Thermodynamics of protein denaturation by sodium dodecyl sulfate

The anionic surfactant sodium n-dodecyl sulfate (SDS) plays a variety of roles with regard to protein conformation, depending on its concentration. SDS at low concentrations mostly induces the compaction of protein (folding). Examples of this include: the molten globule state of acid-unfolded cytochrome c, associated with enhancement of the exothermic enthalpy values of isothermal titration calorimetry and a reversible profile by differential scanning calorimetry; the enzyme activation and compaction of Aspergillus niger catalase, and relationship of calorimetric enthalpy (ΔH_cal) to van’t Hoff enthalpy (ΔH_VH), which proves the existence of intermolecular and intramolecular interaction during enzyme activation by SDS; the production of a new energetic domain for human apotransferrin and folded state for histone H1 by SDS. SDS at moderate concentrations below the critical micelle concentration (cmc) is a potent denaturant for protein in solution. Protein denaturation is a key method in thermodynamics and binding site analysis and can be used to enhance our understanding of the protein structure-function relationship. The interaction between protein and surfactant, such as SDS, at the cmc level is a complicated interaction, thermodynamically, that should bring about enthalpy correction through micellar dissociation and micelle dilution.     

Hair protein removal by sodium dodecyl sulfate

The effect of sodium dodecyl sulfate (SDS) on protein loss was studied. Three kinds of human hair were tested by rubbing or immersion in water or immersion in SDS solution, at 25, 40 and 70 degrees C. Under friction, hair treated with SDS solution loses seven times more protein than in water, while by immersion, protein loss is roughly two times higher in SDS than in water. Protein loss increases at higher temperatures. Estimated activation energy values for protein loss by immersion are 69+/-22 kJ mol(-1) for blended brown hair; 40+/-12 kJ mol(-1) for blond hair (tip-end region) and 61+/-4 kJ mol(-1) for blond hair (root-end region) for samples treated in water, while 53+/-8, 7+/-5 and 32+/-8 kJ mol(-1) were the corresponding activation energy values for samples treated in 5% SDS solution. These values indicate that protein loss is mainly a diffusion-controlled process. The more damaged the hair, the lower the activation energy and the higher the protein loss. From these data, it can be estimated that daily care shampooing at room temperature will cause opacity and combing difficulties in 1 year and split ends after 3 years by removal of all cuticle layers.     

On-line microheterogeneity analysis and rapid phenotyping of haptoglobin by capillary electrophoresis using sodium dodecyl sulfate as additive

To improve the detection sensitivity and determine phenotypes of haptoglobin (Hp), a prefilling technique was developed and tested in capillary electrophoresis (CE) with UV–vis absorbance detection. Adding 0.01% sodium dodecyl sulfate (SDS) to the protein sample and 0.1% SDS to the prefilling buffer solution, on-line stacking and microheterogeneity separation of Hp were achieved. In addition, the influences of pH, buffer concentration, sample and prefilling buffer SDS concentration upon resolution were examined. Under optimized conditions, Hp-microheterogeneity was well resolved and two phenotypes of Hp (Hp 1-1 and Hp 2-2) were differentiated. This method was applied to the analysis of sera from normal individuals and β-Thalassemia patients. After the depletion of albumin (HSA) and immunoglobulin G (IgG), this method allowed to determine two phenotypes in different individuals and to detect the decrease of Hp in β-Thalassemia patients. Featuring high efficiency, speed and simplicity, the proposed method shows great potential for use in clinical diagnosis and proteome research.     

A direct calorimetric determination of denaturation enthalpy for lysozyme in sodium dodecyl sulfate

Thermodynamics of the interaction between sodium dodecyl sulfate (SDS) with lysozyme were investigated at pH 7.0 and 27 °C in phosphate buffer by isothermal titration calorimetry. A new method to follow protein denaturation, and the effect of surfactants on the stability of proteins was introduced. The new solvation model was used to reproduce the enthalpies of lysozyme–SDS interaction over the whole range of SDS concentrations. The solvation parameters recovered from the new equation, attributed to the structural change of lysozyme and its biological activity. At low concentrations of SDS, the binding is mainly electrostatic, with some simultaneous interaction of the hydrophobic tail with nearby hydrophobic patches on the lysozyme. These initial interactions presumably cause some protein unfolding and expose additional hydrophobic sites. The enthalpy of denaturation is 160.81 ± 0.02 kJ mol⁻¹ for SDS.     

无探针荧光光谱法测定十二烷基硫酸钠的临界胶束浓度

建立了无探针荧光光谱法测定表面活性剂临界胶束浓度(CMC)的新方法,测定了典型阴离子表面活性剂十二烷基硫酸钠(SDS)在水溶液中的CMC,并与表面张力法和电导率法的测定结果进行了对比。结果表明,荧光光谱法样品用量少,测定的SDS的CMC与传统方法一致,说明采用无探针荧光光谱法能够测定一些物质的临界浓度。     

Exchange mechanisms for sodium dodecyl sulfate micelles: high salt concentration

Solute exchange experiments for the pyrene-labeled triglyceride TG-Py solubilized in sodium dodecyl sulfate (SDS) micelles in the presence and absence of salt show that the "observed" rate constant k(obs) for solute exchange varies by over 6 orders of magnitude as the free sodium ion concentration [Na(+)](aq) is varied between 10 and 850 mM. There is a sharp break in the log-log plot of k(obs) versus [Na(+)](aq) in the range of [Na(+)](aq) = 200 mM, with the exchange rate showing a weaker dependence on [Na(+)](aq) above this concentration. Up to 100 mM added NaCl, this exchange takes place essentially exclusively by a micelle fission mechanism in which each submicelle carries off one of the solutes. At higher salt concentrations, a bimolecular process becomes increasingly important. This fusion process, which involves formation of a transient supermicelle followed by fission back to two normal micelles, becomes the dominant process at high salt concentrations. The fission rate appears to level off for salt concentrations above 300-400 mM. These fission and fusion processes are related in an intimate way to the changes in the size and shape of the SDS micelles with increasing salt concentration.     

Interaction of cellulase with sodium dodecyl sulfate at critical micelle concentration level

The interactions between Trichoderma reesei cellulase and an anionic surfactant, sodium dodecyl sulfate (SDS), at critical micelle concentration level have been investigated using isothermal titration calorimetry, fluorescence spectroscopy, and circular dichroism. SDS micelles have dual interactions with cellulase: electrostatic at first and then hydrophobic interactions. When the concentration of SDS is smaller than 45.0 mM, SDS micelles cause a partial loss in the hydrolytic activity together with a steep decrease in the -helical content of cellulase. With further increasing the concentration of SDS, however, a re-formation of the -helical structure and a partial recovery of the hydrolytic activity of cellulase induced by SDS micelles are observed. Taken together, these results indicate that SDS micelles exert dual effects on cellulase through binding as both a denaturant and a recovery reagent.     

Ionic liquids as modulators of the critical micelle concentration of sodium dodecyl sulfate

Critical micelle concentration (CMC) of sodium dodecyl sulfate (SDS), an anionic surfactant, has been investigated in aqueous solutions of a variety of room temperature ionic liquids (RTILs): 1,3-dimethylimidazolium iodide (Me2IM-I, 2), 1-butyl-3-methylimidazolium chloride (BMIM-Cl, 3), 1-hexyl-3-methylimidazolium chloride (HxMIM-Cl, 4), 1-methyl-3-octylimidazolium chloride (MOIM-Cl), 5, and 1-methyl-3-octylimidazolium tetrafluoroborate (MOIM-BF4, 6). The CMC of SDS is shown to correlate with the nature of the alkyl groups in the RTILs; SDS showed appreciably higher CMCs in presence of ionic liquids 2 and 3, whereas in the presence of ionic liquids 4, 5, and 6 much smaller CMCs were observed. The nature of the gigenions, Cl- or BF4-, has no noticeable effect on the observed CMC values.     

Preconcentration of proteins using modified micellar phases of sodium dodecyl sulfate

The influence of electrolyte and additives of organic acids and alcohols on the efficiency of the extraction of ovalbumin and casein into micellar phases of sodium dodecyl sulfate is studied. The optimal acidity and the conditions for the preconcentration of the proteins using low-temperature anion-active phases are found. Micellar extraction procedures for the extraction of proteins from fabrics, solid surface, and biological fluids are proposed.     

Effect of sodium dodecyl sulfate on protein separation by hollow fiber flow field-flow fractionation

Effects of protein denaturation and formation of protein-sodium dodecyl sulfate (SDS) complexes on protein separation and identification were investigated using hollow fiber flow field-flow fractionation (HF5) and nanoflow liquid chromatography-electrospray ionization-tandem mass spectrometry (nLC-ESI-MS-MS). Denaturation and formation of protein-SDS complexes prior to HF5 separation resulted an increase in the retention of few protein standards due to unfolding of the protein structures and complexation, yielding ~30% increase in hydrodynamic diameter. In addition, low molecular weight proteins which could be lost from the HF membrane due to the pore size limitation showed an increase of peak recovery about 2-6 folds for cytochrome C and carbonic anhydrase. In the case of proteins composed of a number of subunits, denaturation resulted in a decrease in retention due to dissociation of protein subunits. A serum proteome sample, denatured with dithiothreitol and SDS, was fractionated by HF5, and the eluting protein fractions after tryptic digestion were analyzed for protein identification using nLC-ESI-MS-MS. The resulting pools of identified proteins were found to depend on whether the serum sample was treated with or without denaturation prior to the HF5 run due to differences in the aqueous solubility of the proteins. The enhancement of protein solubility by SDS also increased the number of identified membrane proteins (54 vs. 31).     

Sorption of sodium dodecyl sulfate by highly basic anion-exchange resins

The interaction in the system of sodium dodecyl sulfate (SDS) solution and AB-17 highly basic anion-exchange resins in OH⁻ and Cl⁻ forms were considered, and the distribution coefficients (K _d) of the substance in the resin-solution ion exchange system were calculated. It was found that K _d decreases with increasing concentration of the initial solution, reaching a maximum value at the critical micelle concentration (CMC) of SDS. The effective diffusion coefficients of the surfactant in the anion-exchange resin phase were calculated; based on the IR spectroscopy data, the mechanism of SDS absorption was proposed.     

芘荧光探针法研究海藻酸钠与SDS的作用

采用芘荧光法研究了海藻酸钠(NaAlg)与十二烷基硫酸钠(SDS)在不同pH水溶液中的相互作用.以芘单体的荧光光谱第一峰与第三峰的荧光强度之比(I1/I3)及激基缔合物与单体荧光强度之比(IE/IM)来探测芘分子所处环境的极性.结果表明:NaAlg水溶液随pH值降低,出现了聚合物的疏水微区;pH从7降到5,NaAlg类似简单盐,对SDS的临界胶束浓度(CMC)有明显的影响;在pH 3时,海藻酸主链上有足够的疏水片段,使得SDS与海藻酸通过疏水性作用而聚集.NaCl对NaAlg /SDS体系的影响亦较明显.     

Quasielastic light-scattering studies of micellar sodium dodecyl sulfate solutions at the low concentration limit

Correlation functions of scattered light intensity of carefully purified sodium dodecyl sulfate (SDS) solutions were measured as a function of tenside concentration and NaCl concentration of the aqueous phase. The correlation functions were analyzed by taking into account the influence of the Coulomb interaction between the micelle (macroion) and small electrolyte ions on the diffusion coefficient. Values of the hydrodynamic radius, the aggregation number, and the effective surface charges were obtained. The aggregation number increases from N = 27 to N = 95 upon increasing the NaCl concentration from 0 to 0.05 mole per liter, while it remains constant when the salt concentration increases further up to 0.2 mole per liter. The effective charge of the micelles decreases with increasing NaCl content in the whole concentration region studied. These results could be interpreted qualitatively in terms of a model which relates the existence of an equilibrium size of the micelles to the balance between hydrophobic and Coulomb interactions. Our results lead to the conclusion that at least up to an NaCl concentration of 0.2 mole per liter the SDS-micelles exhibit an oblate spherical shape rather than a cylindrical form.     

Electrical percolation in micellar sodium dodecyl sulfate solutions. a phenomenological consideration

Effects of electrical percolation accompanying variations in overall surfactant concentration с have been studied by the example of micellar sodium dodecyl sulfate solutions. It has been found that, in the studied concentration range of 0.001–1.2 M, dependences of electrical conductivity K on c may exhibit at least three break points, with the dK/dc derivatives changing in the vicinities of these points. At two of these points, which are reliably identified and correspond to critical micelle concentrations (CMC₁ and CMC₂), they decrease. At the third concentration, lying between CMC₁ and CMC₂, the dK/dc derivative increases. A substantiated assumption has been put forward that this break point, at which the dK/dc derivative increases, results from the clustering of micelles and the appearance of channels with a higher specific conductivity, which is provided by the contribution from the electrical conductivity of the diffuse and dense parts of micelle electrical double layers, upon the formation of clusters. The ionic surfactant concentration that corresponds to the break point at which the dK/dc value increases has been denoted as the critical percolation concentration.     

Interaction between casein and sodium dodecyl sulfate

The interaction of the anionic surfactant sodium dodecyl sulfate (SDS) with 2.0 mg/ml casein was first investigated using isothermal titration calorimetry (ITC), dynamic light scattering (DLS), and fluorescence spectra. ITC results show that individual SDS molecules first bind to casein micelles by the hydrophobic interaction. The micelle-like SDS aggregate is formed on the casein chains when SDS concentration reaches the critical aggregation concentration (c1), which is far below the critical micellar concentration (cmc) of SDS in the absence of casein. With the further increase of SDS concentration to the saturate binding concentration c2, SDS molecules no longer bind to the casein chains, and free SDS micelles coexist with casein micelles bound with SDS aggregates in the system. DLS results show that the addition of SDS leads to an increase in the hydrodynamic radius of casein micelles with bound surfactant at SDS concentration higher than 4 mM, and also an increase in the casein monomer molecule (or submicelles) at SDS concentration higher than 10 mM. Fluorometric results suggest the addition of SDS leads to some changes in the binding process of hydrophobic probes to casein micelles.     

Micellization of sodium dodecyl sulfate and polyoxyethylene dodecyl ethers in solution

The effect of polyoxyethylene type nonionic surfactants (C₁₂E _n n = 3, 4, 5, 6, 7 and 8) on the aqueous solution of sodium dodecyl sulfate (SDS) in absence and presence of NaCl was examined using small-angle neutron scattering (SANS), dynamic light scattering (DLS), and viscosity measurements. Upon addition of C₁₂E _n , micellar size of SDS was found to increase significantly, and such micellar elongation was further enhanced in the presence of NaCl. Micellar growth is most significant in presence of shorter moieties of C₁₂E _n (e.g., n = 3, 4) as compared to higher ethereal oxygen content. The results of structural investigations with SANS and DLS to confirm this assumption are reported. The cloud point of C₁₂E _n has increased upon addition of SDS and decrease with NaCl, and a typical behavior is observed when both SDS and NaCl were present.     

Aggregation of sodium dodecyl sulfate in aqueous sodium chloride solutions

Summary Aqueous solutions of sodium dodecyl sulfate with added sodium chloride (0–0.3 mol kg^–1) were studied at 298.2 K in order to calculate the molar standard free energy of micelle formationG _m . The following properties were measured: (i) aggregation number by membrane osmometry, (ii) counter-ion binding and sodium ion activities by electromotive force, (iii) critical micelle concentration by electromotive force and fluorescence spectrophotometry. The results indicate thatG _m . is independent of the NaCl concentration.