Infrared photodissociation spectroscopy of H(+)(H2O)6·M(m) (M = Ne, Ar, Kr, Xe, H2, N2, and CH4): messenger-dependent balance between H3O(+) and H5O2(+) core isomers

Although messenger mediated spectroscopy is a widely-used technique to study gas phase ionic species, effects of messengers themselves are not necessarily clear. In this study, we report infrared photodissociation spectroscopy of H(+)(H(2)O)(6)·M(m) (M = Ne, Ar, Kr, Xe, H(2), N(2), and CH(4)) in the OH stretch region to investigate messenger(M)-dependent cluster structures of the H(+)(H(2)O)(6) moiety. The H(+)(H(2)O)(6), the protonated water hexamer, is the smallest system in which both the H(3)O(+) (Eigen) and H(5)O(2)(+) (Zundel) hydrated proton motifs coexist. All the spectra show narrower band widths reflecting reduced internal energy (lower vibrational temperature) in comparison with bare H(+)(H(2)O)(6). The Xe-, CH(4)-, and N(2)-mediated spectra show additional band features due to the relatively strong perturbation of the messenger. The observed band patterns in the Ar-, Kr-, Xe-, N(2)-, and CH(4)-mediated spectra are attributed mainly to the "Zundel" type isomer, which is more stable. On the other hand, the Ne- and H(2)-mediated spectra are accounted for by a mixture of the "Eigen" and "Zundel" types, like that of bare H(+)(H(2)O)(6). These results suggest that a messenger sometimes imposes unexpected isomer-selectivity even though it has been thought to be inert. Plausible origins of the isomer-selectivity are also discussed.     

Highly resolved scanning tunneling microscopy study of Si(0 0 1) surfaces flattened in aqueous environment

A surface preparation method with fine SiO₂ particles in water is developed to flatten Si(0 0 1) surfaces on the nanometer scale. The flattening performance of Si(0 0 1) surfaces after the surface preparation method is investigated by scanning tunneling microscopy. The observed surface is so flat that 95% of the view area (100 × 100 nm²) is composed of only three atomic layers, namely, one dominant layer occupying 50% of the entire area and two adjacent layers. Furthermore, a magnified image shows the outermost Si atoms regularly distributed along the 〈1 1 0〉 direction on terraces.     

Solid-phase syntheses of olefin-containing inhibitors for HTLV-1 protease using the Horner-Emmons reaction

[reaction: see text] The solid-phase Horner-Emmons reaction was successfully applied for the convenient syntheses of olefin-containing protease inhibitors. The isomerization during the solid-phase Horner-Emmons reaction can be minimized simply by the use of an appropriate amount of the base. The synthesized olefin peptides, which have an olefin gamma-amino acid at the scissile site, were found to act as effective inhibitors for the HTLV-1 protease for the first time.     

Conformation of solvent N,N-dimethylpropionamide in the coordination sphere of the zinc(II) ion studied by Raman spectroscopy and DFT calculations

Solvation structure of the zinc(II) ion in N,N-dimethylpropionamide (DMPA) was studied by Raman spectroscopy at varying temperature and by quantum mechanical calculations. No significant ion-pair formation was found for the Zn(ClO4)2 solution in the molality range m(Zn) < 1.5 mol kg(-1), and the solvation number of the zinc(II) ion was determined to be 4, indicating that 6-coordination of DMPA is sterically hindered. Interestingly, DMPA molecules are under equilibrium between planar cis and nonplanar staggered conformers, and the latter is more preferred in the coordination sphere, while the reverse is the case in the bulk. The DeltaG degrees , DeltaH degrees , and TDeltaS degrees values of conformational change from planar cis to nonplanar staggered in the coordination sphere were obtained to be -0.9, -8.5, and -7.5 kJ mol(-1), respectively. Density functional theory (DFT) calculations show that the planar cis conformer is more favorable than the nonplanar staggered one in the 1:2 cluster, as is the case for a single DMPA molecule and H(DMPA)+, indicating that there hardly occurs solvent-solvent interaction through the metal ion in the Zn2+-DMPA 1:2 cluster. On the other hand, the SCF energy of [Zn(planar cis-DMPA)4-n(nonplanar staggered DMPA)n]2+ (n = 0-4) decreases with increasing n, implying that the nonplanar staggered conformer is preferred in the solvate ion. It is thus concluded that solvent-solvent interaction through space, or solvation steric effect, plays a crucial role in the conformational equilibrium in the coordination sphere of the four-solvate metal ion.     

Effect of tetrabutylphosphonium cation on the physico-chemical properties of amino-acid ionic liquids

Tetraalkylphosphonium-based amino-acid ionic liquids show lower viscosities and higher decomposition temperatures (>300 degrees C) than previously reported ammonium-based amino-acid ionic liquids.     

Enantioselective synthesis mediated by chiral crystal of achiral hippuric acid in conjunction with asymmetric autocatalysis

Enantiomorphous crystals composed of achiral hippuric acid, i.e., naturally occurring N-benzoylglycine, have been used successfully as chiral inducers in enantioselective synthesis in combination with asymmetric autocatalysis to afford the product with extremely high enantiomeric excess.     

Structural study of NO adsorbed on the reconstructed Pt(110)-(1 x 2) surface with X-ray photoelectron diffraction and near-edge X-ray absorption fine structure spectroscopy

The adsorption structure of NO on the reconstructed Pt(110)-(1 x 2) surface was studied with X-ray photoelectron spectroscopy (XPS), X-ray photoelectron diffraction (XPD), low-energy scanned-angle photoelectron diffraction (LESA-PD), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The experiments were performed at 180 K, where no surface lifting from (1 x 2) to (1 x 1) takes place after NO adsorption. XPS indicates that the (1 x 2) unit cell of the Pt(110) surface contains 1.5 NO molecules at the saturated coverage. XPD and LESA-PD analyses allow us to propose a structural model for the NO adlayer, where two-thirds of the NO molecules in the (1 x 2) unit cell are adsorbed on the atop site of the close-packed Pt rows (ridges) along the [10] direction with an inclined geometry and one-third of the NO molecules adsorb on the bridge site between the Pt ridges with an upright configuration. This model is supported by the N K-edge NEXAFS experiments and is consistent with the recently reported model based on the density functional theory (Orita, H.; Nakamura, I.; Fujitani, T. J. Phys. Chem. B 2005, 109, 10312).