Interactions of bovine serum albumin with cationic imidazolium and quaternary ammonium gemini surfactants: Effects of surfactant architecture

Do Ionic Liquids Exhibit the Required Characteristics to Dissolve, Extract, Stabilize, and Purify Proteins? Past-Present-Future Assessment

Proteins are highly labile molecules, thus requiring the presence of appropriate solvents and excipients in their liquid milieu to keep their stability and biological activity. In this field, ionic liquids (ILs) have gained momentum in the past years, with a relevant number of works reporting their successful use to dissolve, stabilize, extract, and purify proteins. Different approaches in protein-IL systems have been reported, namely, proteins dissolved in (i) neat ILs, (ii) ILs as co-solvents, (iii) ILs as adjuvants, (iv) ILs as surfactants, (v) ILs as phase-forming components of aqueous biphasic systems, and (vi) IL-polymer-protein/peptide conjugates. Herein, we critically analyze the works published to date and provide a comprehensive understanding of the IL-protein interactions affecting the stability, conformational alteration, unfolding, misfolding, and refolding of proteins while providing directions for future studies in view of imminent applications. Overall, it has been found that the stability or purification of proteins by ILs is bispecific and depends on the structure of both the IL and the protein. The most promising IL-protein systems are identified, which is valuable when foreseeing market applications of ILs, e.g., in "protein packaging" and "detergent applications". Future directions and other possibilities of IL-protein systems in light-harvesting and biotechnology/biomedical applications are discussed.

Role of Polyanions and Surfactant Head Group in the Formation of Polymer-Colloid Nanocontainers

OBJECTIVES

This study was aimed at the investigation of the supramolecular systems based on cationic surfactants bearing cyclic head groups (imidazolium and pyrrolidinium) and polyanions (polyacrylic acid (PAA) and human serum albumin (HSA)), and factors governing their structural behavior to create functional nanosystems with controlled properties. Research hypothesis. Mixed PE-surfactant complexes based on oppositely charged species are characterized by multifactor behavior strongly affected by the nature of both components. It was expected that the transition from a single surfactant solution to an admixture with PE might provide synergetic effects on structural characteristics and functional activity. To test this assumption, the concentration thresholds of aggregation, dimensional and charge characteristics, and solubilization capacity of amphiphiles in the presence of PEs have been determined by tensiometry, fluorescence and UV-visible spectroscopy, and dynamic and electrophoretic light scattering.

RESULTS

The formation of mixed surfactant-PAA aggregates with a hydrodynamic diameter of 100-180 nm has been shown. Polyanion additives led to a decrease in the critical micelle concentration of surfactants by two orders of magnitude (from 1 mM to 0.01 mM). A gradual increase in the zeta potential of HAS-surfactant systems from negative to positive value indicates that the electrostatic mechanism contributes to the binding of components. Additionally, 3D and conventional fluorescence spectroscopy showed that imidazolium surfactant had little effect on HSA conformation, and component binding occurs due to hydrogen bonding and Van der Waals interactions through the tryptophan amino acid residue of the protein. Surfactant-polyanion nanostructures improve the solubility of lipophilic medicines such as Warfarin, Amphotericin B, and Meloxicam.

PERSPECTIVES

Surfactant-PE composition demonstrated beneficial solubilization activity and can be recommended for the construction of nanocontainers for hydrophobic drugs, with their efficacy tuned by the variation in surfactant head group and the nature of polyanions.

Amphiphilic di-cationic methylene blue for improving antibacterial photodynamic efficiency through high accumulation and low aggregation on bacterial cell surfaces

The aggregation state of photosensitizers on the surface of bacterial cells is an important scientific problem for antibacterial photodynamic therapy (APDT). High accumulation and high photoactive state maintenance of photosensitizers are the prerequisite of high APDT efficiency. In this study, an amphiphilic di-cationic methylene blue photosensitizer (C12-MB) was synthesized through quaternization, and its structure, interface properties, photophysical properties and antibacterial photodynamic properties were studied. The results showed that C12-MB could reduce 4.27 log10 CFU and 4.8 log10 CFU for P. aeruginosa and S. aureus under irradiation of light at 660 nm, higher than the parent methylene blue. Through a spectroscopic study on photosensitizer adsorption over the bacterial surface, C12-MB can be accumulated with higher concentration, and the photo-active monomer content is 73% and 70% over P. aeruginosa and S. aureus, higher than those of methylene blue: 25% and 49%, respectively. The higher content of non-aggregated photo-active monomer could contribute to higher antibacterial photodynamic efficiency. For C12-MB adsorbed over bacterial surfaces, planar packing inhibition and electrostatic repulsion could contribute to lower C12-MB aggregation, which provides an useful reference for the structural design of high-efficiency photosensitizers.

Effect of Rhamnolipid Amidation on Biosurfactant Adsorption Loss and Oil-Washing Efficiency

Surfactant adsorption loss seriously hinders the economy of surfactant binary flooding technology for enhancing oil recovery, especially for biosurfactants with higher manufacturing costs. Here, biosurfactant rhamnolipid (RL) is chemically modified to develop a more efficient surfactant, rhamnolipid monoethanol amide (RL-MEA), which is characterized by decreased adsorption loss and increased oil-washing efficiency for enhanced oil recovery at a laboratory scale. Synthesis and characterization of the rhamnolipid monoethanol amide are carried out using high-performance liquid chromatography (HPLC), HPLC/MS, ¹H nuclear magnetic resonance (NMR), and Fourier transform infrared (FTIR) spectroscopy. The aggregation behavior is disclosed by surface tension, dynamic light scattering, and fluorescence spectra with pyrene as the probe. The applied performances of RL-MEA in the simulated enhanced oil recovery are researched, including the efficiency of oil washing, wettability to crude oil, and adsorption isotherms on silicates. Compared with the critical micelle concentration (CMC) of rhamnolipid of 14.23 × 10^-5 M in pure water and 9.02 × 10^-5 M in 0.2 M NaCl solution, the modified RL-MEA shows a significantly lower CMC of 7.15 × 10^-5 M in pure water and 5.34 × 10^-5 M in 0.2 M NaCl solution. More importantly, the modified RL-MEA reduces adsorption loss by 20% and enhanced oil-washing efficiency at higher temperatures and salt concentrations compared with the parent RLs. These findings would provide valuable information for developing efficient surfactant flooding agents for harsh reservoir geological conditions.

Experimental techniques to study protein-surfactant interactions: New insights into competitive adsorptions via drop subphase and interface exchange

Protein surfactant (PS) interactions is an essential topic for many fundamental and technological applications such as life science, nanobiotechnology processes, food industry, biodiesel production and drug delivery systems. Several experimental techniques and data analysis approaches have been developed to characterize PS interactions in bulk and at interfaces. However, to evaluate the mechanisms and the level of interactions quantitatively, e.g., PS ratio in complexes, their stability in bulk, and reversibility of their interfacial adsorption, new experimental techniques and protocols are still needed, especially with relevance for in-situ biological conditions. The available standard techniques can provide us with the basic understanding of interactions mainly under static conditions and far from physiological criteria. However, detailed measurements at complex interfaces can be formidable due to the sophisticated tools required to carefully probe nanometric phenomena at interfaces without disturbing the adsorbed layer. Tensiometry-based techniques such as drop profile analysis tensiometry (PAT) have been among the most powerful methods for characterizing protein's and surfactant's adsorption layers at interfaces via measuring equilibrium and dynamic interfacial tension and dilational rheology analysis. PAT provides us with insightful data such as kinetics and isotherms of adsorption and related surface activity parameters. However, the data analysis and interpretation can be challenging for mixed protein-surfactant solutions via standard PAT experimental protocols. The combination of a coaxial double capillary (micro flow exchange system) with drop profile analysis tensiometry (CDC-PAT) is a promising tool to provide valuable results under different competitive adsorption/desorption conditions via novel experimental protocols. CDC-PAT provides unique experimental protocols to exchange the droplet subphase in a continuous dynamic mode during the in-situ analysis of the corresponding interfacial adsorbed layer. The contribution of diffusion/convection mechanisms on the kinetics of the adsorption/desorption processes can also be investigated using CDC-PAT. Here, firstly, we review the commonly available techniques for characterizing protein-surfactant interactions in the bulk phase and at interfaces. Secondly, we give an overview for applications of the coaxial double capillary PAT setup for investigations of mixed protein-surfactant adsorbed layers and address recently developed protocols and analysis procedures. Exploring the competitive sequential adsorption of proteins and surfactants and the reversibility of pre-adsorbed layers via the subphase exchange are the particular experiments we can perform using CDC-PAT. Also the sequential and simultaneous competitive adsorption/desorption processes of some ionic and nonionic surfactants (SDS, CTAB, DTAB, and Triton) and proteins (bovine serum albumin (BSA), lysozyme, and lipase) using CDC-PAT are discussed. Last but not least, the fabrication of micro-nanocomposite layers and membranes are additional applications of CDC-PAT discussed in this work.

Gemini and Bicephalous Surfactants: A Review on Their Synthesis, Micelle Formation, and Uses

The use of surfactants in polymerization reactions is particularly important, mainly in emulsion polymerizations. Further, micelles from biocompatible surfactants find use in pharmaceutical dosage forms. This paper reviews recent developments in the synthesis of novel gemini and bicephalous surfactants, micelle formation, and their applications in polymer and nanoparticle synthesis, oil recovery, catalysis, corrosion, protein binding, and biomedical area, particularly in drug delivery.

Mechanism of interactions between soyasaponins and soybean 7S/11S proteins

In this study, the proteins glycinin (11S) and β-conglycinin (7S) were mixed with soyasaponin (Ssa) Ab/Bb to form a composite system. We used fluorescence and synchronous fluorescence spectra to demonstrate the changes in the surrounding environment and the structure of the proteins. Dynamic interface behavior analysis showed the possible interface behavior induced by the composite system. The interactions between Ssa and the proteins, along with the mode of action, were analyzed by molecular docking. The interactions between Ssa and soy protein increased with the change in concentration. The interactions between the two proteins were mediated by tryptophan (Trp) and primarily involved hydrogen bonds, which changed the microenvironment and loosened the protein structure. These results helped in understanding the mechanism underlying the interactions between Ssa Ab/Bb and 7S/11S. Furthermore, these results highlighted the theoretical fundamentals for the future applications of composite systems as surfactants in the food industry.

Refolding of denatured gold nanoparticles-conjugated bovine serum albumin through formation of catanions between gemini surfactant and sodium dodecyl sulphate

The present work elucidates binding interactions of sodium dodecyl sulphate (SDS) with the conjugated gold nanoparticles (AuNPs)-bovine serum albumin (BSA), unfolded by each of two gemini surfactants, 1,4-bis(dodecyl-N,N-dimethylammonium bromide)-butane (12-4-12,2Br⁻) or 1,8-bis(dodecyl-N,N-dimethylammonium bromide)-octane (12-8-12,2Br⁻). Initially, at a low concentration of SDS there is a relaxation of bioconjugates from their compressed form due to the formation of catanions between SDS and gemini surfactants. On moving towards higher concentrations of SDS, these relaxed unfolded bioconjugates renature by removal of residual bound gemini surfactants. Mixed assemblies of SDS and gemini surfactants formed during refolding of bioconjugates are characterized by DLS and FESEM measurements. A step-by-step process of refolding observed for these denatured protein bioconjugates is exactly the inverse of their unfolding phenomenon. Parameters concerning nanometal surface energy transfer (NSET) and Förster's resonance energy transfer (FRET) phenomenon were employed to develop a binding isotherm. Moreover, there remains an inverse relationship between α-helix and β-turns of bioconjugates during the refolding process. Significantly, in the presence of 12-8-12,2Br⁻, SDS induces more refolding as compared to that for 12-4-12,2Br⁻. Bioconjugation shows an effect on the secondary structures of refolded BSA, which has been explored in detail through various studies such as Fourier transform infrared spectroscopy, fluorescence, and circular dichroism (CD). Therefore, this approach vividly describes the refolding of denatured bioconjugates, exploring structural information regarding various catanions formed during the process that would help in understanding distance-dependent optical biomolecular detection methodologies and physicochemical properties.

Demonstration of refolding of conjugated AuNPs-BSA through the formation of various catanions of SDS and gemini surfactants with different spacers in HEPES buffer medium using FRET/NSET methods and material characterization techniques.

On the Effect of pH, Temperature, and Surfactant Structure on Bovine Serum Albumin-Cationic/Anionic/Nonionic Surfactants Interactions in Cacodylate Buffer-Fluorescence Quenching Studies Supported by UV Spectrophotometry and CD Spectroscopy

Due to the fact that surfactant molecules are known to alter the structure (and consequently the function) of a protein, protein–surfactant interactions are very important in the biological, pharmaceutical, and cosmetic industries. Although there are numerous studies on the interactions of albumins with surfactants, the investigations are often performed at fixed environmental conditions and limited to separate surface-active agents and consequently do not present an appropriate comparison between their different types and structures. In the present paper, the interactions between selected cationic, anionic, and nonionic surfactants, namely hexadecylpyridinium chloride (CPC), hexadecyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), polyethylene glycol sorbitan monolaurate, monopalmitate, and monooleate (TWEEN 20, TWEEN 40, and TWEEN 80, respectively) with bovine serum albumin (BSA) were studied qualitatively and quantitatively in an aqueous solution (10 mM cacodylate buffer; pH 5.0 and 7.0) by steady-state fluorescence spectroscopy supported by UV spectrophotometry and CD spectroscopy. Since in the case of all studied systems, the fluorescence intensity of BSA decreased regularly and significantly under the action of the surfactants added, the fluorescence quenching mechanism was analyzed thoroughly with the use of the Stern–Volmer equation (and its modification) and attributed to the formation of BSA–surfactant complexes. The binding efficiency and mode of interactions were evaluated among others by the determination, comparison, and discussion of the values of binding (association) constants of the newly formed complexes and the corresponding thermodynamic parameters (ΔG, ΔH, ΔS). Furthermore, the influence of the structure of the chosen surfactants (charge of hydrophilic head and length of hydrophobic chain) as well as different environmental conditions (pH, temperature) on the binding mode and the strength of the interaction has been investigated and elucidated.

Kinetic and thermodynamic of lactoferrin - Ethoxylated-nonionic surfactants supramolecular complex formation

Understanding nonionic surfactant-protein interactions is fundamental from both technological and scientific points of view. However, there is a complete absence of kinetic data for such interactions. We employed surface plasmon resonance (SPR) to determine the kinetic and thermodynamic parameters of bovine lactoferrin-Brij58 interactions at various temperatures under physiological conditions (pH 7.4). The adsorption process was accelerated with increasing temperature, while the desorption rate decreased, resulting in a more thermodynamically stable complex. The kinetic energetic parameters obtained for the formation of the activated complex, [bLF-Brij58]^‡, indicated that the potential energy barrier for [bLF-Brij58]^‡ formation arises primarily from the reduction in system entropy. [bLF-Brij58]^○ formation was entropically driven, indicating that hydrophobic interactions play a fundamental role in bLF interactions with Brij58.

Interaction of Bis-Guanidinium Acetates Surfactants with Bovine Serum Albumin Evaluated by Spectroscopy

The interactions between cocopropane bis-guanidinium acetates, tallowpropane bis-guanidinium acetates with bovine serum albumin (BSA) in an aqueous solution were studied by fluorescence and circular dichroic spectroscopy measurements. The aim of the study was to elucidate the influence of the hydrophilic group and the length of the hydrophobic chain of these surfactants on the mechanism of binding to BSA. The results revealed that for both surfactants, at low concentrations, the Stern–Volmer plots had an upward curvature and at high concentrations, the quenching efficiency was decreased with increase in surfactant concentration. Different thermodynamics parameters demonstrated the existence of hydrogen bond and van der Waals force which acting as binding forces. Static quenching was observed among the protein and surfactant. The conformation of BSA was changed at higher surfactant concentrations as shown by synchronous fluorescence and CD spectroscopy. This work reveals the mechanism and binding characteristics between guanidine surfactants and protein, and provided the basis for further applications of surfactants.

Synthesis and Properties of Alkyl Bis-Guanidinium Acetates Surfactants

Novel surfactants with double hydrophilic groups (cocopropane and tallowpropane bis-guanidinium acetates), were synthesized and tested to evaluate both the basic surfactant properties and the unique application performance. Surface tension, conductivity and contact angle measurements were used to study the self-aggregation behavior in aqueous solution. Aggregation parameters were calculated such as adsorption efficiency and effectiveness (pC20 and CAC/C20), the maximum surface excess concentration (Гmax) and minimum surface area permolecule (Amin). The thermodynamic parameters of aggregation based conductivity measurements revealed that the aggregation process was spontaneous and entropy-driven. Compared to DTAC and CTAC, the alkyl bis-guanidinium acetates showed a higher emulsification capacity with both liquid kerosene and soybean oil. The evaluation of antimicrobial activity showed that the alkyl bisguanidinium acetates exhibited strong antibacterial activity against the tested strains at a concentration of 50 ppm.

Effect of Single/Mixed Surfactant Systems on Orientations of Liquid Crystals and Interaction of Proteins with Surfactants at Fluid Interfaces

A series of single surfactant systems, i.e, quaternary ammonium-based gemini surfactants with different spacers and alkyl chain lengths (m-n-m; m=12, n=2, 3, 4, 6; n=3, m=12, 14, 16), halogen-free surface-active ionic liquid (HF-SAILs) with different symmetries ([Cnmim][C12H25SO4]; n=6, 8, 10, 12), and single-chain cationic surfactants including 1-dodecyl-3-methylimidazolium bromide ([C12mim]Br) and dodecyltrimethylammonium bromide (DTAB), along with certain combinations of different surfactants (12-3-12/[C12mim]Br and 12-3-12/DTAB) were applied to an aqueous/liquid crystal interface (ALI). All the surfactants could induce an orientational transition of liquid crystals (LCs) from a planar to homeotropic state, which caused a bright-to-dark optical shift. It was proved that double-chain surfactants and the mixed surfactants inclined to adsorb at the ALI triggering the orientational transition. Inspiringly, a quicker and more sensitive dark-to-bright optical response was observed for mixed surfactant system-decorated interfaces in contact with proteins (such as bovine serum albumin (BSA), lysozyme, and trypsin) as opposed to the single surfactant systems. The ALI decorated by the 12-3-12/[C12mim]Br system was particularly efficient and exhibited the most sensitive optical response for BSA (0.01ngmL−1). The order parameters (SCD) of surfactants tails at the interface and the free energy of proteins with 12-3-12 and [C12mim]Br were calculated, respectively. The results explain that the 12-3-12/[C12mim]Br-laden ALI shows a quicker and more sensitive optical response for BSA. This work inspired us to study mixed surfactant systems-decorated LC interfaces and further provides new insights for different chemical and biological applications.

The multi-spectroscopic approach on the interaction between rabbit serum albumin and cationic surfactant: Investigation on the formation and solubilization of the protein aggregation

The protein-surfactant interaction studies have great importance in the range of the application like cosmetics, food, pharmaceutical, detergent industries, and many more. In this study, we have studies protein (rabbit serum albumin, RSA) and a cationic surfactant (cetyltrimethylammonium bromide, CTAB) interaction at different physiological conditions (viz., pH, ionic strength, surfactants concentrations, protein concentration, and many more). They form the protein surfactant complexes. The interchange of electrostatic and hydrophobic force monitors the change in complexes. The three different pHs (below (4.0), above (7.0) and at (4.7) the isoelectric point of RSA) of the medium indicate the three different charges on the protein while surfactant is positive in charge. Critical micelle concentration (CMC) plays a significant role in protein-surfactant interaction. CTAB unfolds the protein at its specific concentration range afterward again; it starts refolded. RSA interacted, with the addition of the CTAB is characterized by many spectroscopic methods like UV-visible, fluorescence, fluorescence time-resolved, circular dichroism, and topographical changes monitored by the AFM. In fluorescence spectra, the blue shift shows the unfolding of RSA. The molecular docking indicates the binding energy of 5.8 kcal mol^-1. The changes below and above the CMC is significant.

Spectroscopic studies of the aggregation behavior of Human Serum Albumin and cetyltrimethylammonium bromide

To check the role of micelle in the interaction studies of human serum albumin (HSA) and cetyltrimethylammonium bromide (CTAB), many spectroscopic techniques, like UV-visible, fluorescence, circular dichroism, fluorescence lifetime measurement, and atomic force microscopy (AFM), are employed. The binding affinity of all compound groups depended on the hydrocarbon chain, indicating the predominant role of hydrophobic forces, electrostatic forces and supported by polar interactions on protein surfaces. The protein has a different effect on the polarity of a microenvironment in fluorescence spectra above and below the critical micelle concentration (CMC) of the suractant. The far-UV-CD spectra show unfolding below the CMC and refolding above the CMC. The binding of the surfactant induces changes in the microenvironment at different pHs around the residues of the aromatic amino acid and the disulfide bond of protein. The AFM images show significant changes in the protein's structure. AFM images show dense aggregation below the CMC and above the CMC, some net-like structure formed in the HSA-CTAB complex. To test the experimental results, we used Auto dock Vina to conduct molecular docking. Above and below the CMC, structural changes can be seen.

Molecular Interaction of Amino Acid-Based Gemini Surfactant with Human Serum Albumin: Tensiometric, Spectroscopic, and Molecular Docking Study

Binding effect and interaction of N,N'-dialkyl cystine based gemini surfactant (GS); 2(C₁₂Cys) with human serum albumin (HSA) were systematically investigated by the techniques such as surface tension measurement, UV-visible spectroscopy, fluorescence spectroscopy, circular dichroism (CD) spectroscopy, and molecular docking studies. The surface tension measurement exhibited that HSA shifted the critical micelle concentration of the 2(C₁₂Cys) GS to the higher side that confirms the complex formation among 2(C₁₂Cys) GS and HSA which was also verified by UV-visible, fluorescence, and CD spectroscopy. Increase in the concentration of 2(C₁₂Cys) GS increases the absorption of the HSA protein but has a reverse effect on the fluorescence intensity. The analysis of UV-visible study with the help of a static quenching method showed that the value acquired for the bimolecular quenching constant (k _q) quenches the intrinsic fluorescence of the HSA protein. Synchronous fluorescence spectrometry declared that the induced-binding conformational changes in HSA and CD results explained the variations in the secondary arrangement of the protein in presence of 2(C₁₂Cys) GS. The present study revealed that the interaction between 2(C₁₂Cys) GS and HSA is important for the preparation and properties of medicines. Molecular docking study provides insight into the specific binding site of 2(C₁₂Cys) GS into the sites of HSA.

Comparative evaluation of antimicrobial activity of different types of ionic liquids

In order to identify most suitable ionic liquids (ILs) for potential applications in infection prevention and control, in the present study we comparatively evaluated the antimicrobial potency and hemolytic activity of 15 ILs, including 11 previously described and four newly synthesized ILs, using standard microbiological procedures against Gram-positive and Gram-negative bacteria. ILs showing the lowest minimum inhibitory concentration (MIC) were tested for their hemolytic activity. Three ILs characterized by low MIC values and low hemolytic activity, namely 1-methyl-3-dodecylimidazolium bromide, 1-dodecyl-1-methylpyrrolidinium bromide, and 1-dodecyl-1-methylpiperidinium bromide were further investigated to determine their minimum bactericidal concentration (MBC), and their ability to inhibit biofilm formation by Staphylococcus aureus or Pseudomonas aeruginosa. Killing kinetics results revealed that both Gram-positive and Gram-negative bacteria are rapidly killed after exposure to MBC of the selected ILs. Furthermore, the selected ILs efficiently inhibited biofilm formation by S. aureus or P. aeruginosa. To our knowledge, this is the first systematic study investigating the antimicrobial potential of different types of ionic liquids using standard microbiological procedures. In the overall, the selected ILs showed low hemolytic and powerful antimicrobial activity, and efficient inhibition of biofilm formation, especially against S. aureus, suggesting their possible application as anti-biofilm agents.

Impact of the alkyl chain length on binding of imidazolium-based ionic liquids to bovine serum albumin

The effects of six imidazolium-based ionic liquids (ILs) with different alkyl chain length ([C_nMim]Cl, n=2, 4, 6, 8, 10, 12) on the structure and functions of bovine serum albumin (BSA) were studied by multi-spectral methods and molecular docking. ILs with the longer alkyl chain length have the stronger binding interaction with BSA and the greater conformational damage to protein. The effects of ILs on the functional properties of BSA were further studied by the determination of non-enzyme esterase activity, β-fibrosis and other properties of BSA. The thermal stability of BSA was reduced, the rate of the formation of beta sheet structures of BSA was lowered, and the esterase-like activity of BSA were decreased with the increase of ILs concentration. Simultaneous molecular modeling technique revealed the favorable binding sites of ILs on protein. The hydrophobic force and polar interactions were the mainly binding forces of them. The calculated results are in a good agreement with the spectroscopic experiments. These studies on the impact of the alkyl chain length on binding of imidazolium-based ionic liquids to BSA are of great significance for understanding and developing the application of ionic liquid in life and physiological system.

Changes in fluorescent dissolved organic matter upon interaction with anionic surfactant as revealed by EEM-PARAFAC and two dimensional correlation spectroscopy

Surfactants are present in significant amounts in both domestic and industrial wastewater, which may interact with dissolved organic matter (DOM). The present study investigated the interactions of sodium dodecyl sulfate (SDS) with three different DOM solutions, including bovine serum albumin (BSA), humic acid (HA), and the mixture of the two (BSA-HA), based on two advanced spectroscopic tools: excitation emission matrix (EEM) combined with parallel factor analysis (EEM-PARAFAC) and two dimensional correlation spectroscopy (2D-COS). The responses of two protein-like components to the addition of SDS differed depending the presence and the absence of HA. A decreasing and an increasing trend was observed for tryptophan-like (C1) and tyrosine-like (C2) components, respectively, in the BSA solution, while the BSA-HA mixture exhibited increasing fluorescence trends for both protein-like components. The conflicting results suggest that HA plays a secondary role in the protein-SDS interactions. No interaction between the SDS and humic-like component was found. 2D-COS combined with fluorescence spectra demonstrated that the protein-SDS interaction occurred on the order of C2 > C1 for the BSA solution but C1 > C2 for the BSA-HA mixture. Analyses of Scatchard plots confirmed the sequential order interpreted from 2D-COS, showing consistent trends in the binding constants. However, the presence of HA affected the protein-SDS interactions in different manners for C1 and C2, enhancing and reducing the binding constants, respectively. Circular dichroism spectra confirmed the occurrence of conformational changes in BSA with SDS. EEM-PARAFAC and 2D-COS successfully explained different interactions of surfactant with protein-like components in the presence of HA.

Electrical impedance monitoring of protein unfolding

We have applied electrical impedance spectroscopy (EIS) to investigate how the dielectric characteristics of protein aqueous solutions respond to varying amounts of a co-dissolved surfactant.

Extracellular polymeric substances protect Escherichia coli from organic solvents

The protective roles of extracellular polymeric substances againstn-butanol have been investigated and determined.