Study on carbon-hydrogen activation of ketones by Gold(III) complexes and the synthesis and characterization of two ketonylgold(III) complexes

The acetonylgold(III) compound [Au(ppy)(CH₂COCH₃)Cl] (1) (ppy = 2-phenylpyridine) was unexpectedly obtained during the crystallization process of Au(III) lactate complex [Au(ppy)(CH₃CHOHCOO⁻)Cl]. This new structure prompted us to further study the role of Au(III) complexes on the carbon-hydrogen activation of ketones. Complex [Au(ppy)(CH₂COCH₃)NO₃] (2) was synthesized by reacting [Au(ppy)(NO₃)₂] with acetone while the ketonyl Au(III) complex [Au(apd)Cl₂] (3) (Hapd = 2-acetylpyridine) was obtained through carbon-hydrogen bond activation of the acetyl group. The crystal structures of 1 and 2 have common features: a square-planar Au(III) centre coordinated by one five-membered chelate ring, one acetonyl ligand and one anion (chloride or nitrate). Both structures show that carbon-hydrogen activation of acetone by 2-phenylpyridine-Au(III) complexes leads to the formation of acetonyl-Au(III) complexes. The Au-CH₂ bond lengths (2.067(7) Å, 1 and 2.059(5) Å, 2) are similar to each other but longer than the Au-C (phenyl) bond lengths. The two softest ligands (carbanion) are also cis to each other in the thermodynamically most stable isomer. In complex 3, the σ-bonded acetyl group is confirmed by ¹³C DEPT NMR spectroscopy.     

Green's-function theory for disordered anisotropic Heisenberg ferromagnets

The Green's function theory for disordered Heisenberg Ferromagnets developed by Montgomery et al. has been extended for anisotropic systems. The densities of spin-wave states for such systems exhibit split-bands. This behavior differs qualitatively from that of the isotropic case and offers a partial explanation for the neutron scattering experiment of Buyers et al. in which they observe two well defined branches of magnetic excitations in disordered substitutional anti-ferromagnetic alloys.     

Role of pH and charge on silk protein assembly in insects and spiders

Silk fibers possess impressive mechanical properties, dependant, in part, on the crystalline β-sheets silk II conformation. The transition to silk II from soluble silk I-like conformation in silk glands, is thought to originate in the spinning ducts immediately before the silk is drawn down into a fiber. However the assembly process of these silk molecules into fibers, whether in silkworms or spiders, is not well understood. Extensional flow, protein concentration, pH and metal ion concentrations are thought to be most important in in vivo silk processing and in affecting structural conformations. We look at how parameters such as pH, [Ca²⁺], [K⁺], and [Cu²⁺], and water content, interact with the domain structure of silk proteins towards the successful storage and processing of these concentrated hydrophobic silk proteins. Our recent domain mapping studies of all known silk proteins, and 2D Raman spectroscopy, NMR, and DLS studies performed on sections of silkworm gland, suggest that low pH and gradual water removal promote intermolecular over intramolecular hydrogen bonding. This discussion helps to provide the necessary ground rules towards the design of silk protein analogues with specific hydrophobicity and charge profiles to optimize expression, solubility and assembly with implications in structural biology and material science. PACS 87.14.Ee; 87.15.Cc; 87.15.Kg     

Dietary Vitamin B6 and Enzymes of Methionine Metabolism in Rat Liver

Hepatic cystathionase activity, but not methionine adenosyl-transterase and cystathionine synthetase, was markedly decreased in weanling female rats fed a vitamin B₆-deficient diet, compared to that of the control animals fed ad libitum or pair-fed. The depressed enzyme activity was restored rapidly to normal by administering pyridoxine to the deficient rats. Excess pyridoxal phosphate added to enzyme reaction mixtures stimulated cystathionase in liver extracts from both control and deficient animals, but it did not raise activity of deficients to normal level. The data indicate that the amount of apocystathionase in rat liver is regulated by the availability of its coenzyme vitamin.     

High-resolution gadolinium-enhanced 3D MRA of the infrapopliteal arteries. Lessons for improving bolus-chase peripheral MRA

Peripheral magnetic resonance angiography (MRA) is growing in use. However, methods of performing peripheral MRA vary widely and continue to be optimized, especially for improvement in illustration of infrapopliteal arteries. The main purpose of this project was to identify imaging factors that can improve arterial visualization in the lower leg using bolus chase peripheral MRA. Eighteen healthy adults were imaged on a 1.5T MR scanner. The calf was imaged using conventional three-station bolus chase three-dimensional (3D) MRA, two dimensional (2D) time-of-flight (TOF) MRA and single-station Gadolinium (Gd)-enhanced 3D MRA. Observer comparisons of vessel visualization, signal to noise ratios (SNR), contrast to noise ratios (CNR) and spatial resolution comparisons were performed. Arterial SNR and CNR were similar for all three techniques. However, arterial visualization was dramatically improved on dedicated, arterial-phase Gd-enhanced 3D MRA compared with the multi-station bolus chase MRA and 2D TOF MRA. This improvement was related to optimization of Gd-enhanced 3D MRA parameters (fast injection rate of 2 mL/sec, high spatial resolution imaging, the use of dedicated phased array coils, elliptical centric k-space sampling and accurate arterial phase timing for image acquisition). The visualization of the infrapopliteal arteries can be substantially improved in bolus chase peripheral MRA if voxel size, contrast delivery, and central k-space data acquisition for arterial enhancement are optimized. Improvements in peripheral MRA should be directed at these parameters.     

A solid lithium electrolyte via addition of lithium isopropoxide to a metal-organic framework with open metal sites

The uptake of LiO(i)Pr in Mg(2)(dobdc) (dobdc(4-) = 1,4-dioxido-2,5-benzenedicarboxylate) followed by soaking in a typical electrolyte solution leads to the new solid lithium electrolyte Mg(2)(dobdc)·0.35LiO(i)Pr·0.25LiBF(4)·EC·DEC (EC = ethylene carbonate; DEC = diethyl carbonate). Two-point ac impedance data show a pressed pellet of this material to have a conductivity of 3.1 × 10(-4) S/cm at 300 K. In addition, the results from variable-temperature measurements reveal an activation energy of just 0.15 eV, while single-particle data suggest that intraparticle transport dominates conduction.     

Synthesis and mesomorphic behaviors of a series of heterocyclic pyridine-imine-ester based liquid crystals

ABSTRACT

A series of new calamitic liquid crystals, 4-{[(5-methylpyridin-2-yl)imino]methyl}phenyl 4-alkoxybenzoates were synthesized. This series consists of nine members wherein they are differed by the length of alkoxy chain. Spectral analysis results were in accordance with the expected structure. Their thermotropic behaviors were analyzed with Differential Scanning Calorimetry (DSC), Polarizing Optical Microscopy (POM) and powder X-ray diffraction techniques. First member with the shortest alkoxy chain (n?=?2) is a non-mesogen. As the alkoxy chain increased to n?=?4, the monotropic nematic phase appeared. An enantiotropic mesophase (nematic) was observed for the following three members (n?=?6, 8, 10). As the alkoxy chain increased to n?=?12, enantiotropic nematic phase exhibited together with monotropic smectic A (SmA) phase. As the alkoxy chain continuously increased to n?=?14 and 16, enantiotropic phases were observed for both N and SmA. When moving to n?=?18, the nematic phase disappeared and this compound only exhibited a single mesophase (SmA).