In order to describe the electrophoretic behavior of
“hairy-layer”-coated particles, local charge density
isotherms have been combined with considerations of hydrodynamic flow
penetration into the layer. An
iterative numerical procedure was employed to calculate the
electrophoretic mobility as a function of both
pH and salt concentration. A major result is that information can
be gained regarding the distribution
functions of oppositely charged groups from the behavior of the point
of zero mobility as a function of pH
and salt concentration. The theoretical results were used to
reinterprete the electrophoretic behavior of
native, neuraminidase-treated and glutaraldehyde-treated human
erythrocytes. Theoretical analysis of
the experimental data revealed that negative groups had occurred
preferentially in the outer regions of
the layer. A penetration depth of 1 nm into the 3.5 nm thick hairy
layer successfully accounted for the
erythrocyte mobility data for all methods of analysis tried. Upon
sialic acid removal, alterations of the
glycocalyx structure occurred, resulting in possible changes in the
fixed charge distribution. It was concluded
that intramolecular, as well as intermolecular, electrostatic
interactions are important for the structure
of the hairy surface layer (glycocalyx). No evidence for the
adsorption of small ions was found.