Reverse micelles dissolved in supercritical xenon: an NMR spectroscopic study

Reverse micelles currently gain increasing interest in chemical technology. They also become important in biomolecular NMR due to their ability to host biomolecules such as proteins. In the present paper, a procedure for the preparation of high-pressure NMR samples containing reverse micelles dissolved in supercritical xenon is presented. These reverse micelles are formed by sodium bis(2-ethylhexyl) sulfosuccinate (AOT). For the first time, NMR spectroscopy could be applied to reverse micelles in supercritical xenon. The AOT/H(2)O/Xe system was studied as a function of experimental parameters such as xenon pressure, water content, and salt concentration. Optimum conditions for reverse micelle formation in supercritical xenon could be determined. It is, furthermore, demonstrated that biomolecules such as amino acids and proteins can be incorporated into the reverse micelles dissolved in supercritical xenon.     

Experimental separation of virtual photon exchange and electron transfer in interatomic coulombic decay of neon dimers

We investigate the interatomic Coulombic decay (ICD) of neon dimers following photoionization with simultaneous excitation of the ionized atom (shakeup) in a multiparticle coincidence experiment. We find that, depending on the parity of the excited state, which determines whether ICD takes place via virtual dipole photon emission or overlap of the wave functions, the decay happens at different internuclear distances, illustrating that nuclear dynamics heavily influence the electronic decay in the neon dimer.     

Color-Changing Sparks from Rare Earth Metal Powders

Commonly, sparks emit light according to the well-known black (gray) body radiation. Recently, we reported on color-changing sparks based on erbium powder, which switch their light emission between black body emission (surface combustion) and element-specific emission (vapor phase combustion). Herein, we investigated the spark formation from the adjacent rare-earth elements. The corresponding boiling points are significantly below (Yb, Sm, Tm) or above (Y, Lu) the boiling point of Er. While Yb and Sm evaporate too fast to form longer sparks, Y, Lu and Tm form color-changing sparks with varying length of the element-specific emission phase. The sparks were investigated by time-resolved emission spectroscopy, long-time exposures, and NIR/MIR imaging. The same basic pyrotechnic formulation containing one of these metal powders reveals a strongly differing burning behavior depending on the boiling point of the metal. The burning characteristics change from a green strobe (Yb) to intense colorful crackling (Tm) and finally a sparkling fountain with long-flying sparks (Lu, Y, Er).     

Resolving Sphingolipid Isomers Using Cryogenic Infrared Spectroscopy

1‐Deoxysphingolipids are a recently described class of sphingolipids that have been shown to be associated with several disease states including diabetic and hereditary neuropathy. The identification and characterization of 1‐deoxysphingolipids and their metabolites is therefore highly important. However, exact structure determination requires a combination of sophisticated analytical techniques due to the presence of various isomers, such as ketone/alkenol isomers, carbon–carbon double‐bond (C=C) isomers and hydroxylation regioisomers. Here we demonstrate that cryogenic gas‐phase infrared (IR) spectroscopy of ionized 1‐deoxysphingolipids enables the identification and differentiation of isomers by their unique spectroscopic fingerprints. In particular, C=C bond positions and stereochemical configurations can be distinguished by specific interactions between the charged amine and the double bond. The results demonstrate the power of gas‐phase IR spectroscopy to overcome the challenge of isomer resolution in conventional mass spectrometry and pave the way for deeper analysis of the lipidome.     

Systematic event generator tuning for the LHC

In this article we describe Professor, a new program for tuning model parameters of Monte Carlo event generators to experimental data by parameterising the per-bin generator response to parameter variations and numerically optimising the parameterised behaviour. Simulated experimental analysis data is obtained using the Rivet analysis toolkit. This paper presents the Professor procedure and implementation, illustrated with the application of the method to tunes of the Pythia 6 event generator to data from the LEP/SLD and Tevatron experiments. These tunes are substantial improvements on existing standard choices, and are recommended as base tunes for LHC experiments, to be themselves systematically improved upon when early LHC data is available.     

Comparison of models and lattice-gas simulations for Liesegang patterns

For more than a century Liesegang patterns – self-organized, quasi-periodic structures occurring in diffusion-limited chemical reactions with two components – have been attracting scientists. The pattern formation can be described by four basic empirical laws. In addition to many experiments, several models have been devised to understand the formation of the bands and rings. Here we review the most important models and complement them with detailed three-dimensional lattice-gas simulations. We show how the mean-field predictions can be reconciled with experimental data by a redefinition of the distances suggested by our lattice-gas simulations.     

Cyclization and Isomerization Reactionsin Silylhydrazine Chemistry

 This review describes the synthesis and isomerization reactions of cyclic silylhydrazines. Topics of discussion are the ring expansion of the three-membered Si(SiN₂) to the four-membered (SiN)₂ ring by lithiation of the (SiN₂) ring and by thermal silyl group insertion into the N*N bond, the ring expansion of a three-membered (SiN₂) to a five-membered (CSi₂N₂) ring by SiCH₂ insertion into the Si*N bond, the formation of isomeric four- and six-membered (SiN₂)₂ rings, the synthesis of five- and six-membered silylhydrazine rings, and the expansion of a five-membered (N₂Si₂N)N ring to the isomeric six-membered (SiNN)₂ ring. The mechanisms of the isomerizations are explained by quantum chemical calculations, and the results are verified by crystal structure determinations.