First seco-C oleananes from nature

[structure: see text] The triterpenes 8,14-seco-oleana-8(26),13-dien-3beta-ol (1) and its acetyl derivative 2 were isolated from Stevia viscida and Stevia eupatoria, respectively. Their structures were elucidated by 2D NMR, including carbon-carbon connectivity experiments, and confirmed by X-ray diffraction analysis of ketone 3. The absolute configuration was determined by NMR analysis of the Mosher esters of 1. The biogenetic implications of the new substances are discussed.     

Surface modification of nanoporous alumina surfaces with poly(ethylene glycol)

Nanoporous alumina surfaces have a variety of applications in biosensors, biofiltration, and targeted drug delivery. However, the fabrication route to create these nanopores in alumina results in surface defects in the crystal lattice. This results in inherent charge on the porous surface causing biofouling, that is, nonspecific adsorption of biomolecules. Poly(ethylene glycol) (PEG) is known to form biocompatible nonfouling films on silicon surfaces. However, its application to alumina surfaces is very limited and has not been well investigated. In this study, we have covalently attached PEG to nanoporous alumina surfaces to improve their nonfouling properties. A PEG-silane coupling technique was used to modify the surface. Different concentrations of PEG for different immobilization times were used to form PEG films of various grafting densities. X-ray photoelectron spectroscopy (XPS) was used to verify the presence of PEG moieties on the alumina surface. High-resolution C1s spectra show that with an increase in concentration and immobilization time, the grafting density of PEG also increases. Further, a standard overlayer model was used to calculate the thickness of PEG films formed using the XPS intensities of the Al2p peaks. The films formed by this technique are less than 2.5 nm thick, suggesting that such films will not clog the pores which are in the range of 70-80 nm.     

Reactions of TiCl4, VCl4 and VOCl3 with tetraalkyldiphosphine disulphides

Summary The reactions of MCl₄ (M = Ti or V) with R₂P(S)P(S)R₂ (R = Me or Et) yield hexacoordinate complexes MCl₄ · R₂P(S)P(S)R₂ (M = Ti or V; R = Me or Et), whereas similar reactions with VOCl₃ lead to reduction of vanadium and give rise to the vanadium(IV) pentacoordinated complexes: VOCl₂-R₂P(S)P(S)R₂ (R = Me or Et). All the compounds have been characterized by elemental analyses, i.r., visible and e.p.r. spectra, which show thecis-chelate character of these ligands, although in the complexes containing Et₄P₂S₂ the i.r. spectra indicates that thegauche conformation of the ligand is implicated in bonding to the metal. The occupation of the sixth coordination site in pentacoordinate complexes, VOCl₂ · R₂P(S)P(S)R₂, by different donor solvents, has been studied by means of visible and e.p.r. spectra.     

An Adjustable Cleft Based on an 8-Sulfonamide-2-Naphthoic Acid with Oxyanion Hole Geometry

Cleft type receptors showing the oxyanion hole motif have been prepared in a straightforward synthesis starting from the commercial 3,7-dihidroxy-2-naphthoic acid. The double H-bond donor pattern is achieved by the introduction of a sulfonamide group in the C-8 position of naphthalene and a carboxamide at the C-2 position. This cleft, for which the geometry resembles that of an oxyanion hole, is able to adjust to different guests, as shown by the analysis of the X-ray crystal structures of associates with methanol or acetic acid. Combination of hydrogen bonds and charge-transfer interactions led to further stabilization of the complexes, in which the electron-rich aromatic ring of the receptor was close in space to the electron-deficient dinitroaromatic guests. Modelling studies and bidimensional NMR experiments have been carried out to provide additional information.     

Delay asymptotics and bounds for multitask parallel jobs

Queueing Systems - We study delay of jobs that consist of multiple parallel tasks, which is a critical performance metric in a wide range of applications such as data file retrieval in coded...     

Chitosan-DNA Particles for DNA Delivery: Effect of Chitosan Molecular Weight on Formation and Release Characteristics

Novel DNA-chitosan particles were prepared based on associative phase separation and interfacial diffusion. These particles formed at water/water emulsion type interfaces were characterized with respect to several properties including stability, DNA conformational state, and entrapment and release of DNA. In particular it was found that the chitosan molecular weight is a good controlling parameter.     

Synthesis of Biaryl‐Bridged Cyclic Peptides via Catalytic Oxidative Cross‐Coupling Reactions

Biaryl‐bridged cyclic peptides comprise an intriguing class of structurally diverse natural products with significant biological activity. Especially noteworthy are the antibiotics arylomycin and its synthetic analogue G0775, which exhibits potent activity against Gram‐negative bacteria. Herein, we present a simple, flexible, and reliable strategy based on activating‐group‐assisted catalytic oxidative coupling for assembling biaryl‐bridged cyclic peptides from natural amino acids. The synthetic approach was utilized for preparing a number of natural and unnatural biaryl‐bridged cyclic peptides, including arylomycin/G0775 and RP 66453 cyclic cores.     

Thermal and microstructural analysis of Cu(II) 2,2′-dihydroxy azobenzene and thin films deposition by MAPLE technique

A newly synthesized copper-complex exhibiting nonlinear optical properties, crystalline nature, and generating interest as a material for non-linear optical applications was investigated. As thermal stability studies are indispensable before attempting any laser-assisted processing experiments, the thermal behavior of 2,2′-dihydroxy azobenzene with Cu²⁺ cations that are found to organize themselves as non-central symmetric crystallites, was investigated. The thin films were deposited on silicon substrates by matrix-assisted pulsed laser evaporation using a Nd:YAG laser working at 266 and 355 nm. Thermal analysis of the bulk compound indicates a higher thermal stability in argon flow when compared to the air atmosphere; as well, since, the adhesion of the compound onto the substrate enhances the bonding, the thermal stability of the Cu complex increases. Fourier transform infrared spectroscopy, atomic force microscopy, scanning electron microscopy, spectroscopic ellipsometry, and ultraviolet–visible spectroscopy investigations were also performed.