A practical, general and efficient protocol for the catalytic epoxidation of alkenes has been developed. The in situ generation of reactive dioxiranes capable of epoxidizing a variety of alkenes under biphasic conditions has been accomplished using phase transfer catalysts bearing a carbonyl group. Optimal epoxidation conditions employ 10 mol % of 1-dodecyl-1-methyl-4-oxopiperidinium triflate (8d(+)OTf(-)) in a CH2Cl2/pH 7.5-8.0 biphase using potassium monoperoxosulfate (Oxone) as the oxidant. Optimization of the conditions identified (1) slow addition rate, (2) pH 7.5-8.0, (3) N-dodecyl chain, and (4) the triflate salt as key experimental and structural variables. A selection of nine olefins was successfully oxidized to the corresponding epoxides in 83-96% yield.
Chirality-Controlled Syntheses of Double-Helical Au Nanowires
作者:Makoto Nakagawa、Takeshi Kawai
DOI:10.1021/jacs.8b00910
日期:2018.4.18
syntheses of double-helical Au nanowires (NWs) using chiral soft-templates composed of two organogelators with their own active functions; one organogelator serves to introduce helicity into the template and the other acts as a capping agent to control the Au shape. One-dimensional twisted-nanoribbon templates are prepared simply by mixing the two organogelators in water containing a small amount of toluene
使用湿化学方法选择性大规模合成具有复杂形状的贵金属纳米晶体仍然是令人兴奋的挑战。在这里,我们报告了使用手性软模板合成双螺旋金纳米线 (NW) 的手性可控合成,该模板由两种具有各自活性功能的有机凝胶剂组成;一种有机凝胶剂用于将螺旋性引入模板,另一种用作封端剂以控制 Au 形状。将两种有机凝胶剂在含有少量甲苯的水中混合,然后加入 LiCl,即可简单地制备一维扭曲纳米带模板;通过选择螺旋性诱导有机凝胶剂的旋向性来控制模板手性。在这些手性模板上合成的双螺旋 Au NW 具有与模板相同的螺旋结构,因为 Au NW 沿着具有右手或左手螺旋的扭曲纳米带的两个边缘生长。右手和左手双螺旋金纳米线的色散表现出相反的 CD 信号。
A pH-Controlled Reversible Phase Transfer and Electrolytic Size-Fractionation of Stable Silver Nanoparticles Capped with a Long Amino Amide Dicarboxylic Acid
作者:Frederic Delbecq、Itsuki Yamano、Takeshi Kawai
DOI:10.1246/bcsj.20150260
日期:2015.12.15
The synthesis of a long alkylaminoamide dicarboxylic acid amphoteric species has been achieved. Employed as capping agent, the reduction of ionic silver in water led to the formation of small (10–100 nm) and hydrophobic diacid bilayer coated silver nanoparticles (AgNPs). In a biphasic system (e.g. H2O–CHCl3), a pH-controlled and reversible phase transfer phenomenon was observed. At different stages, the formation of these nanoparticles was studied by UV–vis spectroscopy, their stability was controlled by zeta-potential measurement and both shape and morphology were observed by transmission electron microscopy (TEM). The ionic strength of the AgNPs was tested by the addition of inorganic salt electrolyte (NaCl, CaCl2). A NaCl concentration dependant size fractionation of the AgNPs between the same above biphasic system was also studied by means of analytical techniques such as dynamic light scattering (DLS), TEM, and UV–vis spectroscopy.
analysis of native supramoleculargels reveal that they can self-assemble into lamellar-like aggregates or in pseudo-cubic structures, depending on the alkyl chain length and the steric hindrance of the polar head. The number of amide bonds and their positions inside gelator structures are determinant for the nature of the packing. For each gelator, we perform a series of gelation tests in each of the
Reversible dispersion–precipitation of single-walled carbon nanotubes by pH change and addition of organic components
作者:Yoshiro Imura、Clara Morita、Takeshi Kawai
DOI:10.1039/c3nj00749a
日期:——
Single-walled carbon nanotubes (SWCNTs) were dispersed in an aqueous solution of a long-chain amidoamine surfactant (C18AA) at a high concentration (>0.5 wt%). The SWCNT dispersion was very stable in the pH range from 7.0 to 11.5. Addition of chloroform into the aqueous dispersion at pH 11.5 brought about the precipitation of SWCNTs in water, although there was no effect on the dispersibility of SWCNTs at pH 7. We demonstrated that reversible dispersionâprecipitation regulation of SWCNTs in water can be achieved by changing pH and adding the C18AA surfactant in a biphasic system of C18AAâwaterâchloroform.
A long-chain amidoamine derivative (C18AA) acts as a normal organogelator in toluene, but changes to a heat-induced gelator, exhibiting a phase transition from sol to gel on heating upon addition of aqueous LiCl to the toluene gel. The thermal response of the heat-induced gel of C18AA was highly sensitive.