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排序方式: 共有211条查询结果,搜索用时 15 毫秒
81.
82.
Dobbs AP Guesné SJ Martinović S Coles SJ Hursthouse MB 《The Journal of organic chemistry》2003,68(20):7880-7883
A versatile and high-yielding indium trichloride mediated cyclization reaction of silylated homoallylic alcohols, thiols, or amines with aldehydes or epoxides is described as a rapid route to a range of unsaturated heterocycles. The excellent diastereoselectivity observed offers a method of wide scope and generality. 相似文献
83.
The reaction between [Fe(III)(dmf)(6)](ClO(4))(3) and the ligand S-methyl-1-phenyl-isothiosemicarbazide, H(2)[L(Me)], and triethylamine (1:3:6) in methanol under an argon blanketing atmosphere at elevated temperatures (reflux) yields a purple solution from which upon cooling to 20 degrees C dark green crystals of [Fe(III)(L(Me)(*))(2)(SCH(3))] (1) were obtained in 15% yield. From a similar reaction mixture using FeCl(3) as starting material in the solvent acetone under anaerobic conditions at -80 degrees C, dark green crystals of [Fe(III)(L(Me)(*))(2)Cl] (2) were obtained in 21% yield. The structures of complexes 1 and 2 have been determined by single-crystal X-ray crystallography at 100 K. Both complexes are five-coordinate square base pyramidal ferric species containing two N,N-coordinated, monoanionic pi radicals, (L(Me)(*))(1)(-), of the parent S-methyl-1-phenyl-isothiosemicarbazide(2-) dianion in the basal positions whereas the axial position is occupied by methylthiolate in 1 and chloride in 2, respectively. The electronic structure of both species has been elucidated by their electronic spectra, magnetic properties, and X-band EPR and M?ssbauer spectra. Both possess an S(t) = (1)/(2) ground state which is attained via an antiferromagnetic coupling between the spins of an intermediate spin ferric ion (S(Fe) = (3)/(2)) and two ligand pi radical anions (S(rad) = (1)/(2)). 相似文献
84.
Cecile F. Rousseau Sebastien Cecillon Eric Da Silva Anne-Marie Freyria Daniel Herbage Edwige Leclere Anthony W. Coleman 《Journal of inclusion phenomena and macrocyclic chemistry》2005,53(1-2):9-13
A spectrometric assay for the determination of concentration of para-sulphonato-calix[n]arenes and their derivatives has been developed using dimethylmethylene blue (DMMB) as a probe. Interaction with para-sulphonato-calix[n]arenes leads to a metachromatic shift in the spectrum of DMMB with appearance of a peak at 536 nm and diminution of the spectral
intensity of the peaks at 594 and 649 nm. The method shows good linearity in the concentration range 0–6 μg/ml for para-sulphonato-calix[n]arenes.
in final form: 27 December 2004 相似文献
85.
Wilds CJ Noronha AM Robidoux S Miller PS 《Journal of the American Chemical Society》2004,126(30):9257-9265
Therapeutic bifunctional alkylating agents generate interstrand cross-links in duplex DNA. As part of our continuing studies on DNA duplexes that contain alkyl interstrand cross-links, we have synthesized a cross-link that bridges the N(3) positions of a mismatched thymidine base pair. This cross-link, which is similar to the N(3)C-alkyl-N(3)C cross-link that has been observed between mismatched cytosine base pairs, was introduced by first incorporating a cross-linked phosphoramidite unit at the 5'-end of an oligonucleotide chain. Fully cross-linked duplexes were then synthesized using an orthogonal approach to selectively remove protecting groups, thus allowing construction of the cross-linked duplex via conventional solid-phase oligonucleotide synthesis. Short DNA duplexes with alkyl cross-links of various lengths (two, four, and seven methylene units) were prepared, and their physical properties were studied via UV thermal denaturation and circular dichroism spectroscopy. These linkers were found to stabilize the duplexes by 37, 31, and 16 degrees C for the two-, four-, and seven-carbon linkers, respectively, relative to a non-cross-linked duplex. Circular dichroism spectra suggested that these lesions induce very little deviation in the global structure relative to the non-cross-linked duplex DNA control. Molecular models show that the two-carbon cross-link spans the distance between the N(3) atoms of the T-T mismatch without perturbing the helix structure, whereas the longer linkers, particularly the seven-carbon linker, tend to push the thymines apart, creating a local distortion. This perturbation may account for the lower thermal stability of the seven-carbon versus two-carbon cross-linked duplex. 相似文献
86.
Sebastien Demers 《Tetrahedron letters》2008,49(21):3368-3371
A series of bicyclic pyridine containing alkaloids related to (−)-cytisine and varenicline are described. Synthetic access via regioisomeric metalation of alkoxy- and halo-pyridines gains entry to all four isomeric [3.3.1]-bicyclic targets. Regioselective and sequential oxidative cleavage of dicyclopentadiene generates a related [3.2.1]-bicyclic analog. 相似文献
87.
Kirschhock CE Kremer SP Vermant J Van Tendeloo G Jacobs PA Martens JA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(15):4306-4313
The crystallization of colloidal silicalite-1 from clear solution is one of the best understood zeolite formation processes. Colloidal silicalite-1 formation involves a self-assembly process in which nanoslabs and nanotablets with a silicalite-1 type connectivity are formed at intermediate stages. During the assembly process, with strongly anisometric particles present, regions appear with orientational correlations, as evidenced with measurements of dynamic light scattering, viscosity, and rotation of polarized light. The presence of such regions rationalizes the unexpected differences between the crystallization kinetics under microgravity and on earth. The discovery of the locally oriented regions sheds new light on currently poorly understood hydrodynamic effects on the zeolite formation processes, such as the influence of stirring on the phases obtained and the subsequent kinetics. Addition of surfactants or polymers modifies the ordering of the zeolitic building units in the correlated regions, and new types of hierarchical materials named zeogrids and zeotiles can be obtained. 相似文献
88.
[Structure: see text] The synthesis of bivalent mannosides by the grafting of alpha-D-mannopyranoside onto monosaccharide acceptors and conjugation to terephthalic acid or phenylenediamine is described. Computational methods were used to predict accessible orientations and distances between the mannose units. 相似文献
89.
Kerisit S Cooke DJ Marmier A Parker SC 《Chemical communications (Cambridge, England)》2005,(24):3027-3029
Molecular dynamics simulations of aqueous solution/goethite interfaces show that the classical models of the electrical double layer do not accurately describe the distribution of ions near the surface (such a distribution is present even when the surface is neutral) and that the explicit treatment of solvent molecules is essential to capture the effects of the surface on the liquid phase. 相似文献
90.