Double electron transfer reactions of CO22+ ions

Time-of-flight techniques have been used to measure fast neutral CO₂ products from double electron transfer reactions of CO₂²⁺ ions with 4.0–7.0 keV impact energies. Double electron transfer cross sections have been determined to be in the range of (1.1–12.5) × 10^?16 cm² for reactions of CO₂²⁺ ions with CO₂, CO, N₂, Ar and O₂.     

Web server to identify similarity of amino acid motifs to compounds (SAAMCO)

Protein-protein interactions are fundamental in mediating biological processes including metabolism, cell growth, and signaling. To be able to selectively inhibit or induce protein activity or complex formation is a key feature in controlling disease. For those situations in which protein-protein interactions derive substantial affinity from short linear peptide sequences, or motifs, we can develop search algorithms for peptidomimetic compounds that resemble the short peptide's structure but are not compromised by poor pharmacological properties. SAAMCO is a Web service ( http://bioware.ucd.ie/ approximately saamco) that facilitates the screening of motifs with known structures against bioactive compound databases. It is built on an algorithm that defines compound similarity based on the presence of appropriate amino acid side chain fragments and a favorable Root Mean Squared Deviation (RMSD) between compound and motif structure. The methodology is efficient as the available compound databases are preprocessed and fast regular expression searches filter potential matches before time-intensive 3D superposition is performed. The required input information is minimal, and the compound databases have been selected to maximize the availability of information on biological activity. "Hits" are accompanied with a visualization window and links to source database entries. Motif matching can be defined on partial or full similarity which will increase or reduce respectively the number of potential mimetic compounds. The Web server provides the functionality for rapid screening of known or putative interaction motifs against prepared compound libraries using a novel search algorithm. The tabulated results can be analyzed by linking to appropriate databases and by visualization.     

Particle formation and surface processes on atmospheric aerosols: A review of applied quantum chemical calculations

Aerosols significantly influence atmospheric processes such as cloud nucleation, heterogeneous chemistry, and heavy-metal transport in the troposphere. The chemical and physical complexity of atmospheric aerosols results in large uncertainties in their climate and health effects. In this article, we review recent advances in scientific understanding of aerosol processes achieved by the application of quantum chemical calculations. In particular, we emphasize recent work in two areas: new particle formation and heterogeneous processes. Details in quantum chemical methods are provided, elaborating on computational models for prenucleation, secondary organic aerosol formation, and aerosol interface phenomena. Modeling of relative humidity effects, aerosol surfaces, and chemical kinetics of reaction pathways is discussed. Because of their relevance, quantum chemical calculations and field and laboratory experiments are compared. In addition to describing the atmospheric relevance of the computational models, this article also presents future challenges in quantum chemical calculations applied to aerosols.     

Hydration of OCS with one to four water molecules in atmospheric and laboratory conditions

Carbonyl sulfide is the most abundant sulfur gas in the atmosphere. We have used MP2 and CCSD(T) theory to study the structures and thermochemistries of carbonyl sulfide interacting with one to four water molecules. We have completed an extensive search for clusters of OCS(H2O)n , where n = 1-4. We located three dimers, two trimers, five tetramers, and four pentamers with the MP2/aug-cc-pVDZ method. In each of the complexes with two or more waters, OCS preferentially interacts with low-energy water clusters. Our results match current theoretical and experimental literature, showing correlation with available geometries and frequencies for the OCS(H2O) species. The CCSD(T)/aug-cc-pVTZ thermochemical values combined with the average amount of OCS and the saturated concentration of H2O in the troposphere, lead to the prediction of 10(6) OCS(H2O) clusters x cm(-3) and 10(2) OCS(H2O)2 clusters x cm(-3) at 298 K. We predict the structures of OCS(H2O)n , n = 1-4 that should predominate in a low-temperature molecular beam and identify specific infrared vibrations that can be used to identify these different clusters.     

Ramachandran-type plots for glycosidic linkages: Examples from molecular dynamic simulations using the Glycam06 force field

The goals of this article are to (1) provide further validation of the Glycam06 force field, specifically for its use in implicit solvent molecular dynamic (MD) simulations, and (2) to present the extension of G.N. Ramachandran's idea of plotting amino acid phi and psi angles to the glycosidic phi, psi, and omega angles formed between carbohydrates. As in traditional Ramachandran plots, these carbohydrate Ramachandran-type (carb-Rama) plots reveal the coupling between the glycosidic angles by displaying the allowed and disallowed conformational space. Considering two-bond glycosidic linkages, there are 18 possible conformational regions that can be defined by (alpha, phi, psi) and (beta, phi, psi), whereas for three-bond linkages, there are 54 possible regions that can be defined by (alpha, phi, psi, omega) and (beta, phi, psi, omega). Illustrating these ideas are molecular dynamic simulations on an implicitly hydrated oligosaccharide (700 ns) and its eight constituent disaccharides (50 ns/disaccharide). For each linkage, we compare and contrast the oligosaccharide and respective disaccharide carb-Rama plots, validate the simulations and the Glycam06 force field through comparison to experimental data, and discuss the general trends observed in the plots.     

Preionization kinetics of an X-ray preionized XeCl gas discharge laser

The influence of preionization conditions on the performance of a XeCl gas discharge laser preionized by a short, high intensity x-ray pulse, has been studied. The laser output energy and optical pulse temporal characteristics have been used to determine the roles of initial electron density and of electron attachment to HCl and to impurities. Although the short pulse preionization technique functions well for XeCl when the laser voltage pulse has a short risetime (?20 ns), it is less well suited to XeCl lasers using slowly rising voltage pulses (>50 ns), or to F₂ containing gas mixtures (KrF and XeF lasers).     

Une remarque sur les isomorphismes de schemas de Bernoulli qui preservent certains facteurs

By slightly strengthening the hypothesis, we quickly arrive at, in a new case, some results from the paperRemarques sur les systèmes dynamiques donnés avec plusieurs facteurs.     

Automated microwave digestion of certifiable color additives for determination of mercury by cold vapor atomic absorption spectrometry

A procedure using an automated microwave flow digestion technique was developed and validated for the digestion of samples of certifiable color additives before mercury determination by cold vapor atomic absorption spectrometry. Recovery studies were performed by spiking most of the color additives subject to batch certification by the U.S. Food and Drug Administration with inorganic mercury (HgNO3) and with organic mercury (CH3HgCl). Successful recoveries of 72-113% Hg added at the 1 microg/g level were obtained. A method detection limit of 0.2 microg Hg/g was estimated from a Hg-spiked FD&C Yellow No. 6 sample. At the specification level of 1 ppm Hg (1 microg Hg/g), the 95% confidence interval was +/- 0.2 ppm (0.2 microg Hg/g).