Signals for scalar top quark atep collider HERA

In the framework of the minimal supersymmetric standard model (MSSM) and theR-parity breaking model (RBM), we investigate production processes of the scalar top (stop) at HERA energies. These models are characterized by the possible existence of the light stop whose mass is lighter than those of the top quark and the other squarks. It is shown that in the MSSM the stop pair production via boson-gluon fusion gives a sizeable cross section and the most serious background $ep \to ec\bar cX$ could be suppressed by appropriate kinematical cuts. We also show that in the RBM the stop is singly produced in the neutral current processes and we have a clear signal as a sharp peak in the Bjorken parameterx distribution of the scattered electron.     

The effect of humidity on thermal process of zinc acetate

The thermal decomposition of zinc acetate dihydrate Zn(CH₃CO₂)₂·2H₂O in some humidity-controlled atmospheres has been successfully investigated by novel thermal analyses, which are sample-controlled thermogravimetry (SCTG), thermogravimety combined with evolved gas analysis using mass spectrometry (TG–MS) and simultaneous measurement of differential scanning calorimetry and X-ray diffractometry (XRD–DSC). The thermal processes of anhydrous zinc acetate in dry gas atmosphere by conventional linear heating experiment initiated with the sublimation around 180 °C, followed by the fusion and the decomposition over 250 °C. SCTG was useful to interpret clearly the successive reaction because the high-temperature parallel decompositions were effectively inhibited. The thermal behavior changed dramatically by introducing water vapor in the atmosphere and the thermal process was quite different from that in dry gas atmosphere. Zinc oxide (ZnO) was formed only in a humidity-controlled atmosphere, and could be easily synthesized at temperatures below 300 °C. XRD–DSC equipped with a humidity generator revealed directly the crystalline change from Zn(CH₃CO₂)₂ to ZnO. A detailed thermal process of Zn(CH₃CO₂)₂·2H₂O and the effect of water vapor are discussed.     

Novel [2 + 2] photocycloaddition-induced rearrangement of bichromophoric naphthalene-tethered resorcinol ethers

The first examples of sequential photocycloaddition-rearrangement reactions of naphthalene-tethered resorcinol ethers are described. Bichromophoric aromatic compounds with naphthalene and resorcinol ether moieties were irradiated in the presence/absence of a small amount of acid to give the corresponding cycloaddition-rearrangement products. From the determination of quantum yields, steady-state fluorescence spectral studies, and fluorescence lifetime measurements, the mechanism of this novel photoinduced multistep reaction was elucidated to involve the initial intramolecular exciplex formation, followed by the intramolecular [2 + 2] photocycloaddition between the two aromatic rings and the subsequent acid-catalyzed skeletal rearrangement of the resulting cyclobutane derivative leading to the final products.     

New highly strained bridgehead imines, 2-azaadamant-1-ene and 4-azaprotoadamant-3-ene

An azaanalog of adamantene, 2-azaadamant-1-ene ($\text{1}$) and 4-azaprotoadamant-3-ene ($\text{7}$) were generated in the nonstatistical ratio via photolysis of 3-azidonoradamantane ($\text{2}$). The highly strained $\text{1}$ and $\text{7}$ could not be isolable but were trapped by MeOH. Acidolysis of $\text{2}$ was also reported, and discussed in comparison with the photolysis.     

Surface-enhanced Raman scattering from crystal violet adsorbed on a silver electrode

SERS from crystal violet (CV) on a Ag electrode was investigated under preresonance and resonance conditions. The excitation profile of the chemisorbed species is like that of dissolved molecules but intensities are ≈ 1000 times larger. The Raman enhancement is ≈ 10⁸ and exhibits a specific potential dependence even in the absence of adsorption-desorption process. At potentials where reduction of CV occurs leuco crystal violet was detected.     

Novel ring transformation reactions of xanthine derivatives

The novel ring transformation reactions were found in the reactions of 1,3,7,9-tetra-alkyl-8,9-dihydroxanthines and acetylenic compounds. The reaction of the dihydroxanthine with DMAD gave a propellane type compound and with methyl propiolate afforded the similar type compound and a pyrimido[4,5-b]diazepine derivative. The mechanism of these reactions was also discussed.     

Cyclic dithio-carbenium ion salts and their conversion to ketene dithioacetals

1,2-Ethanedithiol and 1,3-propanedithiol were treated with perchloric acid in acetic anhydride to give 2-methyl-1,3-dithiolan-2-yl and 2-methyl-1,3-dithian-2-yl perchlorates, respectively, which were converted to ketene dithioacetals by deprotonation with tertiary amines.     

A highly regio- and stereoselective synthesis of internal olefins via an elimination of trimethylstannyl group

Internal reaction of secondary alkyltin(IV) compounds having thionium ion gave internal trans olefins with high yield and regio- and stereoselectivity via 1,5- or 1,6-transfer of a hydride β to the trialkylstannyl group.     

Large-scale separation of metallic and semiconducting single-walled carbon nanotubes

In the applications of single-walled carbon nanotubes (SWNTs), it is extremely important to separate semiconducting and metallic SWNTs. Although several methods have been reported for the separation, only low yields have been achieved at great expense. We show a separation method involving a dispersion-centrifugation process in a tetrahydrofuran solution of amine, which makes metallic SWNTs highly concentrated to 87% in a simple way.     

A lithiation approach to cordycepin analogues variously substituted at the C-8 position

Several 8-substituted cordycepins were prepared via LDA lithiation of 2′,5′-bis-O-(t-butyldimethylsilyl)-cordycepin and successive reactions of its C-8 lithiated species with various types of electrophiles. Wittig reaction of the 8-formyl derivative was also examined.