Propriedades termo-eletrônicas da molécula do DNA

Darlan Araújo Moreira

This thesis presents a comprehensive and up-to-date account of some physical properties of the DNA molecule, such as its thermodynamics (specific heat) and electronic (electronic transmissivity and localization factor, among others) aspects. The DNA molecule can be considered as a symbolic sequence of a four letter alphabet, namely guanine (G), adenine (A), cytosine (C) and thymine (T). It is usually described as a two-dimensional short-ranged correlated random chain, but nothing prevents that the DNA chain can be grown following quasi-periodic sequences as, for instance, the Fibonacci and Rudin-Shapiro ones. In order to reveal the relevance of the underlying correlations in the nucleotides distribution, we have compared the results for the genomic DNA sequence (Ch22) with those of the two artificial sequences cited above, which has long-range correlations, the Fibonacci sequence, and the Rudin-Shapiro one. The analysis of the specific heat is made considering the following suitable formalisms: the classic one, using a Maxwell- Boltzmann distribution; the quantum description, using a Fermi-Dirac distribution; and the recent discussed formalism of nonextensivity, using Tsallis entropy. The energy spectra are calculated using the one dimensional Schrödinger equation in a tight-binding approximation. We have calculated also the electronic transmissivity, the localization length, as well as a I (current) vs V (potential) curve to characterize the electronic properties of a double-strand DNA molecule. The theoretical model considered here makes use of an eective tight-binding Hamiltonian describing one electron moving in a chain with a single orbital per site and nearest-neighbor interactions, together with the Schrodinger equation and the very convenient transfer matrix technique

Propriedades termo-eletrônicas da molécula do DNA

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