Charakterisierung eines schweren Kohleverflüssigungsproduktes durch kombinierte Hochleistungsflüssigkeitschromatographie/Massenspektrometrie

Zusammenfassung Ein Recycleöl wurde semipräparativ auf einer Tetrachlorphthalimidopropylsilan-modifizierten Säule hochleistungsflüssigkeitschromatographisch in 23 Fraktionen getrennt. Zur Identifizierung der Hauptkomponenten wurden die Fraktionen mit einer einfachen Präparationstechnik in das Massenspektrometer eingebracht und die Molekülionenspektren unter Benutzung der Low Voltage-Technik gemessen. Vorteilhaft für die Charakterisierung hochsiedender technischer Gemische ist die Tatsache, daß die chromatographische Trennung streng nach der Anzahl der aromatischen Ringe im Molekül erfolgt, weitgehend unabhängig von der Alkylsubstitution.

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Characterization of a heavy coal liquefaction product by combined high-performance liquid chromatography/mass spectrometry

Summary A recycle-oil was separated on a semi-preparative scale into 23 fractions by means of HPLC with a tetrachlorophthalimidopropylsilane-modified column. Mass spectrometry enabled a more or less complete identification of the main components. For this, the fractions were introduced into the mass spectrometer by a simple preparation technique, followed by measurement of the molecule ion spectra by the low voltage technique. An advantage of HPLC for the characterization of high-boiling oil mixtures is that separation takes place almost exclusively accoding to the number of aromatic rings in the molecule and is largely independent of the degree of alkylation.

     

Differential inhibition of postnatal brain,spinal cord and body growth by a growth hormone antagonist

Background  

Growth hormone (GH) plays an incompletely understood role in the development of the central nervous system (CNS). In this study, we use transgenic mice expressing a growth hormone antagonist (GHA) to explore the role of GH in regulating postnatal brain, spinal cord and body growth into adulthood. The GHA transgene encodes a protein that inhibits the binding of GH to its receptor, specifically antagonizing the trophic effects of endogenous GH.     

Novel microscopic mechanism of intermixing during growth on soft metallic substrates

Generic computer simulations using empiric interatomic potentials suggest a new, collective mechanism that could be responsible for mixing at heteroepitaxial interfaces. Even if single adsorbate atoms diffuse by hopping on the substrate surface and do not mix at the terraces, two-dimensional islands formed by nucleation may become unstable above a certain critical size and explode upwards forming clusters of several atomic layers. This process is accompanied by strong distortions of the underlying atomic layers, and on soft materials it can result in surface etching and incorporation of substrate atoms into the islands.     

Modifying the 5′‐Cap for Click Reactions of Eukaryotic mRNA and To Tune Translation Efficiency in Living Cells

The 5′‐cap is a hallmark of eukaryotic mRNAs and plays fundamental roles in RNA metabolism, ranging from quality control to export and translation. Modifying the 5′‐cap may thus enable modulation of the underlying processes and investigation or tuning of several biological functions. A straightforward approach is presented for the efficient production of a range of N7‐modified caps based on the highly promiscuous methyltransferase Ecm1. We show that these, as well as N²‐modified 5′‐caps, can be used to tune translation of the respective mRNAs both in vitro and in cells. Appropriate modifications allow subsequent bioorthogonal chemistry, as demonstrated by intracellular live‐cell labeling of a target mRNA. The efficient and versatile N7 manipulation of the mRNA cap makes mRNAs amenable to both modulation of their biological function and intracellular labeling, and represents a valuable addition to the chemical biology toolbox.     

Ordering in a nematic side-chain polymer. A proton and deuterium nuclear magnetic resonance study

 The aim of this work is to study in detail the orientational structure of liquid-crystalline polymers with different molecular weight. The advantage of our approach is the use of broad-band ¹H and ²H NMR spectroscopy for the analysis of the orientational order of the main-chain and mesogenic groups in conjunction with small-angle neutron scattering results. Investigations of a series of partially deuterated side-chain polymers with methoxybenzylbenzoate mesogenic groups have been carried out. The deuteration of the main chain enables separate access to order and orientation effects of the side chain and the main chain. The molecular orientation of the substances investigated can be frozen in its nematic phase below the glass-transition temperature. It is independent of the molecular weight, whereas the dynamics of the director reorientation (rotational viscosity) in the nematic phase strongly depends on the molecular weight. The main-chain deuterons provide powder spectra after orientation of the polymer in magnetic fields, indicating a very weak or lacking orientational anisotropy. A complete decoupling of the main and the side group can be deduced. Received: 15 September 1999 Accepted: 7 February 2000     

Catenation and Aggregation of Multi‐Cavity Coordination Cages

A series of metal‐mediated cages, having multiple cavities, was synthesized from Pd^II cations and tris‐ or tetrakis‐monodentate bridging ligands and characterized by NMR spectroscopy, mass spectrometry, and X‐ray methods. The peanut‐shaped [Pd₃L¹₄] cage deriving from the tris‐monodentate ligand L¹ could be quantitatively converted into its interpenetrated [5Cl@Pd₆L¹₈] dimer featuring a linear {[Pd‐Cl‐]₅Pd} stack as an unprecedented structural motif upon addition of chloride anions. Small‐angle neutron scattering (SANS) experiments showed that the cigar‐shaped assembly with a length of 3.7 nm aggregates into mono‐layered discs of 14 nm diameter via solvophobic interactions between the hexyl sidechains. The hepta‐cationic [5Cl@Pd₆L¹₈] cage was found to interact with polyanionic oligonucleotide double‐strands under dissolution of the aggregates in water, rendering the compound class interesting for applications based on non‐covalent DNA binding.