Enhancement of superconducting transition temperature due to the strong antiferromagnetic spin fluctuations in the noncentrosymmetric heavy-fermion superconductor CeIrSi3: A 29Si NMR study under pressure

We report a (29)Si NMR study on the pressure-induced superconductivity (SC) in an antiferromagnetic (AFM) heavy-fermion compound CeIrSi(3) without inversion symmetry. In the SC state at P = 2.7-2.8 GPa, the temperature (T) dependence of the nuclear-spin lattice relaxation rate 1/T(1) below T(c) exhibits a T(3) behavior without any coherence peak just below T(c), revealing the presence of line nodes in the SC gap. In the normal state, 1/T(1) follows a square root T-like behavior, suggesting that the SC emerges under the non-Fermi-liquid state dominated by AFM spin fluctuations enhanced around a quantum critical point. The reason why the maximum T(c) in CeIrSi(3) is relatively high among the Ce-based heavy-fermion superconductors may be the existence of the strong AFM spin fluctuations. We discuss the comparison with the other Ce-based heavy-fermion superconductors.     

Epitaxial growth of isotactic polypropylene on oriented polyethylene from solution

Oriented polyethylene (PE) films with surfaces bounded by the (100) plane were prepared. On the film surfaces, isotactic polypropylene (iPP) was crystallized epitaxially from solution as quadrits with their sides parallel and perpendicular to the polyethylene chain axis. In the through wide-angle x-ray diffraction pattern (taken with incident x-rays normal to the polyethylene film surface), the 111 iPP reflections was observed on the meridian (Parallel to the polyethylene chain axis). In the edge patterns (taken with x-rays incident on the edge of the polyethylene film), 040 and 060 reflections were observed on the equator. From the diffraction patterns, the following lattice coincidence was observed between polyethylene and isotactic polypropylene: (010)iPP//(100) PE, [101]iPP//[001] PE. The Small-angle x-ray scattering patterns showed that edge-on isotactic polypropylene lamellae 9 nm thick were arranged with their long axes inclined at an angle of 40° from the polyethylene axis. Molecular chains were oriented within the lamellae normal to the surfaces.     

Environment-induced morphological changes of polyethylene lamellae during crystallization in solution

Polyethylene (PE) lamellar crystals were grown by two dual-staged crystallization methods: (1) Fractionated PE was first crystallized from n-octane by the self-seeding method, the solvent of the resulting suspension of crystals was exchanged for p-xylene, and thereafter, the suspension was mixed with a solution in p-xylene at various temperatures so that PE grew from p-xylene onto the lamellae pregrown from n-octane, and (2) according to the similar procedure, PE lamellae were first grown from p-xylene and subsequently, PE was deposited from n-octane onto the lamellae pre-grown from p-xylene. In the crystallization procedure (1), triangular lamellae with the 〈010〉 chain folding developed randomly on the {100} lateral surfaces of truncated parent lamellae so that the surfaces were serrated, and otherwise, thin daughter lamellae bordered the parent lamellae along the {110} surfaces, retaining the flat growth fronts with the 〈110〉 folding. In the procedure (2), the {100} sectors with the 〈010〉 folding developed at the apexes of the long diagonal of lozengeshaped parent lamellae, and consequently, their morphology was transfigured into a truncated crystal. These morphological transformations are discussed on the basis of the change in the interfacial free energy between the parent crystal and the surrounding phase due to the substitution of solvent. © 1994 John Wiley & Sons, Inc.     

Synthesis of a well-defined cyclic polystyrene via α-carboxyl, ω-amino heterodifunctional polystyrene

Living anionic polymerization of styrene was carried out in benzene at room temperature using 1-(3-lithiopropyl)-4-methyl-2,6,7-trioxabicyclo[2.2.2]octane and 2,2,5,5-tetramethyl-1-(3-bromopropyl)-1-aza-2,5-disilacyclopentane as an initiator and terminator, respectively, to obtain α-2,2-bis(hydroxymethyl)propoxycarbonyl, ω-amino heterodifunctional polystyrene. It was hydrolyzed to α-carboxyl, ω-amino heterodifunctional polystyrene which gave a well-defined cyclic polystyrene by the intramolecular cyclization under high dilution conditions. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2027–2033, 1999     

Adaptive cross-correlation algorithm for extended scene Shack-Hartmann wavefront sensing

We present an adaptive cross-correlation algorithm for a large dynamic range extended-scene Shack-Hartmann wavefront sensor. We show that it accurately measures very fine image shifts over many pixels under a variety of practical imaging conditions.     

Effect of chelating ring size in catalytic ketone hydrogenation: facile synthesis of ruthenium(II) precatalysts containing an N-heterocyclic carbene with a primary amine donor for ketone hydrogenation and a DFT study of mechanisms

A half-sandwich ruthenium(II) complex, [Ru(η(6)-p-cymene)(C-NH(2))Cl]PF(6) (4·PF(6)), containing an N-heterocyclic carbene (NHC) with a primary amine donor (C-NH(2)) which chelates through the carbene carbon and the amine nitrogen to form a 6-membered ring was synthesized in a one-pot reaction starting from a primary-amine functionalized imidazolium salt 2. Complex 4·PF(6) catalyzed the hydrogenation of ketones using 2-propanol or H(2) as the reductant. A maximum turnover frequency of 1062 h(-1) and a turnover number of 1140 at 5 h were achieved for the transfer hydrogenation of 3'-chloroacetophenone in 2-propanol at 75 °C. A cationic hydride-amine complex 5, [Ru(η(6)-p-cymene)(C-NH(2))H]PF(6), was synthesized, and this reacted very slowly with acetophenone unless first activated by an alkoxide base. Computational studies by DFT methods suggested that the poor reactivity of the hydride-amine complex 5 was attributed to a large barrier for the transfer of its H(+)/H(-) couple to a ketone for bifunctional catalysis. An inner-sphere mechanism, which involves a decoordinated amine group of the C-NH(2) ligand, was computed to be a feasible energetic pathway in comparison to the computed outer-sphere bifunctional mechanism. This explains the catalytic activity and selectivity that is observed for the newly synthesized ruthenium(II) catalysts.     

Design of new chiral phase-transfer catalysts with dual functions for highly enantioselective epoxidation of alpha,beta-unsaturated ketones

A new chiral ammonium bromide, 1-Br, possessing diarylmethanol functionality as a substrate recognition site has been designed as a promising, dual-functioning catalyst for the highly enantioselective epoxidation of alpha,beta-unsaturated ketones under mild phase-transfer conditions. For instance, vigorous stirring of a mixture of chalcone, 1-Br (3 mol %), and 13% NaOCl in toluene at 0 degrees C for 24 h gave rise to epoxy chalcone quantitatively with 96% ee. A variety of alpha,beta-unsaturated ketones can also be epoxidized with rigorous stereochemical control, clearly demonstrating the effectiveness and utility of the present system. Further, a successful single-crystal X-ray diffraction analysis of 1-PF6 uncovered its distinctive three-dimensional molecular architecture and provided useful information for postulating the transition state.     

Convergent Synthesis of (−)‐Quinocarcin Based on the Combination of Sonogashira Coupling and Gold(I)‐Catalyzed 6‐endo‐dig Hydroamination

The total synthesis of the pentacyclic tetrahydroisoquinoline alkaloid quinocarcin, which possesses intriguing structural and biological features, has been achieved through a gold(I)‐catalyzed regioselective hydroamination reaction. It is noteworthy that the regioselectivity of the intramolecular hydroamination of an unsymmetrical alkyne could be completely switched through substrate control. Other key features of this synthesis include the highly stereoselective synthesis of 2,5‐cis‐pyrrolidine through the intramolecular amination of the bromoallene and the Lewis acid mediated ring opening of dihydrobenzofuran.     

Different enantioselectivity of two types of poly(lactic acid) depolymerases toward poly(l-lactic acid) and poly(d-lactic acid)

Poly(lactic acid) (PLA) depolymerases are categorized into protease-type and lipase-type. Protease-types can hydrolyze poly(l-lactic acid) (PLLA) but not poly(d-lactic acid) (PDLA). Lipase-types, including cutinase-like enzyme (CLE) from Cryptococcus sp. strain S-2 preferentially hydrolyze PDLA. Both enzymes degraded not only PLA emulsion but also PLA film, in which amorphous region is preferentially attacked, but crystalline region can be also attacked. Stereocomplex PLA (sc-PLA) formed by 50:50 blending of PLLA and PDLA included no homo crystals, but a tiny homo crystallization peak appeared and crystallinity increased by 5% when attacked by CLE, although no significant change of molecular weight and crystalline size was found. Enantioselective degradation must occur in amorphous region of PLLA/PDLA film and preferentially hydrolyzed PDLA, resulting in a slightly excess amount of PLLA remained, which must be crystallized.