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131.
Summary A model of the
2-adrenergic receptor binding site is built from the primary structure of the receptor, experimental evidence for key binding residues and analogy with a homologous protein of partially determined structure. It is suggested that residues Trp-109, Thr-110 and Asp-113 are involved in ligand binding. Noradrenaline is successfully docked into this model, and the results of an INDO molecular orbital calculation on the complex indicate that a charge transfer interaction between Trp-109 and noradrenaline is possible. 相似文献
132.
Díaz MC Illescas BM Martín N Viruela R Viruela PM Ortí E Brede O Zilbermann I Guldi DM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(8):2067-2077
A new class of pi-extended TTF-type electron donors (11 a-c) has been synthesized by Wittig-Horner olefination of bianthrone (9) with 1,3-dithiole phosphonate esters (10 a-c). In cyclic voltammetry experiments, donors 11 a-c reveal a single, electrochemically irreversible oxidation-yielding the corresponding dicationic products-at relatively low oxidation potentials (approximately 0.7-0.8 V). Theoretical calculations, performed at the DFT level (B3 P86/6-31 G*), predict a highly-folded C(2h) structure for 11 a. In the ground state, the molecule adopts a double saddle-like conformation to compensate the steric hindrance. The calculations suggest that the intramolecular charge transfer associated with the HOMO-->LUMO transition is responsible for an absorption band observed above 400 nm. While the radical cation 11 a*+ retains the folded C(2h) structure predicted for the neutral molecule as the most stable conformation, the dication 11 a(2+) has a fully aromatic D(2) structure, formed by an orthogonal 9,9'-bianthryl central unit to which two singly-charged dithiole rings are attached. The drastic conformational changes that compounds 11 undergo upon oxidation account for their electrochemical properties. By means of pulse radiolysis measurements, radical-induced one-electron oxidation of 11 a-c was shown to lead to the radical cation species (11 a-c*+), which were found to disproportionate with generation of the respective dication species (11 a-c(2+)) and the neutral molecules (11 a-c). 相似文献
133.
Gas-phase proton affinities of cyclophanes containing intra-annular amino groups were calculated using density functional theory (DFT) at the B3LYP/6-31+G∗∗//B3LYP/6-31G∗ level. They are higher in magnitude as those for proton sponges such as 1,8-bisaminonaphthalene, however, they are slightly weaker bases than 1,8-bis(dimethylamino)naphthalene. The high basicity of the cyclophane diamines is attributed mainly to their structural flexibility, which allows them to maximize the hydrogen bond strength in the cations by achieving N-H?N linearity, while strain relief upon protonation is less important. Another contributing factor is the stabilizing interaction of the added proton with adjacent phenyl π systems of the cyclophanes. Barriers for proton transfer between the nitrogen atoms of the diamine cations are also reported. 相似文献
134.
C. Cismaş I. Grosu G. Plé E. Condamine Y. Ramondenc L. Toupet I. Silaghi-Dumitrescu G. Nemeş A. Terec L. Muntean 《Structural chemistry》2005,16(4):369-377
The synthesis and stereochemistry of some new bis(1,3-oxathian-2-yl) derivatives are reported. The conformational behavior of these compounds and the orientation of their substituents are deduced from the NMR spectra, from the X-ray crystal structures of two compounds and from the ab-initio level calculations. The epimerization of diastereoisomers and the chair ⇌ 22,5-twist equilibria were studied by variable temperature NMR. 相似文献
135.
P. R. N. De Souza D. A. G. Aranda J. W. De M. Carneiro C. Da S. B. De Oliveira O. A. C. Antunes F. B. Passos 《International journal of quantum chemistry》2003,92(4):400-411
B3 LYP hybrid functional with LACVP* pseudopotential was applied for the optimization of geometries of complexes resulting from interaction of benzene, pyridine, naphthalene, and quinoline with Ptn (n = 4, 7) clusters. For benzene‐containing complexes, the most stable form corresponds to a bridge adsorption, with benzene undergoing considerable geometric distortions, assuming a boat‐like conformation. C? H bonds are bended upward from the plane of the cluster. C? C bonds stretch, especially when they form π‐complexes with low coordinated Pt atoms. Some arrangements for pyridine complexes involving the N atom of the organic moiety undergo further distortions, apparently preserving a formal C? N π bond. Except for that distortion, the behavior of any heteroaromatic complex is similar to that of benzene in the same arrangement. The quinoline–Pt7 complex can suitably be used for simulation of the cinchonidine (CD) anchorage over Pt. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
136.
Jens Beckmann Dainis Dakternieks Andrew Duthie Naomi A. Lewcenko Cassandra Mitchell Markus Schürmann 《无机化学与普通化学杂志》2005,631(10):1856-1862
The reaction of (p‐MeOC6H4)2TeO with two equivalents of HO3SCF3 and HO2PPh2 provided the tetraorganoditelluroxanes (F3CSO3)(p‐MeOC6H4)2TeOTe(p‐MeOC6H4)2(O3SCF3) ( 1 ) and (Ph2PO2)(p‐MeOC6H4)2TeOTe(p‐MeOC6H4)2(O2PPh2)·2 Ph2PO2H ( 2 ) in good yields. Compounds 1 and 2 were characterized by solution and solid‐state 31P and 125Te NMR spectroscopy, IR spectroscopy, electrospray mass spectrometry, conductivity measurements and single crystal X‐ray diffraction. In solution, compound 1 undergoes an electrolytic dissociation and reversibly reacts with traces of water to give the mononuclear cation [(p‐MeOC6H4)2TeOH]+ and triflate anions. Theoretical aspects of the protonation and hydration of model telluroxanes R2TeO (R = H, Me, Ph) were investigated by preliminary DFT calculations and compared to the corresponding selenoxanes R2SeO. The tellurium dihydroxides R2Te(OH)2 seem to be more stable than the hydrogen‐bonded complexes R2TeO·H2O. 相似文献
137.
The halothane???acetone and fluoroform???acetone complexes are studied using the second‐order Møller–Plesset (MP2) method with a cc‐pVTZ basis set and the density functional theory (DFT) method with a TZVP basis set. Whereas halothane exhibits a small red shift upon complexation, fluoroform shows a pronounced blue shift. To explain this difference in behavior, we perform symmetry‐adapted perturbation theory (SAPT) and natural bond orbital (NBO) analyses. Although the composition of the total stabilization energy of each complex is different, that alone does not provide a satisfactory explanation for the difference in the spectral shifts. This difference is interpreted as a result of the interplay of the hyperconjugation and rehybridization mechanisms. The small and surprising red shift of the C? H stretching frequency of halothane, which resulted from the complexation of this species with acetone,is explained by the compensation of the two above‐mentioned mechanisms. On the other hand, the fluoroform???acetone complex exhibits a blue shift of the C? H stretching frequency upon complexation, the most likely reason for this shift being a concerted occurrence of the hyperconjugation and rehybridization mechanisms. The calculated shift of the C? H stretching vibration frequencies of halothane (+27 cm?1) agree with the experimental value of +5 cm?1. 相似文献
138.
The neutral, cationic, and anionic structures of both prototropic tautomers oftrans- andcis-urocanic acid [(E)- and (Z)-3-(1H-imidazol-4(5)-yl)propenoic acid, respectively] were studied by using semiempirical andab initio gas-phase calculations. Potential energy surfaces of the structures were calculated by using the semiempirical AM1 method, and the geometries corresponding to global minima on these surfaces were optimized up to the MP2/6-31G* level of theory. The calculated protonation forms of each urocanic acid isomer have a planar molecular structure due to a delocalized -electron system, and all of them prefer thes-trans conformation with respect to the bond between the imidazole and the propenoic acid moieties. Thecis-urocanic acid structures are stabilized by an intramolecular hydrogen bond. The chargedcis-urocanic acid isomers have a lower molecular energy than the correspondingtrans-isomers, whereas the neutral molecules have, after inclusion of thermodynamic corrections, approximately the same energy. The cationic urocanic acid structures have about 2500 kJ mol–1 lower energy than the anionic ones and about 1000 kJ mol–1 lower energy than the neutral ones. The nonzwitterionic forms of the neutral urocanic acid isomers have about 200 kJ mol–1 lower energy than the zwitterionic ones. These energy differences are explained by the proton affinities of the imidazole and the propenoic acid moieties of the urocanic acid structures. 相似文献
139.
Krystyna Holderna-Natkaniec Ireneusz Natkaniec Weronika Kasperkowiak Elzbieta Sciesinska Jacek Sciesinski Edward Mikuli 《Journal of Molecular Structure》2006,790(1-3):94-113
FTIR and IINS spectra of 6-Furfurylaminopurine (6-FAP) and 6-Benzylaminopurine (6-BAP) taken at different temperatures have been analysed and compared with the spectra calculated by the ab initio DFT/B3LYP method and the semiempirical PM3 method in the isolated molecule approximation, for the tautomers N3-H, N7-H and N9-H, and dimers with hydrogen bonds. For 6-FAP the best agreement between the calculated and experimental (at 20 K) spectra has been found for the N9-H tautomer, whose structure was established by X-ray diffraction. For 6-BAP the analogous agreement for the N9-H tautomer structure has been poor and much better for the N7-H tautomer. The vibrational spectra calculated for dimers of the molecules studied involved in hydrogen bonds, permitted also an interpretation of the bands whose positions and FWHM in the FTIR spectra changed with temperature. 相似文献
140.
Slootweg JC Vlaar MJ Vugts DJ Eichelsheim T Merhai W de Kanter FJ Schakel M Ehlers AW Lutz M Spek AL Lammertsma K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(16):4808-4818
Reaction of the transient phosphinidene complexes R-P=W(CO)5 with N-substituted-diphenylketenimines leads unexpectedly to the novel 2-aminophosphindoles, as confirmed by an X-ray crystal structure determined for one of the derivatives. Experimental evidence for a methylene-azaphosphirane intermediate was found by using the iron-complexed phosphinidene iPr2N-P=Fe(CO)4, which affords the 2-aminophosphindole together with the novel methylene-2,3-dihydro-1H-benzo[1,3]azaphosphole. Analysis of the reaction pathways with DFT indicates that the initially formed methylene-azaphosphirane yields both phosphorus heterocycles by way of a [1,5]- or [1,3]-sigmatropic shift, respectively, followed by a H-shift. Strain underlies both rearrangements, which causes these remarkably selective conversions that can be tuned by changing the substituents. 相似文献