Short Communication - Der Pharma Chemica ( 2020) Volume 12, Issue 1
Synthesis, Characterization and antibacterial Activity of Copper(II) Mixed Ligand Complexes with Salen Type Ligands and Dithiocarbamates
Meftah Salah Gasibat, Eman Bashir Al-Melah and Hana Bashir Shawish*Hana Bashir Shawish, Department of Chemistry, Faculty of Science, Misurata University, Misurata, Libya, Email: shawishhana@yahoo.com
Received: 26-Jan-2020 Accepted Date: Feb 20, 2020 ; Published: 28-Feb-2020
Abstract
Mixed ligand complexes of Cu(II) with salen type ligands, namely N, Nʹ-bis(salicylidene)-1,2-ethylenediamine (salen) and N, Nʹ-bis(salicylidene)-1,2-pheneylenediamine (salophen) as primary ligands and pyrrolidine dithiocarbamate (pdtc) as a secondary ligand were prepared. The structural characterization of the synthesized complexes was carried out via analytical as well as various spectral studies. The obtained results reinforce that stoichiometry of the mononuclear mixed ligand complexes can be represented as NH4[Cu(II)-Schiff base(L)-pdtc(B)] and both H2L and (B) ligands can act as tetra and bidentates respectively. Additionally, both the schiff bases and the secondary pdtc ligands bind with copper(II) ion to build a stable six, five, six and four membered chelate rings with an octahedral geometry. The mass spectral data confirms the monomeric structure of the metal complexes while the study of the conductivity measurement indicated the 1:1 electrolyte nature of the complexes. The free Salen type ligands and their mixed copper(II) complexes have been tested for their antibacterial activity by using disc diffusion method and the results discussed.
Keywords
Salen, Mixed Copper(II) complexes, Dithiocarbamate Ligand, Spectrophotometry, Antibacterial
Introduction
A considerable attention has been given on Salen-type ligands owing to their simple synthesis, structural versatility, and wide range of applications in many fields including catalysis [1], luminescence [2], magnetism [3] and material science [4]. Salen Schiff base ligands and their metal complexes have been reported to show a variety of biological actions by influence of the azomethine linkage, which is responsible for various antibacterial, antifungal, herbicidal, and in the study of the interaction with DNA [5-8]. Salen schiff base ligands derived from diamines and 2-hydroxybenzaldehyde typically lose two protons and function as quadridentate chelates with O, N, N, O atoms. This provides sufficient coordination sphere, in accordance with the length of carbon-chain linkage that allow metal ions to find an easy approach to bind to the N2O2 ligand. Generally, these N2O2 tetradentate donors coordinate to d-block transition metals to afford stable mononuclear complexes [9]. In addition, there are a number of reports on homometallic as well as heterometallic di- and trinuclear complexes with d-block metals consisting of two salen molecules [10-12]. In these complexes, μ2-phenoxo bridging plays an important role in assembling metal ions and the two salen ligands [13].
Dithiocarbamate ligands have received great consideration, their small bite-angle and the soft nature of the dithiocarbamate moiety makes them capable of stabilizing wide range of metal ions in different oxidation states [14]. Dithiocarbamate ligands are mono anionic chelating ligands and can bind to metal ions in various coordination modes with the monodentate and anisobidentate modes. Dithiocarbamates complexes have been reported to gain wide applications in medicine, agriculture, industry, in analytical and organic chemistry [15-17].
The coordination chemistry of copper has attracted increasing interest among the transition metal complexes, because copper is biocompatible and exhibits many significant roles in biological systems [18]. Copper complexes of salen schiff base ligands have engrossed considerable interest because of their variable bonding properties, structural diversity, and pharmacological properties [19-21]. Several copper Salen complexes and their mixed complexes with anionic co-ligands have been synthesized and their structural diversity was investigated [22, 23]. Biswas and Ghosh have synthesized trinuclear copper(II) salen complexes and have found that the shape of the trinuclear species may vary from linear to triangular depending upon coordination mode of the anionic coligand, coordination ability of the solvent molecules and the nature of the central metal ion [24]. Also, Dong et. al. have reported two novel Cu(II) complexes with Salen type ligands possessing different structural features and investigated the different performance of the ligand [25]. Recently, Asatkar and coworkers synthesized mononuclear cuprous complexes with Salen ligands that have strong binding affinity towards ct-DNA [26].
Taking into consideration the above facts, mixed Cu(II) complexes of Schiff base (derived from condensation of ethylenediamine or o-phenylenediamine with salicylaldehyde) and dithiocarbamate were synthesized. The synthesized compounds were characterized using various spectral techniques and evaluated for their microbial studies against Staphylococcus aureus, Streptococcus, Klebsiella pneumonia, Pseudomonas and Escherichia coli.
Experimental Section
Materials and Instruments
Ethylenediamine, o-phenylenediamine, salicylaldehyde and ammonium pyrrolidine dithiocarbamate were commercial products (from Alfa and Merck) and were used without further purification. Solvents were of reagent grade and were purified by the usual methods. Copper(II) acetate monohydrate was procured from Scharlau Chemie and used as received. The ligands N, N′-bis(salicylidene)ethylenediamine (H2L1) and N, N′- bis(salicylidene)-o-phenylenediamine (H2L2) were prepared according to the published procedure [27] and their purities were checked by spectroscopic data.
Elemental analysis was carried out with a Perkin Elmer model 2400 equipment. Conductivity measurements of 10-3 M solutions in DMSO at room temperature were carried on a Jenway 470 conductivity meter. Infrared spectra were recorded on a PerkinElmer FT-IR Spectrometer (Frontier)-USA. Magnetic susceptibilities at room-temperature were done by using Sherwood Scientific magnetic balance, Cambridge science, England Model no.MKI, Serial no. MSBI/230/95/680. The UV-Vis spectra were recorded in DMSO solution on Agilent Technologies Cary 60 UV-Vis spectrophotometer in 200-800 nm range. The FAB mass spectra were recorded using a Micromass Autospec spectrometer. Synthesis of the Complexes, NH4[CuLn(pdtc)], n=1,2 (Complexes 1 and 2)
Cu(CH3COO)2. H2O (1mmol, 0.2g) solution in methanol (20 mL) was added to a solution of ammonium pyrrolidine dithiocarbamate (1mmol, 1.64g) in methanol (10 mL). The resulting mixture was refluxed for 1h. The corresponding Schiff base H2L1 (1 mmol, 0.268 g) or H2L2 (1 mmol, 0.316g) in 20 mL methanol was then added in the reaction mixture and refluxed for 4 h. The precipitates obtained were filtered, washed successively with water and ethanol and then dried in air.
Antibacterial Study
The ligands H2L1, H2L2 and their complexes were tested against the bacterial species Staphylococcus aureus, Streptococcus, Klebsiella pneumonia, Pseudomonas and Escherichia coli using the standardized Agar-Well diffusion method [28]. The antibiotic Ciprofloxacin was used as the standard reference. The antibacterial activities were done in DMSO solvent. The solutions of ligands and the two complexes 1 and 2 were added to the agar plates. Incubation of the plates was done at 37°C for 24 hours. Zones of inhibition were recorded in millimeters and the experiment was repeated three times.
Statistical Analysis
Experiments were performed in triplicate and the values obtained are presented as the mean ± standard error. The data were statistically performed by SPSS statistical software version 21 (SPSS Inc. Chicago IL, USA).
Conclusion
Two new mixed copper(II) complexes of Salen type ligands and dithiocarbamate were synthesized and characterized. The Salen coordinates to the Cu(II) ion as dibasic tetradentate ONNO chelating ligand whereas the dithiocarbamate bounded to Cu(II) ion as uninegative anisobidentate ligand. From the analytical and spectral data, it was observed that the prepared copper(II) chelates adopted an octahedral geometry. The antibacterial study shows that the mixed copper(II) complexes exhibit good antibacterial property than that of free Salen ligands.
Acknowledgments
The authors thank Misurata University for supporting this work.
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