Surfactant-Amino Acid and Surfactant-Surfactant Interactions in Aqueous Medium: a Review

Enhanced Efficiency of Anionic Guerbet-Type Amino Acid Surfactants

This study investigates the surfactant properties and efficiency of linear and Guerbet-type amino acid surfactants. Utilizing a Wilhelmy plate method, we assessed the colloidal efficiency of these surfactants, with the lowest observed critical micelle concentration at 0.046 mmol L-1, significantly reducing surface tension to as low as 25.1 mN·m-1. Furthermore, the self-diffusion coefficients of the various surfactants have been determined through 1H pulsed-field gradient nuclear magnetic resonance diffusion-ordered spectroscopy. The self-diffusion coefficients are linked to the surface tension reduction as a function of concentration to determine the characteristic time scale of diffusion. In this work, the characteristic time scale of diffusion of a series of surfactants was calculated to investigate the interfacial coverage efficiency. Our findings indicate an inverse relationship between the characteristic time scale of diffusion and critical micelle concentrations across surfactants with hydrocarbon tail lengths of 8-22 carbons. Shorter tails correspond to lower colloidal efficiencies, but rapid surface tension reduction, resulting in the characteristic time scale of diffusion values ranging from 120 ns to 2.15 s. This property is crucial for applications requiring rapid action, such as enhancing aerosol efficiency, improving dispersion, and wetting materials in products.

The role of chelating agent in the self-assembly of amphoteric surfactants

HYPOTHESIS

Limited research has been conducted on the influence of chelating agents on the self-assembly process in surfactant solutions. The traditional approach assumes the chelating agent only interferes as a salting-out ion, therefore promoting surfactant separation. However, the opposite behavior has been observed for iminodipropionate based surfactants, in which the presence of chelating agents of the aminopolycarboxylate type increases solubility of nonionic ethoxylated surfactants in mixed micellar systems. Specific interaction between chelating agents-surfactants can be an important parameter in the self-assembly processes.

EXPERIMENTS

Physicochemical properties of solutions containing amphoteric surfactant and tetrasodium glutamatediacetate have been investigated. Macroscopic properties, such as viscosity and cloud point, were evaluated in the presence of a non-water-soluble alkyl ethoxylated surfactant. Interactions between amphoteric surfactant and chelating agent were monitored by NMR spectroscopy, including 13C chemical shift and lineshape analysis as well as 1H diffusometry.

FINDINGS

The study reveals that there is an interaction between the head group of the surfactant and the chelating agent forming oligomeric surfactant analogues with larger hydrophilic moieties, which results in smaller, more spherical micelles. The combined interactions provide possibilities for tuning the aggregation behavior of systems containing surfactants and chelating agents, and with that, the macroscopic properties of the system.

Revealing protein aggregation behaviour and dispersion properties induced by molecular interactions between sucrose esters and myofibrillar protein in an aqueous phase system

The effects of sucrose esters (SE) with varying hydrophilic-lipophilic balance (HLB) values (SE 11, 13, 15) and different concentrations (0.01, 0.1, 1.0 mM) on the dispersion properties and structure of myofibrillar proteins (MPs) in the aqueous phase were investigated. The results demonstrated that the SE 11 and SE 13 reduced the particle size and enhanced the distribution uniformity of the MPs. All of the SE exhibited a slight reduction in the ζ-potential absolute values of the MPs. Meanwhile, the SE 11 significantly reduced the turbidity of the MPs, especially in the 0.1 mM group. Macroscopic and microscopic images showed that the optimum dispersion state was in the SE 11-0.1 group. Furthermore, the interactions between SE and MPs exerted a significant impact on the proteins structure. The SE 13 and SE 15 caused significant changes, which presented concentration correlation, in the tertiary and secondary spatial structures of the MPs. Nevertheless, slight structural changes were observed in MPs with different SE11 concentrations. The SE did not alter the molecular weight of the MPs, i.e. it did not induce irreversible aggregation, nor degradation of the proteins. These results were verified by the surface hydrophobicity, UV-Vis spectroscopy, intrinsic fluorescence, circular dichroism, and SDS-PAGE. Molecular docking simulation showed that hydrophobic interactions and hydrogen bonds were the main interaction force between SE 11 and MPs. Therefore, our findings provided meaningful insights into the dispersion state of the MPs aqueous containing SEs and contributed to the practical application of non-ionic surfactants in meat protein processing.

Effect of antidiabetic drug metformin hydrochloride on micellization behavior of cetylpyridinium bromide in aqueous solution

Herein, the interaction of an antidiabetic drug, metformin hydrochloride (MHCl), and a cationic surfactant, cetylpyridinium bromide (CPB) is investigated in an aqueous medium. The critical micellar concentration (CMC) of CPB is estimated through conductivity experiments and found to be reduced on adding MHCl and further decreased in the presence of NaCl. The reduced CMC is attributed to the solubilization of MHCl by CPB through micellization and the micellization is found to be thermodynamically spontaneous that experiences an augmentation in the presence of NaCl. This is identified from the negative value of standard free energy (Δ G0m). The higher negative value of Δ G0m (-55.41 kJ mol-1) for CPB + MHCl + NaCl than CPB (-37.89 kJ mol-1) and CPB + MHCl (-34.08 kJ mol-1) is suggestive of the above phenomenon. The positive values of Δ S0m in all three cases confirm that the micellization is entropy driven. The binding of MHCl on CPB is quantified by estimating binding constant using the Benesi-Hildebrand (B-H) plot through UV-visible spectral methods. The binding constant values were calculated to be 2.70 M-1 for CPB + MHCl + NaCl compared to 1.258 M-1 for CPB + MHCl predicting a favoring of micellization in the presence of NaCl which is higher than that in the presence of co-solvents. The molecular interaction of MHCl and CPB is justified using FT-IR and NMR techniques. The surface properties of drug surfactant interactions are assessed using SEM techniques. The point of interaction between the drug and surfactant is visualized through the molecular docking approach. The results suggest that CPB would be an effective solubilizer for developing MHCl drug formulations.Communicated by Ramaswamy H. Sarma.

The different adsorption-degradation behaviors of SARS-CoV-2 by bioactive chemicals in wastewater: The suppression kinetics and their implications for wastewater-based epidemiology

Wastewater-Based Epidemiology (WBE) is widely used to monitor the progression of SARS-CoV-2 pandemic. While there is a clear correlation between the number of COVID patients in a sewershed and the viral load in the wastewater, there is notable variability across different treatment plants. In particular, some facilities consistently exhibit higher viral content per diagnosed patient, implying a potential underestimation of the number of COVID patients, while others show a low viral load per diagnosed case, indicating potential attenuation of genetic material from the sewershed. In this study, we investigated the impact of nonylphenol ethoxylate (NPHE), linear alkylbenzene sulfonic acid (LABS), bisoctyl dimethyl ammonium chloride (BDAC), and didecyldimethylammonium chloride (DDAC), the surfactants that have been commonly used as detergents, emulsifiers, wetting agents on the stability of SARS-CoV-2 in wastewater. The results showed multiple and dynamic mechanisms, including degradation and desorption, can occur simultaneously during the interaction between SARS-CoV-2 and different chemicals depending on the physicochemical properties of each chemical. Through the elucidation of the dynamic interactions, the findings from this study could help the state health organizations and scientific community to optimize the SARS-CoV-2 wastewater-based epidemiology strategies.

Experimental and simulation studies on the improvement of coal dust pollution by an aqueous solution of sodium α-alkenylsulfonate and amino acid-based surfactants

The use of surfactants is crucial for the prevention and control of coal dust pollution in coal mining operation areas, yet there still exist many challenges in the control of coal dust pollution. In this paper, the green biomass-based amino acid surfactant sodium myristoyl glutamate (SMG) and the anionic surfactant sodium α-alkenyl sulfonate (AOS) were selected to investigate the improvement of coal dust wettability by single and binary solutions from the macroscopic and microscopic perspectives. Molecular simulations were used to reveal the microscopic mechanism of the wettability of coal dust by the different solutions. Experimental measurements showed that the contact angle of the AOS + SMG aqueous solution was as low as 13.8° on a coal surface. Coating the coal dust with the AOS + SMG solution reduced the surface tension by 12.02% compared to coating the coal with a single component solution. Additionally, the use of the binary AOS + SMG solution increased the hydrophilic group content in the coating by 11.77% compared to a single component solution, and the linkage between hydrophilic groups was enhanced, which pulls the water molecules to wet the coal dust. These research results should provide a new way to promote more environmentally friendly coal dust pollution control technology.

A Review on Interactions between Amino Acids and Surfactants as Well as Their Impact on Corrosion Inhibition

Amino acid-surfactant interactions are central to numerous studies because of their increased effectiveness in chemical, biological, household and industrial use. This review will focus on the impact and effect of the physicochemical properties, temperature, pH, and surfactant chain length of the amino acid for detailed exploration of amino acids and surfactants in aqueous medium. The impact of cosolvent on self-aggregation, critical micelle concentration (CMC), and binding affinity with other biomolecules, as well as amino acid-surfactant interactions, are the epicenters. The results show that increasing the temperature causes negative enthalpy for ionic surfactants and micellization, implying that micellization and amino acids are thermodynamically spontaneous and exothermic, accompanied by positive entropy. As these physicochemical studies are additive, the amino acid and ionic surfactant interactions provide clues on protein unfolding and denaturation under different media, which further changes with a change in physiological conditions like pH, cosolvent, chain length, and temperature. On varying the pH, the net charge of the amino acid also changes and, subsequently, the binding efficiency of the amino acids to the surfactants. The presence of cosolvent causes a lowering in the hydrophobic chain, which changes the surfactant's CMC. At a reduced CMC, the hydrophobic characteristic of amino acid-surfactant associations is amplified, leading to rapid denaturation of proteins that act as propulsion under the influence of extended chain surfactants. Amino acids are one of the most intriguing classes of chemicals that produce high inhibitory efficacy. Amino acids are also a component of proteins and therefore, found in a significant part of the human body, further making them a promising candidate as corrosion inhibitors. In this review article, authors have also focused on the collection and investigation for application of amino acid-surfactant interactions in corrosion inhibition. Various predictive studies/in silico studies are also reported by many research groups, such as density functional theory (DFT) calculations and molecular dynamics simulations to obtain tentative electronic, structural, and physiochemical characteristics like energies of the highest occupied molecular orbitals and lowest unoccupied molecular orbitals, binding energy, Gibb's free energy, electronegativity, polarizability, and entropy. In silico studies are helpful for the mechanism predictions of the process occurring on metal surfaces.

Study on the Effects of Biologically Active Amino Acids on the Micellization of Anionic Surfactant Sodium Dodecyl Sulfate (SDS) at Different Temperatures

The micellar properties of the anionic surfactant, sodium dodecyl sulfate (SDS) are modified by the biologically active amino acids. Amino acids (AAs) have experienced a variety of interactions and are proposed to influence SDS micelles due to their nominated hydrophobic interactions. The present study determines the critical micellar concentration (CMC) of SDS in aqueous solutions as well as in amino aqueous solutions. Three amino acids (glutamic acid, histidine, and tryptophan) are considered here. The conductometric measurements were carried out using a wide range of SDS concentrations at different temperatures. Surface tension experiments have also been applied to estimate many surface parameters including surface excess concentration (Γmax), surface occupied area per surfactant molecule (Amin), surface tension at CMC (γcmc), surface pressure at CMC (Πcmc) and Gibbs free energy of adsorption (∆Gads°), enthalpy ∆Hm° and the critical packing parameter (CPP). Interestingly, CMC values of SDS in water and in aqueous amino acids estimated by the surface tension method are comparable with the corresponding values obtained by the conductance method. The thermodynamic parameters of SDS micellization were also evaluated in both presence and absence of AAs. The additives of AAs work to reduce the CMC values, as well as the SDS thermodynamic parameters. This reduction is highly dependent on the hydrophobicity of the AA side chain. Negative values of ∆Gm°, ∆Hm° elucidate that micellization of SDS in the presence of amino acids is thermodynamically spontaneous and exothermic. The outcomes here might be utilized for pharmaceutical applications to stabilize proteins and inhibit protein aggregation.

Evaluation of intermolecular interactions required for thermostability of a recombinant adenovirus within a film matrix

Thermostability of vaccines and biologic drugs are key to increasing global access to a variety of life-saving agents. In this report, we characterize interactions between a novel zwitterionic surfactant and adenovirus serotype 5 which allow the virus to remain stable at room temperature in a thin film matrix. Complexity of the adenovirus capsid and the polydispersity of the surfactant required use of a variety of techniques to achieve this goal. The CMC of the surfactant in Tris buffer (pH 6.5) was estimated to be 0.7-1.17 × 10^-4 M by the pyrene 1:3 ratio method. TEM images depict micelle formation around virus capsids. An estimated Kd of the virus-surfactant interaction of 2.25 × 10^-9 M was determined by isothermal titration calorimetry. Associated data suggest that this interaction may be thermodynamically favorable and entropically driven. A competitive saturation study and TEM images indicate that the surfactant also binds to hexon proteins on the virus capsid. Taken together, these data support the working hypothesis that the surfactant is capable of forming micelles in the solid and liquid state and that it forms a protective coating around the virus by binding to hexon proteins on the virus capsid during the film forming process.

Drug Solubilization by Surfactants: Experimental Methods and Theoretical Perspectives

This mini review will give an insight into the need and usefulness of investigating the solubilization of poorly soluble drugs. Commonly used experimental and theoretical models are outlined to study the efficacy of the carrier or excipient for the poorly soluble drugs. Furthermore, the use of surface active agents for drug solubilization is discussed in correlation with the mathematical models suggested from time to time. A few experimental techniques are also discussed which would be very helpful in elucidating the interactions prevailing in the mixed systems of poorly soluble drugs and surface active agents.

Functional and structural properties of soy 11S globulin: Influence of reverse micelle extraction

The effect of the reverse micelle extraction method (RMEM) on the physicochemical properties of soy 11S globulin was studied and compared with that of the traditional alkali solution-acid precipitation method (ASAPM). The results showed that the β-sheet structure content of soy 11S globulin obtained by RMEM was lower, while the β-turn structure content was higher compared with that obtained by ASAPM. Furthermore, the protein unfolding degree and surface hydrophobicity were lower than those observed using ASAPM. Therefore, RMEM better maintained the natural molecular structure of soy 11S globulin. The thermodynamic and rheological properties of soy 11S globulin obtained by these two methods were further compared, showing that the highest denaturation temperature and transition heat of soy 11S globulin extracted using ASAPM were different from those obtained using RMEM. Furthermore, soy 11S globulin extracted by RMEM showed stronger heat resistance and a higher denaturation temperature than that extracted by ASAPM. The final storage modulus and frequency sweep results showed that the gel formed by soy 11S globulin obtained using RMEM had high storage modulus and loss modulus. PRACTICAL APPLICATION: In this study, the effects of two different extraction methods on structural and functional properties of soy 11S globulin, such as thermodynamics and rheology, were investigated. We can know the 11S globulin extracted using the reverse micelle environment was more heat-resistant and heat-induced gel quality of 11S globulin was improved by the reverse micelle environment. These results will provide theoretical basis that would help determine the potential applications of soy 11S globulin in the food system.

Surfactants: physicochemical interactions with biological macromolecules

Macromolecules are essential cellular components in biological systems responsible for performing a large number of functions that are necessary for growth and perseverance of living organisms. Proteins, lipids and carbohydrates are three major classes of biological macromolecules. To predict the structure, function, and behaviour of any cluster of macromolecules, it is necessary to understand the interaction between them and other components through basic principles of chemistry and physics. An important number of macromolecules are present in mixtures with surfactants, where a combination of hydrophobic and electrostatic interactions is responsible for the specific properties of any solution. It has been demonstrated that surfactants can help the formation of helices in some proteins thereby promoting protein structure formation. On the other hand, there is extensive research towards the use of surfactants to solubilize drugs and pharmaceuticals; therefore, it is evident that the interaction between surfactants with macromolecules is important for many applications which includes environmental processes and the pharmaceutical industry. In this review, we describe the properties of different types of surfactants that are relevant for their physicochemical interactions with biological macromolecules, from macromolecules–surfactant complexes to hydrophobic and electrostatic interactions.

Study on methane hydrate formation in gas-water systems with a new compound promoter

The effects of a new promoter on the growth kinetics of methane hydrates were investigated using a visualized constant-pressure autoclave. The experimental results show that when the 1#, 2# and 3# unit promoter was compounded at a ratio of 2 : 1 : 1, the induction time was shortened greatly from 30 h to 0.64 h compared to the no promoter situation. Meanwhile, there was a larger amount of hydrate formation, and final hydrate volume fraction was 83.652%. Then, the hydrate formation characteristics under different additive dosages (500 ppm, 1000 ppm, 2000 ppm, 5000 ppm) and different subcooling degrees (2.5 °C, 3.5 °C, 4.5 °C, 5.5 °C, 6.5 °C) were investigated. The new promoter at these 4 concentrations could effectively shorten the induction time. And the higher the concentration, the smaller the induction time (0.22 h at 5000 ppm). It was also found that gas consumption and hydrate production rate increased first and then decreased with increasing promoter dosage. Finally, the optimal dosage was determined to be 2000 ppm, at which the induction time was shortened to 0.52 h, and the final hydrate volume fraction was 85.74%. Under the dosage of 2000 ppm and the subcooling degree of 6.5 °C, the shortest induction time (0.29 h) and the maximum formation rate (20.950 ml h⁻¹) were obtained among all the experimental conditions in this work. Moreover, the greater the subcooling degree, the faster the hydrate nucleation, and the shorter the induction time. However, if the subcooling degree was too high, a hydrate layer formed rapidly at the gas–liquid interface in the autoclave, which would hinder hydrate formation and lead to the reduction of hydrate volume fraction to 60.153%. Therefore, a reasonable selection of the proportioning of promoters, dosage of the promoter and formation temperature could significantly promote the formation of hydrates. The findings in this work are meaningful to hydrate associated applications and can provide useful references for the selection of hydrate promoters.

The effects of a new promoter on the growth kinetics of methane hydrates were investigated using a visualized constant-pressure autoclave.

Solubilization and Interaction Studies of Bile Salts with Surfactants and Drugs: a Review

In this review, bile salt, bile salt-surfactant, and bile salt-drug interactions and their solubilization studies are mainly focused. Usefulness of bile salts in digestion, absorption, and excretion of various compounds and their rare properties in ordering the shape and size of the micelles owing to the presence of hydrophobic and hydrophilic faces are taken into consideration while compiling this review. Bile salts as potential bio-surfactants to solubilize drugs of interest are also highlighted. This review will give an insight into the selection of drugs in different applications as their properties get modified by interaction with bile salts, thus influencing their solution behavior which, in turn, modifies the phase-forming behavior, microemulsion, and clouding phenomenon, besides solubilization. Finally, their future perspectives are taken into consideration to assess their possible uses as bio-surfactants without side effects to human beings.