Dipole moments of compounds containing a cobalttin bond

The molecular electric dipole moments are reported for the series of tin-substituted tetracarbonyl cobalt compounds R_nY_m?nSn{Co(CO)₄}_4?m (m = 1–3; n ? m; R = alkyl, phenyl; Y = halogen). The effect of the substituents at the tin atom on the nature of the CoSn bond is established on calculating the (CO)₄CoSn group dipole moments. It is shown that the charge transfer in the CoSn bond is mainly determined by the inductive properties of the ligands attached to tin.     

Zur direkten ma?analytischen Bestimmung von Carbamaten als sehr schwache S?uren

Zusammenfassung Eine direkte maßanalytische Methode zur Bestimmung diverser Carbamate wird beschrieben. Die potentiometrische Titration mit käuflicher Tetra-n-butylammoniumhydroxid-Lösung, verdünnt mit Propanol-(2), ist bequem durchzuführen, und die erhaltenen Titrationskurven gestatten eine korrekte Auswertung.

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Direct volumetric determination of carbamates as very weak acids

Summary A volumetric procedure for the determination of some carbamates is described. The potentiometric titration with commercial tetra-n-butylammonium hydroxide solution diluted with propanol-(2) is convenient and the obtained titration curves permit a correct calculation.

     

EFFECT OF MOLYBDENUM PROMOTER ON THE Cu-Co BASED CATALYSTS

The synthesis of mixed alcohols (C1-C5) from syngas has been studied at 6. 0 MPa over modified Co/CuLaZr catalysts. The molybdenum addition enhanced greatly the activity and the selectivity to alcohols. The improvement of hydrogenation capacity of the system via a reversible spillover effect of hydrogen could explain this effect, together with a great capacity of CO insertion, illustrated by the effect of C2H4 addition as a probe to syngas. Under our experimental conditions, a mixed alcohol production of 147.1g/kg. cat/h containing a proportion of 33. 1% of higher alcohols (C2 OH) was obtained with a selectivity to ROH of 52. 8%.     

A microwave-assisted click chemistry synthesis of 1,4-disubstituted 1,2,3-triazoles via a copper(I)-catalyzed three-component reaction

A microwave-assisted three-component reaction was used to prepare a series of 1,4-disubstituted-1,2,3-triazoles from corresponding alkyl halides, sodium azide, and alkynes. This procedure eliminates the need to handle organic azides, as they are generated in situ, making this already powerful click process even more user-friendly and safe.     

Atmospheric pressure electrospray ionization mass spectra of glucose and 2-fluorodeoxyglucose for quantitative analysis of 2-fluorodeoxyglucose by high-performance liquid chromatography

2-Fluoro-2-deoxy-D-glucose (FDG) labeled by fluorine-18 is the most widely used radiopharmaceutical for positron emission tomography (PET). For high-performance liquid chromatography (HPLC)/MS assay and quality control, the mass spectra of FDG and glucose (Glc) in organic + water solutions were studied by flow injection analysis (FIA) and in a chromatographic eluate. In acetonitrile (MeCN) + 0.025% ammonium formate (NH(4)HCO(2)) solvent (80 : 20), electrospray ionisation (ESI) of glucose-FDG provides M.NH(4)(+) and 2M.Na(+) (M = Glc or FDG) as the most intense positive ions. Formation of the latter ions and also of M.MeCN.Na(+) and 2MeCN. Na(+) is typical of the presence of NaCl in the ESI inlet. The positive ions include heavier ions corresponding to the impurities separated by HPLC and also to the cross-ring fragmentation of complexes (2FDG. aMeCNX)L, where a = 0 or 1, L is either Na(+) or NH(4)(+) and X is a fragmented pyranose or anhydropyranose residue. The second most abundant Glc negative ion is m/z = 359 which was interpreted as (2GlcH(+))(). The negative-ion spectrum of FDG has dominating lines due to FDG.HCO(2)() ions at m/z 227 and also (2FDGH(+))() at m/z 363. The m/z 363 signal is suppressed in the presence of NaCl at a molar ratio of 4 : 1 to NH(4)HCO(2), while the ions at m/z 217 and 219, i.e. FDG.Cl(), become three times more intense than FDG.HCO(2)(). The latter ion appears to be most suitable as an analytical signal for chemical analysis of FDG at m/z 226 and 227. Limits of FDG quantitation (LOQ) of 19 ng and 21 ng were found for the 200(+) and 227() ion signals, respectively, and are wholly adequate for verification of total FDG content in radiopharmaceuticals.     

TRANSMISSION OF HUMAN EPIDERMIS AND STRATUM CORNEUM AS A FUNCTION OF THICKNESS IN THE ULTRAVIOLET AND VISIBLE WAVELENGTHS

Abstract The dependence of radiation transmission on sample thickness was studied in isolated samples of human stratum corneum and full-thickness epidermis. The investigation also included samples of skin repeatedly exposed to UV-B. Transmission was measured in the ultraviolet and in the visible from 248–546 nm. Two methods, one microscopic and the other mechanical, were used to measure thickness. There was a good correlation between the results.
The dependence of transmission on thickness in these samples could be described satisfactorily by an exponential function, implying that the Lambert-Beer law is approximately valid. Thus, a single parameter, such as the half-value layer ( d _½), is sufficient to characterize absorption in the skin samples.
Water content of the isolated stratum corneum was influenced by maintenance conditions: samples floating on water containing a small amount of NaCl were more hydrated than samples floating on a more concentrated salt solution, or stored in air. Changes in water content of the samples resulted in changes of thickness and, to a lesser extent, of transmission. Approximate in vivo values of d _½ were computed after estimating the in vivo water content of stratum corneum.
Differences found in the shape of the transmission spectra of stratum corneum and full-thickness epidermis may reflect differences in chemical composition. The influence of wetting of the skin on its sensitivity to sunlight is explained in a new way.     

Identification of extracellular nanoparticle subsets by nuclear magnetic resonance

Exosomes are a subset of secreted lipid envelope-encapsulated extracellular vesicles (EVs) of 50–150 nm diameter that can transfer cargo from donor to acceptor cells. In the current purification protocols of exosomes, many smaller and larger nanoparticles such as lipoproteins, exomers and microvesicles are typically co-isolated as well. Particle size distribution is one important characteristics of EV samples, as it reflects the cellular origin of EVs and the purity of the isolation. However, most of the physicochemical analytical methods today cannot illustrate the smallest exosomes and other small particles like the exomers. Here, we demonstrate that diffusion ordered spectroscopy (DOSY) nuclear magnetic resonance (NMR) method enables the determination of a very broad distribution of extracellular nanoparticles, ranging from 1 to 500 nm. The range covers sizes of all particles included in EV samples after isolation. The method is non-invasive, as it does not require any labelling or other chemical modification. We investigated EVs secreted from milk as well as embryonic kidney and renal carcinoma cells. Western blot analysis and immuno-electron microscopy confirmed expression of exosomal markers such as ALIX, TSG101, CD81, CD9, and CD63 in the EV samples. In addition to the larger particles observed by nanoparticle tracking analysis (NTA) in the range of 70–500 nm, the DOSY distributions include a significant number of smaller particles in the range of 10–70 nm, which are visible also in transmission electron microscopy images but invisible in NTA. Furthermore, we demonstrate that hyperpolarized chemical exchange saturation transfer (Hyper-CEST) with ¹²⁹Xe NMR indicates also the existence of smaller and larger nanoparticles in the EV samples, providing also additional support for DOSY results. The method implies also that the Xe exchange is significantly faster in the EV pool than in the lipoprotein/exomer pool.

Diffusion and xenon NMR based methods to determine a very broad range of sizes and sub-sets of extracellular vesicles.     

Breakthrough of polymers in interactive liquid chromatography

Two separate peaks are observed for narrow polymer standards in both isocratic and gradient HPLC. One peak appears around the solvent front (the "solvent-plug peak" or "breakthrough peak"), whereas the second peak is retained significantly--or even highly. Although the effect has been observed many times before, it has never been rigorously explained. In this paper we provide a detailed explanation for the breakthrough peak. The two completely separate peaks are demonstrated not to represent to different fractions of the sample (e.g., the low- and high-molecular-mass parts of the distribution). Both peaks are representative of the entire polymeric sample for narrow polymer standard. Because the amount of the polymer in the breakthrough peak may vary, the quantitative analysis of the polymers by LC is jeopardized. The effects of the sample solvent, the (initial) mobile phase composition, the injection volume, the injected sample concentration, the column temperature, and the analyte structure and molecular mass on the breakthrough peak were investigated in LC experiments involving standards of polystyrene and poly(methyl methacrylate). Three necessary and sufficient conditionsare suggested for the breakthrough phenomenon to be observed. Recommendations to avoid the breakthrough phenomenon are given, culminating in a structured method for selecting the best possible sample solvents.     

Synthesis and properties of allenic natural products and pharmaceuticals

Nowadays, about 150 natural products comprising an allenic or cumulenic structure are known. The chemistry of these compounds has turned out to be a very attractive and prolific area of interest: advances in the isolation and characterization of new allenic natural products have led to the establishment of efficient synthetic procedures which in many cases also open up an access to enantiomerically pure target molecules. Inspired by the intriguing biological activities of many allenic natural products, allene moieties are now systematically introduced in pharmacologically active classes of compounds (steroids, prostaglandins, amino acids, nucleosides). The functionalized allenes thus obtained often exhibit impressive activities as mechanism-based enzyme inhibitors, cytotoxic, or antiviral agents. A prerequisite for further developments in this field is the efficient stereoselective synthesis of allene derivatives.     

Electron microscopic phase analysis of BN-thin films

A series of BN films was deposited by means of r.f. magnetron sputtering of a h-BN target onto Si(1OO) surfaces. Hereby, the substrate bias voltage was varied. Special interest is focussed to the influence of the deposition parameters on the orientation of the growing hexagonal BN film with respect to the substrate. For structural investigation, cross section samples were prepared. In addition to HRTEM and diffraction investigations, especially electron energy loss spectroscopy (EELS) was applied successfully for phase identification. For negative bias voltages of U _B =–300 V and U _B =–350V, we found a phase system consisting of a first-grown 25 nm thick layer of hexagonal structure with the c axis parallel to the substrate surface followed by the cubic phase.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday