Electric-pulse-induced local conducting area and joule heating effect in VO2/Al2O3 films

We investigated the effect of an electric-pulse on the insulator–metal phase transition of VO₂/Al₂O₃ films using synchrotron-based infrared microspectroscopy. By monitoring the time-resolved optical response, we could demonstrate that local conducting areas are formed under the influence of the electric-pulse, and the Joule heat generated from the local current flow drives a consecutive thermal phase transition in the adjacent sample area.     

Synthesis and styrene polymerization properties of dinuclear half-titanocene complexes with xylene linkage

The new dinuclear half-sandwich complexes of titanium with xylene bridge, [Ti(η⁵-cyclopentadienyl)Cl₂L]₂[CH₂-C₆H₄-CH₂] (L = Cl (3), L = O-2,6-iPr₂C₆H₃ (4), L = N(SiMe₃)(2,6-Me₂C₆H₃) (5)), have been synthesized. The complexes 4 and 5 have been prepared by the reaction of the complex 3 with the corresponding lithium salts of aryloxy and anilide. Structure of these complexes has been characterized by ¹H and ¹³C NMR. The change of substituent from chloride, 3, to anilide, 5, at titanium resulted in chemical shift change of cyclopentadienyl protons from 6.92 and 6.79 to 6.13 and 5.95 ppm probably due to the positive electron density delivery from the anilide group. It was found that all three half-titanocenes were effective catalyst for the generation of SPS (syndiotactic polystyrene). Xylene bridged dinuclear catalyst (4) with aryloxy substituent exhibited very high activity (458 kg of SPS/(mol of [Ti])h), at 40 °C, whereas the analogous hexamethylene bridged dinuclear half-titanocene catalyst (7) showed a lower activity (80.7 kg of SPS/(mol of [Ti])h) under the same conditions. While the catalyst 3 was the most active catalyst among three complexes less than 40 °C the catalyst 5 exhibited the highest activity at 70 °C. Xylene linkage was suggested to be too stiff to permit any kind of intramolecular interaction between two active centers. Lack of steric disturbance due to the rigidity of the xylene bridge might give rise to the similar properties of dinuclear metallocene to the corresponding mononuclear metallocene to result in not only the facile coordination of monomer at the active center to lead high activity but also the easier β-H elimination comparing to the dinuclear catalysts with the flexible bridge to result in the formation of lower molecular weight polymer.     

Full–dimensional quantum molecular dynamics calculations of the rovibrationally mediated X → 2 transition of nitrous oxide

A full dimensional time‐dependent quantum wavepacket approach is used to study the photodissociation dynamics of nitrous oxide for the X → 2 bound–bound transition based on new highly accurate potential energy and transition dipole moment surfaces. The computed 2 absorption spectra at room temperature are characterized by sharp vibrational structures that contribute slightly to the diffuse vibrational structures around the maximum peak at 180 nm of the first ultraviolet absorption band (from the contribution of 2 , 1 , and 2 states) of N₂O. Transitions from different initial rovibrational states reveal that the sharp structures arise mainly from N₂? O bending vibrations, whereas, at higher temperatures, the N₂? O and N? NO stretching vibrations are responsible for enhancing the intensity of the structures. At absorption wavelengths 166 nm and 179 nm, vibrational quantum state distributions of N₂ product fragments decrease monotonically with increasing vibrational quantum number v = 0, 1, 2. At 166 nm, rotational quantum state distributions of N₂ at fixed v = 0 and v = 1 display multimodal profiles with maximum peaks at j = 77 and j = 75, respectively, whereas, the distributions at the 179 nm absorption wavelength display bimodal profiles with maximum peaks at j = 73 and j = 71, respectively. Accordingly, the presence of rotationally hot N₂ from previous experimental and theoretical works in the first band strongly implies a significant influence of the 2 state in determining the final dissociation pathway of N₂ + O. © 2016 Wiley Periodicals, Inc.     

Loss of Acot12 contributes to NAFLD independent of lipolysis of adipose tissue

In this study, we hypothesized that deregulation in the maintenance of the pool of coenzyme A (CoA) may play a crucial role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Specific deletion of Acot12 (Acot12^−/−), the major acyl-CoA thioesterase, induced the accumulation of acetyl-CoA and resulted in the stimulation of de novo lipogenesis (DNL) and cholesterol biosynthesis in the liver. KEGG pathway analysis suggested PPARα signaling as the most significantly enriched pathway in Acot12^−/− livers. Surprisingly, the exposure of Acot12^−/− hepatocytes to fenofibrate significantly increased the accumulation of acetyl-CoA and resulted in the stimulation of cholesterol biosynthesis and DNL. Interaction analysis, including proximity-dependent biotin identification (BioID) analysis, suggested that ACOT12 may directly interact with vacuolar protein sorting-associated protein 33A (VPS33A) and play a role in vesicle-mediated cholesterol trafficking and the process of lysosomal degradation of cholesterol in hepatocytes. In summary, in this study, we found that ACOT12 deficiency is responsible for the pathogenesis of NAFLD through the accumulation of acetyl-CoA and the stimulation of DNL and cholesterol via activation of PPARα and inhibition of cholesterol trafficking.Subject terms: Gene expression, Disease model     

Amide-based nonheme cobalt(III) olefin epoxidation catalyst: partition of multiple active oxidants Co(V)=O, Co(IV)=O, and Co(III)-OO(O)CR

A mononuclear nonheme cobalt(III) complex of a tetradentate ligand containing two deprotonated amide moieties, [Co(bpc)Cl(2)][Et(4)N] (1; H(2)bpc = 4,5-dichloro-1,2-bis(2-pyridine-2-carboxamido)benzene), was prepared and then characterized by elemental analysis, IR, UV/Vis, and EPR spectroscopy, and X-ray crystallography. This nonheme Co(III) complex catalyzes olefin epoxidation upon treatment with meta-chloroperbenzoic acid. It is proposed that complex 1 shows partitioning between the heterolytic and homolytic cleavage of an O-O bond to afford Co(V)=O (3) and Co(IV)=O (4) intermediates, proposed to be responsible for the stereospecific olefin epoxidation and radical-type oxidations, respectively. Moreover, under extreme conditions, in which the concentration of an active substrate is very high, the Co-OOC(O)R (2) species is a possible reactive species for epoxidation. Furthermore, partitioning between heterolysis and homolysis of the O-O bond of the intermediate 2 might be very sensitive to the nature of the solvent, and the O-O bond of the Co-OOC(O)R species might proceed predominantly by heterolytic cleavage, even in the presence of small amounts of protic solvent, to produce a discrete Co(V) ?O intermediate as the dominant reactive species. Evidence for these multiple active oxidants was derived from product analysis, the use of peroxyphenylacetic acid as the peracid, and EPR measurements. The results suggest that a less accessible Co(V)=O moiety can form in a system in which the supporting chelate ligand comprises a mixture of neutral and anionic nitrogen donors.     

Quantitative determination of aceclofenac and its three major metabolites in rat plasma by HPLC-MS/MS

We developed a method for the simultaneous quantification of aceclofenac and its three major metabolites in rat plasma. After protein precipitation with acetonitrile including flufenamic acid as an internal standard (IS), aceclofenac, diclofenac, 4'-hydroxyaceclofenac, 4'-hydroxydiclofenac, and the IS were chromatographed on a reverse-phase C18 analytical column. The isocratic mobile phase of acetonitrile/0.1% formic acid (aq; 9:1 [v/v]) was eluted at 0.3 mL/min. Quantification was performed on a triple-quadrupole mass spectrometer using electrospray ionization, and the ion transitions were monitored in selective reaction-monitoring mode. The coefficient of variation in the assay precision was less than 8%, and the accuracy was 92-103%. This method was successfully used to measure the concentrations of aceclofenac and its three major metabolites in rat plasma following the oral administration of a single 20 mg/kg oral dose of aceclofenac.     

Metal ion-enriched polyelectrolyte complexes and their utilization in multilayer assembly and catalytic nanocomposite films

The mixing of Ag ion-doped poly(ethyleneimine) (PEI) and poly(acrylic acid) (PAA) produced Ag ion-doped polyelectrolyte complex particles (PECs) in solution. Positively charged Ag ion-doped PECs (Ag ion PECs) with a spherical shape were deposited alternatively with PAA to form a multilayer assembly. The multilayered film containing Ag ion PECs was reduced to generate a composite nanostructure. Metal nanoparticle (NP)-enriched nanocomposite films were formed by an additional process of the postadsorption of precursors on PECs within the nanocomposite films, which resulted in the enhancement of the catalytic and electrical properties of the composite films. Because the films contain PECs that are responsive to changes in pH and most of the NPs are embedded in the PECs, interesting catalytic properties, which are unexpected in a particle-type catalyst, were observed upon pH changes. As a result of the reversible structural changes of the films and the immobilization of the NPs within the films, the film-type catalysts showed enhanced performance and stability during catalytic reactions under various pH conditions, compared to particle-type catalysts.     

Self-rotation of elliptically polarized light in Doppler-broadened rubidium atoms

We present a theoretical and experimental study of self-rotation of incident elliptically polarized light on a rubidium atomic vapor. We construct density matrix equations, which are then solved numerically, and further averaged over atomic transit times and a Maxwell-Boltzmann velocity distribution. We calculate the rotation angle as a function of detuning for various laser intensities and polarizations. We compare the calculated results with experimental results and find good agreement between them.     

Adsorption and thermal decomposition of 2-octylthieno[3,4-b]thiophene on Au(111)

The adsorption and thermal stability of 2-octylthieno[3,4-b]thiophene (OTTP) on the Au(111) surfaces have been studied using scanning tunneling microscopy (STM), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). UHV-STM studies revealed that the vapor-deposited OTTP on Au(111) generated disordered adlayers with monolayer thickness even at saturation coverage. XPS and TPD studies indicated that OTTP molecules on Au(111) are stable up to 450K and further heating of the sample resulted in thermal decomposition to produce H(2) and H(2)S via C-S bond scission in the thieno-thiophene rings. Dehydrogenation continues to occur above 600K and the molecules were ultimately transformed to carbon clusters at 900K. Highly resolved air-STM images showed that OTTP adlayers on Au(111) prepared from solution are composed of a well-ordered and low-coverage phase where the molecules lie flat on the surface, which can be assigned as a (9×2√33)R5° structure. Finally, based on analysis of STM, TPD, and XPS results, we propose a thermal decomposition mechanism of OTTP on Au(111) as a function of annealing temperature.