Synthesis, Characterization, and Biological Evaluation of Some 3d-Metal Complexes of Schiff Base Derived from Xipamide Drug

The present paper deals with the synthesis and characterization of metal complexes of Schiff base derived from xipamide, a diuretic drug. The bidentate ligand is derived from the inserted condensation of 5-aminosulfonyl-4-chloro-N-2,6-dimethyl phenyl-2-hydroxybenzamide (Xipamide) with salicylaldehyde in a 1:1 molar ratio. Using this bidentate ligand, complexes of Hg(II), Zn(II), and VO(IV) with general formula ML 2 have been synthesized. The synthesized complexes were characterized by several techniques using molar conductance, elemental analysis, magnetic susceptibility, FT-IR spectroscopy, electronic spectra, mass spectra, and particle size analysis. The elemental analysis data suggest the stoichiometry to be 1:2 [M: L]. All the complexes are nonelectrolytic Aspergillus niger and Aspergillus flavus . The ligand and its Hg(II) and VO(IV) complexes were screened for their diuretic activity too.


Introduction
Coordination complexes are gaining importance in recent years especially in the designing of long acting drugs in metabolism.The metal complexes from bidentate ligands have often been studied recently because of their technical applications [1,2] and applications in enhancement of drug action [3,4].Transition metals are essential for normal functioning of living organism and are, therefore, of great interest as potential drugs [5].The coordination chemistry of nitrogen donor ligands is an active area of research.A great deal of attention in this area has been focused on the complexes formed by 3d metals with bidentate ligands using both sulfur and nitrogen [6,7].The Schiff bases are an important class of ligands in coordination chemistry.The study of structural and binding features of various Schiff base complexes can play an important role in better understanding of the complex biological process.Schiff bases derived from salicylaldehyde are well known for their interesting ligational properties and exclusive applications in different fields [8][9][10].It is well known from the literature that Schiff bases derived from thiazide drugs have a strong ability to form metal complexes [11].The interaction of these donor ligands and metal ions gives complexes of different geometries, and literature survey reveals that these complexes are potentially more biologically active.Thus, in recent years Schiff bases and their metal complexes have attained much attraction because of their extensive biological activities [12,13].Keeping the above fact in our mind and in continuation of our earlier work on transition metal complexes with Schiff bases [14,15], the ligand xipamide-salicylaldimine Schiff base (L) has been synthesized.In the present paper, the synthesis and characterization of the ligand and its complexes with Hg(II), Zn(II), and VO(IV) are being reported.

Experimental
All the chemicals used were of AR/GR grade and purchased from E-Merck (USA).Chemicals were used without any The infrared spectra of the ligand and complexes were recorded in KBr pellets using Perkin-Elmer FT-IR spectrophotometer in the range 4000-400 cm −1 at School of Studies in Chemistry and Biochemistry, Vikram University, Ujjain, India.Particle size analysis was carried out at SICART, Gujarat using, laser diffraction particle size analyzer.The instrument used was CILAS 1064L/D model in the range of 0.04-500 m.The melting points of the ligand and complexes were recorded in open capillaries on a capillary melting point apparatus.
The antifungal activities of both the ligands and their complexes were tested in vitro for growth inhibitory against Aspergillus niger and Aspergillus flavus by agar growth food poison technique [17] at different concentrations compared with Grisofulvin as appositive control.
The diuretic activity of Hg(II) and VO(IV) complexes were tested on white albino mice at Jawaharlal Nehru Cancer Hospital and Research Centre, Bhopal, India.Mice were fed with standard rodent pellet diet and acidified double-distilled water.The selected test compound, ligand, and standard drug xipamide (XM) at a dose of 0.24 mg suspended in 0.5% gum acacia were administrated to animals of respective group.One group of animal was taken as control.For the measurement of weight of urine, Whatman no. 1 filter paper was used.The urine weight was recorded after two hours.

Synthesis of the Ligand (Xipamide Salicylaldimine
). Equimolar (0.01 M) solutions of pure drug (0.22 gm) and salicylaldehyde (0.14 mL) were separately dissolved in methanolwater mixture (1 : 1) and refluxed for four hours and kept for a day.Peach colour crystals of xipamide Schiff base were formed in the reaction mixture and were filtered and washed thoroughly with 50% methanol-water mixture, dried over vacuum, and weighed.Melting point of Schiff base was recorded.The structure of the synthesized ligand is shown in Figure 1.

Synthesis of Complexes.
For the synthesis of complexes, 0.006 M ligand solution was prepared in 50% acetone-water solvent and refluxed for four hours with 0.003 M solution of metal salts separately.The refluxed solutions were kept for some days.Solid crystalline compounds appeared in the solution, which were filtered, washed with 50% acetone-water mixture, dried, and weighed.Melting points of the complexes were recorded.

Results and Discussion
The analytical data of the complexes and their molar conductance values are given in Table 1.All these complexes are analyzed for 1 : 2 stoichiometry of the type ML 2 .On the basis of these characterizations it has been found that all the complexes are nonhygroscopic, stable at room temperature, insoluble in water, but fairly soluble in DMSO.The molar conductance values of these complexes are too low to account for their electrolytic behavior [18,19].

Spectral Studies of Ligand and Its Complexes
3.1.1.IR Spectra.The characteristic vibrations and assignments of ligand and its complexes are described in Table 2.The IR spectra of the complexes indicate that the ligand behaves as bidentate and coordinates with metals via azomethine nitrogen and phenolic -OH groups.The shift of  C=N to lower wave number by 30-40 cm −1 in the complexes indicates that these groups are involved in complexation [20,21].The ligand shows strong band at 3386 cm −1 due to phenolic -OH group [22].This band is absent in all the metal complexes indicating the involvement of this group  in complex formation [23].Moreover, the shift of the  C-O phenolic bands from 1282 cm −1 in ligand to 1282-1312 cm −1 in the spectra of metal complexes supports the coordination of the phenolic oxygen atom to the metal ion [24].The bands for  M-O modes appeared in the range of 580 cm −1 -615 cm −1 in all the complexes [25].The presence of sharp band in the region 503-514 cm −1 in the spectra of all the complexes assigned to  M-N mode [26] further support the involvement of azomethine nitrogen atom in coordination.In addition to these bands VO(IV) complex exhibits the characteristic stretching frequency [27,28] for V=O at 952 cm −1 .

Magnetic Susceptibility and Electronic Spectra.
The magnetic moment obtained for the oxovanadium (IV) complex at room temperature is 1.77 B.M, and its electronic spectra displayed bands at 13986, 17094, and 21740 cm −1 assigned for 2 B 2 → 2 E, 2 B 2 → 2 B 1 , and 2 B 2 → 2 A 1 transitions, respectively.These values suggest the square pyramidal geometry for VO(IV) complex [29].The Hg(II) and Zn(II) complexes are found to be diamagnetic as expected for d 10 systems and may have tetrahedral geometry [30].+ .The base peak at / 117 may be due to the zinc metal linked to the donor atoms of the ligand.Such type of fragmentation pattern has been reported by many workers [31,32].

Particle Size Analysis.
To find out the maximum efficiency of the drugs and their metal complexes, studies on the particle size analysis are being considered very helpful [33].The bioavailability of low-solubility drug is often intrinsically related to the drug particle size.Smaller particle size of the complexes is responsible for the enhanced solubility of the drug [34].The results of the particle size analysis carried  out for the pure drug, ligand, and its Hg(II) and VO(IV) complexes have been recorded in Table 3.These results reveal that, after complexation, the size of the ligand and complexes got reduced to a considerable extent as compared to their parent drug xipamide (XM).It is well known that smaller size leads to better absorption, so it is concluded from our result that complexation enhanced the absorption and potency of the drug [35].

Antimicrobial Activity.
For antifungal activity the ligand and its metal complexes were screened against Aspergillus niger,and the findings are given in Table 4.These complexes showed higher activity with 12-17 mm inhibition than the ligand which showed only 11.48 mm inhibition at the same concentration as that of the test drug.However, ligand and their complexes showed lower activity as compared to standard drug griseofulvin with 19.38 mm inhibition at the same concentration.Antifungal activity studies of ligand and its complexes against Aspergillus flavus showed that all the complexes with 11.47-21.22mm inhibition showed higher activity than the ligand which showed only 10.38 mm inhibition only.VO(IV) complex showed higher activity than standard drug which showed 18.22 mm inhibition at the same concentration as that of the test drug.It is known that chelation tends to make the ligand act as more powerful and potent antimicrobial agent, thus inhibiting more of the microbes than the parent ligand [36].and VO(IV) complexes was tested on white albino mice and recorded in Table 5.The selected test compound, ligand, and standard drug xipamide at a dose of 0.24 mg suspended in 0.5% gum acacia were administrated to animals of the respective group.The result revealed that metal complexes have more diuretic activity as compared to the respective ligand and pure drug.Thus it is revealed that complexation can increase the pharmaceutical activity of the parent drug [37].Statistical analyses were performed by using one-way analysis of variance ANOVA followed by GraphPad InStat 3. Statistical significance was accepted at the 5% level ( < 0.05).The VO(IV) complex is found to be more significant with  < 0.001 whereas Hg(II) complex is also found to be significant with  < 0.05.

Conclusion
The outcome of the above results confirms the stoichiometry of the complexes to be 1 : 2 [M : L] as indicated by elemental analysis and conductometric measurements.IR spectra suggest that the ligand behaves as bidentate and coordinates to the central metal ion through azomethine nitrogen and phenolic -OH group.This has been further confirmed on the basis of NMR spectral studies.Mass spectra further support the above stoichiometry on the basis of respective molecular masses and fragmentation patterns.Thus, on the basis of above physicochemical and spectral studies, the assigned structures for the metal complexes are shown in Figures 3(a) and 3(b).The complexes are found to have higher biological activities as compared to the respective ligand and the parent drug that, somehow, justifies the purpose of the research work.The present work will be further extended to the synthesis of metal complexes using other biologically active metals and evaluation of their biological activities.

3. 1 . 3 .
Mass Spectra.The mass spectrum of [Zn(C 22 H 18 ClN 2 O 5 S) 2 ] as shown in Figure 2 shows a molecular ion peak at / 980 (I) due to [Zn(L) 2 ] ⋅ + which is in accordance with the proposed formula of the complex.The other peaks at / values 151 and 271 may be due to the fragments (C 9 H 11 NO) ⋅ + and [Zn(ClC 6 H 4 COH)SO 2 NH] ⋅

Table 1 :
Analytical data and molar conductance values for ligand and metal complexes.

Table 2 :
IR spectral data (cm −1 ) of ligand and its complexes.

Table 3 :
Particle size measurement of pure drug, ligand and its metal complexes.

Table 4 :
Antimicrobial screening data of the ligand L and its metal complexes.

Table 5 :
Diuretic screening data of the pure drug, ligand, and its metal complexes.