Relaxação em sistemas moleculares complexos / Relaxation in complex molecular systems

AUTOR(ES)

Milton Taidi Sonoda

DATA DE PUBLICAÇÃO

2005

RESUMO

In this Thesis are presented studies by Molecular Dynamics simulations on some molecular systems presenting complex dynamics behavior (i.e., relaxation process caracterized by multiple time scales), including saccharides aqueous solutions, double helix DNA systems, air/water interfaces containing surfactants, and supercooled water. These systems, although clearly distinct, present common points concerning their dynamical properties. In saccharides aqueous solutions, we found clusters of solute molecules stabilized by hydrogen bonds which, depending on the concentration, can be percolated through the whole extension of the system. The water molecules are located within pools created by cavities in this cluster and present very slow dynamic due to confinement. Results of various properties are computed and compared to recent experimental NRM, neutron scattering, and dielectric relaxation data. We studied dynamical process of a double helix DNA using the Generalized Born (GB) Solvation model and compared with results of simulation using the explicit solvation. We observed that the GB model captures the properties of DNA structure, as well the short time dynamics of the DNA bases. However, the slower component of the relaxation are not well described by the implicit solvation model. In the interfacial systems, we studied the solvation dynamics of an adsorbed coumarin at the air/water interface in the presence of anionic surfactant (SDS) at different surface coverage. We found that the principal slow component of relaxation is associated to the interconvertion of two preferention solvation states of the coumarin. Implications of this result to recent non-linear optical spectroscopy experiment are discussed. Finally, we studied the structural relaxation of liquid water in supercooled states through simulation of the non-linear optical Kerr effect and compared to recent experimental findings.

ASSUNTO(S)

dna solution soluções de frutose efeito kerr optico da agua optical kerr effect of water solução de dna interface agua-ar air-water interface fructose solutions

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