Thermokinetic studies of organotin(IV) carboxylates derived from para-methoxyphenylethanoic acid

Thremogravimetric (TG) studies of a new series of organotin(IV) carboxylates of the general formula R_nSnL_4-n (where R = CH₃, C₂H₅, C₄H₉, C₆H₅, C₆H₁₁ and C₈H₁₇, n = 2, 3 and L = para-methoxyphenylethanoate anion) have been carried out. Horowitz and Metzger method has been used to calculate thermokinetic parameters. It has been found that diorganotin dicarboxylates have larger activation energy than those of corresponding triorganotin carboxylates. Furthermore, the activation energy, Gibb’s free energy, entropy and enthalpy of diorganotin compounds shows the following trend, (CH₃)₂SnL₂ < (C₂H₅)₂SnL₂ < (C₄H₉)₂SnL₂ < (C₈H₁₇)₂SnL₂. This is attributed to steady increase in chain length of the alkyl groups. However, triorganotin compounds do not show such behavior.     

The crystallographic and magnetic characteristics of Sr2CrO4 (K2NiF4-type) and Sr10(CrO4)6F2 (apatite-type)

Solid-state reaction between SrCO₃, Cr₂O₃ and SrF₂ has produced the apatite phase Sr₁₀(CrO₄)₆F₂ and Sr₂CrO₄ which adopts the K₂NiF₄-type structure. The reaction outcome was very sensitive to the heating rate with rapid rise times favouring the formation of Sr₂CrO₄, which has been synthesised at ambient pressure for the first time. Powder X-ray diffraction and electron diffraction confirmed that Sr₂CrO₄ adopts a body centred tetragonal cell (space group I4/mmm) with lattice parameters a=3.8357(1) Å and c=12.7169(1) Å, while a combination of neutron and X-ray diffraction verified Sr₁₀(CrO₄)₆F₂ is hexagonal (space group P6₃/m) with lattice parameters a=9.9570(1) Å and c=7.4292(1) Å. X-ray photoelectron spectroscopy and magnetic measurements were used to characterise the oxidation states of chromium contained within these phases.     

A hybrid simplex search and particle swarm optimization for unconstrained optimization

This paper proposes the hybrid NM-PSO algorithm based on the Nelder–Mead (NM) simplex search method and particle swarm optimization (PSO) for unconstrained optimization. NM-PSO is very easy to implement in practice since it does not require gradient computation. The modification of both the Nelder–Mead simplex search method and particle swarm optimization intends to produce faster and more accurate convergence. The main purpose of the paper is to demonstrate how the standard particle swarm optimizers can be improved by incorporating a hybridization strategy. In a suite of 20 test function problems taken from the literature, computational results via a comprehensive experimental study, preceded by the investigation of parameter selection, show that the hybrid NM-PSO approach outperforms other three relevant search techniques (i.e., the original NM simplex search method, the original PSO and the guaranteed convergence particle swarm optimization (GCPSO)) in terms of solution quality and convergence rate. In a later part of the comparative experiment, the NM-PSO algorithm is compared to various most up-to-date cooperative PSO (CPSO) procedures appearing in the literature. The comparison report still largely favors the NM-PSO algorithm in the performance of accuracy, robustness and function evaluation. As evidenced by the overall assessment based on two kinds of computational experience, the new algorithm has demonstrated to be extremely effective and efficient at locating best-practice optimal solutions for unconstrained optimization.     

Synthesis and kinetic modeling of biomass‐derived renewable polyesters

The biomass‐derived polyesters poly(1,3‐propylene 2,5‐furandicarboxylate) (PPF), poly(1,3‐propylene succinate) (PPS) and poly(1,3‐propylene 2,5‐furandicarboxylate‐co‐1,3‐propylene succinate) (PPFPS) have been synthesized via a two‐step process involving polycondensation and azeotropic distillation. The kinetic parameters were obtained by fitting the experimental data from a batch polymerization reactor to three different kinetic models for polyesterification reactions. The activation energies of the all monomer systems were obtained by Arrhenius plots. Given the increasing availability of biomass‐derived monomers their use in renewable polyesters as substitutes for fossil fuel derived chemicals becomes a distinct possibility. The kinetic modeling of the uncatalyzed polyesterification reactions will enable further integrative process simulation of the studied bioderived polymers and provide a reference for future practical study or industrial applications of catalyzed polyesterification reactions and other bioderived monomer systems. © 2016 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2876–2887     

Using HPLC–DAD and GC–MS Analysis Isolation and Identification of Anticandida Compounds from Gui Zhen Cao Herbs (Genus Bidens): An Important Chinese Medicinal Formulation

Gui Zhen Cao is an herbal formulation that has been documented in Chinese traditional medicine as a remedy for diarrhea, dysentery, inflammation, and toxicity. The sources of this formulation (Bidens pilosa L., Bidens biternata (Lour.) Merr. & Sherff, Bidens bipinnata L.) are also listed in ethnomedicinal reports all over the world. In this study, all these plants are tested for in vitro anticandida activity. A quantitative evaluation of the phytochemicals in all these plants indicated that their vegetative parts are rich in tannins, saponins, oxalates, cyanogenic glycoside and lipids; moreover, the roots have high percentages of alkaloids, flavonoids, and phenols. The results indicated significant anticandida activity, especially for the hexane extract of B. bipinnata leaves which inhibited C. albicans (42.54%), C. glabrata (46.98%), C. tropicalis (50.89%), C. krusei (40.56%), and C. orthopsilosis (50.24%). The extract was subjected to silica gel chromatography and 220 fractions were obtained. Purification by High Performance Liquid Chromatography with Diode-Array Detection (HPLC–DAD) and Gas Chromatography tandem Mass Spectrometry (GC-MS/MS) analysis led to the identification of two anticandida compounds: dehydroabietic and linoleic acid having an inhibition of 85 and 92%, respectively.