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181.
Fox OD Cookson J Wilkinson EJ Drew MG MacLean EJ Teat SJ Beer PD 《Journal of the American Chemical Society》2006,128(21):6990-7002
Polymetallic nanodimensional assemblies have been prepared via metal directed assembly of dithiocarbamate functionalized cavitand structural frameworks with late transition metals (Ni, Pd, Cu, Au, Zn, and Cd). The coordination geometry about the metal centers is shown to dictate the architecture adopted. X-ray crystallographic studies confirm that square planar coordination geometries result in "cagelike" octanuclear complexes, whereas square-based pyramidal metal geometries favor hexanuclear "molecular loop" structures. Both classes of complex are sterically and electronically complementary to the fullerenes (C(60) and C(70)). The strong binding of these guests occurred via favorable interactions with the sulfur atoms of multiple dithiocarbamate moieties of the hosts. In the case of the tetrameric copper(II) complexes, the lability of the copper(II)-dithiocarbamate bond enabled the fullerene guests to be encapsulated in the electron-rich cavity of the host, over time. The examination of the binding of fullerenes has been undertaken using spectroscopic and electrochemical methods, electrospray mass spectrometry, and molecular modeling. 相似文献
182.
Giménez R Elduque A López JA Barbera J Cavero E Lantero I Oro LA Serrano JL 《Inorganic chemistry》2006,45(25):10363-10370
Several new cis-[RhCl(CO)2(Ln)] complexes have been prepared using different polycatenar pyrazole ligands (Ln) in order to obtain columnar liquid crystalline arrangements. The topology of the ligand plays an essential role, and a mesophase is induced at room temperature from a nonmesogenic pyrazole only when it is symmetrically substituted with six decyloxy chains. The single-crystal structure of a methoxy-substituted analogue, 3,5-bis(3,4,5-trimethoxyphenyl)pyrazole, is formed by globular tetrameric structures held together by H-bonding. However, parallel dimers are present in the corresponding cis-chlorodicarbonylrhodium(I) complex, a situation that explains the induction of a columnar mesophase in the decyloxy-substituted complex. The XRD pattern of the mesophase is consistent with a hexagonal symmetry in which the columns are formed by molecules assembled in an antiparallel mode. The crystal-to-mesophase transition was also detected by spectroscopic techniques as a shift in the IR carbonyl stretching bands and the appearance of a charge-transfer band in the absorption spectrum with thermochromic behavior. 相似文献
183.
Panagiotou and Stufler recently proved an important fact on their way to establish the scaling limits of random Pólya trees: a uniform random Pólya tree of size consists of a conditioned critical Galton–Watson tree and many small forests, where with probability tending to one, as tends to infinity, any forest , that is attached to a node in , is maximally of size . Their proof used the framework of a Boltzmann sampler and deviation inequalities.In this paper, first, we employ a unified framework in analytic combinatorics to prove this fact with additional improvements for , namely . Second, we give a combinatorial interpretation of the rational weights of these forests and the defining substitution process in terms of automorphisms associated to a given Pólya tree. Third, we derive the limit probability that for a random node the attached forest is of a given size. Moreover, structural properties of those forests like the number of their components are studied. Finally, we extend all results to other Pólya structures. 相似文献
184.
Comparatively little is known about commutative rings of partial differential operators, while in the ordinary case, concrete examples and an algebraic(-geometric) structure can be algorithmically determined for large classes. In this note, by the calculation of the partial μ-shifted differential resultant which we defined in a previous paper, we produce algebraic equations of spectral surfaces for commutative rings in two variables, and Darboux transformations of Airy-type operators that correspond to morphisms of surfaces. There are, however, many elementary differential-algebraic statements that we only observe experimentally, thus we offer open questions which seem to us quite significant in differential algebra, and access to Mathematica code to enable further experimentation. 相似文献
185.
Gatti M Drinkel E Wu L Pusterla I Gaggia F Dorta R 《Journal of the American Chemical Society》2010,132(43):15179-15181
We present the first productive ring-closing metathesis reaction that leads to the construction of cyclic alkenyl bromides. Efficient catalysis employing commercially available Grubbs II catalyst is possible through appropriate modification of the starting bromoalkene moiety. 相似文献
186.
Domínguez M Alvarez R Borràs E Farrés J Parés X de Lera AR 《Organic & biomolecular chemistry》2006,4(1):155-164
(R)-all-trans-3-hydroxyretinal 1, (S)-all-trans-4-hydroxyretinal and (R)-all-trans-4-hydroxyretinal have been synthesized stereoselectively by Horner-Wadsworth-Emmons and Stille cross-coupling as bond-forming reactions. The CBS method of ketone reduction was used in the enantioface-differentiation step to provide the precursors for the synthesis of the 4-hydroxyretinal enantiomers. The kinetic constants of Xenopus laevis ADH8 with these retinoids have been determined. 相似文献
187.
The first fully automated multi-step polymer assisted solution phase (PASP) synthesis is described. An array of histone deacetylase (HDAc) inhibitors was prepared by an unattended 4-5 step sequence incorporating in-line 'catch and release' purification. 相似文献
188.
García-López J Peralta-Pérez E Forcén-Acebal A García-Granda S López-Ortiz F 《Chemical communications (Cambridge, England)》2003,(7):856-857
The first examples of the PN-directed dilithiation of (N-methoxycarbonyl)phosphazenes in the C(alpha) and C(ortho) to the phosphorus, and the use of these dianions in the formation of tri- and tetra-substituted olefins through stereospecific thermolysis of a new type of isolable bicyclic 1,2-oxaphosphetanes are described. 相似文献
189.
Barberá J Cavero E Lehmann M Serrano JL Sierra T Vázquez JT 《Journal of the American Chemical Society》2003,125(15):4527-4533
The present report undertakes a challenge of general interest in supramolecular chemistry: the achievement of helical organizations with controlled structure. To achieve this target we considered the possibility of inducing supramolecular chirality using molecules that were designed to organize into columnar mesophases. The use of oxazoline-derived ligands and metal coordination served as tools to prepare molecules with a phasmidic-like structure, which show columnar organization in the liquid crystalline state. To ensure the formation of chiral mesophases, these complexes bear stereogenic centers in the rigid coordination environment of the metal. X-ray and circular dichroism experiments have revealed that chirality transfer does indeed take place from the chiral molecule to the columnar liquid crystal organization. This chiral columnar organization appears as a helix consisting of stacks of molecules that rotate with respect to one another along the column while maintaining their mean planes parallel to each other. In fact, it has been concluded that packing of these polycatenar molecules must be more efficient upon rotation of a molecule with respect to the adjacent one along the column. Furthermore, the same type of helical supraorganization has been found to be present in the mesophase of the racemic mixture and the mixture of diastereomers prepared from the racemic ligand. In this case, segregation of the optical isomers is proposed to occur to give rise to both types of helix (right-handed and left-handed). 相似文献
190.
Emma E. Smith Leonie A. Cooke Maighréad McCourt James H.R. Tucker 《Tetrahedron letters》2007,48(37):6569-6572
Directed Michaelis-Arbuzov reactions of support-bound internucleotide O-benzyl- or O-methyl-phosphite triesters with meta-phenylazobenzylamine or alkane-/glycol-linked α,ω-diamines were effected in the presence of iodine. The corresponding tritylated phosphoramidate-linked 11-mers were fully deprotected and released from the support under standard conditions and the fast- and slow-diastereoisomers of both the E- and the Z-meta-phenylazobenzyl-appended oligomers were readily resolved by RP-HPLC. The primary amine-functionalised oligonucleotides were either purified, detritylated and then finally treated with N-hydroxysuccinimidyl carboxylic acid ester derivatives of photoswitchable moieties (Route A) or first derivatised and then subsequently purified and detritylated (Route B). This latter route enabled resolution of fast- and slow-isomers of the trityl-on oligomers bearing novel photoswitchable azopyridine or 9-alkoxyanthracene moieties using RP-HPLC, following which the pure diastereoisomers were detritylated and characterised by MALDI-MS. 相似文献