Heterocyclic compounds play a significant role in many biological systems, especially N-donor ligand systems being a component of several vitamins and drugs such as nicotinamide. Nicotinamide is known as a component of the vitamin B complex as well as a component of the coenzyme, nicotinamide adenine dinucleotide (NAD) [
1]. The interaction of nucleic acids and their constituents with metal ions has been a matter of extensive studies in the recent years, because of their chemical and biological interest, covering structural, thermodynamic and kinetic works. In this broad context, certain recent studies have focused on metal complexes that can specifically recognize nucleobases [
2,
3,
4].
1.1. Adenine Metal Complexes and Its Binding Sites
The complexation of metal ions with adenine has been well studied and its binding sites has also been clarified [
5,
6]. Various coordination sites have been observed for adenine in copper complexes as indicated by X-ray studies. Among the four nitrogen’s N(1), N(3), N(7) and N(9) of adenine, the N(9) is the most basic and hence bears a proton rendering it is the most preferred metal binding site. The understanding of the structure and function of RNA and DNA systems depends partly on the binding sites of metal ions to nucleobases [
7,
8].
Adenine (Ad) is a nucleo-base (a purine derivative) with a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate (ATP) and the cofactors nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD), and protein synthesis, as a chemical component of DNA and RNA.
Adenine (Ad) is one of four chemical bases in DNA as in
Figure 1, with the other three being cytosine (C), guanine (G), and thymine (T). Within the DNA molecule, adenine bases located on one strand form chemical bonds with thymine bases on the opposite strand [
9].
1.2. Adenine Metabolism
A form of adenine called adenosine tri phosphate (ATP) serves as an energy storage molecule and is used to power many chemical reactions within the cell. Adenosine tri phosphate is used in cellular metabolism as one of the basic methods of transferring chemical energy between reactions. In DNA, adenine bonds only to thymine. It does so with two strong hydrogen bonds, so the bond is difficult to break and the code is difficult to damage. Adenine, has the chemical structure as shown in (
Figure 2a). Which is known as organic compound belong to the purine family, characterized by its nucleic acid, in this case called nucleotides, where the phosphate esters of adenosine (
Figure 2b) and deoxy adenosine (
Figure 2c) are clear in the structure, The importance of Adenine to RNA is similar to that of DNA. Adenosine tri phosphate is the nitrogenous base adenine bonded to a five carbon sugar. Adenosine tri phosphate is used in cellular metabolism as one of the basic methods of transferring chemical energy between, chemical reactions [
10].
Adenine is one of the two purine nucleo bases used in forming nucleotides of the nucleic acids DNA and RNA. The derivatives of purine are called adenine(A) and guanine(G). The other three bases—thymine(T), cytosine(C), and uracil(U)—are derivatives of pyrimidine, These four "code letters" allow cells to store their blueprint about how that life form is built. All cells of all living organisms, no matter how simple or complex, share this design [
11].
Spectroscopic study of the Cu(II) complexes with adenosine and adenine nucleotides, as adenosine mono phosphate (AMP), adenosine diphosphate (ADP), adenosine tri phosphate (ATP) and with inorganic polyphosphate solutions has been studied as a function of pH in the range 3 to 12, resulted in Cu(II)-adenosine phosphate complexes exist with a variety of forms in equilibrium, according to the state of ionization of the intrinsic adenine, phosphate and ribose groups. Mixed-ligand palladium(II) complexes with amino acids, cytosine, and adenine pH titration have been synthesized and characterized as 1:1:1 mixed-ligand complexes showing, palladium(II) (C5H5N5) (C5H8NO4)Cl complex. The coordination mode of amino acids, cytosine, and adenine to the palladium(II) ion is determined [
12,
13].
In the human body, adenine is synthesized in the liver. Biological systems tend to conserve energy, The vitamin folic acid is essential for adenine synthesis, Adenine forms adenosine, a nucleoside, when attached to ribose, and deoxy adenosine it forms adenosine triphosphate (ATP), a nucleotide, when three phosphate groups are added to adenosine Vitamin B4. Adenine is one of the two purine nucleo-bases (the other being guanine) used in forming nucleotides of the nucleic acids. In DNA, adenine binds to thymine via two hydrogen bonds to assist in stabilizing the nucleic acid structures. Adenine is one of the most interesting biological ligands which used for preparing and synthesizing different types of complexes [
12].
Here in, we report the synthesis, characterizations and thermal stabilities of Adenine complexes with some of the first series transition metals in a stoichiometric ratio of 1:2 (Mn+:L), where Mn+ = Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, and Cd2+ ions. The Complexes were characterized by the physicochemical techniques as, IR, UV–Visible, and molar conductance techniques. The stoichiometric ratios of the synthesized complexes were confirmed by using molar ratio method.