A family of stable silica fullerenes with fully coordinated structures

Theoretical electronic structure techniques have become an indispensable and powerful tool for predicting molecular properties and designing new materials. The discovery of C(60) opened a challenging field in nanoscale materials science, and since then people have been looking for its inorganic analogues. On the basis of the B3LYP/6-31G(d) calculations, here we provide theoretical evidence for a family of stable silica fullerenes with fully coordinated structures, which exhibit highly structural and energetic stabilities, very large energy gaps, and extremely good resistibilities to breakdown of the insulating capability in an applied electric field. Our calculations indicate that the discrete silica fullerenes are a possible polymorph of silica and can be synthesized under some conditions. They are expected to find novel applications in silica-based molecular devices. The present results may provide an aid in the experimental design for controllably producing desired silica clusters.     

Low-temperature strategy to synthesize highly ordered mesoporous silicas with very large pores

By employing a novel low-temperature synthetic pathway, highly ordered cubic mesoporous materials with hitherto the largest pores (up to 27 nm) and unit cells (up to 44 nm) have been successfully obtained.     

Capillary electrophoretic separation of sugars in fruit juices using on-line mid infrared Fourier transform detection

Fourier Transform infrared spectroscopy has been coupled to on-line capillary electrophoresis (CE) for the separation and detection of natural sugars in orange fruit juices. The CE separation electrolyte comprised 50 mM sodium carbonate buffer adjusted to pH 12.3 with NaOH. Galactose was selected as an internal standard. To ensure tight connections between the custom-made IR-transparent flow cell (optical path length was 15 [micro sign]m) and the fused silica capillaries, commercially available O-rings were used. The scanner of the spectrometer was operated at a HeNe laser modulation frequency of 320 kHz, recording interferograms in a double-sided, forward-backward mode with 8 cm(-1) spectral resolution. For each spectrum 64 interferograms (512 for the background) were co-added and a Blackman-Harris 3-term apodization function was performed. A low-pass filter at 1828 cm(-1) was inserted in the IR beam to increase the light throughput in the spectral region of interest (1800 cm(-1)-900 cm(-1)). Using these features a new spectrum could be obtained every two seconds. Sucrose, glucose and fructose were structurally identified and quantified in orange juice samples. The limits of detection (3S/N) for all analytes were in the low millimolar range (0.7-1.9 mM) or, in absolute amounts, the low nanogram range (1.5-3.2 ng). The resolution ranged between 1.14 to 3.15 and the RSD of the proposed method was 1.8-4.4%.     

Catalysis of enantioselective [2+1]-cycloaddition reactions of ethyl diazoacetate and terminal acetylenes using mixed-ligand complexes of the series Rh2(RCO2)n(L*4-n). Stereochemical heuristics for ligand exchange and catalyst synthesis

This paper describes the synthesis of mixed Rh(2)(II) complexes containing bridging acetate and R,R-diphenyl-N-triflylimidazolidinone (DPTI) ligands (1, 2, and 9-19), and their function as enantioselective catalysts for the conversion of ethyl diazoacetate and terminal acetylenes to chiral cyclopropenes. Of these catalysts, 1 and 10 functioned with the highest enantioselectivity, in accord with a mechanistic model in which one of the ligand bridges is broken in the intermediate Rh-carbene complex. The synthetic results allow conclusions with regard to kinetically and thermodynamically favored pathways for the synthesis of mixed acetate-DPTI complexes. A new C(2)-symmetric complex having only two anti-DTBTI bridges (23) is shown to be a highly effective chiral catalyst, as expected from the model.     

低分子量氯磺化聚乙烯对纳米Si3N4粉体表面处理

用降解氯磺化聚乙烯橡胶(CSM)的方法制备了低分子量氯磺化聚乙烯(LMCSM),将其作大分子表面改性剂对纳米氮化硅(Si3N4)粉体进行表面修饰,对改性前后的纳米Si3N4粉体采用沉降实验、FT-IR、TEM、TGA等方法进行了表征. 结果表明,LMCSM对纳米Si3N4粉体的改性主要为化学改性,其化学利用率为54%,物理利用率为29%;改性后的纳米Si3N4粉体的表面自由能从142.6 J/M2降至66.89 J/M2,在三氯甲烷中分散良好.     

Asymmetric synthesis of 1,3-oxathiolan-5-one derivatives through dynamic covalent kinetic resolution

The asymmetric synthesis of 1,3-oxathiolan-5-one derivatives through an enzyme-catalyzed, dynamic covalent kinetic resolution strategy is presented. Dynamic hemithioacetal formation combined with intramolecular, lipase-catalyzed lactonization resulted in good conversions with moderate to good enantiomeric excess (ee) for the final products. The process was evaluated for different lipase preparations, solvents, bases, and reaction temperatures, where lipase B from Candida antarctica (CAL-B) proved most efficient. The substrate scope was furthermore explored for a range of aldehyde structures, together with the potential access to nucleoside analog inhibitor core structures.     

One-pot synthesis of trifluoromethylated phthalans via intramolecular cyclization from 2-alkynylbenzaldehydes

An efficient tandem addition/cyclization procedure for the synthesis of trifluoromethylated phthalans under mild conditions was developed. This procedure involves tetrabutylammonium fluoride (TBAF)-promoted addition of Ruppert–Prakash reagent (TMSCF₃) to 2-alkynylbenzaldehyde to give 2-alkynylbenzylicalcohols, which would then undergo base-catalyzed selective 5-exo-dig cyclization to furnish the corresponding products.     

Catalytic asymmetric synthesis of 3,3-disubstituted oxindoles: diazooxindole joins the field

The catalytic asymmetric synthesis of 3,3-disubstituted oxindoles, a big family of privileged scaffolds in natural products and drugs, is of current interest. Recently, the catalytic asymmetric functionalization of diazooxindoles emerges as a potentially general and flexible strategy for this purpose, with several notable examples coming out in 2013. In this digest, synthetic applications of diazooxindoles have been summarized and discussed, which might be helpful for readers to understand the special properties of this type of donor/acceptor cyclic diazo reagent and to develop new catalytic asymmetric reactions.