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Effect of Polymer Hydration on the Kinetic Release of Drugs: A Study of Ibuprof...
Salsa, T.; Veiga, F.; Teixeira-Dias, J. J. C.; Pina, M. E.Samples of drug/hydroxypropylmethylcellulose (HPMC) mixtures and matrices (drug/HPMC mixtures plus excipients) were allowed to equilibrate in closed chambers with defined relative humidities (RHs). Their water uptake and drug release were evaluated by differential scanning calorimetry/thermogravimetric analysis and dissolution studies, respectively. Analysis of the thermal behaviors of the drug/HPMC mixtures an...
Solvent effects on 2-methoxyethanol conformers: an ab initio DFT study using th...
Gil, Francisco P. S. C.; Teixeira-Dias, J. J. C.The four stable conformers of 2-methoxyethanol, CH3O-CH2-CH2-OH (tgg', ggg', ttg and ttt) are studied by ab initio calculations using the SCRF theory and the SCI-PCModel to assess solvent effects on the structure and vibrational spectra of this compound. Full geometry optimizations were carried out at the B3LYP/6-311+G(3df,2df,2p)//B3LYP/6-31G(d) level, and normal mode calculations were performed within the har...
Hydrogen-Bonded Dimers of CH3OCH2CH2OH: Ab Initio Structures and Multivariate A...
Gil, Francisco P. S. C.; Costa, A. M. Amorim da; Bruns, Roy E.; Teixeira-Dias, J. J. C.Structures and vibrational frequencies of relevant hydrogen-bonded dimers of 2-methoxyethanol are obtained at the 3-21G*//Ah41 level (the 3-21G* basis set included polarization functions deliberately added to second period atoms) and the results analyzed by standard multivariate methods. Dimers built from the same pair of isolated monomers belong to the same homologous series. The most stable dimer is obtained ...
Conformational Analysis of CmH2m+1OCH2CH2OH (m = 1-4): The Role of CH.cntdot..c...
Gil, Francisco P. S. C.; Costa, A. M. Amorim da; Teixeira-Dias, J. J. C.Structures and energies of the more stable conformations of C ~ H ~ ~ + I O C H ~ C(HCm~EOl, Hm = 1-4) have been determined by gradient geometry refinement at ab initio level. For m = 3 (C~EIa)n d m = 4 (C~EI )t,h e results show that attractive CH-O intramolecular interactions associated with the formation of five-membered rings in the alkylic fragments of these molecules lead to the stabilization of gauche arr...
Oxygen-by-Sulfur Substitution in CH3OCH2CH2OH: An Ab Initio Comparative Study o...
Gil, Francisco P. S. C.; Costa, A. M. Amorim da; Teixeira-Dias, J. J. C.Conformational energies, structural parameters and vibrational frequencies for the tgg’, ggg’, ttg, and ttt conformers of CH~XCH~CHZY(XH, Y = 0, S) have been determined by MO ab initio calculations at the MP2/6-31G* level. The results show that the relative strength of the intramolecular X. *HY interaction in tgg’ and ggg‘ conformers diminishes gradually along the series of molecules (0,O) - (0,s) - (S,O) - (S,...
Structures and Vibrational Spectra of CH,OCH,CH,OH : The
Gil, Francisco P. S. C.; Fausto, R.; Costa, A. M. Amorim da; Teixeira-Dias, J. J. C.Ab initio calculations at the MP2/6-31G* and MP2/6-31G*//6-31G* levels have been carried out for the monomer of 2-methoxyethanol (CH,OCH,CH,OH). The MP2/6-31G* results indicate that the two more stable conformers (tGg’ and gGg‘) display intramolecular hydrogen bonds directed from the hydroxy H atom to one of the lone pairs of the ether 0 atom, and that the tGg’ conformer is 6.3 kJ mol-’ more stable than the gGg...
Rotational Isomerism in CH3CH2-C(=S)SR (R = CH3, CH2CH3): A Combined Vibrational
Fausto, R.; Martins, A. Gabriela; Teixeira-Dias, J. J. C.; Tonge, P. J.; Carey, P. R.The vibrational and conformational properties exhibited by CHsCH2C(=S)SCHs and CH~CH~C(=S)SCHZCH3 were studied by Raman and infrared spectroscopies for the liquid and solid phases, and by ab initio calculations for the isolated molecule. It is shown that these molecules tend to adopt nonsymmetricconformations near the C(=S)S group, in contrast to their oxygen analogues whose most stable conformers correspond to...
Elucidation of the conformational properties of N-formylglycine dithio acid by ...
Fausto, R.; Teixeira-Dias, J. J. C.; Carey, P. R.Ab initio SCF-MO calculations were carried out for the molecule N-formylglycine dithio acid using STO-3G and 3-21G basis sets. Structures and energies of several conformations of this molecule determined by gradient geometry refinement are reported, and some conformationally dependent local geometry trends discussed. For conformations involving rotational isomerism about the NH-CH2 and CH,-C(=S) single bonds, t...
A molecular mechanics force field for conformational analysis of aliphatic acyc...
Carvalho, L A. E. Batista de; Teixeira-Dias, J. J. C.; Fausto, R.An improved molecular mechanics force field for conformational and vibrational studies of aliphatic acyclic amines is developed. The resulting force field reproduces molecular structures adequately and provides a good fit for energy differences between conformers and barriers to internal rotation for a large number of amines. In addition, vibrational frequencies are calculated in good agreement with available e...
Raman spectroscopy and molecular mechanics in
Teixeira-Dias, J.J.C.; Fausto, R.Molecular mechanics is used to provide information on the stable conformations of the monochloroacetic acid molecule. In the most stable form, the C-C1 is in the COO plane (syn), while in the other form (gauche) the C1-C-C=O dihedral angle is in the 131O region. Thus in the syn form, the bond dipoles associated with the C-C1 and CEO bonds are approximately aligned, leading to a C=O bond stronger than in the les...
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