Thermodynamics of Solute Partitioning into Immobilized Artificial Membranes

The solute retention mechanism on immobilized artificial membranes (IAMs) was studied using three different IAM.PC phases. IAMs were prepared by immobilizing either single-chain or double-chain phosphatidylcholine (PC) ligands. Solute affinity for the single-chain IAM.PC columns (with a ligand density of 127 mumol of PC/g of IAM) was 3-fold lower compared to solute affinity on the double-chain IAM.PC column (with a ligand density of 98 mumol of PC/g of IAM). This suggests that the solute retention on IAMs is dominated by a solute partitioning mechanism. Temperature-dependent studies indicated that the thermodynamics of solute partitioning is similar on both the single-chain and double-chain IAM.PC surfaces. For a set of phenol derivatives, the partitioning into IAM.PC surfaces is both enthalpy and entropy driven. For beta-blockers, the partitioning into IAM.PC surfaces is entropy driven. The free energy of solute partitioning into IAMs correlates very well with the free energy of solute partitioning into liposomes.