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Molecular structures of cis- and trans-S-Ethyl thiocrotonate. A combined vibrat...
Fausto, Rui; Tonge, Peter J.; Carey, Paul R.Ab initio 6-31G* SCF-MO calculations have been carried out for cis- and trans-S-ethyl thiocrotonate [cis- and trans- CH3—CHCH—C(O)SCH2CH3]. Fully optimized geometries, relative stabilities, dipole moments and harmonic force fields for several conformers of these molecules have been determined and the results compared with those of similar molecules. Combined with FTIR spectroscopic data, the theoretical results...
Five isomers of monomeric cytosine and their interconversions induced
Lapinski, Leszek; Igor Reva, Igor Reva; Nowak, Maciej J.; Fausto, RuiPhotoisomerization processes involving five isomers of cytosine were induced by narrowband tunable UV irradiation of matrix-isolated monomers of the compound. Irradiation of an argon matrix containing cytosine monomers with UV l = 313 nm laser light resulted in syn2anti photoisomerizations between the two imino–oxo forms, whereas the substantially more populated amino–hydroxy and amino–oxo forms stayed intact. ...
Molecular modeling of the interaction of novel hydroxy- and aminobisphosphonate...
Duarte, Luís F.; Teixeira, Fátima C.; Fausto, RuiBisphosphonates (BPs) are a class of drugs widely used in the treatment of several metabolic bone disorders associated with increased bone resorption. Although BPs can directly inhibit the cellular activity of osteoclasts, their ability to adsorb on bone mineral is also an important factor in determining their potency and duration of action. In this study, we performed a molecular mechanics analysis of the mole...
Cycloaddition of trifluoromethyl azafulvenium methides: synthesis of new triflu...
Nunes, Cláudio M.; Silva, Manuela Ramos; Beja, Ana Matos; Fausto, Rui; Melo, Teresa M.V.D. Pinho eThe chemistry of trifluoromethyl azafulvenium methides was explored leading to a new route to trifluoromethylpyrrole-annulated systems. The first evidence of azafulvenium methides acting as 1,3-dipoles is reported. These azafulvenium methides showed site selectivity in the reaction with strong electron-deficient dipolarophiles leading exclusively to 1,3-cycloadducts. In the cycloaddition with less-activated dip...
Infrared Spectra and Photochemistry of Matrix-Isolated Pyrrole-2-carbaldehyde
Giuliano, Barbara Michela; Reva, Igor; Fausto, RuiMonomeric pyrrole-2-carbaldehyde (P2C) was isolated in low-temperature argon and xenon matrices, and its UV-induced photochemistry was studied. The structures of the reagent as well as the reaction photoproducts were characterized by FTIR spectroscopy. Interpretation of the experimental results was assisted by theoretical calculations carried out at the MP2 and DFT (B3LYP) levels with the 6-311++G(d,p) basis se...
Thermal and Photoinduced Control of Relative Populations of 4-Methoxybenzaldehy...
Kus, Nihal; Sharma, Archna; Reva, Igor; Lapinski, Leszek; Fausto, RuiTwo almost isoenergetic conformers of 4-methoxybenzaldehyde (p-anisaldehyde), O-trans and O-cis, are nearly equally populated in gas phase at room temperature. The existence of these two conformers of similar energy makes p-anisaldehyde an attractive molecule for conformational investigations, in which the relative populations of the two forms might be subjected to optical control. In the present study, monomer...
Positive Identification of UV-Generated, Non-Hydrogen-Bonded Isomers of o-Hydro...
Lapinski, Leszek; Rostkowska, Hanna; Reva, Igor; Fausto, Rui; Nowak, Maciej J.Non-hydrogen-bonded isomers were photogenerated by UV (λ > 335 nm) irradiation of o-hydroxybenzaldehyde (salicylaldehyde) and o-hydroxyacetophenone monomers isolated in low-temperature Ar matrixes. These photoisomerizations were found to be photoreversible. Upon shorter wavelength (λ > 235 nm or λ > 270 nm) UV irradiation, the initial forms of the compounds (with intramolecular hydrogen bonds) were partially re...
Conformation, structure, quadrupole coupling constants and van der Waals potent...
Velino, Biagio; Evangelisti, Luca; Caminati, Walther; Fausto, RuiThe rotational spectra of the 35Cl2 and 35Cl37Cl species of dichloromethane–argon have been investigated by molecular beam Fourier-transform microwave spectroscopy. Information on the configuration, structure and internal dynamics of the complex has been obtained, and the 35Cl and 37Cl quadrupole coupling constants have been determined, based on the experimental data.
Infrared spectra of methyl isocyanate isolated in Ar, Xe and N2 matrices
Reva, Igor; Lapinski, Leszek; Fausto, RuiThe infrared spectra of methyl isocyanate monomer isolated in cryogenic argon, xenon and nitrogen matrices were studied. Interpretation of the experimental results was supported by harmonic and anharmonic calculations carried out at the DFT, MP2 and CCSD levels of approximation. Spectral indicators of the molecule structural flexibility were examined, the most striking of these being the multiplet structure of ...
Conformational study of arbutin by quantum chemical calculations and multivaria...
Araujo-Andrade, Cuauhtémoc; Lopes, Susy; Fausto, Rui; Gómez-Zavaglia, AndreaA conformational study of the molecule of arbutin (4-hydroxyphenyl-β-d-glucopyranoside) has been undertaken. The molecule is composed by a glucopyranoside moiety bound to a phenol ring. It has eight conformationally relevant dihedral angles, five of them related with the orientation of the hydroxyl groups and the remaining three taking part in the skeleton of the molecule. A systematic search on the conformatio...
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