ELECTROKINETIC ASPECTS OF SURFACE CHEMISTRY

Abstract

In a recent communication, Moyer and Moyer (1) have shown that particles of quartz and collodion attain different electrophoretic mobilities after being exposed to dilute horse serum.The electrophoretic mobility-pa curve for the collodion particles in serum agreed completely with the curve obtained for particles in solutions of the serum globulin fraction.Comparison of the behavior of the quartz particles with the electric mobility curves of the two albumin constituents, A and B, isolated by the method of Kekwick (2), showed that the quartz when in serum becomes coated with a film resembling albumin A. The conclusions of Kekwick with regard to the identity of the electrophoretic behavior of the dissolved albumins A and B were substantiated by the measurements on the adsorbed albumins but only over the narrow pH range near the isoelectric point which he investigated (pH 4.0 to 5.5).At either end of this range, the mobility of adsorbed albumins A and B was different, with albumin A moving more slowly than B (1).By comparing their data with those of Tiselius (3) for the electrophoresis of the protein constituents in diluted serum, Moyer and Moyer concluded that albumin A may be nearly the same as the albumin Tiselius has isolated electrophoretically, while the coating on the collodion agreed most closely in behavior with his globulin (Y.Rabbit and human serum were also investigated with similar results.Although these investigations show that the films adsorbed on these particles are different, they do not give much information 605 This is an Open Access article under the CC BY license. Serum Proteins and Film Formationabout the mechanisms involved in their formation.This point can best be investigated by following the behavior of particles in mixtures of serum constituents with each other and with serum, In a similar investigation, using mixtures of gelatin with casein and egg albumin, Moyer and Moyer (4) have found that the resultant film depends on the proteins involved and, to a certain extent, on the nature of the particle.Two chief modes of approach were used: (1) coating the particle with one protein and then exposing it to the other, and (2) putting the particles into a mixture of the two proteins.The microscopic method of electrophoresis was used to determine the nature of the surface films formed on the particles.Their results, together with those in the literature, indicate that one protein may replace another at a surface, two proteins may be adsorbed side by side, or one may or may not be able to coat the other.To discuss the various factors involved in film formation on particles when immersed in protein solutions, let us consider the case in which a particle already coated with one protein is placed in a solution of another protein.If enough more free energy is dissipated in film formation by the initial than by the second protein, no replacement of the first protein by the second can occur, in spite of the high concentration of the other protein.It is still possible, however, for the particle to become coated with the second protein by the formation of a double or multiple film.The formation of a double coat would be analogous to interaction between the same two molecules in the solution itself.It is unlikely that the anchored molecule will interact much more readily with a molecule of the second protein than would a free molecule unless it is altered upon adsorption to such an extent that new groups are made available (denaturation and unfolding).To determine definitely whether such profound changes have occurred might require, for any particular case, information from several different sources : chemical, physicochemical (electrophoresis, heat of adsorption, etc.), and immunological.Tentatively, however, we suggest the incomplete criterion that if the electric mobility of the film-coated particles is the same as that of the free molecules and, furthermore, if the protein on the particles is one which does not denature rapidly at the air-water interface at room temperature, no important changes in the