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881.
Lorenzo Di Bari Gennaro Pescitelli Piero Salvadori Michele Rovini Maurizio Anzini Andrea Cappelli Salvatore Vomero 《Tetrahedron: Asymmetry》2006,17(24):3430-3436
Three racemic esters based on the 1,5-diarylpyrrole structure, which proved to be highly selective COX-2 inhibitors endowed with an appreciable anti-inflammatory activity in some animal models, were subjected to chiral resolution. Their absolute configurations were assigned by comparison of the CD spectrum measured on-line with a HPLC–CD detector, with that calculated by means of a TDDFT method. 相似文献
882.
Several supramolecular architectures generated by guanosine derivatives are described. The research started from the fortuitous observation of a lyotropic behavior exhibited by a guanylic nucleotide in water. This observation stimulated extensive research on several natural and lipophilic guanosine derivatives which self-assemble in different architectures (discs, ribbons, helices...), according to their structure and environment. These ordered structures can be used as scaffolds for photo- or electro-active moieties and for the fabrication of molecular electronic devices. 相似文献
883.
Alfredo Camparini Fabio Ponticelli Piero Tedeschi 《Journal of heterocyclic chemistry》1985,22(6):1561-1565
A synthetic pathway to 3-methylisoxazolo[4,5-d]pyridazine and some of its derivatives is described. Uv irratiation of 4,7-dimethoxy (XVII) and 7-chloro-4-hydrazino-3-methylisoxazolo[4,5-d]pyridazine (IX) shows that both intramolecular rearrangements and solvent involving reactions can occur. 相似文献
884.
Solans-Monfort X Sodupe M Branchadell V Sauer J Orlando R Ugliengo P 《The journal of physical chemistry. B》2005,109(8):3539-3545
The adsorption of NH(3) and H(2)O in acidic chabazite has been studied with the B3LYP method within the cluster approach (5T, 48T clusters) and the periodic approach adopting a Si/Al = 11/1 chabazite and a basis set of polarized double-zeta quality. The 5T cluster has been treated fully ab initio at the B3LYP level whereas the 48T cluster has been treated with the ONIOM2 scheme using B3LYP as the high level of theory and the MNDO, AM1, and HF/3-21G methods as low levels of theory. Periodic calculations show that the adsorption of NH(3) in acidic chabazite takes place through an ion pair (NH(4)(+)-CHA(-)) structure, the computed adsorption energy being -32 kcal/mol. The adsorption of H(2)O leads to a hydrogen bonded (H(2)O-HCHA) complex with the computed adsorption energy of -20 kcal/mol. All ONIOM combinations provide similar structures to those obtained with periodic calculations. Adsorption energies, however, are sensitive to the low level used, especially for NH(3). The ONIOM B3LYP:HF/3-21G method is the one that provides more satisfactory results. Present results show that, for larger zeolites, the ONIOM scheme can be successfully applied while drastically reducing the cost of a fully ab initio treatment. 相似文献
885.
Piero Dalla Croce 《Journal of heterocyclic chemistry》1976,13(5):1109-1110
4-Arylmethylene-Δ2 -isoxazolin-5-ones react with carbonyl-stabilized sulfur ylides yielding spiro[cyclopropane-1,4′-Δ2-isoxazolin]-5′-ones identified from spectroscopic data and chemical behaviour. 相似文献
886.
Piero Zanello Renato Seeber Arnaldo Cinquantini Bruno Crociani 《Transition Metal Chemistry》1980,5(1):226-229
Summary The electrochemical behaviour of neutral platinum(II) and palladium(II) isocyanide complexes has been investigated in an aprotic medium at platinum and mercury electrodes. Platinum(II) derivatives are reduced to platinum(0) species, Palladium(II) compounds give rise to palladium(0) species at room temperature, while at 0° it is possible to obtain palladium(I) compounds. 相似文献
887.
A. Di Piero A. Di Piero M. A. Bacchi M. A. Bacchi E. A. N. Fernandes E. A. N. Fernandes 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(2):447-450
Summary The k0-method in INAA has been used at CENA/USP Brazil for analyzing geological and biological materials. With the acquisition of
a well-type detector, it was realized that the true-coincidence effects, originally corrected by semi-empirical procedures
with the in-house k0-software (Quantu-INAA), would affect the accuracy of results. Thus, new coincidence correction algorithms were developed,
based on a theoretical equation for obtaining the correction factors. Validation of the algorithms was performed by analysis
of plant certified reference materials. 相似文献
888.
Liu Y Chen SH Berti D Baglioni P Alatas A Sinn H Alp E Said A 《The Journal of chemical physics》2005,123(21):214909
The phonon propagation and damping along the axial direction of films of aligned 40 wt % calf-thymus DNA rods are studied by inelastic x-ray scattering (IXS). The IXS spectra are analyzed with the generalized three effective eigenmode theory, from which we extract the dynamic structure factor S(Q,E) as a function of transferred energy E=variant Planck's over 2piomega, and the magnitude of the transferred wave vector Q. S(Q,E) of a DNA sample typically consists of three peaks, one central Rayleigh scattering peak, and two symmetric Stokes and anti-Stokes Brillouin side peaks. By analyzing the Brillouin peaks, the phonon excitation energy and damping can be extracted at different Q values from about 4 to 30 nm(-1). A high-frequency sound speed is obtained from the initial slope of the linear portion of the dispersion relation below Q=4 nm(-1). The high-frequency sound speed obtained in this Q range is 3100 ms, which is about twice faster than the ultrasound speed of 1800 ms, measured by Brillouin light scattering at Q approximately 0.01 nm(-1) at the similar hydration level. Our observations provide further evidence of the strong coupling between the internal dynamics of a DNA molecule and the dynamics of the solvent. The effect on damping and propagation of phonons along the axial direction of DNA rods due to divalent and trivalent counterions has been studied. It is found that the added multivalent counterions introduce stronger phonon damping. The phonons at the range between approximately 12.5 and approximately 22.5 nm(-1) are overdamped by the added counterions according to our model analyses. The intermediate scattering function is extracted and it shows a clear two-step relaxation with the fast relaxation time ranging from 0.1 to 4 ps. 相似文献
889.
This article presents a new ab initio force field for the cofactors of bacterial photosynthesis, namely quinones and bacteriochlorophylls. The parameters has been designed to be suitable for molecular dynamics simulations of photosynthetic proteins by being compatible with the AMBER force field. To our knowledge, this is the first force field for photosynthetic cofactors based on a reliable set of ab initio density functional reference data for methyl bacteriochlorophyll a, methyl bacteriopheophytin a, and of a derivative of ubiquinone. Indeed, the new molecular mechanics force field is able to reproduce very well not only the experimental and ab initio structural properties and the vibrational spectra of the molecules, but also the eigenvectors of the molecular normal modes. For this reason it might also be helpful to understand vibrational spectroscopy results obtained on reaction center proteins. 相似文献
890.
Klimova EI Berestneva TK Cinquantini A Corsini M Zanello P Tuscano RA Hernández-Ortega S Martínez-García M 《Organic & biomolecular chemistry》2003,1(24):4458-4464
Reactions of 2,3-diferrocenylcyclopropenone 1 with ethyl- and benzylmagnesium chlorides afford 3,3-diethyl-and 3,3-dibenzyl- 1,2-diferrocenylcyclopropenes 2 and 3, respectively, and products of nucleophilic opening of the three-membered ring resulting from the addition of RMgCl to the carbonyl group, viz., saturated ketones(4,5-diferrocenylheptan-3-ones 4a,b and 3,4-diferrocenyl-1,5-diphenylpentan-2-ones 5a,b as ca. 3: 1 mixtures of two diastereomers) and other products. The spatial structures of compounds 2 and 4a were established by X-ray diffraction analysis of single crystals. Protonation of the cyclopropenes 2 and 3 with tetrafluoroboric acid at -40 degrees C yields the corresponding 3,3-dialkyl-1 ,2-diferrocenylcyclopropylium tetrafluoroborates. Transformation of the latter into diferrocenylallylic cations upon increasing the temperature to 20 degrees C and their eprotonation under the action of N,N-dimethylaniline were studied. Electrochemical investigation of 1 and 2 shows that in both complexes the cyclopropene spacer allows electronic communication between the two outer ferrocenyl groups, this being notably greater for 2 than for 1. 相似文献