Untersuchung der Na+-Verteilung in Kieselglas Mittels der Radiotracertechnik

The mobility of Na⁺ ions has been investigated by²⁴Na radioisotope in silica glass between 800 and 1400 °C. The evaluation was made by autoradiography. It was established that the distribution of sodium ions in the SiO₂ matrix depends on the homogeneity of the substance studied. In inhomogeneous materials Na⁺ migrates along inner surfaces such as grain boundaries, dislocations, etc., while in bubble-free homogeneous substances the diffusion observes the Fick law. For the latter case the diffusion coefficients have been calculated.     

Nucleation and growth of germanium nanowires seeded by organic monolayer-coated gold nanocrystals

Germanium nanowires, ranging from 10 to 150 nm in diameter, were grown several micrometers in length in cyclohexane heated and pressurized above its critical point. Alkanethiol-protected gold nanocrystals, either 2.5 or 6.5 nm in diameter, were used to seed wire formation. Growth proceeded through a solution-liquid-solid mechanism at growth temperatures ranging from 300 to 450 degrees C. At temperatures exceeding 500 degrees C, large Ge particulates formed due to unfavorable growth kinetics. Temperature, the nature of the precursor, precursor concentration, and the Au:Ge ratio were determining factors in nanowire morphology. The Ge nanowires were characterized using a range of techniques, including XPS, XRD, high-resolution TEM and SEM, nanometer-scale EDS mapping, and DTA.     

Pyridinium p-toluenesulfonylmethylide as a formyl anion equivalent

Pyridinium $\text{p}$-toluenesulfonylmethylide serves as a formyl anion equivalent and, in the presence of an alcohol, undergoes 1,4-addition to $\text{N}$-substituted maleimides to give alkoxy- (or aryloxy)-methylene-succinimides. The protected aldehyde group can be liberated readily.     

Solventless synthesis of monodisperse Cu2S nanorods, nanodisks, and nanoplatelets

Cu(2)S nanocrystals with disklike morphologies were synthesized by the solventless thermolysis of a copper alkylthiolate molecular precursor. The nanodisks ranged from circular to hexagonal prisms from 3 to 150 nm in diameter and 3 to 12 nm in thickness depending on the growth conditions. High resolution transmission electron microscopy (HRTEM) revealed the high chalcocite (hexagonal) crystal structure oriented with the c-axis ([001] direction) orthogonal to the favored growth direction. This disk morphology is thermodynamically favored as it allows the extension of the higher energy [100] and [110] surfaces with respect to the [001] planes. The hexagonal prism morphology also appears to relate to increased C-S bond cleavage of adsorbed dodecanethiol along the more energetic [100] facets relative to [001] facets. Monodisperse Cu(2)S nanodisks self-assemble into ribbons of stacked platelets. This solventless approach provides a new technique to synthesize anisotropic metal chalcogenide nanostructures with shapes that depend on both the face-sensitive thermodynamic surface energy and the surface reactivity.     

Evaluation of backbone proton positions and dynamics in a small protein by liquid crystal NMR spectroscopy

NMR measurements of a large set of protein backbone one-bond dipolar couplings have been carried out to refine the structure of the third IgG-binding domain of Protein G (GB3), previously solved by X-ray crystallography at a resolution of 1.1 A. Besides the commonly used bicelle, poly(ethylene glycol), and filamentous phage liquid crystalline media, dipolar couplings were also measured when the protein was aligned inside either positively or negatively charged stretched acrylamide gels. Refinement of the GB3 crystal structure against the (13)C(alpha)-(13)C' and (13)C'-(15)N dipolar couplings improves the agreement between experimental and predicted (15)N-(1)H(N) as well as (13)C(alpha)-(1)H(alpha) dipolar couplings. Evaluation of the peptide bond N-H orientations shows a weak anticorrelation between the deviation of the peptide bond torsion angle omega from 180 degrees and the angle between the N-H vector and the C'-N-C(alpha) plane. The slope of this correlation is -1, indicating that, on average, pyramidalization of the peptide N contributes to small deviations from peptide bond planarity ( = 179.3 +/- 3.1 degrees ) to the same degree as true twisting around the C'-N bond. Although hydrogens are commonly built onto crystal structures assuming the N-H vector orientation falls on the line bisecting the C'-N-C(alpha) angle, a better approximation adjusts the C(alpha)-C'-N-H torsion angle to -2 degrees. The (15)N-(1)H(N) dipolar data do not contradict the commonly accepted motional model where angular fluctuations of the N-H bond orthogonal to the peptide plane are larger than in-plane motions, but the amplitude of angular fluctuations orthogonal the C(alpha)(i-1)-N(i)-C(alpha)(i) plane exceeds that of in-plane motions by at most 10-15 degrees. Dipolar coupling analysis indicates that for most of the GB3 backbone, the amide order parameters, S, are highly homogeneous and vary by less than +/-7%. Evaluation of the H(alpha) proton positions indicates that the average C(alpha)-H(alpha) vector orientation deviates by less than 1 degrees from the direction that makes ideal tetrahedral angles with the C(alpha)-C(beta) and C(alpha)-N vectors.     

Insertion reactions of GaCp*, InCp* and In[C(SiMe3)3] into the Ru-Cl bonds of [(p-cymene)RuIICl2]2 and [Cp*RuIICl]4

The first carbonyl free ruthenium/low valent Group 13 organyl complexes are presented, obtained by insertion of ER (ER = GaCp*, InCp*, In[C(SiMe(3))(3)]) into the Ru-Cl bonds of [(p-cymene)RuCl2]2, [Cp*RuCl]4 and [Cp*RuCl2]2. The compound [(p-cymene)RuCl2]2 reacts with GaCp*, giving a variety of isolated products depending on the reaction conditions. The Ru-Ru dimers [{(p-cymene)Ru}2(GaCp*)4(mu3-Cl)2] and the intermediate [{(p-cymene)Ru}2(mu-Cl)2] were isolated, as well as monomeric complexes [(p-cymene)Ru(GaCp*)3Cl2], [(p-cymene)Ru(GaCp*)2GaCl3] and [(p-cymene)Ru(GaCp*)2Cl2(DMSO)]. The reaction of [Cp*RuCl]4 with ER gives "piano-stool" complexes of the type [Cp*Ru(ER)3Cl](ER = InCp*, In[C(SiMe3)3], GaCp*. The chloride ligand in complex can be removed by NaBPh4, yielding [Cp*Ru(GaCp*)3]+[BPh4]-. The reaction of [Cp*RuCl2]2 with GaCp* however, does not lead to an insertion product, but to the ionic Ru(II) complex [Cp*Ru(GaCp*)3]+[Cp*GaCl3]-. The ER ligands in complexes 3, 5, 6, 7 and 8 are equivalent on the NMR timescale in solution due to a chloride exchange between the three Group 13 atoms even at low temperatures. The solid state structures, however, exhibit a different structural pattern. The chloride ligands exhibit two coordination modes: either terminal or bridging. The new compounds are fully characterized including single crystal X-ray diffraction. These results point out the different reactivities of the two precursors and the nature of the neutral p-cymene and the anionic Cp* ligand when bonding to a Ru(II) centre.     

Perdeuterated Conjugated Polymers for Ultralow‐Frequency Magnetic Resonance of OLEDs

The formation of excitons in OLEDs is spin dependent and can be controlled by electron‐paramagnetic resonance, affecting device resistance and electroluminescence yield. We explore electrically detected magnetic resonance in the regime of very low magnetic fields (<1 mT). A pronounced feature emerges at zero field in addition to the conventional spin‐ Zeeman resonance for which the Larmor frequency matches that of the incident radiation. By comparing a conventional π‐conjugated polymer as the active material to a perdeuterated analogue, we demonstrate the interplay between the zero‐field feature and local hyperfine fields. The zero‐field peak results from a quasistatic magnetic‐field effect of the RF radiation for periods comparable to the carrier‐pair lifetime. Zeeman resonances are resolved down to 3.2 MHz, approximately twice the Larmor frequency of an electron in Earth's field. However, since reducing hyperfine fields sharpens the Zeeman peak at the cost of an increased zero‐field peak, we suggest that this result may constitute a fundamental low‐field limit of magnetic resonance in carrier‐pair‐based systems. OLEDs offer an alternative solid‐state platform to investigate the radical‐pair mechanism of magnetic‐field effects in photochemical reactions, allowing models of biological magnetoreception to be tested by measuring spin decoherence directly in the time domain by pulsed experiments.