Affinity chromatography study of the interaction of ribonucleotides with bovine pancreatic ribonuclease covalently bound to Sepharose 4B

The preparation of immobilized bovine pancreatic ribonuclease by covalent attachment to Sepharose 4B, with and without a spacer arm, is described. The coupling reaction was carried out at two different pH values, 8.5 and 10.5, and the different kinetic properties shown by the resulting preparations probably reflect the influence of the particular amino acid side-chains involved in the covalent coupling of the enzyme to the insoluble matrix. The strength of binding of mononucleotides, at 4 degrees C, as deduced from the salt concentration at which they are eluted from an immobilized RNAase column, follows the order 5'-GMP greater than 5'-AMP greater than 3'-UMP greater than 3'-CMP. When binary mixtures of a 3'-pyrimidine nucleotide and a 5'-purine nucleotide are chromatographed jointly, a co-operative effect is found and the elution of either or both ligands is retarded. This behaviour can be explained in terms of the preferential binding of each kind of nucleotide to different sub-sites in the enzyme. The stoichiometry and association constant for 3'-CMP and 5'-AMP at pH 7.0 were also determined.     

Semiempirical calculation of the surface dipole barrier in metals

The surface dipole barrier D of metals is calculated from experimental work functions and theoretical bulk chemical potentials obtained by the Augmented-Spherical-Waves method of Williams et al. Two independent linear relations between D and the electron density at the boundary of Wigner-Seitz cells are found for transition and non transition metals. An explanation for this difference is offered.     

Determination of the degree of acetylation of chitin and chitosan by thermal analysis

Several methods for the rapid determination of the degree of acetylation of chitin and related polymers have been evaluated, including the use of the infrared and the mass spectra. Chitin and chitosan have characteristic degradation temperatures and it is possible to determine the acetylation degree by the use of empirical correlations based on the weight losses associated with the main decomposition peaks.     

Tandem radical addition and cyclization of epsilon-substituted delta-yne ketimines

The first one-step conversions of ketimines I into cyclized allylamine derivatives of types II and III are reported.     

Radial electric fields and confinement in the TJ-II stellarator

Radial plasma potential profiles have been obtained in the TJ-II by the Heavy Ion Beam Probing (HIBP) diagnostics. Results show that the potential increases up to 1 kV near the magnetic axis in ECRH low-density plasmas. The secondary ion current profiles, which directly reflect the plasma density, are hollow. In low-density ECRH operation, radial electric fields are found to be positive in the plasma core, however, a reduction in these fields is observed with increasing density. Radial plasma potential profiles show evidence of structures in configurations with low-order rational surfaces. In particular, HIBP measurements have permitted characterization of the plasma potential profile during e-ITB formation. Experiments in TJ-II have shown that it is possible to modify the global confinement and edge plasma parameters with limiter biasing, illustrating the direct impact of radial electric fields on confinement properties. Plasma potential measurements by the HIBP diagnostic show a strong impact of heating method (ECRH versus NBI) on radial electric fields.Presented at the Workshop Electric Fields Structures and Relaxation in Edge Plasmas, Nice, France, October 26–27, 2004.     

Liquid-liquid extraction followed by solid-phase extraction for the determination of lipophilic pesticides in beeswax by gas chromatography-electron-capture detection and matrix-matched calibration

Analytical methods for the simultaneous analysis of lindane, chlorpyriphos, z-chlorfenvinphos, endosulfan A and B, 4,4'-DDE, 4,4'-TDE, acrinathrine, bromopropylate, tetradifon, coumaphos and fluvalinate in pure beeswax samples are studied. For the analysis of bleached beeswaxes, a liquid-liquid extraction with acetonitrile followed by a clean-up on polymeric cartridges is the best option in terms of recovery and precision. However, some interferences that hinder the identification and quantification of important varroacides are found when non-bleached beeswaxes are analyzed. The analysis of all compounds in the latter samples require a clean-up by coupling an ODS cartridge before the polymeric cartridge. Considerations about the influence of the matrix in the quantitative analysis by a classical external standard calibration are also made and the use of a matrix-matched calibration is advised. Recoveries resulted to be about 100% with coefficients of variation between 10% and 20% (n = 5) for concentrations of 0.5 and 5 mg/kg.     

Efficient synthesis of enantiomerically pure alpha-alkyl cyclopropanecarbonitrile derivatives from pyrazolines

[reaction: see text] Thermolysis of enantiopure sulfonyl pyrazolines 4 and 5, easily obtained from (Z)-3-p-tolylsulfinylacrylonitriles (1), afforded sulfonyl cyclopropanes (6, 7) in a completely stereoselective manner in almost quantitative yields. Both cyclopropanes and alkylidenecyclopropanes, containing one or two chiral carbon atoms, one of them being quaternary, were obtained by hydrogenolysis of the C-S bonding and under the conditions reported by Julia, respectively. The highly stereoselective extrusion of nitrogen suggests a concerted mechanism.     

Generation of strong, homochiral bases by electrochemical reduction of phenazine derivatives

Electrochemical reduction of enantiomerically pure amino- and alkoxy-phenazine derivatives forms strongly basic radical anions which give asymmetric induction in the conversion of 3,4-epoxytetrahydrothiophene-1,1-dioxide into the allylic ester with facile regeneration of the phenazine.     

Optical trapping microfabrication with electrophoretically delivered particles inside glass capillaries

We have developed a new technique for rapid microfabrication that uses electrophoretically delivered particles and an optical trap. The material particles, micrometer- and nanometer-sized polystyrene beads in aqueous solution, are continuously delivered to an optical trap by means of the electrophoretic effect inside glass capillaries or similar microstructures. The optical trap is used to manipulate and deposit the polystyrene beads onto a substrate. The continuous, on-demand delivery of particles allows for microfabrication in two and three dimensions with high speed and high efficiency and without material waste. This new technique has many potential applications in microelectronics and biotechnology.