Observation of magnetization step at order–disorder transition in MgB2 single crystals

We have studied the order–disorder transition in high quality MgB₂ single crystals, using a torque magnetometry combined with a ‘vortex shaking’ technique. In the wide range of temperature T, field H and the H direction, we succeed in obtaining reversible magnetization curves M_rev(T, H) by shaking the pinned vortices. Especially at low temperatures below 25 K and high fields, where the irreversible magnetization curve exhibits the peak effect due to the order–disorder transition, it is found that the peak is transformed into the clear step in M_rev(H). Similar step-like behavior is also observed in the temperature dependence of magnetization M_rev(T). These results give direct evidence that the order–disorder transition, which is hidden by the large hysteresis of magnetization, has the nature of first-order transition.     

Purcell effect of GaAs quantum dots by photonic crystal microcavities

We fabricate photonic crystal slab microcavities embedded with GaAs quantum dots by electron beam lithography and droplet epitaxy. The Purcell effect of exciton emission of the quantum dots is confirmed by the micro photoluminescence measurement. The resonance wavelengths, widths, and polarization are consistent with numerical simulation results.     

The structure of the complex of cellulose I with ethylenediamine by X-ray crystallography and cross-polarization/magic angle spinning 13C nuclear magnetic resonance

X-ray crystallographic and cross-polarization/magic angle spinning ¹³C nuclear magnetic resonance techniques have been used to study an ethylenediamine (EDA)-cellulose I complex, a transient structure in the cellulose I to cellulose III_I conversion. The crystal structure (space group P2 ₁ ; a = 4.546 Å, b = 11.330 Å, c = 10.368 Å and γ = 94.017°) corresponds to a one-chain unit cell with one glucosyl residue in the asymmetric unit, a gt conformation for the hydroxymethyl group, and one EDA molecule per glucosyl residue. Unusually, there are no O–H···O hydrogen bonds between the cellulose chains; the chains are arranged in hydrophobic stacks, stabilized by hydrogen bonds to the amine groups of bridging EDA molecules. This new structure is an example of a complex in which the cellulose chains are isolated from each other, and provides a number of insights into the structural pathway followed during the conversion of cellulose I to cellulose III_I through EDA treatment.     

Total Synthesis of (−)‐FR182877 through Tandem IMDA–IMHDA Reactions and Stereoselective Transition‐Metal‐Mediated Transformations

Intelligent design : The total synthesis of the cytotoxic (?)‐FR182877 relies on 1) tandem Diels–Alder reactions to close rings A–D (see scheme), 2) a palladium‐mediated 7‐exo‐trig reaction, and 3) an iridium‐mediated isomerization followed by epimerization and stereoselective reduction.

     

The asymptotic relative generation distribution of the closest common ancestor of the multitype Galton–Watson tree conditioned on non-extinction

We extend Geiger’s size-biased tree method to the multitype case to give another proof of Zubkov’s result that the asymptotic relative generation distribution of the closest common ancestor of the multitype Galton–Watson branching process conditioned on non-extinction is uniform.     

4-(Pyrrolidinyl)methoxybenzoic acid derivatives as a potent, orally active VLA-4 antagonist

A novel series of benzoic acid derivatives as VLA-4 antagonists were synthesized. Optimization, focusing on activity and lipophilicity needed for cell permeability, resulted in the identification of 15b and 15e with good activity (IC50 = 1.6 nM each) and moderate lipophilicity (Log D = 2.0, 1.8). Furthermore, 15e demonstrated efficacy in murine asthma model by an oral dose of 30 mg/kg.     

Fast screening of pesticide multiresidues in aqueous samples by dual stir bar sorptive extraction-thermal desorption-low thermal mass gas chromatography-mass spectrometry

A method for fast screening of pesticide multiresidues in aqueous samples using dual stir bar sorptive extraction-thermal desorption-low thermal mass gas chromatography-mass spectrometry (dual SBSE-TD-LTM-GC-MS) has been developed. Recovery of 82 pesticides - organochlorine, carbamate, organophosphorous, pyrethroid and others - for the SBSE was evaluated as a function of octanol-water distribution coefficients (logK(o/w): 1.7-8.35), sample volume (2-20mL), salt addition (0-30% NaCl), and methanol addition (0-20%). The optimized method consists of a dual SBSE performed simultaneously on respectively a 20-mL sample containing 30% NaCl and a 20-mL sample without modifier (100% sample solution). One extraction with 30% NaCl is mainly targeting solutes with low K(o/w) (logK(o/w)<3.5) and another extraction with unmodified sample solution is targeting solutes with medium and high K(o/w) (logK(o/w)>3.5). After extraction, the two stir bars are placed in a single glass desorption liner and are simultaneously desorbed. The desorbed compounds are analyzed by use of LTM-GC-MS with fast temperature programming (75 degrees Cmin(-1)) using a 0.18mm i.d. narrow-bore capillary column and fast scanning (10.83 scan s(-1)) using quadrupole MS. The method showed good linearity (r(2)>0.9900) and high sensitivity (limit of detection: <10ngL(-1)) for most of the target pesticides. The method was applied to the determination of pesticides at nanograms per liter levels in river water and brewed green tea.     

Synthesis and characterization of bromonium ylides and their unusual ligand transfer reactions with N-heterocycles

Stable aliphatic bromonium ylides (RfSO2)2C--Br+C6H4-p-CF3 (Rf = CF3, CF3(CF2)3) have been synthesized and structurally characterized for the first time. X-ray crystallographic analyses indicated a ylide structure with an sp2 hybridization of the ylide carbanions and with little double-bond character for the ylidic bond. The bromonium ylides selectively undergo transfer of the aryl group to nitrogen heterocycles, such as pyridines, yielding N-arylpyridinium salts. This is in a marked contrast to the reaction of the iodonium ylides, which produces pyridinium ylides through transylidations.     

ChemInform Abstract: Facile Synthesis of Glycidates via Oxidation of Acrylates with Aqueous Solution of NaOCl in the Presence of Ammonium Salts.

The green and fast oxidation of acrylates proceeds in the presence of ammonium catalysts with appropriate structures.     

Formation of flat, homogeneous surfaces of organized molecular films of three-armed polymerizable amphiphiles with metal-scavenging properties

Surface complexing (i.e., metal-bridged polymerization in this study) of a three-armed amphiphilic compound with metal-scavenging properties has been investigated using the surface pressure-area (π-A) isotherms of a Langmuir monolayer from the subphase. Inductively coupled plasma mass spectrometry (ICP-MS) was also carried out on eluted solutions from corresponding multilayers of the solid. Furthermore, the molecular arrangement and surface morphology of organized molecular films of the resultant comb polymer were estimated by in-plane and out-of-plane X-ray diffraction (XRD) and by atomic force microscopy. From an analysis of the wide-angle X-ray diffraction of the corresponding monomer in the bulk, the long hydrocarbon chains are observed to pack hexagonally in the solid state. Compared to their monolayer on distilled water as the subphase, a polymerized monolayer on a buffer solution containing Cd(2+) ions is remarkably expanded at 15 °C. From ICP-MS and IR measurements, it is found that this monolayer stoichiometrically contains Cd(2+) ions on the -SH group. It is found by XRD that highly ordered layer structures and regular 2D lattices are constructed in the organized molecular films of the Cd-bridged comb polymer. Furthermore, the surface morphology of Langmuir-Blodgett films fabricated from the monolayers on a buffer solution containing Cd(2+) and Pd(2+) shows flat and smooth domains upon metal scavenging and polymerization.