Carboxylated Ficolls:  Preparation, Characterization, and Electrophoretic Behavior of Model Charged Nanospheres

Abstract

Carboxylated ficolls were prepared as model spherical colloids of variable charge and size, with radii ranging from 3.0 to 19.3 nm. Capillary electrophoresis (CE), electrophoretic light scattering (ELS), and potentiometric titration were used to determine mobilities as a function of pH, degree of ionization R, and surface potential ψ 0 . Measured mobilities typically display a plateau at high pH, corresponding to high R and ψ 0 , confirming the general nature of this effect for charged spheres, seen also for charged dendrimers and charged latex particles. This result is examined in the context of a discontinuity in mobility predicted by the Wiersema, O'Brien, and White (WOW) theory and a more recent primitive model electrophoresis (PME) theory, in which bound counterions are considered either as point charges or as hard spheres. While no mobility maximum can be determined as expected by these two theories, our data seem more to support Belloni's theoretical expectations on charged polymers and spheres. Here we explain the mobility plateaus in terms of counterions accumulated close to the surface (surface potential-determining ions) or within the shear plane (mobilitydetermining ions).

Modulation of Polyelectrolyte–Micelle Interactions via Zeta Potentials

“…While only measurements of the ζ potential are available for nontitratable polyelectrolytes, Cleland et al obtained a relationship between μ 0 and ζ using hyaluronic acid . Thus, the following equation can be used to obtain “surface” potential from zeta potential: While the electrostatic potential at the shear plane is not necessarily equal to that experienced by the micelles upon binding, we can empirically test the correlation between ζ PE and the micelle binding affinity as given by Y c . The values obtained for ζ PE in 0.4 M NaCl are +19.2 ± 0.8 mV for PDADMAC and +24.0 ± 1.6 mV for PTMAEMC (i.e., ∼25% larger for PTMAEMC).…”

“…The micelle surface potential was obtained using atitratable probe according to a procedure described elsewhere . Dodecanoic acid, C 11 COOH, was used as a micelle-solubilized probe at a molar ratio of 1:20 with respect to 20 mM nonionic surfactant.…”

“…After complete dissolution, the solution was cooled and titrated at room temperature with 0.500 N HCl. Inflection points in the titration curve were observed at α = 1 and α = 0. , The mean value of pH + log­[(1 – α)/α] between α = 0.2 and α = 0.8 was used to determine p K a (p K 0 in the case of SDS-free solutions). The surface potential of the mixed micelles, ψ 0 , was then calculated via where kT / e = 25.6 mV at 24 °C.…”

“…The micelle surface potential was obtained using atitratable probe according to a procedure described elsewhere. 36 Dodecanoic acid, C 11 COOH, was used as a micellesolubilized probe at a molar ratio of 1:20 with respect to 20 mM nonionic surfactant. pH titrations were performed in polymer-free solutions of varying Y using a temperature-compensated Orion 811 pH meter and a model 91-00-02 combination electrode.…”

Light scattering studies on Ficoll PM70 solutions reveal two distinct diffusive modes

“…The most common method of separating mixed populations of biological particles is centrifugation in density gradients. It was recognized, from the mid 1960s that Ficolls are suitable in forming density gradients for separating biological particles, such as osmotically sensitive cells or various organelles [1][2][3][4][5]. Ficolls are also important as molecular crowding agents, contributing to a variety of interesting topics mimicking the dense cellular environment [6][7][8].…”