Water Triggers Hydrogen‐Bond‐Network Reshaping in the Glycoaldehyde Dimer

Carbohydrates are ubiquitous biomolecules in nature. The vast majority of their biomolecular activity takes place in aqueous environments. Molecular reactivity and functionality are, therefore, often strongly influenced by not only interactions with equivalent counterparts, but also with the surrounding water molecules. Glycoaldehyde (Gly) represents a prototypical system to identify the relevant interactions and the balance that governs them. Here we present a broadband rotational‐spectroscopy study on the stepwise hydration of the Gly dimer with up to three water molecules. We reveal the preferred hydrogen‐bond networks formed when water molecules sequentially bond to the sugar dimer. We observe that the dimer structure and the hydrogen‐bond networks at play remarkably change upon the addition of just a single water molecule to the dimer. Further addition of water molecules does not significantly alter the observed hydrogen‐bond topologies.     

Identifying Enantiomers in Mixtures of Chiral Molecules with Broadband Microwave Spectroscopy

Chirality‐sensitive broadband microwave spectroscopy was performed on mixtures of carvone enantiomers and conformers to distinguish enantiomers, measure enantiomeric excesses, and determine the absolute configurations of the enantiomers. This method uses microwave three‐wave mixing and is inherently well‐suited to the analysis of mixtures—a unique advantage over other techniques. In contrast to conventional microwave spectroscopy, the phase of the received signal is also exploited. This phase depends upon the signs of the molecules’ dipole‐moment components and is used to identify the excess enantiomer. The measured signal amplitude determines the size of the excess. The broadband capabilities of the spectrometer were used to simultaneously excite and measure two conformers of carvone, demonstrating the analysis of a sample with multiple chiral species. Employing quantum chemical calculations and the measured phases, the absolute configurations of the enantiomers are determined.     

Untersuchung der Intensität der Kß-Strahlung von Elementen der 3. Reihe des Periodensystems mit der Mikrosonde

Zusammenfassung Die Intensität der K- und der Kß-Strahlung von Schwefel, Silicium, Aluminium und Magnesium wurde in Reinelementen und Verbindungen mittels Elektronenstrahlmikroanalyse untersucht. Dabei konnte gezeigt werden, daß das Intensitätsverhältnis des Valenzbandspektrums und des Innerorbitalspektrums, hier als rel. Kß-Intensität bezeichnet, von der BeScizungsdichte im Valenzband abhängt und damit zur Abschätzung der Oxydationszahl herangezogen werden kann.

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Investigation of the intensity of the k\-radiation of the 3^rd row elements by the microprobe

Summary The intensity of the K- and Kß-radiation of sulur, silicon, aluminium and magnesium was investigated by electron beam microanalysis in the pure elements and their compounds. It could be shown, that the relation of the intensity of the valence band spectrum and the inner orbital spectrum, named here rel. Kß-Intensity, depends on the electron density in the valence band and can be used for the estimation of the oxidation number.

     

Hydrogen-Atom Tunneling in a Homochiral Environment

The role-exchanging concerted torsional motion of two hydrogen atoms in the homochiral dimer of trans-1,2-cyclohexanediol was characterized through a combination of broadband rotational spectroscopy and theoretical modeling. The results reveal that the concerted tunneling motion of the hydrogen atoms leads to the inversion of the sign of the dipole moment components along the a and b principal axes, due to the interchange motion that cooperatively breaks and reforms one intermolecular hydrogen bond. This motion is also coupled with two acceptor switching motions. The energy difference between the two ground vibrational states arising from this tunneling motion was determined to be 29.003(2) MHz. The corresponding wavefunctions suggest that the two hydrogen atoms are evenly delocalized on two equivalent potential wells, which differs from the heterochiral case where the hydrogen atoms are confined in separate wells, as the permutation-inversion symmetry breaks down. This intriguing contrast in hydrogen-atom behavior between homochiral and heterochiral environments could further illuminate our understanding of the role of chirality in intermolecular interactions and dynamics.     

Sulfates‐Based Nanothermites: An Expanding Horizon for Metastable Interstitial Composites

Metal sulfates (Ba, Bi, Ca, Cu, Mg, Mn, Na, Zn, Zr) were used as oxidizers in reactive compositions with Al nanopowder. These new kinds of nanothermites have outstandingly high reaction heats (4–6 kJ g^?1) compared to conventional Al/metal oxides (1.5–4.8 kJ g^?1) and also have good combustion velocities (200–840 m s^?1 vs 100–2500 m s^?1). These compositions are extremely insensitive to friction making their preparation and handling easy and safe. The sulfate hydration water increases the reaction heats and has a significant effect on the sensitivity to impact and to electrostatic discharge. The reaction of Al with water is easier to initiate than the one with sulfate which leads to two possible decomposition modes for samples exposed to an open flame. The pyrotechnical properties observed with sulfates have also been found for other sulfur oxygenates (SO₃^2?, S₂O₃^2?, S₂O₈^2?) which opens up new horizons in the domain of metastable interstitial composites.     

Successive minima,intrinsic volumes,and lattice determinants

In Euclideand-spaceE ^d we prove a lattice-point inequality for arbitrary lattices and for the intrinsic volumesV _i (i.e., normalized quermassintegrals) of convex bodies. TheV _i are not equi-affine invariant (except the volume), hence suitable functionals of the lattice have to be introduced. The result generalizes an earlier result of Henk for the integer lattice ℤ ^d .     

The Tl1 + I dissociative state in thallium lodide

Experiments have been performed to determine the fluorescence yield of the 535-nm transition in photodissociated thallium iodide vapor as a function of the excitation wavelength in the range from 182 to 209 nm. The spectral dependence of the fluorescence yield, together with the known structure of the molecular ground state, allowed the calculation of the slope of the Tl¹ + I dissociative potential.