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Abstract I.1. Schiff-bases: Compound with the general structure R2C=NR’ (R’ ≠ H) can be considered a subclass of imines, being either secondary ketimines or secondary aldimines depending on their structure [1]. A number of special naming systems exist for these compounds [2]. For instance a Schiff-base derived from an aniline, where R is a phenyl or a substituted phenyl, can be called an anil [3], while biscompounds are often referred to as salen-type compounds. The term of Schiff- base is normally applied to these compounds when they are being used as ligands to form coordination complexes with metal ions. Such complexes do occur naturally, for instance in Corrin, but the majority of Schiff-base are artificial and are used to form many important catalysts, such as Jacobsen’s catalyst. [2,4] Different Schiff-base and their metal complexes had shown notable bioactivity as chelating therapeutics, as drugs and as inhibitors of enzymes [4]. Also, some Schiff-base acted as important analytical reagents for the gravimetric and colorimetric determination of transition metals [5]. The presence of Cu(II) ion in these complexes had received wide interest in the fields of the magneto-structural relationship and the characterization of active sites in multicopper proteins [6]. Cu(II) complexes had a wide range of biological activity and some of these complexes had been known to be antitumor, antiviral, and anti-inflammatory agents. In addition to Cu(II) complexes especially with Schiff-base ligands were models of physical and chemical behavior of biological Cu systems, considerable attention had been focused on these compounds [7,8] . The Cu(II) complex of 1, Introduction - 3 - 10-phenathroline was the first synthetic transition metal complex effectively exhibiting nucleolytic activity [8]. The development of Schiff-base species based on transition metal compounds and polydentate ligands had been the subject of extensive research due to their potential applications in materials science [9, 10], environmental chemistry and medicine. Schiff-base compounds played a vital role in coordination chemistry are due to their ability to react with a range of metal ions forming stable complexes which had applications in different fields. One interesting application in the field of coordination chemistry had been to investigate the use of Schiffbase ligands to develop phenoxo-bridged binuclear complexes with homometallic and heterometallic centres. This included design molecules containing paramagnetic metal centers were able to self-assemblethrough metal-ligand interactions rendering supramolecular assemblies with interesting structural and magnetic properties [11, 12]. Schiff-base metal complexes also had applications in biomedical [13, 14], biomimetic and catalytic systems [15, 16]. The role of Schiff-base and their metal complexes, in particular cobalt, in the biological systems make them one interested branch in the coordination and organometallic chemistry. Significant publications dealt with the development of coordination chemistry were related to the preparation and characterization of Schiff-base and their metal complexes. These included the investigation of synthetic methods and coordination modes of Schiff-base species upon complexation [17]. It was well known that, Schiff-base species can bind a metal in different coordination modes [18]. The mode of bonding was investigated through physico-chemical and spectroscopic methods. X–ray crystal structures confirmed the preparation of six-coordinate Schiff-base complexes. It was well documented that, Schiff-base compounds and their complexes with transition metals had many applications in medicine, biology, industry, and catalysis [19]. Introduction - 4 - The chemistry of Schiff-base complexes had been broadly investigated [20]. Particularly in Cu(II) and Ni(II) complexes with Schiff-base ligands [21]. The coordination chemistry of the Schiff-base ligands had been widely studied with the 3d metal ions [23, 24]. The Schiff-base imines of ligands capable of withstand higher oxidation states of the central metal ion through strong ligand to metal [LM] σ - donation. The strength of the hydrogen bond in Schiff-base depends on the size and chemical environment around the metal ion. [22]. Schiff-base complexes can be utilized as catalysts for many organic reactions, optical materials, luminescence materials, DNA binding and cleavage reagents [25, 26]. Compounds containing Schiff-base were used as analytical reagent for the separation and determination of some transition metal ions [27]. Schiff-base and their metal complexes had shown notable bioactivity as chelating therapeutics, as drugs, as inhibitors of enzymes and as intermediates in the biosynthesis of nitrogen oxides [28]. The Cu(II) complexes with Schiff-base ligands were models of physical and chemical behavior of biological Cu system, considerably focused on these compounds [28, 29]. The Cu(II) complex of 2, 10 phenopthroline was first synthetic metal complex showed DNA cleavage activity [30]. The ligands containing nitrogen, oxygen and sulphur acted as effective chelating agents for transition and non-transition metal ions [31]. I.1.1. Synthesis of Schiff-bases: Throughout the years Schiff-base have played an important role as chelating ligands for a large variety of metal ions. More emphasis has been put in the Schiff-base complexes of metals as it plays an important role in understanding complex biochemical reactions. Schiff-base complex formation as intermediate in biochemical reactions had already been reported long time ago [32, 33]. Large Introduction - 5 - number of Schiff-base complexes of metal ions are prepared in-situ, but the isolation of the free base before its reaction with a metal ion has many advantages. The major disadvantage in-situ reaction is that the reactants used to prepare Schiff-base are often good coordination agents themselves. Hence, a small excess of the one or the other of these reactants may give rise to other complexes of the metal ion and thus contaminate the product. Also characterization of the free ligand gave the chance of comparative study to be made of its physico-chemical properties with those of the corresponding metal complexes. The synthesis of some multidentate Schiff-base, which are potential ligands for transition metal ions have been carried out and the study their physiological properties and biochemical processes involving these metal ions and Schiff-bases. The preparation and characterization of Schiff-base including diimines had been carried out [30]. The formation was generally driven to the completion separation of the product or removal of water, or both. Many Schiff-bases can be hydrolyzed back to their aldehydes or ketones and amines by aqueous acid or base. The mechanism of Schiff-base formation is another variation on the theme of nucleophilic addition to the carbonyl group. In this case, the nucleophile is the amine. In the first part of the mechanism, the amine reacted with the aldehyde or ketone to give an unstable addition compound called carbinolamine.The carbinolamine losed water by either acid or base catalyzed pathways. Since the carbinolamine is an alcohol, it undergoes acid catalyzed dehydration. Scheme 1 shows this mechanism[29,30] |