Studies on the biomimetic synthesis of SNF4435 C and D

[reaction: see text] The biomimetic synthesis of the bicyclic core of the novel immunosuppresants SNF4435C and SNF4435D is reported. The core framework was efficiently generated from the all-trans tetraene precursor in one step and in good yield.     

Fluorinated calixpyrroles: anion-binding extractants that reduce the Hofmeister bias

Beta-octafluoro-meso-octamethylcalix[4]pyrrole (1) and beta-decafluoro-meso-decamethylcalix[5]pyrrole (2) were found to extract caesium salts of smaller anions (bromide and chloride for 1 and nitrate for 2) as effectively as that of iodide into nitrobenzene (NB) thereby overcoming the Hofmeister bias normally observed for processes of this type.     

Vibrational spectra of stannane: Harmonic force field, Raman and IR intensities from ab initio correlated wavefunctions

The vibrational spectra and the harmonic force field for the stannane molecule has been calculated from ab initio SCF calculations using an effective core potential and two double-zeta basis sets for the valence electrons. Polarized functions and electron correlation effects on the calculated force constants and frequencies are analyzed carefully. At HF SCF level the calculated frequencies are higher than the experimental ones by about 8.15% while at second-order Møller-Plesset perturbation level, the mean absolute percentage deviation of the frequencies is found to be 3.75%. This mean absolute percentage deviation is notably improved at SDCI (3.2%) and SDQCI (2.2%) levels of theory. The integrated molar absorption coefficients and the scattering activities are calculated and their values agree reasonably with experiment.     

Correlated Rayleigh Scattering Spectroscopy and Scanning Electron Microscopy Studies of Au-Ag Bimetallic Nanoboxes and Nanocages

The optical properties of hollow nanoparticles (Au-Ag nanoboxes and nanocages) were investigated by recording Rayleigh scattering spectra of single particles, whose morphology and composition had been analyzed by scanning electron microscopy (SEM). This was achieved by depositing the particles on optically transparent substrates with registration marks, which are compatible with SEM imaging. Fitting the experimental spectra to a Lorentzian function yields the frequencies and homogeneous line widths of the plasmon resonance for the particles. The resonances are extremely broad, with dephasing times of 2-5 fs. Analysis of the line width data using the dimensions determined by SEM shows that the broadening is due to a combination of electron-surface scattering and radiation damping. The sensitivity of the plasmon resonance to the dielectric constant of the environment was also investigated by adding a drop of water to the substrate. The nanoboxes show similar dielectric sensitivities compared to other metal nanoparticle systems. A significant increase in the line width was also observed for the nanoboxes in water compared with air. This was attributed to increased radiation damping in the environment with a higher dielectric constant. Both the red shift and the increase in line width are reversible.     

Enhanced fluorimetric determination of procaine in pharmaceutical preparations by aqueous β- cyclodextrin inclusion and non-aqueous competitive action

The effects of changes in polarity and dielectric constant of the solvent on the fluorescence of procaine hydrochloride in different solvents, and in β-cyclodextrin (β-CD) and micellar media (cetylpyridium chloride and sodium dodecyl sulphate), are described in detail. It is shown that, with N,N-dimethylformamide as solvent procaine is better incorporated in β-CD and micelles. Methods are developed under these conditions based on normal, synchronous first- and second- derivative fluorimetry. The linear dynamic range is 10–680 ng ml^-1 and the detection limit is 2.5 ng ml^-1; the relative standard deviation is 0.68% for the β-CD method with normal fluorimetry. The methods are applied directly to the determination of procaine in different pharmaceutical preparation with recoveries of 88–108%.     

Synthesis,Crystal Structures and Anticancer Activity of the New Chiral Mono‐ and Dinuclear Palladium(II) Complexes derived from (S)‐(‐)‐(1‐phenylethylimino)benzylphenylketone

The enantiopure ketoimine of benzil – the ( S )‐(‐)‐(1‐phenylethylimino)benzyl phenyl ketone ( 1 ) obtained under microwave irradiation in solvent‐free conditions – reacts with Na₂[PdCl₄] to give the new chiral mono‐ and dinuclear Pd‐complexes 2 and 3 , which have been partly characterized by IR, ¹H and ¹³C NMR spectroscopies along with MS‐FAB⁺ spectrometry. The crystal and molecular structures of both complexes has been fully confirmed by single‐crystal X‐ray studies. On the other hand, investigations in vitro of 2 and 3 have displayed growth inhibition against different classes of cancer: leukemia (K‐562 CML), colon cancer (HCT‐15), cancer breast (MCF‐7), central nervous system (U‐251 Glio) and prostate cancer (PC‐3) cell lines.     

One-pot synthesis of Nb-modified Al<Subscript>2</Subscript>O<Subscript>3</Subscript> support for NiMo hydrodesulfurization catalysts

The effect of Nb as a support modifier on the NiMo₆/Al₂O₃–Nb₂O₅(x) (x?=?0, 1, 4, and 8?wt% Nb) catalysts was studied. The supports were prepared by one-pot coprecipitation from soluble precursors. The XRF analysis of the catalysts showed that the contents of Mo and Ni increased slightly with the presence of Nb. Micropore area and pore volume augmented importantly with Nb content, resulting in pore diameters between 5.3 and 9.3?nm. XPS analysis showed that the presence of Nb decreases the active metal–support interaction, improving the Mo and Ni sulfidation degree. The Raman spectra of sulfided catalysts suggested an increase in the number of layers of MoS₂ in the presence of Nb. Generally, the thiophene HDS activity at normal pressure of sulfided NiMo₆/Al₂O₃–Nb₂O₅(8) was greater than that of the sulfided catalysts with x?=?0, 1, and 4?wt% Nb, which can be attributed to the Nb promotion that would have an effect on the type of active site (Brønsted or Lewis acidic sites), since the number of sites by CO chemisorption for sulfided NiMo₆/Al₂O₃–Nb₂O₅(x) did not show correlation with the catalytic activity. The high-pressure HDS activity of dibenzothiophene was also greater in the presence of Nb, and the hydrogenation route was preferred for the Nb-promoted solid, while the unpromoted one showed a larger yield of direct desulfurization products.

Open image in new window

     

Diastereoselective allylation of aldehydes with an enantiopure 2-sulfinylallyl halide under environmentally friendly Barbier-type conditions

[reaction: see text] A simple, efficient, and diastereoselective zinc-promoted allylation of aldehydes with enantiopure (Ss)-3-chloro-2-(p-tolylsulfinyl)-1-propene [(Ss)-1] under aqueous Barbier conditions is described. The observed diastereoselectivity can be explained via an acyclic antiperiplanar transition state model.     

PROSIT: pseudo-rotational online service and interactive tool, applied to a conformational survey of nucleosides and nucleotides

A Pseudo-Rotational Online Service and Interactive Tool (PROSIT) designed to perform complete pseudorotational analysis of nucleosides and nucleotides is described. This service is freely available at http://cactus.nci.nih.gov/prosit/. Files containing nucleosides/nucleotides or DNA/RNA segments, isolated or bound to other molecules (e.g., a protein) can be uploaded to be processed by PROSIT. The service outputs the pseudorotational phase angle P, puckering amplitude numax, and other related information for each nucleoside/nucleotide detected. The service was implemented using the chemoinformatics toolkit CACTVS. PROSIT was used for a survey of nucleosides contained in the Cambridge Structural Database and nucleotides in high-resolution crystal structures from the Nucleic Acid Database. Special cases discussed include nucleosides having constrained sugar moieties with extreme puckering amplitudes, and several specific DNA/RNA helices and protein-bound DNA oligonucleotides (Dickerson-Drew dodecamer, RNA/DNA hybrid viral polypurine tract, Z-DNA enantiomers, B-DNA containing (L)-alpha-threofuranosyl nucleotides, TATA-box binding protein/TATA-box complex, and DNA (cytosine C5)-methyltransferase complexed with an oligodeoxyribonucleotide containing transition state analogue 5,6-dihydro-5-azacytosine). When the puckering amplitude decreases to a small value, the sugar becomes increasingly planar, thus reducing the significance of the phase angle P. We introduce the term "central conformation" to describe this part of the pseudorotational hyperspace in contrast to the conventional north and south conformations.     

Flow-induced molecular segregation in beta-casein-monoglyceride mixed films spread at the air-water interface

In this work, we have used different and complementary interfacial techniques (surface film balance, Brewster angle microscopy, and interfacial shear rheology) to analyze the static (structure, topography, reflectivity, miscibility, and interactions) and flow characteristics (surface shear characteristics) of beta-casein and monoglyceride (monopalmitin and monoolein) mixed films spread on the air-water interface. The structural, topographical, and shear characteristics of the mixed films depend on the surface pressure and on the composition of the mixed film. The surface shear viscosity (etas) varies greatly with the surface pressure. In general, the greater the surface pressure, the greater the values of etas. At higher surface pressures, collapsed beta-casein residues may be displaced from the interface by monoglyceride molecules with important repercussions on the shear characteristics of the mixed films. A shear-induced change in the topography of monoglyceride and beta-casein domains, on one hand, and a segregation between domains of the film-forming components, on the other hand, were also observed. The displacement of the beta-casein by the monoglycerides is facilitated under shear conditions, especially for beta-casein-monoolein mixed films.