Capillary electrophoretic determination of the component monosaccharides in hemicelluloses

This study describes the precolumn derivatization of carbohydrates with p-aminobenzoic acid and their efficient separation as borate complexes by means of capillary zone electrophoresis, using a capillary tube of fused silica containing 150 mmol/L borate buffer, pH 10.0, as carrier. On-column UV-monitoring at 285 nm allowed the detection of aldoses and uronic acids in the lower femtomole range. Reproducible quantification of carbohydrates was achieved at least in the concentration range of 0.1–10 mmol/L by the relative peak area method, using cinnamic acid as internal standard. The method was successfully applied to the determination of the monosaccharide composition of both commercially obtained xylans as well as of hemicelluloses obtained by hydrothermal degradation of biomass.     

One-Dimensional Falling Bodies

It is shown that a macroscopic system of classical hard rods with next neighbor interactions attains a phase separation under a weak gravitational field.     

Bond selective dissociative electron attachment to thymine

Free-electron attachment to thymine and partially deuterated thymine, where D replaces H at all carbon atoms, is studied in the electron energy range from about 0 to 15 eV. The formation of fragment anions that are formed by the loss of one or two H (D) atoms is analyzed as a function of the incident electron energy using a crossed electron/neutral beam apparatus in combination with a quadrupole mass spectrometer. By using partially deuterated thymine and quantum-chemical calculation a bond selectivity for the loss of one and two hydrogen atoms is observed that is determined only by the kinetic energy of the incident electron.     

Finite element error bounds for a curve shrinking with prescribed normal contact to a fixed boundary

We approximate the evolution of a curve subject to motion bycurvature by linear finite elements. The curve evolves insidea given domain and meets orthogonally. We derive optimal boundsfor the error with respect to the L²- and H¹-norms and presentsome computed examples.     

Rotational Brownian motion of solute fluorescent molecules in liquids: Theory and experiment

The theories for the rotational Brownian motion of molecules in liquids were experimentally verified on the example of selected fluorescent probe molecules dissolved in various solvents. Agreement between theories and experimental results as well as some disagreements between them were found. The model of a coloured noise random torque has been employed to diminish the discrepancy between the Hubbard-Morita model of rotational Brownian motion of molecules in liquids and the experimental data. A mass drag effect due to the existence of viscosity shear waves is taken into account in the explanation of inertial effects in molecular motion in liquids. The hypothesis of microviscosity has been confirmed in some experimental situations.     

Vibronic sidebands in ruby

An experimental and group-theoretical study of single phonon vibronic sidebands of theR-lines in ruby has been performed. Restrictions in the electron-phonon-spectra due to crystal symmetry occur only inEC-polarization and for phonons withk-vectors zero or parallel to theC-axis. An analysis of the fluorescence and excitation spectra led to an identification of part of the lines in the vibronic sidebands with normal modes of the lattice. In the regime of acoustical phonons the intensity of the sideband increases with frequency following a potential law with an exponent of slightly less than 5. A strong enhancement of the vibronic transition probability was found on the high frequency side of theR-lines due to a resonance with the electronic transitions⁴ A ₂-² T ₁. Crosssections of the vibronic transitions in the spectral range of Stokes- and anti-Stokessidebands are given in a diagram. For acoustical phonons with energies up to 6 THz they are also expressed in a formula.     

Purification of erucic acid by preparative high-performance liquid chromatography and crystallization.

Erucic acid (C22:l fatty acid) has been found to be useful in the treatment of adrenoleukodystrophy (ALD). It appears to work by reducing the blood levels of very-long-chain fatty acids (VLCFAs) which destroy the myelin sheaths of the nerves. Erucic acid was purified by reversed-phase high-performance liquid chromatography (HPLC) on columns packed with YMC C18 (10-20 microns, 120 A). Using ethanol-water as the mobile phase, the recovery of erucic acid was 69% and the purity was more than 97% as measured by gas chromatography. The amount of saturated VLCFAs was found to be within the limits specified for ALD treatment. The production rate (yield per 8 h shift) was low, however. Using methanol-water instead of ethanol-water as the mobile phase, a ninefold increase in the production rate was achieved. The recovery of erucic acid was 65% and the purity of erucic acid was 98%. All other purity specifications were met. By performing a low-temperature crystallization after the preparative HPLC step, the production rate was increased a further 142%. This represents a 22-fold increase in production rate over the ethanol-water method. The crystalline erucic acid was found to be 99% pure. All other purity requirements were met. The yield for the combined process (HPLC plus crystallization) decreased to 55%, however.     

Batch and simulated moving bed chromatographic resolution of a pharmaceutical racemate

The preparative chromatographic resolution of racemates has become over the past few years a standard approach for the generation of enantiomers in pharmaceutical research and development. This paper will discuss the chromatographic resolution of a racemic pharmaceutical intermediate. Initial analytical method development to determine the best preparative conditions will be presented. Batch resolution of kg quantities of racemate followed by the simulated moving bed resolution of tens and hundreds of kg of racemate will also be discussed. Finally the different approaches used for the separation will be compared.     

Ultrasonic monitoring of zeolite synthesis in real time

Variations of the phase and amplitude of a transmitted ultrasonic wave package were monitored in real time during the synthesis of zeolite A and zeolite X. For both materials, characteristic changes of the measured attenuation and the sound velocity of ultrasonic waves traveling in the reaction fluid were observed, correlating with the processes of gel formation and zeolite crystallization, respectively. Aging effects of the reaction fluids are demonstrated. The observation of the onset of the zeolite crystallization was verified with ex-situ X-ray diffraction (XRD) measurements.