ABSTRACT
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.
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.
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.
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-bacterial Activities
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;
1
Synthesizing two new Schiff
base ligands by capping the amine group in 1,4-phenylenediamine with 4-dimethylaminobenzadehyde
and 2-hydroxylbenzadehyde.
2
Preparation of their
metal complexes by refluxing in absolute ethanol using Co(II), Mo(VI), and
Mn(VI) metal salts.
3
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
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