Stereochemical studies—XXX : Stereoselective synthesis of D-ribose from L-glutamic acid

A new stereoselective synthesis of D-ribose (14) starting from L-glutamic acid (1) is described, by making use of the chiral center of 1 as that at C-4 of 14. Oxidation of methyl 5-O-benzyl-2,3-dideoxy-D-pent-2-enofuranoside (10) with potassium permanganate or osmium tetroxide was shown to occur preferentially from the rear side of the OMe group at C-1.     

Extended studies of the automated odor-sensing system based on plural semiconductor gas sensors with computerized pattern recognition techniques

The odor-sensing system reported earlier is used to measure odors of 47 compounds. Three computerized pattern recognition techniques, the k-NN, simplex and potential function methods, are applied to the data set for the prediction of the odors of the corresponding compounds. The best prediction results (80.9%) were obtained by means of the potential function method.     

Core-exciton induced resonant photoemission in the covalent semiconductor black phosphorus

Valence band photoemission spectra of black phosphorus have shown anomalous behavior at the excitation of 2p core-excitons. The intensity of the 2.7 ev peak shows a clear Fano type interference due to a direct recombination of core-excitons leaving one hole in valence bands. Besides, strong enhancement of the 10.8 eV peak is interpreted as due to a core-exciton induced resonance with two-hole final states. The role of core-excitons as intermediate states for photoemission processes is newly revealed in the experiments.     

Ultraviolet photoemission and 4d core reflectance spectra of SmSe(100)

Ultraviolet photoemission (UPS) and inner core reflectance spectra have been measured on SmSe(100) surface with synchrotron radiation. Besides the multiplet structures observed in UPS spectra for the Sm 4f, 5p and 5s excitations, the reflectance spectrum has revealed a multiplet structure associated with the Sm 4d→4f excitation. Each band of the UPS spectra has shown remarkably different hν dependence and the resonant behavior of the cross section. Sm 4f- and Se 4p-derived valence band features are unambiguously identified by the angle resolved UPS.     

Core-exciton spectra of AlxGa1−xAs studied with synchrotron radiation

Core-exciton spectra of Al_xGa_1?xAs have been measured in the photon-energy region from 19 to 27 eV by use of synchrotron radiation. The core-excitons associated with the Ga 3d core-hole and the conduction electron around the lowest L₆ and X₆ symmetry points are found to be coupled with each other through intervalley electron-hole interactions. Quantitative analyses have elucidated that intervalley Coulomb term is playing a dominant role for this coupling. Another higher energy doublet structure is interpreted as due to the transition from the Ga 3d core-levels to the rather flat region in the second lowest conduction band around the L₆ and L_{4, 5} symmetry points.     

Partial molar enthalphy of formation of solid solution in transition metal sulfides by a combustion calorimetry

The combustion calorimetry on the NbS system has been carried out under an oxygen atmosphere at 453°C using a Calvet-type twin calorimeter. The partial molar enthalphies of the formation of solid solution for both 2S-NbS_x and 3S-NbS_x phase on the NbS system has been determined.     

Resonance condition for asymmetrical triple-barrier structures

The resonance condition for triple-barrier structures with arbitrary potential is studied systematically. The quasisymmetrical triple-barrier (QST) resonance mode and the quasi-asymmetrical double-barrier (QAD) resonance mode may both exist in asymmetric triple-barrier structures. The QST consists of two submodes: a normal mode (doublet) and a degenerate mode (singlet). The critical condition for distinguishing the two modes is examined. It is confirmed that there are both unity resonant transmission and below-unit resonant transmission in the asymmetrical triple-barrier structure. Furthermore, the wavefunctions of an electron at resonance level are calculated and the confining phenomenon is studied.     

Ca2+- and Ba2+-selective receptors based on site-selective transmetalation of multinuclear polyoxime-zinc(II) complexes

Ca2+-selective recognition was achieved by using the site-selective transmetalation of homotrinuclear metallohost [L1Zn3]2+ containing a linear tetraoxime ligand. The selectivity (log(KCa/KMg) > 5.1) is comparable to those of the excellent Ca2+ receptors or sensors such as BAPTA, Quin2, and K23E1. X-ray crystallography revealed that the Ca2+ complex [L1Zn2Ca]2+ has a helical structure. On the other hand, the larger analogue H6L2 gave a mixture of [L2Zn4]2+ isomers, which selectively recognizes Ba2+ to give a single tetranuclear complex, [L2Zn3Ba]2+.