LATERAL DIFFUSION OF RECONSTITUTED ALKYLFERROCENECARBOXAMIDE PHOSPHATIDYLCHOLINE LIPID MONOLAYER AT THE AIR/WATER INTERFACE STUDIED WITH ELECTROCHEMISTRY/

Lateral diffusion of n))/1,2-dilauroyl-sn-glycero-3-phosphatidylcholin e lipid monolayer at the air/water interface was determined with elect rochemical techniques using a fabricated microline electrode. The prep ared homogeneous Langmuir monolayer of electroactive FcCONHC(n)/ phosp holipid was identified with pressure-area isotherms in the subphase of 50 mM HClO4. The diffusion constant of electroactive FcCONHC(n) in th e lipid monolayer was approximately between 0.1 x 10(-6) and 2.6 x 10( -6) cm(2)/s at room temperature. The diffusion constant of ferrocenes in a phospholipid monolayer at the air/water interface was greater for the ferrocene with longer alkyl chains. This is interpreted as the ex tent of hydrodynamic coupling of the hydrophilic ferrocene moiety of F cCONHC(n) to the subphase, which was less for ferrocenes with longer a lkyl chains. This lets the position of the hydrophilic headgroup of Fc CONHC(n) with respect to the air/water interface be shifted upward for the longer alkyl chain because of greater hydrophobic entanglement. T he electrochemistry with the microline electrode was possible in the m ean molecular area range 60-100 Angstrom(2)/mol because of monolayer a dsorption in a mean molecular area that is less than 60 Angstrom(2)/mo l. The linear decrease of the diffusion constant of ferrocenes with de creasing mean molecular area is explained by the decreasing free volum e of the moving headgroup. This is well explained by the modified Cohe n-Turnbull free volume model.