Laccase-catalyzed carbon-carbon bond formation: oxidative dimerization of salicylic esters by air in aqueous solution

The laccase catalyzed oxidative dimerization of salicylic esters, a rare example of a laccase-catalyzed carbon-carbon bond formation, was studied. This reaction allows the use of air as stoichiometric oxidant and proceeds in aqueous solution. The preparative scope and the mechanism of the method, which provides a new and convenient access to functionalized biaryls under mild conditions, were investigated.     

Synthesis and screening of some novel substituted indoles contained 1,3,4-oxadiazole and 1,2,4-triazole moiety

A series of novel 3-[5-(1H-indol-3-yl-methyl)-2-oxo-[1,3,4]oxadiazol-3-yl]propionitrile(5),3-[4- amino-3-(1H-indol-3-yl-methyl)-5-oxo-4,5-dihydro-[1,2.4]triazol-1-yljpropionitrile(6),3-[5-(1H- indol-3-yl-methyl)-2-thioxo-[1,3,4]oxadiazol-3-yl]propionitrile(7) and 3-[4-amino-3-(1H-indol-3-yl-methyl) -5-thioxo-4,5-dihydro-[1,2,4]triazol-l -yljpropionitrile(8) were synthesized in good yields from the intermediate(1H-indol-3-yl)-acetic acid N’-(2-cyanoethyl)hydrazide(4).The chemical structures of the newly synthesized compounds were elucidated by their IR,~1H NMR and MS.Further,all the compounds were screened for their antimicrobial activity against Gram-positive,Gram-negative bacteria and also tested their ability toward anti-inflammatory activity.     

Electron Emission from Nickel-Alloy Surfaces in Cesium Vapor

The cesiated electron emission was measured for three candidate electrodes for use as collectors in thermionic converters. Nickel, Inconel 600 and Hastelloy were tested with a 412°K cesium reservoir. Peak emission from the alloys was found to be comparable to that from pure nickel. Both the Inconel and the Hastelloy samples had work functions of 1.64 ev at peak emission. The minimum work functions were estimated to be 1.37 ev at a probe temperature of 750°K for Inconel and 1.40 ev for Hastelloy at 665°K. The bare work function for both alloys is estimated to be approximately the same as for pure nickel, 4.8 ev.     

New cloud vapor zone (CVZ) coupled headspace solid-phase microextraction technique

A new cloud vapor zone (CVZ)-based headspace solid-phase microextraction (HS-SPME) technique has been demonstrated with the capability of heating the sample matrix and simultaneously cooling the sampling zone. A bi-temperature-controlled (BTC) system, allowing 10 mL of test sample heating and headspace external-cooling, was employed for the CVZ formation around the SPME-fiber sampling area. In the CVZ procedure, the heated headspace vapor undergoes a sudden cooling near the SPME to form a dense cloud of analyte–water vapor, which is helpful for adsorption or absorption of the analyte. The device was evaluated for the quantitative analysis of aqueous chlorothalonil. Parameters influencing sampling efficiency, e.g., SPME fiber coating, SPME sampling temperature and time, solution modifier, addition of salt, sample pH, and temperature, were investigated and optimized thoroughly. The proposed BTC-HS-SPME method afforded a best extraction efficiency of above 94% accuracy (less than 4.1% RSD, n = 7) by using the PDMS fiber to collect chlorothalonil in the headspace at 5 °C under the optimized condition, i.e., heating sample solution (added as 10% ethylene glycol and 30% NaCl, at pH 7.0) at 130 °C for 15 min. The detection was linear from 0.01 to 80 μg L⁻¹ with a regression coefficient of 0.9998 and had a detection limit of 3.0 ng L⁻¹ based on S/N = 3. Practical application was demonstrated by analyzing chlorothalonil in farm water samples with promising results and recoveries. The approach provided a very simple, fast, sensitive, and solvent-free procedure to collect analytes from aqueous solution. The approach can provide a new platform for other sensitive HS-SPME assays.     

An efficient microwave accelerated three component reaction of phenacyl azides and pyridinium phenacyl salts: A facile greener approach to 2-amino-2-ene-1,4-diones/pyrrolidin-2-ones

Abstract

A mild and efficient base promoted, microwave assisted, green synthesis of 2-amino-2-ene-1,4-diones has been described by the decomposition of phenacyl azides followed by treatment with pyridinium salts of phenacyl bromides in aqueous media. A diverse range of substrates bearing electron-releasing and electron-withdrawing substituents were well tolerated and delivered corresponding 2-amino-2-ene-1,4-diones in good yields. Synthesized 2-amino-2-ene-1,4-diones have been further explored in the synthesis of various substituted 4-hydroxypyrrolidin-2-ones.     

A nonlinearly preconditioned conjugate gradient algorithm for rank‐R canonical tensor approximation

Alternating least squares (ALS) is often considered the workhorse algorithm for computing the rank‐R canonical tensor approximation, but for certain problems, its convergence can be very slow. The nonlinear conjugate gradient (NCG) method was recently proposed as an alternative to ALS, but the results indicated that NCG is usually not faster than ALS. To improve the convergence speed of NCG, we consider a nonlinearly preconditioned NCG (PNCG) algorithm for computing the rank‐R canonical tensor decomposition. Our approach uses ALS as a nonlinear preconditioner in the NCG algorithm. Alternatively, NCG can be viewed as an acceleration process for ALS. We demonstrate numerically that the convergence acceleration mechanism in PNCG often leads to important pay‐offs for difficult tensor decomposition problems, with convergence that is significantly faster and more robust than for the stand‐alone NCG or ALS algorithms. We consider several approaches for incorporating the nonlinear preconditioner into the NCG algorithm that have been described in the literature previously and have met with success in certain application areas. However, it appears that the nonlinearly PNCG approach has received relatively little attention in the broader community and remains underexplored both theoretically and experimentally. Thus, this paper serves several additional functions, by providing in one place a concise overview of several PNCG variants and their properties that have only been described in a few places scattered throughout the literature, by systematically comparing the performance of these PNCG variants for the tensor decomposition problem, and by drawing further attention to the usefulness of nonlinearly PNCG as a general tool. In addition, we briefly discuss the convergence of the PNCG algorithm. In particular, we obtain a new convergence result for one of the PNCG variants under suitable conditions, building on known convergence results for non‐preconditioned NCG. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and characterisation of Pd(II) complexes with a derivative of aminoazobenzene: Dynamic H-NMR study of cyclopalladation reactions in DMF

Three new Pd(II) complexes, i.e. [PdCl₂L]₂ (A), PdCl₂L₂ (B) and [Pd(μ-Cl)(L-H)]₂ (C), each with two diethyl [α-(4-benzenazoanilino)-2-hydroxybenzyl]phosphonates (L) bound to either one or two palladium atoms, are synthesized and characterized by elemental analysis, by IR, UV-vis and solid-state ¹³C-NMR spectra. Complexes B and C are additionally characterized by ¹H-, ¹³C- and ³¹P-NMR and electrospray mass spectrometry (ESMS) studies using dimethylformamide (DMF) as a solvent. In DMF solution adducts A and B undergo spontaneous rearrangement into the cyclopalladated complex C. Dynamic ¹H-NMR study of this rearrangement as well as of the reactions of L with PdCl₂ and Na₂PdCl₄ revealed a complex equilibrium in DMF solutions and enabled the formation mechanism of all involved species to be resolved. The complex A is immediately solvolyzed producing two molecules of intermediate M [PdCl₂(L)(DMF)]. Complex M was also the first intermediate in the reaction of L with PdCl₂. Once present in concentration above 10⁻⁵ mol dm⁻³M dimerizes very fast into chloro-bridged dimer [PdCl(μ-Cl)(L)]₂ (D) which undergoes cyclopalladation and converts into the complex C. The formation of C from the intermediate D is clearly demonstrated by the concentration dependence of the cyclopalladation reaction which has order greater than one. Chloride ions, released by cyclopalladation, react with D by splitting chloro-bridge and binding to metal atoms to produce byproduct [PdCl₃(L)]⁻ (T). The same species T are formed in the reaction of L with Na₂PdCl₄ whereby a chloride ion is replaced by the ligand L. The complex B undergoes similar, but slower, solvolytic reaction producing M and L while further reaction steps are identical as in the solvolysis of A.     

[RuCl2(p-cymene)2]2 catalyzed cross dehydrogenative coupling (CDC) toward xanthone and fluorenone analogs through intramolecular C–H bond functionalization reaction

A synthetic approach toward xanthone and fluorenone derivatives through ruthenium catalyzed intra-molecular C–H bond functionalization using an external oxidant has been developed. In the presence of [RuCl₂(p-cymene)₂]₂, a variety of substituted ortho-aryloxy/aryl benzaldehydes underwent cross dehydrogenative coupling to afford the corresponding analogs in moderate to good yields.