Biological studies of Schiff base, 2-(1-hydroxycyclohexyl) phenyl methylene hydrazine carbothioamide and its Cu(II) and Zn(II) metal complexes

Condensation of 1-hydroxycyclohexyl phenyl ketone with hydrazine carbothioamide produced a new Schiff base, 2-(1-hydroxycyclohexyl) phenyl methylene hydrazine carbothioamide. The Cu(II) and Zn(II) metal complexes of the Schiff base were prepared. The different spectroscopic methods such as FT-IR, UV-Visible, 1 H NMR, and 13 C NMR spectroscopy were used to elucidate the structural characteristics of the synthesized compounds. Further, the biological applications of the prepared Schiff bases and its metal complexes were studied for the antibacterial activity. The antimicrobial investigation was carried out against different Gram positive and Gram negative bacteria like Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa . According to the findings, the prepared Cu(II) and Zn(II) metal complexes are more biologically active than Schiff base ligand, and among all tested bacterial species, Staphylococcus aureus growth was most inhibited by prepared compounds. antibacterial the characterization carried out different instrumental methods such as FT-IR, UV-Visible, 1 H NMR, and 13 C NMR spectroscopy. Some common Gram positive and negative bacteria ( Bacillus subtilis, Staphylococcus aureus, Escherichia Pseudomonas aeruginosa ) selected for screening antibacterial activity of the prepared Schiff base and its metal complexes. From the antibacterial experiments, the Cu(II) and Zn(II) complexes having the good zone of inhibition values whereas bare Schiff base was less active against all the bacteria. Among the prepared compounds, Schiff base Cu(II) complex was more active towards the all tested species.


INTRODUCTION
The complexes of Cu(II) and Zn(II) ion containing Schiff bases possess remarkable properties as catalysts in various biological systems, antimicrobial activities, antiviral activities, antifungal activities, anti-inflammatory activities, antiradical activities, insecticidal activities, antitumor and cytotoxic activities [1][2][3][4][5][6] . They are also useful in the disciplines of analytical chemistry, agrochemistry, pharmaceuticals, polymers, and dyes [7] . The importance of this metal complexes as essential bioactive chemicals in vitro and in vivo has sparked a surge of interest in these compounds as possible treatment agents for a variety of ailments [8] .
In coordination chemistry, Schiff bases are most frequently utilised as chelating ligands [9] . Schiff bases with donor atoms such as N, O, S, etc. exhibit structural similarities to neutral biological systems and are used in biological systems owing to the existence of an imine group [10][11][12] . Thiosemicarbazide and its derivatives as ligands with possible sulphur and nitrogen atoms are interesting and have gotten a lot of attention, not only for their structural chemistry but also for their usefulness in the medical and pharmaceutical fields.
Antibacterial [13] , antitumor [14] , antifungal [15] , antiproliferative [16] , antidiabetic [17] , herbicidal [18] , anticancer [19] , anti-inflammatory [20] actions are among the biological activities shown by these compounds. Because they are used as starting materials in the synthesis of commercial goods, Schiff bases are an important family of chemicals. Schiff bases are also considered as favoured ligands because of their capacity to form complexes with various transition metals and serve as catalysts in a variety of processes [21][22][23] . The chelating ability of the thiosemicarbazide moiety is good, and this feature can be improved in thiosemicarbazone by inserting a suitable aldehyde or ketone with an additional donor atom to make the ligand polydentate. Anticancer and antibacterial properties have been documented for many Schiff base transition metal complexes [24,25] .
Some medications have been observed to have more action when supplied as metal complexes rather than as free molecules. As a result, Schiff base transition metal complexes may provide an undiscovered source of medicines [26] . Complexes of transition and non-transition metals with Schiff base ligands have recently emerged as promising materials for electronic applications, owing to their excellent photo and electroluminescent properties, as well as their ease of synthesis, which allows for structural modification for material optimization [27] . These are intensively investigated because to their flexibility, selectivity and sensitivity towards the central metal atom, structural and biological similarities, and the inclusion of an imine group (-C=N-) that confers biological activity [28][29][30] .
Owing to its antimicrobial properties of the Schiff bases

MATERIALS AND METHODS Materials
The starting chemicals such as 1-hydroxycyclohexyl phenyl ketone and hydrazine carbothioamide was acquired from Sigma, India. Solvents like methanol, ethanol and also Cu(II) and Zn(II) metal salts were purchased from Merck, India. Schiff base was dried in hot air oven.

Synthesis of Cu (II) and Zn (II) metal complexes
The metal salts and ligand were taken in 1:2 molar ratios in

UV-Visible Studies
The UV-Visible or electronic spectra (Model: Carey UV-Vis Spectrometer) was used to elucidate different electronic transitions in the prepared compounds. The absorption bands in the range 265 nm and 289 nm can be assigned to the more energy band, π-π* and low energy band, nπ* of the Schiff base.