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81.
Ilieva S Galabov B Musaev DG Morokuma K Schaefer HF 《The Journal of organic chemistry》2003,68(4):1496-1502
The aminolysis of esters is a basic organic reaction considered as a model for the interaction of carbonyl group with nucleophiles. In the present computational study the different possible mechanistic pathways of the reaction are reinvestigated by applying higher level electronic structure theory, examining the general base catalysis by the nucleophile, and a more comprehensive study the solvent effect. Both the ab initio QCISD/6-31(d,p) method and density functional theory at the B3LYP/6-31G(d) level were employed to calculate the reaction pathways for the simplest model aminolysis reaction between methylformate and ammonia. Solvent effects were assessed by the PCM method. The results show that in the case of noncatalyzed aminolysis the addition/elimination stepwise mechanism involving two transition states and the concerted mechanism have very similar activation energies. However, in the case of catalyzed aminolysis by a second ammonia molecule the stepwise mechanism has a distinctly lower activation energy. All transition states in the catalyzed aminolysis are 10-17 kcal/mol lower than those for the uncatalyzed process. 相似文献
82.
Horner-Emmons reaction of phosphonate amides with aldehydes leads to generation of o-substituted aryl-acrylamides. These compounds have been shown to be useful to quickly establish structure-activity relationships (SAR) for soluble guanylyl cyclase (sGC) activator drug discovery. 相似文献
83.
The bismuth basic nitrate [Bi6O4.5(OH)3.5]2(NO3)11 crystallizes in the monoclinic space group P21 with , , , β=107.329(17)° and . Its structure has been determined from , twinned crystal X-ray data (16 781 reflections, 683 parameters, R=0.0703). It is built upon [Bi6Ox(OH)8−x](10−x)+, x=4 and x=5 hexanuclear complexes and nitrate groups. The polycationic entities are linked to the nitrate anions either by hydrogen bonds or through bismuth-oxygen coordination. Even at , the [Bi6O4(OH)4]6+ and [Bi6O5(OH)3]5+ polycations could not be observed as such, the crystal structure refinement only detecting an average [Bi6O4.5(OH)3.5]5.5+ polycation. To prove the presence of both hexanuclear complexes in the structure, we report the existence of a correlation between the bismuth-linked oxygen bond-valence parameters and the presence, or not, of hydroxyl groups. Moreover, the Raman spectrum of the new anhydrous bismuth basic nitrate is compared to those of [Bi6O5(OH)3](NO3)5·3H2O, [Bi6O4(OH)4](NO3)6·4H2O, and two yet uncharacterized bismuth nitrates. 相似文献
84.
Marc Henry 《Journal of Cluster Science》2003,14(3):267-287
Among Achim Müller's prolific crystal structure database, we have selected two crystalline phases in order to perform a whole and complete characterization of water structure at the nanometer scale. The first chosen example involves the Na3(NH4)12[Mo57Fe6(NO)6O174(OH)3(H2O)24] 76H2O compound synthesized and characterized in 1994. Some very interesting yet unnoticed water clusters may be evidenced in the voids generated by the stacking of the polyanionic units. Among them, we have been able to characterized a pure water crown (H2O)18, a loose association of three strongly solvated ammonium ions [H3N–HOH2]+ mediated by two water dimers and one water molecule, a perfectly planar alternating six-member ring [(NH4)3(H2O)3]3+, a puckered chair-shaped hexagonal ring [(NH4)2(H2O)4]3+ and two triangular pyramidal water tetramers (H2O)4. It was also shown that the crown and the chair ring was involved through further hydrogen bonding into the formation of a quite novel supramolecular layer modeling the structure of water in contact with a polyelectrolyte. The second example involves the (gua)32[Mo132O372(H2O)72(SO4)10(H2PO2)20(gua)20]nH2O compound synthesized and characterized in 2002. Here, we provide for the first time a complete structural analysis of all the various hydrogen bond patterns encountered in this system. Among them we may cite, an intramolecular web covering the internal cavity, an intramolecular finite system involving the guanidinium cations and the nine-member ring pores of the Mo132 shell and a central pure water cluster of one hundred water molecules. In this last case, the evolution of the hydrogen bond strengths on a per H-bond basis or within supramolecular aggregates ([H2O]20, [H2O]40, and [H2O]100) is quantitatively studied from standpoints involving both geometry (H–OO bond angles distribution) and energy (partition functions). A survey of other crystalline phases involving water clusters is also presented. It is hoped that the study of these new clusters in a very next future will allow us to solve the well-known water puzzling behaviors. 相似文献
85.
86.
Several iron-catalyzed cross- and homo-coupling reactions involving organolithiums were developed to form diverse carbon-carbon bonds. The usefulness of this protocol was demonstrated by producing gram-scale products in good yields. 相似文献
87.
Niels J. Hauwert Tamara A. M. Mocking Daniel DaCostaPereira Ken Lion Yara Huppelschoten Henry F. Vischer Iwan J. P. DeEsch Maikel Wijtmans Rob Leurs 《Angewandte Chemie (International ed. in English)》2019,58(14):4531-4535
Spatiotemporal control over biochemical signaling processes involving G protein‐coupled receptors (GPCRs) is highly desired for dissecting their complex intracellular signaling. We developed sixteen photoswitchable ligands for the human histamine H3 receptor (hH3R). Upon illumination, key compound 65 decreases its affinity for the hH3R by 8.5‐fold and its potency in hH3R‐mediated Gi protein activation by over 20‐fold, with the trans and cis isomer both acting as full agonist. In real‐time two‐electrode voltage clamp experiments in Xenopus oocytes, 65 shows rapid light‐induced modulation of hH3R activity. Ligand 65 shows good binding selectivity amongst the histamine receptor subfamily and has good photolytic stability. In all, 65 (VUF15000) is the first photoswitchable GPCR agonist confirmed to be modulated through its affinity and potency upon photoswitching while maintaining its intrinsic activity, rendering it a new chemical biology tool for spatiotemporal control of GPCR activation. 相似文献
88.
89.
Horný L Petraco ND Pak C Schaefer HF 《Journal of the American Chemical Society》2002,124(20):5861-5864
The optimized geometries, adiabatic electron affinities, and IR-active vibrational frequencies have been predicted for the long linear carbon chains HC(2n)H. The B3LYP density functional combined with the DZP basis set was used in this theoretical study. The computed physical properties are discussed. The predicted electron affinities form a remarkably regular sequence: 1.78 (HC(12)H), 2.08 (HC(14)H), 2.32 (HC(16)H), 2.53 (HC(18)H), 2.69 (HC(20)H), 2.83 (HC(22)H), and 2.95 eV (HC(24)H). The predicted structures display an alternating triple and very short single bond pattern, with the degree of bond alternation significantly less for the radical anions. 相似文献
90.
Nanotechnology promises to enhance the functionality and sensitivity of miniaturized analytical systems. For example, nanoscale transport systems, which are driven by molecular motors, permit the controlled movement of select cargo along predetermined paths. Such shuttle systems may enhance the detection efficiency of an analytical system or facilitate the controlled assembly of sophisticated nanostructures if transport can be coordinated through complex track networks. This study determines the feasibility of complex track networks using kinesin motor proteins to actively transport microtubule shuttles along micropatterned surfaces. In particular, we describe the performance of three basic structural motifs: (1) crossing junctions, (2) directional sorters, and (3) concentrators. We also designed track networks that successfully sort and collect microtubule shuttles, pointing the way towards lab-on-a-chip devices powered by active transport instead of pressure-driven or electroosmotic flow. 相似文献