Navegando por Autor "Almeida, Wagner Batista de"
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Item A comparison of Li + transport in dimethoxyethane, poly(ethylene oxide) and poly(tetramethylene oxide) by molecular dynamics simulations.(2002) Ferreira, Beatriz Alves; Plathe, Florian Müller; Bernardes, Américo Tristão; Almeida, Wagner Batista dePure dimethoxyethane (DME), poly(ethylene oxide) (PEO) and poly(tetramethylene oxide) (PTME) and their binary mixtures with LiI were investigated by molecular dynamics simulations (Li/O proportion equal to 1:8). The properties analyzed included the relative occurrence of trans and gauche population for selected torsions, radial distribution functions, mean square fluctuations and mobilities. We studied the relation between the ionic transport process of Li + and the conformational behavior in DME, PEO and PTME systems. We investigated the solvation shell around Li + in those systems. The gauche effect of DME and PEO (OCCO torsion) is strongly related to salt addition. This effect is more pronounced in DME-based systems. Li + /O co-ordination occurs in all considered systems. The mobility of the ionic species is larger in DME than in the polymers. In PTME, it is only slightly smaller than in PEO.Item Computer simulation of polydioxolane (PDXL) and poly(tetrahydrofuran) (PTHF) : a comparative study of some poly(ethylene oxide) (PEO) properties.(2001) Ferreira, Beatriz Alves; Bernardes, Américo Tristão; Almeida, Wagner Batista deClassical methods (molecular mechanics and molecular dynamics) and semiempirical calculations were applied to study structural and energetic properties of polydioxolane (PDXL) and poly(tetrahydrofuran) (PTHF). Then, these properties were compared with poly(ethylene oxide) (PEO) in order to investigate the possibility of using PDXL and PTHF as an alternative to PEO based systems. It was found that the behaviour of molecular simulation is similar for all of them, with the folded structure observed in equilibrium. It was noted that the main contribution to potential energy is due to electrostatic term. The O/C ratio and oxygen atom positions have a strong in¯uence on charge distribution. Semiempirical calculations of free energy including enthalpic, entropic and zero point energy (ZPE) contributions showed that the folding process is favourable for PEO, PTHF and PDXL at 300 and 400 K.Item Conformational study of naringenin in the isolated and solvated states by semiempirical and AB Initio methods.(1999) Perry, Katia da Silva Peixoto; Nagem, Tanus Jorge; Almeida, Wagner Batista deNaringenin is a natural widespread flavanone occurring in different foodstuffs that presents several important biological activities. Although its properties are well documented, its mechanisms of action are still controversial. The present article reports a conformational analysis of naringenin, using the semiempirical AM1 and ab initio methods, at the Hartree-Fock level of theory. The 3-21G, 3-21G*, 6-31G, and 6-31G** basis sets were used. The electron correlation effects were included through the M011er-Plesset second-order perturbation theory. The solvation of naringenin has been investigated through the standard SCRF, the supermolecule (SM), and the combined SM/SCRF models. The results have shown that there are two degenerate forms of naringenin, differing mainly by the orientation of a hydroxyl group (C4'—OH). The energy barrier for the interconversion between them is ca. 6 kcal.mol-1, suggesting some conjugation between the p-system of the aromatic B ring and the hydroxyl group (C4'—OH).Item Theoretical study of solvent and temperature effects on the behaviour of poly(ethylene oxide) (PEO).(1999) Ferreira, Beatriz Alves; Santos, Helio Ferreira dos; Bernardes, Américo Tristão; Silva, Glaura Goulart; Almeida, Wagner Batista deMolecular mechanics and molecular dynamics simulations were applied in order to study the behaviour of poly ethylene. oxide PEO in different temperatures and solvents. It was found that over the temperature range of 50–500 K the equilibrium structure of PEO is folded. Both kinetic and potential energies increase with temperature. The behaviour of PEO . in two different solvents – CHCl « s5 and H O « s80 – was found to be similar, with the folded structure observed 32 in equilibrium. The solvation energy calculated using the GBrSA model yielded essentially the same value in CHCl and H2O.