Interaction of surfactants with bilayer of negatively charged lipid: effect on gel-to-liquid-crystalline phase transition of dilauroylphosphatidic acid vesicle membrane

The interaction of surfactants with the vesicle membrane of the negatively charged lipid, dilauroylphosphatidic acid, was investigated through their effect on the gel-to-liquid-crystalline phase transition of the lipid bilayer. Three types of surfactants (anionic, cationic and non-ionic) with different hydrocarbon chain length were examined. (i) Anionic sodium alkylsulfates affected the phase transition temperature, Tm, only weakly. (ii) Non-ionic alkanoyl-N-methylglucamides decreased Tm monotonously with increasing concentration. The depression of Tm induced by these surfactants was analyzed by applying the van't Hoff model for the freezing-point depression, and the partition coefficients of the surfactants between bulk water and lipid membrane were estimated. (iii) Cationic alkyltrimethylammonium bromides affected Tm in a complex manner depending on the hydrocarbon chain length of the surfactants. Octyl-/tetradecyl-trimethylammonium bromide depressed/elevated Tm monotonously with increasing concentration, whereas the change in Tm induced by decyl- and dodecyltrimethylammonium bromides was not monotonous but biphasic. This complex behavior of the phase transition temperature was well explained, based on the statistical mechanical theory presented by Suezaki et al. (Biochim. Biophys. Acta, 818 (1985) 31-37), which takes into account the interaction between surfactant molecules incorporated in the lipid membrane.     

Effect of sodium octanoate and sodium perfluorooctanoate on gel-to-liquid-crystalline phase transition of dipalmitoylphosphatidylcholine vesicle membrane

The gel-to-liquid-crystalline phase transition of dipalmitoylphosphatidylcholine (DPPC) vesicle membrane was measured in the presence of sodium octanoate (SO) (pH 3 and 10) and sodium perfluorooctanoate (SPFO) (pH uncontrolled) by monitoring the scattered light intensity of the vesicle suspension. The phase transition temperature, Tm, decreased linearly with the concentration of added SO within the measured concentration range; the uncharged form of SO (pH 3) was much more effective for the depression of Tm than the charged form (pH 10). On the other hand, with increasing SPFO concentration, levelling off of Tm was observed after depression at an initial stage. From the depression of Tm, the partition coefficients, K, of these surfactants between bulk solution and DPPC vesicle membrane were estimated and compared with those obtained previously for other surfactant systems. The value of K for charged SO fell on the straight line of log K vs. Nc plot for anionic surfactants, where Nc is the carbon number of the hydrocarbon chain of surfactants, whereas K for uncharged SO showed a large positive deviation from the straight line of the plot for non-ionic surfactants. The latter suggested that some specific interaction, presumably hydrogen bond formation, may act between the protonated carboxyl group of SO and the lipid head group. The K value estimated for SPFO was much larger than that for charged SO. This difference in the affinity for the lipid bilayer between fluorocarbon surfactant and hydrocarbon surfactant may be attributed to the difference in their hydrophobicity.     

Interaction of surfactants with vesicle membrane of dipalmitoylphosphatidylcholine: fluorescence depolarization study

The effect of surfactants on the "fluidity" of dipalmitoylphosphatidylcholine (DPPC) vesicle membrane was studied by means of the fluorescence depolarization technique with fatty acid fluorescent probes, in which the anthroyloxy group is introduced at different positions along the acyl chain. Three types of surfactants were examined; anionic sodium alkylsulfates, cationic alkyltrimethylammonium chlorides, and non-ionic alkanoyl-N-methylglucamides (MEGA-n). Perturbing effects of the surfactants depended on both the alkyl chain-length and the type of head group. Sodium alkylsulfates with octyl- and decyl-chain and alkyltrimethylammonium chlorides with octyl-, decyl- and dodecyl-chain did not affect the membrane fluidity when incorporated in the membrane, whereas sodium dodecylsulfate and tetradecyltrimethylammonium chloride decreased the membrane fluidity at both gel and liquid crystalline states of the membrane. All the MEGA series surfactants decreased the membrane fluidity, whose perturbing potency was in the order of MEGA-8 less than MEGA-9 approximately equal to MEGA-10. The perturbation at different depths in the membrane by sodium dodecylsulfate and MEGA-9 was also examined. No significant change in the fluidity gradient across the membrane was induced by the addition of these surfactants.     

The reduction in electroporation voltages by the addition of a surfactant to planar lipid bilayers.

The effects of a nonionic surfactant, octaethyleneglycol mono n-dodecyl ether (C12E8), on the electroporation of planar bilayer lipid membranes made of the synthetic lipid 1-pamitoyl 2-oleoyl phosphatidylcholine (POPC), was studied. High-amplitude ( approximately 100-450 mV) rectangular voltage pulses were used to electroporate the bilayers, followed by a prolonged, low-amplitude ( approximately 65 mV) voltage clamp to monitor the ensuing changes in transmembrane conductance. The electroporation thresholds of the membranes were found for rectangular voltage pulses of given durations. The strength-duration relationship was determined over a range from 10 micros to 10 s. The addition of C12E8 at concentrations of 0.1, 1, and 10 microM to the bath surrounding the membranes decreased the electroporation threshold monotonically with concentration for all durations (p < 0.0001). The decrease from control values ranged from 10% to 40%, depending on surfactant concentration and pulse duration. For a 10-micros pulse, the transmembrane conductance 150 micros after electroporation (G150) increased monotonically with the surfactant concentration (p = 0.007 for 10 microM C12E8). These findings suggest that C12E8 incorporates into POPC bilayers, allowing electroporation at lower intensities and/or shorter durations, and demonstrate that surfactants can be used to manipulate the electroporation threshold of lipid bilayers.     

Secondary structural changes of metmyoglobin and apomyoglobin in anionic and cationic surfactant solutions: Effect of the hydrophobic chain length of the surfactants on the structural changes

Secondary structural changes of metmyoglobin and apomyoglobin were examined in solutions of sodium alkylsulfates with hydrocarbon numbers of 8 and 12, and alkyltrimethylammonium bromides with hydrocarbon numbers of 10, 12, 14, and 16. The relative proportion ofa-helical structure was estimated by the curve-fitting method of circular dichroic spectrum. The helical proportions of metmyoglobin and apomyoglobin were 82 and 63%, respectively. The shorter the hydrocarbon chain the surfactant had, the higher the concentration necessary to disrupt the secondary structures of these proteins. However, the helical proportion had a tendency to decrease down to lower values in solutions of the cationic surfactants with short hydrophobic groups. On the other hand, thea-helical structure of apomyoglobin was disrupted in lower concentrations of each cationic surfactant than that of metmyoglobin, although the disruptions of the same structures in both the proteins occurred in the same concentration range of each anionic surfactant. It appeared likely that the removal of the heme group unstabilized the myoglobin conformation only in the cationic surfactant solutions.     

The effect of surfactant structure on ribonuclease A–surfactant interactions (Short Communication)

The enzymic activity of ribonuclease A was measured in the presence of several surfactants at pH7.2. Cationic surfactants with trimethylammonium and pyridinium head groups do not deactivate or denature the enzyme, whereas n-dodecylamine hydrochloride, like the anionic surfactant sodium n-dodecyl sulphate, deactivates and denatures ribonuclease A.     

The lysis of isolated fish (Oncorhynchus mykiss) gill epithelial cells by surfactants

1. The interaction of a wide range of surfactants with isolated gill epithelial cells of rainbow trout (Oncorhynchus mykiss) was investigated as a function of the surfactant concentration up to and above the critical micelle concentration (cmc). The surfactants included a homologous series of n-alkyl sulphates, single and double chain tri and dimethylammonium bromides (TABs and DABs), cholates and the nonionics n-octylglucoside and Triton X-100.2. With the exception of the C₂₂ alkyl chain TAB and the double chain [(C₁₂)₂] DAB, the surfactants solubilized between 84 and 100% of the cell protein at high concentrations (>cmc).3. At low concentrations n-dodecyltrimethylammonium bromide and, to a lesser extent, Triton X-100 and sodium n-dodecylsulphate release a larger proportion of cell protein than they solubilize lipid in contrast to sodium cholate which initially preferentially solubilizes cell lipid. This differential pattern of solubilization is similar to that observed for other plasma membranes such as those of human erythrocytes and platelets.4. The surfactant concentration required to solubilize 50% (S_50%) of cell protein increases with the cmc. There is an approximately linear relationship between log(S_50%) and log cmc.5. Light microscopy shows that the surfactants at high concentrations (>cmc) fragment the secondary lamellae of the gill filaments.     

The interaction between Beta-lactoglobulin and sodium N-dodecyl sulphate.

1. The binding of sodium n-dodecyl sulphate to beta-lactoglobulin was studied in the pH range 3.5-7.0 by equilibrium dialysis, ultracentrifugation and microcalorimetry. 2. At low binding concentrations (less than 30 bound surfactants anions per protein molecule) the complexes formed aggregates in solution. 3. At higher binding concentrations aggregation does not occur at low ionic strength (0.01 mol/litre), but continues at high ionic strength (0.1 mol/litre). 4. At 25 degrees C the enthalpy of interaction of sodium n-dodecyl sulphate with beta-lactoglobulin can be interpreted as the sum of the enthalpies of formation of a complex with 2 bound surfactant anions, with an enthalpy change of -9.5 kJ-mol-1 of bound surfactant, and complexes containing at least 22 bound surfactant anions, with limiting enthalpies per bound surfactant anion of -12.4 kJ-mol-1 at pH 3.5 and -3.25 kJ-mol-1 at pH 5.5. 5. The binding of surfactant and the enthalpy of interaction at pH 3.5 ARE NOT SIGNIFICANTLY AFFECTED BY THE ADDITION Of 8 M-urea. 6. The data indicate that at low binding concentrations the interaction is of an ionic nature, and is accompanied by a conformational change in the protein.     

Polyacrylamide gel electrophoresis of several proteins in the presence of sodium oligooxyethylene dodecyl ether sulfates or a commercially available analog

The behavior of water-soluble proteins and a typical membrane protein in polyacrylamide gel electrophoresis was studied in the presence of sodium oligooxyethylene dodecyl ether sulfates with a defined number of oxyethylene units or a commercially available analog with distribution and heterogeneity for the oxyethylene chain length and alkyl group, respectively. It was concluded that most water-soluble proteins do not interact with the anionic surfactants as long as their oxyethylene chain lengths are sufficiently long; the commercially available surfactant binds exceptionally well to beta-lactoglobulin without causing denaturation and subsequent dissociation; such surfactants are expected to solubilize membrane proteins without causing denaturation as judged from the result with Na+,K+-ATPase and are promising as new solubilizing agents for membrane proteins which enable efficient electrophoretic analysis or separation after the solubilization.     

Interaction of glucose oxidase with ionic surfactants: a microcalorimetric study

The enthalpies of interaction of glucose oxidase at 25°C with a homologous series of n-alkyltrimethylammonium bromides (TABs) at pH 10 and a homologous series of n-alkylsulfates at pH 3.2 have been measured by microcalorimetry. For the n-dodecyl member of each series, DTAB and sodium n-dodecylsulfate (SDS), the binding of the surfactants to glucose oxidase as measured by equilibrium dialysis has been used in combination with the enthalpy data to obtain the Gibbs energy ( ), enthalpy ( ) and entropy ( ) of binding per surfactant molecule as a function of the number of surfactant molecules bound ( ). The thermodynamic parameters for the glucose oxidase interaction with DTAB at pH 10 and SDS at pH 3.2 are very similar and show that the interactions are entropically driven. The observed enthalpies of interaction of glucose oxidase with the homologous n-alkylsulfates have been analysed in terms of the interactions between the anionic surfactant head group and cationic sites on the protein, hydrophobic binding and the thermal contributions arising from protein unfolding. At surfactant concentrations of 0.5 c.m.c., the enthalpy of unfolding of glucose oxidase is estimated to be 3610 ± 560 kJ mol⁻¹.     

On the effect of surface active agents and their structure on the temperature-induced changes of normal and waxy wheat starch in aqueous suspension. Part I. Pasting and calorimetric studies

Pasting and calorimetric studies of normal and waxy wheat starch were performed in the presence of a series of ionic (sulphates, trimethyl ammonium bromides) and non-ionic (monoglycerides, maltosides) short (12 carbon atoms) and long (16 carbon atoms) n-alkyl chain surfactants. With the exception of the alkyl ammonium bromides, all of the short chain surfactants lower the pasting temperature (PT) in normal wheat starch, while the long chain surfactants have the opposite effect. Contrary, regardless of their chain length, all ionic surfactants lower the PT in waxy wheat starch while the non-ionic surfactants induce small, sometimes almost negligible changes in the PT. Calorimetric studies revealed the absence of a direct connection between the effect of surfactants on the onset of the starch gelatinization transition and the PT. However, in the presence of all surfactants, except the alkyl ammonium bromides, the PT of normal wheat starch was found to lie within or very close the temperature range within which the dissociation of the amylose–surfactant complexes takes place. Waxy wheat starch, in contrast, pasted at temperatures that fell within the temperature range of the starch gelatinization transition. This is taken as evidence of the existence of a correlation between the PT and the dissociation of the amylose–surfactant complexes.     

Surfactant partition between bulk water and DPPC vesicle membrane: solid-gel vs. liquid-crystalline membrane

The main phase transition temperature, Tm, of dipalmitoylphosphatidylcholine (DPPC) vesicle membrane was measured in the presence of the cationic surfactants tetradecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide. Variation of the perturbing effect of these surfactants on Tm with the lipid concentration was analyzed according to the theory recently proposed by Kaminoh et al. (Y. Kaminoh, C. Tashiro, H. Kamaya and I. Ueda (1988) Biochim. Biophys. Acta 946, 215-220), and the partition coefficients of the surfactant into solid-gel and liquid-crystalline membranes were estimated.     

Properties of agents that effectively entrap liquid lipids.

A droplet of an oil-in-water emulsion of methyl linoleate in a saccharide or protein solution that contained with a surfactant, a stabilizer, or both was dehydrated by drying equipment for a single droplet that resembled a spray drier. The lipid exposed on the surface of dehydated samples was extracted and measured by gas chromatography. Gum arabic or gelatin without additives resulted in little lipid being exposed; they were good entrapping agents. Little lipid was exposed with a pullulan solution containing lecithin, sugar ester, carboxymethylcellulose, or sodium caseinate but much was exposed with a maltodextrin solution containing any of the surfactants tested. When both the surfactant lecithin and the stabilizer xanthan gum were added to the emulsion prepared in a maltodextrin solution, lipid was not detected. The results suggested that effective entrapping agents of liquid lipids cause much emulsification, stabilize the emulsion (that is, they cause the continuous phase to be very viscous), and create a dehydrated matrix of fine, dense network layers.     

Mixed micelles and other structures in the solubilization of bilayer lipid membranes by surfactants

The solubilization of lipid bilayers by surfactants is accompanied by morphological changes of the bilayer and the emergence of mixed micelles. From a phase equilibrium perspective, the lipid/surfactant/water system is in a two-phase area during the solubilization: a phase containing mixed micelles is in equilibrium with bilayer structures of the lamellar phase. In some cases three phases are present, the single micelle phase replaced by a concentrated and a dilute solution phase. In the case of non-ionic surfactants, the lipid bilayers reach saturation when mixed micelles, often flexible rod-like or thread-like, start to form in the aqueous solution, at a constant chemical potential of the surfactant. The composition of the bilayers also remains fixed during the dissolution. The phase behavior encountered with many charged surfactants is different. The lamellar phase becomes destabilized at a certain content of surfactant in the membrane, and then disintegrates, forming mixed micelles, or a hexagonal phase, or an intermediate phase. Defective bilayer intermediates, such as perforated vesicles, have been found in several systems, mainly with charged surfactants. The perforated membranes, in some systems, go over into thread-like micelles via lace-like structures, often without a clear two-phase region. Intermediates in the form of disks, either micelles or bilayer fragments, have been observed in several cases. Most noteworthy are the planar and circular disks found in systems containing a large fraction of cholesterol in the bilayer. Bile salts are a special class of surfactants that seem to break down the bilayer at low additions. Originally, disk-like mixed micelles were conjectured, with polar membrane lipids building the disk, and the bile salts covering the hydrophobic rim. Later work has shown that flexible cylinders are the dominant intermediates also in these systems, even if the disk-like structures have been re-established as transients in the transformation from mixed micelles to vesicles.     

Influence of dodecyltrimethylammonium halides on thermotropic phase behaviour of phosphatidylcholine/cholesterol bilayers

Effects of dodecyltrimethylammonium chloride (DTAC), dodecyltrimethylammonium bromide (DTAB) and dodecyltrimethylammonium iodide (DTAI) on thermotropic phase behaviour of phosphatidylcholine bilayers containing cholesterol as well as on 1H NMR spectra were studied. Two series of experiments were performed. In the first one the surfactants were added to the water phase while in the other directly to the lipid phase (a mixed film from cholesterol, surfactant and phosphatidylcholine was formed). The effects of particular surfactants on the main phase transition temperature, Tm, were more pronounced when added to the lipid phase (2nd method) than to the water phase (1st method); the opposite happened when cholesterol was absent (Rózycka-Roszak and Pruchnik 2000, Z. Naturforsch. 55c, 240-244). Furthermore, in the case of the first method the transitions were asymmetrical while in the second method nearly symmetrical. It is suggested that surfactant poor and surfactant rich domains are formed when surfactants are added to the water phase.     

Determination of molecular weight of membrane proteins by the use of low-angle laser light scattering combined with high-performance gel chromatography in the presence of a non-ionic surfactant

An assessment study was carried out to evaluate the performance of the low-angle laser light scattering technique combined with high-performance gel chromatography in the presence of a nonionic surfactant, octaethyleneglycol n-dodecyl ether, precision differential refractometry and ultraviolet photometry. It was found that the combined technique is highly promising as a method for the determination of the molecular weight of a membrane protein solubilized by the surfactant. For trial, molecular weights of the following membrane proteins of Escherichia coli, both solubilized in oligomeric forms, were measured; porin that forms the transmembrane diffusion pore in the outer membrane, and lambda-receptor protein that facilitates the diffusion of maltose-maltodextrins across the outer membrane. The result obtained indicates that both porin and lambda-receptor protein exist as trimers in the surfactant solution.     

Vesicle to micelle transitions of egg phosphatidylcholine liposomes induced by nonionic surfactants, poly(oxyethylene) cetyl ethers.

Vesicle to micelle transitions of sonicated liposomes of egg yolk phosphatidylcholine (EPC) induced by a homologous series of nonionic surfactants, poly(oxyethylene) cetyl ethers [POE(n) cetyl ether], were investigated by using the method of turbidity titrations. The turbidities of the mixed dispersions of sonicated vesicles and surfactant were systematically measured as a function of the surfactant added for a wide range of lipid concentrations (from 0.51 to 6.35 mM EPC). From the titration curves, two threshold points representing onset and complete solubilization of liposomal membranes were determined as a probe for the effect of the length of ethylene oxide (EO) moiety on the phase behavior of ternary system of POE(n) cetyl ethers-EPC-excess water. Patterns of turbidity curves and the surfactant concentrations at two threshold points as well as widths of region between two transitions, where lamellar sheets and mixed micelles may coexist, mainly depended on the length of EO head group. With changing the lengths, solubilization of liposomes and phase diagram showed optimal behavior. That is, in the middle range of EO numbers, it resulted in narrowest coexistence region between onset and complete solubilization. Assuming the equilibrium partitioning model, critical effective molar ratios of surfactant to lipid, Rsat, free surfactant concentrations, Dw, and the partition coefficient of surfactant between bilayer and aqueous phase, K, in surfactant-saturated liposomes were quantitatively determined as a function of EO number. Effective ratios, Rsol, and free surfactant concentration in mixed micelles were also determined. In addition, the effects of CMC and HLB of surfactants on the solubilization of liposome were discussed.     

Dependence of the bilayer to hexagonal phase transition on amphiphile chain length

Several series of amphiphiles of increasing chain length were tested for their abilities to modify the L alpha-HII transition of dielaidoylphosphatidylethanolamine using differential scanning calorimetry. Acylcarnitines, alkyl sulfates, alkylsulfobetaines, and phosphatidylcholines, with chain lengths between about 6 and 12 carbon atoms, show an increasing capacity to raise the L alpha-HII phase transition temperature of phosphatidylethanolamine. This is ascribed to increased partitioning of the added amphiphile from water into the membrane as the chain length increases. Alkyl sulfates and alkyltrimethylammonium bromides have diminished capacities to raise the L alpha-HII transition temperature as the chain length is increased from 12 to 16. This is caused by an increase in the hydrophobic portion of the amphiphile leading to a change in the intrinsic radius of curvature and a decrease in the hydrocarbon packing constraints in the HII phase relative to the shorter chain amphiphiles. The L alpha-HII transition temperature of phosphatidylethanolamine with acylcarnitines of chain length 14-20 carbon atoms, alkylsulfobetaines above 14 carbon atoms, and phosphatidylcholines with acyl groups having above 10 carbon atoms is relatively insensitive to chain length. We suggest that this is caused by a balance between increasing hydrocarbon volume promoting the HII phase through decreased intrinsic radius of curvature and greater relief of hydrocarbon packing constraints vs greater intermolecular interactions favoring the more condensed L alpha phase. This latter effect is more important for amphiphiles with large headgroups which can pack more efficiently in the L alpha phase. The phosphatidylcholines show a gradual decrease in bilayer stabilization between 10 and 22 carbon atoms.(ABSTRACT TRUNCATED AT 250 WORDS)     

Absorption of surfactants by membranes: erythrocytes versus synthetic vesicles.

Three surfactants (chlorpromazine hydrochloride, thioridazine hydrochloride, and sodium deoxycholate) are found to absorb just as strongly into the protein-containing membranes of erythrocytes as into the phospholipid bilayers of synthetic vesicles. In the concentration region where hemolysis occurs and the Langmuir adsorption isotherm is no longer valid, one may use a phase partition model in which the erythrocyte membrane is one of the phases. The partition coefficients, expressed as the ratio of mole fraction surfactant in the membrane lipid phase to concentration of surfactant in the aqueous phase, have been calculated at the point of saturation in the erythrocyte membrane. These values are Ky = 430 M-1 (chlorpromazine, pH 5.9), 550 M-1 (deoxycholate, pH 7.6), and 640 M-1 (thioridazine, pH 5.9), in isotonic buffer at 27 degrees C. Corresponding values for synthetic vesicles made from dimyristoylphosphatidylcholine are Kx = 230 M-1 (chlorpromazine, 0.12 M buffer/KCl pH 5.9), 440 M-1 (deoxycholate, 0.20 M buffer/NaCl pH 8.0) and 510 M-1 (thioridazine, 0.12 M buffer/KCl pH 5.9), at 27 degrees C. It appears that the surfactants become an integral part of the bilayer in both vesicles and natural membranes and that the absorption is not of a peripheral nature. There is no evidence that the presence of proteins in the natural membrane inhibits the absorption of these surfactants in any way.     

On the effect of lysophosphatidylcholine, platelet activating factor and other surfactants on calcium permeability in sarcoplasmic reticulum vesicles.

The effect of low concentrations of lysophosphatidylcholine (LPC), platelet-activating factor (PAF) and other surfactants (Triton X-100, C12E8, sodium dodecyl sulfate, sodium cholate and sodium deoxycholate) on membrane permeability of native sarcoplasmic reticulum vesicles and sarcoplasmic reticulum lipid vesicles, has been studied. Triton X-100, C12E8, sodium dodecyl sulfate, sodium cholate and sodium deoxycholate were all able to permeabilize membranes at concentrations of surfactants below their critical micellar concentration (CMC) in both lipid and native vesicles, being the K0.5 of calcium release from native vesicles lower than that from lipid vesicles. The values of these K0.5 were well correlated with the corresponding CMC values for each type of membrane. However, both LPC and PAF behaved in a different way since, although they induced permeabilization of the native vesicles at values of K0.5 close to their CMC, their K0.5 values for permeabilizing vesicles, prepared by using lipids extracted from sarcoplasmic reticulum, were much higher than their corresponding CMC.