Adjusting the selectivity of inorganic anion separation by capillary electrophoresis

The separation of the principal inorganic anions (bromide, carbonate, chlorate, chloride, fluoride, nitrate, nitrite, sulfate, phosphate) has been achieved using a capillary electrophoresis system with indirect UV detection at 260 nm. Several types of cationic surfactants (quaternary ammonium, phosphonium or methonium) were tested as electroosmotic flow modifiers and added to a chromatebased buffer prepared from potassium dichromate. The influence of many physicochemical parameters such as nature and concentration of cationic surfactant, buffer pH, dichromate concentration buffer, voltage and temperature upon the migration time of an analyte anion, peak efficiency, asymmetry factor, and finally resolution has been investigated. A linear relationship between the corrected area and the anion concentration in the 2.5–50 ppm range was obtained, thus allowing the quantitative analysis of anions in mineral water. Finally, by increasing the hydrodynamic injection time, the separation of inorganic anions at a low concentration level of 50 ng/ml was achieved without any loss of resolution.     

Differential effects of various trivalent and pentavalent organic and inorganic arsenic species on glucose metabolism in isolated kidney cells

We have compared the acute toxicities of the trivalent arsenic species arsenite, oxophenylarsine (PhAsO), 2-chlorovinyloxoarsine (ClvinAsO), methyloxoarsine (MeAsO), and of the pentavalent arsenic species arsenate, methyl- and phenyl-arsonic acid in rat kidney tubules (RKT) and Madin-Darby canine kidney (MDCK) cells. In RKT, PhAsO (1 μmol I⁻¹, 60 min) almost completely (>90%) blocked gluconeogenesis without affecting cell viability as assessed by dye exclusion. In MDCK cells, PhAsO (2 μmol I⁻¹) markedly inhibited glucose uptake (60% of controls) within 30 min, while cell viability, as assessed by formazan formation, was not affected within 180 min. MeAsO and CIvinAsO were similarly effective to PhAsO in both RKT and MDCK cells. Estimated IC₅₀ values for the inhibition of gluconeogenesis were 0.55 (PhAsO), 0.69 (CIvinAsO) and 0.99 μmol I⁻¹ (MeAsO) and for the inhibition of glucose uptake 1.23 (PhAsO). 2.62 (CIvinAsO) and 6.99 μmol I⁻¹ (MeAsO). At longer storage times, aqueous solutions of MeAsO and of CIvinAsO, but not of PhAsO, gradually lost toxic activity in RKT and MDCK cells, especially at alkaline pH. Concomitantly, a gradual decrease in content as assessed by HPLC was detected. Roughly 10-fold higher concentrations of arsenite than of PhAsO were required for comparable effects on gluconeogenesis in RKT, whereas in MDCK cells about 100-fold higher concentrations were needed for similar inhibition of glucose uptake. Pentavalent arsenate and phenylarsonate were two orders of magnitude less effective than PhAsO in RKT, while methylarsonate had virtually no influence on gluconeogenic activity. In MDCK cells the pentavalent arsenic species showed effects only in the millimolar range. It is concluded (1) that different mechanisms are involved in the acute toxicity of oxoarsines and inorganic arsenic and (2) that PhAsO offers advantages as a model substance for mono-substituted trivalent arsenicals, because it is more stable and more readily detectable.     

Benzyl esters of optically active malic acid stereocopolymers as obtained by ring-opening polymerization of (R)-(+) and (S)-(-)-benzyl malolactonates

(R)-(+) and (S)-(-)-benzyl malolactonates were copolymerized anionically by using triethylamine and aluminum porphyrin as initiators. Configurational composition of resulting optically active poly(benzyl β-malate) stereocopolymers depends on the enantiomeric purity in the monomer feed. Stereochemistry during the multistep synthesis starting from aspartic acid enantiomers used as precursors is discussed. It is shown that natural L(+)-aspartic acid yields (-)-poly(benzyl β-malate) which degrades to L(-)-malic acid in alkaline aqueous medium. Configurational structures were investigated by ¹³C NMR (75.47 MHz) and splittings of stereosensitive resonances are discussed in terms of stereosequence distributions. Results show that stereocopolymerization proceeds through random addition of chiral repeating units according to Bernoullian statistics. In order to exemplify the effect of enantiomeric composition on physical properties, thermal characteristics have been investigated by DSC for the whole series of stereocopolymers. Samples with more than 70% (S) or (R)-units are semicrystalline. Melting temperature and crystallinity increase with stereoregularity.     

High-spin structure in154Er

High spin states in the nucleus¹⁵⁴Er have been reinvestigated using the¹²³Sb(³⁵Cl, 4n) reaction and a variety of spectroscopic techniques including excitation functions,γ-γ coincidences,γ angular distribution and linear polarization measurements. From the measured energies, relative intensities and transition multipolarities a new level scheme has been deduced up to an excitation energy of ～12 MeV and spin 36. An interpretation of the experimental results is given in terms of the deformed Woods-Saxon orbitals. Gigantic backbending (superdeformation) effect is studied theoretically within the cranking model.     

The UV,blue and green up-conversion luminescence of PbF2+GeO2:Er2O3 pumped with 650 nm

A detailed study of the spectroscopic properties of the PbF₂+GeO₂:Er₂O₃ vitroceramic sample upon 650 nm excitation was investigated. The absorption, emission, excitation spectra, and time-resolved spectra have been measured. The up-conversion of red radiation (650 nm) into UV (368 nm and 379 nm), blue (406.8 nm) and green (522 nm and 540 nm) emissions is observed for Er³⁺ ions in the sample. The up-conversion process involves a two-photon absorption for the violet, blue, and green emission bands. A three-photon process happens for another violet (379 nm) band.     

Computation of high order derivatives in optimal shape design

Summary. In shape optimization problems, each computation of the cost function by the finite element method leads to an expensive analysis. The use of the second order derivative can help to reduce the number of analyses. Fujii ([4], [10]) was the first to study this problem. J. Simon [19] gave the second order derivative for the Navier-Stokes problem, and the authors describe in [8], [11], a method which gives an intrinsic expression of the first and second order derivatives on the boundary of the involved domain. In this paper we study higher order derivatives. But one can ask the following questions: -- are they expensive to calculate? -- are they complicated to use? -- are they imprecise? -- are they useless? \medskip\noindent At first sight, the answer seems to be positive, but classical results of V. Strassen [20] and J. Morgenstern [13] tell us that the higher order derivatives are not expensive to calculate, and can be computed automatically. The purpose of this paper is to give an answer to the third question by proving that the higher order derivatives of a function can be computed with the same precision as the function itself. We prove also that the derivatives so computed are equal to the derivatives of the discrete problem (see Diagram 1). We call the discrete problem the finite dimensional problem processed by the computer. This result allows the use of automatic differentiation ([5], [6]), which works only on discrete problems. Furthermore, the computations of Taylor's expansions which are proposed at the end of this paper, could be a partial answer to the last question. Received January 27, 1993/Revised version received July 20, 1993     

Damping of Vibrations in a SystemWith Two Beams by Structural Friction

This paper presents the results of tests on free and forced harmonic vibrations in a system with two beams with structural friction taken into account. The beams are clamped together with uniform unitary pressure. The hysteresis loop describing the frictional-elastic properties of the system has a form of a parallelogram. The autor created a mathematical model of the vibrating system with two beams. During free vibrations of the system, its damping characteristics were tested by a digital simulation method. The vibration damping decrement as a function of amplitude displacement was determined. When vibrations were harmonically forced, the amplitude - frequency characteristics of the system were determined numerically. The system was used as a nonlinear vibration damper in a linear system with a harmonic force. The equations of motion of the nonlinear two-degree of freedom system were solved by means of a digital simulation method. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theoretical Evidence for Temperature-induced Proton Mobility in Isolated Lysine-rich Polyalanines

A multistate molecular mechanics method is introduced to model the possible competition between various protonation sites in gas-phase biomolecules with excess protons. The method relies on the Amber force field for each site and is calibrated against density-functional theory benchmark calculations at the 6-31+G(d,p) level. In its adiabatic version, where it has similarities with constant-pH algorithms, the model predicts that the small protonated Ala(4)-Lys peptide, unprotected at the N-terminus, changes protonation site above 400 K. In the larger [Ala(9)-Lys+H ](+) peptide, the proton remains at the lysine amine group in a favored charge/electric dipole conformation. In the three-state Ala(4)-Lys-Ala(4)-Lys peptide, the excess proton is found to be partially delocalized on the amine group of the first lysine and on the N-terminus. The statistical properties of the protonated peptides are found to significantly depend on the localized character of the proton. Finally, the model is extended by considering possible couplings between the protonation sites, in an empirical valence-bond version. Strong couplings can stabilize the peptides into unexpected proton-bound conformations over broad ranges of temperature.     

Chemistry of naphthazarin derivatives. 11. Trisubstituted hydroquinone derivatives in the preparative synthesis of naphthazarins

The Friedel—Crafts acylation of trimethylhydroquinone, 3,5-diethyl-2-hydroxyhydroquinone, and 3,5-diethyl-1,2,4-trimethoxybenzene with dichloromaleic or citraconic anhydride in an AlCl₃—NaCl melt is accompanied by o-C-dealkylation to afford functionally substituted naphthazarins.