Complete stereochemistry of neamphamide A and absolute configuration of the beta-methoxytyrosine residue in papuamide B

The absolute stereochemistry of the three unresolved structural components in neamphamide A (1) was determined to be (R)-beta-methoxy-L-tyrosine, (2R,3R,4S)-4-amino-7-guanidino-2,3-dihydroxyheptanoic acid, and (2R,3R,4R)-3-hydroxy-2,4,6-trimethylheptanoic acid. Stereochemical assignments were made by chemical degradation of 1, derivatization of the resulting products, and then spectroscopic and chromatographic comparison of the derivatives with synthetically prepared standards. Using the same analytical protocol developed for 1, the beta-methoxytyrosine residue in papuamide B (2) was found to be (R)-beta-methoxy-D-tyrosine. This represents a rare example of divergent stereochemistry in an unusual amino acid residue that is present in two closely related classes of peptides.     

Shear and normal stress relaxation in polymer blends: stress predictions from interface velocity and Laplace pressure terms

We derived for the first time the relationships among shear stress and normal stress differences for ellipsoidal interfaces under large step shear strains considering interface velocity term and Laplace pressure term in the expression of the stress tensor for mixtures of two Newtonian fluids. In the derivation, orientation angle of the interface is assumed to be given by the affine deformation assumption and is independent of time based on experimental results for blends with 0.048 ≤ K ≤ 0.54 where K is the ratio of droplet viscosity to matrix viscosity. For ellipsoidal droplets, the shear stress is only proportional to the first normal stress difference. On the other hand, for spheroidal droplets, proportionality among the shear stress, the first and the second normal stress differences was derived, and the ratio of the second normal stress difference to the first normal stress difference was given as a function of step strain. The shear stress and the first normal stress difference obtained experimentally satisfy the derived relationship, indicating applicability of the stress expression for polymer blends.     

Improvement in superconductivity of TlBa2CaCu2Oy system by introduction of oxygen loss

The T_c and oxygen content of TlBa₂CaCu₂O_y have been investigated by quenching experiments, in which the heat-treated samples were dropped into liquid nitrogen. The oxygen loss, v, of TlBa₂CaCu₂O_{yo − v} was determined by thermogravimetry in a nitrogen atmosphere using an oxygen-annealed specimen of TlBa₂CaCu₂O_yo and also by measurements of the weight differences before and after quenching. T_c increased from 80 K of the oxygen-annealed specimen up to about 110 K with increasing oxygen loss up to v = 0.035 by annealing at 500°C in a nitrogen atmosphere. Judging from the high T_c above 110 K achieved by a small oxygen loss about v = 0.035, the as-sintered oxygen-annealed TlBa₂CaCu₂O_yo specimen was in the over-doping state and probably has an oxygen vacancy of 7 − y_o0.     

Shape and structure recovery of an LCP droplet under a large step strain: observation and stress calculation

Shape recovery of a droplet of liquid crystalline polymer (LCP) hydroxypropylcellulose in a matrix of poly(dimethyl siloxane) subjected to a step shear strain has been studied via optical microscopy. Just after application of a large strain, the LCP droplet shape is flat ellipsoid, and then the droplet takes cylindrical shape and band texture perpendicular to the flow direction appears. The band texture fades away before emergence of poly-domain structure. In the final process with the shape of spheroid, poly-domain structure recovers very slowly. Except for the final process, the shape change is identical with that of isotropic droplet at strains smaller than 3, when the LCP viscosity in Region II is taken as an equivalent viscosity for normalization. For a 20:80 blend, the excess relaxation modulus is calculated based on the Doi-Ohta theory, taking account of the distribution of droplet size and compared with experimental modulus data.     

Observations on the reactivity of tris(tetramethylethylenedioxyboryl)methide ion

Treatment of tetrakis(tetramethylethylenedioxyboryl)methane, (Me₄C₂ - O₂B)₄C, in THF with butyllithium at ?78° generates the tris(tetramethylethylenedioxyboryl)methide ion, (Me₄C₂O₂B)₃C^?, which reacts with chlorotrimethylsilane at ?78° to form trichlorosilyltris(tetramethylethylenedioxyboryl)-methane, (Me₄C₂O₂B)₃CSiMe₃. The yield was low, but other attempts to form silyltriborylmethanes have failed altogether. The ion (Me₄C₂O₂B)₃C^? reacts with tetraphenylcyclopentadienone at ?78° to form the expected fulvene, 1,1-bis-(tetramethylethylenedioxyboryl)-2,3,4,5-tetraphenylfulvene. The red color of the tetraphenylcyclopentadienone is converted immediately to the brown of the fulvene product, indicating that the β-elimination of boron and oxygen occurs rapidly under basic conditions at ?78°.     

Estimation of the thickness or composition of a covering layer on a solid by XPS or AES

A method is proposed for semi-quantitative determination of the thickness or composition of a covering layer on a solid by XPS or by micro-AES using neither a series of standard samples nor argon-ion etching. In the case of XPS, the thickness or relative composition of the covering layer is calculated by means of the intensity ratio between one element and another in a specimen and using physical parameters such as inelastic mean free paths of electrons and photoionization cross-sections.In the case of AES, the physical parameters for the quantification can be eliminated by using the ratio of the relative intensity for two elements in the sample to that in a suitable, comparable reference.     

A novel cyclization reaction of oxidodiazoalkanes: formation of pyrazoles and pyridazines

The thermal decomposition of dialkali metal salts of β- and γ-hydroxyketone tosyl-hydrazones in refluxing DME produced pyrazoles and pyridazines, respectively.     

ESCA Investigation of the surface of mixed precipitates

Quantitative ESCA has been used for studying the surface of mixed precipitates. When the precipitation is complete and homogeneous, as with titanium and zirconium hydroxides, almost complete correlation is found between the atomic ratio of the elements in the precipitate and that estimated by the Hirokawa-Ebel method, but not for incomplete mixed precipitation, as with copper and silver hydroxides. When precipitated copper and silver are reduced to the metals with iron or zinc, the surface is enriched in copper.     

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).