Enhanced binding of porphyrin by a laterally organized monolayer

The effect of lateral organization of a mixed monolayer of dioctadecyl-dimethyl-ammonium bromide (DOMA) and methyl stearate (SME) at the air-water interface by interaction with a water-soluble porphyrin (PO) on binding of PO has been investigated with the aim of achieving molecular recognition. The organized monolayers were formed by co-spreading of the lipids DOMA and SME with PO. This technique should be more efficient in generating a laterally organized monolayer than reorganization of the lipid monolayer by molecules adsorbed from the aqueous subphase. By measuring surface pressure-area and surface potential-area isotherms as well as reflection spectra, an optimal molar ratio of PO:DOMA:SME was determined. The monolayers were transferred to hydrophobic glass plates by vertical dipping, and the PO was removed from the immersed plate by changing the pH. Readsorption of PO from dilute aqueous solution showed stronger binding by the organized monolayer as compared with a lipid monolayer of the same average composition.