A semiempirical conformational analysis of the 3-phenyl-1,2,3-oxathiazolidine 2-oxide

An extensive conformational search for the heterocyclic compound 3-phenyl-1,2,3-oxathiazolidine 2-oxide has been carried out using the semiempirical quantum-mechanical method PM3. All torsion angles were varied in the geometry optimization procedure which led to the prediction of four distinct conformers. Barriers to internal rotation leading to conformational interconversions were also calculated. The results of the present study indicate that this five-member ring substituted heterocyclic system may be expected to exist as a mixture of stable conformers rather than a unique molecular entity.     

Pyrocatechol-1-aldehyde salicyloylhydrazone as reagent for the spectrofluorimetric determination of zinc

Summary A procedure is developed for the Spectrofluorimetric determination of 10–800 ppb of zinc with pyrocatechol-1-aldehyde salicyloylhydrazone in a 60% (v/v) ethanol-water medium at apparent pH 6.7 (acetic-acetate buffer). _ex=400 nm, _em=530 nm. Interferences have been evaluated and the method applied to the determination of zinc in alloys and lubricating oils.

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Spektrofluorimetrische Bestimmung von Zink mit Brenzcatechin-1-aldehyd-salizyloylhydrazon

Zusammenfassung Zink bildet mit Brenzcatechin-1-aldehyd-salizyloylhydrazon ein gelbes, fluoreszierendes Chelat in Gegenwart von 60% Ethanol bei pH 6,7 (Essigsäure-Natriumacetat-Puffer); _ex=400 nm, _em=530 nm. Zwischen Intensität der Fluoreszenz und Zink-Konzentration besteht im Bereich von 10 bis 800 ppb Linearität. Das Verfahren wurde zur Bestimmung des Zinks in Legierungen und Schmierölen verwendet.

     

Imide-amide rearrangement of oxazaphosphorimidates: studies towards the application to the synthesis of chiral Lewis bases

The Lewis acid catalysed imide-amide rearrangement of oxazaphosphorimides to diazaphoshoramides is reported for the first time. In spite of the similarity to the previously reported Lewis acid catalysed imide-amide rearrangement of dioxaphosphorimides to oxazaphosphoramides we show that this rearrangement proceeds by a different mechanism, not involving the formation of an oligomeric intermediate. The oxazaphosphorimides are prepared in situ by the Staudinger reaction of the appropriate trivalent phosphorus compound with an azide and after the addition of BF₃·OEt₂, undergo rearrangement to the corresponding diazaphosphoramides. We have found that the rearrangement occurs with retention of configuration at the phosphorus atom and inversion of configuration at the rearranged carbon atom. When starting from chiral 1,2-aminoalcohol, substituted at the carbon atom that undergoes rearrangement, a mixture of diastereomers is obtained, but the diastereomeric ratio, initially obtained in the formation of the trivalent phosphorus compounds is maintained during the whole transformation. This implies that if the rearrangement is to be used for the preparation of chiral phosphoramides with defined stereochemistry at the phosphorus atom, a high diastereoselectivity during the preparation of the trivalent phosphorus precursors should be obtained.     

A comparison of ns and ps steam laser cleaning of Si surfaces

We report a quantitative investigation on the efficiency of the steam laser cleaning process using ns and ps pulses. Well-characterized polymer particles with a diameter of 800 nm dispersed on commercial Si wafers were chosen as a modeling contaminant system. As a result of our investigation, we show for the first time the feasibility of performing efficient steam laser cleaning with ps laser pulses and compare the achieved efficiency with the one obtained for ns pulses. For ns pulses, we found a cleaning fluence threshold of 50 mJ/cm² that is independent of the pulse durations (2.5 ns and 8 ns) and the wavelengths (532 nm and 583 nm) used. The application of ps pulses (FWHM=30 ps, 5=583 nm) lowered this threshold to 20 mJ/cm². Both cleaning thresholds are far below the melting thresholds for these laser parameters. Cleaning efficiencies >90% were reached for both pulse durations.     

Wide transparency range and high refractive index lead–niobium-germanate glass thin films

Lead–niobium-germanate glass thin films have been produced by pulsed laser deposition in a broad O₂ pressure range (10^-6–10^-1 mbar). The cation composition in the films approaches that of the glass target for a pressure of 10^-2 mbar. The oxygen content is only close to or above that of the glass for a pressure close to 10^-1 mbar, for which a Pb enrichment is also observed. Films grown in vacuum are highly absorbing, whereas transparent films with an absorption edge shifted to the UV with respect to the bulk glass are produced for pressures higher than 10^-2 mbar. The evolution of the optical energy gap and the refractive index of the films with the oxygen pressure is correlated to the changes observed in the film composition and discussed in terms of the features of the deposition process, the role of oxygen in the formation of the glass network and the progressive increase of the oxidation state of the cations as the oxygen pressure is increased. PACS 81.05.Kf; 78.20.Ci; 81.15.Fg     

Anomalous dispersion in nanocomposite films at the surface plasmon resonance

Nanocomposite thin films formed by Cu nanocrystals (NCs) embedded in an amorphous aluminium oxide (Al₂O₃) host have been prepared by alternate pulsed laser deposition. Spectroscopic ellipsometry is used to determine the effective refractive index (n=n+ik). The extinction coefficient is non-negligible and shows a broad absorption band related to the surface plasmon resonance. In the neighbourhood of this wavelength, the real part of the refractive index undergoes an anomalous dispersion, leading to a significant increase of the n value of the composite compared to that of the host. When the Cu content is low enough, about 2 at. %, the use of an effective medium approach combined with a regression method allows us to determine the metal content and film thickness from the ellipsometric measurements. For larger concentrations this approach is no longer valid. Received: 31 July 2001 / Revised version: 21 September 2001 / Published online: 15 October 2001     

Electronic Effects of 11β Substituted 17β-Estradiol Derivatives and Instrumental Effects on the Relative Gas Phase Acidity

Numerous studies have highlighted the role of the proton donor characteristics of the phenol group of 17??-estradiol (E₂) in its association with the estrogen receptor alpha (ER??). Since the substitutions at position C₍₁₁₎ have been reported to modulate this association, we hypothesized that such substitutions may modify the phenol acidity. Hence, phenol gas-phase acidity of nine C₍₁₁₎-substituted E₂-derivatives were evaluated using the extended Cooks?? kinetic method, which is a method widely used to determine thermochemical properties by mass spectrometry. To enhance accuracy in data collection we recorded data from several instruments, including quadrupole ion trap, triple quadrupole, and hybrid QqTOF. Indeed, we report for the first time the use of the QqTOF instrument to provide a novel means to improve data accuracy by giving access to an intermediate effective temperature range. All experimental gas-phase acidity values were supported by theoretical calculations. Our results confirmed the ability of distant substituents at C₍₁₁₎ to modulate the phenol acidity through electrostatic interactions, electron withdrawing inductive effects, and mesomeric effects. However, no relationship was found between the phenol gas-phase acidity of investigated steroids and their binding affinity for ER?? assessed in solution. Thus, our results highlight that the intrinsic properties of the hormone do not influence sufficiently the stabilization of the hormone/ER?? complex. It is more likely that such stabilization would be more related to factors depending on the environment within the binding pocket such as hydrophobic, steric as well as direct intermolecular electrostatic effects between ER?? residues and the substituted steroidal estrogens.     

Photoelectrochemical properties of FTO/m-BiVO4 electrode in different electrolytes solutions under visible light irradiation

Photoelectrochemical properties of FTO/BiVO₄ electrode were investigated in different electrolytic solutions, potassium chloride (KCl) and sodium sulphate (Na₂SO₄), and under visible light irradiation condition. In order to accomplish that, an FTO/BiVO₄ electrode was built by combining the solution combustion synthesis technique with the dip-coating deposition process. The morphology and structure of the BiVO₄ electrode were investigated through X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. Photoelectrochemical properties were analyzed through chronoamperometry measurements. Results have shown that the FTO/BiVO₄ electrode presents higher electroactivity in the electrolyte Na₂SO₄, leading to better current stabilization, response time, and photoinduced current density, when compared to KCl electrolyte. Besides, this electrode shows excellent performance for methylene blue degradation under visible light irradiation condition. In Na₂SO₄, the electrode has shown higher degradation rate, 51 %, in contrast to 44 % in KCl, plus higher rate constant, 174?×?10^?4 min^?1 compared to 150?×?10^?4 min^?1 in KCl. Results presented in this communication leads to the indication of BiVO₄ thin films as alternate materials to use in heterogeneous photoelectrocatalysis, more specifically in decontamination of surface water.     

Comments on “Enhancements on the Hyperplanes Arrangements in Mixed-Integer Programming Techniques”

In a recent paper by Prodan et al. (J. Optim. Theory Appl. 154:549–572, 2012), a technique was presented to reduce the number of binary variables needed to represent not convex constraints in a mixed-integer programming (MIP) problem. The proposed technique employs tuples of binary variables, which are associated with feasible regions of the feature space. However, since the number of all possible tuples with a given number of bits is a power of two, there may be several unallocated tuples that must be rendered infeasible by imposing suitable constraints. We show in this paper that it is always possible to partition the tuples so that only one inequality is necessary to render all the unallocated tuples and only them infeasible. Moreover, we develop a systematic procedure to perform this partition and write the referred inequality.