Novel flavanes from Livistona halongensis

A study of the chemical constituents of a methanolic extract of the roots of Livistona halongensis (Arecaceae) led to the isolation of two new flavanes, 2S,3S-3,5,7,3'-tetrahydroxy-5'-methoxyflavane (1) and 3,7,3'-trihydroxy-5'-methoxyflavane 5-O-beta-glucopyranoside (2), together with trans-3,5,3',5'-tetrahydroxy-4-methoxystilbene, saccharose and beta-sitosterol-3-O-beta-glucopyranoside. The structures of these compounds were elucidated on the basis of spectroscopic data.     

Time to Face the Fats: What Can Mass Spectrometry Reveal about the Structure of Lipids and Their Interactions with Proteins?

Since the 1950s, X-ray crystallography has been the mainstay of structural biology, providing detailed atomic-level structures that continue to revolutionize our understanding of protein function. From recent advances in this discipline, a picture has emerged of intimate and specific interactions between lipids and proteins that has driven renewed interest in the structure of lipids themselves and raised intriguing questions as to the specificity and stoichiometry in lipid-protein complexes. Herein we demonstrate some of the limitations of crystallography in resolving critical structural features of ligated lipids and thus determining how these motifs impact protein binding. As a consequence, mass spectrometry must play an important and complementary role in unraveling the complexities of lipid-protein interactions. We evaluate recent advances and highlight ongoing challenges towards the twin goals of (1) complete structure elucidation of low, abundant, and structurally diverse lipids by mass spectrometry alone, and (2) assignment of stoichiometry and specificity of lipid interactions within protein complexes.     

Magnetic-state tuning of the rhombohedral graphite film by interlayer spacing and thickness

Based on first-principles total-energy calculations, we systematically investigate how the electronic and magnetic properties of rhombohedral graphite thin films depend on the interlayer spacing and number of layers. Our calculations show that the magnetic ordering of the thin films depends on the interlayer spacing. Thin films under compression normal to the layers possess finite magnetic moments, indicating parallel spin coupling between the two surfaces. We also find that thin graphite films with seven or more atomic layers exhibit magnetic ordering while films with six or less atomic layers are metallic with no magnetic ordering.     

Time discretization and quantization methods for optimal multiple switching problem

In this paper, we study probabilistic numerical methods based on optimal quantization algorithms for computing the solution to optimal multiple switching problems with regime-dependent state process. We first consider a discrete-time approximation of the optimal switching problem, and analyse its rate of convergence. Given a time step h$h$, the error is in general of order (hlog(1/h))^1/2${(hlog(1/h))}^{1/2}$, and of order h^1/2$h^{1/2}$ when the switching costs do not depend on the state process. We next propose quantization numerical schemes for the space discretization of the discrete-time Euler state process. A Markovian quantization approach relying on the optimal quantization of the normal distribution arising in the Euler scheme is analysed. In the particular case of uncontrolled state process, we describe an alternative marginal quantization method, which extends the recursive algorithm for optimal stopping problems as in Bally (2003) [1]. A priori L^p$L^p$-error estimates are stated in terms of quantization errors. Finally, some numerical tests are performed for an optimal switching problem with two regimes.     

One-pot cyclizations of dilithiated oximes and hydrazones with epibromohydrin. Efficient synthesis of 6-hydroxymethyl-5,6-dihydro-4H-1,2-oxazines and oxazolo[3,4-b]pyridazin-7-ones

The one-pot cyclization of dilithiated oximes with epibromohydrin provided a convenient and regioselective approach to 6-hydroxymethyl-5,6-dihydro-4H-1,2-oxazines. The reaction of the latter with phosphorus tribromide resulted in a Beckmann rearrangement and formation of 5-bromomethyl-2-iminotetrahydrofurans. The reaction of dilithiated hydrazones with epibromohydrin afforded oxazolo[3,4-b]pyridazin-7-ones, which were formed by a novel domino cyclization.     

Electrochemical analysis of gold-coated magnetic nanoparticles for detecting immunological interaction

An electrochemical impedance immunosensor was developed for detecting the immunological interaction between human immunoglobulin (IgG) and protein A from Staphylococcus aureus based on the immobilization of human IgG on the surface of modified gold-coated magnetic nanoparticles. The nanoparticles with an Au shell and Fe oxide cores were functionalized by a self-assembled monolayer of 11-mercaptoundecanoic acid. The electrochemical analysis was conducted on the modified magnetic carbon paste electrodes with the nanoparticles. The magnetic nanoparticles were attached to the surface of the magnetic carbon paste electrodes via magnetic force. The cyclic voltammetry technique and electrochemical impedance spectroscopy measurements of the magnetic carbon paste electrodes coated with magnetic nanoparticles–human IgG complex showed changes in its alternating current (AC) response both after the modification of the surface of the electrode and the addition of protein A. The immunological interaction between human IgG on the surface of the modified magnetic carbon paste electrodes and protein A in the solution could be successfully monitored.     

Raman characterization of localized CdS nanostructures synthesized by UV irradiation in sol–gel silica matrices

A new technique of UV irradiation has been used for the first time to create microstructures of CdS nanoparticles in bulk xerogels. Porous silica matrices, which were first soaked in a solution containing CdS precursors, were subjected to irradiation using a nanopulsed ArF laser with a wavelength of 193 nm and a repetition rate of 10 Hz. Resonant micro‐Raman spectra, recorded using the 325‐nm line of a He‐Cd laser (with a continuous power less than 0.5 mW so as to avoid the thermal formation of nanoparticles) made it possible to identify CdS nanoparticles within the inscribed yellow zones and also to estimate the average particle size (3.6 to 8.0 nm, depending on the number of UV pulses used). The emission of CdS particles embedded in the silica matrix under excitation at 351.1 nm was studied by photoluminescence spectroscopy. It was then possible to show the effect of the number of pulses on the electronic structure of the nanocrystals. Finally, Raman spectra were used to monitor the structural changes in the silica matrix caused by the irradiation. It was found that the pulsed UVirradiation resulted in a local densification of the matrix, which was compensated for by a depolymerization process of the Si O Si network. In spite of this pulsed irradiation and the resulting structural depolymerization, no apparent ablation or cracking of the samples was observed. Copyright © 2010 John Wiley & Sons, Ltd.     

Solid phase asymmetric alkylation reactions using 2-imidazolidinone chiral auxiliary

A novel solid supported 2-imidazolidinone chiral auxiliary was prepared from O-benzyl-l-tyrosine and Wang resin. Asymmetric alkylation reactions in the solid phase proceeded with excellent stereoselectivities, which were even higher than those observed in the conventional solution phase method.     

Gibbs energies of transferring triglycine from water into H2O-DMSO solvent

The Gibbs energies of transferring triglycine (3Gly, glycyl-glycyl-glycine) from water into mixtures of water with dimethyl sulfoxide (χ_DMSO = 0.05, 0.10, and 0.15 mole fractions) at 298.15 K are determined from the interphase distribution. An increased dimethyl sulfoxide (DMSO) concentration in the solvent slightly raises the positive values of Δ_tr G ^○(3Gly), possibly indicating the formation of more stable 3Gly-H₂O solvated complexes than ones of 3Gly-DMSO. It is shown that the change in the Gibbs energy of transfer of 3Gly is determined by the enthalpy component. The relationship of 3Gly and 18-crown-6 ether (18C6) solvation’s contributions to the change in the Gibbs energy of [3Gly18C6] molecular complex formation in H₂O-DMSO solvents is analyzed, and the key role of 3Gly solvation’s contribution to the change in the stability of [3Gly18C6] upon moving from H₂O to mixtures with DMSO is revealed.