Ultrafast changes of molecular crystal structure induced by dipole solvation

Femtosecond photoexcitation of organic chromophores in a molecular crystal induces strong changes of the electronic dipole moment via intramolecular charge transfer as is evident from transient vibrational spectra. The structural response of the crystal to the dipole change is mapped directly for the first time by ultrafast x-ray diffraction or diffuse scattering. Changes of diffracted and transmitted x-ray intensity demonstrate an angular rearrangement of molecules around excited dipoles following the 10 ps kinetics of charge transfer and leaving lattice plane spacings unchanged. Transient x-ray scattering is governed by solvation, masking changes of the chromophore molecular structure.     

Evaluation of VIDAS Salmonella (SLM) easy Salmonella method for the detection of Salmonella in a variety of foods: collaborative study

The VIDAS Salmonella (SLM) Easy Salmonella method is a specific enzyme-linked fluorescent immunoassay performed in the automated VIDAS instrument. The VIDAS Easy Salmonella method is a simple 2-step enrichment procedure, using pre-enrichment followed by selective enrichment in a newly formulated broth, SX2 broth. This new method was compared in a multilaboratory collaborative study to the U.S. Food and Drug Administration's Bacteriological Analytical Manual, Chapter 5 method for five food matrixes (liquid egg, vanilla ice cream, spinach, raw shrimp, and peanut butter) and the U.S. Department of Agriculture's Microbiology Laboratory Guidebook 4.04 method for deli turkey. Each food type was artificially contaminated with Salmonella at three inoculation levels. A total of 15 laboratories representing government, academia, and industry, throughout the United States, participated. In this study, 1583 samples were analyzed, of which 792 were paired replicates and 791 were unpaired replicates. Of the 792 paired replicates, 285 were positive by both the VIDAS and reference methods. Of the 791 unpaired replicates, 341 were positive by the VIDAS method and 325 were positive by the cultural reference method. A Chi-square analysis of each of the six food types was performed at the three inoculation levels tested. For all foods evaluated, the VIDAS Easy SLM method demonstrated results comparable to those of the reference methods for the detection of Salmonella.     

Sound source localization by the plainfin midshipman fish, Porichthys notatus

The aim of this study was to use plainfin midshipman fish (Porichthys notatus) as a general model to explore how fishes localize an underwater sound source in the relatively simple geometry of a monopole sound field. The robust phonotaxic responses displayed by gravid females toward a monopole sound projector (J-9) broadcasting a low-frequency (90 Hz) tone similar to the fundamental frequency of the male's advertisement call were examined. The projector's sound field was mapped at 5 cm resolution azimuth using an eight-hydrophone array. Acoustic pressure was measured with the array and acoustic particle motion was calculated from pressure gradients between hydrophones. The response pathways of the fish were analyzed from video recordings and compared to the sound field. Gravid females at initial release were directed toward the sound source, and the majority (73%) swam to the playback projector with straight to slightly curved tracks in the direction of the source and in line with local particle motion vectors. In contrast, the initial direction of the control (sound-off) group did not differ from random. This paper reports on a comparison of fish localization behavior with directional cues available in the form of local particle motion vectors.     

Site-selective [2 + 2 + n] cycloadditions for rapid,scalable access to alkynylated polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are attractive synthetic building blocks for more complex conjugated nanocarbons, but their use for this purpose requires appreciable quantities of a PAH with reactive functional groups. Despite tremendous recent advances, most synthetic methods cannot satisfy these demands. Here we present a general and scalable [2 + 2 + n] (n = 1 or 2) cycloaddition strategy to access PAHs that are decorated with synthetically versatile alkynyl groups and its application to seven structurally diverse PAH ring systems (thirteen new alkynylated PAHs in total). The critical discovery is the site-selectivity of an Ir-catalyzed [2 + 2 + 2] cycloaddition, which preferentially cyclizes tethered diyne units with preservation of other (peripheral) alkynyl groups. The potential for generalization of the site-selectivity to other [2 + 2 + n] reactions is demonstrated by identification of a Cp₂Zr-mediated [2 + 2 + 1]/metallacycle transfer sequence for synthesis of an alkynylated, selenophene-annulated PAH. The new PAHs are excellent synthons for macrocyclic conjugated nanocarbons. As a proof of concept, four were subjected to alkyne metathesis catalysis to afford large, PAH-containing arylene ethylene macrocycles, which possess a range of cavity sizes reaching well into the nanometer regime. Notably, these high-yielding macrocyclizations establish that synthetically convenient pentynyl groups can be effective for metathesis since the 4-octyne byproduct is sequestered by 5 Å MS. Most importantly, this work is a demonstration of how site-selective reactions can be harnessed to rapidly build up structural complexity in a practical, scalable fashion.

An orthogonal [2 + 2 + n] cycloaddition/alkyne metathesis reaction sequence enables streamlined access to conjugated macrocyclic nanocarbons.     

Struktur des Oxooctathiotriwolframat-Ions W3OS82−

Structure of the Oxooctathiotritungstate Ion W₃OS₈^2? [(ⁿC₄H₉)₄N]₂W₃OS₈ crystallizes with Z = 6 in the monoclinic space group Pc with cell dimensions a = 24.491(5) Å, b = 14.990(5) Å, c = 19.982(5) Å, β = 92.3(2)°. The structure has been determined from single crystal X-ray data by means of Patterson and Fourier syntheses and refined to a final conventional R value of 0.148 using 4032 independent reflexions. The structure of the W₃OS₈^2? ion can be described as consisting of two distorted WS₄ tetrahedra. The third tungsten atom has a distorted quadratic-pyramidal configuration with four sulfur atoms at the base and one oxygen atom at the apex of this polyhedron. The quadratic pyramid is connected with the two tetrahedra by two common S₂ edges.     

Bis[bis(trimethylsilyl)amino]sulfan 2. Kristall- und Molekülstruktur

Bis[bis(trimethylsilyl)amino]sulfane. 2. Crystal and Molecular Structure The title compound [(CH₃)₃Si]₂N? S? N[Si(CH₃)₃]₂ crystallizes with Z = 4 in the monoclinic space group A2/a (Nr. 15) with cell dimensions a = 22.436(4) Å, b = 6.434(5) Å, c = 17.089(6) Å, β = 117.66(2)º. For 5091 independent reflections, measured at ?80°C, the structure could be refined to R = 0.079 and R_w = 0.120. The molecules are linked together by van der Waals interactions and form layers in the bc plane, in agreement with the observed cleavage along (100).     

Über Chalkogenolate. 174. Reaktion von Acetamidin mit Kohlenstoffdisulfid 3. Kristallstruktur von Acetamidinium-N-acetimidoyldithiocarbamat [1]

On Chalcogenolates. 174. Reaction of Acetamidine with Carbon Disulfide. 3. Crystal Structure of Acetamidinium N-Acetimidoyl Dithiocarbamate The title compound [(H₂N)₂C? CH₃][S₂C? N?C(CH₃)? NH₂] crystallizes with Z = 4 in the monoclinic space group P2₁/n with cell dimensions a = 10.354(1), b = 6.798(1), c = 14.013(1) Å, β = 103.32(1)°. The crystal structure has been determined from single crystal X-ray data measured at 20°C and refined to a conventional R of 0.049 for 2 521 independent reflections (R_w = 0.052). The cation is associated with one anion by hydrogen bridges S…H? N and N…H? N forming an 8-membered ring system. The anion is not plane in contrast to hitherto known structures of dithiocarbamates.     

Über Chalkogenolate. 102. Untersuchungen über Halbester der Monothiokohlensäure. 2. Kristallstruktur von Rubidiummethyloxoxanthat

On Chalcogenolates. 102. Studies on Hemiesters of Monothiocarbonic Acid. 2. Crystal Structure of Rubidium Methyl Oxoxanthate Rb[SOC? OCH₃] crystallizes with Z = 4 in the monoclinic space group P2₁/c with cell dimensions a = 4.332(3) Å, b = 11.349(5) Å, c = 10.673(5) Å, β = 92.9(5)°. The structure has been determined from single crystal X-ray data by means of Patterson and Fourier syntheses and refined to a final conventional R value of 0.045 using 983 independent reflexions. The structure consists of Rb⁺ and [SOC? OCH₃]^? ions. The rubidium ion is bonded to five oxygen and three sulfur atoms. The coordination polyhedron is a bicapped trigonal prism.     

Structural characterization of a spin-assisted colloid-polyelectrolyte assembly: stratified multilayer thin films

The assembly of polyelectrolytes and gold nanoparticles yields stratified multilayers with very low roughness and high structural perfection. The films are prepared by spin-assisted layer-by-layer self-assembly (LbL) and are characterized by X-ray reflectivity (XRR), UV-vis spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM). Typical structures have four repeat units, each of which consists of eight double layers (DL) of poly(sodium 4-styrenesulfonate)/poly(allylamine hydrochloride), one monolayer of gold nanoparticles (10 nm diameter), and another layer of poly(allylamine hydrochloride). XRR scans show small-angle Bragg peaks up to seventh order, evidencing the highly stratified structure. Pronounced Kiessig fringes indicate a low global roughness, which is confirmed by local AFM measurements. TEM images corroborate the layered structure in the growth direction and nicely show the distinct separation of the individual particle layers. An AFM study reveals the lateral gold particle distribution within one individual particle layer. Interestingly, the spin-assisted deposition of polyelectrolytes reduces the roughness induced by the particle layers, leading to self-healing of roughness defects and a rather perfect stratification.