Rheological properties of ovalbumin hydrogels as affected by surfactants addition

The gel properties of ovalbumin mixtures with three different surfactants (sodium perfluorooctanoate, sodium octanoate and sodium dodecanoate) have been studied by rheological techniques. The gel elasticities were determined as a function of surfactant concentration and surfactant type. The fractal dimension of the formed structures was evaluated from plots of storage modulus against surfactant concentration. The role of electrostatic, hydrophobic and disulfide SS interactions in these systems has been demonstrated to be the predominant. The viscosity of these structures tends to increase with surfactant concentration, except for the fluorinated one. Unfolded ovalbumin molecules tend to form fibrillar structures that tend to increase with surfactant concentration, except for the fluorinated one. This fact has been related to the particular nature of this molecule.     

Dissipative particle dynamics simulation on the properties of the oil/water/surfactant system in the absence and presence of polymer

Dissipative particle dynamics is used to simulate the oil/water/surfactant system in the absence and presence of polymer. Structural properties, interfacial properties, and their dependence on the surfactant concentration, polymer concentration and oil/water ratio were investigated. The snapshots illustrate the variation of the structure of oil/water/surfactant system. In the presence of polymer, the interface is supersaturated at a lower surfactant concentration. The end-to-end distance increases with surfactant concentration and polymer chains but shows weak dependence on the oil/water ratio. The peak of density grows higher with surfactant concentration, but it is not affected by oil/water ratio. The density profiles of polymer grow higher with polymer chains, indicating that most of the polymer chains stay at the interface for stability. Interfacial thickness shows an adsorption of polymer/surfactant complexes at the interface, where the polymer is in an extended conformation at the interface. The formation of polymer/surfactant complexes is favourable for the decrease of oil/water interfacial tension.     

Surfactant-spreading and surface-compression disturbance on a thin viscous film

Spreading of a new surfactant in the presence of a pre-existing surfactant distribution is investigated both experimentally and theoretically for a thin viscous substrate. The experiments are designed to provide a better understanding of the fundamental interfacial and fluid dynamics for spreading of surfactants instilled into the lung. Quantitative measurements of spreading rates were conducted using a fluorescent new surfactant that was excited by argon laser light as it spread on an air-glycerin interface in a petri dish. It is found that pre-existing surfactant impedes surfactant spreading. However, fluorescent microspheres used as surface markers show that pre-existing surfactant facilitates the propagation of a surface-compression disturbance, which travels faster than the leading edge of the new surfactant. The experimental results compare well with the theory developed using lubrication approximations. An effective diffusivity of the thin film system is found to be Deff = (E*gamma)/(mu/H), which indicates that the surface-compression disturbance propagates faster for larger background surfactant concentration, gamma, larger constant slope of the sigma*-gamma* relation, -E*, and smaller viscous resistance, mu/H. Note that sigma* and gamma* are the dimensional surface tension and concentration, respectively, mu is fluid viscosity, and H is the unperturbed film thickness.     

Downstream protein separation by surfactant precipitation: a review

In a conventional protein downstream processing (DSP) scheme, chromatography is the single most expensive step. Despite being highly effective, it often has a low process throughput due to its semibatch nature, sometimes with nonreproducible results and relatively complex process development. Hence, more work is required to develop alternative purification methods that are more cost-effective, but exhibiting nearly comparable performance. In recent years, surfactant precipitation has been heralded as a promising new method for primary protein recovery that meets these criteria and is a simple and cost-effective method that purifies and concentrates. The method requires the direct addition of a surfactant to a complex solution (e.g. a fermentation broth) containing the protein of interest, where the final surfactant concentration is maintained below its critical micelle concentration (CMC) in order to allow for electrostatic and hydrophobic interactions between the surfactant and the target protein. An insoluble (hydrophobic) protein–surfactant complex is formed and backextraction of the target protein from the precipitate into a new aqueous phase is then carried out using either solvent extraction, or addition of a counter-ionic surfactant. Importantly, as highlighted by past researchers, the recovered proteins maintain their activity and structural integrity, as determined by circular dichroism (CD). In this review, various aspects of surfactant precipitation with respect to its general methodology and process mechanism, system parameters influencing performance, protein recovery, process selectivity and process advantages will be highlighted. Moreover, comparisons will be made to reverse micellar extraction, and the current drawbacks/challenges of surfactant precipitation will also be discussed. Finally, promising directions of future work with this separation technique will be highlighted.     

Solubilization capacity of nonionic surfactant micelles exhibiting strong influence on export of intracellular pigments in Monascus fermentation

In this study, perstractive fermentation of intracellular Monascus pigments in nonionic surfactant micelle aqueous solution had been studied. The permeability of cell membrane modified by nonionic surfactant might have influence on the rate of export of intracellular pigments into its extracellular broth while nearly no effect on the final extracellular pigment concentration. However, the solubilization of pigments in nonionic surfactant micelles strongly affected the final extracellular pigment concentration. The solubilization capacity of micelles depended on the kind of nonionic surfactant, the super‐molecule assembly structure of nonionic surfactant in an aqueous solution, and the nonionic surfactant concentration. Elimination of pigment degradation by export of intracellular Monascus pigments and solubilizing them into nonionic surfactant micelles was also confirmed experimentally. Thus, nonionic surfactant micelle aqueous solution is potential for replacement of organic solvent for perstractive fermentation of intracellular product.     

Extraction of lysozyme and ribonuclease-a using reverse micelles: Limits to protein solubilization

Experiments are reported here on the equilibrium partitioning of lysozyme and ribonuclease-a between aqueous and reversed micellar phases comprised of an anionic surfactant, sodium di-2-ethylhexyl sulfosuccinate (AOT), in isooctane. A distinct maximum, [P](rm,max) was found for the quantity of a given protein that can be solubilized in the reverse micelle phase by the phase-transfer method. This upper limit depended upon the size of the protein, the surfactant concentration, and the aqueous phase ionic strength, and was determined by complex formation between protein and surfactant molecules to form an insoluble interfacial precipitate at high values of [P](rm). In this work, it was found to be possible to dissociate the protein-surfactant complex and recover the precipitated protein. The kinetics of protein-surfactant complex formation depended upon the nature and concentration of the solubilized protein and on the surfactant concentration. Calculations of micellar occupancy and the relative surface areas of protein molecules and surfactant head-groups suggested that it was the exposure of the solubilized protein to the bulk organic solvent which promoted protein-surfactant complex formation as [P](rm) --> [P](rm,max). In the light of the experimental results and calculations described above, a mechanistic model is proposed to account for the observed phenomena. This is based upon the competing effects of increasing the solubilized protein concentration and the corresponding increase in the rate of protein-surfactant complex formation. The dynamic nature of the reverse micelles is inherent in the model, explaining the formation of the interfacial precipitate with time and its dependence on the internal phase volume of the micellar phase. Experiments on the co-partitioning of water and measurement ofthe AOT concentration in both phases verified the loss of protein, water, and surfactant from the organic phase at high values of [P](rm). (c) 1995 John Wiley & Sons Inc.     

Removal of surfactant dodecylbenzenesulfonate by consecutive use of ozonation and biodegradation

Successful surfactant removal from wastewater is often limited by the high concentration of the surfactant. The use of advanced oxidation processes can be the key to aid biological treatment of water containing high amounts of surfactants. The present study analyzes the biodegradation of the anionic surfactant sodium dodecylbenzenesulfonate (SDBS) and the effects of its combination with ozonation. SDBS pre‐ozonation favors the metabolism by microorganisms. Experimental results indicate that the application of a concentration of up to 60 μM of ozone for 60 min, prior to contact with microorganisms, increases the percentage of SDBS removed by biodegradation alone. These results demonstrate that the removal of SDBS and of the total organic carbon is increased by the consecutive use of ozonation and biodegradation.     

Surfactant-induced unfolding of cellulase: kinetic studies

Surfactant-induced unfolding is a significant degradation pathway for detergent enzymes. This study examines the kinetics of surfactant-induced unfolding for endoglucanase III, a detergent cellulase, under conditions of varying pH, temperature, ionic strength, surfactant type, and surfactant concentration. Interactions between protein and surfactant monomer are shown to play a key role in determining the kinetics of the unfolding process. We demonstrate that the unfolding rate can be slowed by (1) modifying protein charge and/or pH conditions to create electrostatic repulsion of ionic surfactants and (2) reducing the amount of monomeric ionic surfactant available for interaction with the enzyme (i.e., by lowering the critical micelle concentration). Additionally, our results illustrate that there is a poor correlation between thermodynamic stability in buffer (DeltaG(unfolding)) and resistance to surfactant-induced unfolding.     

Study of the interactions between lysozyme and a fully-fluorinated surfactant in aqueous solution at different surfactant-protein ratios

The interactions of a fluorinated surfactant, sodium perfluorooctanoate, with lysozyme, have been investigated by a combination of UV absorbance, electrical conductivity and dynamic light scattering to detect and to characterize the conformational transitions of lysozyme. By using difference spectroscopy, the transition was followed as a function of surfactant concentration, and the data were analyzed to obtain the Gibbs energy of the transition in water (DeltaGw(o)) and in a hydrophobic environment (DeltaGh(o)) for saturated protein-surfactant complexes. Electrical conductivity was used to determine the critical micelle concentration of the surfactant in the presence of different lysozyme concentration. From these results, the average number of surfactant monomer per protein molecule was calculated. Finally, dynamic light scattering show that only changes in the secondary structure of the protein can be observed.     

Molecular dynamics simulation of polyelectrolyte with oppositely charged monomeric and dimeric surfactants

Interactions of anionic polyelectrolyte (PE) with cationic monomeric (MS) and dimeric surfactants (DS) have been investigated by coarse-grained molecular dynamics (MD) simulation. A PE/surfactant mixture is observed to evolve over time into micellar complex of increasing size. The critical aggregation concentration (CAC) is qualitatively found to be much lower than the critical micellization concentration (CMC) of the free surfactant. Compared to the monomeric analog, a DS interacts more strongly with the oppositely charged polyion chain. The equilibrium complex size becomes larger with increasing surfactant concentration. Simulation results are consistent with experimental observations and reveal that the electrostatic and hydrophobic interactions play an important role in the formation of micellar complex.     

Effect of a commercial alcohol ethoxylate surfactant (C<Subscript>11-15</Subscript>E<Subscript>7</Subscript>) on

Biodegradation of poorly soluble polycyclic aromatic hydrocarbons (PAHs) has been a challenge in bioremediation. In recent years, surfactant-enhanced bioremediation of PAH contaminants has attracted great attention in research. In this study, biodegradation of phenanthrene as a model PAHs solubilized in saline micellar solutions of a biodegradable commercial alcohol ethoxylate nonionic surfactant was investigated. The critical micelle concentration (CMC) of the surfactant and its solubilization capacity for phenanthrene were examined in an artificial saline water medium, and a type of marine bacteria, Neptunomonas naphthovorans, was studied for the biodegradation of phenanthrene solubilized in the surfactant micellar solutions of the saline medium. It is found that the solubility of phenanthrene in the surfactant micellar solutions increased linearly with the surfactant concentrations, but, at a fixed phenanthrene concentration, the biodegradability of phenanthrene in the micellar solutions decreased with the increase of the surfactant concentrations. This was attributed to the reduced bioavailability of phenanthrene, due to its increased solubilization extent in the micellar phase and possibly lowered mass transfer rate from the micellar phase into the aqueous phase or into the bacterial cells. In addition, an inhibitory effect of the surfactant on the bacterial growth at high surfactant concentrations may also play a role. It is concluded that the surfactant largely enhanced the solubilization of phenanthrene in the saline water medium, but excess existence of the surfactant in the medium should be minimized or avoided for the biodegradation of phenanthrene by Neptunomonas naphthovorans.     

Chromatographic behaviour in reversed-phase high-performance liquid chromatography with micellar and submicellar mobile phases: effects of the organic modifier

Continuing our earlier study of the retention behaviour in reversed-phase systems with aqueous mobile phases containing surfactants in concentrations lower (submicellar systems) and higher (micellar systems) than the critical micellar concentration (CMC), we investigated the chromatographic behaviour of various non-ionic solutes in mixed aqueous-organic micellar and submicellar mobile phases and their dependence on the methanol concentration. CMC values were measured for two cationic surfactant and one anionic surfactant in mixed aqueous-methanolic solvents, and were found to increase slightly with increasing methanol concentration. Depending on the character of the surfactant, a limiting concentration of methanol was found, above which micelles do not occur anymore. Sorption isotherms of the surfactants on an octylsilica gel column were measured as a function of the concentration of methanol in aqueous-methanolic solvents. A modified Langmuir equation was used to describe the distribution of the surfactants between the stationary and the mobile phases in the concentration range below CMC. The retention of several polar solutes was measured on an octylsilica gel column both in micellar and submicellar mobile phases containing methanol. The dependencies of the capacity factors of the solutes studied on the concentration of methanol in the mobile phase can be suitably described by the same form of equation as that conventionally used for aqueous-organic mobile phases that do not contain surfactants, but the slopes of the dependencies for a given solute are different in the two ranges of surfactant concentrations. The ratio of the two slopes is controlled by the interaction with micelles and is approximately equal to, below or above 1, depending on whether the solutes do or do not associate with the micelles, or are repulsed from them. Simultaneous control of the concentrations of the organic solvent and of the surfactant in the mobile phase can be used for fine tuning the selectivity of separation as a complement to commonly used adjusting concentrations of two organic solvents in ternary aqueous-organic mobile phases. These effects are illustrated by practical examples of submicellar HPLC with mobile phases containing methanol.     

Dilution of protein‐surfactant complexes: A fluorescence study

Dilution of protein–surfactant complexes is an integrated step in microfluidic protein sizing, where the contribution of free micelles to the overall fluorescence is reduced by dilution. This process can be further improved by establishing an optimum surfactant concentration and quantifying the amount of protein based on the fluorescence intensity. To this end, we study the interaction of proteins with anionic sodium dodecyl sulfate (SDS) and cationic hexadecyl trimethyl ammonium bromide (CTAB) using a hydrophobic fluorescent dye (sypro orange). We analyze these interactions fluourometrically with bovine serum albumin, carbonic anhydrase, and beta‐galactosidase as model proteins. The fluorescent signature of protein–surfactant complexes at various dilution points shows three distinct regions, surfactant dominant, breakdown, and protein dominant region. Based on the dilution behavior of protein–surfactant complexes, we propose a fluorescence model to explain the contribution of free and bound micelles to the overall fluorescence. Our results show that protein peak is observed at 3 mM SDS as the optimum dilution concentration. Furthermore, we study the effect of protein concentration on fluorescence intensity. In a single protein model with a constant dye quantum yield, the peak height increases with protein concentration. Finally, addition of CTAB to the protein–SDS complex at mole fractions above 0.1 shifts the protein peak from 3 mM to 4 mM SDS. The knowledge of protein–surfactant interactions obtained from these studies provides significant insights for novel detection and quantification techniques in microfluidics.     

Surface deactivation of cellulase and its prevention

When cellulase [1,4-(1,3;1,4)-β-d-glucan 4-glucanohydrolase, EC 3.2.1.4] was exposed to air-liquid interface and subjected to shear, a significant deactivation was observed. The cellulase deactivation due to the interfacial effect combined with the shear effect was found to be far more severe and extensive than that due to the shear effect alone. Both increased cellulase concentration, and addition of surfactant (Zonyl or Triton) reduced the degree of deactivation. By using sufficient surfactant the cellulase deactivation can be prevented, and the cellulase can be stabilized and its use prolonged. The ratio of surface excess to the bulk protein is significantly reduced when the enzyme concentration is increased. The stabilizing effect of surfactant was attributed to the reduction in surface excess of cellulase.     

Investigation on the mechanism of crystallization of soluble protein in the presence of nonionic surfactant

The mechanism of crystallization of soluble, globular protein (lysozyme) in the presence of nonionic surfactant C8E4 (tetraoxyethylene glycol monooctyl ether) was examined using both static and dynamic light scattering. The interprotein interaction was found to be attractive in solution conditions that yielded crystals and repulsive in the noncrystallizing solution conditions. The validity of the second virial coefficient as a criterion for predicting protein crystallization could be established even in the presence of nonionic surfactants. Our experiments indicate that the origin of the change in interactions can be attributed to the adsorption of nonionic surfactant monomers on soluble proteins, which is generally assumed to be the case with only membrane proteins. This adsorption screens the hydrophobic attractive force and enhances the hydration and electrostatic repulsive forces between protein molecules. Thus at low surfactant concentration, the effective protein-protein interaction remains repulsive. Large surfactant concentrations promote protein crystallization, possibly due to the attractive depletion force caused by the intervening free surfactant micelles.     

The interaction between bovine serum albumin and surfactants.

1. Potassium n-decyl phosphate binds exothermically to bovine serum albumin at pH 7.0 to form a specific complex containing approx. 60 phosphate anions. 2. The formation of the complex is accompanied by changes in the u.v. difference spectrum of the protein. 3. At higher phosphate concentrations (above 0.4mM) surfactant molecules continue to be bound, and the protein undergoes a gross change in conformation. 4. n-Dodecyltri-methylammonium bromide binds endothermically to bovine serum albumin at pH7.0 but the extent of binding for a given free surfactant concentration is less than for the phosphate surfactant. 5. Binding is accompanied by a small change in the specific viscosity and by changes in the u.v. difference spectrum of the protein. 6. It is suggested that over the surfactant concentration ranges studied n-decyl phosphate ions first bind to the C-terminal part of the protein and then to the more compact N-terminal part whereas n-dodecyltrimethylammonium ions bind only to the C-terminal part of bovine serum albumin.     

Separation and concentration of amino acids using liquid emulsion membranes

The separation and concentration of amino acids using liquid emulsion membranes (LEMs) are discussed. Using L- phenylalanines as a model solute, it is experimentally shown using a facilitated transport system that separation and concentration can be simultaneously achieved. The rate of separation, final product concentration, and membrane swell are shown to increase with increasing chloride driving forces in the membrane, These effects are shown to be insensitive to the particular salt used as the driving force. Changes in the carrier concentration are shown to result in higher initial fluxes and higher swell rates. Hydrodynamically induced membrane breakage is minimal for the system under consideration. Experiments indicate that osmotically induced water transport ("swelling") in the LEM system is mediated by both the carrier and the emulsion-stabilizing surfactant. The data suggest that this swell is a diffusion-limited process. The specificity of the carrier is examined and is found to be directly related to the hydrophobicity of the solute. Strategies for optimizing LEM formulations are discussed. Emphasis is placed on the hydration characteristics of the surfactant and the specificity of the carrier.     

The measurement of cell growth in coal slurries

Summary Microbial growth in coal slurries can be detected if surfactant is present in the samples by analysing the protein concentration after disintegration of the cells. Without surfactant present in the samples, the proteins are readily adsorbed on the coal surfaces. A suitable surfactant is sodium dodecyl sulphate at 0.5 to 1% of the sample volume.     

Optimization of Nanoemulsion Fabrication Using Microfluidization: Role of Surfactant Concentration on Formation and Stability

Nanoemulsions have some important potential advantages over conventional emulsions for certain commercial applications due to their optical clarity, high physical stability, and ability to increase the bioavailability of lipophilic bioactives. In this study, the factors influencing droplet size and stability in nanoemulsions fabricated from a hydrocarbon oil and an anionic surfactant were examined. Octadecane oil-in-water nanoemulsions were produced by a high pressure homogenizer (microfluidizer) using sodium dodecyl sulfate (SDS) as a model anionic surfactant. The influence of homogenization pressure, number of passes, and surfactant concentration was examined. The droplet size decreased with increasing homogenization pressure, number of passes, and surfactant concentration. Nanoemulsions with low turbidity and small droplet diameters (≈62 nm) could be produced under optimized conditions. Interestingly, nanoemulsions containing relatively high surfactant levels were highly susceptible to creaming when they were only passed through the homogenizer a few times, which was attributed to depletion flocculation. These results show the importance of optimizing surfactant levels to produce small droplets that are also stable to creaming.     

Silicone antifoam performance enhancement by nonionic surfactants in potato medium

The ability of a silicone antifoam to retard foaming in a liquor prepared from potatoes is enhanced by the addition of ethoxylated nonionic surfactants. The enhancement is non-linear for surfactant concentration, with all 12 surfactants tested possessing a concentration at which foam heights strongly diminish, referred to as the surfactant critical antifoaming concentration (SCAFC). SCAFCs vary between surfactants, with lower values indicating better mass efficiency of antifoaming enhancement. SCAFCs decrease with degree of ethoxylation and decrease with the hydrophilic–lipophilic balance for ethoxylated nonionic surfactants. Surfactant addition produces a mixed water-surface layer containing surfactant and surface-active components in the potato medium. Surface tension reduction does not correlate well with antifoam performance enhancement. A model is proposed where surfactant adsorption promotes desorption of surface-active potato medium components from the water surface. At the SCAFC, desorption is not complete, yet the rate of bubble rupture is sufficiently enhanced to provide excellent foam control. Electronic Publication