Electrostriction of supported lipid films at presence of cationic surfactants, surfactant–DNA and DNA–Mg 2+ complexes

Abstract

The method of electrostriction has been applied to study the physical properties of supported lipid membranes (sBLM) during membrane formation at application of negative potential. Application of negative potential −350 mV to the sBLM during its formation resulted in more compact membrane structure as revealed by higher elastic modulus in comparison with sBLM formed without application of this potential. We also studied interaction with sBLM cationic surfactant hexadecylamine (HDA), HDA–DNA and DNA–Mg 2+ complexes. Interaction of HDA with sBLM resulted in decrease of membrane capacitance and two-directional effect on elasticity modulus (increase or decrease), which can be caused by different aggregation state of surfactant at the surface of sBLM. In contrast with effect of HDA, the complexes of HDA–DNA resulted, in most cases, increase of elasticity modulus and increase of membrane capacitance, which can be caused by incorporation of these complexes into the hydrophobic interior of the membrane. Certain part of these complexes can, however, be adsorbed on the sBLM surface. DNA itself does not cause substantial changes of physical properties of sBLM; however, addition of bivalent cations Mg 2+ to the electrolyte-contained DNA caused substantial increase of elasticity modulus and surface potential. These changes are, however, much slower than that observed for HDA–DNA complexes, which can be caused by slow competitive exchange between Na + and Mg 2+ ions.