Kernresonanzuntersuchungen an verstrecktem und getempertem linearem Polyäthylen

Zusammenfassung Es wurden die NMR-Spektren von bei 80 °C mit einem Verstreckgrad von 10,5 verstrecktem linearem Polyäthylen, das bis zu 10⁴ min bei 120 °C getempert wurde, sowie von drei weiteren Proben (schmelzkristallisiert, bulk, hochdruckkristallisiert) gemessen. Im verstreckten Material treten drei verschieden breite Linien auf. Die breite Komponente rührt von Protonen im kristallinen Anteil her, die mittlere wird Protonen in den lateralen Fibrillengrenzen und im nichtkristallinen Bereich zugeschrieben, während die schmale Komponente durch Kettenenden. die nicht in den kristallisierten Teil eingebaut wurden, erklärt wird. Im bulk und schmelzkristallisierten Material wird die schmale Komponente, im hochdruckkristallisierten die mittlere Komponente nicht beobachtet. Im verstreckten Material wird bei Temperzeiten zwischen 3 und 5 min der Kristallisationsprozeß unterbrochen, die relativen Anteile der drei Komponenten ändern sich nicht, das zweite Moment der breiten Linie durchläuft ein Maximum. Anteil und zweites Moment der schmalen Komponente ist unabhängig von der Temperzeit.

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Summary The NMR-spectra of hot stretched (80 °C, degree of stretching 10,5) and up to 10⁴ min annealed linear polyethylene, and of 3 other samples (melt crystallized, bulk and high pressure crystallized) are measured. In the stretched material one obtains three components with different width. The broad component is caused by protons inside the crystalline part, the mean component is adjoined with protons in the lateral fibril boundaries and in the noncrystalline part and the narrow component comes from chain ends, not included in the crystallites. The bulk- and meltcrystallized material shows no narrow, the high-pressure sample no mean component. In the stretched material the crystallization process is stopped between 3 and 5 min annealing time, the relative portions of the three components are unchanged, the second moment of the broad line goes through a maximum. Relative portion and second moment of the narrow component is independent of annealing time.

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Den Herren Prof. Dr.Jahr und Dr.Knoll danken wir herzlich für die uns gebotene Möglichkeit, die NMR-Messungen im Institut für Anorganische Chemie der Freien Universität Berlin durchzuführen.Der Deutschen Forschungsmeinschaft danken wir für finanzielle Unterstützung dieser Arbeit, einer der Verfasser (FrauJ. Loboda- akovi) außerdem dem DAAD für ein Stipendium; Herrn Prof. Dr.B. Wunderlich gilt unser Dank für die Überlassung des hochdruckkristallisierten Polyäthylens.     

Kernresonanzuntersuchungen an zeolithischen Heptagermanaten, 2. Mitt.

Zusammenfassung An zeolithischen Heptagermanaten der FormelMe ₃HGe₇O₁₆·xH₂O, (Me=NH₄, Li, Tl, Cs und Na;x=0–6) wurden Kernresonanzuntersuchungen durchgeführt. Es wurden Messungen an¹H und¹⁴N in Ammoniumzeolith sowie an⁷Li,²⁰⁵Tl,¹³³Cs und²³Na zwischen Zimmertemp. und der Temperatur des flüssigen Stickstoffs ausgeführt. Es zeigt sich, daß die Kationen Diffusionsbewegungen ausführen, die sowohl durch höhere Temperatur als auch durch das Vorhandensein von Wassermolekülen begünstigt werden.

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NMR investigation of zeolitic heptagermanates, II

Zeolitic heptagermanates with compositionMe ₃HGe₇O₁₆·xH₂O, (Me=NH₄, Li, Tl, Cs and Na;x=0–6) have been investigated by NMR. Measurements on¹H and¹⁴N in ammoniumzeolites and on⁷Li,²⁰⁵Tl,¹³³Cs and²³Na have been performed between room temperature and liquid nitrogen temperature. It is observed that the cations execute diffusional motions, which are favoured by higher temperature as well as by the presence of water molecules.

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Mit 9 Abbildungen     

Kernresonanzuntersuchungen an Thalliumverbindungen,besonders Thallium–Phosphat-Gläsern

NMR Studies on Thallium Compounds, especially of Thallium Phosphate Glasses Nuclear magnetic resonance techniques with ²⁰⁵Tl have been used to study the Character of the Tl–O bond in different Tl-salts and phosphate systems containing Tl. Generally the covalent contribution to the Tl–O bond increases in the order of the Tl Content. Tl₃PO₄ has the highest covalent contribution on the systems investigated. If Tl is successively substituted by K no influence on the Tl–O bond-character has been observed, but Mg causes diminishing of the covalent character. It follows from Paper chromatography that high condensated phosphates (P₈) in acid solutions are hydrolysed the easier the higher the covalent contribution of the Tl–O–bond.     

Kernresonanzuntersuchungen am 1,10-Phenanthrolin und seinen Komplexverbindungen—V: Zum Ligandenaustausch an einigen diamagnetischen Phenanthrolin-Komplexen

The ligand exchange of 1,10-phenanthroline between its diamagnetic coordinated site (central ions: [Zn]²⁺, [Fe]²⁺, [Co]³⁺) and its free site has been studied by proton magnetic resonance spectroscopy. The mean lifetimes of ligands in systems with the central atoms Zn and Fe are computed by a complete line shape analysis and are estimated from line width measurements, respectively. The activation energy, the free energy of activation, the activation enthalpy and the activation entropy are calculated from the temperature dependence of the mean lifetimes.     

Kernresonanzuntersuchungen des Tunneleffekts der Methylgruppen in Hochpolymeren bei sehr tiefen Temperaturen,I. Teil

Ohne Zusammenfassung The online version of the original article can be found at     

Kernresonanzuntersuchungen am 1.10-Phenanthrolin und seinen Komplexverbindungen—IV: 13C-Resonanzen des freien und protonierten 1.10-Phenanthrolins

The ¹³C chemical shifts of free and protonated 1,10-phenanthroline have been measured and interpreted by means of π- and (σ + π)-MO-electron calculations as described in Parts I¹ and III.² For the protonated molecule a high field ¹³C shift of the C-atom adjacent to the N-atom is characteristic; this effect is explained in terms of a decrease of the N–C overlap population. For the mono- and diprotonated 1,10-phenanthroline the best correlation with the experimental shift values was obtained by assuming a small formal charge on the nitrogen atom (Δ = 0·0 to 0·3).     

Converting an Esterase into an Epoxide Hydrolase

Entering the fold : A common structural motif in hydrolytic enzymes is the α,β‐hydrolase fold. The interconversion of one enzyme into another by introduction of mechanistically important residues is not enough; only substitution of a loop allows epoxide hydrolase activity in the esterase scaffold to be formed (see picture; structure comparison of epoxide hydrolases (green) with the esterase (orange)). The result is an enantioselective chimeric enzyme.

     

Neutralisationstitrationen an der Tantal- und an der Mobelektrode

Ohne Zusammenfassung     

Multicut-HDMR with an application to an ionospheric model

A new High Dimensional Model Representation (HDMR) tool, Multicut-HDMR, is introduced and applied to an ionospheric electron density model. HDMR is a general set of quantitative model assessment and analysis tools for improving the efficiency of deducing high-dimensional input-output system behavior. HDMR describes an output [f(x)] in terms of its input variables (x = [x(1), x(2), em leader, x(n)]) via a series of finite, hierarchical, correlated function expansions. Various forms of HDMR are constructed for different purposes such as modeling laboratory or field data, or reproducing a complicated mathematical model. The Cut-HDMR technique, which expresses f(x) with respect to a specified reference point x in the input space, is appropriate when the input space is sampled in an orderly fashion. However, if the desired domain of the input space is too large, the HDMR function expansion may not converge, and Cut-HDMR will be unable to accurately approximate f(x). The new Multicut-HDMR technique addresses this problem through the use of multiple reference points in the input space.     

Synthesis of an isostere of an O-linked glycopeptide

[reaction: see text] A route for the synthesis of an electrophilic, carbocyclic galactose equivalent from D-galactose is described. The strategy utilizes ring-closing metathesis with Grubbs's second-generation catalyst as the key step. The galactose-derived electrophile reacted in an S(N)2 fashion with N-Boc-cysteine methyl ester to provide an alpha-galactosylserine isostere. The method was extended to the synthesis of a glycopeptide isostere.     

Effect of an electric field on an interfacial profile

We consider the interface between two dielectric liquids in an electric field which is parallel to the interface. Using the Ginsburg-Landau model for binary fluids we add a term for the electric field energy and show that near the critical point the effect of the electric field is to change both the interface width and the critical temperature.     

Activating an enzyme by an engineered coiled coil switch

We designed a de novo protein based on a circular permutant of RNaseT1, in which the enzymatic activity can be manipulated by engineered peptide binding. The circular permutant of RNaseT1 was obtained by tethering the original C- and N-termini with a GPAG linker and cleaving the molecule between Glu82 and Asn83. This mutant lacked enzymatic activity, due to the destabilization of entire protein structure. We previously reported the construction of ABC-type heterotrimeric coiled coil peptides, in which the A- and B-type peptides cannot form the folded trimeric structure without the C-type peptide. The introduction of the A- and B-type coiled coil peptides to the C- and N-termini of the circular permutant of RNaseT1, respectively, and the subsequent addition of the C-type coiled coil peptide enabled the RNaseT1 domain to refold properly, thus, restoring the enzymatic activity. The formation of the trimeric coiled coil structure should bring the cleaved sites of RNaseT1 close enough to refold the RNaseT1 domain spontaneously.     

The first example of an ene reaction between an ester of cyclopropenecarboxylic acid and an alkyne

Methyl cyclopropenecarboxylate (I) enters into the ene reaction with the cyclic acetylene (II), giving vinylcyclopropene (III) with a high yield.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1229–1230, May, 1991.