Mole Fraction Of Sodium Dodecyl Sulfate Research Articles

Susceptibility of Cu(I) transport ATPases to sodium dodecyl sulfate. Relevance of the composition of the micellar phase

Sodium dodecyl sulfate (SDS) is a well-known protein denaturing agent. A less known property of this detergent is that it can activate or inactivate some enzymes at sub-denaturing concentrations. In this work we explore the effect of SDS on the ATPase activity of a hyper-thermophilic and a mesophilic Cu(I) ATPases reconstituted in mixed micelles of phospholipids and a non-denaturing detergent. An iterative procedure was used to evaluate the partition of SDS between the aqueous and the micellar phases, allowing to determine the composition of micelles prepared from phospholipid/detergent mixtures. The incubation of enzymes with SDS in the presence of different amounts of phospholipids reveals that higher SDS concentrations are required to obtain the same degree of inactivation when the initial concentration of phospholipids is increased. Remarkably, we found that, if represented as a function of the mole fraction of SDS in the micelle, the degree of inactivation obtained at different amounts of amphiphiles converges to a single inactivation curve. To interpret this result, we propose a simple model involving active and inactive enzyme molecules in equilibrium. This model allowed us to estimate the Gibbs free energy change for the inactivation process and its derivative with respect to the mole fraction of SDS in the micellar phase, the latter being a measure of the susceptibility of the enzyme to SDS. Our results showed that the inactivation free energy changes are similar for both proteins. Conversely, susceptibility to SDS is significantly lower for the hyperthermophilic ATPase, suggesting an inverse relation between thermophilicity and susceptibility to SDS.

The effect of temperature, composition and alcohols on the microstructures of catanionic mixtures of sodium dodecylsulfate and cetyltrimethylammonium bromide in water.

The influence of mixing protocol, composition, temperature, ageing and added alcohols on the characteristics of the microstructures of sodium dodecylsulfate (SDS) + cetyltrimethylammonium bromide (CTAB) mixtures has been investigated in this paper. In this catanionic mixture (1 weight% total surfactant content) temperature induced microstructural transition occurs, which is (i) a micelle-to-vesicle transition (MVT) if αSDS (mole fraction of SDS) = 0.7, 0.8 or 0.9 and (ii) a vesicle-to-micelle transition (VMT) if αSDS = 0.1, 0.2 or 0.3. In the mixture of αSDS = 0.7, specific conductivity and dynamic light scattering measurements also support the occurrence of MVT. Transition electron microscopy and small angle neutron scattering measurements were also made to assess the characteristics of the microstructures. Alcohols added to the mixture of αSDS = 0.7 reduced the size of the vesicle, while only monohydric alcohols suppressed the temperature induced transition indicating that the number and location of -OH groups of the alcohols have a dramatic modulating influence on the structural transition occurring in catanionic mixtures. The influence of the alcohols is explained in terms of changes produced in the dielectric constant and hydrophobicity of the medium.

Micellization behavior of amphiphilic drug promazine hydrochloride and sodium dodecyl sulfate mixtures at various temperatures: Effect of electrolyte and urea

The aim of the current study is the characterization of interaction of amphiphilic drug promazine hydrochloride (PMZ) with sodium dodecyl sulfate (SDS) in the absence and presence of inorganic salt and urea. Conductometric measurements were carried out to estimate the critical micelle concentrations (CMC) of drug and surfactant along with their mixtures. A gradual reduce in the surface charge of the micelles was recognized due to the adding of salt pursued by a speedy enlargement of the micelles hence the CMC value of amphiphiles decreases. In the presence of urea an increase in the surface charge of the micelles was obtained ensuing halt of the micelle formation. Different parameters like ideal critical micelle concentration (CMCid), degree of dissociation (g), thermodynamic parameters, micellar mole fraction of SDS, and interaction parameter have been evaluated using relevant formula given in the literature. All results pointed out attractive interactions in the mixtures of drug and surfactant and showed effective involvement of the surfactant (SDS) component in the mixture. The combined effect of non-covalent is accountable for the micellization phenomena. Excess free energy of micellization (ΔGex) values was also evaluated and discussed in detail.

Conductometric Study of the Interaction of Cetrimide with Sodium Dodecyl Sulfate in Aqueous Medium

Synergistic interactions between cetrimide and sodium dodecyl sulfate (SDS) were studied at three different temperatures. Aqueous solutions of pure cetrimide, SDS and their mixtures were investigated conductometrically. The mixed surfactants exhibited nonideal behavior as the CMCs are less than the ideal CMC values calculated by using Clint’s equation. In addition, Rubingh’s model was used and various parameters such as the activity coefficients f1 and f2, micelllar mole fraction, X, interaction parameter, β, excess Gibbs energy and enthalpy of mixing, \( \Delta G_{\text{ex}} \) and \( \Delta H_{\text{ex}} \), respectively, were calculated. The values of f1, f2, and β indicate strong interaction between cetrimide and SDS and the interaction increases with increasing mole fraction of SDS in the mixture. Negative β values and |β| > |ln(CMC1/CMC2)| clearly confirm synergism in the surfactant mixture. Negative \( \Delta G_{\text{ex}}^{{}} \) and \( \Delta H_{\text{ex}}^{{}} \) values of the mixed systems at different bulk mole fractions also reflect the behaviors of β and f. The values of the standard Gibbs energy and enthalpy of mixed micelle formation are negative, suggesting that micellization is thermodynamically favorable and exothermic in nature. Larger positive contributions of the entropic component, \( T\Delta S_{\text{m}}^{ 0} \), than the enthalpic component, \( \Delta H_{\text{m}}^{ 0} \), to \( \Delta G_{\text{m}}^{ 0} \) are ascribed to the destruction of the structured water surrounding the hydrophobic groups of the surfactants when these groups are transferred from the bulk into the interior of the micelle.

How Chain Length and Charge Affect Surfactant Denaturation of Acyl Coenzyme A Binding Protein (ACBP)

Using intrinsic tryptophan fluorescence, equilibria and kinetics of unfolding of acyl coenzyme A binding protein (ACBP) have been investigated in sodium alkyl sulfate surfactants of different chain length (8-16 carbon atoms) and with different proportions of the nonionic surfactant dodecyl maltoside (DDM). The aim has been to determine how surfactant chain length and micellar charge affect the denaturation mechanism. ACBP denatures in two steps irrespective of surfactant chain length, but with increasing chain length, the potency of the denaturant rises more rapidly than the critical micelle concentration (cmc) declines. Increasing proportions of DDM, which significantly reduce the amount of monomeric sodium dodecyl sulfate (SDS), make the first denaturation step occur at lower concentrations but weaken and eventually remove the second denaturation step. The logarithm of the unfolding rate constants increases linearly with denaturant concentration below the cmc but declines at higher concentrations. Both shortening chain length and decreasing micellar charge reduce the overall kinetics of unfolding and makes the dependence of unfolding rate constants on surfactant concentration more complex. This behavior contrasts with the simplicity of unfolding in chemical denaturants and highlights the changing properties of surfactant micelles. We suggest that the transition from spherical to more elongated micelles leads to inhibition of unfolding kinetics, while weaker binding sites may cause a subsequent rise in unfolding rate constants at higher surfactant concentrations. We propose that shifting micellar binding sites on globular proteins such as ACBP, as opposed to the predefined binding sites on membrane protein surfaces, may lead to nonlinear correlations between activation unfolding energies and SDS mole fraction.

Adsorbed Monolayers of Mixed Surfactant Solutions of Sodium Dodecylsulfate and Cetylpyridinium Chloride Studied by Infrared External Reflection Spectroscopy

Infrared external reflection (IER) spectra of monolayers adsorbed on mixed surfactant solutions of sodium dodecylsulfate (SDS) and cetylpyridinium chloride were measured as a function of mole fraction of SDS (X SDS ). The alkyl chains of the surfactants in the adsorbed monolayer (Gibbs monolayer) at the air-solution interface were in all-trans conformations in the solid state, regardless of X SDS . The adsorbed monolayers at any X SDS had a single layer structure, except for X SDS ≈ 0.6-0.7, which had multilayer structures. Furthermore, the time dependency of the IER spectra revealed that the formation of the multilayer structures occurs in two processes: a faster single layer formation followed by subsequent slower multilayer formation.

Enhanced desorption and biodegradation of phenanthrene in soil–water systems with the presence of anionic–nonionic mixed surfactants

The effects of anionic–nonionic mixed surfactants, sodium dodecyl sulfate (SDS) mixed with Triton X-100 (TX100), on the desorption and biodegradation of phenanthrene in soil–water system were investigated in an aim to improve the efficiency of surfactant bioremediation technology. Results indicated that the presence of SDS not only increased the solubilization of TX100 for phenanthrene, but also reduced the sorption of TX100 onto soils. As a result, the desorption efficiency of phenanthrene from the contaminated soil was greatly enhanced by mixed surfactant solutions compared with that by single TX100 solution and appeared to be positively related with the mole fraction of SDS in solution. Mixed surfactants with relatively smaller ratio promoted phenanthrene biodegradation, for example, the biodegradation percentage of phenanthrene in 1:9 SDS–TX100 mixed solutions was about 165% of that in the single TX100 solution at the same TX100 concentration of 1.6 mmol/L in 24 h. But the biodegradation was inhibited with larger ratio of SDS in the mixed solutions, which may be due to the preferential utilization of SDS by phenanthrene degraders. Thus, the selection of mixed surfactants should consider simultaneously the effects of SDS on desorption and biodegradation. The experimental results can be used to provide valuable information in designing the surfactant bioremediation technology for contaminated soils.

Folding of DsbB in Mixed Micelles: A Kinetic Analysis of the Stability of a Bacterial Membrane Protein

Measuring the stability of integrated membrane proteins under equilibrium conditions is hampered by the nature of the proteins' amphiphilic environment. While intrinsic fluorescence is a useful probe for structural changes in water-soluble proteins, the fluorescence of membrane proteins is sensitive to changes in lipid and detergent composition. As an attempt to overcome this problem, I present a kinetic analysis of the folding of a membrane protein, disulfide bond reducing protein B (DsbB), in a mixed micelle system consisting of varying molar ratios of sodium dodecyl sulfate (SDS) and dodecyl maltoside (DM). This analysis incorporates both folding and unfolding rates, making it possible to determine both the stability of the native state and the process by which the protein folds. Refolding and unfolding occur on the second to millisecond timescale and involve only one relaxation phase, when monitored by conventional stopped-flow. The kinetic data indicate that denaturation occurs around 0.3 mole fraction of SDS, in agreement with CD analysis and acrylamide quenching data. The rate constants have been fit to a three-state folding scheme involving the SDS-denatured state, the native state and an unfolding intermediate that accumulates only under unfolding conditions at high mole fractions of SDS. The stability of DsbB is around 4.4 kcal/mol in DM, and this is halved upon reduction of the two periplasmic disulfide bonds, and is sensitive to mutagenesis. With the caveat that kinetic data are always open to alternative interpretations, time-resolved studies in mixed micelles provide a useful approach to measure membrane protein stability over a wide range of concentrations of SDS and DM, as well as a framework for the future characterization of the DsbB folding mechanism.

Analytical investigation of the self-desorption of the oligomers of mixtures of a polydisperse ethoxylated surfactant with sodium dodecylsulfate from a silica/water interface

The adsorption isotherms onto a hydrophilic silica of mixtures of sodium dodecylsulfate (SDS) and of all the oligomers of a polydisperse nonylethylene glycol n-dodecyl ether (C 12E 9) surfactant were determined using a high-performance liquid chromatography (HPLC) technique. Incorporation of the anionic surfactant to the negatively charged silica surface is favored by the adsorption of the nonionic surfactant. Comparison between the adsorption isotherms of mixtures of SDS with a monodisperse C 12E 9 and a polydisperse C 12E 9 shows that the adsorption of SDS at the silica/water interface is stronger with the latter material than with the former in a large surface coverage domain. The composition of the surface aggregates and the variation of the oligomer distribution in these aggregates were determined. The previously described phenomena called self-desorption which was observed for the global C 12E 9 and SDS surfactant mixtures was confirmed: increasing the total concentration at a fixed surfactant ratio induces at high concentration a desorption of the anionic surfactant and all of the less polar oligomers from the solid/water interface. An interpretation scheme is proposed which assumes that the interaction of SDS is larger with the less polar oligomers than with the polar ones. The self-desorption effect could then be considered as the consequence of the polydispersity of the nonionic surfactant and to the net repulsion interaction between SDS and the silica surface as the mole fraction of SDS in the surfactant mixture increases.

Removal of copper ions and dissolved phenol from water using micellar-enhanced ultrafiltration with mixed surfactants

A laboratory study was conducted to evaluate the effects of composition and concentration of mixed anionic/nonionic surfactants on the efficiency of a micellar-enhanced ultrafiltration (MEUF) operation in removing metal ions/organic solutes from aqueous solutions. Based on the analysis of surface tensions and micelle sizes, it was found that for mixed sodium dodecylsulfate (SDS)/Triton X-100 surfactants, the critical micelle concentration (cmc) was significantly lower than that of SDS and mixed micelles formed. The mixed surfactant system was then applied in a cross-flow mode of MEUF, in which the concentration polarization can be neglected, to remove Cu 2+ from aqueous solutions. With a surfactant concentration of 10 mM, the Cu 2+ rejection was negligible by using pure Triton X-100 and increased with increasing SDS mole fraction with a value as high as 85%, which suggests that the rejection of Cu 2+ was due to the electrostatic attraction between Cu 2+ and SDS. Furthermore, pronounced Cu 2+ rejection was obtained for a 5 mM SDS solution, which was attributable to a decrease in the cmc of SDS by the existence of Cu 2+. When the MEUF technique was applied to remove Cu 2+ and phenol simultaneously from aqueous solutions, the Cu 2+ rejection was slightly enhanced in the presence of phenol. However, the rejection of phenol was comparatively low, ∼27%, which may be caused by its relatively hydrophilic characteristic.

Micellization of Sodium Dodecyl Sulfate with a Series of Nonionic n-Alkyl Malono-bis-N-methylglucamides in the Presence and Absence of Gelatin

The critical micelle concentrations (cmc's) for binary mixtures of sodium dodecyl sulfate (SDS) and nonionic n-alkyl malono-bis-N-methylglucamides (CnBNMG) have been measured by surface tension. Synergistic interactions over the entire mole fraction range are observed when the nonionic alkyl chain length n is either 10 or 12. A switch from antagonistic behavior at low SDS solution mole fractions to synergistic behavior at high SDS solution mole fractions is observed for the C14BNMG/SDS mixture. The dodecyl sulfate unimer concentrations in binary mixtures of C12BNMG/SDS are well described by regular solution theory (Rubingh, D. N. Solution Chemistry of Surfactants; Plenum: New York, 1979), using the experimentally determined cmc values. On addition of gelatin, the cmc is depressed for the binary C10BNMG/SDS and C12BNMG/SDS combinations, but only above a critical SDS solution mole fraction, . Therefore, interaction between the gelatin and the mixed micelles is only seen above . No corresponding value is found for the C14BNMG/SDS system. Here, cmc's are unchanged by the presence of gelatin for any mixture, thus indicating no interaction between the mixed C14BNMG/SDS micelle and gelatin. On increasing the nonionic alkyl chain length from 10 to 12, increases. For the latter system where both components possess dodecyl tails, the dodecyl sulfate unimer concentration is reduced for solutions above but remains unchanged for solutions below , relative to the no-gelatin case. The composition of the bound micelle is very different from that formed in the absence of gelatin. Furthermore, whereas the compositions of the micelle and solution are vastly different in the absence of gelatin, they are very similar in the presence of gelatin. Not only does the nonionic surfactant promote binding of SDS to gelatin, but at the highest SDS mole fraction studied, it induces pre-cmc(1) nonmicellar SDS binding.

Polyelectrolyte−Micelle Coacervation: Effects of Micelle Surface Charge Density, Polymer Molecular Weight, and Polymer/Surfactant Ratio

The effects of micelle charge density, polymer molecular weight, and polymer-to-surfactant ratio on coacervation were studied by turbidity, dynamic light scattering, and electrophoretic mobility in the system composed of the strong cationic polymer poly(diallyldimethylammonium chloride) (PDADMAC) and oppositely charged mixed micelles of Triton X-100 (TX100) and sodium dodecyl sulfate (SDS). Phase boundaries in the range of SDS mole fraction from 0.30 to 0.50 and in the range of polymer molecular weight from 8.2 × 103 to 4.28 × 105 were obtained, and coacervate volume fraction as a function of polymer molecular weight was subsequently determined. Three-dimensional phase boundaries were used to represent the effects on coacervation of micelle surface charge density, polymer molecular weight, and PDADMAC-to-SDS ratio. The coacervation region is seen to increase with micelle surface charge density and polymer molecular weight (MW). Both higher and lower polyelectrolyte-to-surfactant ratio can suppress coacervation. An increase in MW reduces the micelle charge required for coacervation and also increases coacervate volume fraction. Coacervation is found to occur when the following conditions are satisfied: the electrophoretic mobility is close to zero, and the size of polyelectrolyte−micelle complex is at least about 45 nm.

Spontaneous Vesicle Formation from Aqueous Solutions of Didodecyldimethylammonium Bromide and Sodium Dodecyl sulfate Mixtures

Spontaneous vesicle formation in the aqueous mixture of didodecyldimethylammonium bromide (DDAB) and sodium dodecyl sulfate (SDS) has been investigated with differential interference microscopy, transmission electron microscopy, glucose trapping experiments, ζ potential measurements, and surface tension measurements. The micrographs of the DDAB-SDS mixtures confirm the spontaneous formation of polydispersed vesicles including giant vesicle with a diameter less 40 μm. The captured volume of the DDAB -SDS mixtures is 2.2 L/mol at the SDS mole fraction (X SDS ) of 0.64 and decreases with increasing X SDS . Vesicle formation in DDAB-SDS mixtures will occur in the X SDS range of 0.64-0.75, below the total surfactant concentration of 2.2 wt %. Surface tension measurements for the mixtures exhibit very low values, 23 mN/m, indicating the ion-pairing of DDAB and SDS, a pseudo-zwitterionic surfactant. This surfactant favors the morphology of a vesicle. The mechanism of vesicle self-formation is the penetration of SDS into the DDAB molecules. In addition, spontaneous vesicles are also formed in the mixture of DDAB and sodium decyl sulfate.

Interaction of the chloropentaamminecobalt(III) cation with mixed micelles of anionic and non-ionic surfactants: a kinetic study

Alkaline hydrolysis rates of the cholropentaamminecobalt(III) cation have been studied at 25.0 °C and an ionic strength of 0.05 mol dm–3 in aqueous mixed micelles composed of anionic sodium dodecyl sulfate (SDS) and non-ionic n-dodecylpenta(oxyethylene glycol) monoether (C12E5) surfactants over a wide range of total surfactant concentration (Ct) and SDS mole fraction (α). The critical micelle concentrations (c.m.c.s) of mixtures of the two surfactants over the entire α range have also have been determined and found to follow the regular solution model for non-ideal mixing. The kinetic results have shown that interactions of the cationic cobalt complex with the mixed micelles cause a decrease of the reaction rate with increasing Ct(at constant α) and α(at constant Ct). The estimated binding constant of the complex decreases markedly as α decreases as a result of the reduction of the charge density at the mixed micellar surface. The present findings are compared with those obtained previously concerning the effect of urea and its alkyl derivatives upon the rate of the same hydrolysis reaction in SDS micellar solutions.

Effects of inorganic electrolytes and of pH on micelle formation of amphoteric-anionic mixed surfactant systems

The effect of inorganic electrolytes on micelle formation of mixed amphoteric-anionic surfactant systems has been studied for various surface tensions, pH values, and relative viscosities. These systems are N α, N α-dimethyl- N ϵ-lauroyl lysine (DMLL)-sodium dodecyl sulfate (SDS), which include different inorganic electrolytes (NaCl, NaOH, or HCl). The critical micelle concentration (CMC) values of the surfactant, except that of DMLL, decrease with increasing concentration of NaCl. The ratio of decrease of CMC {[CMC 0 (CMC of salt-free system) — CMC s (CMC of added NaCl system)]/CMC 0} increases with increasing mole fraction of SDS in the mixed surfactant systems including NaCl. The pH value at every molar ratio decreases with increasing NaCl. The ratio of decrease of pH values { [a s , (activity of H + in added NaCl system) − a 0, (activity of H + in salt-free system) ] a s } for mixed surfactant systems is greater than that for each single surfactant system, and increases with increasing mole fraction of SDS in the mixed surfactant system including NaCl. The CMC values and relative viscosities increase monotonically with increasing mole fraction of DMLL in the mixed surfactant systems including NaOH. The CMC values of mixed surfactant systems including HCl are much smaller than those of systems including NaCl. Inorganic electrolytes appear to affect the magnitude of the hydrophilic-hydrophilic interaction between DMLL and SDS molecules in mixed micelles.

Base-Catalyzed Hydrolysis of Acetylcholine Chloride in the Presence of Anionic and Nonionic Surfactants

Abstract Base-catalyzed hydrolysis of acetylcholine chloride (Ach) in the presence of anionic and nonionic surfactants was investigated. The rate of hydrolysis was determined by measuring the rate of disappearance of Ach with a spectrophotometer. At a constant pH of 9.0, addition of heptaethylene glycol dodecyl ether (HED) at concentrations above the critical micelle concentration (cmc) results in a slight increase in the apparent rate, υ, which is expressed by two reaction rates, υf and υm, in the aqueous and micellar phases, respectively. The increase in the apparent rate is due to increase in υm. In the presence of sodium dodecyl sulfate (SDS), the apparent rate constant, kapp, is approximately constant at concentrations below the cmc, and kapp decreases above the cmc. In the presence of SDS–HED mixed micelles, kapp decreases with the mole fraction of SDS. In these cases, the decrease in the apparent rate is due to the decrease in both υf and υm. These two kapp decreases are due, respectively, to the decrease in Ach in the aqueous phase and the electrostatic repulsion between OH− and DS− at the micelle surface in conformity with the Gouy-Chapman theory.