A 3D-analysis of the Cl?�Cbenzene dimer solvation by Ar atoms

The solvation of the Cl^??Cbenzene (Cl^??CBz) aggregate by Ar atoms has been investigated employing molecular dynamics (MD) simulations. The gradual evolution from cluster rearrangement to solvation dynamics is discussed by considering ensembles of n (n = 1,...,30) Ar atoms around the Cl^??CBz clusters. The energetic of the solvated cluster is decomposed as a sum of pairs (including both the Ar?CAr and the Cl^??CAr terms), Cl^??CBz and Ar?CBz interactions and their relative contributions are analyzed as a function of the cluster size. The geometrical distribution of Ar atoms around Cl^??CBz is investigated in terms of radial distribution functions (RDF), bidimensional (2D) angular distributions and tridimensional (3D) probability densities. The variation on the spatial distribution of the Ar atoms around Cl^??CBz when the Ar number increases is investigated from a novel prospective, employing spherical coordinates of the solvent atoms within an inertial reference frame. Isomerization processes are also studied.     

Measurement of the change in the partial molar volume during electrode reaction by gravity electrode—I. Theoretical examination

Gravity electrode is an electrode system, which is operated in a high gravity field arising from centrifugal force, and allows us to measure the change in the partial molar volume between product and reactant ions in an electrode reaction. In this paper, in the presence of a large amount of supporting electrolyte, the partial molar volume of each active ion in equilibrium state is first formulated on the basis of thermodynamics. Then, the change in the partial molar volume applicable to gravity electrode is derived. Therefore, it is possible to validate the equation obtained for gravity electrode by the thermodynamic measurement.     

Reconstruction of the 3D coordinates of α-carbon atoms of proteins from a pair of stereographic figures

Summary In an attempt to promptly use the experimentally determined structures of proteins in modeling studies, we have developed the program ReconstC to generate the 3D coordinates of -carbon atoms from a pair of stereographic figures. Calculations of the 3D coordinates were performed by estimating the stereo parameters systematically. Geometrical features of C traces were used to evaluate the integrity of the calculated structure. The program was applied to four kinds of protein structures to examine the performance. It was found that the root-mean-square deviation of atomic positions between constructed and reference crystal structures ranged from 0.36 to 0.78 Å. The range represents a reasonable accuracy and its automatic feature suggests that our approach would be expedient for providing initial structures for protein modeling studies.     

Development of an analytical method for the determination of the residues of four pyrethroids in meat by GC–ECD and confirmation by GC–MS

The development of an analytical method for the determination of four selected pyrethroid insecticides at residue level in beef meat is presented. Acetone and petroleum ether at 40-60 degrees C were chosen as extraction solvents. A two-step clean-up was performed using an Extrelut NT3-C(18) system followed by a Florisil column, with disposable, ready-to-use cartridges. Instrumental analysis was carried out on a gas chromatograph equipped with an electron capture detector (GC-ECD), using matrix-matched and internal standard calibration techniques. Confirmatory analysis by GC-MS was performed. Recoveries at the EU Maximum Residue Limit (MRL), 0.5 x MRL and 1.5 x MRL levels and the repeatabilities were widely satisfactory. The main advantage of the method was the reduction of analysis time as compared with previously published works. The applicability of the method to different matrices and pesticide classes will be investigated.     

One-step Synthesis of ε-Caprolactam by the Liquid Phase Nitrosation of Cyciohexane over the Catalysts Containing CH3COO-or-COOH

ε-Caprolactam（CL or CPL） is one of the most important intermediates used in polymer industry for the production of several million tons of nylon-6 every year^[1]. All current commercial processes for the production of caprolactam are based on either benzene or tolueneI21. Caprolactam is synthesized by the Beckmann rearrangement of cyclohexanone oxime with fuming sulfuric acid or sulfuric acid as the reaction medium, and cyclohexanone oxime is produced by the reaction between cyclohexanone and hydro- xylamine（only one exception is the Toray PNC process）.     

One-step Synthesis of ε-Caprolactam by the Liquid Phase Nitrosation of Cyciohexane over the Catalysts Containing CH3COO-or-COOH

ε-Caprolactam(CL or CPL) is one of the most important intermediates used in polymer industry for the production of several million tons of nylon-6 every year[1].All current commercial processes for the production of caprolactam are based on either benzene or toluene[2].     

Unimolecular reactions in the CF3CH2Cl ↔ CF2ClCH2F system: isomerization by interchange of Cl and F atoms

The recombination of CF(2)Cl and CH(2)F radicals was used to prepare CF(2)ClCH(2)F* molecules with 93 ± 2 kcal mol(-1) of vibrational energy in a room temperature bath gas. The observed unimolecular reactions in order of relative importance were: (1) 1,2-ClH elimination to give CF(2)═CHF, (2) isomerization to CF(3)CH(2)Cl by the interchange of F and Cl atoms and (3) 1,2-FH elimination to give E- and Z-CFCl═CHF. Since the isomerization reaction is 12 kcal mol(-1) exothermic, the CF(3)CH(2)Cl* molecules have 105 kcal mol(-1) of internal energy and they can eliminate HF to give CF(2)═CHCl, decompose by rupture of the C-Cl bond, or isomerize back to CF(2)ClCH(2)F. These data, which provide experimental rate constants, are combined with previously published results for chemically activated CF(3)CH(2)Cl* formed by the recombination of CF(3) and CH(2)Cl radicals to provide a comprehensive view of the CF(3)CH(2)Cl* ? CF(2)ClCH(2)F* unimolecular reaction system. The experimental rate constants are matched to calculated statistical rate constants to assign threshold energies for the observed reactions. The models for the molecules and transition states needed for the rate constant calculations were obtained from electronic structures calculated from density functional theory. The previously proposed explanation for the formation of CF(2)═CHF in thermal and infrared multiphoton excitation studies of CF(3)CH(2)Cl, which was 2,2-HCl elimination from CF(3)CH(2)Cl followed by migration of the F atom in CF(3)CH, should be replaced by the Cl/F interchange reaction followed by a conventional 1,2-ClH elimination from CF(2)ClCH(2)F. The unimolecular reactions are augmented by free-radical chemistry initiated by reactions of Cl and F atoms in the thermal decomposition of CF(3)CH(2)Cl and CF(2)ClCH(2)F.     

A Novel 2D→3D Network with the Coexistence of Polythreading and Inclined Polycatenation Constructed by the Tripodal Linker

A new cadmium(II) coordination polymer with unique structure was synthesized under diffusion process by employing triangular N-containing ligand tris(4-(pyridyl) phenyl) amine(Tppa). Complex 1 crystallizes in the space group Pbcn, with a = 28.906(3), b = 13.5294(14), c = 17.8727(18), V = 6989.7(12) 3, C66H48 Cd Cl2N8, Mr = 1136.42, Dc = 1.080 g/cm3, F(000) = 2328, μ = 0.428 mm-1 and Z = 4. Complex 1 features a 2D → 3D framework with the coexistence of inclined polycatenation and polythreading. In addition, the luminescent property of complex 1 was studied.     

Development of an analytical procedure for the determination of polybrominated diphenyl ethers in environmental water samples by GC–ICP-MS

Polybrominated diphenyl ethers (PBDEs) are flame retardants, which due to their widespread use are frequently present as pollutants in the environment. In the EU Water Framework Directive (WFD) six PBDE congeners (BDE 28, BDE47, BDE 99, BDE 100, BDE 153 and BDE 154) are listed as priority substances. The uncertainty of the analytical method used for their determination in water samples at environmental quality standard (EQS) level (0.5 ng L⁻¹ for the ΣPBDEs) should be equal or less than 50% and the limit of quantification (LOQ) for ΣPBDEs below 0.15 ng L⁻¹. To meet these requirements, an analytical procedure for the determination of these six PBDEs in environmental water samples by gas chromatography–inductively coupled plasma mass spectrometry (GC–ICP-MS) was developed. The acidification of water samples to pH 2 maintained the stability of PBDEs for at least 20 days. The use of Tris–citrate buffer enabled efficient desorption of PBDEs from suspended particulate matter (SPM) and humic acids (HA), and their further quantitative solvent extraction into 2 mL of iso-octane. When 300 mL of water sample was used for analysis and the organic phase concentrated to 25 μL, the expanded uncertainty for determination of PBDEs at EQS level was found to be around 40% (a coverage factor for a confidence level of 95%, k = 2), and the LOQ for the ΣPBDEs 0.109 ng L⁻¹. Finally, to demonstrate the applicability of the newly developed GC–ICP-MS procedure, PBDEs were determined in river and sea water samples.     

Facile Construction of the 7,8‐Olefin Linkage in Vitamin D3: A Practical Synthesis Benefiting the Vitamin D3 Analog Study

Abstract

A facile procedure for construction of the 7,8‐olefin linkage in vitamin D₃ is described. Treatment of a mixture of A‐ring phosphine oxide and CD‐ring ketone in THF with lithium hexamethyldisilazide (LHMDS) at ?20°C followed by gradual heating to 50°C gives the key intermediate of vitamin D₃ analogs in excellent yield. This simplified procedure makes possible small‐scale synthesis benefiting the vitamin D₃ analog study.     

The relevance of the nuclearity of the metal in the cocyclization of α, ω-diynes and nitriles catalyzed by mesitylene solvated cobalt atoms; preliminary EPR studies

The clustering when mesitylene-solvated cobalt atoms are allowed to warm from the cocondensation temperature, affords cobalt compounds of both low and high nuclearity which have different catalytic properties in the synthesis of pyridines from α, ω-dialkynes and nitriles.     

Elucidating 2D Charge-Density-Wave Atomic Structure in an MX–Chain by the 3D-ΔPair Distribution Function Method**

Many solids, particularly low-dimensional systems, exhibit charge density waves (CDWs). In one dimension, charge density waves are well understood, but in two dimensions, their structure and their origin are difficult to reveal. Herein, the 2D charge-density-wave atomic structure and stabilization mechanism in the bromide-bridged Pd compound [Pd(cptn)₂Br]Br₂ (cptn=1R,2R-diaminocyclopentane) is investigated by means of single-crystal X-ray diffraction employing the 3D-Δpair distribution function (3D-ΔPDF) method. Analysis of the diffuse scattering using 3D-ΔPDF shows that a 2D-CDW is stabilized by a hydrogen-bonding network between Br⁻ counteranion and the amine (NH₂) group of the cptn in-plane ligand, and that 3D ordering is prevented due to a weak plane to plane correlation. We extract the effective displacements of the atoms describing the atomic structure quantitatively and discuss the stabilization mechanism of the 2D-CDW. Our study provides a method to identify and measure the key interaction responsible for the dimensionality and stability of the CDW that can help further progress of rational design.     

Stereochemistry Control in Direct 1α-Hydroxylation of 5,6-trans-Vitamin D3 by Solid Support

1α-Hydroxyvitamin D3 1 (1α-hydroxycholecalciferol) is a biologically active form ofvitamin D3 2 which exhibits a much broader spectrum of biological activities thanvitamin D3 . 1,2 Recently a number of analogues have been found to have specificenhanceme…     

Development of an analytical procedure for the determination of emerging and priority organic pollutants in leafy vegetables by pressurized solvent extraction followed by GC–MS determination

A new multiresidue method for the determination of 13 emerging and priority pollutants in lettuce, including pesticides, pharmaceuticals, personal care products, polycyclic aromatic hydrocarbons (PAHs), and phenolic estrogens, has been developed using matrix solid-phase dispersion combined to pressurized fluid extraction (PFE) followed by gas chromatography coupled to mass spectrometry determination. A sequential optimization strategy based on solvent optimization first, followed by experimental design, was performed in order to maximize target analyte extraction with the aid of response surface methodology. Firstly, a full factorial design was applied to choose the significant variables in PFE; extraction time and temperature were found to have the biggest overall effect on response for most of analytes. They were later optimized performing a central composite design and the variable response of these factors was modeled for all analytes. It was found that marked differences in physicochemical nature exerted a strong influence on extraction conditions and yield. Therefore, the effect of parameters on the response was rather different for some compounds. To overcome this conflicting behavior, a multiple response simultaneous optimization was applied using the desirability function to achieve global optimal operating conditions. The optimal conditions were attained at 13.5 min (two extraction cycles) and 104 °C in the PFE by using hexane acetone mixture (1:1). Limit of detection and limit of quantitation values were found to be between 6.6 and 58 and 7.6 and 61.7 μg kg⁻¹, respectively.     

Magnetic canting or not? Two isomorphous 3D CoII and NiII coordination polymers with the rare non-interpenetrated (10,3)-d topological network, showing spin-canted antiferromagnetism only in the CoII system

The in situ solvothermal reaction of 3,4-dicyano-1,2,5-thiadiazole with MCl(2) (M = Co, Ni) and NaOH afforded two isomorphous complexes, [M2(L)2(H(2)O)2]n (L = 2,1,3-thiadiazole-4,5-dicarboxylate), which exhibit a rare non-interpenetrated (10,3)-d (utp) network topology and interesting magnetic behaviors: spin-canted antiferromagnetism for the Co(II) complex, but simple antiferromagnetic coupling for the Ni(II).     

Speciation analysis of chromium in drinking water samples by ion-pair reversed-phase HPLC–ICP-MS: validation of the analytical method and evaluation of the uncertainty budget

The approach presented in this article refers to the modification of a method for the detection and quantitative determination of chromium species in water by high-performance liquid chromatography inductively coupled plasma mass spectrometry. The main aim of this work was to establish a detailed validation of the analytical procedure and an estimation of the budget of measurement uncertainty which was helpful in recognizing the critical points of the presented method. As a result of the method validation experiment, the obtained limit of quantification, repeatability and intermediate precision were satisfied for the quantification Cr(III) and Cr(VI) in water matrices. The trueness of the method was verified via an estimation of the recovery of the spiked real samples. The recovery rate of both determined analytes was found to be between 93 and 115 %. Considering that the validation of the method and the evaluation of measurement uncertainty are crucial for quantitative analysis, the above-mentioned assessment of the uncertainty budget was performed in two different ways: a modelling approach and a single-laboratory validation approach. The measurement uncertainties of the results were found to be 4.4 and 7.8 % for Cr(III), 4.2 and 7.9 % for Cr(VI) using the classical concept and method validation data, respectively. This paper is the first publication to presenting all the steps needed to evaluate the measurement uncertainty for the speciation analysis of chromium species. In summary, the obtained results demonstrate that the method can be applied effectively for its intended use.     

New Procedure for the Determination of 3-Nitrotyrosine in Plasma by GC–ECD

A method suitable for the determination of 3-nitrotyrosine, a well known marker of nitro-oxidative stress, in plasma by GC–ECD has been investigated. After deproteinisation, SPE and LC separation, 3-nitrotyrosine was derivatised by a single-step procedure to the corresponding N-heptafluorobutyryl heptafluorobutyl ester and analysed. The precision and reliability of the procedure were assured by using 4-nitrophenylalanine as internal standard and a diverter valve to protect the detector. The method was applied to the analysis of volunteers’ plasma samples.     

On the inhibition of positronium formation by NO3− ions in different solvents

In previous papers [1, 2] the inhibition of the Ps formation by certain solutes was investigated and a new equation based on a hot Ps reaction model was proposed for describing the dependence of the Ps survival probability on the inhibitor concentration. In this equation a constant K appears which depends both on the reaction cross section of the solute and on the moderating power of the solvent for hot Ps atoms. It was also hypothesized that the moderating power of the solvent molecule should be linearly correlated with the number of its vibrational modes. In the present paper it is reported that the experimental results agree with this hypothesis. The results are also discussed in the framework of the model mentioned above.     

Chemiluminescence activated by Β- diketonate complexes of Eu3+ in the thermolysis of diphenyldiazomethane in the presence of oxygen

Chemiluminescence activated by the chelates Eu(tta)₃phen and Eu(dbm)₃phen in the thermal decomposition of diphenyldiazomethane in benzene in the presence of oxygen was examined at 333 K. The following photophysical characteristics of the luminescence emitter, excited triplet benzophenone (BP), were found: the phosphorescence quantum yield ϕ _BP ⁰ = 1.0 × 10⁻⁵, the true lifetime τ _BP ⁰ = 7 × 10⁻⁸ s, and the rate constant of radiative deactivationk _{r, BP} = ϕ _BP ⁰ τ _BP ^{0 −1} = 160 s⁻¹.