Mechanism of enhancement of sonochemical-reaction efficiency by pulsed ultrasound

The enhancement of sonochemical-reaction efficiency by pulsed ultrasound at 152 kHz has been studied experimentally through absorbance measurements of triiodide ions from sonochemical oxidation of potassium iodide at different liquid volumes to determine sonochemical efficiency defined by reacted molecules per input ultrasonic energy. The mechanism for enhancement of the reaction efficiency by pulsed ultrasound is discussed using captured images of sonochemiluminescence (SCL), and measured time-resolved signals of the SCL pulses and pressure amplitudes. The high sonochemical-reaction efficiency by pulsed ultrasound, compared with that by continuous-wave ultrasound, is attributed both to the residual pressure amplitude during the pulse-off time and to the spatial enlargement of active reaction sites.     

Mechanism of elastic softening behavior in a superlattice

We measured the out-of-plane elastic constants C(33) of a Co/Pt superlattice by picosecond ultrasound, and found that they were closely related to the thickness ratio of Co and Pt layers; C(33) was smaller than the prediction from the bulk values except for a specific thickness ratio. This behavior can be explained by the weak bonding at the interfaces that occurs to reduce the elastic strain energy, not by the interfacial strain. This view explained the relationship among C(33), the elastic strain energy, and perpendicular magnetic anisotropy.     

Superconducting transition temperature and the thickness of CoO2 planes of NaxCoO2·yH2O

The superconductivity of Na_xCoO₂·yH₂O appears in two regions of ν_Q divided by a narrow nonsuperconducting phase in the T_c–ν_Q phase diagram, where T_c and ν_Q are the superconducting transition temperature and ⁵⁹Co-nuclear quadrupole frequency, respectively. It suggests that the existence/nonexistence of the superconductivity depends on the local structure around Co sites or on the thickness of the CoO₂ planes, through the change of the crystal field. We have carried out specific heat measurements on several samples with different ν_Q values distributing over both the superconducting ν_Q regions, and found that the electronic specific heat coefficient γ does not change significantly with ν_Q. It suggests that a topological change of the Fermi surface which has been proposed as a possible origin of the existence of the two superconducting regions, does not take place with the change of the local structure around Co sites or thickness of the CoO₂ planes. We have also carried out neutron inelastic measurements on aligned crystals of Na_xCoO₂·yD₂O, and found that ferromagnetic fluctuations with two-dimensional character observed in the high temperature region lose their intensities with decreasing T and becomes inappreciable below 25 K. It indicates that the hole-pockets near the K points in the reciprocal space do not exist in these crystals. Combining these results, we can exclude, in the entire region of ν_Q, the existence of the hole-pockets, on which arguments of the possible triplet superconductivity are based. The present results are consistent with the singlet pairing which we showed in previous papers.     

Studies on Phosphorus-Containing Polymers. V. Ring-Opening Polymerization of Tetrahydrofuran Catalyzed by Linear Phosphonitrilic Chloride

It was found that linear phosphonitrilic chloride could be used as a catalyst for ring-opening polymerization of tetrahydrofuran. Bulk polymerizations were carried out in a nitrogen atmosphere. After termination of polymerization, the reaction mixture was poured into water, thereby decomposing the catalyst. The product was dissolved in benzene and then subjected to lyophilization. The polymerization of tetrahydrofuran in the presence of linear phosphonitrilic chloride was found to be an equilibrium and a “living” polymerization. The polymerization product includes little phosphorus, and its infrared absorption spectrum agrees well with that of the polymer obtained with PF₅ catalyst. The results of the polymerization using epichlorohydrin as a promoter show that the number of active sites in the molecule of linear phosphonitrilic chloride is considerably smaller. Consequently it is conceivable that the catalytic activity of the linear phosphonitrilic chloride is attributed to its terminal ～～P⁺Cl₃PCl_?6 structure. Furthermore we presume that the polymerization of tetra-hydrofuran in the presence of this catalyst proceeds through a cationic ring-opening mechanism.     

Kinetics of ion transfer at the ionic liquid/water nanointerface

Ion transfer (IT) processes in ionic liquids (ILs) are essential for their applications in electrochemical systems and chemical separations. In this Article, the first measurements of IT kinetics at the IL/water interface are reported. Steady-state voltammetry was performed at the nanometer-sized polarizable interface between water and ionic liquid, [THTDP(+)][C(4)C(4)N(-)], immiscible with it that was formed at the tip of a nanopipet. Kinetic measurements at such interfaces are extremely challenging because of slow mass-transfer rates in IL, which is ～700 times more viscous than water. The recently developed new mode of nanopipet voltammetry, common ion voltammetry, was used to overcome technical difficulties and ensure the reliability of the extracted kinetic parameters of IT. The results suggest that the rate of interfacial IT depends strongly on solution viscosity. Voltammetric responses of nanopipets of different radii were analyzed to evaluate the effect of the electrical double layer at the liquid/liquid interface on IT kinetics. The possibility of the influence of the charged pipet wall on ion transport was investigated by comparing currents produced by cationic and anionic species. Possible effects of relaxation phenomena at the IL/water interface on IT voltammograms have also been explored.     

Diarylprolinol in an asymmetric aldol reaction of an α-alkyl-α-oxo aldehyde as an electrophile

The direct aldol reaction of an α-alkyl-α-oxo aldehyde was catalyzed by trifluoromethyl-substituted diarylprolinol 1 to afford a γ-oxo-β-hydroxy-α-substituted aldehyde in good yield with excellent anti-selectivity and excellent enantioselectivity.     

Relationship between magnetic structure and ferroelectricity of systems with CuO2 ribbon chains

Results of experimental studies carried out by various methods on systems with CuO₂ ribbon chains are presented. For LiVCuO₄, which was found to have helimagnetic and ferroelectric simultaneous transitions (multiferroic transitions), the relationship between the magnetic structure and the ferroelectricity is described in detail by showing their magnetic field dependences. For Li₂ZrCuO₄, NMR studies have revealed that the system has ac-helical magnetic structure. However, we have not observed the ferroelectricity in this ordered phase. This result suggests that there may exist the antiferro-type ordering, for example, of the helical axis vectors, of the CuO₂ chains. Several new findings are also shown on the magnetic and dielectric properties of other ribbon chain systems, LiVCuO₄, Li₂ZrCuO₄, LiCu₂O₂ and NaCu₂O₂ and a related system Na₂Cu₃(GeO₃)₄.