SOLUTE INTERACTIONS WITH IMMOBILIZED ARTIFICIAL MEMBRANES

Solute binding to immobilized aritifical membrane (IAM) chromatography surfaces was studied. The IAM surfaces studied were (ether)IAM.PCC10/C3 and (ether)IAM.PG(C10/C3). The solutes studied were tryptophan (Trp) and glycocholic acid (GA). Equilibrium binding constants (K) and the free energy of adsorption (Delta G) were obtained from fitting experimental equilibrium binding data to Langmuir adsorption isotherms. Trp adsorbs to both (ether)IAM.PCC10/C3 ether IAM.PG(C10/C3) surfaces at both acidic (pH 3.4) and neutral pH (pH 7.0). Surface-associated Trp did not change the P-31 NMR line shape of (ether)IAM.PG(C10/C3) at either pH 3.4 or 7.0; however, the P-31 NMR line shape of (ether)IAM.PCC10/C3 was broadened from surface-associated Trp. The line broadening was directly proportional to the amount of surface-associated Trp. Spectral simulations of the P-31 NMR line shape indicated that Trp, bound to the interfacial region of the (ether)IAM.PCC10/C3 surface, slowed the wobbling motion of the phospholipid head group. The correlation time (tau perpendicular to) for the lipid head group wobbling motion increased linearly with the amount of surface-associated Trp. GA strongly adsorbed to both (ether)IAM.PG(C10/C3) (K similar to 7.06 x 10(4)) and (ether)IAM.PCC10/C3 (K similar to 3.44 x 10(4)) at acidic conditions (pH 3.4). However, in contrast to Trp, surface-associated GA did not change the P-31 NMR line shape of (ether)IAM.PCC10/C3 but broadened the P-31 NMR line shape of (ether)IAM.PG(C10/C3). The extent of line broadening and tau perpendicular to of immobilized PG increased exponentially with the amount of surface-associated GA. In addition, P-31 NMR line shape analysis and T-2 measurements indicated that for Trp the adsorption rate (on) and desorption rate (off) of the (ether)IAM.PCC10/C3 surface was faster than the exchange rates measurable by the NMR time scale (i.e., on/off rates > 10(3) s(-1)). For GA, the on/off rates from the (ether)IAM.PG(C10/C3) surface were slower than the NMR time scale (i.e., on/off rates < 10(3) s(-1)).