H-Solid State NMR Studies of Tunneling Phenomena and Isotope Effects in Transition Metal Dihydrides

In many transition metal dihydrides and dihydrogen complexes the hydrogens are relatively weakly bound and exhibit a fairly high mobility, in particular with respect to their mutual exchange. Part of this high mobility is due to the exchange symmetry of the two hydrogens, which causes an energy splitting into even and odd spatial energy eigenfunctions, resulting in the typical coherent tunneling of a two-level system. Owing to the quantum mechanical symmetry selection principles the eigenfunctions are connected to the possible nuclear spin states of the system. If the tunneling frequency is in the proper frequency window it is thus possible to observe these tunneling transitions by NMR at very low temperatures, where no thermally induced exchange reactions overshadow the tunneling. The first part of this review gives an introduction into the interplay of chemical kinetics and tunneling phenomena in general, rotational tunneling of dihydrogen in a two-fold potential in particular and the Bell tunnel model, followed by a summary of solid state NMR techniques for the observation of these tunnel processes. Then a discussion of the effects of these processes on the ²H NMR line shape is given. The second part of the review reports results of a ²H-solid state NMR spectroscopy and T₁ relaxatiometry study of trans-[Ru(D₂)Cl(PPh₂CH₂CH₂PPh₂)₂]PF₆, in the temperature regime from 5.4 to 320 K. In the Ru-D₂ sample coherent tunneling and incoherent exchange processes on the time scale of the quadrupolar interaction are observed. From the spectra and T₁-data the height of the tunneling barrier is determined. Next results of ²H-spin–lattice relaxation measurements for a selectively η² − D₂ labeled isotopomer of the complex W(PCy₃)₂(CO)₃)(η² − D₂) are presented and discussed. The relaxation measurements are analyzed in terms of a simple one dimensional Bell tunnel model and comparison to incoherent neutron scattering (INS) data from the H₂ complex. The comparison reveals a strong isotope effect of 2 × 10³ for the exchange rates of the deuterons versus hydrons.     

Lichtmikroskopische Untersuchungen über Antiphasengrenzen in Eisen-Silizium-Legierungen

Anätzbarkeit von Antiphasengrenzen in Eisen-Silizium-Legierungen. Isotrope B 2- und anisotrope DO₃-Antiphasengrenzen. Abhängigkeit der Antiphasenstruktur von der Wärmebehandlung und Legierungszusammensetzung.     

Untersuchungen über das metastabile System Eisen-Chrom mit Hilfe des Mössbauer-Effektes

Die Mischungslücke im metastabilen System Eisen-Chrom. Aussagen der Mössbauer-Spektren über die Atomanordnung in Eisenlegierungen. Nachweis der einphasigen Entmischung in übersättigten Eisen-Chrom-Legierungen in eisen- und chromreiche Phasenteile.     

Hydrogen Bond Compression during Triple Proton Transfer in Crystalline Pyrazoles. A Dynamic 15N NMR Study

Using dynamic solid state ¹⁵N CPMAS NMR spectroscopy (CP ≡ cross polarization, MAS ≡ magic-angle spinning), the kinetics of degenerate intermolecular triple proton and deuteron transfers in the cyclic trimers of ¹⁵N-labeled polycrystalline 4-nitropyrazole (4NO₂P) and 4-bromopyrazole (4BrP) have been studied as a function of temperature and are compared to the kinetics of triple proton transfer in bulk solid 3,5-dimethylpyrazole (DMP) studied previously. The results show that the transfer kinetics in the new trimers are much faster than in DMP. However, the kinetic HHH/HHD/HDD/DDD isotope effects of 4NO₂P are similar to those of DMP. These effects indicate a single barrier for the triple proton transfers where all three protons lose zero-point energy in the transition state, as expected for a structure with three compressed hydrogen bonds. At low temperatures, strong deviations from an Arrhenius-behavior are observed which are described in terms of a modified Bell tunneling model and a concerted proton motion. The barrier for the triple proton transfer in 4NO₂P and 4BrP is substantially smaller than in DMP. As there is no correlation with the electronic properties of the substituents, we assign this finding to steric effects where the bulky methyl groups of DMP in the 3- and 5-positions hinder the hydrogen bond compression, in contrast to 4NO₂P and 4BrP exhibiting substitutents in the 4-position. These results lead to a minimum energy pathway of the proton transfer following in the absence of steric hindering the hydrogen bond correlation line q₁ = f(q₂), established previously, where q₁ represents the deviation of the proton from the hydrogen bond center and q₂ the N…N distance. Tunneling occurs at constant N…N distances.     

Hydrodynamische Einlauflänge und Widerstandsgesetz von reibungsmindernden kationschen Tensidlösungen

Zusammenfassung Durch Zugabe geeigneter Tensidsysteme in Wasser kann der Str?mungsdruckverlust in geraden Rohren erheblich gesenkt werden. Die diesem Effekt zugrunde liegenden Mechanismen wurden in früheren Arbeiten eingehend diskutiert. In dieser Arbeit werden neue Ergebnisse vorgestellt, die sowohl die Bestimmung der hydrodynamischen Einlaufl?nge als auch die Ermittlung der Widerstandsbeiwerte im ausgebildeten Str?mungszustand erm?glichen. Für den Bereich der ausgebildeten Rohrstr?mung wird eine neue Berechnungsgleichung vorgeschlagen. Durch Erweiterung der bisherigen Modellvorstellungen ergibt sich ein Widerstandsgesetz für den gesamten Wirkungsbereich des Tensids. Die Ergebnisse stützen sich auf Untersuchungen mit zwei verschiedenen Additivsystemen, bei denen die Parameter Str?mungsgeschwindigkeit, Temperatur und Einsatzkonzentration variiert wurden.     

The distribution of lithium between erythrocytes and plasma: in vitro studies on the transport of lithium in human erythrocytes

Distribution ratiors of intracellular lithium (Lii) and extracellular Li (Lie) were determined in vitro after incubation of Li-free or Li-loaded red cells in media containing varying Li-concentrations (37 degrees C, pH 7.4). The distribution ratios Lii/Lie obtained in vitro after 24 h of incubation corresponded to those found in vivo. The results indicate that Li can be extruded from red cells against an electrochemical gradient. This Li extrusion is inhibited by replacing extracellular Na+ with K+ or choline+, but is not affected by ouabain or by glucose depletion.     

Das Keilzinken von Holz—Dritte Mitteilung: Maschinentechnik und Wirtschaftlichkeit eines neuen Keilzinkenverfahrens

Zusammenfassung Maschinen herk?mmlicher Art sind für die Herstellung der neuen Keilzinkung nicht geeignet. Die baulichen Grundlagen für eine neue Maschine werden dargestellt. Die Ergebnisse von Untersuchungen im Laboratorium und im einj?hrigen Probebetrieb in einem Werk sind erfolgversprechend. Das Verfahren ist durch folgende Tatsachen gekennzeichnet: Kurze Zinkenl?nge, dadurch Einsparung von Holz, sehr geringe Zinkenspitzenbreite, dadurch sehr geringes Zinkenspiel, das Vorfr?sen oder Vors?gen von Zinkenprofilen entf?llt, stark verminderter Kraftverbrauch auf Grund geringer Schnittarbeit, doppelseitiger, kontrollierter und verlustarmer Leimauftrag, hohe Anfangsfestigkeit der neuen Keilzinkenverbindung bei Pressung ohne W?rmezufübrung, hohe Endfestigkeit.

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Finger-Jointing of Wood—Part III: Machine processing and economic aspects of a new finger jointing method

Summary Conventional finger jointing equipment are inappropriate for the manufacture of the new finger-joint. The principles of design for a machine according to the new method have been developed. The results from laboratory tests as well as the experiences gained from tests in the industrial field are very promising. The method is determined by the following facts: Extremely short finger-length and thus wood savings, very little width of the fingertips and thus little pin-clearance, precutting or presawing of the profiles is eliminated, power consumption is considerably reduced because of little excised wood-volume, controlled glue application on both profiles and thus little waste of glue, high initial strength without additional heat when pressing the glued pieces, and finally high ultimate strength.

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Dieses Keilzinkverfahren wurde unter Leitung von Prof. Dr.-Ing. J. E. Marian, Universíty of California, Berkeley, USA, zusammen mit Civ. Ing. B. O. Ivansson, Civ. Ing. H. Str?m und den Verfassern an der K?nigl. Technischen Hochschule, Stockholm, Institut für Bautechnik, Leitung Prof. Dr.-Ing. H. Brosenius, entwickelt. Die Finanzierung erfolgte durch den staatl. technischen Forschungsrat, Stockholm. Die Verfasser danken den Mitarbeitern für eine vorbildliche Zusammenarbeit, Prof. Brosenius für die freizügige überlassung der Einrichtungen des Institutes und den Finanzierungsinstitutionen besonders Civ, Ing. N. Bergling von EFOR, Stockholm, für vielfach geleistete Hilfe.     

Solid State and Gas Phase NMR Studies of Immobilized Catalysts and Catalytic Active Nanoparticles

In the current study two new classes of stabile, catalytic active nanomaterials are investigated. The first class of nanoparticles consists of an inner metal core. To stabilize their structure the metal core is surrounded by organic ligands or embedded in a polymer. The second class consists of catalysts immobilized on mesoporous silica supports of SBA-3 type silica. Employing a combination of ¹H, ²H, ¹³C and ²⁹Si-solid state NMR spectroscopy the structure of the catalysts is analyzed. As a simple model for the catalytic properties of the particles, the activation of ²H₂ gas on the surface of the particles is studied. Employing ¹H and ²H gas phase NMR the kinetics of simple catalytic model reactions is studied. Employing ²H-NMR solid state NMR spectroscopy, the interaction of the metal surface with the substrate is characterized and kinetic data, which characterize the mobility of the deuterium on the surface, are extracted. For the interpretation of these data, parallel NMR studies of model η²-bound transition metal complexes are employed, which allow, owing to their simpler geometry and higher sensitivity, a quantitative modeling of the spin dynamics in the NMR experiment.     

Improved Performance and Stability of All‐Inorganic Perovskite Light‐Emitting Diodes by Antisolvent Vapor Treatment

All‐inorganic perovskite light‐emitting diodes (LEDs) reveal efficient luminescence with high color purity, but their modest brightness and poor stability are still critical drawbacks. Here, the luminescent efficiency and the stability of perovskite LEDs (PeLEDs) are boosted by antisolvent vapor treatment of CsPbBr₃ embedded in a dielectric polymer matrix of polyethylene oxide (PEO). A unique method is developed to obtain high quality CsPbBr₃ emitting layers with low defects by controlling their grain sizes. CsPbBr₃ in PEO matrix is post‐treated with antisolvent of chloroform (CF), leading to microcrystals with a size of ≈5 µm along the in‐plane direction with active emitting composite of 90%. A device based on CF post‐treatment (CsPbBr₃‐PEO‐CF) film displays a brightness of up to 51890 cd m^?2 with an external quantum efficiency of 4.76%. CsPbBr₃‐PEO‐CF PeLED still maintains 82% of its initial efficiency after 80 h continuous operation in ambient air, which indicates relatively good device stability. This work highlights that film quality is not only key to promoting fluorescence in CsPbBr₃, but also to achieving higher performance PeLEDs.