Biomedical subjects

Marcelo Galván

Publications and source records attributed to Marcelo Galván.

5 recordsLinked to original sources

PubMed2006

Potential energy landscape of monolayer-surface systems governed by repulsive lateral interactions: the case of (3 x 3)-I-Pt(111).

Combined density functional theory (DFT) and Monte Carlo (MC) approach is applied to study the potential energy landscape of four iodine atoms adsorbed on the Pt(111) surface in a (3 x 3) unit cell. Three critical points were identified: (3 x 3)-sym and (3 x 3)-asym, corresponding to structures well known from experimental studies, while the third one (3 x 3)-zigzag is a new structure not reported before. An interaction model fitted to DFT calculations allows us to explain the difference between arrangements of iodine monolayer in vacuum, air, and solution environments as a result of different repulsion regimes.

Journal Article↗

PubMed2006

Effect of double bonds on the conducting properties of ciguatoxin 3C and tetrahydropyrane-based polymers: a theoretical study.

The electronic structure of the ciguatoxin 3C is analyzed through the Kohn-Sham model by using two different kinds of basis sets: localized basis set (Gaussian functions) and nonlocalized basis set (plane wave functions). With the localized basis functions, two approximations are used for the exchange-correlation functional: the local density approximation and the generalized gradient approximation. With the nonlocalized basis set, just the local density approximation is used. The energy gap, obtained from the frontier molecular orbitals, for this molecule predicts that this system is a semiconductor, even when the number of double bonds is increased inside the structure. However, as large molecules built with the basic unit--the tetrahydropyrane--of the ciguatoxin 3C are found in nature, it suggests studying the gap in polymeric systems built with the basic unit of this molecule. It is demonstrated that the presence of double bonds reduces considerably the gap, indicating the possibility of forming conducting materials by introducing double bonds in this kind of molecular systems. Thus, molecules strongly linked with biological systems can be used as precursor to build electric conducting systems.

Ciguatoxins↗

PubMed2005

Structural transitions in the polyalanine alpha-helix under uniaxial strain.

We analyzed the response to strain of an infinite polyalanine chain in the alpha-helical conformation using density functional theory. Under compressive strain the alpha-helix is found to undergo structural transitions to a pi-helix when the length of the helix is reduced by more than 10%. Under tensile strain the structure changes into a 3(10)-helix when the length is stretched by more than 10%. Our analysis of these transitions shows that they proceed essentially in two steps: At first there is mainly a length change, and only with some delay the helix twist adjusts.

Journal Article↗

PubMed2005

Substituent effects.

Inductive and resonance effects of different substituents (CH3, Cl, NH3, CN, NO2) on the reactivity of the nitrogen and oxygen centers of several saturated and unsaturated hydroxylamine derivates toward hard and soft electrophiles are analyzed in terms of various conceptual DFT based descriptors calculated using B3LYP/6-311G** method. In most cases, the +/-I and +/-M effects are correctly described by these descriptors. The way the substituent effect dies down as the distance between the substituent and the active center increases is also analyzed. It is observed that more than one effect is to be considered to properly understand the effect of a substituent on reactivity.

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PubMed2004

Basis set effects on frontier molecular orbital energies and energy gaps: a comparative study between plane waves and localized basis functions in molecular systems.

In order to study the Kohn-Sham frontier molecular orbital energies in the complete basis limit, a comparative study between localized functions and plane waves, obtained with the local density approximation exchange-correlation functional is made. The analyzed systems are ethylene and butadiene, since they are theoretical and experimentally well characterized. The localized basis sets used are those developed by Dunning. For the plane-waves method, the pseudopotential approximation is employed. The results obtained by the localized basis sets suggest that it is possible to get an estimation of the orbital energies in the limit of the complete basis set, when the basis set size is large. It is shown that the frontier molecular orbital energies and the energy gaps obtained with plane waves are similar to those obtained with a large localized basis set, when the size of the supercell and the plane-wave expansion have been appropriately calibrated.

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