Synthesis of chiral mesoporous silica and its potential application to asymmetric separation

Chiral mesoporous silica (CMS) has been successfully synthesized in the presence of basic amino acids; the use of basic amino acids in combination with the chiral anionic surfactant is advantageous for the formation of CMS in terms of uniformity in the twisted morphology. We first demonstrate that thus obtained chiral mesoporous silicas can be used for the enantioselective separation of racemic compounds; the helical rod-shaped CMS is found to be capable of asymmetric separation of racemic N-trifluoroacetylalanine ethyl ester (CF₃CO-Ala-OEt). The left handedness-rich CMS shows asymmetric preferential adsorption of the L isomer and vice versa.     

Iron-catalyzed synthesis of glycine derivatives via carbon-nitrogen bond cleavage using diazoacetate

Treatment of tertiary amines with diazoacetate in the presence of a catalytic amount of an iron salt, FeCl(3), in ethanol gave glycine derivatives. In this reaction, a carbon-nitrogen single bond of the amine was cleaved.     

Synthesis of functionalized pentacenes from isobenzofurans derived from C-H bond activation

The synthesis of unsymmetric functionalized pentacenes from 1,4-anthraquinones and functionalized isobenzofurans, which were prepared by transformation via C-H bond activation, was successfully accomplished. Examples of the synthesis of pentacenes with functional groups at the 5-position are still rare. These obtained functionalized pentacenes are highly soluble in hexane, toluene, and THF.     

Double-pulse LIBS of gadolinium oxide ablated by femto- and nano-second laser pulses

Emission characteristics of gadolinium (Gd) oxide are studied, using ns and fs laser pulses for ablation in double-pulse laser induced breakdown spectroscopy (LIBS). In the current conditions of pulse energy and signal detection timing, emission intensity enhancement in the reheating mode is 25-fold, but little effect can be observed in a pre-pulse mode. It is shown that the optimum focus position of the ablation pulse is about 5 mm apart from the sample surface in the reheating mode. Although little emission can be observed in the single-pulse configuration with fs ablation pulses, the intense emission can be observed in the reheating mode in the double-pulse configuration.     

Atomic and nanostructures of monolayer c(2 × 2)NiN on Cu(0 0 1)

Structures of monolayer nickel nitride (NiN) on Cu(0 0 1) surface are studied by X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Formations of Ni–N chemical bonds and NiN monolayer at the surface are confirmed by XPS on the N-adsorbed Cu(0 0 1) surfaces after Ni deposition and subsequent annealing to 670 K. A c(2 × 2) structure is always observed in the LEED patterns, which is a quite contrast to the (2 × 2)p4g structure observed usually at the N-adsorbed Ni(0 0 1) surface. Atomic images by STM indicate the mixture of Ni–N and Cu–N structures at the surface. Density of the trenches on the N-saturated surface decreases and the grid pattern on partially N-covered surfaces becomes disordered with increasing the Ni coverage. These results are attributed to the decrease of the surface compressive stress at the N-adsorbed Cu surface by mixing Ni atoms.     

Insertion of polar and nonpolar unsaturated molecules into carbon-rhenium bonds generated by C-H bond activation: synthesis of phthalimidine and indene derivatives

A rhenium complex, [ReBr(CO)(3)(thf)](2), catalyzes the reaction of an aromatic aldimine with an isocyanate and an acetylene to give a phthalimidine and an indene derivative in a quantitative yield, respectively. The reactions proceed via C-H bond activation, insertion of the isocyanate or the acetylene, intramolecular nucleophilic cyclization to the aldimine of the generated amido- or alkenyl-rhenium species, and reductive elimination. In contrast to ruthenium and rhodium catalysts, which are usually employed in this type of reaction, the rhenium catalyst promotes the insertion of a polar unsaturated molecule. This occurs more easily than the insertion of a nonpolar unsaturated molecule.     

Rhenium-catalyzed insertion of aldehyde into a C-H bond: synthesis of isobenzofuran derivatives

A rhenium complex, [ReBr(CO)3(thf)]2, catalyzed reactions of aromatic ketimines with aldehydes to give isobenzofuran derivatives in good to excellent yields. In contrast to ruthenium and rhodium catalysts, aldehydes, which are polar unsaturated molecules, inserted into the C-H bond after activation by the rhenium complex.     

SEPARATION OF THE MINOR FLAVONOLS FROM FLOS GOSSYPII BY HIGH-SPEED COUNTERCURRENT CHROMATOGRAPHY

An effective high-speed countercurrent chromatography (HSCCC) method was established for further separation and purification of four minor flavonols in addition to five major flavonols which were reported by our previous study from extracts of Flos Gossypii. HSCCC was performed with three two-phase solvent systems composed of n-hexane-ethyl acetate-methanol-water (7.5:15:6:7, v/v), (2.5:15:2:7, v/v) and (0:1:0:1, v/v). The separation was repeated 3 times, and 3.8 mg of 8-methoxyl-kaempferol-7-O-β-D-rhamnoside (HPLC purity 98.27%), 6.7 mg of astragalin (HPLC purity 94.18%), 3.3 mg of 4'-methoxyl-quercetin-7-O-β-D-glucoside (HPLC purity 94.30%) and 8.2 mg of hyperoside (HPLC purity 93.48%) were separated from 150 mg of the crude sample. The chemical structures of the flavonols were confirmed by MS, (1)H NMR and (13)C NMR. Meanwhile, the results indicated that the target compound with smaller K value (<0.5) can be separated by increasing column length of HSCCC. And four separation rules of flavonols according to the present study and references were summarized, which can be used as a useful guide for separation of flavonols by HSCCC.