On the ionic strength dependence of the electrophoretic mobility: From 2D to 3D slope-plots.

Determining the charge and the nature (small ion, nanoparticle, or polyelectrolyte) of an unknown solute from its electrophoretic characteristics remains a challenging issue. In this work, we demonstrate that, if the knowledge of the effective electrophoretic mobility (μ ) at a given ionic strength is not sufficient to characterize a given solute, the combination of this parameter with (i) the relative decrease of the electrophoretic mobility with the ionic strength (S), and (ii) the hydrodynamic radius (R ), is sufficient (in most cases) to deduce the nature of the solute and its charge. These three parameters are experimentally accessible by CZE and Taylor dispersion analysis performed on the same instrumentation.

Specific ion effects on the electrophoretic mobility of small, highly charged peptides: a modeling study.

In this work, we use coarse-grained modeling to study the free solution electrophoretic mobility of small highly charged peptides (lysine, arginine, and short oligos thereof (up to nonapeptides)) in NaCl and Na2SO4 aqueous solutions at neutral pH and room temperature. The experimental data are taken from the literature. A bead modeling methodology that treats the electrostatics at the level of the nonlinear Poisson Boltzmann equation developed previously in our laboratory is able to account for the mobility of all peptides in NaCl, but not Na2SO4.

The electrophoretic mobility of a weakly charged "soft" sphere in a charged hydrogel: application of the Lorentz reciprocal theorem.

The electrophoretic mobility of a dilute, weakly charged "soft" particle in a charged hydrogel modeled as an effective medium is investigated in this work. This is closely related to previous work (Li, F.; Allison, S.

Nanoparticle gel electrophoresis: soft spheres in polyelectrolyte hydrogels under the Debye-Hückel approximation.

A mathematical model for electrophoresis of polyelectrolyte coated nanoparticles (soft spheres) in polyelectrolyte hydrogels is proposed, and evaluated by comparison to literature models for bare-sphere gel electrophoresis and free-solution electrophoresis. The utilities of approximations based on the bare-particle electrophoretic mobility, free-solution mobility, and electroosmotic flow in hydrogels are explored. Noteworthy are the influences of the particle-core dielectric constant and overlap of the polyelectrolyte shell.

Coarse-grained modeling of the titration and conductance behavior of aqueous fullerene hexa malonic acid (FHMA) solutions.

The coarse-grained continuum primitive model is developed and used to characterize the titration and electrical conductance behavior of aqueous solutions of fullerene hexa malonic acid (FHMA). The spherical FHMA molecule, a highly charged electrolyte with an absolute valence charge as large as 12, is modeled as a dielectric sphere in Newtonian fluid, and electrostatics are treated numerically at the level of the non-linear Poisson-Boltzmann equation. Transport properties (electrophoretic mobilities and conductances) of the various charge states of FHMA are numerically computed using established numerical algorithms.

Extracting information from the ionic strength dependence of electrophoretic mobility by use of the slope plot.

The effective mobility (μ(ep)) is the main parameter characterizing the electrophoretic behavior of a given solute. It is well-known that μ(ep) is a decreasing function of the ionic strength for all solutes. Nevertheless, the decrease depends strongly on the nature of the solute (small ions, polyelectrolyte, nanoparticles).

Determination of effective charge of small ions, polyelectrolytes and nanoparticles by capillary electrophoresis.

In this paper, a systematic and comparative study related to the effective charge determination of three kinds of solutes (small ions, polyelectrolytes and nanoparticles) was performed. Four approaches were compared regarding their conditions of validity and their advantages/disadvantages. Three of them allow the effective charge determination from the electrophoretic mobility and the hydrodynamic radius of the solutes using electrophoretic mobility modelings based on Nernst-Einstein (NE), O'Brien-White-Ohshima (OWO) and Yoon and Kim (YK) equations.

Modeling the electrophoresis of highly charged peptides: application to oligolysines.

The "coarse-grained" bead modeling methodology, BMM, is generalized to treat electrostatics at the level of the nonlinear Poisson-Boltzmann equation. This improvement makes it more applicable to the important class of highly charged macroions and highly charged peptides in particular. In the present study, the new nonlinear Poisson-Boltzmann, NLPB-BMM procedure is applied to the free solution electrophoretic mobility of low molecular mass oligolysines (degree of polymerization 1-8) in lithium phosphate buffer at pH 2.

Modeling the electrophoresis of oligolysines.

CE is used to measure the electrophoretic mobility of low molecular mass oligo-L-lysines (n=1-8) in aqueous LiH₂PO₄ buffer, BGE, at pH 2.5 over a range of temperatures (25-50 °C) and ionic strengths (10-100 mM). Mobilities are corrected for Joule heating and under the conditions of the experiment, interaction of the peptides with the capillary walls can be ignored.

Numerical solution of the nonlinear Poisson-Boltzmann equation for a macroion modeled as an array of non overlapping beads.

In this work, an approximate numerical procedure, AB, is developed to solve the nonlinear Poisson-Boltzmann equation around a macroion modeled as an array of non overlapping beads containing charges placed at their centers. The bead radii, their charges, and the relative bead configuration are arbitrary. In the limit of a single bead of arbitrary charge, the AB procedure is exact.

Modeling the electrophoresis and transport of peptides: the effective sphere model and complex formation.

Modeling the electrophoretic mobility of peptides is examined in this study using a "coarse grained" bead model, or B model for short 8 and also a simpler "effective sphere" (ES) model. A comparison between the B and ES models is carried out for peptide models covering a broad range of ionic strength, peptide charge, and peptide length. At ionic strengths lower than approximately 0.

Modeling the electrophoresis of oligoglycines.

The electrophoretic mobility of low molecular mass oligoglycines is examined in this study using a "coarse-grained" bead modeling methodology [Pei, H., Allison, S. A.

The dependence of the electrophoretic mobility of small organic ions on ionic strength and complex formation.

The ionic strength dependence of the electrophoretic mobility of small organic anions with valencies up to -3 is investigated in this study. Provided the anions are not too aspherical, it is argued that shape and charge distribution have little influence on mobility. To a good approximation, the electrophoretic mobility of a small particle should be equal to that of a model sphere with the same hydrodynamic radius and same net charge.

Viscosity of dilute model bead arrays at low shear: inclusion of short range solute-solvent interactions.

The intrinsic viscosity, [eta], of certain polymer-solvent systems, such as alkanes in benzene, are "anomalous" in the sense that [eta] for low molecular weight fractions are low and in certain cases negative (Dewan, K. K.; Bloomfield, V.

Translational diffusion constants of short peptides: measurement by NMR and their use in structural studies of peptides.

In this work, pulsed field gradient NMR is used to measure the translational self-diffusion constants (D(T)'s) of five simple peptides (GG, GR, GGR, GGNA, and GGRA) as well as glycine, G, at low concentration. The experiments were carried out in D(2)O at 298 K at pD = 3.5 in 80 mM sodium phosphate buffer.

Viscosity of dilute suspensions of rigid bead arrays at low shear: accounting for the variation in hydrodynamic stress over the bead surfaces.

In this work, we examine the viscosity of a dilute suspension of irregularly shaped particles at low shear. A particle is modeled as a rigid array of nonoverlapping beads of variable size and geometry. Starting from a boundary element formalism, approximate account is taken of the variation in hydrodynamic stress over the surface of the individual beads.

Using electrophoretic mobility and bead modeling to characterize the charge and secondary structure of peptides.

Using a modeling methodology developed in our laboratory previously, the free solution electrophoretic mobilities of several peptides are examined to see what they can tell us about: (i) the pK(a)s of specific side groups, and (ii) possible secondary structure. Modeling is first applied to mobility versus pH data of several small peptides (Messana, I. et al.

Modeling the free solution and gel electrophoresis of biopolymers: the bead array-effective medium model.

Free solution and gel electrophoresis is an extremely useful tool in the separation of biopolymers. The complex nature of biopolymers, coupled with the usefulness of electrophoretic methods, has stimulated the development of theoretical modeling over the last 30 years. In this work, these developments are first reviewed with emphasis on Boundary Element and bead methodologies that enable the investigator to design realistic models of biopolymers.

Electrophoresis of spheres with uniform zeta potential in a gel modeled as an effective medium.

The effective medium model [H.C. Brinkman, Appl.

Translational diffusion constants of the amino acids: measurement by NMR and their use in modeling the transport of peptides.

In this work, the translational self-diffusion constants, DT's, of 12 amino acids (Ala, Arg, Asn, Asp, Cys, Glu, His, Ile, Lys, Met, Phe, and Ser) are measured by field gradient NMR and extrapolated to infinite dilution. The experiments were carried out in D2O at 298 K at pD approximately =3.5 in 50 mM sodium phosphate buffer.

Modeling the electrophoretic mobility and diffusion of weakly charged peptides.

A bead model to determine the electrophoretic mobilities and translational diffusion constants of weakly charged peptides is developed that is based on a approximate structural model of peptides and is also grounded in electrohydrodynamic theory. A peptide made up of X amino acids is modeled as N=2X beads with 2 beads representing each amino acid in the chain. For the two beads representing a particular amino acid in a peptide, the radius of one bead is set to one-half the nearest neighbor Calpha-Calpha distance, and the radius of the other bead is chosen on the basis of the diffusion constant of the free amino acid.

Electrokinetic transport of rigid macroions in the thin double layer limit: a boundary element approach.

A boundary element (BE) procedure is developed to numerically calculate the electrophoretic mobility of highly charged, rigid model macroions in the thin double layer regime based on the continuum primitive model. The procedure is based on that of O'Brien (R.W.

Use of T4 lysozyme charge mutants to examine electrophoretic models.

The electrophoretic mobility of a macro-ion is affected in a complex manner by a variety of forces that arise from the applied field. Coupling of the macro-ion and small-ion flows gives rise to non-conserved forces that are greater than those expected from ordinary hydrodynamic considerations. It is difficult to separate the steady-state hydrodynamic and electrodynamic contributions to the macro-ion mobility.

Modeling the gel electrophoresis of short duplex DNA by Brownian dynamics: cubic gel lattice with direct interaction.

The technique of Brownian dynamics is used to model the electrophoretic mobility of spherical and rod-like particles in a three-dimensional cubic gel lattice. In addition to excluded volume interactions between the migrating particle and the gel, direct interactions are also included. The methodology is first applied to spherical particles in the absence of direct interactions and the resulting mobilities are shown to agree with independent studies.