Sodium N-dodecyl Sulfate Research Articles

Domain analysis of human apotransferrin upon interaction with sodium n-dodecyl sulphate: differential scanning calorimetry and circular dichroism approaches

The domain analysis of human apotransferrin (apo hTF) upon interaction with sodium n-dodecyl sulphate (SDS) was studied by differential scanning calorimetry (DSC) and circular dichroism (CD) using Hepes buffer, 100 mM, at pH=7. The DSC profile for apo hTF depicts two distinct peaks, while when interacted with SDS, the DSC peaks are shifted to the left as well as the area under the peaks are reduced. The DSC profile without the presence of SDS has two dissimilar peaks including two melting points ( T m=60 °C, T m=70 °C). This profile in the presence of low concentrations of SDS shows two nearly similar peaks and decrement of T m values about 5 °C relative to profile in the absence of SDS. The DSC excess heat capacity was deconvoluted for apo hTF in the presence of SDS. The interaction of SDS with apo hTF induced two dissimilar subdomains for each domain, but each domain having two subdomains similar to each other. The CD experiment of apo hTF–SDS complexes shows the decrement of α-helix content and the increment of β-sheet structure relative to protein in the absence of SDS. The α-helix tendency calculation shows more α-helix content for N domain relative to C domain. Here SDS at low concentration plays a role as a good probe to define the electrostatic moiety for N domain relative to C domain that is initiated from dissimilarity of α-helicity of two domains.

Characterization of the Solvation Properties of Surfactants by Solvatochromic Indicators

Kamlet-Taft solvatochromic scales have been used for the characterization of three different micellar electrokinetic chromatography (MEKC) systems, providing information about the polarity parameters of both the aqueous phase and the micellar phase of each system. The surfactants studied are sodium cholate (SC), which belongs to the family of bile salts, lithium perfluoro-n-octanesulfonate (LPFOS), a fluoro-surfactant, and n-hexadecyl-trimethylammonium bromide (HTAB), a cationic surfactant. Sodium n-dodecyl sulfate, the most commonly used surfactant in MEKC, was already studied in a previous work. The solvatochromic measurements allow the determination of the critical micellar concentration (cmc) of the surfactants and also the partition coefficients of the solvatochromic indicators in each system. Both cmc and partition coefficients have been also determined through MEKC experiments, and good agreement is observed between the two methods. The results of the solvatochromic study indicate that LPFOS is the surfactant that has properties more similar to those of the aqueous phase, whereas SC is the most hydrogen-bond basic and acidic surfactant. and HTAB has the lowest hydrogen-bond acidity.

Aquamethemoglobin reduction by sodium n-dodecyl sulfate via coordinated water oxidation

The influence of sodium n-dodecyl sulfate (SDS) on hemoglobin reduction has been studied in the presence of 100 mM phosphate buffer (pH 7.0) using spectrophotometry, cyclic voltammetry and chemiluminescence (CL) methods. Spectroscopic studies have revealed that the SDS concentration up to 1 mM reduces the methemoglobin (metHb) to its deoxy form. Such a redox reaction is believed to occur by water oxidation of the sixth coordination in aquametHb. The proposed mechanism is supported by a CL method which monitors H 2O 2 during the conversion of metHb to its deoxy form by addition of SDS at low concentrations (up to 1 mM).

Ionic Equilibria of Fluorophores in Organized Solutions: The Influence of Micellar Microenvironment on Protolytic and Photophysical Properties of Rhodamine B

Ionic equilibria and fluorescence decay of rhodamine B were studied in micellar solutions of sodium n-dodecyl sulfate (SDS) with various additives (NaCl, pentanol-1, crown ether, and tetra-n-butyl ammonium salt), and five nonionic surfactants (Brij 35, nonyl phenol 12, Triton X-100, Triton X-305, Tween 80), as well as in β-cyclodextrin solutions. The apparent dissociation constants, \(K_a^a\), of rhodamine B (HR+ ⇄ R + H+) were obtained. The distribution of the dye species HR+ and R in the ultramicroheterogeneous systems was studied using absorption and emission spectra, fluorescence life-times, τ, and the plots of p\(K_a^a\) versus surfactant concentration. The p\(K_a^a\) values under conditions of complete binding, p\(K_a^a\), were found to be markedly higher than that in water \({\text{p}}K_a^w\). The medium effects, \(\Delta {\text{p}}K_a^{{\text{a}}c} = {\text{p}}K_a^{{\text{a}}c} {\text{ - p}}K_a^w\), in organized solutions studied are in accord with the charge type of the acid-base couple +/±, confirming the zwitterionic nature of rhodamine B neutral species. Both τ and \(\Delta {\text{p}}K_a^{{\text{a}}c}\) a values of the dye were shown to sense the changes in the micellar microenvironments, and the possibility of using rhodamine B as an interfacial acid-base indicator, for example, for monitoring of surface potentials and of bulk ionic strength, were demonstrated.

Characterization of the Solvation Properties of Sodium n-Dodecyl Sulfate Micelles in Buffered and Unbuffered Aqueous Phases by Solvatochromic Indicators

The solvation properties of a micellar electrokinetic chromatography (MEKC) system composed of an aqueous phosphate buffer at pH 7.0 and sodium n-dodecyl sulfate (SDS) have been determined with solvatochromic indicators and compared with those of pure unbuffered water−SDS micellar system. The solvatochromic measurements allow calculation of the critical micellar concentrations (CMC), partition coefficients for the test compounds, and solvation properties of the two micellar systems studied. The results obtained are in good agreement with data obtained here and in previous works from MEKC measurements for the phosphate−SDS system. The solvent properties and partition coefficients in phosphate−SDS buffer are very similar to those obtained in water−SDS system, but the CMC values are lower in the phosphate buffer. The obtained results indicate that SDS micelles are very polar (π* = 1.02±0.01), quite hydrogen-bond donor (HBD) acidic (α = 0.80±0.02), and moderately hydrogen-bond acceptor (HBA) basic (β = 0.62±0...

Mechanisms of aggregation of alpha- and beta-amylases in aqueous dispersions

A lot of attention has been paid to elucidate the mechanisms of enzyme inactivation and aggregation so that stabilization strategies can be specifically applied to prevent thermal and/or physical denaturation of enzymes in industrial processes. In the present study, we have investigated the mechanisms of aggregate formation of two model enzymes, α-amylase from Bacillus subtilis and soybean β-amylase, under different experimental conditions. Aggregation can be observed among α-amylase particles after 1 week of aging either through physical contacts or through the intermolecular disulfide bond formed by the surface Cys residues from two enzyme monomer. In contrast, β-amylase does not form any aggregation probably due to the electrostatic repulsion and steric hindrance. Both surfactant sodium n-dodecyl sulfate and reducing agent beta-mercaptoethanol (BME) dramatically reduce the aggregate size, especially for α-amylase, by destroying the intermolecular disulfide linkages. Sonication appears to improve the formation of aggregates only for α-amylase. The average aggregate sizes are usually the largest at the isoelectric points of these two enzymes. A protein having more free Cys residues on its surface does not guarantee disulfide bond-induced aggregation.

Inhibition of human hemoglobin autoxidation by sodium n-dodecyl sulphate.

The effect of sodium n-dodecyl sulphate (SDS) on hemoglobin autoxidation was studied in the presence of a 100 mM phosphate buffer (pH 7.0) by different methods. These included spectrophotometry, fluorescence technique, cyclic voltametry, differential scanning calorimetry, and densitometry. Spectroscopic studies showed that SDS concentrations up to 1 mM increased deoxy-, decreases oxy-, and had no significant effect on the met- conformation of hemoglobin. Therefore, a SDS concentration up to 1 mM increased the deoxy form of hemoglobin as the folded, compact state and decreases the oxy conformation. The turbidity measurements and differential scanning calorimetry techniques indicated a more stable conformation for hemoglobin in the presence of SDS up to 1 mM. Electrochemical studies also confirmed a more difficult oxidation under these conditions. The induction of the deoxy form in the presence of SDS was confirmed by densitometry techniques. The compact structure of deoxyhemoglobin blocks the formation of met-conformation in low SDS concentrations.

Thermodynamic domain analysis of fresh and incubated human apotransferrin

The thermal denaturation of human apotransferrin was studied by a differential scanning calorimeter (DSC) in 100mM Hepes buffer at pH 7.0. Deconvolution analysis of excess molar heat capacity was adjusted by four transitions of which two transitions were linked to N-domain and the remaining two were connected to C-domain. The same experiment was carried out for the incubated sample for a period of 24h at 27°C. The deconvolution subpeaks exhibited five transitions. The free energy, ΔGH2O∘, in the absence of sodium n-dodecyl sulphate (SDS), as a criterion of stability measurement, was obtained based on Pace theory on UV spectrophotometry. The result indicates that incubated sample was stabilized by 14kJmol−1 relative to the fresh sample. The circular dichroism (CD) study confirms the presence of additional secondary structures for the incubated sample compared with the fresh one because of Hepes molecule interaction with protein domains.

Peroxidase-like activity of cytochrome c in the presence of anionic surfactants

Peroxidase-like activity of cytochrome c is significantly higher in the presence of anionic surfactants, sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and sodium n-dodecyl sulphate (SDS). The enhancement is due to the higher reaction rate of the cytochrome c with H2O2, which is the rate determining step in the peroxidase cycle of cytochrome c. An intermediate formed in the cycle rapidly oxidizes the substrates or reacts with further molecule(s) of H2O2, causing heme degradation. Thus, the specific microenvironment provided by anionic surfactants facilitates also degradation of heme iron by H2O2.

Effect of Anionic Surfactants on Crystal Growth of Calcium Hydrogen Phosphate Dihydrate

The effect of anionic surfactants (single-chained sodium n-dodecyl sulfate (SDS), asymmetric double-chained sodium bis(2-ethylhexyl) sulfosuccinate (AOT), and two-headed disodium oleoamido PEG-2 sulfosuccinate) on the crystallization process of calcium hydrogen phosphate dihydrate (DCPD) was investigated. All surfactants, depending on the type and actual concentration, showed inhibitory effects on the overall crystallization process. Below the critical micelle concentration (cmc), electrostatic adsorption of surfactant anions on lateral crystal faces inhibited crystal growth and changed crystal morphology. Above the cmc, SDS and AOT caused phase changes; that is, a mixture of DCPD and octacalcium phosphate was formed.

Simultaneous electrochemical formation of Al 2O 3/polypyrrole layers (I): effect of electrolyte anion in formation process

We studied the capability of various kinds of sulfonate-based electrolytes to form a bilayered Al 2O 3/polypyrrole (PPy) film on an aluminum substrate in aqueous solution. As electrolytes, we selected sodium p-toluenesulfonate (monovalent sulfonate), sodium naphthalene-trisulfonate (trivalent sulfonate), poly(sodium 4-styrenesulfonate), poly(sodium vinylsulfonate) (sulfonate polymer), sodium n-dodecylbenzenesulfonate (SDBS), sodium butylnaphthalenesulfonate(BNS), and sodium n-dodecylsulfate (SDS, surfactant sulfonate/sulfate). Among the sulfonates we investigated, SDBS, BNS and SDS appeared to form a barrier-type Al 2O 3 layer with high coulombic efficiency in the absence of pyrrole. In the presence of pyrrole, anodization of these electrolytes resulted in the formation of Al 2O 3 and PPy layers, simultaneously.

Determination of critical micelle concentration of SDS in formamide by capillary electrophoresis

Using an organic solvent and a surfactant, the uncharged, hydrophobicp-arylacetophenones have been separated by micellar electrokinetic chromatography. As an example, the effect of formamide containing sodium n-dodecyl sulfate (SDS) on the separation has been studied. Separations of all selected uncharged hydrophobic compounds were shown to be strongly dependent on the concentration of surfactant. It is suggested that if there is no micelle formed in the formamide solvent, the uncharged hydrophobic compound cannot be separated even though in the presence of surfactant. The electro-migration of solutes was considered zero. After micelle formation, the uncharged compounds were partitioned between the micellar and the organic solvent phases. Neutral molecule partition in and out of micelles depends on the hydrophobicity of each analyte. Based on this suggestion the critical micelle concentrations of SDS, di-(ethylhexyl) sodium sulfosuccinate (AOT) and taurodexycholic acid sodium salt (STDC) in formamide were determined.

Conductivity and Relative Permittivity of Sodium n-Dodecyl Sulfate and n-Dodecyl Trimethylammonium Bromide

The electrical conductivity and relative permittivity of the amphiphilics sodium n-dodecyl sulfate (SDS) and n-dodecyl trimethylammonium bromide (DTAB) were measured as a function of frequency (200 kHz to 20 MHz) at various concentrations. Both methods lead to similar values of the critical micelle concentration (cmc) for both surfactants despite the greater sensitivity of the relative permittivity to structural transformations derived from the formation of the micelles. The electrical conductivity is seen to be rather independent of frequency whereas the relative permittivity exhibits abrupt transitions in the neighborhood of the cmc. Tridimensional plots of the electrical conductivity as a function of the frequency and molar concentration show a gradual transition to the micellar state that takes place in the cmc concentration range. Relative permittivity values have been analyzed independently for concentrations above and below the cmc. In the micellar state both substances show a quadratic dependence of the relative permittivity on concentration. Below the cmc the relative permittivity shows a linear dependence on concentration in the monodisperse (SDS) region and a quadratic dependence in the polydisperse (DTAB) region. The relative permittivity is a better indicator of the existence of amphiphilic preaggregation than the electrical conductivity.

Interfacial Compositions and Phase Structures in Mixed Surfactant Microemulsions

Well-defined mixtures of didodecyldimethylammonium bromide (DDAB), with either n-dodecyltrimethylammonium bromide (DTAB), sodium n-dodecyl sulfate (SDS), or pentaethylene glycol monododecyl ether (C12E5), have been used to stabilize water-in-heptane microemulsions. Using DTAB or C12E5 with DDAB causes a synergistic effect, and the water solubilization capacity of the microemulsion is increased. However, with SDS there is a destabilization, indicating surfactant antagonism. Structure and dynamics in these systems have been studied as a function of surfactant type and composition using small-angle neutron scattering (SANS) and pulsed-field gradient NMR (PFG-NMR). Compositions of mixed films at these oil−water interfaces have also been measured, by blending deuterated DDAB with proteated DTAB or C12E5, and carrying out contrast variation SANS experiments. For both the DDAB/DTAB and DDAB/C12E5 mixtures, all the added surfactant was strongly adsorbed and there was no evidence for any significant partitioning i...

Thermodynamics of Micellization of n-Alkyl Sulfates in an Alkaline Medium at Different Temperatures

Critical micelle concentrations (cmc) have been calculated from conductivity measurements at 293.15, 298.15, 303.15, 308.15, and 313.15 K for sodium n-decyl sulfate (SDES), sodium n-undecyl sulfate (SUNDS), and sodium n-dodecyl sulfate (SDS) in a medium of pH 10.0 and ionic strength 0.0312. Thermodynamic parameters of micellization, standard Gibbs energies (), standard enthalpies (), and standard entropies (), have been obtained by application of the model of Evans and Ninham in terms of hydrophobic and surface contributions.

Influence of different types of effectors on the kinetic parameters of suicide inactivation of catalase by hydrogen peroxide

The effects of cyanide and azide ions (class A), sodium- n-dodecyl sulphate (SDS) and 2-mercaptoethanol (class B), 3-aminotriazole (class C) and NADPH (class D) on the initial activity ( a i), inactivation rate constant ( k i) and the partition ratio ( r) of bovine liver catalase reaction with its suicide substrate, hydrogen peroxide, were studied in 50 mM sodium phosphate buffer, pH 7.0 at 27°C. The above kinetic parameters were determined by processing the progress curve data. In class A, which contains fast and reversible inhibitors of catalase, a proportional decrease in a i and k i was observed by inhibitors, so that the r remained constant. In class B, which contains slow and irreversible inactivators, a decrease in a i and constancy of k i and r were observed when catalase was incubated in the presence of such inactivators for a determined time. In class C, containing effector which can combine with intermediate compound I, a i was relatively unchanged but an increase in k i and a decrease in r were observed. In class D, containing effector which reduces compound I to ferricatalase, a i was not affected significantly but some decrease in k i was detected which was linked with an increase in r. These results demonstrate that different classes of effectors affect the determined kinetic parameters of catalase in various ways. Thus, determination of such parameters by simple kinetic experiments can be carried out for classification of the agents which have an effect on the kinetics of catalase.

Structural analysis of metal-surface protect surfactants by tandem mass spectrometry.

The applicability of tandem mass spectrometry to the quality analysis of metal-surface protect surfactants without any pretreatment or purification of the sample solution was investigated. Three typical spectra were constructed and verified by FAB CID-MS/MS using sodium n-dodecylsulfate (anionic surfactant), tetradecyl dimethylbenzylammonium chloride (cationic surfactant) and heptaethylene glycol mono-n-dodecyl ether (nonionic surfactant) as a model. The FAB CID-MS/MS spectra of metal-surface protect surfactants provided useful structural information that analyte surfactants have a polyoxyethylene structure, which has been identified as a nonionic surfactant. The authors concluded that FAB CID-MS/MS will be a good analytical method for direct quality analysis without any pretreatment or purification of the metal-surface protect surfactant for industrial use.

Kinetic approach to the interaction of sodium n-dodecyl sulphate with heme enzymes

The kinetics of interaction of sodium n-dodecyl sulphate (SDS) with catalase has been studied by absorbance and fluorescence changes. The results have been compared with circular dichroism spectra and activity measurements. The tertiary structure of catalase is modified by SDS in the monomeric and micellar form. The secondary structure of catalase is altered only in the presence of SDS micelles. On the other hand, neither spectroscopic properties nor activity of horseradish peroxidase change in the presence of SDS below micellar concentration. In the presence of SDS micelles, however, changes of secondary and tertiary structure of this protein are detected. The reason for relatively high stability of horseradish peroxidase in the presence of SDS is discussed.

α-Chymotrypsin superactivity in aqueous solutions of cationic surfactants

α-Chymotrypsin (α-CT) activity was tested in aqueous media with the following cetyltrialkylammonium bromide surfactants in the series methyl, ethyl, propyl and butyl, different in the head group size, and for the sake of comparison also with the anionic sodium n-dodecyl sulfate and the zwitterionic myristyldimethylammonium propanesulfonate. N-glutaryl- l-phenylalanine p-nitroanilide hydrolysis rate was monitored at surfactant concentration above the critical micellar one. Only some cationic surfactants gave superactivity and the head group size had a major weight. The highest superactivity was measured in the presence of cetyltributylammonium bromide. The effect of both nature and concentration of three different buffers was also investigated. There is a dependence of enzyme superactivity on buffer type. Michaelis–Menten kinetics were found. The binding constants of substrate with micellar aggregates were determined in the used buffers and the effective improvement of reaction rate (at the same free substrate concentration in the medium) was calculated. k cat significantly increased while K m was little changed after correction to free substrate concentration. The ratio of k cat to K m was between 12 and 35 times higher than in pure buffer, depending on buffer and surfactant concentrations. The increase of α-CT activity (30%) was less important in the presence of 1×10 −2 M tetrabutylammonium bromide, a very hydrophobic salt, unable to micellise. Fluorescence spectra showed differences of enzyme conformation in the presence of various surfactants.

A Comparative Study of the Determination of the Critical Micelle Concentration by Conductivity and Dielectric Constant Measurements

Conductivities and dielectric constant measurements in water at 25 °C have been made on the amphiphilics sodium n-dodecyl sulfate, n-dodecyltrimethylammonium bromide, and chlorpromazine hydrochloride. By using the conductivity/concentration data, critical micelle concentrations (cmc) have been determined by applying the Williams definition and two forms of the Phillips method. This first Phillips form consists of an approximation to Gaussians of the second derivative of the conductivity/concentration data followed by two consecutive integrations. The second form, which is proposed here, consists of the application of a combination of the Runge−Kutta numerical integrations method and the Levenberg−Marquardt least-squares fitting algorithm. The proposed method permits the determination of the cmc in systems with low aggregation numbers and with slow variations of physical property/concentration curves allowing the determination of the so-called second cmc. A comparative study with results obtained by dielec...