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101.
102.
Surprisingly large, spontaneous electric dipole moments recently observed in homonuclear niobium clusters below 100 K are explained using first-principles electronic structure calculations. The calculated moments for Nb(n) (n < or =15) generally agree with the experimental data. A strong correlation is found between the geometrical asymmetry of the cluster and electric dipole: its magnitude is proportional to the spread in the principal moments of inertia and its direction aligns with the axis of the largest principal moment. Charge deformation densities reveal directional, partially covalent bonds that stabilize structural asymmetry. Classical simulations of the deflection of a cluster in a molecular beam reveal that the electronic dipole may persist at higher temperatures, but is masked by the rotational dynamics of the cluster. 相似文献
103.
104.
Functionalization of acetylene-terminated monolayers on Si(100) surfaces: a click chemistry approach
Ciampi S Böcking T Kilian KA James M Harper JB Gooding JJ 《Langmuir : the ACS journal of surfaces and colloids》2007,23(18):9320-9329
In this article, we report the functionalization of alkyne-terminated alkyl monolayers on Si(100) using "click" chemistry, specifically, the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction of azides with surface-bound alkynes. Covalently immobilized, structurally well-defined acetylene-terminated organic monolayers were prepared from a commercially available terminal diyne species using a one-step hydrosilylation procedure. Subsequent derivatization of the alkyne-terminated monolayers in aqueous environments with representative azide species via a selective, reliable, robust cycloaddition process afforded disubstituted surface-bound [1,2,3]-triazole species. Neither activation procedures nor protection/deprotection steps were required, as is the case with more established grafting approaches for silicon surfaces. Detailed characterization using X-ray photoelectron spectroscopy and X-ray reflectometry demonstrated that the surface acetylenes had reacted in moderate to high yield to give surfaces exposing alkyl chains, oligoether anti-fouling moieties, and functionalized aromatic structures. These results demonstrate that click immobilization offers a versatile, experimentally simple, chemically unambiguous modular approach to producing modified silicon surfaces with organic functionality for applications as diverse as biosensors and molecular electronics. 相似文献
105.
Kristopher Tapp 《Proceedings of the American Mathematical Society》1999,127(10):3035-3041
The volume growth of an open manifold of nonnegative sectional curvature is proven to be bounded above by the difference between the codimension of the soul and the maximal dimension of an orbit of the action of the normal holonomy group of the soul. Additionally, an example of a simply-connected soul with a non-compact normal holonomy group is constructed.
106.
Preparation of mixed carbonates proceeded in one step from ketones and aldehydes via treatment with NaBH4 in dimethyl or diethyl carbonate solvent at elevated temperatures. This is an efficient and convenient alternative to the traditional two-step sequence of carbonyl reduction to alcohol and subsequent carbonate formation by treatment with an alkyl chloroformate. 25 examples are presented from 49 to 92% yield, highlighting the versatility of this reaction. 相似文献
107.
In this Letter, we describe the first total synthesis of cremastrine, a pyrrolizidine alkaloid from Cremastra appendiculata, with anticholinergic activity as well as an unnatural analogue. The streamlined synthesis proceeds in nine steps, seven steps longest linear sequence, in 25.2% overall yield, and features novel methodology to construct the pyrrolizidine core. Biological evaluation of cremastrine and the unnatural analogue indicated that both are pan-mAChR functional antagonists. 相似文献
108.
109.
Kristopher Lee 《Journal of Mathematical Analysis and Applications》2011,375(1):108-117
Let A and B be uniform algebras on first-countable, compact Hausdorff spaces X and Y, respectively. For f∈A, the peripheral spectrum of f, denoted by σπ(f)={λ∈σ(f):|λ|=‖f‖}, is the set of spectral values of maximum modulus. A map T:A→B is weakly peripherally multiplicative if σπ(T(f)T(g))∩σπ(fg)≠∅ for all f,g∈A. We show that if T is a surjective, weakly peripherally multiplicative map, then T is a weighted composition operator, extending earlier results. Furthermore, if T1,T2:A→B are surjective mappings that satisfy σπ(T1(f)T2(g))∩σπ(fg)≠∅ for all f,g∈A, then T1(f)T2(1)=T1(1)T2(f) for all f∈A, and the map f?T1(f)T2(1) is an isometric algebra isomorphism. 相似文献