Modular synthesis of candidate indole-based insulin mimics by Claisen rearrangement

A modular synthetic route to (indolyl)kojic acid anti-diabetes agents has been developed. Sonogashira coupling of a protected iodoaniline with a propargyl kojate was used to construct an (indole)methyl kojate. Its heteroaromatic Claisen rearrangement, followed by tautomerization to return the indole and pyrone rings, was used to create the biaryl C-C bond. This route should enable collections of insulin mimic drug candidates to be prepared from a few basic building blocks.     

Distribution of Selmer groups of quadratic twists of a family of elliptic curves

We study the distribution of the size of the Selmer groups arising from a 2-isogeny and its dual 2-isogeny for quadratic twists of elliptic curves with full 2-torsion points in Q. We show that one of these Selmer groups is almost always bounded, while the 2-rank of the other follows a Gaussian distribution. This provides us with a small Tate-Shafarevich group and a large Tate-Shafarevich group. When combined with a result obtained by Yu [G. Yu, On the quadratic twists of a family of elliptic curves, Mathematika 52 (1-2) (2005) 139-154 (2006)], this shows that the mean value of the 2-rank of the large Tate-Shafarevich group for square-free positive integers n less than X is , as X→∞.     

Cobalt-catalyzed hydrogen desorption from the LiNH2-LiBH4 system

A doping of 5 wt% CoCl2 considerably decreases the dehydrogenation temperature of a mixture of LiNH2 and LiBH4. More that 8 wt% of hydrogen can be released at ca. 155 degrees C. X-Ray absorption near edge structure (XANES) spectroscopy indicated the formation of metallic Co after ball milling CoCl2 with LiNH2 and LiBH4. Extended X-ray absorption fine structure (EXAFS) spectroscopy measurements revealed that Co particles have poor crystallinity and are finely dispersed in the sample, which could lead to a high catalytic efficiency.     

Addition reactions of fluoroalkanesulfonyl azides to [60] fullerene under thermal or microwave irradiation condition

The reactions of [60] fullerene with excess fluoroalkanesulfonyl azides R_fSO₂N₃ in o-dichlorobenzene under thermal or microwave irradiation condition afforded monoadduct opened [5,6]-bridged azafulleroids. While, similarly treatment of 2,2,2-trifluoroethyl azides CF₃CH₂N₃ with C₆₀ gave two monoadducts, i.e., opened [5,6]-bridged azafulleroids, closed [6,6]-bridged Aziridino-fullerene, and some multi-addition product. A general mechanism for these addition reactions was proposed.     

Cloud point extraction combined with micellar electrokinetic capillary chromatography determination of benzophenones in cosmetic matrix

A method has been developed for the separation and determination of three hydrophobic benzophenones: 2,4-dihydroxybenzophenone (BP-1), 2,2'4,4'-tetrahydroxybenzophenone (BP-2), and 2-hydroxy-4-methoxybenzophenone (BP-3) in sunscreen by micellar electrokinetic capillary chromatography (MEKC) combined with cloud point extraction (CPE). The analytes were extracted at pH 5.0 by micelles of the nonionic surfactant polyoxyethylene-7.5-octylphenyl ether (Triton X-114). A 150 microL aliquot from the extracted surfactant-rich phase was diluted up to 500 microL with ethanol to reduce its viscosity before separation by MEKC. A background electrolyte of 25 mmol/L sodium tetraborate containing 30 mmol/L sodium dodecyl sulfate at pH 9.25 was used as the separation medium to avoid the adsorption of hydrophobic substances and Triton X-114 onto the inner surface of the separation capillary, ensuring the separation efficiency and reproducibility. Detection is performed at 290 nm. Under the optimized conditions, an enrichment factor of 20 was obtained and the determination limits of BP-1, BP-2, and BP-3 were found to be 3.90 x 10(-) (7), 3.83 x 10(-7), and 6.42 x 10(-8) mol/L, respectively. In comparison with the earlier reported methods, the LODs of this method are superior to the other methods. The presented procedure was successfully applied to the determination of BP-1, BP-2, and BP-3 in sunscreen with satisfactory results.     

Novel tetrazole-functionalized ion exchanger for weak cation-exchange chromatography of proteins

A new type of weak cation exchanger, tetrazole-functionalized silica, was developed for bioseparation. It was prepared conveniently by modifying silica gel initially with gamma-glycidoxypropyltrimethoxysilane, then with 3-hydroxypropionitrile and finally with ammonium-catalyzed (3+2) azide-nitrile cycloaddition, which is an element of click chemistry. The prepared stationary phase was characterized and evaluated for its separation performance, protein retention behavior, loading capacity, protein recovery and chemical stability. The results show that the stationary phase developed has excellent performance for protein separations with high mass recoveries, and has long-term stability. Some remarkable differences were observed between this new exchanger and a carboxylic methyl-functionalized ion exchanger, which is typically used in weak cation-exchange chromatography of proteins. The obtained column was also used for the purification of lysozyme from chicken egg white, and the purity and specific bioactivity of the obtained lysozyme were about 90% and 67 IU/mg, respectively.     

3D framework containing Cu4Br4 cubane as connecting node with strong ferroelectricity

The methanolothermal reaction of (S)-1,4-diallyl-2-methylpiperazine (DAMP) with an excess CuBr affords a novel homochiral 3D framework (DAMP)3(Cu4Br4)2(H2O)3 (1) in which Cu4Br4 cubane acts as a connecting node to mimic the pure inorganic role in the ferroelectricity to enhance the remnant polarization value which is comparable to that of BaTiO3 synthesized by peptide-assisted synthesis.     

Stable aqueous ZnO@polymer core-shell nanoparticles with tunable photoluminescence and their application in cell imaging

Stable aqueous solutions of ZnO@polymer core-shell nanoparticles with tunable photoluminescence are prepared through a simple sol-gel route. The copolymer shell has many hydrophilic external groups and a hydrophobic internal layer which connects ZnO cores through covalent bonds. The optimal samples show quantum yield above 50% and stable emission for months. These samples with their concentrations of below 0.2 mg/mL are nontoxic to human cells. After uptake of these ZnO@polymer nanoparticles, the luminescent cells have enough life under UV light for microscopic imaging.     

Reaction kinetics in anionic copolymerization: A revisit on Mayo-Lewis equation

Reactivity ratio is a traditional parameter quantifying the reaction kinetics in copolymerization, which is important for potentially controlling microstructures of polymers and guiding the copolymerization process. Our recent experiments using tube-NMR technique enable us to in situ monitor the concentration profiles of the co-monomers during the anionic copolymerization process. This motivates us to revisit the Mayo-Lewis(ML) equation, which is the basis for derivation of reactivity ratio and has been extensively utilized in addition copolymerization. We found that although an explicit ML expression is desirable for ease of calculation and correlation with experimental data, it fails in our anionic copolymerization experiment as well as some data available in the literature. The origin is ascribed to the validity of the steady state assumption which is essential in the ML equation. This assumption can be released in anionic copolymerization and replaced by the fact that the overall concentration of the living chain ends keeps constant throughout the copolymerization. Alternative numerical method has been utilized to obtain the rate constants and consequently the reactivity ratios. Our work suggests that the ML equation should be applied with caution.