Site-isolation effects in a dendritic nickel catalyst for the oligomerization of ethylene

Dendrimers, specifically suited to construct site-isolated groups due to their well-defined hyperbranched structure, have been used as a ligand design element for the construction of nickel catalysts for ethylene oligomerization. The dendritic P,O ligand indeed suppresses the formation of inactive bis(P,O)Ni complexes in toluene, as is evident from NMR studies, and, as a consequence, outperforms the parent ligand in catalysis in this solvent. The dendritic effect observed in methanol is more subtle because both the dendritic ligand 1 and the parent 2 form bis(P,O)nickel complexes in solution according to NMR spectroscopy. Unlike the parent complex 8, the dendritic bis(P,O)Ni complex 7 derived from dendrimer ligand 1 is able to dissociate to a mono-ligated species under catalytic conditions, that is, 40 bar ethylene and 80 degrees C, which can enter the catalytic cycle. Indeed, dendritic ligand 1 gives much more active nickel catalysts for the oligomerization in methanol than does 2.     

Saludimerines A and B, novel-type dimeric alkaloids with stereogenic centers and configurationally semistable biaryl axes

The first biarylic bis-morphinanedienone alkaloids, saludimerines A (3a) and B (3b), isolated from a tree of Croton flavens (Euphorbiaceae) are described. These naturally occurring dimers of the known alkaloid salutaridine are joined together via a rotationally hindered biaryl axis, giving rise to atropo-diastereomers that are configurationally stable at room temperature but slowly interconvert in methanolic solution within several days. Their structures were established by spectroscopic methods and by partial synthesis, which was achieved by a highly atropo-diastereoselective biomimetic oxidative coupling of the monomeric precursor, salutaridine. Their axial configurations were elucidated by circular dichroism (CD) investigations, which succeeded despite the fact that the two atropo-diastereomers exhibit near-identical CD spectra. This remarkable phenomenon was rationalized by quantum chemical CD calculations. The configurational assignment of saludimerines A (3a) as P-axial and B (3b) as M was corroborated by atropisomer-specific NOE interactions between protons of the one molecular half with nuclei in the other.     

Variations in trace element concentrations in human blood serum in the normal state investigated by instrumental neutron activation analysis

Using instrumental neutron activation analysis, the variations in the serum levels of Br, Cs, Na, Rb, Se, and Zn were investigated in 18 persons in the normal state. By determining the element levels in relation to changes is the serum water content, information about the binding to the serum protein was obtained. The influence of physiological factors on the serum element levels was investigated. Changes in the concentrations due to variations in the protein/water ratio and in the zinc level as a result of different posture were observed. When standardized sampling procedures were used, the variations in the serum element concentrations during one hour and from day were found to be less than 10%.     

Thermal analytic study of the adsorption of crystal violet by laponite

The adsorption of crystal violet on laponite was investigated by X-ray diffraction and thermal analysis. DTA, TG and DTG curves were recorded in air. The evolved H₂O, CO₂, NO₂, H₂ and C₂H₆ were simultaneously determined by mass spectrometry. The thermal analysis curves were compared on one hand with the thermal analysis curves of laponite and on the other hand with thermal analysis curves of non-adsorbed crystal violet and of crystal violet adsorbed on montmorillonite. The thermal analysis curves of crystal violet adsorbed on laponite show similarities to the curves of the non-adsorbed crystal violet, but differ from the curves of crystal violet adsorbed on montmorillonite. The differences in the thermal behaviour were attributed toπ interactions which do not occur between crystal violet and laponite but do occur between this dye and montmorillonite.     

Analysis, purification and properties of a 50,000-dalton membrane-associated phosphoprotein from human platelets

Recently, the development of a monospecific antiserum against a 46,000/50,000-dalton membrane protein from human platelets which was stoichiometrically and reversibly phosphorylated in intact human platelets in response to vasodilators was reported. Using this antiserum, the subcellular distribution and the purification of this vasodilator-stimulated phosphoprotein (VASP) from human platelets has now been analysed. The VASP of human platelets is primarily a membrane-associated protein and can be purified to apparent homogeneity by salt extraction and sequential ion-exchange and dye-ligand chromatography with a purification factor of 1200 and a yield of 13%. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis under reducing and non-reducing conditions indicated that purified monomers of this VASP are linked by interchain disulphide bonding.     

Fast systematic approach for the determination of drugs in biological fluids by fully automated high-performance liquid chromatography with on-line solid-phase extraction and automated cartridge exchange. Application to cebaracetam in human urine.

A fast stepwise systematic approach for the conversion of conventional reversed-phase high-performance liquid chromatographic (HPLC) assays involving liquid-liquid extraction of biological fluids into fully automated HPLC assays using solid-phase extraction and cartridge exchange is described. The suitability of this procedure is demonstrated for the determination of cebaracetam in human urine.     

Application of a green fluorescent fusion protein to study protein-protein interactions by electrophoretic methods

A screening procedure for protein-protein interactions in cellular extracts using a green fluorescent protein (GFP) and affinity capillary electrophoresis (ACE) was established. GFP was fused as a fluorescent indicator to the C-terminus of a cyclophilin (rDmCyp20) from Drosophila melanogaster. Cyclophilins (Cyps) belong to the ubiquitously distributed enzyme family of peptidyl-prolyl cis/trans isomerases (PPlases) and are well known as cellular targets of the immunosuppressive drug cyclosporin A (CsA). The PPlase activity of the GFP fused rDmCyp20 as well as the high affinity to CsA remain intact. Using native gel electrophoresis and ACE mobility-shift assays, it was demonstrated that the known moderate affinity of Cyp20 to the capsid protein p24 of HIV-1 was detectable in the case of rDmCyp20 fused to the fluorescent tag. For the p24 / rDmCyp20-GFP binding an ACE method was established which allowed to determine a dissociation constant of Kd = 20+/-1.5 x 10(-6) M. This result was verified by size-exclusion chromatography and is in good agreement with published data for the nonfused protein. Moreover the fusion protein was utilized to screen rDmCyp20-protein interactions by capillary electrophoresis in biological matrices. A putative ligand of rDmCyp20 in crude extracts of embryonic D. melanogaster was discovered by mobility-shift assays using native gel electrophoresis with fluorescence imaging and ACE with laser-induced fluorescence detection. The approach seems applicable to a wide range of proteins and offers new opportunities to screen for moderate protein-protein interactions in biological samples.     

Application of ligand-exchange capillary electrophoresis to the chiral separation of alpha-hydroxy acids and beta-blockers

The application of the principle of ligand-exchange capillary electrophoresis to two substance classes is described. As chiral selector N-(2-hydroxyoctyl)-L-4-hydroxyproline-copper(II) complex was used. This principle was applied to the chiral separation of alpha-hydroxy acids and drugs containing amino alcohol structure such as beta-blockers. The enantioselectivity was found to be strongly dependent on pH corresponding to the optimal conditions for complex formation for each structure class.     

Impedance study of Ni–Co electro-deposition on Fe powder particles in fluidised bed systems

The electrochemical impedance method was applied during the electrochemical deposition of a binary Ni–Co coating on iron powder in a fluidised bed electrode system. The influence of the suspension density on the charge transfer in the course of the electro-deposition process was studied. At a potential of −900 mV (vs. Ag/AgCl/3 M KCl), when the binary Ni–Co layer was formed, the impedance data were characterised by two semicircles with the semicircle at high frequencies being larger in magnitude. A contribution of the diffusion process to the overall current was observed. The optimal suspension density for the charge transfer in the bed was 10×10⁻³–15×10⁻³ (i.e., 4–6 g of iron powder in 50 ml of electrolyte). The most probable mechanism of the charge transfer for the studied concentrations of powder particles is the convective mechanism. The iron particles dispersed in the electrolyte were considered to act as either a depolariser or an additional working electrode depending on the applied electrode potential and on the suspension density.     

Thermodynamic Data for the Complex Formation of Alkylamines and Their Hydrochlorides with α-Cyclodextrin in Aqueous Solution

The formation of complexes between α-cyclodextrin and n-alkylamines and their hydrochlorides has been studied in aqueous solution using calorimetric titrations. All alkylamines form stronger complexes than the corresponding hydrochlorides. The values of the reaction enthalpies are smaller for the alkylamine hydrochlorides compared with the alkylamines. By increasing the number of methylene groups, these differences become smaller. In addition, the reaction enthalpies for protonation of the alkylamines and their complexes with α-cyclodextrin have been measured. The heat of protonation of these complexes is always smaller compared with the alkylamines. Due to the protonation and the formation of a strong solvation shell around the ammonium group the interactions with α-cyclodextrins are weakened. From a thermodynamic cycle using all measured reactions, it can be concluded that the aggregation of the alkylamines with long alkyl chains (heptyl-, octyl-, and nonylamine) has an influence on the values of the reaction enthalpies and entropies for the protonated form only.This revised version was published online in July 2005 with a corrected issue number.