Protein Surfactant Mixtures Research Articles

Exclusive behaviour of asymmetric zwitterionic gemini surfactants towards lysozyme

Being essential to industrial, cosmetic and biomedical domains, protein-surfactant mixtures are enduring to be an expanse of vigorous research. Consequently, in this research article, we have explored the behaviour of two asymmetric zwitterionic geminis with lysozyme. The results of multi-spectroscopic methods (fluorescence, UV–visible, CD) have revealed that the n(−)-2-(+)m geminis form complex with Hen-Egg-White Lysozyme (HEWL). The binding parameters suggest that 10(−)-2-(+)16 complexes significantly to HEWL than 8(−)-2-(+)16. Pyrene and synchronous fluorescence disclosed microenvironmental fluctuations in the lysozyme solution upon zwitterionic gemini combination. CD spectra have demonstrated mitigation of negative helicity, thereby confirming conformational changes in HEWL on surfactant addition. Molecular docking hints at the binding of n(−)-2-(+)m in the locality of Trp-108, Trp-62 and Trp-63. Intriguingly, exceptional hydrogen bonding interaction was observed between Trp-63 of HEWL and phosphate group of 8(−)-2-(+)16. However, no such bonding was observed in 10(−)-2-(+)16. Moreover, lower root-mean-square deviations (RMSD) and radius- of-- gyration (Rg) values obtained in molecular simulation indicated the formation of stable protein-surfactant complexes. This study would be significant in understanding the in-depth molecular interactions of zwitterion-protein mixtures.

Two-tier supramolecular encapsulation of small molecules in a protein cage

Expanding protein design to include other molecular building blocks has the potential to increase structural complexity and practical utility. Nature often employs hybrid systems, such as clathrin-coated vesicles, lipid droplets, and lipoproteins, which combine biopolymers and lipids to transport a broader range of cargo molecules. To recapitulate the structure and function of such composite compartments, we devised a supramolecular strategy that enables porous protein cages to encapsulate poorly water-soluble small molecule cargo through templated formation of a hydrophobic surfactant-based core. These lipoprotein-like complexes protect their cargo from sequestration by serum proteins and enhance the cellular uptake of fluorescent probes and cytotoxic drugs. This design concept could be applied to other protein cages, surfactant mixtures, and cargo molecules to generate unique hybrid architectures and functional capabilities.

Multispectroscopic and Computational Analysis Insight into the Interaction of Cationic Diester-Bonded Gemini Surfactants with Serine Protease α-Chymotrypsin

Accumulation of different protein–surfactant mixtures affords further knowledge about the structure–property interactions of biomacromolecules. They will help design suitable surfactants, which, in turn, can enhance the utilization of protein–surfactant complexes in biotechnologies, cosmetics, and food industry realms. Owing to their adaptable and remarkably notable properties, we are describing herein the interaction of Cm-E2O-Cm gemini surfactants (m = 12, 14, and 16) with α-CHT by employing various spectroscopic techniques including with molecular docking and density functional theory (DFT) method. Results have revealed complex formation, unfolding, and a static quenching mechanism in the interaction of gemini surfactants with α-CHT. The Stern–Volmer constant (KSV), quenching constant (kq), the number of binding sites (n), and binding constant (Kb) were interrogated by utilizing the fluorescence quenching method, UV–vis, synchronous, 3-D, and resonance Rayleigh scattering fluorescence studies. The data perceive the α-CHT–Cm-E2O-Cm complex formation along with conformational alterations induced in α-CHT. The contribution of aromatic residues to a nonpolar environment is illustrated by pyrene fluorescence. Fourier transform infrared spectroscopy and circular dichroism outcomes reveal conformational modifications in the secondary structure of α-CHT with the permutation of gemini surfactants. The computational calculations (molecular docking and DFT) further corroborate the complex formation between α-CHT and Cm-E2O-Cm gemini surfactants and the contribution of electrostatic/hydrophobic interaction forces therein.

Tailoring the gastrointestinal fate of emulsions through interfacial engineering: Impact of lipid type and coating lipid droplets with protein-surfactant mixture

The bioaccessibility of bioactives incorporated in oil-in-water (O/W) emulsions may be modulated by controlling emulsion structure through the rational selection of an oily phase and emulsifier or mixture of emulsifiers. In this context, emulsions were produced with protein-surfactant mixtures and different oils to understand how the nature of ingredients and the interaction between them can affect the structure of emulsions and their behavior during digestion in vitro.

Nonlinear Surface Dilatational Rheology and Foaming Behavior of Protein and Protein Fibrillar Aggregates in the Presence of Natural Surfactant.

The surface and foaming properties of native soy glycinin (11S) and its heat-induced fibrillar aggregates, in the presence of natural surfactant steviol glycoside (STE), were investigated and compared at pH 7.0 to determine the impact of protein structure modification on protein-surfactant interfacial interactions. The adsorption at, and nonlinear dilatational rheological behavior of, the air-water interface were studied by combining drop shape analysis tensiometry, ellipsometry, and large-amplitude oscillatory dilatational rheology. Lissajous plots of surface pressure versus deformation were used to analyze the surface rheological response in terms of interfacial microstructure. The heat treatment generates a mixture of long fibrils and unconverted peptides. The presence of small peptides in 11S fibril samples resulted in a faster adsorption kinetics than that of native 11S. The addition of STE affected the adsorption of 11S significantly, whereas no apparent effect on the adsorption of the 11S fibril-peptide system was observed. The rheological response of interfaces stabilized by 11S-STE mixtures also differed significantly from the response for 11S fibril-peptide-STE mixtures. For 11S, the STE reduces the degree of strain hardening in extension and increases strain hardening in compression, suggesting the interfacial structure may change from a surface gel to a mixed phase of protein patches and STE domains. The foams generated from the mixtures displayed comparable foam stability to that of pure 11S. For 11S fibril-peptide mixtures STE only significantly affects the response in extension, where the degree of strain softening is decreased compared to the pure fibril-peptide system. The foam stability of the fibril-peptide system was significantly reduced by STE. These findings indicate that fibrillization of globular proteins could be a potential strategy to modify the complex surface and foaming behaviors of protein-surfactant mixtures.

Characterization of Interfacial Rheology of Protein-Stabilized Air–Liquid Interfaces

In this review, the definition of interfacial dilatational and shear rheology is outlined and the basis of different experimental methods for their characterization is provided. The connection between interfacial rheology and structure of proteins and other macromolecules is highlighted through the application of polymer theories. Key experimental results on interfacial rheology of air–liquid interfaces stabilized by proteins and protein surfactant mixtures are then presented. This is followed by the analysis of the effect of interfacial rheology on stability of air–liquid interface.

Comparing foam and interfacial properties of similarly charged protein–surfactant mixtures

The foam stability of protein–surfactant mixtures strongly depends on the charge of the protein and the surfactant, as well as on their mixing ratio. Depending on the conditions, the mixtures will contain free proteins, free surfactants and/or protein–surfactant complexes. To be able to compare different protein–surfactant mixtures, generic knowledge about the occurrence of each of these states and their relative contribution to foam stability is essential. In this work, the foam stability and interfacial properties of bovine serum albumin (BSA) mixed with sodium dodecyl sulphate (SDS) as well the binding of SDS to BSA as are studied at different molar ratios (MR). A comparison is made with β-lactoglobulin (BLG) mixed with SDS. Both proteins and SDS are negatively charged at pH 7. The foam stability in the presence of small amounts (up to MR 1) of SDS is half the value of the pure protein solutions. The foam stability for both protein surfactant mixtures reaches a minimum at MR 20. A further increase of the MR leads to an increase of foam stability. The foam stability of BLG–SDS at MR >20 follows the foam stability of pure SDS solutions at equivalent concentrations, while BSA–SDS mixtures have an offset and begin to increase from MR >50. This behaviour was also reflected in the surface pressure and complex dilatational elastic moduli, and could be linked to the binding of the surfactant to the proteins. Both proteins bind SDS at high and low affinity binding sites. BSA's high affinity binding sites have a binding stoichiometry of 5.5 molSDS/molprotein, and BLG's high affinity binding site has a stoichiometry of 0.8 molSDS/molprotein (determined by isothermal titration calorimetry). Binding to the low affinity binding sites, occurs with a binding ratio, leading to an accumulation of free surfactants. While the basic mechanisms underlying the foam properties of mixed systems are not explained in detail by this approach, the foam stability plots of both protein surfactant mixtures could be superimposed using the concentration of free SDS.

Influence of Small Amphiphiles on Aqueous Dispersions of <i>β</i>-Lactoglobulin A and Bovine Serum Albumin: (2) Surface Energy and Emulsifying Properties

Influence of amphiphiles on surface energy (γ), emulsifying activity index (EAI) and emulsion stability (ES) of fatty-acid free bovine serum albumin (FAF-BSA), bovine serum albumin (BSA), and β-lactoglobulin A (β-LGA) was studied. Contact angle measurements (θ) of sessile drops of protein-surfactant mixtures were determined using water and α-bromonaphthalene as solvents of known parameters to calculate γ. All surfactants except zwitterionic Z8 increased γ. The greatest increase was by anionic SDS. All surfactants significantly reduced EAI in spite of increased γ. ES was reduced by all surfactants except cationic TDTM which, conversely, enhanced ES by up to 186% for BSA and β-LGA.

Identifying changes in chemical, interfacial and foam properties of β-lactoglobulin–sodium dodecyl sulphate mixtures

Techno-functional properties of proteins, such as foam stability, can be affected by the presence of low-molecular-weight surfactants. In order to understand and control the foam properties of such protein–surfactant mixtures, a thorough characterization of foam and interfacial properties needs to be supplemented by a detailed analysis of the structural changes of the protein and possible complexation with the surfactant. In this study, β-lactoglobulin (BLG) was mixed with sodium dodecyl sulphate (SDS) in different molar ratios (MRs). The foam half-life time of BLG-SDS mixtures decreased from that of pure BLG (315min at MR 0) to 44min at MR 20, which is close to the half-life of SDS at the respective concentration. With a further increase in the MR, the foam stability of the mixture increased, similar to the stability of SDS, to 250min at the highest MR (MR 100). The minimum in the foam stability curve was not reflected in the interfacial properties (Π and Ed). Π decreased and Ed increased continuously with increasing MR from values close to those of protein towards values typically found in pure surfactant solutions.The results show no clear correlation between the interfacial and foaming properties. In addition, it was shown by isothermal titration calorimetry and mass spectrometry that SDS molecules bind to the BLG. This leads to the formation of BLG-SDS complexes. These complexes have large influence on the foam properties in the mixture. The combination of analytical methods that were used give insights about protein complexation and the resulting change of foam properties of the mixture.

Spontaneous surface self-assembly in protein-surfactant mixtures: interactions between hydrophobin and ethoxylated polysorbate surfactants.

The synergistic interactions between certain ethoxylated polysorbate nonionic surfactants and the protein hydrophobin result in spontaneous self-assembly at the air-water interface to form layered surface structures. The surface structures are characterized using neutron reflectivity. The formation of the layered surface structures is promoted by the hydrophobic interaction between the polysorbate alkyl chain and the hydrophobic patch on the surface of the globular hydrophobin and the interaction between the ethoxylated sorbitan headgroup and hydrophilic regions of the protein. The range of the ethoxylated polysorbate concentrations over which the surface ordering occurs is a maximum for the more hydrophobic surfactant polyoxyethylene(8) sorbitan monostearate. The structures at the air-water interface are accompanied by a profound change in the wetting properties of the solution on hydrophobic substrates. In the absence of the polysorbate surfactant, hydrophobin wets a hydrophobic surface, whereas the hydrophobin/ethoxylated polysorbate mixtures where multilayer formation occurs result in a significant dewetting of hydrophobic surfaces. The spontaneous surface self-assembly for hydrophobin/ethoxylated polysorbate surfactant mixtures and the changes in surface wetting properties provide a different insight into protein-surfactant interactions and potential for manipulating surface and interfacial properties and protein surface behavior.

Interfacial viscoelasticity, yielding and creep ringing of globular protein–surfactant mixtures

Protein–surfactant mixtures arise in many industrial and biological systems, and indeed, blood itself is a mixture of serum albumins along with various other surface-active components. Bovine serum albumin (BSA) solutions, and globular proteins in general, exhibit an apparent yield stress in bulk rheological measurements at surprisingly low concentrations. By contrasting interfacial rheological measurements with corresponding interface-free data obtained using a microfluidic rheometer, we show that the apparent yield stress exhibited by these solutions arises from the presence of a viscoelastic layer formed due to the adsorption of protein molecules at the air–water interface. The coupling between instrument inertia and surface elasticity in a controlled stress device also results in a distinctive damped oscillatory strain response during creep experiments known as“creep ringing”. We show that this response can be exploited to extract the interfacial storage and loss moduli of the protein interface. The interfacial creep response at small strains can be described by a simple second order system, such as the linear Jeffreys model, however the interfacial response rapidly becomes nonlinear beyond strains of order 1%. We use the two complementary techniques of interfacial rheometry and microfluidic rheometry to examine the systematic changes in the surface and bulk material functions for mixtures of a common non-ionic surfactant, polysorbate 80, and BSA. It is observed that the nonlinear viscoelastic properties of the interface are significantly suppressed by the presence of even a relatively small amount of surfactant (csurf > 10−3 wt.%). Preferential interfacial adsorption of the mobile surfactant at these surfactant concentrations results in complete elimination of the bulk apparent yield stress exhibited by surfactant-free BSA solutions.

Adsorption layer and foam film properties of mixed solutions containing β-casein and C 12DMPO

The interrelations between adsorption layer properties and surface forces in thin foam films of protein/surfactant mixtures were investigated. The adsorption from β-casein/dodecyl dimethyl phosphine oxide (C 12DMPO) mixed solutions was studied by Profile Analysis Tensiometry (PAT). The adsorption of protein/surfactant mixtures at the air/water interface is of competitive nature. The obtained adsorption isotherms suggest a gradual displacement of the protein molecules from the interface with increasing surfactant concentration. Foam films were studied by microinterferometry, originally introduced by Scheludko and Exerowa. The obtained experimental results show that the composition of the mixed adsorption layers changes with increasing amount of added surfactant. At a certain mixing ratio the corresponding foam film thickness decreases dramatically. This change happens above the surfactant concentration where the surface tension of the protein–surfactant mixtures approaches the values obtained for the respective pure surfactant solutions. The thickness, refractive index and adsorbed amount of the respective adsorption layers were determined by ellipsometry. These results correlate with the above-mentioned PAT and foam film data. The refractive index and adsorbed amount decrease monotonically and reach values close to those for pure surfactant solutions. On the contrary, a continuous increase can be observed in the layer thickness up to the above-mentioned concentration, indicating the formation of a more diffuse layer at the air–water interface formed by β-casein and C 12DMPO molecules upon increase of surfactant concentration. For foam films the electrolyte concentration can change the equilibrium thickness of the films and the Π(h)-isotherms significantly.

Mixed monolayers of bovine serum albumin with a nonionic surfactant (Tween 80)

Mixed monolayers of bovine serum albumin (BSA) with a nonionic surfactant (Tween 80) are obtained by spreading solutions containing both components over the surface of a subphase (water with pH 6) over a wide range of solution compositions. According to compression-expansion isotherms, the mixed monolayers are of the condensed type when the BSA concentrations in the solution are far higher than or equal to the surfactant concentration. Such monolayers mostly consist of BSA-Tween 80 (1: 1) complexes. In contrast, a BSA monolayer is of the expanded type. When Tween 80 in the solution prevails over Tween 80, the monolayers become unstable. The results of this work pertain to the monitoring of the properties of protein-surfactant mixtures and design of Langmuir-Blodgett (LB) films.

Polymorphic Behavior in Protein−Surfactant Mixtures: The Water−Bovine Serum Albumin−Sodium Taurodeoxycholate System

Mixtures containing water, bovine serum albumin (BSA), and sodium taurodeoxycholate (NaTDC), a component of the bile in mammals, have been investigated in a wide range of composition and pH. Depending on the concentration of both solutes and the pH, solutions, precipitates, and gels are formed. Under spontaneous pH conditions, the transport properties in dilute solutions indicate the occurrence of significant interactions between BSA and the surfactant. Conversely, acidic media favor the formation of nonsoluble protein-surfactant complexes, with subsequent precipitation. The nucleation kinetics of the protein-surfactant complexes in solid form and the related precipitation processes can be slow or fast, depending on the overall solute content and the mole ratio. At high concentrations, a gel, extending on both sides of the charge neutralization line, and two-phase regions are observed. Gels shrink in open air and swell in the presence of excess water. Depending on concentration and temperature, the gels transform from an essentially liquidlike behavior to that peculiar to true gels (when G' > or = G''). The thermal gelation threshold, the temperature above which G' > or = G'', depends on BSA and NaTDC content and is concomitant to moderate heat effects, inferred by differential scanning calorimetry (DSC). The above data also indicate that the protein thermal denaturation in the gel is shifted to higher temperatures compared to water. Such a stabilizing effect is presumably related to the occurrence of both electrostatic and hydrophobic interactions with NaTDC. Water self-diffusion in the gels is slightly slower than that in the bulk and poorly sensitive to composition: it is about 65% the value of neat H2O in a wide concentration range, irrespective of the BSA, or NaTDC, concentration. A peculiar behavior is also observed in 23Na longitudinal and transverse relaxation rates. The T1 and T2 values, measured at 105.75 MHz on BSA-NaTDC gels, indicate that the motions determining the NMR relaxation of the sodium ions in the hydration layer of the protein-surfactant aggregates are not slow, having frequencies comparable with the Larmor one. The above properties, especially the rheological and the spectroscopic ones, are important for understanding the behavior of gels based on protein-surfactant mixtures.

Reduction of albumin adsorption onto silicon surfaces by Tween 20

The ability of Tween 20 to reduce the adsorption of albumin on silicon surfaces of different hydrophobicity was investigated by ellipsometry. As expected, protein adsorption was found to depend on the degree of hydrophobicity of the surfaces and on the concentration of the surfactant. A reduction of 90% in albumin adsorption on hydrophobic methylated surfaces by 0.05% Tween 20 was achieved, whereas a reduction of only 15% on hydrophilic surfaces was observed. Experiments of time-dependent protein adsorption in both pure protein and protein-surfactant mixtures were conducted to ascertain the stability of physically adsorbed Tween 20 films on intermediate silicon surfaces. It was found that the adsorbed Tween 20 film was robust and there was no evidence of exchange of the Tween molecules with albumin for up to 240 min exposure. Adsorption minima were confirmed to correlate with minima in contact angle and critical micelle concentration (CMC). (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 618-625, 1997.