Athar Adil Hashmi

Au(III)–CTAB reduction by ascorbic acid: Preparation and characterization of gold nanoparticles

Upon addition of tetrachloroauric(III) (HAuCl(4)) to a solution of cetyltrimethylammonium bromide (CTAB), a perfect transparent yellow colored and yellowish-precipitate appears within the time of mixing, indicating the formation of a complex between HAuCl(4) and CTAB. Morphology of gold nanoparticles in situ via chemical reduction of title reaction has been determined by using conventional techniques. The position and shape of the surface plasmon resonance (SRP) band strongly depends on the [ascorbic acid], [HAuCl(4)], [CTAB] and mixing ratio of the reactants. Sub-, post- and dilution-micellar effects are accountable to the aggregation and/or adsorption of gold nanoparticles onto the surface of CTAB. The morphology of particles was altered by changing the [reactants] as well as [CTAB]. A mechanism of nanoparticle formation has been proposed comprising different steps of particle growth.

Shape-directing role of cetyltrimethylammonium bromide in the green synthesis of Ag-nanoparticles using Neem (Azadirachta indica) leaf extract.

The shape-directing role of cetyltrimethylammonium bromide, CTAB, is reported to the green synthesis of Ag-nanoparticles for the first time using Neem (Azadirachta indica) leaf extract. UV-vis spectroscopy, transmission electron microscopy (TEM), and selected area electron diffraction (SAED) patterns were used to monitor the growth kinetics, morphology and crystalline nature of Ag-nanoparticles, respectively. It was observed that the growths of Ag-nanoparticles are stopped within 40 min of reaction time. The Ag-nanoparticles are polydispersed spherical and exhibiting an interesting triangle, flat, plate-like hexagonal and some irregular morphology in presence of different [CTAB]. Hexagonal particles aggregated in a systematic manor, leads to produce a fine tiles-like arrangement of Ag-nanoparticles with dimensions between 10 and 37 nm. The nature of reaction-time curves to the reduction of Ag(+) ions by Neem leaf extract are much different than those observed by us in our earlier studies using different bio-reductants.

Silver nanoplates and nanowires by a simple chemical reduction method

This paper describes a simple preparation of single-crystalline Ag-nanoparticles including plates, and wires in water by truncated triangular particles for the first time during the reduction of [Ag(NH₃)₂]⁺ complex with glucose at room temperature. Silver particles were characterized by means of the conventional transmission electron microscopy (TEM) and UV-VIS spectroscopy. Cetyltrimethylammonium bromide, CTAB, plays a number of roles during the redox process by solubilizing the reactants, controlling the nucleation and/or growth of nanoparticles, stabilizing the thus-prepared Ag-nanoparticles and minimizing the formation of Ag₂O, AgCl, and AgBr precipitates. It was found that the rate constant and absorbance of silver nanoparticles were sigmoidal to the concentration of silver nitrate.

Design, synthesis, characterization and antimicrobial/antioxidant activities of 1, 4-dicarbonyl-phenyl-dihydrazide based macrocyclic ligand and its Cu(II), Co(II) and Ni(II) complexes.

Mononuclear transition metal complexes of Cu(II), Co(II) and Ni(II) with a newly synthesised macrocyclic ligand derived from 1, 4-dicarbonyl-phenyl-dihydrazide and 1,2-diphenylethane-1,2-dione (2:2) have been synthesised. The synthesised compounds were characterised by various physical and spectroscopic techniques including elemental analysis, FTIR, Uv-Vis., 1H NMR, mass spectra, magnetic moment and XRD. The investigation of these macrocyclic complexes established that the stability of metal-ligand coordination through N atoms as tetradentate chelates. The metal/ligands ratio of 1:1 was proposed to afford octahedral geometry for the complexes. The antimicrobial activity of the compounds against some bacterial and fungal species were done by well diffusion method and the results shows that the metal complexes have a promising biological activity comparable with the parent ligand against all bacterial and fungal species. The antioxidant activity of the compounds was also studied through scavenging effect on DPPH radicals with the copper complex showing enhanced activity than other compounds. Additionally, the docking studies predicted the high antimicrobial activity due to the interaction of ligand with the protein.

Kinetics and mechanism of chromic acid oxidation of oxalic acid in absence and presence of different acid media. A kinetic study

Kinetics and mechanism of the reaction of Cr(VI) with oxalic acid have been studied in presence and absence of H2SO4, HClO4, and CH3COOH by monitoring the formation of Cr(III)-oxalic acid complex at 560 nm. The effect of total [oxalic acid], [Cr(VI)], [H2SO4], [HClO4], and [CH3COOH] on the reaction rate was determined at 30°C. Formation of carbon dioxide was also confirmed. The oxidation rate increases with [oxalic acid] and [CH3COOH] while it decreases with [H2SO4], [HClO4], and pH. The rate law governing the oxidation of oxalic acid over a wide range of conditions is rate=k1Kes1 [oxalic acid]T [Cr(VI)]T 1+Kes1 [oxalic acid]T, where only undissociated oxalic acid is kinetically active. Kinetic evidence for the formation of a Cr(VI)(SINGLEBOND)oxalic acid 1:1 complex has been obtained and the equilibrium constant for their formation has been determined. The 1:1 complex exists most likely in an open chain form. The rate-limiting step of the oxidation reaction involves the breaking of the C(SINGLEBOND)C bond in the 1:2 complex. Oxidizing ability of Cr(VI) species have been discussed. Mechanism with the associated reaction kinetics is assigned.

Biological Activity Studies on Metal Complexes of Macrocyclic Schiff Base Ligand: Synthesis and Spectroscopic Characterization

In this study, we prepared the macrocyclic Schiff base ligand (L) derived from 1,4-dicarbonylphenyl- dihydrazide and pentane-2,4-dione (2:2) and its CoII, CuII and NiII complexes. The compounds were characterized by the analytical and spectroscopic methods like elemental analysis, molar conductance measurements, mass spectrometry, 1H nuclear magnetic resonance (NMR), and Fourier transform infrared (FTIR) spectroscopy. The ligand behaves as a tetradentate ligand and coordinates to the metal ions via the nitrogen atoms and the complexes have the mononuclear structures. The analytical and spectroscopic results indicated that the complexes are non-electrolytes in nature and may be formulated as [M(C26H28N8O4)X2], where M = CoII, CuII and NiII and X = Cl–. The antimicrobial activities of the ligand and its complexes, as growth inhibiting agents, have been screened in vitro against different species of bacteria and fungi and the results concluded that the metal complexes are effective drugs against the tested strains as compared to the macrocyclic ligand.

Organotin(IV) oxo -homoscorpionate: preparation, spectroscopic characterization and antimicrobial properties

An oxo-homoscorpionate ligand [potassium bis(phthalato)borate] (KL) was prepared by solid state reaction of potassium borohydride and phthalic acid (1 : 3 molar ratio). The ligand is uninegative and can be a bi, tri and tetra-dentate chelating agent. The di- and tri-organotin(IV) complexes of this ligand are formed by replacement of chloride in R2SnCl2 and (R = methyl, butyl and R′ = phenyl and butyl). The ligand and all its complexes were characterized by elemental analyses and spectral studies (IR, 1H, 13C, 119Sn NMR and ESI mass spectra). Spectroscopic data reveal that all the complexes are hexacoordinate; the diorganotin complexes have trans octahedral geometry while the triorganotin complexes are distorted octahedral geometry. The toxicity of these organotin(IV) derivatives on selected microbes was considered. The compounds exhibit antibacterial (Bacillus anthracius and Escherichia coli) and antifungal (Candida albicans and Penicillium italicum) activities in vitro. The ligand shows less toxicity towards the microorganisms and its toxicity significantly increased after complexation with organotin(IV). Triorganotin derivatives (R3SnL) of the ligand are more effective compared to diorganotin derivatives (R2SnL2).

Reduction of chromium(VI) by phosphonic acid

The kinetics of electron transfer between chromium(VI) and H3PO3, yielding chromium(III), have been investigated in HClO4 and H2SO4 media by visible spectrophotometry. The rate of reaction increased with increasing [H2SO4] and [HClO4]. A rate law based on ester formation preceding the electron transfer has been established and a possible mechanism has been proposed. The mechanism and the derived rate law are consistent with the observed kinetics.

Design and synthesis of Co(II) and Cu(II) complexes of a dendrimeric chelate: promising anticandidal potential of chelotherapeutic agents

In response to an increasing demand for effective anticandidal agents, a new water-soluble dendrimeric ligand (L) was synthesized by Michael addition of ethylenediamine to methyl methacrylate. The prepared ligand was complexed with Cu(II) and Co(II) ions. Both the ligand and its complexes were characterized by elemental analysis and spectroscopic studies (FT-IR, UV–vis, 1H NMR, and ESI-MS). Square-planar and square-pyramidal geometries were proposed for Cu(II) and Co(II) on the basis of UV–vis spectroscopic data and molar conductance measurements. The ligand and its Cu(II) and Co(II) complexes were screened on Candida albicans ATCC 90028 by determining MICs (minimal inhibitory concentrations) and inhibition in solid media (disk diffusion assay). Hemolysis assays on human RBCs indicated that the toxicity of the copper complex was lower as compared to fluconazole. These results taken with limited toxicity make them eligible for further development as antifungals.

Antimicrobial studies of newly synthesized organotin(IV) complexes of dihydrobis(2-mercaptothiazolinyl)borate

Four organotin(IV) complexes of dihydrobis(2-mercaptothiazolinyl)borate were synthesized and characterized by elemental analysis and spectroscopic techniques (IR, 1H-NMR, 13C-NMR, 11B-NMR, and 119Sn-NMR). All the compounds were screened against bacterial, fungal, and cyanobacterial strains. Among the complexes, triorganotin(IV) complexes show better inhibition growth as compared to diorganotin(IV) complexes.