Interpretation of initial stage of 3C-SiC growth on Si(1 0 0) using dimethylsilane

The initial stage of cubic silicon carbide (3C-SiC) growth on a Si(0 0 1) surface using dimethylsilane (DMS) as a source gas was observed using scanning tunneling microscopy (STM) and reflection high-energy electron diffraction (RHEED). It was found that the dimer vacancies initially existing on the Si(0 0 1)-(2 × 1) surface were repaired by the Si atoms in DMS molecules, during the formation of the c(4 × 4) surface. From the STM measurement, nucleation of SiC was found to start when the Si surface was covered with the c(4 × 4) structure but before the appearance of SiC spots in the RHEED pattern. The growth mechanism of SiC islands was also discussed based on the results of RHEED, STM and temperature-programmed desorption (TPD).     

Thickness decrease of a grafted polyelectrolyte membrane exposed to shear flow

The effect of the shear flow on the thickness change of a polyelectrolyte membrane grafted onto a glass substrate was directly investigated with a flow cell combined with a confocal laser scanning microscope. The membrane thickness decreased proportionally to an increase in the shear stress of the flow when the shear rate exceeded a critical value of 1 s^?1. The higher the ionic strength was of the fluid, the greater the thinning effect was. The correlation between the critical shear rate and the relaxation of the polymer in the gel membrane was examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2808–2815, 2003     

Classical Valence Similarity in Fullerene Derivatives

Summary.  The generalized Pauling bond order was enumerated in the C₆₀ fullerene cage molecule (truncated icosahedral symmetry). This index measures chemical similarity in fullerene derivatives such as dihydrofullerene (C₆₀H₂), anionized monohydrofullerene (C₆₀H⁻), N-substituted monohydrofullerene (C₅₉NH), the fullerene dimer ((C₆₀)₂), and the dianionic fullerene dimer ((C₆₀)₂ ²⁻). It is also useful in judging the chemical stability of isomers. Received October 9, 2001. Accepted November 9, 2001     

Studies on macrolide antibiotics I. Synthesis and antibacterial activity of erythromycin A 9-O-substituted oxime ether derivatives against Mycobacterium avium complex

A series of erythromycin A 9-O-substituted oxime ether derivatives have been synthesized and evaluated for antibacterial activity against Mycobacterium avium complex (MAC) and Staphylococcus aureus. These compounds possessed stronger in vitro activity against MAC including macrolide-resistant strains than clarithromycin (2), although in vitro antibacterial activities of these compounds were less than that of 2 against Staphylococcus aureus. Our studies found that several factors contribute to the antibacterial activity against MAC. The length and spatial orientation of the substituent at 9-position were found to significantly influenced the anti-MAC activity, especially against macrolide-resistant strains. Of all the compounds prepared, erythromycin A 9-[O-(4-phenylbutyl)oxime] (12q) and erythromycin A 9-[O-(3-phenoxypropyl)oxime] (12t) possessed 16 times stronger antibacterial activity than 2 against clarithromycin-resistant strains. Surprisingly, the minimum inhibitory concentrations (MICs) of 12q and 12t against the resistant strains were almost same as those against the susceptible strains. These results suggest that the erythromycin A 9-O-substituted oxime ether derivatives would be promising macrolide antibiotics.     

Fibrinolytic effect of tissue plasminogen activator on cerebral embolism in stroke-prone spontaneously hypertensive rats.

To study the thrombolytic effect of tissue plasminogen activator (t-PA) on cerebral emboli, we characterized cerebral embolization in stroke-prone spontaneously hypertensive rats (SHRSPs) and Wistar Kyoto rats (WKYs). [125I]Fibrin clot particles (20-100 microns diameter) were injected twice at an interval of 90 min into the left internal carotid artery of WKYs and SHRSPs. After each injection, spontaneous embolus dissolution was monitored with a gamma-ray detector placed on the head of the embolic rats. Embolus dissolution was spontaneously generated in 15 min after the injection of fibrin clots. In WKYs, 21% and 42% of the clots were dissolved 30 and 90 min after the second embolization, respectively. On the other hand, the spontaneous embolus dissolution in SHRSPs was significantly lower than that of WKYs, indicating that the endogenous fibrinolytic ability of SHRSPs is less potent than that of normotensive rats. The intravenous administration of t-PA at doses of 75, 250 and 750 micrograms/kg caused a dose-dependent embolus dissolution in SHRSPs. Furthermore, systematically applied t-PA produced embolus dissolution without causing systemic plasminogen activation, fibrinogen breakdown or bleeding. In conclusion, the intravenous administration of t-PA produces selective embolus dissolution without systemic fibrino(geno)lysis in a cerebral embolic SHRSP.     

Dependence of the Reactivities of Titanium Enolates on How They Are Generated: Diastereoselective Coupling of Phenylacetic Acid Esters Using Titanium Tetrachloride

Oxidative coupling of phenylacetic acid esters was easily achieved by treating the esters with TiCl(4) and then adding Et(3)N to the resulting solution. The products consisted of dl- and meso-2,3-diphenylsuccinic acid esters with the Claisen condensation product, and the ratio of these products depended on the reaction conditions. Reaction conditions suitable for high dl selectivity were determined, and a dimer of titanium enolate was postulated as an intermediate responsible for the high dl selectivity. The selectivities were compared with those in known oxidative couplings in which titanium enolate intermediates are prepared through lithium enolates and silyl enol ethers. The results suggest that the reactivities of titanium enolates intermediates depend on how they are generated.     

Polymerization of acrylamide initiated with pinacol–ceric ion redox system

Polymerization of acrylamide initiated with a pinacol–ceric ion redox system was investigated. The polymer obtained was found to contain one cerium atom in a polymer molecule. It was considered that the cerium atom was introduced into the polymer molecule by the termination reaction as there is no cerium atom in the initiating radical in the present system. A similar termination reaction was attained by ferric ion but not by cerous ion. The metal ion was considered to terminate the polymerization to form a stable polymer. Some considerations on the structure of the reaction product relating to the polymerization mechanism were discussed.