Oxygen nonstoichiometry in high-Tc superconductor HoBa2Cu3O6+x and application of coulometric tritration

Nonstoichiometry in the perovskite-type compound, HoBa₂Cu₃O_6+x, was determined as a function of oxygen partial pressure (5 × 10⁻¹ 1 × 10⁵ Pa) in the temperature range of 8631173 K by coulometric titration using a stabilized zirconia electrolyte. Electromotive force of the cell, EMF, was measured as a function of oxygen content at constant temperature, and as a function of temperature at constant oxygen content. The perovskite-type compound was found to have a tendency to decompose into Ho₂O₃, BaO, CuO and some double-oxides at low oxygen partial pressures. Defect equilibria are discussed on the basis of the dependence of nonstoichiometry on oxygen partial pressure. Variation of the relative partial molar entropy with composition is explained in terms of a well-known defect model. A new technique which was developed for measuring the electrical conductivity of a non-stoichiometric oxide, in situ, at constant oxygen content as a function of temperature in the coulometric titration cell, is presented.     

Novel and efficient synthesis of difficult sequence-containing peptides through O-N intramolecular acyl migration reaction of O-acyl isopeptides

A novel and efficient method for the synthesis of difficult sequence-containing peptides has been developed based on the synthesis of O-acyl isopeptides followed by an O-N intramolecular acyl migration reaction, resulting in a remarkable improvement of the yields.     

Two new galloylglucosides from the leaves of Mallotus furetianus

Two new galloylglucosides, mallophenols A (1) and B (2), were isolated from the leaves of Mallotus furetianus (Euphorbiaceae), together with seven known compounds, (6S,9R)-roseoside (3), aviculin (4), (+)-lyoniresinol-3alpha-O-alpha-L-rhamnopyranoside (5), (Z)-3-hexenyl-beta-D-glucopyranoside (6), 3,3,8,9,10-pentahydroxydibenzo[b,d]pyran-6-one (7), 3-hydroxy-4,5(R)-dimethyl-2(5H)-furanone (8) and gallic acid (9). The stereostructures of 1 and 2 were elucidated on the basis of spectroscopic analysis and chemical evidence.     

3-epicabraleahydroxylactone and other triterpenoids from camellia oil and their inhibitory effects on Epstein-Barr virus activation

The structure of a triterpenoid isolated from the nonsaponifiable lipid (NSL) of the seed oil of the camellia (Camellia japonica L.; Theaceae) was established to be (20S)-3beta-hydroxy-25,26,27-trisnordammaran-24,20-olide (1; 3-epicabraleahydroxylactone) on the basis of spectroscopic and chemical methods. Six other triterpenoids isolated from the NSL were identified as 3-epicabraleadiol (2), ocotillol II (3), ocotillol I (4), dammarenediol II (5), (20R)-taraxastane-3beta,20-diol (6), and lupane-3beta,20-diol (7). Upon evaluation of the seven triterpenoids (1-7) with respect to their inhibitory effects on the induction of Epstein-Barr virus early antigen (EBV-EA) by 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells, three compounds (5-7) showed potent inhibitory effects against EBV-EA induction (IC(50) values of 277-420 mol ratio/32 pmol TPA).     

Measurement of the kaonic hydrogen x-ray spectrum

The DEAR (DAPhiNE exotic atom research) experiment measured the energy of x rays emitted in the transitions to the ground state of kaonic hydrogen. The measured values for the shift epsilon and the width Gamma of the 1s state due to the K(-)p strong interaction are epsilon(1s)=-193 +/- 37 (stat) +/- 6 (syst) eV and Gamma(1s)=249 +/- 111 (stat) +/- 30 (syst) eV, the most precise values yet obtained. The pattern of the kaonic hydrogen K-series lines, K(alpha), K(beta), and K(gamma), was disentangled for the first time.     

Specific-heat anomaly caused by ferroelectric nanoregions in Pb(Mg(1/3)Nb(2/3))O3 and Pb(Mg(1/3)Ta(2/3))O3 relaxors

The specific heat of typical relaxors, Pb(Mg(1/3)Nb(2/3))O3 (PMN) and Pb(Mg(1/3)Ta(2/3))O3 (PMT), was measured by adiabatic and relaxation methods between 2 and 420 K. A broad anomaly was found in the specific heat curve over the wide temperature range between 150 and 500 K for PMN, and between 50 and 400 K for PMT, which provides evidence for the formation of ferroelectric nanoregions (FNR) in the paraelectric matrix. The entropy of the anomaly was estimated as 3.3 J K(-1) mol(-1) and 2.9 J K(-1) mol(-1) for PMN and PMT, respectively, which implies an order-disorder-type mechanism for the formation of FNR.     

Superconductivity in the graphite-potassium intercalation compound C8K

Superconducting properties of pseudo-single crystals of C₈K were investigated by low frequency a.c. magnetic susceptibility and electrical resistivity measurements. The measured values of T_c were between 128 and 198 mK for 13 samples. Measurements of the superconducting transition in a magnetic field revealed a remarkable anisotropy, such that if θ is defined as the angle between the applied magnetic field and the layer plane, type II superconductivity was observed for 0° ≦ ∣ θ ∣ ? 25° and type I superconductivity for 25° ? ∣ θ ∣≦ 90°. The angular dependences of H_c2 and H_c3 were fairly well-explained by the effective mass model.     

Heat capacity anomalies due to successive phase transitions in 1,1′-biphenyl

Precision heat capacity measurements on 1,1′-biphenyl revealed two broad anomalies at 11.0 K and 40.4 K. The excess enthalpies and entropies are 0.28 ± 0.02 J mol^?1 and 0.026 ± 0.002 J K^?1mol^?1 for the anomaly extending from 7.5 to 14.0 K, and 5.02 ± 0.08 J mol^?1 and 0.129 ± 0.003 J K^?1mol^?1 for the anomaly extending from 30.0 to 47.0 K, respectively. A possible molecular mechanism is suggested.     

Orientation of the remaining amorphous chains during crystallization: Isotactic polystyrene

The orientation of statistical chain segments in the amorphous regions of a semicrystalline polymer can be characterized quantitatively by x-ray diffraction. A calculated background (which is orientation independent) must be subtracted, which requires that the intensity profile of the amorphous halo be measured on an absolute scale. Application is illustrated to samples of isotactic polystyrene which were isothermally crystallized at fixed elongation. These samples differ from those of the previous study due to the unintentional introduction of a small amount of crystallinity (0.25% to 1%) which serves as tie points in the drawing operation, giving a stronger amorphous orientation. Preferred orientation of the amorphous chain segments is rapidly depleted during the first few percent of crystallization. The crystallite orientation distribution is quite sharp, and broadens only slowly with crystallization. These results imply that, for the crystallization conditions employed, the crystallite orientation must be determined by nuclei which are formed at the earliest stages of the crystallization process.