Capillary electrophoretic separation of dicarboxylic acids in atmospheric aerosol particles

2,3-Pyrazinedicarboxylic acid (PZDA), 2,6-pyridinedicarboxylic acid (PDA) and 2,3-pyridinedicarboxylic acid (QUIN) solutions were studied as background electrolytes (BGEs) in the capillary electrophoretic analysis of dicarboxylic acids in aerosol particles with indirect UV detection. The BGEs were selected on the basis of similarity in structure with the analytes so that mobilities would be compatible. Optimised pH values for PZDA, PDA and QUIN solutions were 10.6, 11.0 and 10.2, respectively. Myristyltrimethylammonium hydroxide and myristyltrimethylammonium bromide were added to reverse the electroosmotic flow in the solutions in the direction of anode to enable fast anion detection. Separation was obtained for nine dicarboxylic acids (C₂–C₁₀) differing in the number of CH₂ groups in their skeleton. The electrophoretic mobilities were determined to lie in the range 3.0×10⁻⁴–7.0×10⁻⁴ cm² V⁻¹ s⁻¹. The relative standard deviations (RSDs) for the absolute migration times of the analytes were mostly less than 0.5% (n=6) in PZDA solution. In PDA solution the within-day and day-to-day RSD values for migration were less than 1% and between 2 and 4%, respectively. Peak heights and areas mostly deviated between 1 and 15% in both PZDA and PDA solutions. Detection limits ranged between 1 and 5 mg/l. Methods were applied to the analysis of dicarboxylic acids isolated from aerosol particles.     

Conformational isomerization of formic acid by vibrational excitation at energies below the torsional barrier

Photoinduced conformational isomerization of formic acid has been studied in a low-temperature argon matrix. It is found that conformational isomerization occurs when the photon energy is below the energy barrier for this process. The quantum yield for the process near the top of the barrier is comparable with the quantum yield above the barrier and drops at lower energies. The isomerization takes place via a tunneling mechanism.     

Vapor-phase photodecomposition of chloropicrin (trichloronitromethane)

Under simulated environmental (atmospheric) conditions, chloropicrin vapor was readily converted in light to phosgene, which remained stable, and nitrosyl chloride which was subsequently photolyzed to nitric oxide and chlorine; a portion of the nitric oxide was oxidized to nitrogen dioxide and dinitrogen tetroxide. The unexpected dependence of the reaction upon oxygen, the initial photoproducts, and the incorporation of ¹⁸O when the photolysis occurred in the presence of ¹⁸O₂ suggest an intramolecular rearrangement involving a trioxazole N-oxide.     

Matrix isolation and ab initio studies of the H2S---CO complex

The structure, energetics, and vibrational properties of complexes formed between H₂S and CO have been investigated by matrix isolation FTIR spectroscopy and ab initio molecular orbital theory. Two stable computational minima were found representing nearly linear hydrogen bonds between the subunits. The H₂S---CO and H₂S---OC species were calculated to be bound by 5.22 and 1.54 kJ mol⁻¹, respectively. The computational results were reproduced by experimental assignments for the carbon attached complex. The stretching vibrations of the complex subunits were found to be similarly perturbed upon complexation both experimentally and computationally.     

Structures of bisphosphonate metal complexes: zinc and cadmium complexes of clodronate and its partial ester derivatives

Four new zinc and cadmium bisphosphonates [{NaZn(Cl2CP2O6H)(H2O)5}]n (1), [{Cd2(Cl2CP2O6)(H2O)4}.H2O]n (2), [{Zn(Cl2CP2O6Pri2)(H2O)3}.H2O]n (3), and [{Cd2(Cl2CP2O6Pri2)2(MeOH)2(H2O)2}.H2O]2 (4) have been prepared and their crystal structures determined by single-crystal X-ray diffractometry. Two bisphosphonate ligands were used: clodronate, (dichloromethylene)bis(phosphonate) and its symmetrical P,P'-diisopropyl ester derivative. The structure of the Zn complex 1 is three-dimensional, consisting of one-dimensional Zn-clodronate chains connected to the three-dimensional network by Na+ ions. The structure of Cd complex 2 consists of double layers, and a unique bond was found between the Cd2+ cation and a Cl atom of clodronate. Zn complex 3 consists of one-dimensional chains, but the binding of the bisphosphonate ligands is unique: in 3 the bisphosphonate ligand is only bidentate. Compound 4 is a tetramer, and hydrogen bonds hold the tetramers together, forming a layered structure.     

Gas chromatographic determination of serum branched-chain alpha-keto acids derivatized by extractive alkylation

The procedure presented for gas-liquid chromatographic analysis of alpha-keto acids is relatively simple, requiring only a few steps for the formation of derivatives suitable for measurement. The recoveries of the branched-chain alpha-keto acids varied from 92.7% to 106.7%, being sufficiently good especially when smaller amounts of the alpha-keto acids were added to serum. In addition, the coefficients of variation are satisfactorily small, also for biological samples. The measured values of branched-chain alpha-keto acids correspond well with those presented earlier by different methods. There exists a slight but insignificant difference between women and men, the values being lower in sera of women for the three branched-chain alpha-keto acids studied.     

Architecture dependence on the steric constrains of the ligand in cyano-bridged copper(I) and copper(II)-copper(I) mixed-valence polymer compounds containing diamines: crystal structures and spectroscopic and magnetic properties

A family of cyano-bridged copper(II)-copper(I) mixed-valence polymers containing diamine ligands of formula [Cu(pn)(2)][Cu(2)(CN)(4)] (1, pn = 1,2-propanediamine), [Cu(2)(CN)(3)(dmen)] (2, dmen = N,N-dimethylethylenediamine), and [Cu(3)(CN)(4)(tmen)] (3, tmen = N,N,N',N'-tetramethylethylenediamine) have been prepared with the aim of analyzing how their architecture may be affected by steric constraints imposed by the diamine ligands. In the absence of diamine and with use of the voluminous NEt(4)(+) cation, the copper(I) polymer [NEt(4)][Cu(2)(CN)(3)] (4) forms. The structure of 1 consists of a three-dimensional diamond-related anionic framework host, [Cu(2)(CN)(4)](2-), and enclathrated [Cu(pn)(2)](2+) cations. The structure of 2 is made of neutral corrugated sheets constructed from fused 18-member nonplanar rings, which contain three equivalent copper(I) and three equivalent copper(II) centers bridged by cyanide groups in an alternative form. The 3D structure of 3 consists of interconnected stair-like double chains built from fused 18-member rings, which adopt a chairlike conformation. Each ring is constructed from two distorted trigonal planar Cu(I) centers, two bent seemingly two-coordinated Cu(I) centers, and two pentacoordinated Cu(II) atoms. The structure 4 is made of planar anionic layers [Cu(2)(CN)(3)](n)(n-) lying on mirror planes and NEt(4)(+) cations intercalated between the anionic layers. From the X-ray structural results and calculations based upon DFT theory some conclusions are drawn on the structure-steric factors correlation in these compounds. Compound 1 exhibits very weak luminescence at 77 K with a maximum in the emission spectrum at 520 nm, whereas compound 4 shows an intense luminescence at room temperature with a maximum in the emission spectrum at 371 nm. Polymers 2 and 3 exhibit weak antiferromagnetic magnetic exchange interactions with J = -0.065(3) and -2.739(5) cm(-1), respectively. This behavior have been justified on the basis of the sum of two contributions: one arising from the pure ground-state configuration and the other one from the charge-transfer configuration Cu(I)-CN-Cu(II)-CN-Cu(II) that mixes with the ground-state configuration.     

Estimation methods for choice-based conjoint analysis of consumer preferences

Conjoint analysis, a preference measurement method typical in marketing research, has gradually expanded to other disciplines. Choice-based conjoint analysis (CBC) is currently the most popular type. Very few alternative estimation approaches have been suggested since the introduction of the Hierarchical Bayes (HB) method for estimating CBC utility functions. Studies that compare the performance of more than one of the proposed approaches and the HB are almost non- existing. We compare the performance of four published optimization-based procedures and additionally we introduce a new one called CP. The CP is an estimation approach based on convex penalty minimization. In comparison with HB as the benchmark we use eight field data sets. We base the performance comparisons on holdout validation, i.e. predictive performance. Among the optimization based procedures CP performs best. We run simulations to compare the extent to which CP and HB can recover the true utilities. With the field data on the average, the CP and HB results are equally good. However, depending on the problem characteristics, one may perform better than the other. In terms of average performance, the other four methods were inferior to CP and HB.     

Replicated Polymer Light Guide Interconnector with Depth Modified Surface Relief Grating Couplers

Planar light guide plate with one in-coupling and N out-coupling surface relief gratings is designed to perform as optical backplane broadcasting system for board-to-board connections. The performance of the element is analyzed theoretically with rigorous electromagnetic theory and results are confirmed experimentally. In addition, optical backplane elements have been replicated using conventional injection molding and UV-replication techniques.