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51.
The chemisorption of 3-pyrroline (C(4)H(7)N) on Si(100) is studied from first principles. Three different structures can be realized for which, depending on the temperature, the chemisorption process is facile (for two of them it is essentially barrierless); among these configurations the most favored one, from a thermodynamical point of view, is a dissociated structure obtained through an exothermic reaction characterized by the formation of a N-Si bond and a H-Si bond in which the H atom is detached from the molecule. Several other chemisorption structures are possible which, however, require overcoming a significant energy barrier and often breaking multiple bonds. A number of reaction paths going from one stable structure to another have been investigated. We have also generated, for the two basic adsorption structures, theoretical scanning tunneling microscopy images which could facilitate the interpretation of experimental measurements, and we propose a possible reaction mechanism for nitrogen incorporation. 相似文献
52.
Carlo Rigotti 《Communications in Mathematical Physics》1978,61(3):267-273
In this paper we give a characterization of the modular group of a von Neumann algebra , with a cyclic and separating vector, which provides at the same time a necessary and sufficient condition so that two von Neumann algebras 1 and 2, such that 12, are the mutual commutants, i.e. 1=2.An application is made to the duality property in Quantum Field Theory, and we give a sufficient condition for PCT invariance in a theory of local observables.Partially supported by C.N.R. 相似文献
53.
Semiempirical iterative extended Hückel calculations are performed for the dipolar ions of cystine, cysteine, methionine and their selenium analogues. An attempt has been made to interprete the wave function of cysteine in terms of localized molecular orbitals.
Work performed with the financial support of the Consiglio Nazionale delle Ricerche. 相似文献
Zusammenfassung Semiempirische iterative Rechnungen wurden nach der erweiterten Hückeltheorie für die dipolaren Ionen Cystin, Cystein, Methionin und ihre Selen-Homologen durchgeführt. Für den Fall des Cysteins wurde die Wellenfunktion auf lokalisierte Orbitale transformiert.
Résumé On a analisé les ions dipolaires de la cystine, cystéine, methionine et leurs analogues séléniates avec la méthode semiempirique de Hückel étendue itérative. On a cherché à intérpreter la fonction d'onde pour la cystéine dans le schème des orbitales moleculaires localisées.
Work performed with the financial support of the Consiglio Nazionale delle Ricerche. 相似文献
54.
The Smiles rearrangement was successfully applied to 4-hydroxybenzo[b]thiophene furnishing a facile entry to the 4-amino derivative. The rearrangement was extended to 5-methoxy-4-methoxycarbonyl[1]benzothieno[2,3-b]pyridine obtained via aza-Wittig/electrocyclization reaction of novel N-(4-methoxybenzothiophen-2-yl)iminomethyldiphenylphosphorane with methyl trans-4-oxo-2-pentenoate. The preparation of a novel 5-amino-4-methoxycarbonyl[1]benzothieno[2,3-b]pyridine, which is of interest as a potential secondary peptide structure mimic, was successfully achieved. 相似文献
55.
Franco Cecconi Carlo A. Ghilardi Stefano Midollini Annabella Orlandini Piero Zanello 《Polyhedron》1986,5(12):2021-2031
The reaction of hydrogen sulphide with [Co(H2O)6](BF4)2 and triethylphosphine in the presence of sodium tetraphenylborate or tetrabutylammonium hexafluorophosphate gave the paramagnetic clusters [Co6(μ3-S)8(PEt3)6](Y) (Y = BPh4, (1), PF6, (2)). These compounds can be easily reduced by sodium napthalenide to the diamagnetic species [Co6(μ3-S)8(PEt3)6] · 2C4H8O (3). The molecular structures of 1 and 3 have been established by single-crystal X-ray diffraction methods. Crystal data: (1) space group P
, a = 19.481(9), b = 15.562(7), c = 12.390(b) Å, α = 92.70(8), β = 94.50(7), γ = 94.10(9)°, Z = 2, (3) space group R
, a = 11.780(6) Å, α = 92.50(7)°, Z = 1. Both structures were solved by the heavy atom method and refined by full-matrix least-squares techniques to the conventional R factors values of 0.050 for 1 and 0.044 for 3 on the basis of 4251 and 1918 observed reflections, respectively. The two clusters [Co6(μ3-S)8)(PEt3)6]1+,0 are isostructural, the inner core consisting of an octahedron of cobalt atoms with all the faces symmetrically capped by triply bridging sulphur atoms. Each metal centre is additionally linked to a triethylphosphine group so that each cobalt atom is co-ordinated by four sulphur atoms and one phosphorus in a distorted square pyramidal environment. The addition of one electron whilst leaving unchanged the geometry of the inner framework, induces small changes in the structural parameters, the average Co---Co and Co---P distances being 2.794 (3) and 2.162 (2) Å for 1 and 2.817 (3) and 2.138 (2) Å for 3 respectively. Electrochemistry in non-aqueous solvents shows the electron-transfer sequence
The tricationic species is stable only in the short time of cyclic voltammetric tests. 相似文献
Full-size image (3K)
56.
Domenico Osella Mauro Ravera Carlo Floriani Euro Solari 《Journal of organometallic chemistry》1996,510(1-2):45-50
We describe the redox behaviour in non-aqueous solvents of some cyclopentadienyl(oxo)titanium derivatives. The derivative [Ti4{η5-C5H4(SiMe3)}4(μ-O)6] shows an electrochemically and chemically reversible le reduction process, followed by a multi-electron, chemically complicated reduction at a fairly cathodic potential. On the basis of the overall electrochemical features and the comparison with the redox behaviour of the quasi-planar compound [[Ti{η5-C5H4(SiMe3)}Cl(μ-O)]4] we propose an EECCEE mechanism for the first derivative, where the second electron-transfer induces a cascade of chemical reactions giving rise to irreversible cluster breakdown. The electrochemically induced fragmentation can be viewed as a retrosynthetic pathway. The heterometallic derivative [{Ti(η5-C5H4Me)2(μ2-MoO4)2}2] shows two consecutive reduction processes; the first is chemically reversible, and the second quasi-reversible. The molybdate bridges apparently increase the stability of the electrogenerated anions. However none of these poly-oxo clusters can be considered as good models of electron ‘sinks’. 相似文献
57.
The intensities of the ΔM = ± 1 component of the 7fo→ 5D2 transition in D3 complexes containing the [ EuO9] cluster, and of other d-d or f-f transitions in D3 complexes with the yz- and xz-components of the electric quadrupole as the leading moment, are found to be dependent upon the polarizability anisotropy of the ligands. The expectation is supported by determinations of the single-crystal absorption intensities of Na3 [Eu(diglycollate)3]·2NaClO4·6H2O and [Eu(H2O)9] (C2H5SO4)3. 相似文献
58.
Giovanni Greco Ettore Novellino Maurizio Pellecchia Carlo Silipo Antonio Vittoria 《Journal of computer-aided molecular design》1994,8(2):97-112
Summary An example of a CoMFA study is described with the aim to discuss one of the major problems of this 3D QSAR method: lack of variable selection. It is shown that the use of nonrelevant energy parameters might produce CoMFA contour maps which poorly reflect the actual nature of the binding site and are in part statistical artefacts. The data set employed in our analysis comparises triazine inhibitors of dihydrofolate reductase (DHFR), isolated from chicken liver, which have already been the object of a QSAR study by other authors. Since three-dimensional structures of triazine-DHFR complexes are known, it was possible not only to reduce ambiguities in the superimposition of the ligands, but also to compare the resulting CoMFA contour maps with the enzyme active site.Supplementary material available: The Cartesian coordinates and the atomic charges of the PM3-optimized structures used in the CoMFA study are available as MOL2 files upon request.To whose memory this paper is dedicated. 相似文献
59.
Summary Five-coordinate bis(benzeneseleninato)tris(ethylenediamine) cobalt (II)complexes are obtained by reaction of Co(H2O)2 (XC6 H4 SeO2)2 complexes (X = H, p-Cl, m-CI, p-Br, ni-Br, p-Me,p-NO2) with ethylenediamine. The diaquo complexes (one mole)react with ethylenediamine (three moles)to form O-seleninato derivatives. Spectral and magnetic properties show that the complexes are low-spin (s = 1/2) and,on the basis of the electronic spectra a distorted trigonal geometry,D
3h
, is suggested. Assignments for the electronic spectra are proposed. Conductivity data indicate that these derivatives are nonelectrolytes. Both ethylenediamine and [RSeO2 ]– behave as monodentate ligands. 相似文献
60.
Carlo Sempi 《Annali dell'Universita di Ferrara》1977,23(1):25-28
Riassunto Si introducono alcune operazioni sullo spazio delle funzioni di ripartizione e si studiano, in corrispondenza, le proprietà
dell’entropia con errore
.
Lavoro eseguito nell’ambito del G.N.f.M. del C.N.R. 相似文献
Summary Some operations on the space of distribution functions are introduced. The corresponding invariance properties of the entropy with error , are then studied.
Lavoro eseguito nell’ambito del G.N.f.M. del C.N.R. 相似文献