Evidence for formation of silenes strongly influenced by reversed Si[double bond]C bond polarity

[reaction: see text] Transient silenes that are strongly influenced by reversed Si[double bond]C bond polarization are formed upon heating of tris(trimethylsilyl)silylamides. The silenes are trapped with 2,3-dimethyl-1,3-butadiene to quantitatively yield only one of the possible diastereomers of the functionalized cyclic allylsilanes.     

Plausible origins of homochirality in the amino acid catalyzed neogenesis of carbohydrates

The intrinsic ability of amino acids to catalyze the asymmetric formation of carbohydrates, which enzymes have mediated for millions of years, with significant amplification of enantiomeric excess suggests a plausible ancient catalytic process for the evolution of homochirality.     

Metabolic trajectory characterisation of xenobiotic-induced hepatotoxic lesions using statistical batch processing of NMR data

Multivariate statistical batch processing (BP) analysis of 1H NMR urine spectra was employed to establish time-dependent metabolic variations in animals treated with the model hepatotoxin, alpha-naphthylisothiocyanate (ANIT). ANIT (100 mg kg(-1)) was administered orally to rats (n = 5) and urine samples were collected from dosed and matching control rats at time-points up to 168 h post-dose. Urine samples were measured via 1H NMR spectroscopy and partial least squares (PLS) based batch processing analysis was used to interpret the spectral data, treating each rat as an individual batch comprising a series of timed urine samples. A model defining the mean urine profile over the 7 day study period was established, together with model confidence limits (+/-3 standard deviation), for the control group. Samples obtained from ANIT treated animals were evaluated using the control model. Time-dependent deviations from the control model were evident in all ANIT treated animals consisting of glycosuria, bile aciduria, an initial decrease in taurine levels followed by taurinuria and a reduction of tricarboxylic acid cycle intermediate excretion. BP provided an efficient means of visualising the biochemical response to ANIT in terms of both inter-animal variation and net variation in metabolite excretion profiles. BP also allowed multivariate statistical limits for normality to be established and provided a template for defining the sequence of time-dependent metabolic consequences of toxicity in NMR based metabonomic studies.     

Resonance coupling in the fourth OH-stretching overtone spectrum of formic acid

The room-temperature vibrational overtone spectra of the formic acid isotopomers HCOOH and DCOOH have been recorded in the third and fourth OH-stretching overtone regions with intracavity laser photoacoustic spectroscopy. Resonance coupling between the OH- and CH-stretching vibrations in HCOOH is clearly identified in the fourth overtone region. This is an example of strong coupling across bonds. In the third overtone region, no resonance is observed. Vibrational energies and intensities of the OH- and CH-stretching overtones and combination bands have been calculated with an anharmonic oscillator local mode model. The pure OH-stretching bright state carries almost all the intensity prior to resonance coupling.     

Electronic control of the regiochemistry in the Heck reaction

The migratory insertion of propene into the Pd-phenyl bond of a set of neutral palladium(II) complexes with N-N, P-O, and N-O chelating ligands has been investigated by using density functional methods. In contrast to cationic palladium(II)-diimine complexes, which favor 1,2-insertion, the more electron-rich neutral complexes lead to 2,1-insertion. Trans influences are substantial in the unsymmetrical ligand systems, primarily affecting the insertion barrier. Introducing steric effects leads toward improving 1,2-selectivity, due to destabilization of the 2,1-transition state. Electronic and steric influences can be systematically combined to control the regiochemistry in the Heck reaction.     

Theoretical study of chemisorption on niobium clusters: carbon monoxide and oxygen

We have studied chemisorption on niobium clusters based on the local spin density approximation in a scheme which uses pseudopotentials and a plane wave expansion of the electronic wave functions. Results are presented for geometries and the electronic structure of Nb₄ and Nb₈, and compared with experimental data of ionization potentials. Key issues concerning atomic and molecular adsorption on metal clusters are the nature of the binding, the preferred configurations, and the changes induced on the cluster properties. We have examined these questions in the case of carbon monoxide and oxygen. For carbon monoxide, we calculate a significant reduction of the stretch vibration frequency and, in the case of oxygen, shifts of the ionization potentials were obtained. Our results for oxygen are in agreement with experimental data, indicating only a minor shift of the ionization potential due to oxidation, also as a function of coverage.     

Packing of protein structures in clusters with magic numbers

Recently we have proposed a model for folding proteins into packed’ clusters’. We have constructed a local homology measure for protein fold classes by projecting consecutively secondary structures onto a lattice. Taking into account hydrophobic forces we have found a mechanism for formation of clusters containing magic numbers of secondary structures and multipla of these clusters. A scheme for the relation between the sequence information and the native fold is given. We have performed a statistical analysis of available protein structures and found agreement with the predicted preferred abundances. In this paper we demonstrate that the results are robust to variations in the coordination number of the model.     

Properties and Solution Methods for Large Location—Allocation Problems

Location-allocation with l _p distances is studied. It is shown that this structure can be expressed as a concave minimization programming problem. Since concave minimization algorithms are not yet well developed, five solution methods are developed which utilize the special properties of the location-allocation problem. Using the rectilinear distance measure, two of these algorithms achieved optimal solutions in all 102 test problems for which solutions were known. The algorithms can be applied to much larger problems than any existing exact methods.     

Capillary Electrophoresis Method for the Chiral Purity Determination of Pregabalin Derivatized with Dansyl Chloride

A capillary electrophoresis method for the determination of the chiral purity of pregabalin upon derivatization with dansyl chloride was developed using design of experiment methodologies. A D-optimal design was used for the identification of the critical process parameters, while a central composite face centered design and Monte Carlo simulations were employed for defining the design space of the method. Final working conditions consisted of a background electrolyte composed of a 100 mM sodium phosphate buffer, pH 2.5, containing 40 mg mL^?1 heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin, a separation voltage of 15 kV and a capillary temperature of 25 °C. The analyses were carried out in a 40/50.2 cm fused-silica capillary with an inner diameter of 50 µm. Upon testing the robustness using a Plackett–Burman design, the method was validated according to the International Council on Harmonization guideline Q2(R1). The method allowed the detection of the (R)-enantiomer at the 0.015% level with a limit of quantitation at the 0.05% level with regard to a sample containing 1.59 mg mL^?1 pregabalin. The method was subsequently applied to the determination of the stereochemical purity of the drug in commercial capsules.     

Rapid Analysis of Cell–Nanoparticle Interactions using Single‐Cell Raman Trapping Microscopy

Iron oxide nanoparticles have been used in preclinical studies to label stem cells for non‐invasive tracking and homing. The search continues for novel particle candidates that are suitable for clinical applications. Since standard analyses to investigate cell–particle interactions and safety are labor‐intensive, an efficient procedure is required to guide future particle development and to exclude adverse health effects. The application of combined Raman trapping microscopy with fluidic chips is reported for the analysis of single cells labeled with different types of aminated iron oxide particles. Multivariate data analysis revealed Raman signal differences that could be clearly assigned to cell–particle interactions and cytotoxicity, respectively. A validation dataset verified that more than 95 % of the spectra were correctly classified. Thus, our approach enables rapid discrimination of non‐hazardous from cytotoxic nanoparticles as a prerequisite for safe clinical applications.