VANADIUM ( V ) COMPLEXES CONTAINING 1 , 2 , 4-TRIAZOLE MOIETY AND THEIR ANTIMICROBIAL ACTIVITY

Mohamed Abdelbaset* 1,2 and Sami A. Zabin 1 . 1. Chemistry Department, Faculty of Science, AlBaha University, Al-Baha, KSA. 2. Chemistry Department, Faculty of Science, Al Azhar University, Assiut Branch, Assiut 71524, Egypt. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

It is known that ligands containing heterocyclic ring play an important role in the development of coordination chemistry [1][2]. In the literature, it is shown that ligands with five-membered ring systems such astriazoles represent an interesting class of compounds due to the presence of three nitrogen atomsthat can coordinate to the metal ions [3][4][5].
The ligands with 1,2,4-triazolemoeity show a great coordination diversity, especially when the triazole nucleus issubstituted with additional donor groups. When the triazole ring has other coordination groups such as NH 2 , OH, NH-NH 2 or SH the triazole unit can coordinate in many different ways [29][30][31][32][33]. According to our literature survey, no vanadium(V) complexes containing 1,2,4-triazole ring with hydrazine, amino and thiol groups are found.

ISSN: 2320-5407
Int. J. Adv. Res. 4 (12), 1861-1871 1862 Based on the above mentioned importance and properties, we thought that it is interesting to synthesize a new complexes containing vanadium (v) as central metal atom with two types of ligands containing 1,2,4-triazole ring. The ligands used in this work are: 4-amino-5-mercapto-3-phenyl-1,2,4-triazole (L 1 ) and 4-Amino-3-hydrazino-5mercapto-1,2,4-triazole (L 2 ). This investigation was devoted for the synthesis, characterization and examining the biological activity of the synthesized compounds. The structural features of the metal complexes have been elucidated by various spectral and analytical techniques.

Physical Measurements and Analytical Methods:-
Melting points were measured on Electrothermal (Cat NO. TA9100) melting point apparatus.Carbon, hydrogen, nitrogen and sulphur were analyzed micro analytically using CHNS analyzer Leco Model VTF-900 CHN-S-O 932 version 1.3x (ThermoFisher Scientific-USA) instrument. Electronic spectra of the solutions of the complexes in 10 -5 MDMSO were recorded onEvolution 300 UV-visibledouble beam Spectrophotometer. FT-IR spectra (400-4000 cm -1 ) were recorded as KBr discs using Nicolet IS50 FT-IR spectrophotometer. Thermo gravimetric (TGA) studies was recorded on Shimadzu thermo-analyzer 50 in a dynamic nitrogen atmosphere (100 ml/min) at a heating rate 10°C/min in an atmosphere of nitrogen in the temperature range 25-1000 °C. Circular NMR spectra were obtained in CD 3 OD solutions with a Varian Mercury-400BB (400 MHz) spectrometer using TMS ( 1 H) as standard.
Antimicrobial Activity:-To assess the microbial susceptibility of the vanadium (V) complexes and their parent ligands, the synthesized compounds were examined against six types of pathogenic bacteria (Staphylococcus aureus, Enterococcus faecalis, and Group B streptococcus (GBS)) as Gram-positive bacteria, and (Proteus Mirabilis, Escherichia coli, Klebsiellapneumoniae) as Gram-negative bacteria.In addition, the compounds were tested against one kind of fungi (Candida Albicans).
Well Diffusion Assay method as the susceptibility testing method was used perform the antibacterial and antifungal activities test [1,35]. The antimicrobial activities were tested for their in vitro growth inhibitory activity against the bacterial and fungal strains cultured on the surface of a sterile Muller-Hinton agar as growth medium. The stock solutions of the compounds were prepared by dissolving 0.02gm of each tested compound in 5mL DMSO solvent. A small hole was made in the middle of each dish using sterile metal cork borer (5mm). Then, Solutions of the ligands L 1 and L 2 and their corresponding vanadium complexes in DMSO were poured into the holes made in the cultured agar medium and incubated at 37°C for a period of 24 hours. The microbial susceptibilitieswere monitored by measuring the zones of inhibition (in cm) around each hole after the incubation period. All samples were repeated in triplicate, and statistical analysis were performed using SPSS 16.0 for windows. Thep-values < 0.05 were considered statistically significant for the statistical purpose. In addition, we have performed the antifungal susceptibility against Candida albicansof the organic ligands L 1 and L 2 and their corresponding vanadium complexes using the solid form of the compounds by spreading the solid powder (0.02gm) on the surface of the Muller-Hinton agar medium.

Results and Discussion:-
The structures of the synthesized compounds have been characterized by UV-visible, FT-IR, 1 H-NMR spectrum, thermal analyses and elemental analysis. All synthesized complexes were colored solids and stable at room temperature to air and moisture. All complexes were insoluble in water and alcohols but soluble in DMF and DMSO. The vanadium complexes have melting points above 300 °C. The elemental analysis data is presented in table 1.From the elemental analysis data it is evident that the complexes were of two types:1:2 (M:L 1 ) ratio in case of the ligand L 1 and 1:1 (M:L 2 ) in case of ligand L 2 ). The analytical data results obtained for the complexes were in good agreement with the proposed structuresas shown in schemes 1 and 2.The analytical and spectroscopic results showed that all vanadium (V) complexes are monomeric in nature.
1864  figure 2.The IR spectrum of the ligands (L 1 and L 2 ) show bands in the regions 3370-3120cm -1 which can be assigned to ν(NH 2 ), and in the regions 2810-2930cm -1 due to thiol group ν(OH) disappeared in metal complexeswhich indicates the deprotonation and coordination through S atom to metal ion [36][37].
In case of the complexes these bands were slightly shifted to lower positions indicating that the N of the amino groupare linked with the vanadium metal ion [38]. The complexes display a sharp band in the region 986-945cm -1 due to the ν(V=O) mode (39). In the IR spectrum of the vanadium complexes of the L 2 Ligand two absorption bands were observed at the range of 920 and 930 cm -1 . These bands can be assigned to symmetrical (O=V=O) and asymmetrical (O=V=O) streching vibrations respectively, which are expected for dioxovanadium(V) compounds [40 -44]. The IR spectrum of vanadium (V) complexes of both the ligands in the solid state shows signals above 900 cm -1 . These values supports the proposed structure of square pyramidal geometry, since it is known that ν(V=O) modes are always above 900 cm -1 for vanadium complexes having such coordination geometry [45] New bands were observed in the regions of 615 -580 cm -1 520-440 cm -1 in the spectra of the complexes which can be assigned to νM-N and νM-S respectively (29,33,46]. A broad band was observed at 3380-3200 cm -1 in all the spectra of complexes, assigned to a νO-H and related to the presence of water molecules in the crystal lattice of the complexes [46,[47][48][49][50].

UV-Vis spectra:-
The electronic spectral of the ligands and their vanadium complexes were recorded in 10 -5 M DMSO solutions, and some representative spectra are shown in figure 3. The complexes show different characteristic λ max , compared with the ligand and this was another indication for occurrence of coordination [51 -54]. The UV spectrum of the vanadium(V) complexes with the ligands(L 1 and L 2 ) ( fig. 3.) exhibit one absorption band at λ max within the region 277 -280 nm 350 nm to 405 nm with a small shoulder at 370 nm, and these can be assigned to LMCT transitions [55]. There was no evidence of any d-d transitions. These results are consistent with the presence of vanadium (V) system in the synthesized complexes and are close to reported values for other monoperoxovanadium(V) complexes [55,56]. .3H 2 Owas investigated by means of TGA measurement under N 2 atmosphere up to 650⁰C at heating rate 10 ⁰C/min.. The TGA curve (Fig. 4) gave information about the thermal stability and the product formed on heating. The figure shows initially a weight loss starting from 50-100 ⁰C that corresponds to weight loss of 10.41%. This can be attributed to the liberation of three outer sphere water molecules (theoretical weight loss 10.35%). On heating from 100-350 ⁰C shows a gradual weight loss of 33.33% Which corresponds to the removal of NH 3 gasand two C 6 H 6 molecules (theoretical weight loss Abs. Wavelength, nm 1866 33.10) [57,58]. The weight loss continues beyond this temperature up to 650⁰C (observed 37.6 % and calculated 37.10 %) attributed to the loss of two moles of triazole ring, that requires more energy, viz, higher temperatures leaving Vanadium oxide as residue.Finally attains a constant mass and composition of the complex as 1:2which is also supported by C, H, N, S analyses [38,59]. coordination through the sulphur atom with the central metal ion [30,32].
Also, in the 1 H NMR Spectra ( fig. 5) the signalsof NH 2 protons appear at δ5.76 ppm [34].These signals shifted to high field in the spectra of theVanadium complexes (V)indicating bonding through the nitrogen atomof the amine group to the central vanadium ion.

Scheme 2:-Antimicrobial activity:-
The organic ligands and their prepared corresponding vanadium(V) complexes were screened in vitro for the biological susceptibility against three strain Gram-positive bacteria Enterococcus faecalis, Staphylococcus aureus, and Group B streptococcus (GBS) and three Gram-negative bacteria Klebsiella pneumonia, Escherichia coli and Proteus Mirabilis in addition, to one kind of pathogenic fungus named Candida Albicans. The microbial activity method used in this study was well Diffusion method using DMSO as solvent and as a control [1]. The bacterial and fungal susceptibility was monitored by measuring the zones of inhibition (in cm) around each hole at which the visible growth was completely inhibited. The results indicated that organic ligands (L 1 and L 2 ) did not show any activity against nearly all types of bacteria.Some moderate activity was noticed against the fungusC.Albicans(inhibition zone of 0.9-1.12 cm). The tested vanadium complexes showed antifungal activity when used in the powder form against the pathogenic fungus C. Albicans with highest sensitivity was noticed for the compound N(Pr) 4  and did not show antibacterial activity. The increased antifungal activity of the vanadium complexes may be due to chelation that increases the permeability of the chemicals and may be the presence of vanadium ion [1]. Our results in this work were similar to other reported work of other researchers [37].