Beryllium

Ohne Zusammenfassung     

Versatility of the dipolar filter selection: from 1H nuclear spin diffusion experiment to the measurement of nuclear Overhauser effect in homopolymer melts

Dipolar filters select ¹H magnetization according to local dipolar dephasing, which corresponds to site mobility in systems with heterogeneous molecular mobility. Combined with a conventional exchange experiment, it is usually applied to polymeric samples exhibiting structures on the nanometer length scale associated with a strong dynamic contrast. There, the resulting ¹H nuclear spin diffusion experiment yields the size of the structure. When the same experiment is applied to homopolymer melts exhibiting a weak dynamic contrast and dynamic heterogeneities on significant shorter length scales, the recorded magnetization decay is in agreement with decays expected from a heterogeneous nanostructure. However, dipolar filters actually can also select mobile parts of the repeat unit, e.g. the end of the alkyl side chains and the subsequent magnetization transfer then can occur via cross relaxation due to non coherent zero-quantum transitions (nuclear Overhauser effect, NOE). The difficulties of distinguishing these two cases are examined and it is demonstrated that NOE experiments exploiting magnetization selection via the dipolar filter allow quantifying the local dynamics of the side chains. This opens new possibilities for measurements of local dynamics in non isotopically labeled homopolymer melts.     

Als ein neues Reagens auf Phlorogluzin, Katechin und ihre Derivate

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Investigations on atomization mechanisms in hydride-generation atomic absorption spectrometry

Summary Experiments are carried out where hydrides are collected in a cold trap, revolatilized, and conducted into a heated quartz tube with a controlled stream of pure or mixed gases. In the presence of hydrogen, atomization proceeds via hydrogen radicals formed in the quartz tube in a rather restricted area. Lifetime of the analyte atoms is at least three orders of magnitude longer than that of the H radicals. In the absence of hydrogen the hydrides are thermally decomposed but only in part atomized. The species formed during the thermal decomposition, probably an oxide and/or the element, are retained in the heated quartz tube to essentially 100%. The deposited species can be re-volatilized and atomized in part when hydrogen enters the heated quartz tube at a later time.

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Untersuchungen über Atomisierungsmechanismen in der Hydrid-Atomabsorptionsspektrometrie

Zusammenfassung Es wurden Versuche durchgeführt, bei denen die Hydride in einer Kühlfalle gesammelt, wieder verflüchtigt und mit einer kontrollierten Strömung reiner oder gemischter Gase in ein beheiztes Quarzrohr geleitet werden. In Gegenwart von Wasserstoff erfolgt die Atomisierung über H-Radikale, die sich in einer begrenzten Zone in dem Quarzrohr bilden. Die Lebensdauer der Analytatome ist mindestens drei Größenordnungen länger als die der H-Radikale. In Abwesenheit von Wasserstoff werden die Hydride thermisch zersetzt, aber nur teilweise atomisiert. Die bei der thermischen Zersetzung gebildete Substanz, wahrscheinlich ein Oxid oder das Element, verbleibt praktisch zu 100% in dem beheizten Quarzrohr. Die abgelagerte Substanz kann teilweise wieder verflüchtigt und atomisiert werden, sobald Wasserstoff in das beheizte Quarzrohr gelangt

     

Wolfram

Ohne Zusammenfassung     

Synthesis and characterization of synthetic polymer colloids colloidally stabilized by cationized starch oligomers

A method is developed for anchoring enzymatically degraded cationized starch as electrosteric stabilizers onto synthetic latices, using cerium(IV) to create free‐radical grafting sites on the starch. Direct anchoring of debranched starch onto a poly(methyl methacrylate) seed latex yields a latex stabilized by well‐defined oligosaccharides. Using α‐amylase to randomly cleave starch to form (1→4)‐α‐glucans, and a comonomer, N‐isopropyl acrylamide (NIPAM), whose corresponding polymer exhibits a lower critical solution temperature (LCST), creates a means to synthesize block (or graft) oligomers of oligosaccharide and synthetic polymer, which are water soluble at room temperature. Above 30 °C, they become amphiphilic and form self‐emulsifying nanoparticles (sometimes termed “frozen micelles”) from which a synthetic latex is grown after addition of methyl methacrylate, the collapsed NIPAM‐containing entities functioning as a type of in situ seed. This synthesis of stable synthetic latex particles is shown to have a high grafting efficiency. The starch fragments were characterized by ¹H solution‐state NMR before grafting, and ¹³C solid‐state cross‐polarization magic‐angle spinning (CP‐MAS) NMR was used to characterize the starch oligomers actually grafted on the final latex. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1836–1852, 2009     

Thermally induced alkylation of diamond

We present an approach for the thermally activated formation of alkene-derived self-assembled monolayers on oxygen-terminated single and polycrystalline diamond surfaces. Chemical modification of the oxygen and hydrogen plasma-treated samples was achieved by heating in 1-octadecene. The resulting layers were characterized using X-ray photoelectron spectroscopy, thermal desorption spectroscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and water contact angle measurements. This investigation reveals that alkenes selectively attach to the oxygen-terminated sites via covalent C-O-C bonds. The hydrophilic oxygen-terminated diamond is rendered strongly hydrophobic following this reaction. The nature of the process limits the organic layer growth to a single monolayer, and FTIR measurements reveal that such monolayers are dense and well ordered. In contrast, hydrogen-terminated diamond sites remain unaffected by this process. This method is thus complementary to the UV-initiated reaction of alkenes with diamond, which exhibits the opposite reactivity contrast. Thermal alkylation increases the range of available diamond functionalization strategies and provides a means of straightforwardly forming single organic layers in order to engineer the surface properties of diamond.