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91.
92.
Advances on the Determination of the Astatine Pourbaix Diagram: Predomination of AtO(OH)2− over At− in Basic Conditions 下载免费PDF全文
Dumitru‐Claudiu Sergentu Dr. David Teze Dr. Andréa Sabatié‐Gogova Dr. Cyrille Alliot Ning Guo Dr. Fadel Bassal Dr. Isidro Da Silva Prof. Dr. David Deniaud Dr. Rémi Maurice Dr. Julie Champion Dr. Nicolas Galland Dr. Gilles Montavon 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(9):2964-2971
It is generally assumed that astatide (At?) is the predominant astatine species in basic aqueous media. This assumption is questioned in non‐complexing and non‐reductive aqueous solutions by means of high‐pressure anion‐exchange chromatography. Contrary to what is usually believed, astatide is found to be a minor species at pH=11. A different species, which also bears a single negative charge, becomes predominant when the pH is increased beyond 7. Using competition experiments, an equilibrium constant value of 10?6.9 has been determined for the formation of this species from AtO(OH) with the exchange of one proton. The identification of this species, AtO(OH)2?, is achieved through relativistic quantum mechanical calculations, which rule out the significant formation of the AtO2? species, while leading to a hydrolysis constant of AtO(OH) in excellent agreement with experiment when the AtO(OH)2? species is considered. Beyond the completion of the Pourbaix diagram of astatine, this new information is of interest for the development of 211At radiolabeling protocols. 相似文献
93.
94.
Yella-Reddy Nelli Céline Douat-Casassus Paul Claudon Brice Kauffmann Claude Didierjean Gilles Guichard 《Tetrahedron》2012,68(23):4492-4500
A new N-Boc-protected monomer for the synthesis of oligourea foldamers containing the (1H-imidazolyl-4yl)methyl side chain of histidine, has been prepared in seven steps from Trt-His(τ-Trt)-OMe. This protecting group combination on histidine was found to be critical to ensure efficient access to the requisite activated building block. This new derivative, suitable for solid phase synthesis, expands the current arsenal of building blocks with proteinogenic side chains useful for the design of peptidomimetic oligourea foldamers. 相似文献
95.
Irene Bravo-Osuna Christine Vauthier Alessandra Farabollini Gioconda Millotti Gilles Ponchel 《Journal of nanoparticle research》2008,10(8):1293-1301
Surface modified nanoparticles composed of poly(isobutylcyanoacrylate) (PIBCA) cores surrounded by a chitosan and thiolated
chitosan gel layer were prepared and characterized in previous works. The presence of such biopolymers on the nanoparticle
surface conferred those nanosystems interesting characteristics that might partially overcome the gastrointestinal enzymatic
barrier, improving the oral administration of pharmacologically active peptides. In the present work, the antiprotease behaviour
of this family of core–shell nanoparticles was in vitro tested against two model metallopeptidases present in the gastrointestinal
tract (GIT): Carboxypeptidase A -CP A- (luminal protease) and Leucine Aminopeptidase M -LAP M- (membrane protease). As previous
step, the zinc-binding capacity of these nanoparticles was evaluated. Interestingly, an improvement of both the zinc-binding
capacity and the antiprotease effect of chitosan was observed when the biopolymers (chitosan and thiolated chitosan) were
used as coating component of the core–shell nanoparticles, in comparison with their behaviour in solution, thanks to the different
biopolymer chains rearrangement. The presence of amino, hydroxyl and thiol groups on the nanoparticle surface promoted zinc
binding and hence the inhibition of the metallopeptidases analysed. On the contrary, the occurrence of a cross-linked structure
in the gel layer surrounding the PIBCA cores of thiolated formulations, due to the formation of interchain and intrachain
disulphide bonds, partially limited the inhibition of the proteases. The low accessibility of cations to the active groups
of the cross-linked polymeric shell was postulated as a possible explanation of this behaviour. Results obtained in this work
make this family of surface-modified nanocarriers promising candidates for the successfull administration of pharmacologically
active peptides and proteins by the oral route. 相似文献
96.
A Topological Criterion for the Existence of Half-Bound States 总被引:1,自引:0,他引:1
The following theorem is proved: if (M4n+1,g) is a completeRiemannian manifold and M is an oriented hypersurface partitioningM and with non-zero signature, then the spectrum of the HodgedeRhamLaplacian is [0,]. This result is obtained by a new Callias-typeindex. This new formula links half-bound harmonic forms (thatis, nearly L2 but not in L2) with the signature of . 相似文献
97.
We show that suitable upper estimates of the heat kernel are sufficient to imply the L
p
boundedness of several families of operators associated with the Schr?dinger group in various situations. This generalizes
results by Sj?strand and others in the Euclidean case, and by Alexopoulos in the case of Lie groups and Riemannian manifolds.
RID="*"
ID="*"Research partially supported by the European Commission (European TMR Network "Harmonic Analysis" 1998-2001, Contract
ERBFMRX-CT97-0159). 相似文献
98.
Brownstein SK Ding J Robertson G Roovers J Enright G 《The Journal of organic chemistry》2002,67(3):663-667
A new example of magnetic nonequivalence of chemically equivalent atoms is identified from the proton and carbon resonance spectra of 9,10-di(9,9-dioctylfluorenyl)anthracene with the aid of its conformation in the crystalline state. Molecular modeling suggests that it has a similar conformation in solution. 相似文献
99.
The Mg(0001) face is subjected to oxygen adsorption from 0 to 103 L. Three characteristic stages of oxygen adsorption are detected from 0 to 10 L. The AES signal of clean Mg decays exponentially against exposure with slopes α ai such that αA2 (0.75 → 3 L) >αA1 (0 → 0.75 L)>αA3 (3 → 10 L). For increasing exposures, they correspond to: (1) a clear (1 × 1)-Mg(0001), (2) a diffuse (1 × 1)-Mg(0001) and (3) a (1 × 1) with a weaker (1 × 1)-R30°-MgO(111) LEED patterns, respectively. At the end of the third stage, a supplementary ( pattern is observed. In ELS, a very fast intensity decrease of energy loss peaks due to surface and bulk plasmon excitations of the clean metal is recorded during the first stage. The energy loss peak due to the oxidized surface plasmon excitation reaches a maximum intensity at the end of the second stage. Energy loss peaks to be attributed to excitations in bulk MgO appear during the third stage. The work function of the sample decreases and shows a minimum around 6 L, and then slowly increases. Beyond 10 L, a logarithmic relation between oxide thickness and exposure seems to exist. These results are interpreted by the following sequential processes: stage 1: random oxygen chemisorption followed by oxygen incorporation (αA1); stage 2: assembling into islands and lateral island growth (αA2); stage 3: oxide formation (αA3) and stage 4: oxide thickening. Lattice models describing these processes are proposed and discussed. The influence of surface roughness on the results is emphasized. 相似文献
100.
Claude Delmas Francis Menil Gilles Le Flem Claude Fouassier Paul Hagenmuller 《Journal of Physics and Chemistry of Solids》1978,39(1):51-53
A Mössbauer study of the dimensionality of magnetic interactions in the layer oxide LiCr0.99Fe0.01O2 shows a 2-D behaviour. 相似文献