Alkenyl selenols and selenocyanates: synthesis, spectroscopic characterization by photoelectron spectroscopy, and quantum chemical study

Vinyl, allyl, and homoallyl selenols were easily prepared by a chemoselective reduction of the corresponding selenocyanates with aluminum hydrides. Two stable vinyl and five stable allyl conformers of both series were predicted on the potential-energy surface. The interaction of SeH or SeCN groups with the vinyl group has been investigated with UV photoelectron spectroscopy and quantum chemical calculations, using the MP2/cc-pVTZ and B3LYP/cc-pVTZ levels. In the vinyl derivatives, a surprisingly strong direct conjugation of the selenium lone electron pair and the C=C double bond was observed. On the other hand, in allyl position the selenium lone pair is independent on the C=C double bond, and the hyperconjugation between the Se-C bond and the double bond is the ruling effect. Thus is clarified the type and extent of the interaction between the SeH or SeCN group and the unsaturated moiety.     

A Convenient Regiospecific Synthesis of New Conjugated Tetrazole Derivatives via the Reaction of Dienones with the Tetrachlorosilane-Sodium Azide Reagent and their NMR Structural Assignment

Several new 1-aryl-, aralkyl-, and heteroaryl-5-(4-phenylbuta-1,3-dienyl)tetrazole derivatives and annulated tetrazole derivatives were efficiently and regiospecifically prepared in nearly quantitative yield via a facile one step reaction of dienones with a combination of tetrachlorosilane and sodium azide in acetonitrile under mild conditions. A complete structure assignment of three representative examples of the tetrazoles was achieved by advanced 2D NMR measurements including COSY, TOCSY, HSQC, HMBC, NOESY, and ROESY experiments.     

An overview of laboratory performance studies conducted by the IAEA for marine pollution studies of metals and organic contaminants

Aspects of the International Atomic Energy Agency (IAEA) Analytical Quality Control Services (AQCS) for marine environmental studies are discussed, focusing on recent laboratory performance studies (LPS) and the production of reference materials for trace metals and organic compounds in various marine matrices. The IAEA has organized seventeen global interlaboratory studies for a range of organic contaminants. Of note has been the inclusion of numerous polychlorinated biphenyl congeners (PCBs) and some sterols of anthropogenic origin. Concurrently, there have been eleven worldwide intercomparison exercises for trace metals in the marine environment, most of which included methylmercury. Although such interlaboratory studies can help improve performance in individual laboratories and regional laboratory networks, the results reveal that problems remain in the determination of some metals and many organic contaminants.     

CuSO<Subscript>4</Subscript> as a Mild,Green, and Efficient Catalyst for the One-pot Conversion of <Emphasis Type="Italic">THP</Emphasis> Ethers to Acetates

Summary. An efficient direct conversion of THP ethers into the corresponding acetates was achieved with acetic anhydride in the presence of CuSO₄ · 5H₂O as an available and green catalyst in high yields.     

Fenugreek mucilage as a flocculating agent for sewage treatment

The use of fenugreek mucilage, a natural polysaccharide and a direct food additive, as a flocculating agent for removal of suspended and dissolved solids from sewage effluent has been reported. A flocculation study has been done by the standard jar test method. The percent removal of suspended solid (SS) and dissolved solid (TDS) was determined by varying the polymer dose, pH and contact time. X-ray diffraction patterns of the solid waste material of mucilage and flocs (so obtained after treatment) were used to suggest the incorporation of the crystalline waste material in the mucilage. The optimal mucilage concentration was found to be 0.16 mg/l. The suitable pH range for maximum solid removal (SS and TDS) was alkaline and the time required for treatment was 1-3 h.     

Evaluation of measurement uncertainty for analytical procedures using a linear calibration function

In the EURACHEM/CITAC draft ”Quantifying uncertainty in analytical measurement” estimations of measurement uncertainty in analytical results for linear calibration are given. In this work these estimations are compared, i.e. the uncertainty deduced from repeated observations of the sample vs. the uncertainty deduced from the standard residual deviation of the regression. As a result of this study it is shown that an uncertainty estimation based on repeated observations can give more realistic values if the condition of variance homogeneity is not correctly fulfilled in the calibration range. The complete calculation of measurement uncertainty including assessment of trueness is represented by an example concerning the determination of zinc in sediment samples using ICP-atomic emission spectrometry. Received: 9 February 2002 Accepted: 17 April 2002     

An expeditious,solvent-free synthesis of some 5-aryl-2-(2-hydroxyphenyl)-1,3,4-oxadiazoles

An efficient, rapid, microwave-accelerated one-step synthesis of some 5-aryl-2-(2-hydroxy-phenyl)-1,3,4-oxadiazoles by reaction of salicylic hydrazide with carboxylic acids in the presence of thionyl chloride under neat conditions is described. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1264–1267, August, 2007.     

Relativistic calculations on the ground and excited states of AgH and AuH in cylindrical harmonic confinement

The relativistic ground and low-lying excited state potential energy curves of AgH and AuH in the presence of a cylindrical harmonic confining potential were calculated using the multi-state multi-reference perturbation theory with the spin-free no-pair Hamiltonian obtained via the third-order Douglas–Kroll transformation, incorporated with the full two-electron Breit–Pauli spin–orbit operator. The spectroscopic parameters were obtained for both the scalar- and quasi-relativistic potentials. The spin–orbit coupling constants were calculated for several strengths of the confining potential, and the effects of the applied potential on the coupling constants were analyzed using configuration interaction. This paper is dedicated to Serafín Fraga—colleague, mentor, and friend.     

Drag on two nonuniformly structured flocs moving along the axis of a cylindrical tube

The boundary effect on the drag on two identical, nonuniformly structured flocs moving along the axis of a cylindrical tube filled with a Newtonian fluid is investigated at a small to medium larger Reynolds number. A two-layer model is adopted to simulate various possible structures of a floc, and the flow field inside is described by Darcy–Brinkman model. The results of numerical simulation reveal that a convective flow is present in the rear region of a floc when Reynolds number is on the order of 40. The presence of the tube wall and/or the porous structure of a floc has the effect of reducing that convective flow. For a fixed level of the volume-average permeability of a floc, the influence of the tube wall on the drag depends upon floc structure; the influence on a nonuniformly structured floc is more significant than that on a uniformly structured floc. The more nonuniform the floc structure, the more appreciable the deviation of the drag coefficient–Reynolds number curve from a Stokes’-law-like relation becomes. The smaller the volume-average permeability of a floc and/or the smaller the separation distance between the two flocs, the greater is the deviation, but the presence of the tube wall has the effect of reducing that deviation.     

Capillary electrochromatography with monolithic silica columns III. Preparation of hydrophilic silica monoliths having surface-bound cyano groups: chromatographic characterization and application to the separation of carbohydrates, nucleosides, nucleic acid bases and other neutral polar species

Two synthetic routes have been introduced and evaluated for the preparation of hydrophilic silica-based monoliths possessing surface-bound cyano functions. In one synthetic scheme, the silica monolith was reacted in a single step with 3-cyanopropyldimethylchlorosilane to yield a cyano phase referred to as CN-monolith. In a second synthetic route, the silica monolith was first reacted with gamma-glycidoxypropyltrimethoxysilane (gamma-GPTS), followed by a reaction with 3-hydroxypropionitrile (3-HPN) to give a stationary phase denoted CN-OH-monolith. Although the gamma-GPTS was intended to play the role of a spacer arm to link the 3-HPN to the silica surface, this spacer arm became an integral part of the hydrophilic stationary phase. Thus, the CN-OH-monolith can be viewed as a double-layered stationary phase (i.e., stratified phase) with a hydroxy sub-layer and a cyano top layer. Due to its stronger hydrophilic character, the CN-OH-monolith yielded higher retention and better selectivity than the CN-monolith. The CN-OH-monolith was demonstrated in the normal-phase capillary electrochromatography (CEC) of various polar compounds including phenols and chloro-substituted phenols, nucleic acid bases, nucleosides, and nitrophenyl derivatives of mono- and oligosaccharides. The CN-OH-monolith yielded a relatively strong electroosmotic flow over a wide range of mobile phase composition, thus allowing rapid separation of the polar compounds studied.