Ion transfer mechanism of fluorescence-labeled octa-arginine on model biomembrane surfaces

Abstract

The interfacial behavior of a synthesized fluorescent polycationic cell-penetrating peptide, octa-arginine covalently labeled with carboxyfluorescein (FAM-R8), was investigated through spectroelectrochemical analysis at the bare and phospholipid-modified water|1,2-dichloroethane (DCE) interfaces. The potential modulated fluorescence (PMF) analysis indicated that the adsorption of FAM-R8 from the aqueous side of the bare interface occurred in the wide potential range at lower FAM-R8 concentrations, while the ion transfer across the interface proceeded at the positive edge of the polarizable potential window as the concentration increased. The complicated interfacial reaction behavior of FAM-R8 was further observed at the biomimetic interface in the presence of a phospholipid layer, where the adsorption potential of FAM-R8 was positively shifted as compared with the bare interface. Moreover, the ion transfer process of FAM-R8 became predominant when the surface excess of FAM-R8 was substantially increased at the biomimetic interface. The FAM-R8 concentration and its interaction with the phospholipid layer were found to play an important role for the membrane permeation mechanism.