Pyrene Fluorescence Research Articles

Cu(II)‐Amino Acid Ionic Liquid Surfactants: Metallovesicles as Nano‐Catalytic Reactors for Cross Dehydrogenative Coupling Reaction in Water

AbstractUtilization of the water as a reaction medium is very challenging due to the organic molecules insolubility in the aqueous medium. Still, self‐assembled structures like micelles and vesicles can act as nanoreactors to perform the organic reactions in water. In our efforts to achieve a chemical reaction in water, we have synthesized sustainable Cu (II) based amino acid (phenylalanine or valine) ionic liquid surfactants [AAC12]2[CuCl4], constructed their metallovesicles, and utilized these as nano‐catalytic reactors for C−C bond formation in the propargyl amines under the oxidative conditions. Aggregation of [AAC12]2[CuCl4] in an aqueous medium was studied using surface tension, pyrene fluorescence, and specific conductivity measurements. TEM and DLS analysis confirmed the formation of metallovesicles. [AAC12]2[CuCl4] metallovesicles acted as multitasking nanoreactors to provide a bio‐based template, water as a solvent, no additional catalyst to perform the reaction, and high yield (up to 94 % in low Cu(II) 0.012 mol%). Furthermore, The retention in the chirality of amino acid is observed in [AAC12]2[CuCl4], which can be a promising approach for one‐pot synthesis of chiral moieties in a greener way for future pharmaceutical manufacturing and other Cu(II) catalyzed reactions.

The Amphoteric Surfactant N,N-Dimethyldodecylamine N-Oxide Unfolds β-Lactoglobulin above the Critical Micelle Concentration.

Understanding the interactions between surfactants and proteins is important for the formulation of consumer products as surfactant binding can alter protein activity and stability. Additionally, the structure of the protein-surfactant complex can influence surface activity, which is important for emulsion and foam development. N,N-Dimethyldodecylamine N-oxide (DDAO) is an amphoteric surfactant that is nonionic at high pH. It is often used as a foam booster in detergent formulations and for the extraction of membrane proteins. In this study, a variety of biophysical characterization methods was used to investigate the impact of DDAO at pH 8 on the structure of the globular protein β-lactoglobulin (βLG). Pyrene fluorescence and surface tension studies show that βLG had minimal impact on the critical micelle concentration (CMC) of DDAO, while fluorescence and circular dichroism spectroscopy found unfolding of βLG at concentrations of DDAO greater than the CMC. Small-angle X-ray scattering results confirm changes in the structure of βLG at DDAO concentrations above the CMC. Taken together, DDAO behaves like nonionic and zwitterionic surfactants below its CMC with limited interaction with βLG, while it induces protein unfolding at concentrations higher than the CMC, resulting in a protein-surfactant complex structure that resembles a protein-decorated micelle.

Light-controlled shape-changing azomacrocycles exhibiting reversible modulation of pyrene fluorescence emission.

We report the design, synthesis, and study of light-induced shape-changing azomacrocycles. These systems have been incorporated with azobenzene photoswitches using alkoxy tethers and triazole units to afford flexibility and binding. We envision that such azomacrocycles are capable of reversibly binding with the guest molecule. Remarkably, we have demonstrated fully light-controlled fluorescence quenching and enhancement in the monomeric emission of pyrene (guest). Such modulations have been achieved by the photoisomerization of the azomacrocycle and, in turn, host-guest interactions. Also, the azomacrocycles tend to aggregate and can also be controlled by light or heat. We uncovered such phenomena using spectroscopic, microscopic, and isothermal titration calorimetry (ITC) studies and computations.

Pyrene-Functionalized Fluorescent Nanojars: Synthesis, Mass Spectrometric, and Photophysical Studies.

Nanojars are a class of supramolecular coordination complexes based on pyrazolate, Cu2+, and OH– ions that self-assemble around highly hydrophilic anions and serve as efficient anion binding and extraction agents. In this work, the synthesis, characterization, and photophysical properties of pyrene-functionalized fluorescent nanojars are presented. Three pyrene derivatives, 4-(pyren-1-yl)pyrazole (HL1), 4-(5-(pyren-1-yl)pent-4-yn-1-yl)pyrazole (HL2), and 4-(3-(pyrazol-4-yl)propyl)-1-(pyren-1-yl)-1,2,3-triazole (HL3), and the corresponding nanojars were synthesized and characterized using nuclear magnetic resonance spectroscopy and mass spectrometry. Electronic absorption, steady-state, and time-resolved fluorescence measurements were carried out to understand the interaction between the pyrene fluorophore and copper nanojars. Optical absorption measurements have shown minor ground state interaction between the fluorophore and nanojars. The fluorescence of pyrene is significantly quenched when attached to nanojars, suggesting strong contribution from the paramagnetic Cu2+ ions. Significant static quenching is observed in the case of L1, when pyrene is directly bound to the nanojar, whereas in the case of L2 and L3, when pyrene is attached to the nanojars using flexible tethers, both static and dynamic quenching are observed.

Synthesis and Characterization of a Pyrene-Labeled Gemini Surfactant Sensitive to the Polarity of Its Environment.

The cationic gemini surfactant PyO-3-12 was designed to include two dimethyl ammonium groups, one dodecyl tail, and 1-pyrenemethyl hexyl ether tail into the structure of the surfactant. The pyrenyl label ensured that the fluorescence of pyrene could be employed to probe the behavior of PyO-3-12 at the molecular level. The introduction of the oxygen atom in the β-position to pyrene was found to be critical for restoring the sensitivity of the pyrenyl label to the polarity of its environment. The properties of PyO-3-12 were characterized in water by surface tension and a fluorescence methodology that involved the global model-free analysis (MFA) of the pyrene monomer and excimer fluorescence decays to provide quantitative information about the state (unassociated-vs-aggregated) of PyO-3-12. The MFA was combined with a fluorescence quenching study with 2,6-dinitrotoluene to determine the size of the PyO-3-12 micelles. PyO-3-12 was found to behave like a typical gemini surfactant, exhibiting a critical micelle concentration (CMC) of 0.38 (±0.05) mM and an aggregation number (Nagg) equal to 23 (±2). Besides allowing PyO-3-12 to probe the polarity of its environment, the oxygen atom in the β-position next to pyrene brought some pyrenyl labels closer to the interface between the micellar interior and the aqueous phase, in a process that increased the effective volume of the hydrophobic part of PyO-3-12. This led to an increase in the packing parameter of PyO-3-12 and, consequently, an increase in Nagg compared to the Nagg value of 14 (±0.2) obtained for Py-3-12, a gemini surfactant, whose chemical structure was similar to that of PyO-3-12 but without the oxygen in the β-position to pyrene. The methodology described in this study to prepare and characterize pyrene-labeled surfactants is general and can be applied to study any pyrene-labeled surfactant and its interactions with oppositely charged macromolecules.

Role of chain length and electrolyte on the micellization of anionic fluorinated surfactants in water

The micellization of ionic surfactants in aqueous media reflects a balance between the hydrophobic attraction of surfactant tails and the electrostatic repulsion of surfactant headgroups. We investigate here the effect on surfactant micellization of the hydrophobic chain length and electrolyte composition, by focusing on the fluorinated surfactants sodium perfluorohexanoate (NaPFHx) and sodium perfluorooctanoate (NaPFO) in aqueous solution without/with NaCl, and analyzing experimental data from surface tension, pyrene fluorescence, small-angle neutron scattering (SANS), and viscosity techniques. The CMC of NaPFHx in water was 200 mM, much higher than that of NaPFO, 30 mM, due to the additional two -CF2- groups of the latter. Upon addition of 0.25 M NaCl to the aqueous solution, the CMC of NaPFHx and NaPFO decreased by about 50% and 80%, respectively. The NaPFHx and NaPFO micelles are both ellipsoid in shape. NaPFHx forms smaller micelles compared to NaPFO: the association number for NaPFHx in D2O was 15 compared to 25 for NaPFO. Upon NaCl addition, the micelle shape became more elongated. This is the first report on the NaPFHx micelle structure. The information presented here supports the re-formulation and replacement of long-chain fluorinated surfactants with relatively safer long-chain surfactants.

Plant Sterol Clustering Correlates with Membrane Microdomains as Revealed by Optical and Computational Microscopy.

Local inhomogeneities in lipid composition play a crucial role in the regulation of signal transduction and membrane traffic. This is particularly the case for plant plasma membrane, which is enriched in specific lipids, such as free and conjugated forms of phytosterols and typical phytosphingolipids. Nevertheless, most evidence for microdomains in cells remains indirect, and the nature of membrane inhomogeneities has been difficult to characterize. We used a new push–pull pyrene probe and fluorescence lifetime imaging microscopy (FLIM) combined with all-atom multiscale molecular dynamics simulations to provide a detailed view on the interaction between phospholipids and phytosterol and the effect of modulating cellular phytosterols on membrane-associated microdomains and phase separation formation. Our understanding of the organization principles of biomembranes is limited mainly by the challenge to measure distributions and interactions of lipids and proteins within the complex environment of living cells. Comparing phospholipids/phytosterol compositions typical of liquid-disordered (Ld) and liquid-ordered (Lo) domains, we furthermore show that phytosterols play crucial roles in membrane homeostasis. The simulation work highlights how state-of-the-art modeling alleviates some of the prior concerns and how unrefuted discoveries can be made through a computational microscope. Altogether, our results support the role of phytosterols in the lateral structuring of the PM of plant cells and suggest that they are key compounds for the formation of plant PM microdomains and the lipid-ordered phase.

Adsorption and Aggregation Behavior of Mixtures of Quaternary-Ammonium-Salt-Type Amphiphilic Compounds with Fluorinated Counterions and Surfactants.

The surface adsorption and aggregation behavior of a mixture of quaternary-ammonium-salt-type amphiphilic monomeric compounds (C4 FSA, C8 FSA, and C4 NTf2) or gemini compounds (C10-2-C4 FSA) and various surfactants (nonionic hexaoxyethylene dodecyl ether (C12EO6), anionic sodium dodecyl sulfate (SDS), cationic dodecyltrimethylammonium bromide (C12TAB), and zwitterionic N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (C12Sb)) was investigated. Both types of compounds contained alkyl chains of nonidentical lengths that used bis(fluorosulfonyl)imide (FSA-) or bis(trifluoromethanesulfonyl)imide (NTf2-) as counterions. The mixtures were analyzed for surface tension, viscosity, electrical conductivity, and pyrene fluorescence, in addition to evaluation by cryogenic transmission electron microscopy, small-angle X-ray scattering, and dynamic light scattering. Our results showed that the surface tension depended on the surfactant structure. For the mixture of C8 FSA and SDS, as the SDS concentration increased, the surface tension first decreased and became constant at the critical micelle concentration (CMC). In this concentration range, C8 FSA and SDS were approximately equimolar (2.5 mmol dm-3), the mixture adsorbed efficiently at the air-water interface, and vesicles and linear-type micelles were formed in the solution owing to the decreased electrostatic repulsion between the hydrophilic groups. As the SDS concentration further increased, the surface tension increased and reached another constant value. The C8 FSA at the interface was replaced by SDS and the aggregates transformed into spherical micelles. The surface tension plot of the mixture of the amphiphilic compounds and C12Sb showed a minimum at the CMC. The lowest CMC and surface tension were observed for C10-2-C4 FSA, indicating that the gemini compounds offer excellent adsorption and orientation at the air-water interface. It was revealed that the quaternary-ammonium-salt-type amphiphilic compounds in this study acted as ionic liquids on their own and as surfactants in aqueous solution. Further, they could improve the surface activity of conventional ionic surfactants.

Pyrene interaction with selected heavy metal ions in aqueous sodium dodecyl sulphate (SDS)

Pyrene interaction with Fe3+, Cu2+, Cr3+, Ni2+, Pb2+ was studied in 0.02 mol L-1 SDS. All the studied heavy metal ions quenched the fluorescence intensity of pyrene though variations were found in the level of quenching. Stern-Volmer equation fitted the pyrene quenching by heavy metal ions. Stern-Volmer constants (KSV) were obtained with the fitting of the quenching data with the Stern-Volmer equation. KSV shows the level of quenching and the sensitivity of the method. Greater the KSV larger will be the detection and quantification limit and vice versa. KSV, detection limit (DL) and quantification limit (QL) varied from 9.26 × 103 mol L-1 to 4.13 × 103 mol L-1, 1.61 × 10-6 mol L-1 to 5.85 × 10-6 mol L-1 and 5.38 × 10-6 mol L-1 to 19.49 × 10-6 mol L-1 respectively. The overall sensitivity, DL and QL were observed in the order Fe3+ > Cu2+ > Cr3+ > Ni2+ > Pb2+. Pyrene fluorescence quenching by the studied heavy metal ions is a fruitful method for their determination in environmental samples.

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.

Determination of the Aggregation Number of Pyrene-Labeled Gemini Surfactant Micelles by Pyrene Fluorescence Quenching Measurements.

A cationic gemini surfactant referred to as Py-3-12 and composed of two alkylated diammonium bromide head groups, a propyl spacer, and dodecyl and 1-pyrenehexyl hydrophobic tails was synthesized. Its critical micellar concentration (CMC) was determined to equal 0.15 (±0.02) mM by surface tension and time-resolved fluorescence measurements. The state of the pyrene molecules, whether they were incorporated inside the Py-3-12 micelles or unassociated in the aqueous solution, was determined by applying the global model-free analysis (MFA) to the fluorescence decays acquired with Py-3-12 aqueous solutions. The unassociated Py-3-12 surfactants emitted as pyrene monomers and showed a long fluorescence lifetime. The excited pyrenyl groups located inside Py-3-12 micelles formed an excimer by a rapid encounter with a ground-state pyrene with an average rate constant equal to 0.69 (±0.06) ns-1. After having the photophysical properties of Py-3-12 in aqueous solution characterized, the number (Nagg) of surfactants per micelle was determined by conducting quenching experiments with dinitrotoluene (DNT). Although DNT is fairly hydrophobic, it was found to partition itself between the Py-3-12 micelles and the aqueous phase. Fluorescence quenching experiments performed on the pyrene monomer and excimer generated by the Py-3-12 aqueous solutions yielded the concentration ([Q]b) of DNT bound to the Py-3-12 micelles and the average number ⟨n⟩d of DNT quenching an excimer by diffusive encounters. A combination of steady-state and time-resolved fluorescence quenching experiments on the excimer yielded the number (⟨n⟩s) of DNT molecules that were bound to the micelles and quenched the excimer in a static manner. A plot of the sum ⟨n⟩d + ⟨n⟩s as a function of [Q]b yielded an Nagg value of 14.0 (±0.2) Py-3-12 units per micelle. This study represents the first example in the literature where Nagg is determined for a micelle, where each surfactant molecule is labeled with pyrene.

Bis-Pyrene Photo-Switch Open- and Closed-Form Differently Bind to ds-DNA, ds-RNA and Serum Albumin and Reveal Light-Induced Bioactivity.

Newly designed and synthesized diarylethene (DAE) derivatives with aliphatic amine sidearms and one with two pyrenes, revealed excellent photo-switching property of central DAE core in MeOH and water. The only exception was bis-pyrene analogue, its DAE core very readily photochemically closed, but reversible opening completely hampered by aromatic stacking interaction of pyrene(s) with cyclic DAE. In this process, pyrene fluorescence showed to be a reliable monitoring method, an open form characterized by strong emission at 480 nm (typical for pyrene-aggregate), while closed form emitted weakly at 400 nm (typical for pyrene-DAE quenching). Only open DAE-bis-pyrene form interacted measurably with ds-DNA/RNA by flexible insertion in polynucleotide grooves, while self-stacked closed form did not bind to DNA/RNA. For the same steric reasons, flexible open DAE-bis-pyrene form was bound to at least three different binding sites at bovine serum albumin (BSA), while rigid, self-stacked closed form interacted dominantly with only one BSA site. Preliminary screening of antiproliferative activity against human lung carcinoma cell line A549 revealed that all DAE-derivatives are non-toxic. However, bis-pyrene analogue efficiently entered cells and located in the cytoplasm, whereby irradiation by light (315–400 nm) resulted in a strong, photo-induced cytotoxic effect, typical for pyrene-related singlet oxygen species production.

Catalytic Performance of a Recombinant Organophosphate-Hydrolyzing Phosphotriesterase from Brevundimonas diminuta in the Presence of Surfactants

Phosphotriestease (PTE), also known as parathion hydrolase, has the ability to hydrolyze the triester linkage of organophosphate (OP) pesticides and chemical warfare nerve agents, making it highly suitable for environment remediation. Here, we studied the effects of various surfactants and commercial detergents on the esterase activity of a recombinant PTE (His6-tagged BdPTE) from Brevundimonas diminuta. Enzymatic assays indicated that His6-tagged BdPTE was severely inactivated by SDS even at lower concentrations and, conversely, the other three surfactants (Triton X-100, Tween 20, and Tween 80) had a stimulatory effect on the activity, especially at a pre-incubating temperature of 40 °C. The enzyme exhibited a good compatibility with several commercial detergents, such as Dr. Formula® and Sugar Bubble®. The evolution results of pyrene fluorescence spectroscopy showed that the enzyme molecules participated in the formation of SDS micelles but did not alter the property of SDS micelles above the critical micelle concentration (CMC). Structural analyses revealed a significant change in the enzyme’s secondary structure in the presence of SDS. Through the use of the intentionally fenthion-contaminated Chinese cabbage leaves as the model experiment, enzyme–Joy® washer solution could remove the pesticide from the contaminated sample more efficiently than detergent alone. Overall, our data promote a better understanding of the links between the esterase activity of His6-tagged BdPTE and surfactants, and they offer valuable information about its potential applications in liquid detergent formulations.

The interaction mechanism between liposome and whey protein: Effect of liposomal vesicles concentration

The interaction mechanism between liposomes (Lips) and whey protein isolates (WPI) with different mass ratios was explored in this paper. After binding with different concentration of Lips, the changes in hydrophilic and hydrophobic regions of WPI were investigated with fluorescein isothiocyanate (FITC) and pyrene fluorescence probes. The spatial structure changes of WPI were further characterized by differential scanning calorimetry, Fourier transform infrared spectroscopy, and circular dichroism. The results indicated that the structure of WPI was changed due to binding with Lips in hydrophilic and hydrophobic groups. The binding process might result in the migration, recombination, and alignment of WPI and Lip groups. Moreover, the oil-water interfacial tension with WPI decreased from 9.20 mN/m to 3.29 mN/m upon increasing the Lip-to-WPI ratio. This work suggests that the physiochemical properties of Lip-WPI complexes could be manipulated by adjusting the Lip-to-WPI ratio. This study shed some light on the mechanism explanation of the WPI structural changes due to the interaction with Lips during food processing.

Photoinduced Electron Transfer in a Self-Assembled Bis(β-cyclodextrin)-Linked Pyrene/Bis(adamantane)-Linked Methyl Viologen Donor-Acceptor System in Aqueous Solution.

Pyrene linked to two β-CD (CD = cyclodextrin; PY = pyrene) molecules (CD-PY-CD) and methylviologen (MV2+) linked to two adamantane (AD) groups (AD-MV2+-AD) self-assembled in water to give toroidal nanostructures. Photoprocesses taking place in the femtosecond and nanosecond time ranges within the assembly are reported. Fluorescence of the pyrene chromophore was quenched in the toroid, suggesting very efficient electron transfer. Fast quenching of the pyrene fluorescence with a time constant of 6.85 ns was attributed to photoinduced electron transfer from pyrene to methyl viologen within the toroid assembly. Electron transfer leads to the formation of radical ion products, PY•+ and MV•+, which were identified in the nanosecond transient absorption spectra. Because of the close packing of chromophores, the radical ions undergo fast reactions with chromophores or similar ions in adjacent stacks to give dimeric products. Since the dimeric species are not very stable, the reactions are reversed at longer time scales to generate the radical ions, which then undergo back electron transfer and regenerate the starting materials.

Fluorescence sensing of microplastics on surfaces

Microplastics, nanoplastics and related products have been recently found in marine ecosystems worldwide, calling for new analytical methods for rapid detection and risk assessment. Fluorescence is a sensitive technique that when used with polarity probes can potentially detect low-polarity plastic particles in environments. Here, we evaluated the fluorescence technique to sense polystyrene microparticles directly on salt, silica and sand surfaces, using Nile Red and pyrene as polarity probes. Results show that all probes displayed fluorescence on silica and sand, whereas strong fluorescence quenching was observed on NaCl. Polystyrene particles increase the fluorescence intensity due to probe migration into their nonpolar microenvironment. In the presence of polystyrene, the spectra of Nile Red are shifted to shorter wavelengths, while the ratio of vibronic bands I1/I3 of fluorescence of pyrene decreases to about 1. Pyrene showed similar sensitivity toward surface-modified carboxyl polystyrene particles. On NaCl, the emission of pyrene increases linearly with polystyrene content for concentrations from 0.5 to 20 µg/g. The detection limit of polystyrene microparticles on natural sea salt using pyrene as probe is about 0.2 µg/g, while on sand, the sensitivity is about one order of magnitude lower. Overall, although being of relatively low selectivity, the fluorescence technique can be used to determine a maximum content of plastic particles of few micrometers size with little sample preparation. Fluorescence, when used in conjunction with pyrene probe, allows for detection and quantification of microplastic particles in the sub-ppm range.

A Fluorescence Study on Surface Properties of Cationic Gemini Surfactant with Some Special Alcohols

Alcohols are very important additives and played a measure role as co-surfactants in various industrial and research applications. While, Gemini surfactants are mainly used as effective emulsifiers, antifoaming agents, bactericidal agents, coating agents and corrosion inhibitors etc. Therefore, it is important to study about the variations in alkanol concentrations which affects the aggregation number and other related parameters. Surface properties of gemini surfactant butanediyl-1,4-bis(dimethyldodecylammonium bromide) (12-4-12) has been studied by using fluorescence method. This method has been used to calculate the aggregation number (Nagg) and the other related parameters like dielectric constant (D), Stern Volmer binding constant (KSV) of mixed system. This method is also very important for the calculation of the micropolarity of the mixed system (gemini/alcohol). The micropolarity has been obtained with the help of the ratio of intensity of peaks (I1/I3) of the pyrene fluorescence emission spectrum. Cetylpridinium chloride and pyrene were used as quencher and probe, respectively.
 Keywords: Gemini surfactant, special alcohols, aggregation number, micropolarity

Molecular binding interaction of pyridinium based gemini surfactants with bovine serum albumin: Insights from physicochemical, multispectroscopic, and computational analysis

To study the interaction of the series of pyridinium based gemini surfactants (GS) (referred to as m-Py-m, m = 14, 16); 4,4′-(propane-1,3-diyl)bis(1-(2-(tetradecyloxy)-2-oxoethyl) dipyridinium chloride (14-Py-14), and 4,4′-(propane-1,3-diyl) bis(1-(2-(hexadecyloxy)-2-oxoethyl)dipyridinium chloride (16-Py-16) with bovine serum albumin (BSA), various physicochemical and spectroscopic tools such as tensiometry, steady-state fluorescence, synchronous fluorescence, pyrene fluorescence, UV–visible, far-UV circular dichroism (CD) were utilized at physiological pH (7.4) and 298 K in combination with computational molecular modeling analysis. The tensiometric results show significant modifications in interfacial and thermodynamic parameters for m-Py-m GS upon BSA combination, deciphering the gemini surfactant-BSA interaction. Steady-state fluorescence analysis evaluates the structural alterations of BSA with the addition of m-Py-m GS. The plots of Stern-Volmer, modified Stern-Volmer, and thermodynamic parameters were used to determine the binding type of m-Py-m GS to BSA. The synchronous fluorescence spectra state a mild effect of gemini surfactants on the emission intensity of tyrosine (Tyr) residues, on the other hand, tryptophan (Trp) residues showed a significant effect. Post addition of GS, the plot of pyrene fluorescence reveals the mild micropolarity fluctuations via the probe (pyrene) molecules encapsulated in BSA. UV–visible experiments support the complex formation between the BSA and m-Py-m GS. Far-UV CD measurements revealed the modifications in the secondary structure of protein produced by m-Py-m GS. Furthermore, we also used the computational molecular modeling for attaining deep insight into BSA and m-Py-m GS binding and the results are supported with our experimental results.

Morphology of bile salts micelles and mixed micelles with lipolysis products, from scattering techniques and atomistic simulations

HypothesesBile salts (BS) are biosurfactants released into the small intestine, which play key and contrasting roles in lipid digestion: they adsorb at interfaces and promote the adsorption of digestive enzymes onto fat droplets, while they also remove lipolysis products from that interface, solubilising them into mixed micelles. Small architectural variations on their chemical structure, specifically their bile acid moiety, are hypothesised to underlie these conflicting functionalities, which should be reflected in different aggregation and solubilisation behaviour. ExperimentsThe micellisation of two BS, sodium taurocholate (NaTC) and sodium taurodeoxycholate (NaTDC), which differ by one hydroxyl group on the bile acid moiety, was assessed by pyrene fluorescence spectroscopy, and the morphology of aggregates formed in the absence and presence of fatty acids (FA) and monoacylglycerols (MAG) – typical lipolysis products – was resolved by small-angle X-ray/neutron scattering (SAXS, SANS) and molecular dynamics simulations. The solubilisation by BS of triacylglycerol-incorporating liposomes – mimicking ingested lipids – was studied by neutron reflectometry and SANS. FindingsOur results demonstrate that BS micelles exhibit an ellipsoidal shape. NaTDC displays a lower critical micellar concentration and forms larger and more spherical aggregates than NaTC. Similar observations were made for BS micelles mixed with FA and MAG. Structural studies with liposomes show that the addition of BS induces their solubilisation into mixed micelles, with NaTDC displaying a higher solubilising capacity.

Studies on the self-aggregation, interfacial and thermodynamic properties of a surface active imidazolium-based ionic liquid in aqueous solution: Effects of salt and temperature

The influence of four sodium salts (NaCl, NaBr, Na2SO4, and Na3PO4) on the self-aggregation, interfacial, and thermodynamic properties of a surface active ionic liquid (1-hexadecyl-3-methylimidazolium chloride, C16MImCl) has been explored in aqueous solutions by conductometry, tensiometry, spectrofluorimetry, isothermal titration calorimetry and dynamic light scattering (DLS). Analyses of the critical micellar concentration (cmc) values indicate that the anions of the added salts promote the self-aggregation of C16MImCl in the order: Cl− < Br− < PO43−< SO42−. Dehydration of imidazolium head groups, in general, governs the process of micellization of aqueous C16MImCl in presence of the investigated salts within the investigated temperature range (298.15–318.15 K), while the melting of iceberg takes the leading role below 303.15 K for the C16MImCl-Na3PO4 system. The results indicate that addition of salt leads to a greater spontaneity of micellization, and that exothermicity prevails in these systems. Differential effect of the salts on the interfacial properties of C16MeImCl has been interpreted on the basis of the coupled influence of the electrostatic charge neutralization of surfactants at the interface, and the van der Wa-als repulsion of surfactant tails and electrostatic repulsion of surfactant head groups. C16MeImCl has been predicted to form spherical micelles in presence of varying amounts of NaCl, Na2SO4 and Na3PO4, while there occurs probably a transition in the micellar geometry from spherical to non-spherical shape when added NaBr concentration exceeds 0.01 mol.kg−1. Fluorescence studies demonstrate that a combined quenching mechanism is operative for the quenching of pyrene fluorescence in the investigated C16MImCl-salt systems. Micellar aggregation numbers obtained from Steady State Fluorescence Quenching method have always been found be somewhat smaller than those estimated from Time Resolved Fluorescence Quenching method. The order of instability of the C16MImCl-micelles ascertained from Zeta potential measurements conform to what has been inferred from the cmc values. The hydrodynamic diameters of C16MImCl-micelles, obtained from DLS studies, have been found to increase with increasing salinity of the solutions.