds, with alkyl or aryl diamines and a wide range of aldehyde or ketone functionalities, as well as their metal(II) complexes have been of interest due to their preparative accessibility, structural variability and tunable electronic properties allowing to carry out systematic reactivity studies based ancillary ligand modifications. In recent years much effort has been put in synthesis and characterization of mono- and bi-nuclear transition metal complexes (Trujillo et. al., 2008).Schiff bases are used in optical and electrochemical sensors, as well as in various chromatographic methods to enable detection of enhanced selectivity and sensitivity (Valcared et. al., 1994, spichiger et. al., 1998,Lawerence et. al., 1998). Among the organic reagents actually used, Schiff bases possess excellent characteristics, structural similarities with natural biological substances, relatively simple preparation procedures and the synthetic flexibility that enables design of suitable structural properties (Patai 1970).

1.3 APPLICATIONS OF SCHIFF BASES

Schiff bases are widely applicable in analytical determination, using reactions of condensation of primary amines and carbonyl compounds in which the azomethine bond is formed (determination of compounds with an amino or carbonyl group) using complex forming reactions (determination of amines, carbonyl compounds and metal ions) or utilizing the variation in their spectroscopic characteristics following changes in pH and solvent (Metzler et, al., 1980). Schiff bases play important roles in coordination chemistry as they easily form stable complexes with most transition metal ions (Clarke et. al., 1998). In organic synthesis, Schiff base reactions are useful in making carbon-nitrogen bonds.

1.3.1 Biological Importance of Schiff Bases

Many biologically important Schiff bases have been reported in the literature possessing antimicrobial, antibacterial, antifungal, anti-inflammatory, anticonvulsant, antitumour and anti HIV activities (Pandeya et. al., 1999, Singh et. al., 1988, Kelly et. al., 1995). Another important role of Schiff base structure is in transamination (Schmid 1996). Transamination reactions are catalysed by a class of enzymes called transaminases. Transaminases are found in mitochondria and cytosal of eukaryotic cells. Schiff base formation is also involved in the chemistry of vision, where the reaction occurs between the aldehyde function of 11-cis-retinal and amino group of the protein (opsin) (Carry 1992).

1.3.2 Anti-bacterialActivities

Methicillin resistance staphylococcus aureus causes many problems as it has become resistance to almost currently available antibiotics. Two Antibiotics, vancomycin and Teicoplanin does not show resistance to s.aureus. But recently studies and data from many countries show that VISA(Vancomycin-intermediate s.aureus) and VRSA (Vancomycin-resistance s.aureus) increasing in many countries, as susceptibility toward Vancomycin has been decrease. The Schiff base derived from 2-furancarboxaldehyde and 2-aminobenzoic acid and its metal complexes with Cu (II), Ni (II), Co (II), and Fe (III) has biological activities against bacteria staphylococcuspyogenes, E.coli and pseudomonasaeruginosa (Duca et. al.,1979 ,Zota et. al.,1985).Taking streptomycin as a standard, using Mueller- Hinton agar as a medium with 2% glucose. The diameter of inhibition was visualized after 24 hous at 37oc and found to be effective against them.

1.3.3 Antifungal Activities

Studies have shown that some of the Schiff Base are very effective in prevention of fungal infection. As fungal infection is not only limited to superficial tissues but in some cases it is become life threatening (Sundriyalet, al., 2006, Nucci et. al., 2005, Martin et. al., 2009). Production of most of the cruciferous crops like cauliflower, cabbage, mustard, radish etc is effective by Fungi like Alterneriabrassicae and Alterneriabrassicicola (Przybyiski et. al., 2009). Schiff base N-(salicylidene)-2-hydroxyaniline inhibited the growth of both fungi by 67-68% at the concentration of 500 ppm (Cleiton et. al., 2011).

1.3.4 Enzymatic Activities

Schiff base linkage with pyridoxal 5’ phosphate (PLP) a derivative of pyridoxine commonly known as vitamin B₆abolished the enzyme activities of Proteins. PLP binds to some number of specific enzymes and play a critical role in helping here these enzymes tocatalyze their reaction. Most enzymes that interact with PLP catalyzereactions involved in the metabolism of amino acids. In many PLP dependent enzymatic reactions, PLP forms a Schiff base link with Lysine residue on the enzyme. Another Schiff Base complex of 2-pyridine carboxyaldehyde and its derivative show high super oxide dismutase activities(Sivasankaran et. al., 2000). Ternary complex of Cu (II) containing NSO donar Schiff base showed DNA cleverage activities.

1.4 STOICHIOMETRY

Stoichiometry is the calculation of reactants and products in chemical reactions. Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equals the total mass of the products, leading to the insight that the relations among quantities of reactants and products typically form a ratio of positive integers. This means that if the amounts of the separate reactants are known, then the amount of the product can be calculated. Conversely, if one reactant has a known quantity and the quantity of the products can be empirically determined, then the amount of the other reactants can also be calculated.

This is illustrated in the image here, where the balanced equation is:

CH₄ +2O₂ → CO₂ + 2H₂O.

Here, one molecule of methane reacts with two molecules of oxygen gas to yield one molecule of carbon dioxide and two molecules of water. This particular chemical equation is +n example of complete combustion. Stoichiometry measures these quantitative relationships, and is used to determine the amount of products and reactants that are produced or needed in a given reaction. Describing the quantitative relationships among substances as they participate in chemical reactions is known as reaction stoichiometry. In the example above, reaction stoichiometry measures the relationship between the methane and oxygen as they react to form carbon dioxide and water.

1.4.1 Uses of Stoichiometry

Stoichiometry is also used to find the right amount of one reactant to "completely" react with the other reactant in a chemical reaction that is, the stoichiometric amounts that would result in no leftover reactants when the reaction takes place. A stoichiometric amount (Carmen 2016) or stoichiometric ratio of a reagent is the optimum amount or ratio where, assuming that the reaction proceeds to completion:

All of the reagent is consumed
There is no deficiency of the reagent
There is no excess of the reagent.

Stoichiometry rests upon the very basic laws that help to understand it better, i.e., law of conservation of mass, the law of definite proportions (i.e., the law of constant composition), the law of multiple proportions and the law of reciprocal proportions. In general, chemical reactions combine in definite ratios of chemicals. Since chemical reactions can neither create nor destroy matter, nor transmute one element into another, the amount of each element must be the same throughout the overall reaction. For example, the number of atoms of a given element X on the reactant side must equal the number of atoms of that element on the product side, whether or not all of those atoms are actually involved in a reaction.

Chemical reactions, as macroscopic unit operations, consist of simply a very large number of elementary reactions, where a single molecule reacts with another molecule. As the reacting molecules (or moieties) consist of a definite set of atoms in an integer ratio, the ratio between reactants in a complete reaction is also in integer ratio. A reaction may consume more than one molecule, and the stoichiometric number counts this number, defined as positive for products (added) and negative for reactants. (Carmen J.2016)

Different elements have a different atomic mass, and as collections of single atoms, molecules have a definite molar mass, measured with the unit mole (6.02 × 1023 individual molecules, Avogadro's constant). By definition, carbon-12 has a molar mass of 12 g/mol. Thus, to calculate the stoichiometry by mass, the number of molecules required for each reactant is expressed in moles and multiplied by the molar mass of each to give the mass of each reactant per mole of reaction. The mass ratios can be calculated by dividing each by the total in the whole reaction.Elements in their natural state are mixtures of isotopes of differing mass, thus atomic masses and thus molar masses are not exactly integers. For instance, instead of an exact 14:3 proportion, 17.04 kg of ammonia consists of 14.01 kg of nitrogen and 3 × 1.01 kg of hydrogen, because natural nitrogen includes a small amount of nitrogen-15, and natural hydrogen includes hydrogen-2 (deuterium). A stoichiometric reactant is a reactant that is consumed in a reaction, as opposed to a catalytic reactant, which is not consumed in the overall reaction because it reacts in one step and is regenerated in another step.

1.4.2 Stoichiometry as it relates to complexation reactions

Complexationreactions of the form

:xM + yL ↔_ MxLy

are based on the reaction of a metal cation (M) and a ligand (L). These reactions are widely used in analytical chemistry. Absorption spectroscopy is a powerful tool for exploring these complexation reactions. In this experiment, two general approaches to studying the composition of complexes are used to demonstrate the necessity of carefully evaluating theproperties of a particular chemical system in order to select the best method for determining the composition (metal to ligand ratio) of a complex by absorption measurements.

Method of Continuous Variation (Job’s Method)

In this method, metal cation and ligand solutions with identical concentrations are mixedin different amounts such that the total volume of the mixture solutions and the total moles of reactants in each mixture is constant. This procedure causes the mole ratio of reactants to be varied across the set of mixture solutions. The absorbance of each solution is then measuredand plotted vs. the volume fraction of one of the reactants (M or L). For example, the volume fraction of the metal is

VM/(VM + VL)

Mole-Ratio Method (Yoe-Jones Method)

In this method, a series of solutions is prepared in which the concentration of one reactant is held constant while that of the other is varied. The absorbance of each solution ismeasured and plotted against the mole ratio of the reactants. Assuming the complex absorbs more than the reactants, this plot will produce an increasing absorbance up to the combining ratio. At this point, further addition of reactant will produce less increase in absorbance. Thus a break in the slope of the curve occurs at the mole ratio corresponding to the combining ratio of the complex.

1.5 AIM AND OBJECTIVES OF THE RESEARCH

The relationship between metal ions and biological activity of certain systems is obvious and a subject of great interest. It has been demonstrated that biologically inactive compounds become active and less biologically active compounds become more active upon coordination with the metal ions (Okeke, 2018). The apparent role played by metal ions in the induction or enhancement of biological activity of the organic compounds is therefore definite, but how, is still not well understood.

In order to get an insight into this role, the behaviour of Schiff bases has gained a great deal of attraction. The imine linkage (– N = CH-) is a significant feature that makes Schiff base ligands interesting for biological activities as well as coordination with the metal ions. The interaction between these metal ions and such biologically active ligands should serve as a route in designing new metal-based drugs for bacteria, fungi, microbes, HIV, etc strains that have become resistant to the use of conventional drugs.

This study therefore is aimed at;

Synthesizing two new Schiff base ligands by capping the amine group in 1,4-phenylenediamine with 4-dimethylaminobenzadehyde and 2-hydroxylbenzadehyde.
Preparation of their metal complexes by refluxing in absolute ethanol using Co(II), Mo(VI), and Mn(VI) metal salts.
Characterizing the formed ligands and their different metal complexes on the basis of their;

i) Melting point

ii) Electronic Spectra

iii) Infrared spectra

iv)Microbial analysis