Catalytic activity of nanocrystalline ZnM2O4 (M = Fe,Co) prepared via simple and facile synthesis of thermal decomposition of mixed metal complexes of Schiff bases generated from α-ketobutyric acid and diaminoguanidine

Metal complexes ([ML₂], where M = Fe, Co, or Zn; HL = 2-[(6-ethyl-5-oxo-4,5-dihydro-2H-[1,2,4]triazin-3-ylidene)-hydrazono]-butyric acid, C₉H₁₃N₅O₃) of a Schiff base derived from α-ketobutyric acid (α-KBA) and diaminoguanidine (Damgu) were synthesized and characterized using elemental, spectral, and thermal studies. The metal complexes exhibited similar decomposition behavior, with a highly exothermic final decomposition step resulting in the formation of metal oxides. Isomorphism among the complexes was revealed using a powder X-ray diffraction (PXRD) technique. Solid solution precursors ([Zn_1/3M_2/3(L)₂], where M = Fe, Co) were synthesized and characterized using various physico-chemical techniques. A thermal decomposition technique was used to prepare spinel-type zinc cobaltite (ZnCo₂O₄) and zinc ferrite (ZnFe₂O₄) nanocrystalline particles with the synthesized single source precursors. Structural studies using PXRD ascertained the predominant crystal phase to be spinel. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) showed a mean nanoparticle size of 18 ± 2 nm. Magnetic measurements revealed a weak magnetic behavior in the synthesized spinels. In the aqueous phase, the spinels exhibited catalytic activity, reducing 4-nitrophenol (4-NP) in the presence of NaBH₄ at room temperature. Additionally, the study demonstrated that the catalyst can be recovered and reused for five cycles with a more than 85% conversion efficiency.     

An efficient synthesis of medicinally important indole based triarylmethanes by using propylphosphonic anhydride (T3P®)

Abstract

We have developed an economical and efficient method for the synthesis of medicinally and synthetically important indole-based triarylmethanes by using indoles and benzhydrols in the presence of propylphosphonic anhydride (T3P^®). This methodology is an alternate approach for the C–C bond formation with good to excellent yields. In this T3P-mediated dehydration approach, the by-product is highly soluble in water, so that it can be done at larger scale also. In addition to that this efficient protocol has several advantages such as mild reaction conditions, short reaction time and operational simplicity. We have successfully synthesized pyrrole, imidazothiadiazole and imidazolo pyridine based triarylmethanes also.     

The first stereoselective synthesis of dendrodolide A

The first stereoselective total synthesis of natural product, dendrodolide A (1) is described from readily available (R)-propylene oxide and 3-buten-1-ol as starting materials. The synthesis was achieved in 10 steps with an overall yield of 19.1%. The key steps involved in the synthesis are Jacobsen hydrolytic kinetic resolution, epoxide ring opening with 2-allyl-1, 3-dithiane, Yamaguchi esterification, and ring-closing metathesis (RCM).     

α-Telluration of 2-acetylthiophene: Electronic influence of the heteroaromatic moiety on solid state structures

Room temperature oxidative addition of α-bromo-2-acetylthiophene to elemental tellurium and aryltellurium(II) bromide provides direct routes to (2-thiophenoylmethyl)tellurium(IV) dibromides, (2-(C₄H₃S)COCH₂)₂TeBr₂ (1b) and 2-(C₄H₃S)COCH₂ArTeBr₂ (Ar = 1-C₁₀H₇, Npl, 2b; 2,4,6-Me₃C₆H₂, Mes, 3b). The chloro analogues, 2-(C₄H₃S)COCH₂ArTeCl₂ (Ar = Npl, 2a; Mes, 3a) were prepared by the condensation reaction of the parent methyl ketone with NplTeCl₃ or MesTeCl₃. Metathesis of these products with an alkali iodide affords the iodo analogues 1c, 2c and 3c. These diorganotellurium dihalides are reduced with aqueous bisulfite to diorganotellurides 1-3, which can be oxidized readily with dihalogens to the desired diorganotellurium(IV) dihalides. Compound 1 is a rare example of a symmetrical telluroether with C_sp3-Te-C_sp3 grouping that has been characterized by single-crystal diffraction techniques. Preference of the 2-thiophenoylmethyl ligand for small-bite (C, O) chelation over less strained (C, S) coordination is evident in the crystal structures of the Te(IV) compounds 1b, 2a, 2b and 3a. The unexpected transoidal orientation of the two acylmethyl ligands in the solid state molecular configuration of symmetrical diorganotellurium(IV) dibromide 1b appears to be a combined effect of electronic repulsion due to the thiophene moieties and steric repulsion of bromo ligands.     

One pot synthesis of structurally different mono and dimeric Ni(II) thiosemicarbazone complexes and N-arylation on a coordinated ligand: a comparative biological study

One pot synthesis of three structurally different Ni(II) thiosemicarbazone complexes 1, 2 and 3 were obtained from the reaction between [NiCl(2)(PPh(3))(2)], 1,2-bis(diphenylphosphino)ethane, and [H(2)-(Sal-tsc)]. The obtained products were characterized by various spectral and analytical techniques. From the X-ray crystallographic analysis, an unexpected N-arylation on the coordinated salicylaldehydethiosemicarbazone was found in complex 2. The comparative biological evolutions such as DNA/protein binding, antioxidant, cytotoxicity (MTT, LDH, and NO) and cellular uptake studies have been examined for [Ni(Sal-tsc)(PPh(3))] (1) and [(Ni(Sal-tsc))(2)(μ-dppe)] (3). When comparing the cytotoxicity of the complexes, 1 exhibited higher activity than 2 and 3 and by comparing with standard cis-platin, both of them were found to exhibit better activity under identical conditions.     

Development and validation of liquid chromatography–tandem mass spectrometry method for the estimation of a potential genotoxic impurity 2-(2-chloroethoxy)ethanol in hydroxyzine

2-(2-Chloroethoxy)ethanol (CEE) belongs to the so-called cohort of concerns which were classified as highly potent mutagenic carcinogens by the World Health Organization. It is widely used in the synthesis of the essential anti-histamine drug hydroxyzine. In addition, it is used as a primary solvent in dyes, nitrocellulose, paints, inks and resins. Owing to its potential genotoxicity, an efficient liquid chromatography–tandem mass spectrometry method was developed for the quantitative estimation of CEE traces in an active pharmaceutical ingredients and in tablet dosage forms of hydroxyzine-free base. The chromatographic separation was achieved on a C₁₈ column using a gradient elution mode with a binary solvent system (ammonium formate and methanol). Mass detection was performed for CEE using a positive mode with selected ion monitoring technique at m/z value of [M + NH₄]⁺. The developed method was validated as per the International Conference on Harmonizaiton guidelines. The quantitation limit, linearity and recoveries were found to be 0.56 ppm, 0.56–7.49 ppm (r² > 0.9985) and 93.6–99.3%, respectively. The proposed method was highly compatible and was used effectively to estimate CEE traces in different stages of drug synthesis and in tablet dosage forms of hydroxyzine for routine and stability testing.     

A novel Raman spectroscopic approach to identify polymorphism in leflunomide: a combined experimental and theoretical study

Polymorphism is an important characteristic which affects the activity, solubility and other physical properties of a compound and can be induced by varying temperature, pressure and solvent. The presence and conversion of α to β polymorphic forms of an anti‐rheumatic drug leflunomide have been studied by temperature‐dependent and in situ Raman observations. Both α and β polymorphs were found to co‐exist in the temperature interval 367–372 K. The α form alone exists below 367 K and the β form alone above 373 K. The CO stretching band clearly demonstrates the α → β conversion because of breaking of N–H···O bond and formation of N–H···N bond. On cooling the Raman spectra suggest the irreversibility of this conversion. Thermodynamic stability, crystal parameters and surface morphology of both forms in the leflunomide powder used for the present study have been verified by differential scanning calorimetry, X‐ray powder diffraction and scanning electron microscopy. Copyright © 2015 John Wiley & Sons, Ltd.     

Influence of terminal substitution on structural, DNA, protein binding, anticancer and antibacterial activities of palladium(II) complexes containing 3-methoxy salicylaldehyde-4(N) substituted thiosemicarbazones

The variable chelating behavior of 3-methoxysalicylaldehyde-4(N)-substituted thiosemicarbazones was observed in equimolar reactions with [PdCl(2)(PPh(3))(2)]. The new complexes were characterized by various analytical, spectroscopic techniques (mass, (1)H-NMR, absorption, IR). All the new complexes were structurally characterized by single crystal X-ray diffraction. Crystallographic results showed that the ligands H(2)L(1) and H(2)L(4) are coordinated as binegative tridentate ONS donor ligands in the complexes 1 and 4 by forming six and five member rings. However, the ligands H(2)L(2) and H(2)L(3) bound to palladium in 2 and 3 as uninegative bidentate NS donors by forming a five member chelate ring. From this study, it was found that the substitution on terminal 4(N)-nitrogen may have an influence on the chelating ability of thiosemicarbazone. The presence of hydrogen bonding in 2 and 3 might be responsible for preventing the coordination of phenolic oxygen to the metal ion. The interaction of the complexes with calf-thymus DNA (CT-DNA) has been explored by absorption and emission titration methods. Based on the observations, an electrostatic binding mode of DNA has been proposed. The protein binding studies were monitored by quenching of tryptophan and tyrosine residues in the presence of complexes using Lysozyme as model protein. Antibacterial activity studies of the complexes have been screened against pathogenic bacteria such as Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia and Pseudomonas aeruginosa. MIC50 values of the complexes showed that they exhibited significant activity against the pathogens and among them, 3 exhibited higher activity. Further, anticancer activity of the complexes on the lung cancer cell line A549 has also been studied.