Phospholipid-Modified ODS Monolithic Column for Affinity Prediction of Hydrophobic Basic Drugs to Phospholipids

A phospholipid-modified octadecyl silica (ODS) monolithic column was prepared and its interaction with basic hydrophobic drugs was studied. These drugs are of interest in pharmaceutical research because of their strong interaction with biomembranes. The amount of dimyristoylphosphatidylcholine trapped on the ODS surface was reproducible, and the results of the trinitrobenzenesulfonic acid assay suggested the formation of a monolayer on the surface. Both hydrophobic and electrostatic interactions acted between the model drugs and the phosphatidylcholine. The column was stable for 10 days at least. The column was applied to the affinity screening of basic drugs to phospholipid. Good correlation was obtained between log k and log P for the basic drugs lidocaine, quinidine, propranolol, imipramine, and chlorpromazine. The monolithic silica column allowed highly hydrophobic basic drugs such as imipramine and chlorpromazine to be assayed; these are difficult to analyze by using a conventional particle-packed column. These drugs were clearly separated from acidic drugs naproxen and warfarin on the log k versus log P plots. The thermodynamic studies revealed that the retention of the drug was an enthalpy-driven process, and that the decrease in enthalpy for the phospholipid-modified ODS monolithic column was larger than those for immobilized artificial membrane columns. Our results suggest that the phospholipid-modified ODS monolithic column is applicable to affinity screening of drugs to phospholipids.