Stability of Colloids in Negatively Co‑operative Melittin–Phospholipid
The adsorption of melittin on 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine membranes is analysed. Rising melittin concentration, a multilayer adsorption is observed and discussed in terms of either monomer or tetramer stacking to the surface. An electrostatic adsorption model is applied because of the cationic peptide. According to the Derjaguin–Landau–Verwey–Overbeek theory, the energy well corresponding to melittin aggregation in membranes is rather broad and, practically, no barrier exists opposing the aggregation of melittin molecules. Such aggregation corresponds to a small energy variation relative to the thermal energy, which suggests that spontaneous thermal fluctuations can affect the aggregation state of melittin at the membrane–solution interface. The results of the work make evident the multilayer formation of melittin on phospholipid membranes. Melittin tetramers, which are formed in solution, bind directly to the phospholipid membrane, which results in multilayers on the surface. Adsorption is treated via Langmuir adsorption isotherm modified by electrostatic effects. The theoretical treatment is an elegant method because both Gouy–Chapman and Debye–Hückel formalisms apply Poisson–Boltzmann equation to calculate the potential.
Keywords: Peptide-lipid interaction, Thermodynamic treatment, Binding isotherm, Scatchard plot, Hill plot.