Synthese von 4-[3β, 14-Dihydroxy-5β, 14β-androstan-17β-yl]-3-pyrrolin-2-on (Hothesimogenin). Partialsynthetische Versuche in der Reihe der Herzgifte, 11. Mitteilung

Synthesis of 4-[3β, 14-Dihydroxy-5β, 14β-androstan-17β-yl]-3-pyrrolin-2-one (hothesimogenin) We describe the synthesis of 4-[3β, 14-Dihydroxy-5β, 14β-androstan-17β-yl]-3-pyrrolin-2-one (24-aza-24-desoxa-digitoxigenin) (7) , starting from 3-O-acetyl-digitoxigenin (1) .     

The Gaussian measure of shifted balls

Summary Let be a centered Gaussian measure on a Hilbert spaceH and let be the centered ball of radiusR>0. ForaH and , we give the exact asymptotics of (B _R(t)+t·a) ast. Also, upper and lower bounds are given when is defined on an arbitrary separable Banach space. Our results range from small deviation estimates to large deviation estimates.Supported in part by NSF grant number DMS-9024961     

Surface modification of oxidic nanoparticles using 3-methacryloxypropyltrimethoxysilane

Tin oxide, antimony-doped tin oxide (ATO), and silica nanosized particles in aqueous dispersion were reacted with various amounts of 3-methacryloxypropyltrimethoxysilane (MPS). The kinetics were followed by 29Si NMR and the products were analyzed by FTIR and 29Si NMR. The kinetic experiments on ATO and silica revealed that the hydrolysis is the rate-determining step in these reactions. The reaction of MPS with the particles is favored over the homocondensation of MPS. Quantitative analysis using FTIR revealed that the amount of MPS grafted onto the tin oxide and silica particles is limited to the amount needed to fill one monolayer. For ATO the maximum amount of grafted MPS was only 50-70% of the amount that is needed for a closed monolayer. The MPS molecules are for the most part oriented parallel to the oxide surface, and a hydrogen bond between the MPS-carbonyl and the oxide is formed.     

Decomposition of Copper Formate Clusters: Insight into Elementary Steps of Calcination and Carbon Dioxide Activation

The decomposition of copper formate clusters is investigated in the gas phase by infrared multiple photon dissociation of Cu(II)_n(HCO₂)_2n+1⁻, n≤8. In combination with quantum chemical calculations and reactivity measurements using oxygen, elementary steps of the decomposition of copper formate are characterized, which play a key role during calcination as well as for the function of copper hydride based catalysts. The decomposition of larger clusters (n > 2) takes place exclusively by the sequential loss of neutral copper formate units Cu(II)(HCO₂)₂ or Cu(II)₂(HCO₂)₄, leading to clusters with n=1 or n=2. Only for these small clusters, redox reactions are observed as discussed in detail previously, including the formation of formic acid or loss of hydrogen atoms, leading to a variety of Cu(I) complexes. The stoichiometric monovalent copper formate clusters Cu(I)_m(HCO₂)_m+1⁻, (m=1,2) decompose exclusively by decarboxylation, leading towards copper hydrides in oxidation state +I. Copper oxide centers are obtained via reactions of molecular oxygen with copper hydride centers, species containing carbon dioxide radical anions as ligands or a Cu(0) center. However, stoichiometric copper(I) and copper(II) formate Cu(I)(HCO₂)₂⁻ and Cu(II)(HCO₂)₃⁻, respectively, is unreactive towards oxygen.     

The annular space between rotating cylinders as a geometry for open-channel liquid chromatography

Summary The annular slit between two cylinders, one of which is rotating, looks attractive for carrying out open channel LC, with chromatographic flow in the axial direction. Under ideal conditions, the dynamics of chromatographic separation are as good as those prevailing in an open tubular column.As is the case for Myers and Gidding's open parallelplate LC, the sample capacity of the proposed geometry can be much higher than of open tubular chromatography.Rotation of one of the cyclinders offers two advantages, which may be helpful in achieving the ideal situation. First, the thickness of the slit between the cylinders tends to be more uniform at higher rotation speeds. Second, the increased mixing of the liquid in the direction perpendicular to chromatographic flow can be expected to diminish the detrimental effect of any remaining lack of uniformity in the thickness of the slit and the capacity factors.Preliminary results with such a system are reported.Dedicated to Professor J. F. K. Huber on the occasion of his 60th birthday.     

Silica versus polymer-based stationary phases for reversed-phase high-performance liquid chromatographic analyses of rat insulin biosynthesis. A comparison of resolution and recovery

Because of the problems caused by the irreversible binding of insulins and proinsulins to several silica-based reversed-phase columns, the use of polymeric reversed-phase columns was investigated for the analysis of rat islet polypeptides involved in insulin biosynthesis. No irreversible binding of insulins and proinsulins was observed for the polymeric reversed-phase columns, probably due to the absence of silanol groups. The six polypeptides involved in insulin biosynthesis in rat islets were equally well resolved in shallow trifluoroacetic acid-acetonitrile gradients on the silica-based Nucleosil 300-5C4 column (45 degrees C), the polymer-based Asahipak C4P-50 (25 and 45 degrees C), and ODP-50 columns (45 degrees C). In shallow triethylammonium phosphate-acetonitrile gradients (25 degrees C) satisfactory resolution of the two rat proinsulins was only obtained on the polymer-based Asahipak C4P-50 and C8P-50 columns. Increasing the separation temperature to 45 degrees C improved the separation of the two insulins and the two proinsulins in all cases. The shifts in retention times for the individual islet polypeptides observed in relation to the increased separation temperature were found to be different for the silica C4 and the polymer C4 columns. Recoveries of rat islet polypeptides were comparably high from the silica- and the polymer-based C4 columns and linear load-response curves were obtained in the microgram to picogram mass range on both columns.     

Metal speciation of metallothionein in white sea catfish, Netuma barba, and pearl cichlid, Geophagus brasiliensis, by orthogonal liquid chromatography coupled to ICP-MS detection

Metal speciation analysis in MTs was carried out in two tropical fish species of Brazil, the freshwater fish pearl cichlid (Geophagus brasiliensis) and the marine fish white sea catfish (Netuma barba), that are presently used to monitor the effects of heavy metal pollution in aquatic ecosystems in Brazil. In order to obtain the MT fraction, liver cytosols from both fish species where subjected to size exclusion fractionation, monitoring on-line the metal signal (Cd, Cu and Zn) by ICP-MS while protein elution was followed by on-line UV detection. That MT fraction was then separated by anion-exchange (AE)-FPLC, whose optimal chromatographic conditions were optimized for the separation of the different hepatic MT isoforms existing in both fish species. Specific detection of separated metalloforms was carried out again by the hyphenation of the AE chromatographic system with the ICP-MS instrument. The analytical results showed that MTs of these fish species, unknown so far, exhibited unique characteristics in comparison with standard MTs and other fish liver MTs. In fact, MT isoforms of N. barba turned out to be very anionic, as indicated by their high retention in the Mono Q column and the strong ionic strength required to separate them. As for G. brasiliensis, cadmium was exclusively present in only one of the peaks of the MT isoforms showing a unique metal-binding behavior for MT in this fish species. The differences between the MTs among these species and the different association of metals in particular MT isoforms display the importance of the metal speciation analysis in these proteins prior to its use as bioindicators.