Diffusion Coefficient Of Sodium Dodecyl Sulfate Research Articles

Molecular dynamics studies of the protective and destructive effects of sodium dodecyl sulfate in thermal denaturation of hen egg-white lysozyme and bovine serum albumin

To investigate the protective and destructive effects of sodium dodecyl sulfate (SDS) in thermal denaturation of proteins, we carried out twelve independent atomistic molecular dynamics (MD) simulations of bovine serum albumin (BSA) and hen egg-white lysozyme (LYZ) in pure water and SDS solutions at 25 and 80 °C, using SDS concentrations of 0.01, 0.05, 0.1 and 1 M. In the case of the BSA in pure water and SDS solutions, it was found that its helicity decreased from 67.02% in reference structure to 35% in pure water at 80 °C due to thermal denaturation, whereas it increased to 49.34, 52.36 and 54% at 0.01, 0.05 and 0.1 M SDS, respectively, owing to the SDS protective effect. In 1 M SDS, however, the surfactant’s protective effect was weak, and consequently the helicity of the BSA decreased to 47.01%. In contrast, no protection by SDS was observed for the LYZ in SDS solutions as the loss of its helices increased with SDS concentration from 0.01 to 1 M. In attempt to interpret the SDS effects molecularly, we calculated the diffusion coefficients of SDS in the protein solutions. The calculated values were found to decrease with increasing SDS concentration in the BSA solutions, but to increase with SDS concentration in the LYZ solutions. The decrease or increase in the diffusion coefficient of SDS was attributed to the net negative or positive charge on the proteins at neutral pH, indicating that electrostatic repulsions or attractions affect diffusivity significantly and can moderate SDS-proteins non-covalent interactions. Communicated by Ramaswamy H. Sarma

A dynamic light scattering study of hydrogels with the addition of surfactant: a discussion of mesh size and correlation length

We report a study of the interaction of sodium dodecyl sulfate (SDS) with hydrogels made of hydroxyethylcellulose (HEC) and hydrophobically modified hydroxyethylcellulose (HMHEC) by means of dynamic light scattering. The results reveal that the interaction between the hydrogels and SDS only affects the cooperative diffusion, while the slow relaxation of the hydrogels was not influenced by the interaction. Gel swelling due to the presence of SDS is also examined by measuring the weight change of the gel. The main observation is that when the gel swells due to increasing SDS concentration, the cooperative diffusion becomes faster. As such, we raise the question of whether the correlation length obtained from DLS is still proportional to the mesh size inferred from gel swelling. In the discussion, we attribute the cause to the quantity of bound surfactants. The mutual diffusion of SDS micelles could be detected at high SDS concentrations, and the diffusion coefficient of SDS in the gel matrix was determined. HEC (or HMHEC) gel swells due to increasing SDS concentration, while the cooperative diffusion becomes faster. This indicates that the HEC (or HMHEC) gel can swell until the osmotic pressure equals the modulus when the charge effect dominates over the effect of configurational entropy for uncharged gels interacting with charged surfactants.

Sorption of Sodium Dodecyl Sulfate by Polyaniline-Cellulose Acetate Blends: Equilibrium and Kinetic Studies

The interaction between sodium dodecyl sulfate (SDS) and blends of polyaniline (PANi) and cellulose acetate (CA) is discussed. The diffusion coefficients of SDS in the blends show that the transport process is accompanied by interactions between the diffusant and the polymeric matrix. In the visible absorption spectrum, the interaction between SDS and CA-PANi blends results in a red shift of the maximum absorption wavelength. This behaviour is explained on the basis of alterations in the lamellar phase of the polymer upon SDS sorption. The interactions between SDS and the blend film are of the Langmuir-type. These blends also show an interesting selective behaviour to SDS with respect to a set of similar surfactants.

Combined sorption/transport of sodium dodecyl sulfate and hydrochloric acid in a blend of cellulose acetate butyrate with cellulose acetate hydrogen phthalate

The transport of hydrochloric acid (0.001–0.1 M) and sodium dodecyl sulfate (0.001–0.1 M) has been measured through a membrane consisting of a blend of cellulose acetate butyrate and cellulose acetate hydrogen phthalate. The cellulose derivative blend is suggested to suffer an alteration in the degree of hydrophobicity when in equilibrium with sodium dodecyl sulfate (SDS) through hemimicelle formation. An increase in surface hydrophobicity of the blend when in equilibrium with SDS solution was observed by fluorescence measurements using the vibronic bands of the probe pyrene, as well as by water desorption kinetics; a decrease of the effective diffusion coefficients from 1.2 × 10 −11 m 2 s −1 in the absence of SDS to approximately 2 × 10 −13 m 2 s −1 in its presence was found. The value obtained for the mutual diffusion coefficient of HCl in the concentration range 0.001–0.1 M ( D=4.2×10 −14 m 2 s −1) shows also that the membrane presents hydrophobic features. The flux of SDS in the blend membrane at different pH values shows two distinct permeation rates depending on the cmc. However, from the calculation of permeability coefficients at SDS concentrations below the cmc a clear decrease in P is found, whilst, at concentrations above the cmc the permeability coefficients are nearly constant, only showing a slightly increase. The diffusion coefficients of SDS in the blend increase over the whole SDS concentration range analysed and show an effective diffusion coefficient 2–3 orders of magnitude below the diffusion coefficients of SDS in aqueous solutions. This fact suggests that the only diffusing species are SDS unimers. The presence of HCl in the SDS bulk solution has the effect of increasing the permeability and diffusion coefficients. Mutual analysis of permeation and diffusion coefficients and sorption isotherms shows that, on decreasing the pH, the interactions between SDS and the polymer network decrease. This is also reflected in a clear decrease of the hydrophobic interactions between the diffusing and polymeric species, provoked by a decrease in the unimer–unimer association.

Diffusion coefficients of sodium dodecylsulfate in aqueous solutions and in aqueous solutions of β-cyclodextrin

Differential diffusion coefficients have been measured of sodium dodecylsulfate (SDS) in aqueous solutions of β-cyclodextrin (β-CD) at 298.15 K over the concentration range 0.001 M to 0.0817 M using a conductimetric cell and an automatic apparatus to follow the diffusion. The cell uses an open ended capillary method, while a conductimetric technique is used to follow the diffusion process by measuring the resistance of a solution inside the capillaries, at various recorded times. The β-CD is known to for strong 1:1 complexes with SDS, and the effect of this on the diffusion of this electrolyte was investigated. The presence of β-cyclodextrin can influence the diffusion coefficients of sodium dodecylsulfate both above and below the critical micelle concentration (cmc) of this surfactant. For concentrations of β-cyclodextrin of 0.001 mol dm−3 the behaviour of the diffusion of SDS in aqueous solutions is the same in the absence or the presence of β-cyclodextrin. In contrast, when the β-CD concentration is 0.016 mol dm−3 we obtain diffusion coefficients higher than those obtained in aqueous solutions. Further, we do not observe the dramatic decrease in diffusion normally found at the cmc of the surfactant. These results are interpreted in terms of the effect of incorporation of dodecylsulfate chains inside the cyclodextrin cavities.

Diffusion coefficients of sodium dodecylsulfate in aqueous solutions of sucrose and in aqueous solutions

Differential diffusion coefficients of sodium dodecylsulfate (SDS) in aqueous solutions of sucrose and in aqueous solutions at 298.15 K, over the concentration range 0.0018 M to 0.0817 M, have been measured using a conductimetric cell and an automatic apparatus to follow the diffusion. The results are discussed on the basis of the Onsager-Fuoss model. The cell uses an open ended capillary method, while a conductimetric technique is used to follow the diffusion process by measuring the resistance of a solution inside the capillaries, at recorded times. The influence of molecules of sucrose on the diffusion of this electrolyte was investigated. The presence of sucrose increases the diffusion coefficients of sodium dodecylsulfate both above and below the critical micelle concentration (cmc) of the surfactant.

Aggregation number of aqueous sodium cholate micelles from mutual diffusion measurements

With reported values ranging from about 3 to 16, the aggregation number of aqueous sodium cholate micelles is not well established. To provide new information on the aggregation of a bile salt, Taylor dispersion is used to measure the binary mutual diffusion coefficientD of aqueous sodium cholate at concentrations from 0.001 to 0.100 mol-dm-3 at 25°C. The results are compared with calculatedD values based on the association equilibrium nCholate- + βnNa+ ⇋ (NaβCholate) n (β-1)n wheren is the aggregation number and β is the degree of sodium counterion binding. Fitting the association model to the diffusion data givesn = 3.9±0.6 and β = 0.21 ±0.08. In contrast to the drop inD with increasing concentration of sodium cholate, the diffusion coefficients of sodium dodecylsulfate and other long-chain ionic surfactants increase above the critical micelle region. The ent diffusion behavior of the surfactants is related to changes in the driving forces and mobilities caused by ion association.