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.     

The effect of chain length on the melting temperature and size of dialkyldimethylammonium bromide vesicles

Differential scanning calorimetry (DSC) and dynamic light scattering (DLS) were used to obtain the gel to liquid-crystalline phase transition temperature (Tm) and the apparent hydrodynamic radius (Rh) of spontaneously formed cationic vesicles of dialkyldimethylammonium bromide salts (CnH2n+1)2(CH3)2N+.Br-, with varying chain lengths. The preparation of cationic vesicles from aqueous solution of these surfactants, for n=12, 14, 16 and 18 (DDAB, DTDAB, DHDAB and DODAB, respectively), requires the knowledge of the surfactant gel to liquid-crystalline phase transition temperature, or melting temperature (Tm) since below this temperature these surfactants are poorly or not soluble in water. That series of cationic surfactants has been widely investigated as vesicle-forming surfactants, although C12 and C18, DDAB and DODAB are by far the most investigated from this series. The dependence of Tm of these surfactants on the number n of carbons in the surfactant tails is reported. The Tm obtained by DSC increases non-linearly with n, and the vesicle apparent radius Rh is about the same for DHDAB and DODAB, but much smaller for DDAB.     

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.     

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.     

Phase transition in dioctadecyldimethylammonium bromide and chloride vesicles prepared by different methods

The gel to liquid crystalline phase transition of the double-chained cationic dioctadecyldimethylammonium chloride and bromide (DODAX, X = Cl- or Br-) in aqueous vesicle dispersions prepared by non-sonication. sonication and extrusion has been investigated using high-sensitivity differential scanning calorimetry (DSC). The transition temperature (Tm) is a function of the preparation method, amphiphile concentration, vesicle curvature and nature of the counterion. DSC thermograms for DODAB and DODAC non-sonicated vesicle dispersions exhibit a single endothermic peak at Tm roughly independent of concentration up to 10 mM. Extrusion broadens the transition peak and shifts Tm downwards. Sonication, however, broadens slightly the transition peak and tends to shift Tm upwards suggesting that extrusion and sonication form vesicles with different characteristics. DODAC always exhibits higher Tm than DODAB irrespective of the preparation method. Tm changes as follows: Tm (sonicated) > or = Tm (non-sonicated) > Tm (extruded). Hysteresis of about 7 degrees C was observed for DODAB vesicle dispersions.     

Comparative effects of four surfactants on growth,contraction and adhesion of cultured human fibroblasts

A range of surfactants, including the anionic sodium dodecyl sulfate, the cationic cetyltrimethylammonium bromide and the nonionics octylphenoxy polyethoxyethanol (Triton X100) and polyoxyethylene 20 sorbitan monoleate (Tween 80) was studied for effects on proliferation, contractibility and attachment of cultured human fibroblasts. Only ionic surfactants exhibited a stimulatory effect on fibroblast proliferation, whereas all the surfactants tested increased the contraction of collagen gels containing fibroblasts, with the greatest effect from the non-ionic surfactants. This activity was not correlated with an increase of cell population or cell attachment within the collagenous matrix. The activity of the surfactants was seen only at levels close to their LD₅₀ values and in a narrow range of concentrations. Thus, we consider that they are the result of the so-called hormesis phenomenon.Abbreviations CTAB cetyltrimethyl-ammonium bromide - FCS fetal calf serum - LD₁₀₀ dose lethal to 100% of exposed - MCD maximal contraction dose - PDL population doubling level - SDS sodium dodecyl sulfate     

Studies on surfactant-biopolymer interaction. I. Microcalorimetric investigation on the interaction of cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) with gelatin (Gn), lysozyme (Lz) and deoxyribonucleic acid (DNA)

The interaction of the surfactants cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) with the biopolymers gelatin (Gn), lysozyme (Lz) and deoxyribonucleic acid (DNA) was studied by isothermal titration microcalorimetry at varied biopolymer concentration, pH and temperature. The nature of interaction of the surfactants with the biopolymers was assessed from the observed enthalpy-[surfactant] profiles. The biopolymer-induced aggregation of the surfactants was observed. The enthalpies of aggregation of amphiphiles, binding of aggregates with macromolecules, organisational change of bound aggregates, and threshold concentrations for micelle formation of surfactants in the presence of biopolymers were estimated. The results collected on the three biopolymers were analysed and compared.     

Isolation, characterization, and investigation of surface and hemolytic activities of a lipopeptide biosurfactant produced by Bacillus subtilis ATCC 6633

Bacillus subtilis ATCC 6633 was grown in BHIB medium supplemented with Mn2+ for 96 h at 37 degrees C in a shaker incubator. After removing the microbial biomass, a lipopeptide biosurfactant was extracted from the supernatant. Its structure was established by chemical and spectroscopy methods. The structure was confirmed by physical properties, such as Hydrophile-Lipophile Balance (HLB), surface activity and erythrocyte hemolytic capacity. The critical micelle concentration (cmc) and erythrocyte hemolytic capacity of the biosurfactant were compared to those of surfactants such as SDS, BC (benzalkonium chloride), TTAB (tetradecyltrimethylammonium bromide) and HTAB (hexadecyltrimethylammonium bromide). The maximum hemolytic effect for all surfactants mentioned was observed at concentrations above cmc. The maximum hemolytic effect of synthetic surfactants was more than that of the biosurfactant produced by B. subtilis ATCC 6633. Therefore, biosurfactant would be considered a suitable surface-active agent due to low toxicity to the membrane.     

Characterization of dewatering process of activated sludge assisted by cationic surfactants

In this work, the dewatering of activated sludge assisted by cationic surfactants was investigated. Dose of dodecyl trimethyl ammonium bromide (DTAB) and cetyl trimethyl ammonium bromide (CTAB) resulted in the release of extracellular polymeric substances (EPS) from sludge and decrease in sludge negative charge. The surfactants significantly promoted sludge dewaterability, as reflected by decreased specific resistance of filtration (SRF) and water content in sludge cakes. The treated sludge were analyzed by combined use of differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) analysis. CTAB was found more effective in releasing bound water from sludge than DTAB, due to its superior surface activity and strong adsorption/bridge capacities with sludge. The specific surface area and pore size of sludge cakes declined after surfactant treatment, indicating an enhanced compressibility. With these results, the surfactant-assisted dewatering mechanism could be attributed to the integrated effects of electrostatic neutralization, enhanced compaction and release of EPS and bound water. Our study clearly characterizes the accelerated dewatering process assisted by cationic surfactants, and demonstrates that cationic surfactants could be used as a potential agent for sludge dewatering.     

Reverse micelles‐mediated transport of lipase in liquid emulsion membrane for downstream processing

This work deals with the downstream processing of lipase (EC 3.1.1.3, from Aspergillus niger) using liquid emulsion membrane (LEM) containing reverse micelles for the first time. The membrane phase consisted of surfactants [cetyltrimethylammonium bromide (CTAB) and Span 80] and cosolvents (isooctane and paraffin light oil). The various process parameters for the extraction of lipase from aqueous feed were optimized to maximize activity recovery and purification fold. The mechanism of lipase transport through LEM consisted of three steps namely solubilization of lipase in reverse micelles, transportation of reverse micelles loaded with lipase through the liquid membrane, and release of the lipase into internal aqueous phase. The results showed that the optimum conditions for activity recovery (78.6%) and purification (3.14‐fold) were feed phase ionic strength 0.10 M NaCl and pH 9.0, surfactants concentration (Span 80 0.18 M and CTAB 0.1 M), volume ratio of organic phase to internal aqueous phase 0.9, ratio of membrane emulsion to feed volume 1.0, internal aqueous phase concentration 1.0 M KCl and pH 7.0, stirring speed 450 rpm, and contact time 15 min. This work indicated the feasibility of LEM for the downstream processing of lipase. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2012     

Dependence of buffer acidity and surfactant chain-length on electro-osmotic mobility in thermoplastic microchannels

In this paper, we report the dependence of buffer pH and coating surfactant chain-length on electro-osmotic (EO) mobility in co-polyester microchannels. Thermoplastics co-polyester hydrolyzes to anionic functionality to create electrical double layer on the micro-channel walls. These negatively charged sites are partially or completely screened when long-chain surfactants are added into the buffer. This ancillary technique to modify surface charge polarity to avoid analyte adsorption is known as dynamic coating. We develop a theory to predict the EO mobility tendency on buffer acidity considering the combination of pH-dependent surfactant aggregation and surface dissociation. Our findings of pH-dependent EO mobility in coated channels, using three types of quaternary ammonium surfactants, lauryltrimethyammonium bromide (LTAB), trimethyl (tetradecyl) ammonium bromide (TTAB), and cetyltrimethyammonium bromide (CTAB), agree with our theoretical prediction. We also explain the chain-length dependence of mobility with a collaborative adsorption mechanism of surfactant aggregates.     

Relationship of hyperthermia-induced hemolysis of human erythrocytes to the thermal denaturation of membrane proteins

Hemolysis of human erythrocytes as a function of time of exposure to 47.4-54.5 degrees C was measured and correlated to thermal transitions in the membranes of intact erythrocytes as determined by differential scanning calorimetry (DSC). Curves of hemoglobin leakage (a measure of hemolysis) as a function of time have a shoulder region exhibiting no leakage, indicative of the ability to accumulate sublethal damage (i.e., damage not sufficient to cause lysis), followed by a region of leakage approximating pseudo-first-order kinetics. Inverse leakage rates (Do) of 330-21 min were obtained from 47.4-54.5 degrees C, respectively. A relatively high activation energy of 304 +/- 22 kJ/mol was obtained for leakage, eliminating the involvement of metabolic processes but implicating a transition as the rate-limiting step. Membrane protein involvement was suggested by the very low rate (10(-2) of the rate from erythrocytes) and low activation energy (50 +/- 49 kJ/mol) of hemoglobin leakage from liposomes containing no membrane protein. A model was developed that predicts a transition temperature (Tm) for the critical target (rate-limiting step) of 60 degrees C when measured at a scan rate of 1 K/min. DSC scans were obtained from intact erythrocytes and a procedure developed to fit and remove the transition for hemoglobin denaturation which dominated the scan. Three transitions remained (transitions A, B, and C) with Tm values of 50.0, 56.8, and 63.8 degrees C, respectively. These correspond to, but occur at slightly different temperatures than, the A, B, and C transitions of isolated erythrocyte membranes in the same salt solution (Tm = 49.5, 53-58, and 65.5 degrees C, respectively). In addition, the relative enthalpies of the three transitions differ between isolated membranes and erythrocytes, suggestive of membrane alterations occurring during isolation. Thus, all analyses were conducted on DSC scans of intact erythrocytes. The B transition is very broad and probably consists of several transitions. An inflection, which is seen as a distinct peak (transition B3) in fourth-derivative curves, occurs at 60.8 degrees C and correlates well with the predicted Tm of the critical target. Ethanol (2.2%) lowers the Tm of B3 by 4.0-4.5 K, close to the shift of 3.3 K predicted from its effect on hemolysis. Glycerol (10%) has very little effect on both hemolysis and the Tm of B3, but it stabilizes spectrin (delta Tm = 1.5 K) against thermal denaturation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of external high pressures on the clay mineral sodium montmorillonite intercalated with methylated octadecylammonium bromide surfactants

Raman microprobe spectra of the clay mineral Wyoming SWy-2-sodium montmorillonite intercalated with the surfactants, methyltrioctadecylammonium bromide (TOMA) dimethyldiotadecylammonium bromide (DODMA) and octadecyl-trimethylammonium bromide (ODTMA), have been measured in the CH₂ stretching region at external pressures up to ∼40 kbar with the aid of a diamond-anvil cell. In the case of the intercalated clays containing TOMA and DODMA, the Raman data afford evidence for gauche to trans conformational changes in the orientation of the CH₂ chains in the surfactants with increasing pressure. These conformational changes are reversed completely upon the release of pressure.     

Effect of various surfactants (cationic,anionic and non-ionic) on the growth of <Emphasis Type="Italic">Aspergillus parasiticus</Emphasis> (NRRL 2999) in relation to aflatoxin production

The effect of surfactants (two cationic, one anionic and three non-ionic) at 0.001, 0.01, 0.1 and 1.0 % concentrations on aflatoxin production, ergosterol content and sugar consumption by Aspergillus parasiticus (NRRL 2999) in YES liquid culture medium is reported. At 0.01% concentration, the cationic surfactants, cetyl dimethyl ammonium bromide (CDAB) and dodecyl trimethyl ammonium bromide (DTAB), and the anionic surfactant, sodium dodecyl sulfate (SDS), completely inhibited spore germination, while DTAB also inhibited the production of ergosterol and toxin (p < 0.05). At a concentration of 0.001%, CDAB was found to enhance toxin production, while SDS was found to inhibit it when compared with other surfactants. Non-ionic surfactants, polyoxyethylene sorbitan monolaurate (Tween-20), polyoxyethylene lauryl ether (Brij-35) and ethoxylated p-tert-octylphenol (Triton X-100) delayed the spore germination up to day 5 at all concentrations and inhibited toxin and ergosterol production at 0.001% concentration. The affect was found to be dose-dependent from 0.001% to 1%, for Triton X-100 only. Positive correlation between ergosterol content and toxin production in the presence of different surfactants at various time periods (3, 5, 7, 9 and 12 days) was found. Tween-20 was most effective in inhibiting toxin production on day 7, when aflatoxin production was found to be maximal in control group. Sugar consumption was directly proportional to the ergosterol content, showing a significant correlation with aflatoxin production.     

Cationic surfactant mediated fibrillogenesis in bovine liver catalase: a biophysical approach

Protein aggregation into oligomers and mature fibrils are associated with more than 20 diseases in humans. The interactions between cationic surfactants dodecyltrimethylammonium bromide (DTAB) and tetradecyltrimethylammonium bromide (TTAB) with varying alkyl chain lengths and bovine liver catalase (BLC) were examined by various biophysical approaches. The delicate coordination of electrostatic and hydrophobic interactions with protein, play imperative role in aggregation. In this article, we have reconnoitered the relation between charge, hydrophobicity and cationic surfactants DTAB and TTAB on BLC at pH 7.4 and 9.4 which are two and four units above pI, respectively. We have used techniques like turbidity, Rayleigh light scattering, far-UV CD, ThT, ANS, Congo red binding assay, DLS, and transmission electron microscopy. The low concentration ranges of DTAB (0–600 μM) and TTAB (0–250 μM) were observed to increase aggregation at pH 9.4. Nevertheless, at pH 7.4 only TTAB was capable of inducing aggregate. DTAB did not produce any significant change in secondary structure at pH 7.4 suggestive of the role of respective charges on surfactants and protein according to the pI and alkyl chain length. The morphology of aggregates was further determined by TEM, which proved the existence of a fibrillar structure. The surfactants interaction with BLC was primarily electrostatic as examined by ITC. Our work demystifies the critical role of charge as well as hydrophobicity in amyloid formation.     

Study of the secondary and tertiary structure of phage MS2 RNA using nucleases and fluorescent dyes specific for secondary structure

The binding of ethidium bromide (EtBr) and acridine orange (AO) to RNA in native state or after hydrolysis by S1 and SV nucleases that specifically split single-stranded and double-stranded segments was studied. Nuclease S1 hydrolysis of RNA does not increase the number of EtBr strong binding sites, Tm and hyperchromic effect being also unchanged. Hydrolysis by double-stranded segments accessible to EtBr is followed by the diminishing of Tm and hyperchromism. A supposition is put forward that the main role in stabilization of the RNA tertiary structure is played by double-stranded segments arranged so that some of them are hidden and do not interact with dyes. One of the possible models may be parallel oriented intramolecular "hair-pins" forming compact "rod-like" structures.     

Location and mobility of ubiquinones of different chain lengths in artificial membrane vesicles

Ubiquinone (UQn with n = 2, 3, or 10 isoprenoid groups) was incorporated into small, sonicated vesicles made of dipalmitoylphosphatidylcholine (DPPC) or dimyristoylphosphatidylcholine (DMPC). (1) The accessibility of oxidized UQ in DPPC or DMPC vesicles to the reductant sodium borohydride (NaBH4), measured by UV spectroscopy, was UQ2 greater than UQ3 greater than UQ10 (DPPC) and UQ2 greater than UQ3 approximately UQ10 (DMPC). (2) Catalysis of the reduction of entrapped ferricyanide by exogenous NaBH4 was more effective with UQ2 than UQ10 but was slower with all quinones than reduction by added dithionite. (3) The methoxy protons of UQ2 and UQ3 in DPPC and DMPC vesicles exhibited a single NMR resonance centered at approximately 3.95 ppm, whereas the methoxy groups of UQ10 gave rise to two separate proton resonances, at 3.93 ppm and a more narrow resonance at 3.78 ppm. The UQ10 population characterized by the 3.78 ppm resonance was present at a higher concentration in DPPC than in DMPC vesicles and was relatively insensitive to reduction by NaBH4. (4) UQ10 perturbed the melting temperature (Tm) of DPPC vesicles to a smaller extent (delta Tm = -1 degrees C) than did UQ2 and UQ3 (delta Tm = -3 to -4 degrees C). The combined UV and NMR data imply the following: The UQ10 pool characterized by the 3.78 ppm peak corresponds to a more mobile UQ10 fraction that is not reduced by NaBH4 in 2-3 min and is thought to be localized close to the center of the DPPC bilayer since it has little effect on the DPPC Tm.(ABSTRACT TRUNCATED AT 250 WORDS)     

Surfactant-induced refolding of lysozyme

The surfactant-lysozyme interaction was investigated by circular dichroism, fluorescence, UV, dynamic light scattering, surface tension, turbidity measurements and lysozyme activity assay. A new way of refolding of lysozyme was found. It was shown that the lysozyme unfolded by anionic surfactants could be renatured by adding cationic surfactants. That is, lysozyme formed precipitate with anionic surfactants, the precipitates could be dissolved by adding a cationic surfactant solution, and then the lysozyme was refolded to its native state spontaneously. Different couples of anionic surfactants and cationic surfactants including C10SO3/C10NE, C12SO3/C10NE, C10SO3/C12NE, C10SO3/C12NB, C10SO4/C10NE and C12SO4/C10NE (C(n)SO3, C(n)SO4, C(n)NE and C(n)NB represent sodium alkyl sulfonate/sulfate, alkyl triethyl/butyl ammonium bromide respectively) were investigated, all of them gave similar results. The results were explained in terms of the differences between the interaction of anionic-cationic surfactants and that of surfactant-lysozyme. It was thought that the formation of mixed micelles of anionic-cationic surfactants is a more favorable process than that of lysozyme-surfactant complexes, which induces the dissociation of lysozyme-surfactant complexes when cationic surfactants were added.     

Inhibition of Mussel Suspension Feeding by Surfactants of Three Classes

Effects of three surfactants on the filtration rates by marine mussels were studied. The xenobiotics tested represented anionic, cationic and non-ionic surfactants (tetradecyltrimethylammonium bromide, a representative of a class of cationic surfactants; sodium dodecyl sulphate, a representative of anionic alkyl sulfates; and Triton X-100, a representative of non-ionic hydroxyethylated alkyl phenols). All three surfactants inhibited the clearance rates. The significance of the results for the ecology of marine ecosystems is discussed.     

Formation of 2-D paracrystals of F-actin on phospholipid layers mixed with quaternary ammonium surfactants.

Two-dimensional paracrystalline arrays of F-actin have been formed on positively charged lipid layers composed of phosphatidylcholine (PC) and quaternary ammonium surfactants. These quaternary ammonium surfactants were found to be better promoters of two-dimensional order than PC lipid layers mixed with stearylamine. In addition, the length of the hydrocarbon chain was found to influence the achievement of 2-D order. Lipid layers composed of dilauryl-PC and didodecyldimethylammonium bromide, which are saturated C12 lipids, promoted 2-D crystallization better than mixtures of dipalmitoyl-PC, a saturated C16 lipid, and dioctadecyldimethylammonium bromide, a saturated C18 lipid. Thus, the hydrocarbon chain length, which influences lipid layer fluidity, had a significant effect on paracrystal formation. We suggest that quaternary ammonium surfactants may have advantages in some cases for forming ordered arrays on lipid layers. In addition to investigating the effect of lipid layer composition on paracrystal formation, we found that the injection of G-actin rather than F-actin under a fluid lipid layer into a polymerizing solution produced better ordered paracrystals.