The cecropin-melittin hybrid antimicrobial peptide BP100 (H-KKLFKKILKYL-NH2) is selective for Gram-negative bacteria, negatively charged membranes, and weakly hemolytic. We studied BP100 conformational and functional properties upon interaction with large unilamellar vesicles, LUVs, and giant unilamellar vesicles, GUVs, containing variable proportions of phosphatidylcholine (PC) and negatively charged phosphatidylglycerol (PG). CD and NMR spectra showed that upon binding to PG-containing LUVs BP100 acquires α-helical conformation, the helix spanning residues 3-11. Theoretical analyses indicated that the helix is amphipathic and surface-seeking. CD and dynamic light scattering data evinced peptide and/or vesicle aggregation, modulated by peptide:lipid ratio and PG content. BP100 decreased the absolute value of the zeta potential (ζ) of LUVs with low PG contents; for higher PG, binding was analyzed as an ion-exchange process. At high salt, BP100-induced LUVS leakage requires higher peptide concentration, indicating that both electrostatic and hydrophobic interactions contribute to peptide binding. While a gradual release took place at low peptide:lipid ratios, instantaneous loss occurred at high ratios, suggesting vesicle disruption. Optical microscopy of GUVs confirmed BP100-promoted disruption of negatively charged membranes. The mechanism of action of BP100 is determined by both peptide:lipid ratio and negatively charged lipid content. While gradual release results from membrane perturbation by a small number of peptide molecules giving rise to changes in acyl chain packing, lipid clustering (leading to membrane defects), and/or membrane thinning, membrane disruption results from a sequence of events - large-scale peptide and lipid clustering, giving rise to peptide-lipid patches that eventually would leave the membrane in a carpet-like mechanism.

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The properties of a novel complex between pyranine (a photoacid and an electron donor species) and methyl viologen (an efficient electron acceptor, MV+2) in aqueous and in micellar solutions were determined. On the basis of the electrostatic driven force for pyranine/methyl viologen (pyranine/MV2+) complexation, the distribution of the complexant species could be manipulated using ionic micellar aggregates. This distribution permits control over competitive photochemical and photophysical pathways and therefore allowed maximization of electron- and proton-transfer capabilities. Pyranine/MV2+ complexes (for the acid and conjugated base pyranine species) were characterized by UV−Vis and fluorescence titrations. Pyranine/MV2+ photoredox reactions were investigated by monitoring the transients (laser flash photolysis) due to the solvated electron, the reduced (PO-•) and oxidized (PO+•) forms of pyranine, and the semireduced methyl viologen (MV+•). Ionic aqueous micelles (sodium dodecyl sulfate and cetyltrimethylammonium chloride) and anionic reversed micelles (sodium bis(2-ethylhexyl)sulfosuccinate) were used to disassemble the complex by attraction of one of its species by an oppositely charged micellar aggregate. Present findings demonstrate the formation of a complex and its manipulation, which may allow the development of a photocatalyst agent whose properties can be adjusted by the appropriate disposition of the complex partners in supramolecular aggregates.