Chemical and Biological Characterization of Newly Synthesized Drug Based Metal Complexes

Amina Mumtaz^1,2*, Tariq Mahmud², Weaver, G. W.³ & Elsegood, M. R. J.³

¹PCSIR Laboratories Complex, Ferozepur Road, Lahore-Pakistan
²Institute of Chemistry, University of the Punjab, Lahore 54590, Pakistan
³Department of Chemistry, Loughborough University, Loughborough, LE11 3TU, England

*Correspondence to: Dr. Amina Mumtaz, Department of Chemistry, PCSIR Laboratories complex, Ferozepur Road, Lahore, Pakistan.

Copyright © 2018 Dr. Amina Mumtaz, et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Introduction
The rise of safe human pathogens is a noteworthy issue in current antimicrobial treatment, urging endeavors to synthesize new drugs. Metal complexes were observed to be especially valuable in this issue, as contributing in drug designing. Schiff bases have assumed an extraordinary part in metal coordination science because of stability under different type of reaction i.e. reductive and oxidative conditions and to the way that they are fringe amongst soft and hard Lewis bases [1].

Schiff bases have been reported by Hugo Schiff. It is prepared by condensation of primary amines with carbonyl compounds. Schiff base sustain azomethine or imine (-C = N) group which coordinated with transition metal ions [2]. Schiff base ligands and their transition metal complexes have been studies extensively because of their wide use and applications in different fields.

Many drugs have improved pharmacological properties when forms Schiff base metal complexes. The Schiff base metal chelate have gained attention in fields like medicine and pharmaceutical because of wide spectrum of biological activities such as anti-inflammatory drugs, antimicrobial, antifungal, antispasmodic, tuberculosis, anti-cancer, anthelmintic, antioxidant and so forth [3-10].

Schiff bases include have a wide variety of applications in organic and inorganic chemistry. Aside from biological activities, Schiff bases are additionally utilized as catalysts, [11-13] dyes and pigments, [14,15] polymers [16,17] and corrosion inhibitors [18-20]. Schiff base assumed an impact part in the improvement of coordination science and were included as key point in the advancement of inorganic biochemistry and optical materials [21].

The metal complexes of Schiff base derived from different drugs are good antibacterial and antifungal agents. So present work has endeavored to broaden the extent of derivatization by giving more adaptability through Schiff base ligand. Here we report preparation, characterization and biological studies of new Schiff base transition metal complexes obtained from sulphadoxine and 2-hydoxybenzaldehyde.

Materials and Methods
Pure chemicals and solvent were used throughout the studies. Sulphadoxine and 2-hydroxybenzaldehyde were taken from BDH while other chemicals and solvent were purchased from Alfa Aesar.

Microanalysis was performed utilizing normal strategies. Metals were assessed by atomic absorption spectroscopy. Basic investigation was resolved on a CE-440 Elemental analyzer, FT-IR spectra were recorded with a Perkin Elmer Spectrum-100 spectrometer utilizing KBr plates. ¹H NMR, ¹³C NMR spectra were measured on a Jeol ECS 400 spectrometer. Mass spectra were measured with the assistance of Thermo Scientific Exactive TM Plus Orbitrap spectrometer. Thermogravimetric examination for the buildings were completed on a SDT-Q600 instrument. Magnetic moments were estimated using Evans balance with anhydrous calcium chloride. Electronic absorption spectra of all the complexes were recorded on a Shimadzu-1800 spectrophotometer. Jenway-4510 conductivity meter was used for conductance measurement of the complexes by using DMSO (10^-3 mol L^-1) as a solvent.

Preparation of Schiff Base Ligand
2.0 mmole of sulphadoxine was dissolved in 2ml (1N) sodium hydroxide. To this ethanolic solution of 2-hydroxybenzaldehyde (2.0mmole) was added and refluxed for one hour. After this ligand was collected by crystallization. The crystalline product was washed with alcohol, dried under vacuum and kept in a desiccator for further use.

Preparation of Schiff Base Metal Complexes
EPreparation of copper (II), cobalt (II), zinc (II), nickel (II), manganese (II), iron (II) complexes were done by using the same protocol as described in literature. The salts and ligand were dissolved in ethanol separately and combine with 2:1 proportion. The reaction mixture was then refluxed for 1h. After preparation, the colored precipitate of Schiff base ligand was filtered off, washed with water, ethyl alcohol and dried under reduced pressure at room temperature.

Biological Assay
In vitro antimicrobial and antifungal tests were estimated by agar well diffusion method [22]. The antimicrobial activities of synthesized compounds were investigated against Escherichia coli, Enterobacter aerogenes, Staphylococcus aureus, Bacillus pumilus, Klebsiella oxytoca and Clostridium butyrium. Mucor and Aspergillus niger were used for antifungal studies.

Results
The results obtained after characterization are reported as below:

Synthesis of N-4-(2-hydroxybenzylideneamino) - (5,6-dimethoxy-4-pyrimidine) benzene sulfonamide.
Yield 70% (yellow). m. p. 218-220^°C. IR (KBr, cm^-1) 3442 (OH), 1617 (HC=N azomethine), 1570 (C=Npyrimidine), 1151(O=S=O), 1082 (C-N).

Anal. Calcd. For C₁₉H₁₈N₄O₅S (414.45); Calcd: C,55.01; H, 4.34; N, 13.51; Found: C,55.09; H, 4.25; N, 13.43 %.

1H NMR (DMSO-D₆, δ ppm) 10.21 (NH), 8.93 (-CH=N),7.81-6.94 (phenyl) 3.57-3.70 (OCH3); ¹³C NMR (DMSO-D₆, δ ppm) 164.5 (-CH=N), 146.2 (C-S=O), 112.4-160.8 (phenyl), 58.3-58.8 (OCH3). MS (EI); m/z (%) = 415.4501 [M⁺].

Copper (ll) Complex of Ligand
Yield 79% (Green). m. p. (decomp.) 265-268°C. IR (KBr, cm^-1) 3250 (OH), 1614 (HC=N azomethine), 1581 (C=N- pyrimidine), 1153 (O=S=O), 430 (M-N), 383 (M-O).

UV (DMSO) λ_max (cm^-1) 16611, 24630; B.M (1.90μ_eff); molar conductance ( 147 μS cm^-1). Anal. Calcd. For C₃₈H₃₆N₈O₁₀S₂Cu (928.44); Calcd: C,49.11; H 3.87; N, 12.06; Co, 6.84 Found: C,49.22; H 3.89; N, 12.15; Cu, 6.92%.

Cobalt (ll) Complex of Ligand
Yield 75% (Pink). m. p. (decomp.) 279-282^°C. IR (KBr, cm^-1) 3460 (OH), 1615 (HC=N azomethine), 1582 (C=N- pyrimidine), 1197 (O=S=O), 481 (M-N), 345 (M-O).

UV (DMSO) λ_max (cm^-1) 17668, 25575; B.M (4.26μ_eff); molar conductance (110 μS cm^-1). Anal. Calcd. For C₃₈H₃₆N₈O₁₀S₂Co (923.83); Calcd: C,49.35; H 3.89; N, 12.12; Co, 6.37 Found: C,49.22; H 3.89; N, 12.15; Co, 6.92%.

Zinc (ll) Complex of Ligand
Yield 73% (Orange) M. p. (decomp.) 269-272^°C. IR (KBr, cm^-1) 3378 (OH), 1612 (HC=N azomethine), 1573 (C=N- pyrimidine), 1182 (O=S=O), 454 (M-N), 340 (M-O).

UV (DMSO) λ_max (cm^-1) 29325; Diamagnetic; molar conductance (119 μS cm^-1). Anal. Calcd. For C₃₈H₃₆N₈O₁₀S₂Zn (930.28); Calcd: C,49.01; H 3.86; N, 12.03; Zn, 7.02 Found: C, 50.49; H 3.37; N,12.11; Zn,7.19%.

Nickle (ll) Complex of Ligand
Yield 72% (Dirty Green) M. p. (decomp.) 262-266^°C. IR (KBr, cm^-1) 3310 (OH), 1618 (HC=N azomethine), 1581 (C=N- pyrimidine), 1113 (O=S=O), 456 (M-N), 378 (M-O).

UV (DMSO) λ_max (cm^-1) 16122, 25000; B.M (2.96μ_eff); molar conductance (89 μS cm^-1). Anal. Calcd. For C₃₈H₃₆N₈O₁₀S₂Ni (923.59); Calcd: C, 49.37; H 3.89; N,12.12; Ni, 6.35 Found: C,50.01; H 3.55; N,12.23; Ni, 6.77%.

Manganese (ll) Complex of Ligand
Yield 71% (Brown) M. p. (decomp.) 277-279^°C. IR (KBr, cm^-1) 3255 (OH), 1614 (HC=N azomethine), 1581 (C=N- pyrimidine), 1155 (O=S=O), 433 (M-N), 342 (M-O).

UV (DMSO) λ_max (cm^-1) 17889, 23696; B.M (5.36μ_eff); molar conductance (90 μS cm^-1). Anal. Calcd. For C₃₈H₃₆N₈O₁₀S₂Mn (919.83); Calcd: C,49.57; H 3.91; N, 12.17; Mn, 5.97 Found: C,49.66; H 3.97; N, 12.22; Mn, 5.94%.

Iron (ll) Complex of Ligand
Yield 75% (Reddish brown) M. p. (decomp.) 279-283⁰C. IR (KBr, cm^-1) 3236 (OH), 1624 (HC=N azomethine), 1581 (C=N- pyrimidine), 1151 (O=S=O), 475 (M-N), 362 (M-O).

UV (DMSO) λ_max (cm^-1) 28409, 31250; B.M (5.81μ_eff); molar conductance (102 μS cm^-1). Anal. Calcd. For C₃₈H₃₆N₈O₁₀S₂Fe (920.74); Calcd: C, 49.52; H 3.90; N, 12.16; Fe, 6.06 Found: C,51.03; H 3.98; N, 12.31; Fe,6.53%.

Discussion
The synthesis of ligand was accomplished by refluxing the sulphadoxine and 2-hydoxybenzaldehyde in a molar ratio 1:1 in ethanol as reported in literature. The metal complexes of ligand were prepared using metal chloride and ligand in a 2:1 molar ratio as shown in scheme1.

The structure elucidation of Schiff base and complexes was done with Elemental analyzer, FT-IR, ¹H NMR, ¹³C NMR Mass spectroscopy, Thermo-gravimetric analysis and micro-analytical data. All the metal complexes are amorphous solids and have decomposition point. They are insoluble in water, organic solvents, partially soluble in acetone and completely soluble in DMF and DMSO. Molar conductance value (75-144 μS cm^-1) point out the electrolytic nature of metal complexes. The structure of synthesized Schiff base ligand along with metal complexes were investigated by different techniques.

Spectroscopic Studies
The important infrared spectral bands of the synthesized Schiff base ligand were compared with the spectra reported in the literature on similar systems. FT-IR spectra of the ligand showed the absence of bands of carbonyl and amino and a new band appeared at ~ 1617 cm-assigned to the azomethine (HC=N) linkage. This suggested that amino and aldehyde moieties of the starting reagents have been converted into their corresponding Schiff base.

¹H NMR and ¹³C NMR Spectra were taken in d₆-DMSO. The peaks of all the proton and carbon atoms were fixed in their expected region. The NMR spectra of Schiff base ligand was confirmed the absence of aldehyde peak at δ 9-10 and presence of azomethine at δ 8.93. ¹³C NMR spectra also verify azomethine peak at δ 164.5.

FT-IR Spectra
The metal ligand bond was verified by comparing the FT-IR spectra of the Schiff base ligand with metal (II) complexes. The FT- IR spectra predicted all the absorption bands of the Schiff base ligand and some new bands at specific frequency confirmed the modes of absorption and the completion of the ligands with the metal ions through nitrogen and oxygen. The azomethine group of ligand was shifted to value 1614- 1624 cm^-1 in all the complexes thus suggested the coordination of metal to ligand bond through azomethine (HC=N). Absorption bands of the sulfonamides moiety in the synthesized ligand and in metal complexes have same frequency. Further definitive proof of the coordination of the Schiff base with the metal ions were confirmed by the appearance new bands at 430-481 and 340-383 cm^-1 designate to the metal nitrogen (MN) and metal-oxygen (M-O) extending vibrations, individually [23]. These bands were not present in the spectra of the free ligand, therefore affirming the presence of O and N in coordination.

Electronic Spectra and Magnetic Susceptibility
The studies of electronic absorption spectra of transition metal(II) complexes were recorded in DMSO. 10^-3 M solutions of each complex was prepared and spectra were recorded in the range 2000-10000 cm^-1 at room temperature.

The electronic absorption spectra of metal complexes showed bands at specific wavelength which supports octahedral geometry as shown in table 1. Also, the magnetic moment value for all the complexes suggests the octahedral geometry.

The spectrum of Zn(II) complex exhibited only one band which was assigned to a ligand→metal charge transfer. The zinc (II) complex of ligand was observed to be diamagnetic obviously and in this manner, its magnetic properties could not be calculated [24-25].

Thermal Studies
Thermogravimetric analyses (TGA) for the transition metal complexes were done from room temperature to 1000^°C. Calculated and found mass losses are shown in Table below.

Biological Activity
Antimicrobial and Anti-inflammatory Activities
Antimicrobial and antifungal activity of all the synthesized transition metal complexes and Schiff base ligand were tested against Escherichia coli, Enterobacter aerogenes, Staphylococcus aureus, Bacillus pumilus, Klebsiella oxytoca, Clostridium butyrium, Mucor and Aspergillus niger by using Ager well method. The results showed enhanced activity when coordinated with transition metals. It was reported previously that metal complexes suppressed the microorganism growth and involved in blocking the proteins. Presently, various bacterial strains (E. Coli , E. Aerogenes, S. Aureus, B. Pumilus, K. Oxytoa, and C. Butyrium) and fungal strains (A. Niger and Mucor) were used to investigate the inhibitory effects of newly synthesized schiff base metal complexes. All compounds were found to be significantly active against bacterial and fungal strains when compared with ligand and reference drug. No significant different was found between reference drug and ligand for their antimicrobial activities. Metal complexes easily penetrate into the lipid membrane and block the enzymes in the microorganism. Metal complexes convert the super coiled DNA to open chain and cleave the DNA in the presence H₂O₂ [26-27].

Conclusion
The results got after investigation demonstrate that after derivatization the antibacterial activities were enhanced against chosen bacterial strains. The metal complexes additionally demonstrate action against aspergillus niger and mucor though parent drug and ligand showed no antifungal activity. These observations, in accordance with different studies, prescribe that metal based drugs have potential as therapeutics.

Acknowledgements
The authors are thankful to Higher Education Commission (HEC), Government of Pakistan for financial support.

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