On the stability of Caesium-covered ZnO surfaces

The characterisation of the Cs/ZnO system using LEED and AES, results in the observation of new superstructures on the (000$\text{1}$)—O polar surface, a (2 × 2) structure and a combined (2 × 2) and (√3 × √3) configuration. A possible explanation is proposed for the existence of these superstructures in terms of electrostatic energy calculations.     

Progress toward a peptidomimetic of laminin-derived pentapeptide YIGSR: synthesis of the unique tricyclic core structure

The peptide sequence YIGSR, a segment of the basement membrane matrix glycoprotein laminin, has been identified as a key component in tumor cell invasion. Guided by extensive NMR work and de novo design algorithms, a nonpeptide mimetic of this pentapeptide was identified as a lead candidate for synthesis. The target displays the key amino acid side chains from a novel tricyclic scaffold. The first synthesis of this unique scaffold is completed in 11 steps and 7% overall yield.     

Multicentred QM/QM methods for overlapping model systems

An improved, more general method for performing multicentred integrated QM/QM calculations is presented. The new approach allows the multicentred approximation to be extended to overlapping model systems, removing a significant limitation of the original approach. The usefulness and numerical accuracy of the equations presented are confirmed via some applications to dipole–dipole, charge–dipole and charge–charge complexes. The method performs well for all of these complexes, which range from very weakly to very strongly bound and in which non-additivity effects on interaction energies range from 0.2 to 17kcalmol^?1.     

Xe+ formation following photolysis of Au-Xe: a velocity map imaging study

The photodissociation dynamics of Au-Xe leading to Xe(+) formation via the Ξ(1∕2)-X(2)Σ(+) (v('), 0) band system (41?500-41?800 cm(-1)) have been investigated by velocity map imaging. Five product channels have been indentified, which can be assigned to photoinduced charge transfer followed by photodissociation in either the neutral or the [Au-Xe](+) species. For the neutral species, charge transfer occurs via a superexcited Rydberg state prior to dissociative ionization, while single-photon excitation of the gold atom in Au(+)-Xe accesses an (Au(+))?-Xe excited state that couples to a dissociative continuum in Au-Xe(+). Mechanisms by which charge transfer occurs are proposed, and branching ratios for Xe(+) formation via the superexcited Rydberg state are reported. The bond dissociation energy for the first excited state of Au(+)-Xe is determined to be ～9720 ± 110 cm(-1).     

Hypervalent Iodine Oxidation of Amines in the Presence of Nitroso Compounds: A Method for the Preparation of Unsymmetrically Substituted Azoxy Compounds

Various amines and amino derivatives such as (tert-butylamine, 4-amino-1,2,4-triazole-p-toluenesulfonamide), and cyanamide, when treated with |(diacetoxy)iodo|benzene in the presence of nitroso compounds (2) yield unsymmetrically substituted azoxy compounds (3).     

The effects of age and cochlear hearing loss on temporal fine structure sensitivity, frequency selectivity, and speech reception in noise

Temporal fine structure (TFS) sensitivity, frequency selectivity, and speech reception in noise were measured for young normal-hearing (NHY), old normal-hearing (NHO), and hearing-impaired (HI) subjects. Two measures of TFS sensitivity were used: the "TFS-LF test" (interaural phase difference discrimination) and the "TFS2 test" (discrimination of harmonic and frequency-shifted tones). These measures were not significantly correlated with frequency selectivity (after partialing out the effect of audiometric threshold), suggesting that insensitivity to TFS cannot be wholly explained by a broadening of auditory filters. The results of the two tests of TFS sensitivity were significantly but modestly correlated, suggesting that performance of the tests may be partly influenced by different factors. The NHO group performed significantly more poorly than the NHY group for both measures of TFS sensitivity, but not frequency selectivity, suggesting that TFS sensitivity declines with age in the absence of elevated audiometric thresholds or broadened auditory filters. When the effect of mean audiometric threshold was partialed out, speech reception thresholds in modulated noise were correlated with TFS2 scores, but not measures of frequency selectivity or TFS-LF test scores, suggesting that a reduction in sensitivity to TFS can partly account for the speech perception difficulties experienced by hearing-impaired subjects.     

Off-resonance laser frequency stabilization using the Faraday effect

We present a simple technique for stabilization of a laser frequency off resonance using the Faraday effect in a heated vapor cell with an applied magnetic field. In particular, we demonstrate stabilization of a 780 nm laser detuned up to 14 GHz from the (85)Rb D(2) 5(2)S(1/2) F = 2 to 5(2)P(3/2) F' = 3 transition. Control of the temperature of the vapor cell and the magnitude of the applied magnetic field allows locking ~6-14 GHz red and blue detuned from the atomic line. We obtain an rms fluctuation of 7 MHz over 1 h without stabilization of the cell temperature or magnetic field.     

Metal-specific interactions of H2 adsorbed within isostructural metal-organic frameworks

Diffuse reflectance infrared (IR) spectroscopy performed over a wide temperature range (35-298 K) is used to study the dynamics of H(2) adsorbed within the isostructural metal-organic frameworks M(2)L (M = Mg, Mn, Co, Ni and Zn; L = 2,5-dioxidobenzene-1,4-dicarboxylate) referred to as MOF-74 and CPO-27. Spectra collected at H(2) concentrations ranging from 0.1 to 3.0 H(2) per metal cation reveal that strongly red-shifted vibrational modes arise from isolated H(2) bound to the available metal coordination site. The red shift of the bands associated with this site correlate with reported isosteric enthalpies of adsorption (at small surface coverage), which in turn depend on the identity of M. In contrast, the bands assigned to H(2) adsorbed at positions >3 ? from the metal site exhibit only minor differences among the five materials. Our results are consistent with previous models based on neutron diffraction data and independent IR studies, but they do not support a recently proposed adsorption mechanism that invokes strong H(2)···H(2) interactions (Nijem et al. J. Am. Chem. Soc.2010, 132, 14834-14848). Room temperature IR spectra comparable to those on which the recently proposed adsorption mechanism was based were only reproduced after contaminating the adsorbent with ambient air. Our interpretation that the uncontaminated spectral features result from stepwise adsorption at discrete framework sites is reinforced by systematic red shifts of adsorbed H(2) isotopologues and consistencies among overtone bands that are well-described by the Buckingham model of molecular interactions in vibrational spectroscopy.     

Chemical analysis of bleach and hydroxide-based solutions after decontamination of the chemical warfare agent O-ethyl S-2-diisopropylaminoethyl methylphosphonothiolate (VX)

Detailed chemical analysis of solutions used to decontaminate chemical warfare agents can be used to support verification and forensic attribution. Decontamination solutions are amongst the most difficult matrices for chemical analysis because of their corrosive and potentially emulsion-based nature. Consequently, there are relatively few publications that report their detailed chemical analysis. This paper describes the application of modern analytical techniques to the analysis of decontamination solutions following decontamination of the chemical warfare agent O-ethyl S-2-diisopropylaminoethyl methylphosphonothiolate (VX). We confirm the formation of N,N-diisopropylformamide and N,N-diisopropylamine following decontamination of VX with hypochlorite-based solution, whereas they were not detected in extracts of hydroxide-based decontamination solutions by nuclear magnetic resonance (NMR) spectroscopy or gas chromatography-mass spectrometry. We report the electron ionisation and chemical ionisation mass spectroscopic details, retention indices, and NMR spectra of N,N-diisopropylformamide and N,N-diisopropylamine, as well as analytical methods suitable for their analysis and identification in solvent extracts and decontamination residues.