Experimental and theoretical study on the olefin metathesis of alkenyl Baylis-Hillman adducts using second-generation Grubbs catalyst

[reaction: see text] We have investigated the olefin metathesis from alkenyl Baylis-Hillman adducts using second-generation Grubbs catalyst. In the experiment, the ring-closing metathesis (RCM) product could not be found, while the cross-metathesis (CM) products were found. The computational studies provided consistent explanations for the experimental result. The most limiting factor for the RCM process using second-generation Grubbs catalyst is caused by the high strain and steric effect in the metallacyclobutane intermediates.     

Separation of carbon nanotubes by frit inlet asymmetrical flow field-flow fractionation

Flow field-flow fractionation (flow FFF), a separation technique for particles and macromolecules, has been used to separate carbon nanotubes (CNT). The carbon nanotube ropes that were purified from a raw carbon nanotube mixture by acidic reflux followed by cross-flow filtration using a hollow fiber module were cut into shorter lengths by sonication under a concentrated acid mixture. The cut carbon nanotubes were separated by using a modified flow FFF channel system, frit inlet asymmetrical flow FFF (FI AFIFFF) channel, which was useful in the continuous flow operation during injection and separation. Carbon nanotubes, before and after the cutting process, were clearly distinguished by their retention profiles. The narrow volume fractions of CNT collected during flow FFF runs were confirmed by field emission scanning electron microscopy and Raman spectroscopy. Experimentally, it was found that retention of carbon nanotubes in flow FFF was dependent on the use of surfactant for CNT dispersion and for the carrier solution in flow FFF. In this work, the use of flow FFF for the size differentiation of carbon nanotubes in the process of preparation or purification was demonstrated.     

Direct determination of estriol 3- and 16-glucuronides in pregnancy urine by column-switching liquid chromatography with electrospray tandem mass spectrometry

Using column-switching liquid chromatography/tandem mass spectrometry (LC-MS/MS), we developed an improved analytical method of urinary estriol glucuronides. This new method is derived predominantly from maternal and fetal precursors in pregnancy. We used in the following procedure: first, we filtered urine samples with a membrane filter. Next, we directly injected the 50 microL aliquot of urine samples onto a pre-column. Then, after activating the column-switching valve, we backflushed the loaded samples onto the C(18) analytical column. Urine samples can be assayed within 20 min without any sample preparation steps. We monitored separated estriol glucuronides by negative electrospray ionization (ESI) and selected-reaction monitoring (SRM). The calibration range of estriol-3-glucuronide (E3-3G) and estriol-16-glucuronide (E3-16G) was 0.1-20 microg/mL and the linearity of the method was 0.9984 for E3-3G and 0.9987 for E3-16G. The limits of detection at a signal-to-noise (S/N) ratio of 3 were 10 ng/mL (E3-3G) and 5 ng/mL (E3-16G). The analytical recovery was over 85% and, in general, inter-day and intra-day variability for precision and accuracy were less than 10%. When applied to a pregnancy urine sample to biomedical monitoring of the function of the maternal/fetal unit, the proposed method allowed rapid and sensitive screening for the detection of E3-3G and E3-16G.     

Azinoiminophosphorane mediated synthesis of 5H, 7H‐1,2,4‐triazolo[1,5‐c][1,3]benzoxazepin‐7‐ones and 6H,8H‐1,2,4‐triazolo‐[1,5‐c][1,3]oxazepin‐6‐ones

The aza‐Wittig reactions of benzophenone‐, acetophenone‐ and benzaldehyde l‐[(triphenylphosphoranyl‐idene)amino]ethylidenehydrazones (4) with phthalic anhydride, 2,3‐dimethylmaleic anhydride and 7‐oxabi‐cyclo[2,2,l]hept‐5‐ene‐2,3‐dicarboxylic anhydride ( 5a ) provide a new route to 5H,7H‐1,2,4‐triazolo[1,5‐c]‐[1,3]benzoxazepin‐7‐ones 8a‐c or 6H,8H‐1,2,4‐triazolo[1,5‐c][1,3]oxazepin‐6‐ones 8d‐h via the thermal reaction of the expected azinoimine lactones 6 .     

Photochemistry of 2-Allyl-3-oxo-2,3-dihydro-1H-pyrrole-2-carboxyalates

On acetone-sensitized irradiation the title compounds 3a–c are converted to 2-allyl-3-hydroxy-1H-pyrrole-2-carboxylates 4 in reasonable yields.     

Highly stereoselective synthesis of 2,5-disubstituted 3-vinylidene tetetrahydrofurans via Prins-type cyclization

[reaction: see text]. A novel synthetic methodology for 2,5-disubstituted tetrahydrofurans having an allenyl group at the 3-position via Prins-type cyclization was developed. The reaction led to excellent selectivity and moderate to high yields.     

Quantitative analysis of bilobalide and ginkgolides from Ginkgo biloba leaves and Ginkgo products using (1)H-NMR

1H-NMR spectrometry was applied to the quantitative analysis of the bilobalide, ginkgolides A, B, and C in Ginkgo biloba leaves and six kinds of commercial Ginkgo products without any chromatographic purification. The experiment was performed by the analysis of each singlet H-12, which were well separated in the range of delta 6.0-7.0 in the (1)H-NMR spectrum. However, the H-12 protons of bilobalide and ginkgolides may have overlapped with H-6 or H-8 protons of the Ginkgo flavonoids. Therefore, the optimum (1)H-NMR solvent for the analysis of the compound was selected through the evaluation of solvent effects on the resolution of these signals from the compounds. Acetone-d(6)-benzene-d(6) (50 : 50) was found to be the best one among the solvents evaluated. The quantity of the compounds was calculated by the relative ratio of the intensity of each compound to the known amount of internal standard (25 microgram), phloroglucinol. This method allows rapid and simple quantitation of underivatized bilobalide and ginkgolides in 5 min without any pre-purification steps.     

A new approach to the design of surface treatments for reinforcing agents

A new approach for design of improved interfacial bonding between carbon fibers and polymeric matrices is described. In this method the affinity of surface-treated carbon fibers to various polymer matrices is simulated by analyzing the adsorption characteristics of model compounds, typical of the polymer units, onto very high surface area carbon fibers. The affinity can be evaluated by the use of Thermogravimetric Analysis (TGA) to measure adsorption–desorption characteristics. Since high surface area, activated carbon fibers (ACF) can be chemically treated to obtain acidic, basic, nonpolar or highly polar surfaces, it should be possible to assess the interactions of chemically modified surfaces with model compounds such as methanol (MeOH), acetone, dimethylformamide (DMF), dimethylether, tetrahydrofuran (THF) and water. Some preliminary results are presented, indicating that surface treatments for carbon fibers other than oxidation may lead to enhanced bonding with polymeric matrices.