Changes in phospholipid bilayers caused by sodium dodecyl sulfate/nonionic surfactant mixtures

Abstract

The interaction of mixtures of sodium dodecyl sulfate (SDS) and oxyethylenated nonylphenol (30 mol of ethylene oxide) [NP(EO) 30 ] with phosphatidylcholine liposomes was investigated. Permeability alterations were detected as a change in 5(6)-carboxyfluorescein (CF) released from the interior of vesicles, and bilayer solubilization was measured as a decrease in the static light scattered by liposome suspensions. Three parameters were described as the effective surfactant/lipid molar ratios (Re) at which the surfactant system: (i) resulted in 50% CF release (Re 50%CF ); (ii) saturated the liposomes (Re SAT ); (iii) led to complete solubilization of these structures (Re SOL ). The corresponding surfactant partition coefficients (K 50%CF , K SAT , and K SOL ) were determined from these parameters. The free surfactant concentrations S W were lower than the mixed surfactant critical micellar concentration at subsolubilizing levels, whereas they remained similar to these values during saturation and solubilization of bilayers. Although the Re values increased linearly as the mole fraction of the SDS rose (X SDS ), the K parameters showed maximum values at X SDS 0.6 for K 50%CF and approximately at X SDS 0.2 for K SAT and K SOL , respectively. Thus, the lower the surfactant contribution in the surfactant/lipid system, the higher the X SDS at which the maximum bilayer/water partitioning of added mixed surfactant systems occurred. As a consequence, the influence of SDS in this partition appears to be more significant at the sublytic level (monomeric effect), whereas the influence of NP(EO) 30 seems to be greater during saturation and solubilization of liposomes via formation of mixed micelles. JAOCS 74, 9-17 (1997). KEY WORDS: Carboxyfluorescein release, partition coefficients, permeability alterations and bilayer solubilization, phosphatidylcholine liposomes, sodium dodecyl sulfate/nonylphenol oxyethylenated [NP(EO) 30 ] mixtures, static light-scattering, surfactant/phospholipid molar ratios.The interaction of sodium dodecyl sulfate (SDS) with skin induces structural changes in the epidermal surfaces (1-3) and in the stratum corneum transcutaneous permeability barrier (4,5). Mixtures of this anionic surfactant with oxyethylenated nonylphenols of different oxyethylenation levels in aqueous solution show negative deviation from ideal solution behavior (6-10). These mixtures also exhibit changes in the surface properties that improve the wetting ability of water on hydrophobic surfaces (11,12) and the salinity tolerance with regard to that of the anionic component (13). The change in the physico-chemical properties of mixed micelles and their additional stability arises from the charge separation of the ionic head groups, which affects the mean aggregation numbers of these micelles (8,14).A number of investigations have been devoted to the understanding of the principles that govern the interaction of SDS with simplified membrane models, such as phospholipid or stratum corneum lipid bilayers, when this surfactant interact...

Mixtures of Nonionic Surfactants Made from Renewable Resources with Alkyl Sulfates: Comparison of Headgroups

“…One would perhaps expect a size dependence on this mechanism; if the nonpolar group is very long and hence much larger ionic moiety, then the effect might be reduced. De la Maza and Parra [26] demonstrate an oxyethylenated nonylphenol (30 mol EO)/S12S mixture that has an interaction parameter of only -0.916 when the head group on the nonionic surfactant in this mixture is 30 EOs long-5 times the length of a MEGA headgroup.…”

Additive and Synergistic Membrane Permeabilization by Antimicrobial (Lipo)Peptides and Detergents

“…On the other hand, this terminology leads to the confusing paradox that most detergents do not primarily permeabilize membranes by the so-defined detergent-like mechanism. Instead, detergents have been found to induce toroidal pores or transient membrane failure due to asymmetric expansion, chain disordering, and membrane thinning at concentrations well below those needed for the appearance of mixed micelles (20)(21)(22)(23). This explains why other authors used the term to describe membrane pores with short lifetime or variable size (24)(25)(26).…”

Solubilization of phosphatidylcholine unilamellar liposomes caused by alkyl glucosides

“…Unilamellar PC liposomes (PC concentration ranging from 0.1 to 10.0 mM) of a defined size (about 200 nm) were prepared by extrusion of large unilamellar vesicles obtained previously by a reverse-phase evaporation method (18,22). Vesicles of about 200 nm were obtained by extrusion through 800, 400, and 200 nm polycarbonate membranes at 25°C using a thermobarrel extruder (Lipex; Biomembranes Inc., Vancouver, Canada).…”

“…Studies were made by particle number measurement (22). The sample was adjusted to an appropriate concentration range with PIPES buffer, and measurements were taken at 25°C at a reading angle of 90°.…”