Oxovanadium(IV) and -(V) complexes of dithiocarbazate-based tridentate Schiff base ligands: syntheses,structure, and photochemical reactivity of compounds involving imidazole derivatives as coligands

The tridentate dithiocarbazate-based Schiff base ligands H(2)L (S-methyl-3-((5-R-2-hydroxyphenyl)methyl)dithiocarbazate, R = NO(2), L = L(2); R = Br, L = L(3)) react with [VO(acac)(2)] in the presence of imidazole derivatives as coligands to form oxovanadium(IV) and cis-dioxovanadium(V) complexes. With benzimidazole and N-methylimidazole, the products are oxovanadium(IV) complexes, viz. [VOL(3)(BzIm)].0.5CH(3)CN (1a) and [VOL(N-MeIm)(2)] (L = L(3), 1b; L = L(2), 1c), respectively. In both 1a,b, the O and S donor atoms of the tridentate ligand are cis to the terminal oxo group (in the "equatorial" plane) and mutually trans, but the N donor atom is respectively cis and trans to the oxo atom, as revealed from X-ray crystallography. When imidazole or 4-methylimidazole is used as the ancillary ligand, the products obtained are water-soluble cis-dioxovanadium(V) complexes [VO(2)L(R'-ImH)] (L = L(3) and L(2), R' = H and Me, 2a-d). These compounds have zigzag chain structures in the solid state as confirmed by X-ray crystallographic investigations of 2a,d, involving an alternating array of LVO(2)(-) species and the imidazolium counterions held together by Coulombic interactions and strong hydrogen bonding. Complexes 2a-d are stable in water or methanol. In aprotic solvents, viz. CH(3)CN, DMF, or DMSO, however, they undergo photochemical transformation when exposed to visible light. The putative product is a mixed-oxidation divanadium(IV/V) species obtained by photoinduced reduction as established by EPR, electronic spectroscopy, and dynamic (1)H NMR experiments.     

Design,synthesis, and biological evaluation of indolylidinepyrazolones as potential anti-bacterial agents

A series of indolylidinepyrazolones were synthesized using a simple, green, and effective route and evaluated as anti-bacterial agents. The compounds were further studied via structure-guided docking study. One of the compounds exhibiting H-bonding interactions with conserved residue Arg144 turned out to be the most potent compound of the series. The minimum inhibitory concentration values ranged from 50 to 25 μg/mL against Staphylococcus aureus in their anti microbial evaluation.     

Lipase mediated separation of triterpene structural isomers, α- and β-amyrin

Pentacyclic triterpenoids α- and β-amyrin possess a wide range of biological and pharmacological activities. High structural similarity between these two structural isomers makes their chromatographic separation an ineffective and tedious choice. In this study, Candida rugosa lipase catalyzed separation protocol for the isolation of individual isomers has been developed. In the presence of vinyl acetate as the acyl donor, Candida rugosa lipase carried out acetylation of β-amyrin more efficiently as compared to α-amyrin leading to a kinetic separation. The conditions of transesterification reaction were optimized systematically, which was utilized to separate α- and β-amyrin from a mixture obtained from the latex of Plumeria obtusa.     

3 d Transition Metal‐Catalyzed Hydrogenation of Nitriles and Alkynes

Selective hydrogenation of nitriles and alkynes is crucial considering the vast applications of reduced products in industries and in the synthesis of bioactive compounds. Particularly, the late 3d transition metal catalysts (manganese, iron, cobalt, nickel and copper) have shown promising activity for the hydrogenation of nitriles to primary amines, secondary amines and imines. Similarly, semihydrogenation of alkynes to E‐ and Z‐alkenes by 3d metals is adequately successful both via the transfer hydrogenation and by using molecular hydrogen. The emergence of 3d transition metals in the selective synthesis of industrially relevant amines, imines and alkenes makes this protocol more attractive. Herein, we provide a concise overview on the late 3d transition metal‐catalyzed hydrogenation of nitriles to amines and imines as well as semihydrogenation of alkynes to alkenes.     

Thermal properties of N-substituted 4-vinylpyridinium ions and their polymers

4-Vinylpyridinium trifluoromethanesulfonate monomers substituted at nitrogen with H, O, CH₃, C₂H₅, C₆H₁₃, and C₁₂H₂₅ were synthesized and characterized spectroscopically. Thermal analyses (DSC and TGA) were carried out on all the compounds. The solid monomers (N? H, N? CH₃, N? C₆H₁₃, and N? C₁₂H₂₅) exhibited endothermic melting followed by exothermic polymerization and exothermic decomposition (>400°C). Liquid N? C₂H₅ monomer revealed only exothermic polymerization and decomposition. The N? O polymer underwent thermal decomposition below 300°C. The N–C₁₂H₂₅ homopolymer, prepared from monomer in the DSC or in bulk, displayed an unusual thermal transition at 250°C, which has been attributed to a polymer backbone reorientation leading to side-chain ordering of the dodecyl groups.     

Influence of media nutrients on synthesis of lignin peroxidase from Aspergillus sp

The effect of carbon and nitrogen sources, lignocellulosic substrates, and metal ions on lignin peroxidase (LiP) activity of Aspergillus sp., which was isolated from a mangrove area, was studied. Glucose (1%) was found to be the best carbon source. Among the various lignocellulosic substrates used, coir pith at 3% concentration increased LiP activity twofold on the second day of incubation. Peptone and KNO₃ completely inhibited the enzyme synthesis while (NH₄)₂SO₄ at 12.5 mM produced maximum activity. Since seawater contained all the requisite metal ions, any added ions had a negative effect on activity. Cu²⁺ had the most inhibiting effect while K⁺ the least. When all the optimized conditions were provided, in nitrogen- and carbon-sufficient medium, a maximum LiP activity of 345 U/mL was obtained on the second day of incubation.     

Design,synthesis, molecular docking,and spectral studies of new class of carbazolyl polyhydroquinoline derivatives as promising antibacterial agents with noncytotoxicity towards human mononuclear cells from peripheral blood

In the present study, we report the design and eco-benign synthesis of new class of carbazolyl-1,4-dihydropyridine (1,4-CDHP) and carbazolyl-1,8-dioxodecahydroacridine (CAD) derivatives via a three-component coupling reaction of substituted carbazole aldehydes, ethyl acetoacetate/dimedone, and ammonium acetate under solvent-free conditions at 112°C to 115°C. We also report an efficient one-pot synthesis of new class of carbazolyl polyhydroquinoline (CPQ) derivatives via a four-component coupling reaction of substituted ethyl acetoacetate, dimedone, ammonium acetate, and carbazole aldehydes in acetonitrile/water medium (3:1) at 73°C to 75°C in moderate yields. All the products were thoroughly characterized by ¹H NMR, ¹³C NMR, Fourier transform infrared (FTIR), mass spectral, and CHN analysis. The synthesized heterocyclic compounds were evaluated for their in vitro antibacterial activity against pathogenic strains of both Gram-negative and Gram-positive bacteria. Minimum inhibitory concentration (MIC) of the active compounds was evaluated by macrodilution method. The CPQ derivative ( 8a ) displayed superior antibacterial activity against Escherichia coli, Pseudomonas aeruginosa, and Salmonella typhi with the MIC values of 16.0 to 32.0 μg/mL in comparison with the reference drug. The mechanism of antibacterial action of the CPQ derivatives was investigated via scanning electron microscope (SEM) studies. The molecular docking studies indicate that the CPQ derivative ( 8a ) binds to the cell wall protein of E coli and P aeruginosa by formation of hydrogen bonds with amino acid residues (TYR328 and GLU249) of the bacterial cell wall protein. The 1,4-CDHP, CAD, and CPQ derivatives were either noncytotoxic or exhibited minimal cytotoxicity towards human mononuclear cells from peripheral blood. All the products were evaluated for Lipinski rule of five (RO5) and were found to have good oral bioavailability.     

Long distance laser ultrasonic propagation imaging system for damage visualization

Wind turbine blade failure is the most prominent and common type of damage occurring in operating wind turbine systems. Conventional nondestructive testing systems are not available for in situ wind turbine blades. We propose a portable long distance ultrasonic propagation imaging (LUPI) system that uses a laser beam targeting and scanning system to excite, from a long distance, acoustic emission sensors installed in the blade. An examination of the beam collimation effect using geometric parameters of a commercial 2 MW wind turbine provided Lamb wave amplitude increases of 41.5 and 23.1 dB at a distance of 40 m for symmetrical and asymmetrical modes, respectively, in a 2 mm-thick stainless steel plate. With this improvement in signal-to-noise ratio, a feasibility study of damage detection was conducted with a 5 mm-thick composite leading edge specimen. To develop a reliable damage evaluation system, the excitation/sensing technology and the associated damage visualization algorithm are equally important. Hence, our results provide a new platform based on anomalous wave propagation imaging (AWPI) methods with adjacent wave subtraction, reference wave subtraction, reference image subtraction, and the variable time window amplitude mapping method. The advantages and disadvantages of AWPI algorithms are reported in terms of reference data requirements, signal-to-noise ratios, and damage evaluation accuracy. The compactness and portability of the proposed UPI system are also important for in-field applications at wind farms.     

Crystal structures of four δ‐keto esters and a Cambridge Structural Database analysis of cyano–halogen interactions

The revived interest in halogen bonding as a tool in pharmaceutical cocrystals and drug design has indicated that cyano–halogen interactions could play an important role. The crystal structures of four closely related δ‐keto esters, which differ only in the substitution at a single C atom (by H, OMe, Cl and Br), are compared, namely ethyl 2‐cyano‐5‐oxo‐5‐phenyl‐3‐(piperidin‐1‐yl)pent‐2‐enoate, C₁₉H₂₂N₂O₃, (1), ethyl 2‐cyano‐5‐(4‐methoxyphenyl)‐5‐oxo‐3‐(piperidin‐1‐yl)pent‐2‐enoate, C₂₀H₂₄N₂O₄, (2), ethyl 5‐(4‐chlorophenyl)‐2‐cyano‐5‐oxo‐3‐(piperidin‐1‐yl)pent‐2‐enoate, C₁₉H₂₁ClN₂O₃, (3), and the previously published ethyl 5‐(4‐bromophenyl)‐2‐cyano‐5‐oxo‐3‐(piperidin‐1‐yl)pent‐2‐enoate, C₁₉H₂₁BrN₂O₃, (4) [Maurya, Vasudev & Gupta (2013). RSC Adv. 3 , 12955–12962]. The molecular conformations are very similar, while there are differences in the molecular assemblies. Intermolecular C—H...O hydrogen bonds are found to be the primary interactions in the crystal packing and are present in all four structures. The halogenated derivatives have additional aromatic–aromatic interactions and cyano–halogen interactions, further stabilizing the molecular packing. A database analysis of cyano–halogen interactions using the Cambridge Structural Database [CSD; Groom & Allen (2014). Angew. Chem. Int. Ed. 53 , 662–671] revealed that about 13% of the organic molecular crystals containing both cyano and halogen groups have cyano–halogen interactions in their packing. Three geometric parameters for the C—X...N[triple‐bond]C interaction (X = F, Cl, Br or I), viz. the N...X distance and the C—X...N and C—N...X angles, were analysed. The results indicate that all the short cyano–halogen contacts in the CSD can be classified as halogen bonds, which are directional noncovalent interactions.