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961.
Polymer-supported phosphine ligand 3b derived from ferrocene was prepared,and applied in palladium-catalyzed Suzuki- Miyaura reactions.A range of aryl bromides can couple with phenylboronic acid to obtain corresponding biaryls in excellent yields. The recycling of the polymer-bound catalyst was tested without adding palladium. 相似文献
962.
963.
Yingkai Zhang 《Theoretical chemistry accounts》2006,116(1-3):43-50
This perspective article mainly focuses on the development and applications of a pseudobond ab initio QM/MM approach to study enzyme reactions. The following aspects of methodology development are discussed: the approaches for the QM/MM covalent boundary problem, an efficient iterative optimization procedure, the methods to determine enzyme reaction paths, and the approaches to calculate free energy change in enzyme reactions. Several applications are described to illustrate the capability of the methods. Finally, future directions are discussed. 相似文献
964.
A. Rivaton B. Mailhot M. Lounaci J.-L. Gardette 《Polymer Degradation and Stability》2006,91(3):565-572
This paper is devoted to the analysis of the photochemical behaviour of copolymers with carbazole units exposed to long-wavelength radiation. These copolymers are constituted of two types of carbazolylethyl methacrylate units (CEM) with octyl methacrylate moieties (OMA). The exposure of copolymers and PVK to UV light results in dramatic modifications of the physical and photophysical properties of the polymer. These modifications can be correlated with modifications of the chemical structure of the matrix. The photoageing of copolymers and PVK has been analysed by fluorescence, ESR, UV-vis and infrared spectroscopies. The effects of crosslinking and chain scissions were determined by gel fraction measurements and size exclusion chromatography. 相似文献
965.
István Szatmári 《Tetrahedron letters》2006,47(23):3881-3883
As a new extension of the Mannich reaction of naphthols, 1-(hydroxynaphthyl)-substituted 1,2,3,4-tetrahydroisoquinolines were synthesized by the nucleophilic addition of 1- or 2-naphthol to 3,4-dihydroisoquinolines under solvent-free conditions, using microwave irradiation. The additions to 3-methyl-6,7-dimethoxy-3,4-dihydroisoquinoline proved to be a highly diastereoselective processes, resulting in the cis isomers as the main or the only products. 相似文献
966.
The semi-empirical quantum chemical MNDO-PM3 calculations of the enthalpies of formation of Meisenheimerortho- andipso--complexes of 1,3,5-trinitrobenzene (TNB) and 2,4,6-trinitrotoluene (TNT) with the phenoxide anion in the gas phase and in water are performed within the framework of the point dipole model. Based on the calculated heats and activation barriers to substitution of the nitro group by the phenoxyl group in TNB and TNT, the possibility of the reactions of TNB and TNT with the phenoxide anion in water is shown. These reactions in water occurvia the SNAr mechanism involving the correspondingipso--complex as an intermediate. In the gas phase, the SNAr mechanism is impossible, because the reaction is strongly endothermic. In the case of TNT, the exothermic reaction of elimination of a proton from the methyl group by the phenoxide anion competes with nucleophilic substitution in a polar solvent. The activation energy calculated for this exothermic reaction is 8 kcal mol–1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 624–628, April, 1995. 相似文献
967.
John Fielden Patrick T. Gunning De-Liang Long Margaret Nutley Arkady Ellern Paul Kgerler Leroy Cronin 《Polyhedron》2006,25(18):3474-3480
The coordination chemistry of the tetradentate pyridyl N-donor ligand cis-3,5-bis-[2-pyridinyleneamin]-trans-hydroxycyclohexane (DDOP) has been investigated with zinc(II) nitrate and triflate. The resulting complexes, [Zn(DDOP)(H2O)(NO3)](NO3) (1), and [Zn(DDOP)(H2O)(OTf)](OTf) (2) differ not only in their counterions, but also the arrangement of the axial ligands and their solid state hydrogen bonded networks. Isothermal titration calorimetry was used to assess the difference in binding properties exhibited by the two zinc complexes at physiological pH in an aqueous environment. A series of coordinating amino acids were found to preferentially bind to the mononuclear zinc triflate (1) complex over the corresponding nitrate (2) assembly, with histidine exhibiting a two centre binding mode. 相似文献
968.
969.
In this study we have compared different ligands containing three or more hetero-atoms (N, O and/or S) with respect to their ability to form tridentate complexes with a Tc-tricarbonyl moiety. Comparison of each ligand in a competition reaction with histidine first and then with each other compound allowed to rank the ligands according to their ability of complex formation with the [99mTc(CO)3]+ precursor from diethylenetriamine (most efficient of the studied ligands) to nitrilotriacetic acid (weakest complexing properties). The results provide insight in the structural requirements for the formation of stable Tc-tricarbonyl complexes and suggest preferred combinations and arrangements of the hetero-atoms involved in the complex formation. They also give a good indication which type of ligand is most appropriate to modify biomolecules for an efficient and stable labelling with a Tc-tricarbonyl moiety. 相似文献
970.