Aminul Huq Mirza

Biological activity of palladium(II) and platinum(II) complexes of the acetone Schiff bases of S-methyl- and S-benzyldithiocarbazate and the X-ray crystal structure of the [Pd(asme)2] (asme=anionic form of the acetone Schiff base of S-methyldithiocarbazate) complex.

Palladium(II) and platinum(II) complexes of general empirical formula, [M(NS)(2)] (NS=uninegatively charged acetone Schiff bases of S-methyl- and S-benzyldithiocarbazate; M=Pt(II) and Pd(II)) have been prepared and characterized by a variety of physicochemical techniques. Based on conductance, IR and electronic spectral evidence, a square-planar structure is assigned to these complexes. The crystal and molecular structure of the [Pd(asme)(2)] complex (asme=anionic form of the acetone Schiff base of S-methyldithiocarbazate) has been determined by X-ray diffraction. The complex has a distorted cis-square planar structure with the ligands coordinated to the palladium(II) ions as uninegatively charged bidentate NS chelating agents via the azomethine nitrogen and the mercaptide sulfur atoms. The distortion from a regular square-planar geometry is attributed to the restricted bite angles of the ligands. Antimicrobial tests indicate that the Schiff bases exhibit strong activities against the pathogenic bacteria, Bacillus subtilis (mutant defective DNA repair), methicillin-resistant Staphylococcus aureus, B. subtilis (wild type) and Pseudomonas aeruginosa and the fungi, Candida albicans (CA), Candida lypotica (2075), Saccharomyces cerevisiae (20341) and Aspergillus ochraceous (398)-the activities exhibited by these compounds being greater than that of the standard antibacterial and antifungal drugs, streptomycin and nystatin, respectively. The palladium(II) and platinum(II) complexes are inactive against most of these organisms but, the microbe, Pseudomonas aeruginosa shows strong sensitivity to the platinum(II) complexes. Screening of the compounds for their cytotoxicities against T-lymphoblastic leukemia cancer cells has shown that the acetone Schiff base of S-methyldithiocarbazate (Hasme) exhibits a very weak activity, whereas the S-benzyl derivative (Hasbz) is inactive. However, the palladium(II) complexes exhibit strong cytotoxicities against this cancer; their activities being more than that of the standard anticancer drug, tamoxifen. The [Pt(asme)(2)] complex exhibits a very weak cytotoxicity, whereas [Pt(asbz)(2)] is inactive against leukemic cells.

Synthesis, characterization, antifungal properties and X-ray crystal structures of five- and six-coordinate copper(II) complexes of the 6-methyl-2-formylpyridine4N-dimethylthiosemicarbazone ☆

Abstract Copper(II) complexes of formulas, [Cu(NNS)(NO3)(H2O)]·H2O and [Cu(NNS)2] (NNS=anionic form of the 6-methyl-2-formylpyridine4N-dimethylthiosemicarbazone) have been synthesized and characterized by a variety of physico-chemical techniques. Magnetic and spectroscopic data support a five-coordinate structure for the [Cu(NNS)(NO3)(H2O)]·H2O complex and a distorted octahedral structure for the [Cu(NNS)2] complex. The crystal structures of both complexes have also been determined by X-ray diffraction. The mono-ligated nitrato-complex has a five-coordinate geometry, with the thiosemicarbazone ligand coordinated to the copper(II) ion as a uninegatively charged NNS tridentate chelating agent via the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom. The fourth and fifth coordination positions around the copper(II) ion are occupied by the nitrato and aqua ligands, respectively. The bis-ligand copper(II) complex, [Cu(NNS)2] has a distorted octahedral structure with two uninegatively charged tridentate NNS thiosemicarbazone ligands coordinated to the copper(II) ion via the pyridine nitrogen atoms, the azomethine nitrogen atoms and the mercaptide sulfur atoms in a meridional arrangement. The ligand is fungitoxic against the phytopathogenic fungi, A. alternata, F.equiseti and M. phaseolina but the complexes are less active than the free ligand.

Synthesis and characterization of mono- and bis-ligand zinc(II) and cadmium(II) complexes of the di-2-pyridylketone Schiff base of S-benzyl dithiocarbazate (Hdpksbz) and the X-ray crystal structures of the [Zn(dpksbz)2] and[Cd(dpksbz)NCS]2 complexes

New mono- and bis-chelated zinc(II) and cadmium(II) complexes of formula, [M(dpksbz)NCS] (dpksbz = anionic form of the di-2-pyridylketone Schiff base of S-benzyldithiocarbazate) and [M(dpksbz)(2)] (M = Zn-II, Cd-II) have been prepared and characterized. The structure of the bis-ligand complex, [Zn(dpksbZ)(2)] has been determined by X-ray diffraction. The complex has a distorted octahedral geometry in which the ligands are coordinated to the zinc(II) ion as uninegatively charged tridentate chelates via the thiolate sulfur atoms, the azomethine nitrogen atoms and the pyridine nitrogen atoms. The distortion from a regular octahedral geometry is attributed to the restricted bite angles of the Schiff base ligands. X-ray structural analysis shows that the [Cd(dpksbz)NCS](2) complex is a centrosymmetric dimer in which each of the cadmium(II) ions adopts a five-coordinate, approximately square-pyramidal configuration with the Schiff base acting as a tetradentate chelating agent coordinating a cadmium(II) ion via one of the pyridine nitrogen atoms, the azomethine nitrogen atom and the thiolate sulfur atom; the second pyridine nitrogen atom is coordinated to the other cadmium(II) ion of the dimer. The fifth coordination position around each cadmium(II) is occupied by an N-bonded thiocyanate ligand

Synthesis and characterization of copper(II) complexes of the methylpyruvate Schiff base of S-methyldithiocarbazate (Hmpsme) and the X-crystal structures of Hmpsme and (Cu(mpsme)Cl)

Abstract New copper(II) complexes of general formula, [Cu(mpsme)X] (mpsme=anionic form of the methylpyruvate Schiff base of S-methyldithiocarbazate; X=Cl−, Br−) have been prepared and characterized by a variety of physico-chemical techniques. Based on magnetic and spectral evidence, a square-planar structure is assigned to these complexes. Reaction of the Schiff base with copper(II) nitrate does not yield a nitrato–copper(II) complex of the ligand. Instead, hydrolysis of the Schiff base occurs with the concomitant formation of the copper(II) complex of the pyruvic acid Schiff base of S-methyldithiocarbazate. Based on magnetic and spectral evidence, an oxygen-bridged square-planar structure is assigned to this complex. The crystal and molecular structures of the Schiff base, Hmpsme and its chlorocopper(II) complex, [Cu(mpsme)Cl] have been determined by X-ray diffraction. The [Cu(mpsme)Cl] complex has a distorted square-planar structure with the ligand coordinated to the copper(II) ion as a uninegatively charged tridentate chelating agent via the carbonylic oxygen atom, the azomethine nitrogen atom and the thiolato sulfur atom. The fourth coordination position around the copper(II) ion is occupied by the chloride ligand. The distortion from regular square-planar geometry is attributed to the restricted bite size of the ligand.

The preparation and characterization of mono- and bis-chelated cadmium(II) complexes of the di-2-pyridylketone Schiff base of S-methyldithiocarbazate (Hdpksme) and the X-ray crystal structure of the [Cd(dpksme)2] · 0.5 MeOH complex

New cadmium(II) complexes of empirical formulae, [Cd(dpksme)X] (dpksme = anionic form of the Schiff base; X = NCS−, Cl−, I−) and [Cd(dpksme)2] · 0.5MeOH, respectively have been prepared and characterized. The mono-ligated cadmium(II) complexes, [Cd(dpksme)X] are four-coordinate and tetrahedral but the bis-ligand complex, [Cd(dpksme)2] · 0.5MeOH is six-coordinate and octahedral. The crystal and molecular structure of [Cd(dpksme)2] · 0.5MeOH has been determined by X-ray diffraction. The complex has a distorted mer-octahedral structure in which the ligands are coordinated as uninegatively charged tridentate chelating agents via the pyridine nitrogen atoms, the azomethine nitrogen atoms and the thiolate sulfur atoms. The distortion from regular octahedral geometry is ascribed to the restricted bite angles of the ligands. The Schiff base and its cadmium(II) complexes exhibit mild antibacterial activities against Shigella dysenteriae, Bacillus cereus, Staphylococcus aureus and Escherichia coli. They are also mildly fungitoxic against the phytopathogenic fungi, Alternaria alternata and Macrophomina phaseolina.

Mono- and bis-chelated nickel(II) complexes of the di-2-pyridylketone Schiff base of S-methyldithiocarbazate and the X-ray crystal structure of the bis[S-methyl-β-N-(di-2-pyridyl)-methylenedithiocarbazato]nickel(II) complex

Abstract The di-2-pyridylketone Schiff base of S-methyldithiocarbazate (Hdpksme) reacts with nickel(II) salts giving both mono- and bis-chelated complexes of empirical formulae, [Ni(dpksme)X] (dpksme=anioninc form of the Schiff base; X=NCS−, Cl−) and [Ni(dpksme)2], respectively. These compounds have been characterized by magnetic and spectroscopic techniques. The mono-ligated nickel(II) complexes are four-coordinate and square-planar but the bis-ligand complex is six-coordinate and octahedral. The crystal and molecular structure of [Ni(dpksme)2] has been determined by X-ray crystallography. The complex has a distorted mer-octahedral structure in which the ligands are coordinated as uninegatively charged tridentate chelating agents via the pyridine nitrogen atoms, the azomethine nitrogen atoms and the thiolate sulfur atoms. The distortion from regular octahedral geometry is ascribed to the restricted bite angles of the ligands. The ligand and its nickel(II) complexes exhibit weak antimicrobial activity against the pathogenic bacteria, S. dysenteriae, B. cercus, S. aureus and E. coli and the fungi, A. alternata and M. phaseolina.

Preparation, characterization and antifungal properties of nickel(II) complexes of tridentate ONS ligands derived from N-methyl-S-methyldithiocarbazate and the X-ray crystal structure of the [Ni(ONMeS)CN]·H2O complex

Nickel(II) complexes of general empirical formula, NiLX·nH2O (L = deprotonated form of the Schiff base formed by condensation of N-methyl-S-methyldithiocarbazate with 2-hydroxybenzaldehyde or 5-bromo-2-hydroxybenzaldehyde; X = Cl−, Br−, NCS−, AcO− or CN−; n = 0, 1) have been prepared and characterized by a variety of physico-chemical techniques. Magnetic and spectroscopic data support a square-planar structure for these complexes. The crystal structure of the [Ni(ONMeS)CN]·H2O complex (ONMeS = anionic form of the 2-hydroxybenzaldehyde Schiff base of N-methyl-S-methyldithiocarbazate) has been determined by X-ray diffraction. The complex has a distorted square-planar structure in which the Schiff base is coordinated to the nickel(II) ion as a uninegatively charged anion coordinating via the phenolic oxygen atom, the azomethine nitrogen atom and the thione sulfur atom. The fourth coordination position is occupied by a cayano ligand. The antifungal properties of the Schiff bases and their nickel(II) complexes were studied against three plant pathogenic fungi. The ligands display moderate fungitoxicities against these organisms but their nickel(II) complexes are less active than the free ligands.

The trivalent copper complex of a conjugated bis-dithiocarbazate schiff base: stabilization of Cu in three different oxidation states

The new tribasic N(2)S(2) ligand H(3)ttfasbz has been synthesized by condensation of 4-thenoyl 2,2,2-trifluoroacetone and S-benzyl dithiocarbazate. On complexation with copper(II) acetate, spontaneous oxidation to the Cu(III) oxidation state is observed, and the complex [Cu(ttfasbz)] has been isolated and characterized structurally. Reduction to the EPR active Cu(II) analogue has been achieved chemically and also electrochemically, and in both cases, the process is totally reversible. The Cu(III/II) redox potential of the complex is remarkably low and similar to that of the ferrocenium/ferrocene couple. Further reduction to the formally monovalent (d(10)) dianion [Cu(I)(ttfasbz)](2-) may be achieved electrochemically. Computational chemistry demonstrates that the three redox states [Cu(ttfasbz)], [Cu(ttfasbz)](-), and [Cu(ttfasbz)](2-) are truly Cu(III), Cu(II), and Cu(I) complexes, respectively, and the potentially noninnocent ligand does not undergo any redox reactions.

Potential natural sensitizers extracted from the skin of Canarium odontophyllum fruits for dye-sensitized solar cells.

Possibility of use of dye extract from skin samples of a seasonal, indigenous fruit from Borneo, namely Canarium odontophyllum, in dye sensitized solar cells (DSSCs) are explored. Three main groups of flavonoid pigments are detected and these pigments exhibit different UV-vis absorption properties, and hence showing different light harvesting capabilities. When applied in DSSCs. The detected pigment constituents of the extract consist of aurone (maritimein), anthocyanidin (pelargonidin) and anthocyanidin (cyanidin derivatives). When tested in DSSC, the highest conversion efficiency of 1.43% is exhibited by cyanidin derivatives, and this is followed by conversion efficiencies of 0.51% and 0.79% for aurone and pelargonidin, respectively. It is shown that individual pigments, like cyanidin derivatives and pelargonidin, exhibit higher power conversion efficiency when compared to that of C.odontophyllum skin pigment mixture (with a conversion efficiency of only 0.68%). The results indicate a possibility of masking effects of the pigments when used as a mixture. The acidification of C.odontophyllum skin pigments with concentrated hydrochloric acid improves the conversion efficiency of the mixture from 0.68% to 0.99%. The discussion in this paper will draw data and observations from the variation in absorption and adsorption properties, the HOMO-LUMO levels, the energy band gaps and the functional group compositions of the detected flavonoids.

Heterocyclic dithiocarbazate iron chelators: Fe coordination chemistry and biological activity

The iron coordination and biological chemistry of a series of heterocyclic dithiocarbazate Schiff base ligands is reported with regard to their activity as Fe chelators for the treatment of Fe overload and also cancer. The ligands are analogous to tridentate heterocyclic hydrazone and thiosemicarbazone chelators we have studied previously which bear NNO and NNS donor sets. The dithiocarbazate Schiff base ligands in this work also are NNS chelators and form stable low spin ferric and ferrous complexes and both have been isolated. In addition an unusual hydroxylated ligand derivative has been identified via an Fe-induced oxidation reaction. X-ray crystallographic and spectroscopic characterisation of these complexes has been carried out and also the electrochemical properties have been investigated. All Fe complexes exhibit totally reversible Fe(III/II) couples in mixed aqueous solvents at potentials higher than found in analogous thiosemicarbazone Fe complexes. The ability of the dithiocarbazate Schiff base ligands to mobilise Fe from cells and also to prevent Fe uptake from transferrin was examined and all ligands were effective in chelating intracellular Fe relative to known controls such as the clinically important Fe chelator desferrioxamine. The Schiff base ligands derived from 2-pyridinecarbaldehyde were non-toxic to SK-N-MC neuroepithelioma (cancer) cells but those derived from the ketones 2-acetylpyridine and di-2-pyridyl ketone exhibited significant antiproliferative activity.