Chemical sensing and imaging with pulsed terahertz radiation

Over the past decade, terahertz spectroscopy has evolved into a versatile tool for chemically selective sensing and imaging applications. In particular, the potential to coherently generate and detect short, and hence, broadband terahertz pulses led to the development of efficient and compact spectrometers for this interesting part of the electromagnetic spectrum, where common packaging materials are transparent and many chemical compounds show characteristic absorptions. Although early proof-of-principle demonstrations have shown the great potential of terahertz spectroscopy for sensing and imaging, the technology still often lacks the required sensitivity and suffers from its intrinsically poor spatial resolution. In this review we discuss the current potential of terahertz pulse spectroscopy and highlight recent technological advances geared towards both enhancing spectral sensitivity and increasing spatial resolution.     

Studies on the biodegradation of fosfomycin: synthesis of 13C-labeled intermediates, feeding experiments with Rhizobium huakuii PMY1, and isolation of labeled amino acids from cell mass by HPLC

Racemic (1R*,2R*)‐1,2‐dihydroxy‐[1‐¹³C₁]propylphosphonic acid and 1‐hydroxy‐[1‐¹³C₁]acetone were synthesized and fed to R. huakuii PMY1. Alanine and a mixture of valine and methionine were isolated as their N‐acetyl derivatives from the cell hydrolysate by reversed‐phase HPLC and analyzed by NMR spectroscopy. It was found that the carbon atoms of the respective carboxyl groups were highly ¹³C‐labeled (up to 65 %). Hydroxyacetone is therefore considered an obligatory intermediate of the biodegradation of fosfomycin by R. huakuii PMY1.     

Inseparable Körpererweiterungen

Ohne Zusammenfassung     

Effect of the orientation of substituents on the chemical shifts of 13C. IV—13C NMR spectra of N,N-diisopropylamides and -thioamides

N,N-diisopropylamides and -thioamides show hindered rotation around the N? CH bonds, and the presence of mixtures of conformational isomers can be demonstrated at temperatures below 273 K in solution. ¹H and ¹³C NMR spectra of these conformers are measured and assigned. The ¹³C data serve to study through-space effects on ¹³C chemical shifts, which strongly depend on the conformations of the isopropyl groups. For amides, a through-space shielding of the N-methine carbons is found to exist only for conformers in which the methine hydrogen atom is spatially close to the oxygen atom. Chemical shift differences between amides and thioamides can be rationalized in terms of through-bond and through-space contributions, and serve for a better understanding of the shift differences in N,N-dialkylamides and -thioamides.     

Der Satz von Hahn-Banach und Fixpunktsätze in limitierten Vektorräumen

Ohne Zusammenfassung     

Non-Hamiltonian molecular dynamics implementation of the Gibbs ensemble method. I. Algorithm

In this paper (paper I) and the following paper (paper II) [C. Bratschi, H. Huber, and D. J. Searles, J. Chem. Phys. 126, 164105 (2007)], a new molecular dynamics algorithm implementing the Gibbs ensemble will be presented and then on applied to the liquid-vapor coexistence curve for two ab initio CO2 potentials. In paper I, the Gibbs ensemble molecular dynamics algorithm using non-Hamiltonian molecular dynamics techniques is introduced. It is shown that states of the correct probability density function are sampled and the correct exchange probability is generated. The extended system Nose-Hoover formalism is used to generate a constant temperature ensemble with equal pressures in the subsystems, combined with single particle transfers between the subsystems, over several time steps, to get equal chemical potentials.     

Aesculaxanthin,a New Carotenoid Isolated from Pollens of Aesculus hippocastanum

From the pollens of Aesculus hippocastanum, a new apocarotenoid was isolated as the main carotenoid and, based on the spectroscopic data, identified as (all-E,3R)-3-hydroxy-6′-apo-β-caroten-6′-al ( 4 , aesculaxanthin). In addition, (all-E)-lutein ( 3 ) and (all-E)-β-citraurin ( 5 ) were isolated. Furthermore, 6 (aesculaxanthol) was prepared by reduction of 4 with NaBH₄ and tentatively identified as natural carotenoid.