BEHAVIOR OF AVIDIN AND AVIDIN BISBIOTIN POLYMERS AT THE AIR-WATER-INTERFACE

The surface behavior of avidin and two polymers, formed by affinity polymerization from two different stoichiometric mixtures of avidin and the bifunctional ligand bisbiotin, has been investigated at the air/water interface. Strong hysteresis in the pressure-area isotherms is attributed to mechanical distortion of the molecules. When subjected to a step change in pressure, the monolayer area relaxes to a new equilibrium value following first-order dynamics, the time constant being of the order of minutes for a pressure change of 5 mN m-1. Equilibrium isotherms for the fully relaxed monolayers are linear over most of the pressure range, with both compression and expansion isotherms exactly coincident. Monolayers of the avidin/bisbiotin polymer were deposited onto electron microscope grids by the LB technique and imaged in a TEM. The area per repeat unit was estimated to be ca. 30 nm2 in good agreement with previous estimates, but much smaller than the area per molecule obtained by extrapolating the pressure-area isotherm to zero pressure. Finally it is shown that spreading solvents containing a high percentage of chloroform cause avidin to denature at the air/water interface, this manifesting itself as a large molecular area at low surface pressure. However, it appears that denaturation may be reversed almost completely when the monolayer is compressed. The investigation suggests that it may be feasible to fabricate molecular electronic networks based on affinity polymerization. © 1991.