Computational Studies on Reaction Mechanism and Origins of Selectivities in Nickel-Catalyzed (2 + 2 + 2) Cycloadditions and Alkenylative Cyclizations of 1,6-Ene–Allenes and Alkenes

The reaction mechanism and origins of ligand-controlled selectivity, regioselectivity, and stereoselectivity of Ni-catalyzed (2 + 2 + 2) cycloadditions and alkenylative cyclizations of 1,6-ene-allenes and alkenes were studied by using density functional theory. The catalytic cycle involves intermolecular oxidative coupling and an intramolecular concerted 1,4-addition step to afford a stable metallacycloheptane intermediate; these steps determine both the regioselectivity and stereoselectivity. Subsequent C–C reductive elimination leads to the cyclohexane product, whereas the β-hydride elimination leads to the <i>trans</i>-diene product. The selectivity between (2 + 2 + 2) cycloadditions and alkenylative cyclizations is controlled by the ligand. Irrespective of the nature of the terminal substituents on the ene–allene and alkene, the P­(<i>o</i>-tol)₃ ligand always favors the C–C reductive elimination, resulting in the cyclohexane product. On the other hand, the flexibility of the PBu₃ ligand means that electronic and steric factors play important roles. Electron-withdrawing groups such as CO₂Me in the ene–allene terminal substituent induce obvious substrate–ligand repulsion and destabilize the C–C reductive elimination, giving rise to the <i>trans</i>-diene product

Additional file 1: of Self-Catalyzed Growth of Vertical GaSb Nanowires on InAs Stems by Metal-Organic Chemical Vapor Deposition

A typical SEM image of the GaSb nanowires grown on InAs stems with relatively high TMGa and TMSb flow rates (S1), a typical SEM image of the InAs stems before the GaSb growth (S2), a typical SEM image of the GaSb nanowires grown on InAs stems at 545 °C (S3), a top-view SEM image of the GaSb nanowires directly grown on Si (111) substrates (S4), and EDS spectra of point analyses from different positions in a GaSb nanowire (S5). (DOCX 510 kb

Cycloaddition of Benzyne to Armchair Single-Walled Carbon Nanotubes: [2 + 2] or [4 + 2]?

The reaction mechanism and regioselectivity of cycloaddition reactions of benzyne to armchair single-walled carbon nanotubes were investigated with quantum chemical methods. The [2 + 2] cycloaddition reaction follows the diradical mechanism, whereas the [4 + 2] cycloaddition reaction adopts the concerted mechanism. More importantly, the [2 + 2] product is always more stable thermodynamically than the [4 + 2] ones, regardless of the diameter, while the [4 + 2] cycloaddition becomes kinetically more favored as the diameter goes up

Scale-up purification for rutin hyrdrolysates by high-performance counter-current chromatography coupled with semi-preparative high-performance liquid chromatography

<p>The study made the isolation of three constituents from rutin and exemplified how to achieve quercetin separation and quantification in rapid and scale-up processes by high-performance counter-current chromatography (HPCCC). Meanwhile, we also isolated the other two constituents, kaempferol and isorhamnetin, by semi-preparative high-performance liquid chromatography. After systematic optimization of solvent systems, sample concentration and flow rate on analytical Mini-DE centrifuge, the same conditions were scale-up by 50-fold in preparative Midi-DE centrifuge to purify quercetin, and the maximum sample loading achieved 1.65 g. Eventually, we successfully isolated quercetin, kaempferol and isorhamnetin with the purity of 99.80%, 99.84% and 99.95%, respectively. The process, therefore, provided an efficient method of obtaining sufficient quantities of highly purified quercetin, as well as kaempferol and isorhamnetin.</p

Nickel-Catalyzed Reductive Alkene Cross-Dialkylation with Unactivated Alkyl Electrophiles

A Ni-catalyzed reductive dialkylation of 8-aminoquinoline-tethered aliphatic alkenes with two unactivated alkyl electrophiles is disclosed here. Key to the development of this transformation is the combination of primary alkyl (pseudo)halides and secondary alkyl iodides that produce products in a single regioselective manner. The reaction exhibits good functional group compatibility, and its synthetic utility was demonstrated by the concise synthesis of the precursors of biologically relevant molecules

Effects of the aptamers on human mast cell degranulation induced by IgE-crosslinking.

<p>LAD2 were sensitized with 500 ng/mL biotinylated human IgE overnight. Cells were washed and resuspended (2×10⁵ cells/200 μL) in HEPES-Tyrode’s buffer and stimulated with 500 ng/mL streptavidin in the presence or absence of the indicated aptamers (final concentration of 2 μg/mL for 30 min. The cells were centrifuged, and the percent release of β-hexosaminidase (β-HEX) into the supernatant was calculated. β-HEX release (%) is expressed as the mean ± SEM for 3 separate experiments with LAD2 cells. * indicates p<0.05 compared with Group 2, and ** indicates <i>P</i> > 0.05 compared with Group 1 (0 nM aptamers) as determined by one-way ANOVA followed by Tukey's post-test. 1. No aptamers; 2. round one products of SELEX; 3. Aptamer Y1; 4. the control oligonucleotide ONT1.</p

Agarose gel (3%) electrophoretic analysis.

<p>Lanes 7–12: PCR products for the insert fragments from the six recombinant plasmids; lane M₂: DNA ladder.</p

Relative binding affinities of the ssDNA pools to the Orai1 peptide as determined by ELONA analysis.

<p>Orai1 peptide was coated onto a 96-well microplate, and biotin-labelled aptamer pools (from rounds 1, 3, 5, 7, 9, 11 and 12) were added into the wells individually. The absorbance was determined at 450 nm. All data shown were calculated as the mean ± SEM, and data were obtained from three independent experiments. The highest relative affinities of the aptamers are indicated by arrows.</p

The binding affinities between the Orai1 peptide and different oligonucleotides.

<p>ELISA plates were coated with the Orai1 peptide. Different biotin-oligonucleotides were added into the wells (1. Aptamer Y1; 2. ONT1; 3. ONT2; 4. ONT3). The absorbance was determined at 450 nm. All data shown were calculated as the mean ± SEM, and data were obtained from three independent experiments. * indicates <i>P</i> < 0.05 compared with the Aptamer Y1 group.</p

Agarose gel (0.8%) electrophoretic analysis.

<p>Lanes 1–6: the recombinant plasmid DNA from six positive clones. Lane M₁: DNA ladder.</p