Zwitterionic surfactants in ion binding and catalysis

Synthesis of zwitterionic asymmetric and symmetric carboxy-imidazolium derivatives and their use in molecular interactions with bovine serum albumin

For the first time asymmetric and symmetric carboxytriazoleimidazolium derivatives with different structures were synthesized. The critical micellization concentration (CMC) value was estimated using a pyrene fluorescent probe and the solubility of Orange OT. The complexation ability of carboxytriazoleimidazolium derivatives toward bovine serum albumin (BSA) has been investigated by various physico-chemical methods: fluorescence spectroscopy, electrophoretic light scattering and circular dichroism. The effect of the oxo-bridge and the presence of a hydrophobic fragment in the structure of the molecules and its influence on their aggregation properties and interaction with BSA has also been studied. According to the fluorescence data, only in the case of the asymmetric derivatives with long alkyl fragments a shift of the BSA emission maximum is observed, indicating a change in the BSA microenvironment. The secondary structure of BSA remains virtually unchanged in the presence of carboxytriazoleimidazolium derivatives, as shown by circular dichroism. No significant changes in the structure of BSA were observed in the presence of zwitterionic compounds with an oxo-bridge at concentrations where fluorescence quenching occurs, as shown by time-resolved fluorescence measurements. Electrophoretic light scattering showed a recharging of BSA from a negative to a positive zeta potential in the presence of amphiphilic derivatives.

A fluorescent probe based on scopoletin-3-carboxylic acid: pH and micellization evaluation

Coumarins are a class of compounds known for their synthetic and structural versatility, as well as their properties of great interest, such as biological and photophysical activities, and their application in the analysis of molecular microenvironments and their characteristics, such as pH. In this work, the synthesis of 7-hydroxy-6-methoxy-2-oxo-2H-chromene-3-carboxylic acid (3-SCA) was reported, and its absorption, emission and excitation spectral properties, along with photophysical properties such as molar absorption coefficient, lifetime, and Stokes Shift (Δν) in different solvents and pHs, were evaluated for the first time. High values of fluorescence quantum yield were observed for 3-SCA in solvents of different polarities, with a lifetime of approximately 5 ns. The Stokes shift values for 3-SCA were high, with these values greater in aqueous medium. Additionally, the acid equilibrium constant values of 3-SCA were evaluated through absorption, emission, and excitation measurements, resulting in two pKa values of 3.7 for the carboxylic acid group at C-3 and 6.6 for the hydroxyl group at C-7. 3-SCA was successfully applied in determining the critical micellar concentration of the surfactants: anionic (SDS), zwitterionic (SB3-14), neutral (F-127), and cationic (CTAB). The high sensitivity of the spectral properties of 3-SCA as a function of pH, combined with the high Stokes shift values in different media, indicates that 3-SCA is an interesting probe with applications in evaluating local pH and micelle formation.

New Carboxytriazolyl Amphiphilic Derivatives of Calix[4]arenes: Aggregation and Use in CuAAC Catalysis

This work focuses on the synthesis of a new series of amphiphilic derivatives of calix[4]arenes for the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The aggregation properties of synthesized calix[4]arenes were studied using various techniques (fluorescence spectroscopy, nanoparticle tracking analysis, and dynamic light scattering). Increasing the length of the alkyl substituent led to stronger hydrophobic interactions, which increased polydispersity in solution. The zwitterionic nature of the synthesized calix[4]arenes was established using different types of dyes (Eosin Y for anionic structures and Rhodamine 6G for cationic structures). The synthesized calix[4]arenes were used as organic stabilizers for CuI. The catalytic efficiency of CuI-calix[4]arene was compared with that of the phase transfer catalyst tetrabutylammonium bromide (TBAB) and the surfactant sodium dodecyl sulfate (SDS). For all calixarenes, the selectivity in the CuAAC reaction was higher than that observed when TBAB and SDS were estimated.

Green Surfactants (Biosurfactants): A Petroleum-Free Substitute for Sustainability-Comparison, Applications, Market, and Future Prospects

Surfactants are a group of amphiphilic molecules (i.e., having both hydrophobic and hydrophilic domains) that are a vital part of nearly every contemporary industrial process such as in agriculture, medicine, personal care, food, and petroleum. In general surfactants can be derived from (i) petroleum-based sources or (ii) microbial/plant origins. Petroleum-based surfactants are obvious results from petroleum products, which lead to petroleum pollution and thus pose severe problems to the environment leading to various ecological damages. Thus, newer techniques have been suggested for deriving surfactant molecules and maintaining environmental sustainability. Biosurfactants are surfactants of microbial or plant origins and offer much added advantages such as high biodegradability, lesser toxicity, ease of raw material availability, and easy applicability. Thus, they are also termed "green surfactants". In this regard, this review focused on the advantages of biosurfactants over the synthetic surfactants produced from petroleum-based products along with their potential applications in different industries. We also provided their market aspects and future directions that can be considered with selections of biosurfactants. This would open up new avenues for surfactant research by overcoming the existing bottlenecks in this field.

Strong synergistic interactions in zwitterionic-anionic surfactant mixtures at the air-water interface and in micelles: The role of steric and electrostatic interactions

HYPOTHESIS

The milder interaction with biosystems makes the zwitterionic surfactants an important class of surfactants, and they are widely used in biological applications and in personal care formulations. An important aspect of those applications is their strong synergistic interaction with anionic surfactants. It is anticipated that the strong interaction will significantly affect the adsorption and self-assembly properties.

EXPERIMENTS

Surface tension, ST, neutron reflectivity, NR, and small angle neutron scattering, SANS, have been used here to explore the synergistic mixing in micelles and at the air-water interface for the zwitterionic surfactant, dodecyldimethylammonium propanesulfonate, C₁₂SB, and the anionic surfactants, alkyl ester sulfonate, AES, in the absence and presence of electrolyte, 0.1 M NaCl.

FINDINGS

At the air-water interface the asymmetry of composition in the strong synergistic interaction and the changes with added electrolyte and anionic surfactant structure reflect the relative contributions of the electrostatic and steric interactions to the excess free energy of mixing. In the mixed micelles the synergy is less pronounced and indicates less severe packing constraints. The micelle structure is predominantly globular to elongated, and shows a pronounced micellar growth with composition which depends strongly upon the nature of the anionic surfactant and the addition of electrolyte.

Thermodynamics of anion binding to zwitterionic sulfobetaine micelles

One of the most intriguing aspects of zwitterionic surfactant micelles is their propensity to exhibit selectivity in the binding of the anions of added salts. In this work we examine the thermodynamics of the interaction of the strongly bound perchlorate ion and the more weakly bound bromide ion with micelles of N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (SB3-14) in aqueous solution employing enthalpies derived from isothermal titration calorimetry combined with Gibbs free energies derived from literature data for the binding equilibria. In both cases, the binding is exothermic and enthalpy driven, but entropically unfavorable, with only modest changes in the Gibbs free energy as a function of the extent of anion binding. Likewise, perchlorate ion binding was found to have little or no effect on the aggregation numbers of SB3-14 micelles determined by time-resolved fluorescence quenching of pyrene by the N-hexadecylpyridinium cation. The results are interpreted within the context of the factors involved in the ion-pairing between the anions and the positive charge center of the zwitterion headgroup and the interplay between electrostatics, solvent reorganization and a net loss of translational degrees of freedom that accompany anion binding.

Geometry transformation of ionic surfactants and adsorption behavior on water/n-decane-interface: calculation by molecular dynamics simulation and DFT study

Understanding the effect of surfactant structure on their ability to modify interfacial properties is of great scientific and industrial interest. In this work, we have synthesized four amide based ionic surfactants under acidic or basic conditions, including CTHA·HCl, CTEA·HCl, CTHA-Na+ and CTEA-Na+. Experiments have proved that the anionic surfactant with polyethylene oxide groups (CTEA-Na+) had the lowest surface tension on the water/n-decane interface. Molecular dynamics simulations have been applied to investigate the structural effect on the adsorption behavior of four different surfactants. The surface tension, interface thickness, interface formation energy, density profiles, order parameters, radial distribution function on the water/n-decane interfaces were calculated and compared. During the equilibrium states, we found that the interface configuration of two cationic surfactants are almost linear while the two anionic surfactants are changed to bending shapes due to the different positions of the hydrophilic head groups. Further DFT study and wavefunction analysis of surfactants have shown that CTEA-Na+ can form stronger vdW interactions with n-decane molecules due to a more neutral electrostatic potential distribution. Meanwhile, the introduction of polyethylene oxide groups has offered more H-bonding sites and resulted in more concentrated H-bonding interactions with water molecules. The difference of weak interactions may contribute to the conformational change and finally affect the interface properties of these ionic surfactants.

Peripherally substituted soluble nickel phthalocyanines: Synthesis, characterization, aggregation behavior and antioxidant properties

Tetra-zwitterionic-substituted nickel(II) phthalocyanine derivatives were newly synthesized starting from nonionic 2(3),9(10),16(17),23(24)-tetrakis-[2-([Formula: see text]-((3-dimethylamino)propyl)carbamate)oxyethyl)phthalocyaninato nickel (II). The novel compounds have been characterized by a combination of UV-vis, FT-IR and mass spectroscopies and elemental analysis. The critical micelle concentrations of the prepared compounds were measured, and the antioxidant activities were analyzed with radical scavenging ability of 1,1-diphenyl-2-picrylhydrazyl (DPPH) and with 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS). The zwitterionic molecules showed aggregated spectra in the UV-vis region, and they might be good surfactant candidates for the detergent industry with their appropriate critical micelle concentration (CMC) properties in water. The compounds exhibited ABTS radical scavenging activity and thus they have antioxidant activity.

Dehydration Determines Hydrotropic Ion Affinity for Zwitterionic Micelles

Specific ion effects in zwitterionic micelles, especially for anions, are evident in reaction kinetics, zeta potential, and critical micelle concentration measurements. However, anion adsorption to zwitterionic micelles does not produce significant changes in shape, aggregation number, or interfacial hydration. Here we used molecular dynamics simulation of systems containing sulfobetaine zwitterionic micelles of N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DPS) and nine different salts to explore ion adsorption in terms of group dehydration. Our results, in line with those obtained for cationic micelles, showed that the adsorption degree of anions containing both hydrophobic and hydrophilic portions, i.e., hydrotropes, were correlated with the ion dehydration and were governed mainly by the hydrophobic portion dehydration upon adsorption.

The role of surfactants in wastewater treatment: Impact, removal and future techniques: A critical review

Wastewater treatment has an important responsibility to react to changing consumer and industrial produced wastes that pose environmental challenges. Surfactants are one of these emerging contaminants. They are of interest because of their increasingly ubiquitous domestic and industrial use and the difficulty their presence causes traditional treatment. In response to this developing area, this critical review considers research from a variety of technical backgrounds to provide an up to date overview of the impact of surfactants on the environment, health and their removal. This found major concerns about surfactants on the environment and on health being corroborated in the past five years. Current research into removal focuses on existing biological and chemical wastewater treatment optimisation. Despite improvements being found to traditional biological methods using chemical pre-treatments there is a clear lack of consensus regarding the ideal strategy. Drawbacks and potential solutions for a range of these technologies, including Fenton reaction and aerobic degradation, are discussed. In this field the authors recommend an improved diversity in surfactants used for the research and addressing of significant knowledge gaps. Novel methods, such as Carbon Nanotube (CNT) use are also discussed. These methods, while showing promising results, will require continual research effort to resolve present issues such as variable performance and environmental concerns. Larger scale work is also needed to validate the initial work done. Potential uses of surfactants to optimise wastewater treatment, such as Surfactant Modified Zeolites (SMZs), are also discussed. This review finds that surfactant removal from wastewater is a promising and challenging field that warrants further investigation.

Specific Ion Effects on Zwitterionic Micelles Are Independent of Interfacial Hydration Changes

Zwitterionic micelles adsorb anions and several techniques were used to determine the specificity of this interaction. Although at a lower intensity, this adsorption can be compared to those observed in cationic micelles, which showed that interfacial dehydration is a fundamental property for the geometry and size of micelles. Because there is no information on the interfacial hydration of zwitterionic micelles, we used dielectric relaxation spectroscopy (DRS) together with molecular dynamics (MD) simulations to evaluate the importance of surface dehydration promoted by the binding of anions at the micellar interface (sodium bromide, sodium methanesulfonate, sodium trifluoroacetate, and sodium triflate) in N-dodecyl- N, N-dimethyl-3-ammonio-1-propanesulfonate (DPS) micelles. Our results, showing good agreement between DRS and MD simulations, strongly suggest that specific ion effects on zwitterionic micelles are unrelated to global changes in the interfacial hydration and depend on specific interactions of the headgroups with selected anions.