High-temperature phase transitions in CsH2PO4 under ambient and high-pressure conditions: a synchrotron x-ray diffraction study

To clarify the microscopic origin of the temperature-induced three-order-of-magnitude jump in the proton conductivity of CsH(2)PO(4) (superprotonic behavior), we have investigated its crystal structure modifications within the 25-300 degrees C temperature range under both ambient- and high-pressure conditions using synchrotron x-ray diffraction. Our high-pressure data show no indication of the thermal decomposition/polymerization at the crystal surface recently proposed as the origin of the enhanced proton conductivity [Phys. Rev. B 69, 054104 (2004)]. Instead, we found direct evidence that the superprotonic behavior of the title material is associated with a polymorphic structural transition to a high-temperature cubic phase. Our results are in excellent agreement with previous high-pressure ac impedance measurements.     

Electrokinetic partial filling technique as a powerful tool for enantiomeric separation of DL-lactic acid by CE with contactless conductivity detection

A modified partial filling method for chiral separation of DL-lactic acid as the model chiral compound with vancomycin chloride as the chiral selector was developed by CE with contactless conductivity detection. Electrokinetic partial filling technique (EK-PFT) was used as an alternative method to the conventional hydrodynamic partial filling method. EK-PFT, in contrast to the hydrodynamic partial filling technique, allowed the removal of the chloride counterions from the chiral selector which otherwise led to poor sensitivity in conductivity detection. The baseline separation of DL-lactic acid as the model analyte was achieved in 5 min in a polyacrylamide-coated capillary. The best resolution was achieved by electrokinetic partial filling of vancomycin cations from the injection solution containing 5 mmol/L oxalate L-histidinium at pH 4.5 with 10 mmol/L vancomycin chloride. Computer simulation was used to explain the observed phenomena in the boundary between the inject vial and the capillary during the EK-PFT of vancomycin cations.     

Liouville theorems,a priori estimates,and blow-up rates for solutions of indefinite superlinear parabolic problems

In this paper we establish new nonlinear Liouville theorems for parabolic problems on half spaces. Based on the Liouville theorems, we derive estimates for the blow-up of positive solutions of indefinite parabolic problems and investigate the complete blow-up of these solutions. We also discuss a priori estimates for indefinite elliptic problems.     

Determination of quinine in beverages by online coupling capillary isotachophoresis to capillary zone electrophoresis with UV spectrophotometric detection

The present study illustrates the possibilities of capillary isotachophoresis (CITP) online coupled with capillary zone electrophoresis (CZE) and hyphenated with fiber-based spectrophotometric diode array detection (DAD) for the direct, highly reliable, and ultrasensitive determination of quinine (QUI) in real multicomponent ionic matrices (beverages). Here, the CITP provided an effective online sample pretreatment (preseparation and preconcentration) prior to the CZE separation. Due to the CITP sample preconcentration, a simple UV-visible absorbance spectrophotometric detection was sufficient for obtaining very low concentration limits of detection (~2.3 ng/mL). Enhanced separation selectivity due to the combination of different separation mechanisms (CITP vs. CZE) enabled to obtain a pure analyte zone, suitable for its detection and quantitation in the directly injected real samples. The spectrophotometric DAD, unlike single wavelength UV detection, enabled to characterize the purity (i.e. spectral homogeneity) of the analyte zone and preliminary data indicate structurally related compounds via characteristic spectra recorded in the interval of 200-600 nm. The proposed CITP-CZE-DAD method was characterized by favorable performance parameters (sensitivity, linearity, precision, recovery, accuracy, robustness, and selectivity) and successfully applied to the control of QUI and potential QUI impurities in commercial beverages. This method is proposed as a routine automatized method for the highly reliable quality food control.     

Charge carrier mobility in poly[methyl(phenyl)silylene] studied by time-resolved terahertz spectroscopy and molecular modelling

Time-resolved terahertz spectroscopy and combination of quantum chemistry modeling and molecular dynamics simulations were used for the determination of charge carrier mobility in poly[methyl(phenyl)silylene]. Using time-resolved THz spectroscopy we established the on-chain charge carrier drift mobility in PMPSi as 0.02 cm(2) V(-1) s(-1). This value is low due to the formation of polarons: the hole is self-trapped in a potential formed by local chain distortion and the transient THz conductivity spectra show signatures of its oscillations within this potential well. This view is supported by the agreement between experimental and calculated values of the on-chain charge carrier mobility.     

Preparative isotachophoresis with surface enhanced Raman scattering as a promising tool for clinical samples analysis

A surface enhanced Raman scattering (SERS) spectrometry is an interesting alternative for a rapid molecular recognition of analytes at very low concentration levels. The hyphenation of this technique with advanced separation methods enhances its potential as a detection technique. Until now, it has been hyphenated mainly with common chromatographic and electrophoretic techniques. This work demonstrates for a first time a power of preparative isotachophoresis-surface enhanced Raman scattering spectrometry (pITP-SERS) combination on the analysis of model analyte (buserelin) in a complex biological sample (urine). An off-line identification of target analyte was performed using a comparison of Raman spectra of buserelin standard with spectra obtained by the analyses of the fractions from preparative isotachophoretic runs. SERS determination of buserelin was based on the method of standard addition to minimize the matrix effects. The linearity of developed method was obtained in the concentration range from 0.2 to 1.5 nmol L(-1) with coefficient of determination 0.991. The calculated limit of detection is in tens of pico mols per liter.     

Einfluß der Temperung auf die optische Homogenität von Korund-Einkristallen

The influence of annealing corundum rods was investigated in controlling the number of interference stripes. Annealing at least of 1100-1200°C improves optical homogeneity of the perfect crystals. Annealing at 1900-1980°C only slightly improves optical homogeneity of rubies.     

Properties of polystyrene/poly(butyl acrylate) core/shell polymers modified with N‐methylol acrylamide

Polystyrene/poly(butyl acrylate) PS/PBA polymer dispersions with core/shell particles functionalized by N‐methylol acrylamide (N‐MA) were prepared through two‐step emulsion polymerization. The influence of N‐MA situated in shell and/or in core/shell of particles on the crosslinking reaction was studied to relate its mechanical properties and organic solvent resistance of films cast from basic and modified PS/PBA latexes. The changes in the phase arrangement of functionalized and unfunctionalized films after treatment with solvent and annealing were monitored. It was found that at the presence of N‐MA the crosslinking reaction occured already during the polymerization. Films from functionalized dispersions exhibit improved tensile strength and higher resistance against organic solvent.     

Azo‐group labelled polyesters by end‐capping with 2‐oxazoline derivatives – preparation

Two azobenzene containing 2‐oxazolines were used for labelling of polyesters with carboxylic end groups by the end‐capping method. The reaction proceeded under the conditions of reactive processing, and in a solution. High conversions in melt were achieved in several minutes. The coupling of the modifiers was proved by NMR spectroscopy.