Charging and structure of zwitterionic supported bilayer lipid membranes studied by streaming current measurements, fluorescence microscopy, and attenuated total reflection Fourier transform infrared spectroscopy

Abstract

The authors report on the characterization of the charge formation at supported bilayer lipid membranes (sBLMs) prepared from the zwitterionic lipid 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine on planar silicon dioxide substrates. The charging of the sBLMs was studied in KCl solutions of different ionic strengths between 0.1 and 10 mM by streaming current measurements. In addition, attenuated total reflection Fourier transform infrared spectroscopy and fluorescence microscopy were applied to determine the lipid concentration in the membrane and to study the influence of the harsh conditions (pH 9-2, shear forces) during the electrokinetic measurements on the membrane stability and the lipid diffusion coefficient. The sBLMs were found to be extremely stable. Isoelectric points of about 4 revealed that unsymmetrical adsorption of hydroxide and hydronium ions determined the charging of the outer leaflet of the membrane in the investigated pH range. The diffusion coefficients were found to be rather independent on the ionic strength at neutral and alkaline pH. However, significantly decreased lipid diffusion at pH<4 indicated a charge-induced transition of the fluidic bilayer into a gel/ordered-phase bilayer.

Formation of supported lipid bilayers containing phase-segregated domains and their interaction with gold nanoparticles

“…6) and was irreversible with respect to dilution (rinsing with AuNP-free buffer for 20 min). 71 Streaming current measurements 72 The ζ of the DOPC/SM/Chol vesicles were similar to those composed of solely DOPC (identical at 0.1 M NaCl; Table 1). The ζ app for the MPNH 2 -AuNPs was positive at both NaCl concentrations (26 ± 1 mV).…”

Hydroxide and hydronium ion adsorption — A survey

“…Both, the strong variation of the zeta potential with solution pH and the IEP of 4 indicate that charging of the interface between zwitterionic sBLMs and the electrolyte solution is not only caused by ionization of the lipid headgroups but is superposed by pH-dependent adsorption of hydroxide and hydronium ions from the solution. Importantly, the sign reversal of the membrane charge at pH 4 was accompanied by a significant drop in membrane fluidity, suggesting a transition from a fluid phase bilayer into a gel/ordered phase bilayer [65]. This demonstrates the relevance of asymmetric ion adsorption for secondary charge-induced characteristics of interfaces and interfacial material structures.…”

“…When bilayer lipid membranes are exposed to aqueous environments, the pH strongly determines membrane charge. In a recent study [65], we observed that water ion adsorption is also important for charging bilayer lipid membranes prepared from the zwitterionic lipid 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC). As the DOPC head group contains both an acidic phosphate and a basic quaternary ammonium moiety, which are oppositely charged at neutral pH, one would expect an electrically neutral membrane at the intermediate pH range.…”

Control of the stability and structure of liposomes by means of nanoparticles

“…Firstly, the adsorption of increasing amounts of particles has only a very small effect on the membrane transition temperature as the temperature at the peak maximum decreases only somewhat from around 42 curved surfaces, where increasing curvature has been found to induce a decrease in the transition temperature coming along with a widening of the transition peak, 38 thereby suggesting that in our system, the particle adsorption leads to local bending of the membrane at the particle location (as depicted in Fig. 5).…”