Effects of acrylic acid incorporation on the pressure–temperature behavior and the calorimetric properties of poly(N-isopropylacrylamide) in aqueous solutions

 We studied the effects of pH on the pressure–temperature dependence of coil–collapse transition for aqueous solutions of copolymers of N-isopropylacrylamide and acrylic acid (Ac). At low pressures, the transition temperature (T _tr) increased with pressure, but T _tr decrease with increasing pressure at pressures higher than 50–100 MPa. By increasing the pH, the transition contour shifted to a higher temperature. When the Ac content was increased, the effects of pH became more evident. From a calorimetric study at atmospheric pressure, ΔH _tr was found to become smaller by increasing the portion of the ionized residues in the copolymer. The ratio to the van't Hoff enthalpy changes became larger with an increase in pH, which indicated that the production of charge decreased the cooperative domain size. Received: 19 July 1999 /Accepted in revised form: 7 September 1999     

Association Model and Its Representation of Phase Equilibria and Excess Enthalpies of Alcohol, Aniline, and Acetonitrile Mixtures

An association model is presented to describe vapor–liquid equilibria,liquid–liquid equilibria, and excess enthalpies of binary and ternary liquid solutionscontaining alcohols, aniline, and/or acetonitrile using the concepts of linearself-association of associated components and of solvation between unlike molecules.Calculated results also show that the model works well in representing thethermodynamic properties for alcohol + aniline, alcohol + acetonitrile, andalcohol + alcohol mixtures.     

Reactions of 2-Pyridyl Substituted Phosphine Oxides and Phosphonium Salts with Organometallic Reagents and in Aqueous Media

Phosphine oxides bearing two or three 2-pyridyl groups react with organometallic reagents affording 2,2′-bipyridyl, 2-substituted pyridines and pyridine in good yields. Phosphonium salts and phosphine oxides, bearing at least two 2-pyridyl or substituted 2-pyridyl groups also give the corresponding 2,2′-bipyridyls and pyridines upon treatment with acid or neutral solvents such as water and alcohols in substantial yields. The 2,2′-bipyridyls are considered to be formed by ligand coupling within the pentacoordinated phosphorus intermediate formed incipiently during the reaction.     

Migration-enhanced epitaxy (MEE) growth of five-layer asymmetric coupled quantum well (FACQW) and its cross-sectional STM observation

The five-layer asymmetric coupled quantum well (FACQW) is a new potential-tailored quantum well that is promising for ultra-fast and ultra-low-voltage optical modulators and switches. FACQW samples were grown by the migration-enhanced epitaxy (MEE) and the conventional molecular beam epitaxy methods with steep and flat heterointerfaces in the monolayer accuracy. They were characterized with the cross-sectional scanning tunneling microscopy (STM). In the cross-sectional STM image, double-stripe structures with different contrast were observed. The stripe area corresponds to the FACQW (about 10 nm wide), sandwiched with the AlGaAs barrier layers (15 nm wide). A dark line observed at the middle of the FACQW stripe area corresponds to the 3-monolayer-thick AlAs layer. The cross-sectional STM images of the high-quality heterointerface FACQW structures were successfully observed for the samples grown by the MEE method. More detailed studies of this kind of cross-sectional STM observations will be very effective to obtain the optimized growth conditions for fine and complicated ultra-thin structures.     

Mössbauer study on Fe0.068Ni0.932Cl2 with competing spin anisotropies

Mössbauer measurements on Fe_0.068Ni_0.932Cl₂ were done at temperatures between 55K and 4.2K. We have found that below T_N-50K an observed spectrum is composed of two kinds of spectra and that the composition ratio changes gradually with temperature. The average angle of Fe²⁺ spins, \(\overline {\theta _{Fe} } \) , with the c-axis is smaller than \(\overline {\theta _c } \) by ?15° at each temperature below T_N, where \(\overline {\theta _c } \) is the average angle of total spins with the c-axis in this system obtained from the neutron scattering measurements. This is reasonably understood if we take into account that Fe²⁺ spins have the strong uniaxial anisotropy along the c-axis. We discuss the coexistence of the two kinds of spectra by considering the exchange energy of Fe²⁺ spins and the local magnetic anisotropy.     

Formation of ionic liquid submicron particles. 1H and 19F nuclear magnetic resonance spectroscopic studies

We prepared novel ionic liquid submicron particles (ILSPs) in water by emulsifying the ionic liquid (IL) N-(2-methoxyethyl)-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr_12O1TFSI), which is immiscible with water, with the nonionic surfactants Tween 20 and Span 80. The mean particle size and zeta potential of the ILSPs were about 580?nm and ?30?mV, respectively. The ILSPs were characterized using ¹H and ¹⁹F nuclear magnetic resonance (NMR) spectroscopic methods. The chemical shifts of the Pyr_12O1⁺ cation and TFSI^? anion in the ¹H and ¹⁹F NMR spectra of the ILSP suspension were consistent with those corresponding to pure Pyr_12O1TFSI. This indicated that most of the Pyr_12O1TFSI was still in the IL state in the ILSP suspension. In addition, ¹H–¹H nuclear Overhauser effect correlated spectroscopic measurements showed that the ILSP droplets contained Pyr_12O1TFSI in the neat IL steric state even in the ILSP suspension, and Pyr_12O1TFSI species localized in the droplet surfaces interacted with the hydrophobic acyl side chains of the surfactants. These NMR spectroscopic results show that the ILSPs formed an IL-in-water microemulsion in which droplets of neat Pyr_12O1TFSI were surrounded by the two surfactants, that is, Tween 20 and Span 80.     

Chemical activation of cytochrome c proteins via crown ether complexation: cold-active synzymes for enantiomer-selective sulfoxide oxidation in methanol

Supramolecular complexation with 18-crown-6 significantly converted catalytically inactive cytochrome c (biological form) to catalytically active synzyme (artificial form). Although a family of cytochrome c proteins does not work as enzymes in nature, crown ether complexation modified their heme coordination structures and functionally activated them to promote the asymmetric oxidation of racemic sulfoxides at low temperature. Horse heart, pigeon breast, and yeast cytochrome c proteins were demonstrated to form supramolecular complexes with 18-crown-6 in methanol, which effectively oxidized (S)-isomers of naphthyl methyl sulfoxide, methyl tolyl sulfoxide, isopropyl phenyl sulfoxide, benzyl methyl sulfoxide, and 4-methylsulfenyl acetophenone at -40 degrees C. Because horse heart and pigeon breast cytochromes c exhibited more efficient and higher enantiomer-selective activities than yeast cytochrome c, a proper combination of cytochrome c and crown ether offers a new class of cold-active synzymes promoting nonbiological asymmetric oxidation.     

Comparison of temperature,pressure and isotope effects on the proton jump between the hydroxide and oxonium ion

The limiting molar conductances ° of potassium deuteroxide KOD in D₂O and potassium hydroxide KOH in H₂O were determined at 5 and 45°C as a function of pressure to clarify the difference in the temperature, pressure and isotope effects on the proton jump between an OD^– (OH^–) and a D₃O⁺ (H₃O⁺) ion. The excess conductances of the OD^– ion in D₂O and the OH^– ion in H₂O, _E ⁰ (OD^-) and _E ⁰ (OH^-), increase with increasing temperature and pressure as in the case of the excess deuteron and proton conductances, _E ⁰ (D⁺) and _E ⁰ (H⁺). However, the temperature effect on the excess conductance is larger for the OD^–(OH^–) ion than for the D₃O⁺ (H₃O⁺) ion but the pressure effect is much smaller for the OD^– (OH^–) ion than for the D₃O⁺ (H₃O⁺) ion. These findings are correlated with larger activation energies and less negative activation volumes found for the OD^– (OH^–) ion than for the D₃O⁺ (H₃O⁺) ion. Concerning the isotope effect, the value of _E ⁰ (OH^-)/ _E ⁰ (OD^-) deviates considerably from at each temperature and pressure in contrast with that of _E ⁰ (H⁺)/ _E ⁰ (D⁺), although both of them decrease with increasing temperature and pressure. These results are discussed mainly in terms of the difference in repulsive force between the OD^– (OH^–) or the D₃O⁺ (H₃O⁺) ion and the adjacent water molecule, the difference in strength of hydrogen bonds in D₂O and H₂O, and their variations with temperature, pressure, and isotope.     

Kinetic and DFT studies on the Ag/TiO2-photocatalyzed selective reduction of nitrobenzene to aniline.

TiO2 particles loaded with silver nanoparticles with a mean diameter of 1.5 nm exhibit a high photocatalytic activity (84 % conversion after 1 h irradiation) for the reduction of nitrobenzene to aniline with 100 % selectivity in the presence of CH3OH (concentration=100 mM). High-resolution transmission electron microscopic studies of Pt-photodeposited Ag/TiO2 demonstrate that the Ag nanoparticles act as reduction sites in the photocatalytic reaction. Both spectroscopic measurements and density functional theory (DFT) calculations reveal that nitrobenzene is selectively adsorbed onto the Ag surfaces of Ag/TiO2 via partial electron transfer from Ag to nitrobenzene, whereas the interaction between aniline and Ag/TiO2 is weak. The kinetic analysis indicates that the recombination between the electrons flowing into the Ag nanoparticle and the holes left in the TiO2 valence band is significantly suppressed, particularly in the presence of CH3OH. The high activity and selectivity in the present Ag/TiO2-photocatalyzed reduction are rationalized in terms of the charge separation efficiency, the selective adsorption of the reactants on the catalyst surfaces, and the restriction of the product readsorption.