Size dependence of transition temperature in polymer nanowires

We studied the effect of changing temperature on the mechanical properties of nanosized poly(methyl methacrylate) wires fabricated by two-photon fabrication. At around room temperature, the nanowires showed a transition temperature where the shear modulus suddenly changed. This transition temperature was observed to decrease more than 40 K by decreasing the radius of the nanowires from 450 to 150 nm. This size is several times larger in nanowires than reported values of polymer thin film thickness showing a depression of the glass transition temperature.     

Comparative examination of titania nanocrystals synthesized by peroxo titanic acid approach from different precursors

Titanium dioxide nanocrystalline particles were synthesized by peroxo titanium acid (PTA) approach from titanium alkoxide and inorganic salt precursors, and their structural and surface properties, porosities, and photocatalytic activities were comparatively examined by XRD, TG/DTA, DRIFT, UV-vis, low temperature N(2) adsorption, and methyl orange (MO) degradation. It was found that nanoparticles with single anatase phase can be obtained from alkoxide precursor even near room temperature if synthesis conditions are appropriately controlled. PTA-derived anatase nanoparticles from titanium alkoxide precursor have smaller crystalline sizes and better porosities, and contain less amount of peroxo group and no organic impurities as compared to those from TiCl(4) precursor. The advantages in structural property, porosity, and surface properties (few deficiencies) lead to a much better photocatalytic activity for TiO(2) nanoparticles from titanium alkoxide precursor in comparison with those from TiCl(4) precursor.     

Flexible transparent conducting single-wall carbon nanotube film with network bridging method

Hollow ZrO(2) microspheres with mesoporous shells have been synthesized by a novel hydrothermal reaction of zirconium oxychloride in the presence of urea, hydrochloric acid, and ethanol. The morphology and shell thickness of the hollow microspheres can be controlled by varying synthesis conditions. After calcination at high temperature, the morphologies of the hollow microspheres are essentially preserved. Pt catalyst supported on the hollow calcined ZrO(2) microspheres exhibits more excellent catalytic performance in CO oxidation than those on ZrO(2) powders derived from conventional precipitation methods.     

Vertical alignment of single-walled carbon nanotube films formed by electrophoretic deposition

Films of chemically shortened and functionalized single-walled carbon nanotubes (SWNTs) have been formed on a gold electrode by electrophoretic deposition. Applying ultrasonic energy resulted in dramatic changes of the film morphology; the deposited SWNT bundles reassembled and oriented normal to the electrode. Oriented SWNT bundles with high density (more than 250 bundles/microm (2)) not only presented narrow size distributions, but uniformly spread on the electrode. We discuss the mechanism of SWNT orientation by analyzing the variation in the film morphology with ultrasonication time. In addition, we suggest that the 3D displays of AFM images can lead to misjudgment of nanotube alignment. The method for aligning SWNTs normal to the electrode may be competitive with chemical vapor deposition or screen printing, the predominant methods by which vertically aligned SWNT films have been fabricated to date.     

γ‐Cyclodextrin as Inhibitor of the Precipitation Reaction between Berberine and Glycyrrhizin in Decoctions of Natural Medicines: Interaction Studies of Cyclodextrins with Glycyrrhizin and Glycyrrhetic Acid by 1H‐NMR Spectroscopy and Molecular‐Dynamics Calculation

To prevent the precipitation reaction between glycyrrhizin ( 1 ) and berberine ( 3 ) in the decoctions of Glycyrrhiza/Coptis rhizome or Glycyrrhiza/Phellodendron bark, the presence of cyclodextrin (CD) in the mixture was proven to be effective. The preventing effect decreased in the order γ‐CD>β‐CD, and no effect was observed for α‐CD. On the other hand, the extraction degree of 1 from the natural medicine Glycyrrhia was considerably increased in the presence of γ‐CD, γ‐CD being much more effective than α‐ or β‐CD. Thus, the blocking effect of CD on the precipitate formation between 1 and 3 is suggested to be primarily dependent on the stability of the inclusion complex of the CD with 1 . To establish the structure of such a preferred inclusion complex, the interactions of 1 with β‐ and γ‐CDs were investigated by ¹H‐NMR spectroscopy and molecular‐dynamics (MD) calculations. The ¹H‐NMR measurements showed that the increase in solubility of 1 in H₂O is dependent on the degree of its inclusion into the CD, which depends on the molecular size of the CD. The MD calculations suggested that the H‐bond interactions are sufficiently strong to form a stable [ 1 /γ‐CD] complex, in which the lipophilic rings C, D, and E of 1 are fully inserted into the molecular cavity of γ‐CD, thus forming a kind of structure covered by a hydrophilic molecular capsule, while such an interaction mode is impossible for α‐ or β‐CD.     

Virtually complete E-selective alpha,beta-unsaturated ester synthesis by Hg(OTf)2-catalyzed hydration of sec-ethoxyalkynyl acetate

The reaction of alkyl-substituted sec-ethoxyalkynyl acetates with water catalyzed by Hg(OTf)2 afforded alpha,beta-unsaturated esters in excellent yield with high catalytic turnover up to 1000 times under very mild reaction conditions with virtually complete E-selectivity, superior even to that of the HWE reaction.     

Hg(OAc)(2).0.1Sc(OTf)(3)-catalyzed cycloisomerization of 2-(4-pentynyl)furan

[structure: see text]. Although the Hg(OTf)2.3TMU-catalyzed Friedel-Crafts-type reaction of 3-(4-pentynyl)furan afforded the exo cyclization product, the reaction of 2-(4-pentynyl)furan furnished a very low yield. We found a 10:1 mixed reagent of Hg(OAc)2 and Sc(OTf)3 showed remarkable catalytic activity for the latter transformation. The actual reacting species is presumed to be Hg(OAc)(OTf), which is efficiently generated in situ by mixing the two reagents.     

Catalytic activation of the leaving group in the S(N)2 reaction

A novel catalytic activation of the leaving group in the S(N)2 reaction is achieved as an extension of our mercuric triflate-catalyzed reactions. Derivatives of anilinoethyl 4-pentynoate reacted smoothly with catalytic amounts of Hg(OTf)(2) to give indoline derivatives in excellent yield with efficient catalytic turnovers under very mild conditions. The reaction of optically pure secondary alcohol derivatives resulted in inversion of stereochemistry, which is a definitive feature of the S(N)2 reaction. The procedure is applicable for benzoazepine synthesis.     

RBM band shift-evidenced dispersion mechanism of single-wall carbon nanotube bundles with NaDDBS

The dispersion process of single-wall carbon nanotube (SWNT) by using sodium dodecylbenzene sulfonate (NaDDBS) was studied by means of surface tension measurements, ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), and transmission electron spectroscopy (TEM). The critical micelle concentration (CMC) and the concentration where the surface tension begins to drop increase by the presence of SWNT. The isotherm of NaDDBS amount adsorbed on SWNT shows the plateau region at 0.2-6 mM and the saturated region above 40 mM. The external surface of SWNT bundle is fully covered with adsorbed NaDDBS at the plateau region, showing that SWNTs can be dispersed with the bundle form. On the other hand, SWNTs are dispersed in individual tubes at the saturated region, where the adsorption amount corresponds to coating of individual tube surfaces with NaDDBS. This dispersion state was confirmed by SEM and TEM observations. The effect of the dispersion state of SWNTs on radial breathing mode in Raman spectrum gave inherent peak shifts, being the in situ evidences on the step-wise dispersion mechanism of the SWNT bundle to the individual tubes.