Initial Adsorption Kinetics in a Rectangular Thin Channel, and Coverage-Dependent Structural Transition Observed by Streaming Potential

One fundamental parameter contributing to the analysis of protein-solid surface interactions is the adsorption kinetic constant

k

a

. For a rectangular channel we give a global representation of the initial experimental adsorption constant

k

at distance

x

from the entrance channel, as a function of wall shear rate

γ

, through the variable 1.86

k

(

x/γ

)

1/3

. It is possible to visualize on a single graph the adsorption kinetic constant, the diffusion coefficient, depletion magnitude at the interface, and its thickness relative to that of the transport-limited Lévêque limit. With radiolabeled molecules (with a

γ

emitter like

125

I) and well-defined geometries, calibration does not require a known solute diffusion coefficient and is obtained fromthe abrupt variation of radioactivity at the buffer-protein solution change and vice-versa. Experimental data obtained for the system

±

-chymotrypsin/mica show that when surface coverage reaches some critical level, the streaming potential becomes almost independent of further interfacial concentration increase; this suggests an interfacial structural transition induced by interactions between adsorbed molecules. Several models based on protein-protein dipolar interactions are proposed.