An efficient metal catalyst free approach to synthesize 5-(4-(1,2,4,5 tetrazin-3-yl)benzylamino)-5-oxopentanoic acid

Despite the wide use of 1,2,4,5- tetrazines in biomaterials and materials science, currently there does not exist synthetic method(s) that can yield significant amount of 1,2,4,5- tetrazines without the use of potentially toxic metal catalysts. Here, we report a less energy intensive and more efficient metal catalyst free approach for the synthesis of an asymmetric tetrazine. A range of operating parameters such as extraction pH and temperature were regulated to achieve a practical yield nearly 1.5 times greater than the yields reported in the literature for similar synthetic procedures.     

The effect of mixing methods on the dispersion of carbon nanotubes during the solvent-free processing of multiwalled carbon nanotube/epoxy composites

Several solvent-free processing methods to disperse multiwalled carbon nanotubes (MWCNTs) in bisphenol F-based epoxy resin were investigated, including the use of a microfluidizer (MF), planetary shear mixer (PSM), ultrasonication (US) and combinations. The processed mixture was cured with diethyl toluene diamine. Three complimentary techniques were used to characterize the dispersion of the MWCNTs in cured composite samples: optical microscopy, micro Raman spectroscopy, and scanning electron microscopy (SEM). For sample MF + PSM, optical micrographs and Raman images showed reduced agglomeration and a homogeneous distribution of MWCNTs in the epoxy matrix. SEM analysis of fractured specimen after tensile testing revealed breakage of nanotubes along the fracture surface of the composite. A comparison of the MWCNT dispersion in the epoxy samples processed using different methods showed that a combination of MF and PSM processing yields a more homogeneous sample than the PSM or US + PSM processed samples. Mechanical testing of the composites showed about 15% improvement in the tensile strength of samples processed by the MF + PSM method over other methods. Thermogravimetric analysis (TGA) results showed a small decrease in the onset degradation temperature for poorly dispersed samples produced by PSM compared with the well-mixed samples (MF + PSM). These results strongly suggest that the MF + PSM processing method yield better-dispersed and stronger MWCNT/epoxy composites. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Vickrey–Dutch procurement auction for multiple items

We consider a setting where there is a manufacturer who wants to procure multiple items from a set of suppliers each of whom can supply one or more of these items (bundles). We design an ascending price auction for such a setting which implements the Vickrey–Clarke–Groves outcome and truthful bidding is an ex post Nash equilibrium. Our auction maintains non-linear and non-anonymous prices throughout the auction. This auction has a simple price adjustment step and is easy to implement in practice. As offshoots of this auction, we also suggest other simple auctions (in which truthful bidding is not an equilibrium by suppliers) which may be suitable where incentives to suppliers are not a big concern. Computer simulations of our auction show that it is scalable for the multi-unit case, and has better information revelation properties than its descending auction counterpart.     

Spectroscopic identification of S-Au interaction in cysteine capped gold nanoparticles

This study deals with the synthesis of cysteine capped gold nanoparticles with an average size of 12 nm by borohydride reduction and spectroscopic identification of SAu interaction. We have studied the interaction of thiol with gold nanoparticles in aqueous medium by employing UV-vis, Raman, NMR, and FT-IR spectroscopy. The shifting of gold plasmon resonance in the UV-vis spectra shows the stabilization of gold nanoparticles by cysteine. The disappearance of S-H stretching in both the IR and Raman spectra and the shifting of the NMR signals of the protons in close proximity to the metal center supported the existence of the S-Au interaction in cysteine capped gold nanoparticles. The TEM images shows cysteine capped gold nanoparticles as distinct and spherical entities as compared to free colloidal gold nanoparticles.     

Ruthenium(II) complexes containing bidentate Schiff bases and their antifungal activity

The reactions of ruthenium(II) complexes, [RuHCl(CO)(PPh₃)₂(B)] [B = PPh₃, pyridine (py) or piperidine (pip)], with bidentate Schiff base ligands derived by condensing salicylaldehyde with aniline, o-, m- or p-toluidine have been carried out. The products were characterised by analytical, i.r., electronic, ¹H-n.m.r. and ³¹P-n.m.r. spectral studies and are formulated as [RuCl(CO)(L)(PPh₃)(B)] (L = Schiff base anion; B = PPh₃, py or pip). An octahedral structure has been tentatively proposed for the new complexes. The Schiff bases and the new complexes were tested in vitro to evaluate their activity against the fungus Aspergillus flavus.     

Bismaleimide/rice husk silica reinforced composites

Silica derived from the renewable resource rice husk is modified using stearic acid and N-[4-(chlorocarbonyl)phenyl]maleimide. These materials are used as fillers in the bismaleimide, 4,4′-bismaleimidodiphenylmethane (BMIM), and thermally cured. The thermogravimetric (TG) curves for polyBMIM/silica composites showed no pronounced changes compared to the TG curve for the pure polyBMIM. Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa, and Friedman methods are used to compute the activation energy (E _a) for degradation. Silica and surface-modified silica using stearic acid dispersed by ultrasonication increase the activation energy for degradation and show considerable influence on the thermal stability of cured BMIM. The long alkyl chain present in the stearic acid modified silica and the bulky spacer present in the chemically modified silica definitely alter the degradation process of cured BMIM. The SEM studies indicated uniform dispersion of the silica particles in the polyBMIM.     

Effect of substitution and planarity of the ligand on DNA/BSA interaction, free radical scavenging and cytotoxicity of diamagnetic Ni(II) complexes: a systematic investigation

Four new bivalent nickel hydrazone complexes have been synthesised from the reactions of [NiCl(2)(PPh(3))(2)] with H(2)L {L = dianion of the hydrazones derived from the condensation of salicylaldehyde or o-hydroxy acetophenone with p-toluic acid hydrazide (H(2)L(1)) (1), (H(2)L(2)) (2) and o-hydroxy acetophenone or o-hydroxy naphthaldehyde with benzhydrazide (H(2)L(3)) (3) and (H(2)L(4)) (4)} and formulated as [Ni(L(1))(PPh(3))] (5), [Ni(L(2))(PPh(3))] (6), [Ni(L(3))(PPh(3))] (7) and [Ni(L(4))(PPh(3))] (8). Structural characterization of complexes 5-8 were accomplished by using various physico-chemical techniques. In order to study the influence of substitution in the ligand and its planarity on the biological activity of complexes 5-8 containing them, suitable hydrazone ligands 1-4 have been selected in this study. Single crystal diffraction data of complexes 5, 7 and 8 proved the geometry of the complexes to be distorted square planar with a 1 : 1 ratio between the metal ion and the coordinated hydrazones. To provide more insight on the mode of action of complexes 5-8 under biological conditions, additional experiments involving their interaction with calf thymus DNA (CT DNA) and bovine serum albumin (BSA) were monitored by UV-visible and fluorescence titrations respectively. Further, the ligands 1-4 and corresponding nickel(ii) chelates 5-8 have been tested for their scavenging effect towards OH and O(2)(-) radicals. The effect of complexes 5-8 to arrest the growth of HeLa and Hep-2 tumour cell lines has been studied along with the cell viability against the non-cancerous NIH 3T3 cells under in vitro conditions.     

Synthesis, crystal structure, electrochemistry and studies on protein binding, antioxidant and biocidal activities of Ni(II) and Co(II) hydrazone complexes

Bivalent transition metal hydrazone complexes of the composition [Ni(L₁)₂] (1), [Co(L₁)₂] (2), [Ni(L₂)₂] (3) and [Co(L₂)₂] (4) have been synthesised from the reactions of [MCl₂(PPh₃)₂] (where M = Ni or Co) with hydrazones derived from 2-acetyl pyridine and carboxylic acid hydrazides of benzhydrazide (HL₁) or thiophene-2-carboxylic acid hydrazide (HL₂), respectively. Structure of the ligands HL₁ and HL₂ and their corresponding complexes with Ni(II) and Co(II) ions were proposed based on the elemental analysis, infrared and ¹H NMR spectral methods. Single crystal X-ray diffraction study of complex 1 revealed a distorted octahedral geometry around the metal ion provided by two units of the ligand. To explore the potential medicinal value of the new complexes, binding interaction of all the complexes with bovine serum albumin (BSA) was studied at normal physiological conditions using fluorescence and UV-Vis spectral techniques. The number of binding sites (n) and binding constant (K_a) were calculated according to the double logarithm regression equation. The results of synchronous fluorescence spectrum showed that binding of metal hydrazones with BSA induced conformational changes in BSA. The in vitro antioxidant and antimicrobial potentials of the new chelates were also carried out.     

Mesoporous nickel hydroxyapatite nanocomposite for microwave-assisted Henry reaction

The utility of nickel hydroxyapatite nanocomposite (Ni-HAp) as a green catalyst for solvent free, microwave-assisted Henry reaction using nitromethane and a series of aromatic aldehydes as substrates is presented. The selected catalyst performed well to afford the respective nitrostyrenes which were quantified by gas chromatography equipped with a mass spectral detector (GC–MS). A few of the products were identified from the respective nuclear magnetic resonance (NMR) spectral data.     

<em>Cassia spectabilis </em>(DC) Irwin et Barn: A Promising Traditional Herb in Health Improvement

The genus Cassia, comprising about 600 species widely distributed worldwide is well known for its diverse biological and pharmacological properties. Cassia spectabilis (sin Senna spectabilis) (DC) Irwin et Barn (Fabaceae) is widely grown as an ornamental plant in tropical and subtropical areas. C. spectabilis has been commonly used in traditional medicine for many years. Information in the biomedical literature has indicated the presence of a variety of medicinally-important chemical constituents in C. spectabilis. Pharmacological studies by various groups of investigators have shown that C. spectabilis possesses significant biological activity, such as antibacterial, antibiofilm, antifungal and antioxidant properties. Beside this, toxicity studies of this plant have revealed no toxic effect on mice. In view of the immense medicinal importance of C. spectabilis, this review aimed at compiling all currently available information on C. spectabilis's botany, phytochemistry, pharmacology, and mechanism of actions, toxicology and its ethnomedicinal uses.