Two novel arginine-based surfactants, Bz-Arg-NHC 10 and Bz-Arg-NHC 12 , were characterized with respect to surface properties and their interaction with human red-blood-cell (HRBC) membranes. The values for critical micellar concentration (CMC), the maximum surfactant adsorption at the air-liquid interface, and the area per molecule indicated better surface properties for Bz-Arg-NHC 12 . The observation of cylindrical worm-like aggregates of Bz-Arg-NHC n via atomic-force microscopy supported the predictions based on the value of the surfactant-packing parameter (SPP). Erythrocyte-membrane solubilization was effected by surfactant aggregates since cell lysis became evident at only surfactant concentrations above the CMC. Changes in HRBC shape observed at different surfactant concentrations led to the conclusion that a slow mechanism based on the insertion of surfactant monomers into the HRBC membrane, followed by a shedding of microvesicles was responsible for the hemolysis produced by both surfactants at the lower concentrations tested. In contrast, the extraction of membrane lipids upon collisions between HRBCs and surfactant aggregates competes with and prevents microvesicle release at the higher concentrations assayed.
Highlights Arginine-based surfactant Bz-Arg-NHC12 has both hemolytic and antihemolytic effects. Both processes depend on the lipid composition of the erythrocyte membrane. SRBC is more resistant than HRBC to the hemolytic effect of the surfactant.
Cationic amino acid-based surfactants are known to interact with the lipid bilayer of microorganism resulting in cell death through a disruption of the membrane topology. To elucidate the interaction of a cationic surfactant synthesized in our lab, investigations involving N α -benzoyl-arginine decyl amide (Bz-Arg-NHC 10 ), and model membranes composed by 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) were done. Bz-Arg-NHC 10 was able to penetrate into DPPC monolayers up to a critical pressure of 59.6 mN m −1 . Differential scanning calorimetry revealed that as the concentration of Bz-Arg-NHC 10 increased, the main transition temperature of DPPC slightly decreased. Atomic force microscopy (AFM) in situ experiments performed on supported DPPC bilayers on mica allowed monitoring the changes induced by Bz-Arg-NHC 10 . DPPC bilayer patches were partially removed, mainly in borders and bilayer defects for 50 µM Bz-Arg-NHC 10 solution. Increasing the concentration to 100 µM resulted in a complete depletion of the supported bilayers. Surface plasmon resonance (SPR) experiments, carried out with fully DPPC bilayers covered chips, showed a net increase of the SPR signal, which can be explained by Bz-Arg-NHC 10 adsorption. When patchy DPPC bilayers were formed on the substrate, a SPR signal net decrease was obtained, which is consistent with the phospholipids' removal observed in the AFM images. The results obtained suggest that the presence of the benzoyl group attached to the polar head of our compound would be the responsible of the increased antimicrobial activity against gram-negative bacteria when compared with other arginine-based surfactants.
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