HREELS, STM, and STS study of CH(3)-terminated Si(111)-(1x1) surface

An ideally (1x1)-CH(3)(methyl)-terminated Si(111) surface was composed by Grignard reaction of photochlorinated Si(111) and the surface structure was for the first time confirmed by Auger electron spectroscopy, low energy electron diffraction, high-resolution electron energy loss spectroscopy (HREELS), scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS). HREELS revealed the vibration modes associated to the CH(3)-group as well as the C-Si bond. STM discerned an adlattice with (1x1) periodicity on Si(111) composed of protrusions with internal features, covering all surface terraces. The surface structure was confirmed to be stable at temperatures below 600 K. STS showed that an occupied-state band exists at gap voltage of -1.57 eV, generated by the surface CH(3) adlattice. This CH(3):Si(111)-(1x1) adlayer with high stability and unique electronic property is prospective for applications such as nanoscale lithography and advanced electrochemistry.     

Syntheses of (5E)-PGE2 and New 6-Functionalized Derivatives by the Use of Palladium-Catalyzed Decarboxylative Allylic Alkylation

(5 )-Prostaglandin E₂ (7) was synthesized fron ( )-4- -butyldimethylsilyloxy-2-cyclopentenone (1) by 2-alkenyloxycarbonylatlon of the organocopper conjugate-addition adduct (3) followed by intramolecular palladium-catalyzed decarboxylative allylic alkylation. The (5 )-prostaglandin E₂ skeleton was also obtained from the β-keto allylic ester (11) by a similar decarboxylative allylic alkylation. The decarboxylative allylic alkylation of another type of the three-component coupling product (12) gave new 6-methyleneprostaglandin E1 skeleton (15a), which was converted into new 6-methylprosta-glandin I methyl ester (20) 6-methyleneprostaglandin F₁ derivative (16) by two different ways. The stereochemistry of this intramolecular decarboxylative allylic alkylation was discussed in the reaction of 2-[( )- or ( )-2-butenyloxy-carbonyl] cyclopentanone systems.     

Preparation of non-peptide,highly potent and selective antagonists of arginine vasopressin V1A receptor by introduction of alkoxy groups

A series of compounds structurally related to 4'-[(4,4-difluoro-5-methylidene-2,3,4,5-tetrahydro-1H-1-benzoazepin-1-yl)carbonyl]benzanilide were synthesized and evaluated for arginine vasopressin (AVP) antagonistic activity. Compounds with alkoxy groups (especially ethoxy group) at the 2'-position of benzanilide possessed potent affinity and selectivity for the V1A receptor versus V2 receptor. Further study has shown that the introduction of 4,4-dimethylaminopiperidino and morpholino groups at carbonylmethylene exhibited more potent affinity and selectivity for V1A receptors. Consequently, we found that the (Z)-4'-([4,4-Difluoro-5-[(4-dimethylaminopiperidino)carbonylmethylene]-2,3,4,5-tetrahydro-1H-1-benzoazepin-1-yl]carbonyl)-2-ethoxybenzanilide monohydrochloride (8d) and the (Z)-4'-[(4,4-Difluoro-5-morpholinocarbamoylethylene-2,3,4,5-tetrahydro-1H-1-benzoazepin-1-yl)carbonyl]-2-ethoxybenzanilide (8q) exhibited potent and selective V1A receptor antagonist activity. The synthesis and pharmacological properties of these compounds are detailed in this paper.     

Photoconductivity of poly(vinyl alcohol) films containing Cu2+ complexes

Photoconductivity has been measured in well-dried poly(vinyl alcohol) (PVAl) films containing Cu²⁺ complexes prepared by treatment with Cu(NO₃)₂, CuSO₄, CuCl₂, and CuBr₂. When the ratio [Cu²⁺]/[MU] ([MU] denoting the concentration of PVAl monomer residues) is greater than 0.015, illumination at the charge-transfer (UV) band produces a strong photocurrent in PVAl-CuCl₂ and PVAl-CuBr₂, but not in PVAl-Cu(NO₃)₂ or PVAl-CuSO₄. Optical absorption spectra suggest that two halide ions enter the first coordination sphere in the cis configuration. The temperature dependence of ESR indicates the existence of antiferromagnetic superexchange interaction via intervening halide ions. Hence, there exists a network structure of the PVAl-CuCl₂ or PVAl-CuBr₂ complex. The dependence of the photocurrent on the polarity of the illuminated electrode shows that the majority of carriers are holes. Holes in the network structure produced by charge transfer from halogen to Cu²⁺ ions are concluded to be responsible for the photoconduction.     

Exciton band structure of crystalline anthracene

The density of states in the first exciton band of crystalline anthracene has been obtained at room, dry-ice-alcohol, and liquid nitrogen temperatures by applying a thermal modulation technique to observe the hot band-first exciton band optical transition (1-0 transition). The density of states function obtained has been interpreted in terms of the exciton band structure and the Davydov splitting. The K dependent selection rule for the 1-0 transition is discussed. The bandwidth of the first exciton band is 0.09 eV.     

Relationship between formation conditions, properties, and crystallite size of boehmite

Boehmites (gamma-AlOOH) with a variety of crystallite sizes were prepared under various precipitation conditions from solutions of aluminum nitrate and sodium aluminate and also by hydrothermal treatment of a commercial boehmite powder. The relationships between the crystallite size and other properties of the boehmites were investigated. Crystalline boehmite was formed in the pH range 7 to 10 while gels precipitated below pH 7 and bayerite (Al(OH)3) formed at pH 11. The crystallite size of the boehmite increased at higher pH, higher temperature of the precursor solution, and longer aging time. As the crystallite size of the boehmite increased, the specific surface area, pore volume, and excess water decreased. Boehmites of small crystallite size, called pseudoboehmite, showed broadened X-ray peak widths and increased d-spacing of the 020 reflection. These changes are attributed to the small crystallite size (smaller numbers of stacking layers) and also to excess water in the interlayers of the boehmite structure.     

Synthesis and determination of the relative structure of akaterpin, a potent inhibitor of PI-PLC

We describe the first total synthesis and structural determination of akaterpin, an inhibitor of phosphatidylinositol-specific phospholipase C (PI-PLC). The key features of the synthetic strategy include a regio- and stereoselective C-alkylation at the angular C1′ position and an exo-selective intermolecular Diels-Alder reaction. The relative stereochemistry was determined by a comparison of the NMR spectra of synthetic akaterpin with those of natural akaterpin.     

Silicon vacancies in 3C-SiC observed by positron lifetime and electron spin resonance

54 , 2512 (1996)]. The trapping coefficient of single-negative silicon vacancies was also derived. Received: 25 August 1997/Accepted: 27 March 1998