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Papers by Claudio Contreras Aburto

The Journal of Chemical Physics, 2016

The topological analysis tool known as the common neighbor analysis (CNA) is used for the first t... more The topological analysis tool known as the common neighbor analysis (CNA) is used for the first time in this work to analyze crystallization kinetics and excess entropy of charge-stabilized colloidal suspensions. For this purpose, Brownian dynamics computer simulations are implemented to investigate the crystallization kinetics of homogeneously melted colloidal crystals that are composed of hard-core-screened-Coulomb interacting particles. The results are in agreement with recent static structure factor measurements that could indicate the presence of icosahedral units in the metastable melt, and with the fact that weakly screened charged colloids crystallize into body-centered-cubic (bcc) ordering. A two-step crystallization pathway is found, in which the population of bcc-subunit CNA-pairs satisfactorily obeys a Verhulst model. Moreover, the CNA helped to unveil that the excess entropy obeys a quasi-universal functional form, relating the behavior of colloidal, molecular, and meta...

Archives of Biochemistry and Biophysics, 1984

The electrical properties of sarcoplasmic reticulum vesicles were studied using electrophoretic m... more The electrical properties of sarcoplasmic reticulum vesicles were studied using electrophoretic mobility measurements by laser Doppler velocimetry. Combined with quasielastic light scattering analysis, this method enabled us to monitor changes in membrane surface charge density upon addition of NaCl, CaC12, and MgC12 solutions. At low ionic strength (4.7 mM), and in the absence of divalent salts, sarcoplasmic reticulum vesicles displayed a zeta potential value of-32.6 mV and a surface charge density of 5.4 lop3 C/m2, corresponding to one elementary negative charge per 30 nm2 or about 2900 negative charges per vesicle. Upon addition of NaCl (up to 100 mM) vesicles became more negative (from 2900 to 6200 negative charges per vesicle), suggesting chloride binding or adsorption on the membrane. A noticeable increase of the vesicular size was observed upon addition of calcium or magnesium (25 to 30% increase of the hydrodynamic radius for 2.5 mM CaCl, or MgC12). This effect was prevented or suppressed by addition of relatively low concentrations of NaCl(50 mM). At low divalent cation concentrations one-third of the total net charge of the vesicles was neutralized suggesting a specific binding of cation on the membrane. At higher salt concentrations no modification of this parameter was observed. These results support the Gouy and Chapman theory about the electrical properties of sarcoplasmic reticulum vesicles.

The Journal of Chemical Physics, 2014

The long-time self-diffusion coefficient, D L , of charged spherical colloidal particles in paral... more The long-time self-diffusion coefficient, D L , of charged spherical colloidal particles in parallel planar layers is studied by means of Brownian dynamics computer simulations and mode-coupling theory. In the model, all particles interact with each other via the screened Coulomb potential, regardless which layer they are located on, and there is no particle transfer between layers. As a result of the geometrical constraint, the simulations show that D L is conveniently controlled by the separation between layers. On the basis of the so-called contraction of the description formalism [J. Chem. Phys. 132, 174111 (2010)], the effective potential between particles in a layer is obtained by integrating out the degrees of freedom of particles in the remaining layers. The effective potential is used in a Brownian dynamics computer simulation of the effective one-layer system. We find that the D L determined from the simulations of the effective one-layer system is different from the D L determined via the simulations of the full system.

EPISTEMUS, 2016

Las técnicas de simulación computacional se usan extensivamente para estudiar sistemas biológicos... more Las técnicas de simulación computacional se usan extensivamente para estudiar sistemas biológicos, y en general, materiales sólidos y blandos. Debido a la complejidad de los fenómenos biológicos, y a la imposibilidad de estudiar teóricamente el comportamiento de sistemas tales como proteínas y membranas, la simulación computacional se utiliza para estudiar la estructura y dinámica de estos sistemas en diferentes escalas temporales. En este artículo describiremos brevemente algunas de las técnicas de simulación computacional más utilizadas en Biología: la Dinámica Molecular, la Dinámica Browniana y el Método de Monte Carlo. Nuestra intención es proporcionar un panorama introductorio de la utilidad de los métodos de simulación molecular en Biología.

The Journal of Chemical Physics, 2013

We develop a general method for calculating conduction-diffusion transport properties of strong e... more We develop a general method for calculating conduction-diffusion transport properties of strong electrolyte mixtures, including specific conductivities, steady-state electrophoretic mobilities, and selfdiffusion coefficients. The ions are described as charged Brownian spheres, and the solvent-mediated hydrodynamic interactions (HIs) are also accounted for in the non-instantaneous ion atmosphere relaxation effect. A linear response expression relating long-time partial mobilities to associated dynamic structure factors is employed in our derivation of a general mode coupling theory (MCT) method for the conduction-diffusion properties. A simplified solution scheme for the MCT method is discussed. Analytic results are obtained for transport coefficients of pointlike ions which, for very low ion concentrations, reduce to the Deby-Falkenhagen-Onsager-Fuoss limiting law expressions. As an application, an unusual non-monotonic concentration dependence of the polyion electrophoretic mobility in a mixture of two binary electrolytes is discussed. In addition, leading-order extensions of the limiting law results are derived with HIs included. The present method complements a related MCT method by the authors for the electrolyte viscosity and shear relaxation function [C. Contreras-Aburto and G. Nägele, J. Phys.: Condens. Matter 24, 464108 (2012)], so that a unifying scheme for conduction-diffusion and viscoelastic properties is obtained. We present here the general framework of the method, illustrating its versatility for conditions where fully analytic results are obtainable. Numerical results for conduction-diffusion properties and the viscosity of concentrated electrolytes are presented in Paper II [C.

An unbalanced composition of lipids and proteins in brain membranes is related to the appearance ... more An unbalanced composition of lipids and proteins in brain membranes is related to the appearance neurodegenrative diseases and recent investigations show that the 14-3-3 tau protein might relate to some of these diseases. This article reports results from a coarse-grained model brain membrane with and without a 14-3-3 τ/θ protein inside the membrane. We investigated the symmetrized partial density, thickness, diffusion coefficients, and deuterium order parameters of the membrane with and without protein. We observe a slight increase in heads and linkers in the symmetrized partial density of the membrane with the protein inserted and higher values of the deuterium order parameters for the brain model membrane with protein. We observe a reduction in the diffusion coefficient of the fluid membrane in the presence of the transmembrane tau protein. Our findings show that the protein can modify the structural and dynamical properties of the membrane. This work will serve as a guide for fu...

Journal of Statistical Mechanics: Theory and Experiment