Membrane surfactant interactions

Model membranes surfactant in low density lipoprotein interactions... 

Photon correlation spectroscopy was used to study the effects of a series of nonionic surfactants on the Stokes radius (R) of low density lipoprotein (LDL2) particles (Jl, 32). LDL2 interacted with surfactants in a manner similar to membranes. 

Efficient extraction of proteins has been reported with reverse micellar liquid membrane systems, where the pores of the membrane are filled with the reverse micellar phase and the enzyme is extracted from the aqueous phase on one side of membrane while the back extraction into a second aqueous phase takes place at the other side. By this, both the forward and back extractions can be performed using one membrane module [132,208]. Armstrong and Li [209] confirmed the general trends observed in phase transfer using a glass diffusion cell with a reverse micellar liquid membrane. Electrostatic interactions and surfactant concentration affected the protein transfer into the organic membrane and... 

Thrbidity is a spectroscopic technique determining the optical density of colloidal particles. A wavelength between 350 and 500 nm is the first choice for such studies [56], Thrbidity measurements can offer important information on the kinetics of membrane-surfactant interactions since membrane solubilization changes reflect changes to the optical density of the dispersion [57-60], It is also widely used as a technique to investigate liposome aggregation and fusion [61]. However the exact particle size of liposomes cannot be determined using turbidity techniques. 

Many drug carriers are made of hydrophobic materials such as lipids and poly(butyl cyanoacrylate). It will be thermodynamically unstable for submicron particles made of these materials to remain dispersed in an aqueous environment such as blood circulation. Surfactants or block co-polymers are therefore routinely included in these formulations to prevent particle aggregation. Studies showed that a number of these agents, most noticeably the nonionic surfactants such as polysorbates (also known as Tweens) and Tritons and block co-polymers such as poloxamers (also known as Pluronics), may inhibit the ABC transporters [97-99]. As previously discussed, ABC transporters interact with their substrates in the lipid bilayers of the plasma membrane. Surfactants can disrupt the arrangement of the lipid bilayer expressing the transporters and subsequently inhibit their drug efflux activities [97, 100]. It... 

The presence of surfactants in drug formulations may produce unwanted side or toxic effects because of their interaction with proteins, lipids, membranes and enzymes. To fully understand these interactions, it is essential to have information on the metabolic fate of the ingested surfactant. Membrane disruption by surfactants involves binding of the surfactant monomers to the membrane components, followed by the formation of co-micelles of the surfactant with segments of the membrane. The interaction between surfactants and proteins can lead to solubilization of the insoluble-bound protein or to changes in the biological activity of enzyme... 

Until more is known of the molecular interactions of surfactants with membrane components and the factors controlling such interactions it will remain virtually impossible to predict which surfactants will be capable of enhancing permeability of membranes without causing damage. Careful choice of solubilizer both of appropriate structure and optimum concentration is obviously paramount. In experiments on goldfish the effects of polyoxyethylene non-ionic surfactants on the absorption of various barbiturates is dependent on the surfactant hydro-phobic and hydrophilic chain lengths and possibly also on the size of the... 

Interactions of surfactants with membranes and membrane components... 

The possible adverse effects of surfactants in cosmetics and personal care products must, of course, be studied in depth for obvious safety reasons as well as for questions of corporate liability and image. Unfortunately, our understanding of the chemical reactions or interactions among surfactants, biological membranes, and other components and stmctures is not sufficiently advanced to allow the formulator to say with sufficient certainty what reaction an individual will have when in contact with a surfactant. In the end, we unfortunately still need the rabbit s assistance. 

Contact of surfactants with the skin and mucus membranes occurs either accidentally or as a consequence of normal use. Examples of this normal and everyday use are cleaning formulations, shampoos, foam baths, and toothpastes. Again this contact is seldom made with individual surfactants, in this case alcohol sulfates and alcohol ether sulfates, but through formulated products. It is known that surfactants present significant interactions, so that mixed systems are generally less aggressive than their individual components. However, the effect of pure surfactants merits attention, particularly sodium dodecyl sulfate, which is commonly used as a reference for many studies because of its high purity and availability. 

Figure 7.17 shows the asymmetry ratios of a series of compounds (acids, bases, and neutrals) determined at iso-pH 7.4, under the influence of sink conditions created not by pH, but by anionic surfactant added to the acceptor wells (discuss later in the chapter). The membrane barrier was constructed from 20% soy lecithin in dodecane. All molecules show an upward dependence on lipophilicity, as estimated by octanol-water apparent partition coefficients, log KdaA). The bases are extensively cationic at pH 7.4, as well as being lipophilic, and so display the highest responses to the sink condition. They are driven to interact with the surfactant by both hydrophobic and electrostatic forces. The anionic acids are largely indifferent... 

Schwuger MJ, Bartnik FG. Interaction of anionic surfactants with proteins, enzymes and membranes, in Anionic Surfactants (Gloxhuber C, ed.), Marcel Dekker, New York, 1980, pp. 1—49. 

It is important for the theoretical understanding of the formation of various topologies that these aggregates have entropic contributions on the scale of the objects, i.e. on a much larger scale than set by the molecules. These cooperative entropic effects should be included in the overall Helmholtz energy, and they are essential to describe the full phase behaviour. It is believed that the mechanical parameters discussed above kc,k and J0, control the phase behaviour, where it is understood that these quantities may, in principle, depend on the overall surfactant (lipid) concentration, i.e. when the membranes are packed to such a density that they strongly interact. 

---