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971.
We show that there is a close relation between standing-wave solutions for the FitzHugh-Nagumo system
where 0<a<1/2 and δ
γ=β
2 ∈ (0,a), and the following combinatorial problem:
(*) Given K points Q
1 , . . . , Q
K
∈R
N
with minimum distance 1, find out the maximum number of times that the minimum distance 1 can occur.
More precisely, we show that for any given positive integer K, there is a δ
K
>0 such that for 0<δ<δ
K
, there exists a standing-wave solution (u
δ
,ν
δ
) to the FitzHugh-Nagumo system with the property that u
δ
has K spikes Q
δ
1,. . .,Q
δ
K and
approaches an optimal configuration in (*), where
. 相似文献
972.
We use a high resolution atomic force microscopy technique to mechanically unzip and rezip single coiled-coil proteins. This allows us to read off the complete stability profile of the protein turn by turn. We investigated three coiled coils with different length as well as a point mutation and find force fluctuations between 9 and 15 pN that can be directly related to the amino-acid sequences. An equilibrium model previously applied to DNA fully describes the mechanical unzipping process including free-energy contributions of the individual turns and seed formation energy. 相似文献
973.
In a metal, a magnetic impurity is fully screened by the conduction electrons at low temperature. In contrast, impurity moments coupled to spin-1 bulk bosons, such as triplet excitations in paramagnets, are only partially screened, even at the bulk quantum critical point. We argue that this difference is not due to the quantum statistics of the host particles but instead related to the structure of the impurity-host coupling, by demonstrating that frustrated magnets with bosonic spinon excitations can display a bosonic version of the Kondo effect. However, the Bose statistics of the bulk implies distinct behavior, such as a weak-coupling impurity quantum phase transition, and perfect screening for a range of impurity spin values. We discuss implications of our results for the compound Cs2CuCl4, as well as possible extensions to multicomponent bosonic gases. 相似文献
974.
975.
976.
Neumann H Strübing D Lalk M Klaus S Hübner S Spannenberg A Lindequist U Beller M 《Organic & biomolecular chemistry》2006,4(7):1365-1375
Corollosporine is an antimicrobial metabolite, which was isolated from the marine fungus Corollospora maritima. Owing to its basic 4-hydroxyphthalic acid anhydride structure, it has become an attractive target for a structure/activity relationship modelling of derived compounds with potential antibiotic activity. In this regard we report on the straightforward synthesis of hetero analogous corollosporines, which were easily prepared by a three-step reaction sequence, taking advantage of a novel multicomponent reaction (AAD-reaction) and a subsequent aromatization/Grignard reaction protocol. Furthermore, the obtained products were tested in several biological assays to evaluate their antimicrobial activity. 相似文献
977.
Hayer A de Halleux V Köhler A El-Garoughy A Meijer EW Barberá J Tant J Levin J Lehmann M Gierschner J Cornil J Geerts YH 《The journal of physical chemistry. B》2006,110(15):7653-7659
A concept for highly ordered solid-state structures with bright fluorescence is proposed: liquid crystals based on tetraethynylpyrene chromophores, where the rigid core is functionalized with flexible, promesogenic alkoxy chains. The synthesis of this novel material is presented. The thermotropic properties are studied by means of differential scanning calorimetry (DSC), cross-polarized optical microscopy (POM), and X-ray diffraction. The mesogen possesses an enantiotropic Col(h) phase over a large temperature range before clearing. The material is highly fluorescent in solution and, most remarkably, in the condensed state, with a broad, strongly red shifted emission. Fluorescence quantum yields (Phi(F)) have been determined to be 70% in dichloromethane solution and 62% in the solid state. Concentration- and temperature-dependent absorption and emission studies as well as quantum-chemical calculations on isolated molecules and dimers are used to clarify the type of intermolecular interactions present as well as their influence on the fluorescence quantum yield and spectral properties of the material. The high luminescence efficiency in the solid state is ascribed to rotated chromophores, leading to an optically allowed lowest optical transition. 相似文献
978.
[reaction: see text] The first total synthesis of an N,C-coupled naphthylisoquinoline alkaloid-ancisheynine-was achieved by condensing a monocyclic diketone or the respective benzopyrylium salt with an aminonaphthalene. The presence of a rotationally hindered axis in ancisheynine was demonstrated by resolution of its two atropo-enantiomers by HPLC on a chiral phase with LC-CD coupling. The assignment of their axial configurations succeeded by quantum chemical CD calculations. 相似文献
979.
Sin KK Chan CP Pang TH Seydack M Renneberg R 《Analytical and bioanalytical chemistry》2006,384(3):638-644
Nanocrystals of the fluorogenic precursor fluorescein diacetate (FDA) were applied as labels in order to improve on the assay
sensitivity achieved in our previous studies. Each FDA nanocrystal can be converted into ∼2.6×106 fluorescein molecules, which is useful for improving immunoassay sensitivity and limits of detection. NeutrAvidin was simply
adsorbed onto the surface of the FDA nanocrystals, which were coated with distearoylglycerophosphoethanolamine (DSPE) modified
with amino(poly(ethylene glycol))(PEG(2000)-Amine) as an interface for coupling biomolecules. This can be applied to detect
different kinds of analytes that are captured by corresponding biotinylated biomolecules in different bioanalytical applications.
The applicability of the NeutrAvidin-labeled nanocrystals was demonstrated in an immunoassay using the labeled avidin–biotin
technique. Biotinylated antibody and FDA-labeled avidin were applied to the assay sequentially. The performance was compared
with the traditional sandwich-type assay for mouse immunoglobulin G detection. Following the immunoreaction, the nanocrystals
were released by hydrolysis and dissolution instigated by adding a large volume of organic solvent/sodium hydroxide mixture.
The limit of detection was lower (by a factor of 2.5–21) and the sensitivity was (3.5–30-fold) higher than immunoassays using
commercial labeling systems (FITC and peroxidase). This study shows that using fluorescent nanocrystals in combination with
the avidin–biotin technique can enhance assay sensitivity and provide a lower limit of detection without requiring long incubation
times as in enzyme-based labels. 相似文献
980.
Abu-Youssef MA Langer V Ohrström L 《Chemical communications (Cambridge, England)》2006,(10):1082-1084
We present a three- and four-connected 3D-net based on 4-aminopyridine coordinated to Ag(I) and hydrogen bonded to nitrate with the unusual, high symmetry, topology (8(3))(8(6))2-tfa. 相似文献