Interaction of aminoazoles with Meldrum’s acid and dialkyl ketones or cyclohexanone

Interaction of 3-amino-5-methylpyrazole, 3-amino-5-methylthio-, and 3,5-diamino-1,2,4-triazole with Meldrum’s acid, acetone, ethyl methyl ketone, and cyclohexanone leads to alkyl-substituted pyrazolo[3,4-b]pyridin-6-ones and 1,2,4-triazolo[1,5-a]pyrimidin-7-ones respectively. The structure of 5,5-dimethyl-2-methylthio-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5-a]pyrimidin-7-one was demonstrated by an X-ray structural investigation. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 595–601, April, 2007.     

Study on the nature of interaction of BrCl with HF,H2O,and NH3

By counterpoise‐corrected optimization method, the interactions of BrCl with the first‐row hydrides (HF, H₂O, NH₃) have been investigated at the MP2/6–311++G(3d,3p) level. To understand that the X? Br‐type (X = F, O, N) structure is more stable than the corresponding hydrogen‐bonded structure in these complexes, the electronic properties were also investigated. Symmetry‐adapted perturbation theory (SAPT) analysis has been carried out to understand the nature of the weak hydrogen bond and X? Br‐type interactions. On the other hand, for the weak hydrogen‐bonded complexes and the X? Br‐type complexes charges transfer is well correlated with the total induction energies. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Zhang–Zhang Polynomials of Multiple Zigzag Chains Revisited: A Connection with the John–Sachs Theorem

Multiple zigzag chains Zm,n of length n and width m constitute an important class of regular graphene flakes of rectangular shape. The physical and chemical properties of these basic pericondensed benzenoids can be related to their various topological invariants, conveniently encoded as the coefficients of a combinatorial polynomial, usually referred to as the ZZ polynomial of multiple zigzag chains Zm,n. The current study reports a novel method for determination of these ZZ polynomials based on a hypothesized extension to John–Sachs theorem, used previously to enumerate Kekulé structures of various benzenoid hydrocarbons. We show that the ZZ polynomial of the Zm,n multiple zigzag chain can be conveniently expressed as a determinant of a Toeplitz (or almost Toeplitz) matrix of size m2×m2 consisting of simple hypergeometric polynomials. The presented analysis can be extended to generalized multiple zigzag chains Zkm,n, i.e., derivatives of Zm,n with a single attached polyacene chain of length k. All presented formulas are accompanied by formal proofs. The developed theoretical machinery is applied for predicting aromaticity distribution patterns in large and infinite multiple zigzag chains Zm,n and for computing the distribution of spin densities in biradical states of finite multiple zigzag chains Zm,n.     

Parameter identification of thermophilic anaerobic degradation of valerate

The considered mathematical model of the decomposition of valerate presents three unknown kinetic parameters, two unknown stoichiometric coefficients, and three unknown initial concentrations for biomass. Applying a structural identifiability study, we concluded that it is necessary to perform simultaneous batch experiments with differenitial conditions for estimating these parameters. Four simultaneous batch experiments were conducted at 55°C, characterized by four different initial acetate concentrations. Product inhibition of valerate degradation by acetate was considered. Practical identification was done optimizing the sum of the multiple determination coefficients for all measured state viariables and for all experiments simultaneously. The estimated values of kinetic parameters and stoichiometric coefficients were characterized by the parameter correlation matrix, the confidence interval, and the student's t-test at 9% significance level with positive results except for the saturation constant, for which more eperiments for improving its identifiability should be conducted. In this article, we discussekinetic parameter estimation methods.     

Stereoselective synthesis of (Z)-γ-cyano-β-perfluoroalkyl-β,γ-unsaturated esters

(Z)-γ-Cyano-β-perfluoroalkyl-β,γ-unsaturated esters have been synthesized by the reaction of perfluoroacylated phosphonates with organozinc reagent in 50-71% (three steps) yields.     

Electrochemical response of ascorbic acid at conducting and electrogenerated polymer modified electrodes for electroanalytical applications: a review

The present short review deals with electroanalytical aspects of electrochemical response of ascorbic acid (Vitamin C) at conducting and electrogenerated polymer modified electrodes. Two main topics are considered: (i) electrocatalytic oxidation of ascorbate at conducting polymer modified electrodes, leading to electroanalytical techniques for ascorbate assay, and (ii) retardation of ascorbate penetration through a layer of electrogenerated polymers, leading to permselective coatings and their diverse uses, especially for biosensing devices.     

Determination of selenium, zinc and cadmium in antidandruff shampoos by atomic spectrometry after microwave assisted sample digestion

Microwave assisted pre-treatments for atomic spectrometric determination (inductive coupled plasma-optical emission spectrometry, ICP-OES or flame atomic absorption spectrometry, FAAS) of metallic elements, usually present in antidandruff shampoos, are proposed. They are based on the digestion of the sample with HNO₃ into a closed reactor, which is irradiated at 800 W for a few minutes. Selenium was determined by ICP-OES. The limit of detection was 0.11 mg l⁻¹; the relative standard deviation (R.S.D.) for the selenium content in the samples was in the 0.6–3.6% range. The results obtained were in agreement with the label contents and the recovery of the proposed method was in the 100–106% range. Zinc and cadmium were determined by FAAS. The limit of detection for zinc determination was 0.078 mg l⁻¹; the R.S.D. for zinc contents was in the 0.8–8.6% range. A limit of detection of 0.09 mg l⁻¹ was obtained for cadmium determination; the R.S.D. for cadmium contents was in the 0.7–2.7% range. The determinations were performed after two different sample mineralization pre-treatments — dry ashing (in an electric furnace) and wet mineralization (in a microwave oven). Both methodologies provided comparable results for zinc and cadmium determination in shampoos. The proposed microwave assisted digestion procedures allow a precise and accurate determination of selenium, zinc and cadmium in commercial antidandruff shampoos, and the sample pre-treatment is less time-consuming than the classic methods.     

Fermentation characteristics and the dynamic trend of chemical components during fermentation of Massa Medicata Fermentata

As a representative of traditionally fermented Chinese medicine, Massa Medicata Fermentata (MMF) shows the functions of invigorating the spleen and stomach and promoting digestion, which plays an important role in the treatment of gastrointestinal diseases. The fermentation mechanism and the key factors that affect the quality of MMF have not been revealed yet, which has become an urgent issue that limits its clinical application. This article aims to systematically and comprehensively reveal the transformation of physical properties and the dynamic trend of chemical components including substrate components, volatile components, and lactic acid as anaerobic fermentation product during MMF fermentation. Along with obvious hyphae growth observed for MMF, the weight of MMF decreased, and the moisture and temperature increased. Through the quantified 14 components from substrate, ferulic acid increased from 45.53 ± 6.94 to 141.89 ± 78.40 μg/g, while glycosides and phenolic acids declined except caffeic acid. Also, within the 66 volatile components analyzed, alcohols and acids increased, while aldehydes and ketones decreased. Lactic acid was not detected in the fermentation substrate, but an apparent increase in lactic acid content was observed along with the increased fermentation days, resulting in 2.54 ± 0.15 mg/g on day 8. Based on the tested components, the fermentation process of MMF was discriminated into three distinct stages by principal component analysis, and an optimal fermentation time of four days was proposed. The results of this study will be of great significance to clarify the characteristics of fermentation and conduce to improving quality standards of MMF.     

Copper(II) tetrafluoroborate as a novel and highly efficient catalyst for Michael addition of mercaptans to α,β-unsaturated carbonyl compounds

Copper(II) tetrafluoroborate has been found to be a new and highly efficient catalyst for Michael addition of thiols to α,β-unsaturated carbonyl compounds under solvent-free conditions and in H₂O at room temperature. The reactions are very fast and are completed in 2 min to 1 h affording high yields. The rate of thiol addition was dependent on the steric hindrance at the β-carbon of the α,β-unsaturated carbonyl substrate. In the case of chalcones, the reactions are best carried out in MeOH as solvent.     

Structural evolution of (Ca0.35Sr0.65)TiO3 perovskite at high pressures

Lattice parameters of a synthetic powder sample of Ca_0.35Sr_0.65TiO₃ perovskite have been determined by the method of Le Bail refinement, using synchrotron X-ray diffraction patterns collected at pressures up to 15.5 GPa with a membrane-driven diamond anvil cell. At ambient conditions, diffraction data were consistent with the I4/mcm structure reported previously in the literature for the same composition. Diffraction data collected at high pressures were consistent with tetragonal (or, at least, pseudo-tetragonal) lattice geometry, and no evidence was found for the development of any of the orthorhombic structures identified in other studies of (Ca, Sr)TiO₃ perovskites. Additional weak reflections, which could not be accounted for by the normal I4/mcm perovskite structure, were detected in diffraction patterns collected at pressures of 0.9-2.5 GPa, and above ∼13.5 GPa, however. Small anomalies in the evolution of unit cell volume and tetragonal strain were observed near 3 GPa, coinciding approximately with breaks in slope with increasing pressure of bulk and shear moduli for a sample with the same composition which had previously been reported. The anomalies could be due either to new tetragonal↔tetragonal/pseudo-tetragonal phase transitions or to subtle changes in compression mechanism of the tetragonal perovskite structure.