Dehydrative amide couplings with 2-pyridylamines suffer from variable yields. A mild and high-yielding synthesis of N-(pyridin-2-yl)amides employing 2-aminopyridine-N-oxides is presented as a solution. 相似文献
Experiments which have been undertaken over a number of years have shown that a rotating magnetic field can drive a significant
non-linear Hall current in a plasma. Successful experiments of this concept have been made with a device called rotamak. In
its original configuration this device was a field reversed configuration without a toroidal magnetic field but with a vertical
field to establish the MHD equilibrium. However, modifications have shown that current can also be driven if a central current-carrying
rod is used to provide an applied toroidal field. The new rotamak has then a spherical tokamak magnetic field structure.
Article presented at the International Conference on the Frontiers of Plasma Physics and Technology, 9–14 December 2002, Bangalore,
India. 相似文献
The interaction of metallosupramolecular cylinders with DNA three-way junctions has been studied by gel electrophoresis. A recent X-ray crystal structure of a palindromic oligonucleotide forming part of a complex with such a cylinder revealed binding at the heart of a three-way junction structure. The studies reported herein confirm that this is not solely an artefact of crystallisation and reveal that this is a potentially very powerful new mode of DNA recognition with wide scope. The cylinders are much more effective at stabilizing three-way junctions than simple magnesium di-cations or organic or metallo-organic tetra-cations, with the M cylinder enantiomer being more effective than P. The recognition is not restricted to three-way junctions formed from palindromic DNA with a central AT step at the junction; non-palindromic three-way junctions and those with GC steps are also stabilised. The cylinder is also revealed to stabilise other Y-shaped junctions, such as that formed at a fraying point in duplex DNA (for example, a replication fork), and other DNA three-way junction structures, such as those containing unpaired nucleotides, perhaps by opening up this structure to access the central cavity. 相似文献
Curcumin possesses wide‐ranging anti‐inflammatory and anti‐cancer properties and its biological activity can be linked to its potent antioxidant capacity. Superparamagnetic maghemite (γ‐Fe2O3), called surface‐active maghemite nanoparticles (SAMNs) were surface‐modified with curcumin molecules, due to the presence of under‐coordinated FeIII atoms on the nanoparticle surface. The so‐obtained curcumin‐modified SAMNs (SAMN@curcumin) had a mean size of 13±4 nm. SAMN@curcumin was characterized by transmission and scanning electron microscopy, UV/Vis, FTIR, and Mössbauer spectroscopy, X‐ray powder diffraction, bulk susceptibility (SQUID), and relaxometry measurements (MRI imaging). The high negative contrast proclivity of SAMN@curcumin to act as potential contrast agent in MRI screenings was also tested. Moreover, the redox properties of bound curcumin were probed by electrochemistry. SAMN@curcumin was studied in the presence of different electroactive molecules, namely hydroquinone, NADH and ferrocyanide, to assess its redox behavior. Finally, SAMN@curcumin was electrochemically probed in the presence of hydrogen peroxide, demonstrating the stability and reactivity of bound curcumin. 相似文献
A self-consistent study of the slow resistive evolution of an axisymmetric toroidal plasma gives rise to a set of transport equations involving one space variable which require input from the solution of a generalized differential equation obtained from the time-differentiated Grad-Shafranov equation. An iterative scheme is presented for the numerical solution of this generalized differential equation which overcomes the problems of the non-standard boundary conditions. As an illustration this method is used to compute the instantaneous diffusion velocity of a class of model toroidal equilibria. A more detailed study is presented of the time evolution of this model in the cylindrical limit in order to illustrate techniques which can be used in a more complete toroidal simulation. 相似文献
The syntheses and mass spectra of 5,6-tetramethylenetetrahydro-1,3-oxazine-2-thione and its 4-mono- and 4,4-disubstituted analogs are reported. The primary decay processes under electron impact are loss of the 1,3-oxazine ring, formation of hydrocarbon ions, and rearrangement of the [M–C6H9]+ ion.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1668–1672, December, 1989. 相似文献
Thermal decomposition of an amorphous precursor for S-doped titania (TiO2) nanopowders, prepared by controlled sol–gel hydrolysis–condensation of titanium(IV) tetraethoxide and thiourea in aqueous ethanol, has been studied up to 800 °C in flowing air. Simultaneous thermogravimetric and differential thermal analysis coupled online with quadrupole mass spectrometer (TG/DTA-MS) and FTIR spectrometric gas cell (TG-FTIR) have been applied for analysis of released gases (EGA) and their evolution dynamics in order to explore and simulate thermal annealing processes of fabrication techniques of the aimed S:TiO2 photocatalysts with photocatalytic activities under visible light. The precursor sample prepared with thiourea, released first water endothermically from room temperature to 190 °C, carbonyl sulfide (COS) from 120 to 240 °C in two stages, ammonia (NH3) from 170 to 350 °C in three steps, and organic mater (probably ether and ethylene) between 140 and 230 °C. The evolution of CO2, H2O and SO2, as oxidation products, occurs between 180 and 240 °C, accompanied by exothermic DTA peaks at 190 and 235 °C. Some small mass gain occurs before the following exothermic heat effect at 500 °C, which is probably due to the simultaneous burning out of residual carbonaceous and sulphureous species, and transformation of amorphous titania into anatase. The oxidative process is accompanied by evolution of CO2 and SO2. Anatase, which formed also in the exothermic peak at 500 °C, mainly keeps its structure, since only 10% of rutile formation is detected below or at 800 °C by XRD. Meanwhile, from 500 °C, a final burning off organics is also indicated by continuous CO2 evolution and small exothermic effects. 相似文献
Monodentate DNA binding of [PtCl(dien)]+ (dien=diethylenetriamine) complexes may considerably affect the biophysical properties of DNA and consequently downstream cellular processes as a result of a large increase in the bulkiness of the nonleaving ligand by multiple methylation (see illustration).