Impact of chemical and structural anisotropy on the electrophoretic mobility of spherical soft-multilayer particles: the case of bacteriophage MS2
Jeremie Langlet 1, Fabien Gaboriaud 1, Christophe Gantzer 1 and Jerome F.L. Duval 2*
1 Laboratory of Physical Chemistry and Microbiology for the Environment, Nancy-University, CNRS
2 Laboratory Environment and Mineral Processing, Nancy-University, CNRS
* To whom correspondence should be addressed. E-mail: jerome.duval{at}ensg.inpl-nancy.fr.
Submitted on June 21, 2007
Revised on September 26, 2007
Accepted on 8 November 2007
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Abstract |
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We report a theoretical investigation of the electro-hydrodynamic properties of spherical soft particles composed of permeable concentric layers that differ in thickness, soft material density, chemical composition and flow penetration degree. Starting from a recent numerical scheme developed for the computation of the DC electrophoretic mobility [µ) of diffuse soft bioparticles, the dependence of µ on the electrolyte concentration and solution pH is evaluated taking the known 3-layers structure of bacteriophage MS2 as a supporting model system (bulk RNA, RNA-protein bound layer and coat protein). The electrokinetic results are discussed for various layer thicknesses, hydrodynamic flow penetration degrees, chemical compositions and are commented on the basis of the equilibrium electrostatic potential and hydrodynamic flow field profiles that develop within and around the structured particle. This study allows for identifying the cases where the electrophoretic mobility is a function of the inner structural and chemical specificity of the particle and not only of its outer surface properties. Along these lines, we demonstrate the general inapplicability of the notions of zeta-potential (z) and surface charge for quantitatively interpreting electrokinetic data collected for such systems We further shed some light on the physical meaning of the iso-electric point (iep). In particular, numerical and analytical simulations performed on structured soft layers in indifferent electrolytic solution demonstrate that the iep is a complex ionic-strength dependent signature of the flow permeation properties and chemical and structural details of the particle. Finally, electrophoretic mobilities of MS2 virus measured at various ionic strength levels and pH values are interpreted on the basis of the theoretical formalism aforementioned. It is shown that the electrokinetic features of MS2 are for a large extent determined not only by the external proteic capsid but also by the chemical composition and hydrodynamic flow permeation of/within the inner RNA-protein bound layer and bulk RNA part of the bacteriophage. The impact of virus aggregation, as revealed by decreasing diffusion coefficients for decreasing pH values, is also discussed.
Key Words:
RNA, aggregation, chemical heterogeneity, proteic capsid, soft particle electrophoresis, virus
