Aqueous Micelles Research Articles

High intensity focused ultrasound responsive release behavior of metallo-supramolecular block PPG-PEG copolymer micelles.

An amphiphilic metallo-supramolecular poly(propylene glycol)-block-poly(ethylene glycol) block copolymer containing a bis(2,2':6',2″-terpyridine) ruthenium (II) complex as a supramolecular connection between the two constituting blocks was used to prepare stable aqueous micelles which displayed a high intensity focused ultrasound (HIFU) triggered release behavior. By adjusting the HIFU time and intensity, the novel modality of HIFU triggered release allows for fine-tuning of the release kinetics of the encapsulants from the micelles in a remote and controlled way. Nuclear magnetic resonance spectroscopy, ultraviolet spectroscopy, and matrix-assisted laser desorption/ionization-time of flight mass spectrometry confirmed that the degradation of the micelles was due to the cleavage of the ether bond connected to the pyridine ring. This well controlled HIFU-copolymer micelle drug delivery system has considerable potential in targeted therapy.

Sterically controlled and pH-dependent self-aggregation of synthetic zinc 3-(alkylamino)methylated chlorophyll-a derivatives in aqueous micellar solution

Zinc methyl 3-(methyl/ethylamino)methyl-pyropheophorbides-[Formula: see text] were prepared as models of photosynthetically active bacteriochlorophyll-[Formula: see text] possessing the 3[Formula: see text]-hydroxy group. The synthetic methylamino analog predominantly dimerized via two Zn[Formula: see text]N coordination bonds in aqueous Triton X-100 micelles, while the more sterically crowding and less coordinating ethylamino derivative self-aggregated to form large oligomers through single coordination and hydrogen bonds, Zn[Formula: see text]N–H[Formula: see text]O=C-13, similarly as in the natural self-aggregates of bacteriochlorophyll-[Formula: see text]. The artificial self-aggregates were dependent on the aqueous pH, but the dimer was less pH-sensitive and also more tolerant to the additional Triton X-100.

Scalable α-Arylation of Nitriles in Aqueous Micelles using Ultrasmall Pd Nanoparticles: Surprising Formation of Carbanions in Water

A scalable synthetic method is described for both the preparation of ultrasmall palladium nanoparticles and their subsequent use in catalyzing an α-arylation reaction of nitriles in aqueous micelle...

Stereoselective self-aggregation of zinc bacteriochlorophyll-d analogs possessing an O-substituted oxime moiety at the 13-position

Zinc methyl 3-hydroxymethyl-131-deoxo-pyropheophorbides-a possessing a variety of O-substituted oxime moieties at the 13-position were prepared as models of bacteriochlorophyll-d, which could be found in the main light-harvesting system of green photosynthetic bacteria by chemical modification of naturally occurring chlorophyll-a. The E/Z-stereoisomers of the synthetic O-substituted oximes were successfully separated by silica gel column chromatography. Most of these zinc bacteriochlorophyll-d analogs formed J-type self-aggregates in an aqueous Triton X-100 micelle solution, affording large oligomers whose Soret and Qy bands were red-shifted, compared with those of their monomers in tetrahydrofuran. The self-aggregation was dependent on their E/Z-stereochemistry. Thus, the E-stereoisomers showed the red-shifted electronic absorption bands, which were similar to those of the original bacteriochlorophyll-d bearing the 131-oxo group. On the other hand, the Z-stereoisomers exhibited the less red-shifted absorption bands than did the E-stereoisomers, to give different self-aggregates. In addition, the self-aggregation could be controlled by the size of the O-substituents in the oxime moiety.

Integrated Optofluidic Chip for Oscillatory Microrheology

We propose and demonstrate an on-chip optofluidic device allowing active oscillatory microrheological measurements with sub-μL sample volume, low cost and high flexibility. Thanks to the use of this optofluidic microrheometer it is possible to measure the viscoelastic properties of complex fluids in the frequency range 0.01–10 Hz at different temperatures. The system is based on the optical forces exerted on a microbead by two counterpropagating infrared laser beams. The core elements of the optical part, integrated waveguides and an optical modulator, are fabricated by fs-laser writing on a glass substrate. The system performance is validated by measuring viscoelastic solutions of aqueous worm-like micelles composed by Cetylpyridinium Chloride (CPyCl) and Sodium Salicylate (NaSal).

The ionic liquid-surfactant bmim-AOT and nontoxic lipophilic solvents as components of reverse micelles alternative to the traditional systems. A study by 1H NMR spectroscopy

Abstract Aqueous reverse micelles (RMs) of the ionic liquid-surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT) in the biocompatible nonpolar solvents isopropyl myristate (IPM) and methyl laurate (ML) were formulated and characterized by DLS and 1H NMR techniques; the goal is to develop less toxic and more environmentally friendly reverse micellar systems than traditional RMs formed by organic solvents such as n-heptane (n-Hp). The interfacial composition of these new micellar systems was compared with water/bmim-AOT/n-Hp RMs, analyzing the effect of changing the conventional external nonpolar solvent n-Hp for the biocompatible solvents IPM and ML. Also, they were compared with the RMs of the traditional surfactant sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) in IPM and ML to analyze the role of the bmim+ counterion compared to Na+ in the interfacial properties of the generated RMs. The results indicate that both ML and IPM can be used as nonpolar solvents to prepare RMs using bmim-AOT as surfactant. In comparison to n-Hp, IPM and ML penetrate more to the micellar interface, therefore, the ester group of the biocompatible solvent located at the micellar interface interacts with the bmim+ cation. As a consequence of this fact, the bmim+-AOT− interaction decreases when IPM or ML are used as the external solvent instead of n-Hp. In the Na-AOT/IPM and Na-AOT/ML systems, the dissimilar penetration of the external solvent makes the interfacial properties of both RMs clearly different. Interestingly, in the bmim-AOT/biocompatible solvent systems, the micellar interface properties are strongly governed by the bmim+ counterion, finding similar behavior if the external biocompatible solvent is IPM or ML.

Novel Cationic Prodrug of Ubiquinol-10 Enhances Intestinal Absorption via Efficient Formation of Nanosized Mixed-Micelles with Bile Acid Anions.

The aim of this study was to develop a prodrug of ubiquinol-10 (UqH-10), the active form of ubiquinone-10 (Uq-10), for oral delivery. Bioavailability of UqH-10 is hampered by its high susceptibility to oxidation and water-insolubility. We prepared three novel N,N-dimethylglycine ester derivatives of UqH-10, including a 1-monoester (UqH-1-DMG), 4-monoester (UqH-4-DMG), and 1,4-bis-ester (UqH-DMG), and assessed their physicochemical properties in vitro and in vivo. UqH-DMG spontaneously formed an aqueous micelle solution comprising 20 nm particles at 36.5 °C. Cationic UqH-DMG formed nano-sized (5 nm) mixed-micelles with taurocholic acid. Reconversion of the derivatives to UqH-10 was accelerated in human liver microsomes. The oral bioavailability of UqH-10 after administration of UqH-derivatives or Uq-10 was determined in fasted and postprandial rats secreting normal and high levels of bile, respectively. In fasted rats, plasma UqH-10 after UqH-derivatives administration reached Cmax at 2–3 h and after Uq-10 administration, it remained low. The AUC0-24h of UqH-10 after UqH-derivatives administration was 2–3-fold higher than that after Uq-10 administration. In postprandial rats, the Tmax of UqH-10 after UqH-derivatives administration was an hour earlier than after Uq-10 administration. In conclusion, cationic UqH-derivatives are convenient prodrugs that enhance UqH-10 bioavailability by forming nanosized mixed-micelles with intestinal bile acids.

Computer simulation study of fluorocarbon phosphate surfactant based aqueous reverse micelle in supercritical CO2: roles of surfactant functional groups, ionic strength, and phase changes in CO2.

Structural and dynamic properties of an aqueous micelle organized from fluorocarbon phosphate surfactant molecules in supercritical carbon dioxide (CO2) are investigated via molecular dynamics computer simulations. The roles of the functional groups and ionic strength of the surfactants on the formation of reverse micelles in supercritical CO2, and related water dynamics characterized as translational and reorientational dynamics, are systematically demonstrated by employing three different phosphate-based surfactants paired with sodium cations. The strong electrostatic interactions between the phosphate head groups and sodium cations result in formation of an aqueous core inside the surfactant aggregates, where water molecules are bonded together with loss of the tetrahedral hydrogen bonded network found in bulk water. It is found that all the three surfactants with CO2-philic fluorocarbon double tails build up well-stabilized reverse micelles in supercritical CO2, avoiding direct contacts between CO2 and water molecules. Despite this, the surfactant with a carboxylic ester linkage between the phosphate head and fluorocarbon tail group tends to coordinate water molecules toward sustaining the inter-water hydrogen bonds, indicating better efficiency at covering the aqueous core with hydrophobic groups compared to one without a carboxylic ester group. As for water molecules confined in the reverse micelle, their translational and reorientational motions, and fluctuating dynamics of the inter-water hydrogen bonds, significantly slow down compared to bulk water at ambient temperature. The water dynamics become more restricted with an increase in ionic strength of the anionic surfactant; this is attributed to divalent surfactant heads and sodium cations being more tightly bound together with bonding to water compared to monovalent ones. Lastly, the structural and dynamic changes of the reverse micelle caused by a phase change in CO2 are monitored with gradually decreasing temperature and pressure from the supercritical to gaseous state for CO2. The average reverse micelle structure equilibrated in supercritical CO2 is found to remain stable over a time period of 0.2 ms through a depressurization process to gaseous CO2. We note that the diverse pathways of surfactant self-aggregation in gaseous CO2 could be controlled by the preceding solvation procedure in the supercritical regime which governs the final aggregated structures in gaseous CO2.

Electrochemical Methodology as an Useful Tool for the Interfacial Characterization of Aqueous Reverse Micelles

AbstractIn this work, for the first time, the electrochemical behavior of hydroquinone (H2Q) by linear voltammetry in aqueous reverse micelles (RMs) of sodium 1,4‐bis(2‐ethylhexyl) sulfosuccinate (AOT)/n‐heptane, as well in homogenous media at different pH values, were studied. The choice of this molecular probe is because of its electrochemical response in water, strongly depend on the pH value thus, our goal is to know more about an intriguing issue in the soft matter field, what is the pH value for water encapsulated in the water pool of AOT RMs. Our work will demonstrate that the interfacial apparent pH value of AOT RMs is not strongly acidic as some of the literature works claim, but it is around a pH value of 6.7. Thus, through the electrochemistry technique, the present work reinforces the idea that the concept of is strongly dependent on the water‐interface interactions and the molecular probe location.

Synthesis of zinc bacteriochlorophyll-d analogs bearing an alkoxyimino group at the 131-position and their self-aggregation in an aqueous micelle solution

Zinc complexes of methyl 3-hydroxymethyl-131-deoxo-131-alkoxyimino-pyropheophorbides-a were prepared through the condensation of the 13-keto carbonyl group with several alkoxyamines. The E/Z-stereoisomers of the synthetic alkoximes were successfully separated by silica gel column chromatography. The zinc bacteriochlorophyll-d analogs formed J-type self-aggregates in an aqueous micelle solution to give red-shifted electronic absorption bands, which were similar to those of the original bacteriochlorophyll-d bearing the 131-oxo group. The self-aggregation was largely dependent on the size of the alkoxyimino groups and their E/Z-stereochemistry.

Binding of lanthanide salts to zwitterionic phospholipid micelles

As the use of lanthanide salts in biophysical systems increases and the separation of lanthanides from nuclear and other wastes with extraction processes has become an important technological challenge, a deeper understanding of the behavior of lanthanides at lipid interfaces is urgently needed. In this work the interaction of lanthanide salts with zwitterionic phospholipids is probed using aqueous micelles of the surfactant dodecyl phosphocholine (DPC), which are useful membrane-mimetic model systems, widely used for the solubilization of membrane proteins in aqueous solutions. Because more than one species exists in lanthanide salt solutions, even at the pH value of 4 used in this experiment, the major goal of this investigation is to examine which species are actually binding to the micelles. Using static and time-dependent europium fluorescence, strong indications are obtained that both the Eu3+ cation and its 1:1 chloride, nitrate, or sulfate complexes bind to the micelles, whereas the europium species do not appear to interact strongly with DPC molecules below the cmc. From isothermal titration calorimetry (ITC) measurements it is found that the lanthanide interaction with DPC micelles increases to the right of the lanthanide series and is - surprisingly – endothermic, underlying the important role of hydration effects in the interaction. The anion of the lanthanide salt strongly influences the thermodynamics: perchlorate and sulfate salts give extraordinary results, switching the interaction to exothermic. A multi-level phenomenological electrostatic model of the europium fluorescence lifetimes strongly suggests that in the case of nitrate salts both Ln3+ and LnNO32+ ions bind to the micelles. Overall a detailed molecular picture of the complexity of lanthanide-lipid interactions at interfaces is emerging from these experiments and the associated modelling effort.

Impact of ripening inhibitors on molecular transport of antimicrobial components from essential oil nanoemulsions

The objective of this study was to provide insights into the mechanisms involved in the mass transport of antimicrobial compounds from essential oil nanoemulsions to bacterial cell membranes. Origanum oil-in-water nanoemulsions were produced using spontaneous emulsification by titrating a mixture of essential oil, ripening inhibitor, and surfactant (Tween 80) into 5 mM sodium citrate buffer (pH 3.5). Stable nanoemulsions containing relatively small droplets (d < 60 nm) were produced using this low-energy method. The nature of the ripening inhibitor used in the oil phase of the nanoemulsions affected the antimicrobial activity of the nanoemulsions: corn (LCT) > medium-chain triglycerides (MCT). Differences in antimicrobial activity were attributed to the differences in the rate of transfer of hydrophobic antimicrobial constituents from the nanoemulsion to the MCT emulsion, which was used to mimic the hydrophobic region of the bacterial cell membranes. Each antimicrobial nanoemulsion was separated from the MCT emulsion by a dialysis tubing. Dialysis tubing with two different pore sizes was used, one excluding nanoemulsion droplet and micelle delivery, allowing the delivery of antimicrobial compounds only through the aqueous phase and the other by both the aqueous phase and micelles. For origanum oil nanoemulsions, the delivery of all antimicrobial agents occurred more efficiently when micelles were present.

Discerning the Structure Factor of Charged Micelles in Water and Supercooled Solvent by Contrast Variation X-ray Scattering.

Sodium dodecyl sulfate (SDS) is a well-known anionic surfactant that forms micelles in various solvents including supercooled sugar-urea melt. Here, we explore the application of contrast variation small-angle X-ray scattering (SAXS) in discerning the structure and interactions of SDS micelles in aqueous solution and in a room-temperature supercooled solvent. The SAXS patterns can be analyzed in terms of a core-shell ellipsoid model. For aqueous SDS micelles, at low volume fractions, the features due to intermicellar interaction, S(q), in the SAXS pattern are poorly resolved because of the prominent contribution from shell scattering. Increasing the electron density of the solvent by the addition of the urea or fructose-urea mixture (at a weight ratio of 6:4) permits the systematic variation of shell scattering without influencing the structure drastically. For a 10% solution of SDS in water, the contribution from the shell can be completely masked by the addition of 40% urea or fructose-urea mixture. The fructose-urea mixture is a preferred additive as it can vary the scattering length density over a wide range and serves as a matrix to form supercooled micelles. The structural parameters of micelles in supercooled fructose-urea melt are obtained from contrast variation SAXS, small-angle neutron scattering, and high-resolution transmission electron microscopy.

Water Structure and Dynamics in the Stern Layer of Micelles: Femtosecond Mid-Infrared Pump-Probe Spectroscopy Study.

Molecular-level understanding of the water structure and dynamics in the Stern layer of micelles is important to elucidate the active role of water in biological processes on membrane surfaces. Micelles and reverse micelles are considered to be excellent membrane model systems. Here, to address the question of whether or not the spatial confinement effect on water in reverse micelles and nanometric water pool systems plays a role in modulating water dynamics, we consider four different aqueous micelle solutions and study the water dynamics in the Stern layer of micelles using a femtosecond mid-infrared pump-probe spectroscopy technique. Vibrational energy relaxation and rotational dynamics of the O?D stretch mode of HDO and the azido stretch mode of hydrazoic acid are critically dependent on the charge, polarity, and chemical structure of the surfactant head group. In particular, water molecules in the Stern layer of micelles, which are not in spatially confined environments, are notably different from those in bulk water. This finding clearly indicates that changes in the vibrational and rotational dynamics of water molecules, even in spatially confined systems, are mainly induced by surface effects instead of spatial confinement effects. We believe that the present experimental results are of importance for understanding water-involved biochemical processes on biological membranes.

Conformational Preferences of Aβ25-35 and Aβ35-25 in Membrane Mimicking Environments

The structural transition of aggregating Abeta peptides is the key event in the progression of Alzheimer's Disease (AD). In the present work, the structural modifications of toxic Aβ25-35 and the scrambled Aβ35-25 were studied in Trifluoroethanol (TFE) and in aqueous SDS micelles. Using CD spectroscopic investigations, the conformational transition of Aβ25-35 and Aβ35-25 peptides were determined in different membrane mimicking environments such as TFE and SDS. An interval scan CD of the peptides on evaporation of TFE was performed. TFE titrations were carried out to investigate the intrinsic ability of the structural conformations of peptides. We show by spectroscopic evidence that Aβ25-35 prefers beta sheet structures upon increasing TFE concentrations. On the other hand, the non-toxic scrambled Aβ35-25 peptide only undergoes a transition from random coil to α-helix conformation with increasing TFE. In the interval scan studies, Aβ25-35 did not show any structural transitions, whereas Aβ35-25 showed transition from α-helix to β-sheet conformation. In membrane simulating aqueous SDS micelles, Aβ25-35 showed a transition from random coil to α-helix while Aβ35-25 underwent transition from random coil to β-sheet conformation. Overall, the current results seek new insights into the structural properties of amyloidogenic and the truncated sequence in membrane mimicking solvents.

Full Gamut Wall Tunability from Persistent Micelle Templates via Ex Situ Hydrolysis.

The predictive self-assembly of tunable nanostructures is of great utility for broad nanomaterial investigations and applications. The use of equilibrium-based approaches however prevents independent feature size control. Kinetic-controlled methods such as persistent micelle templates (PMTs) overcome this limitation and maintain constant pore size by imposing a large thermodynamic barrier to chain exchange. Thus, the wall thickness is independently adjusted via addition of material precursors to PMTs. Prior PMT demonstrations added water-reactive material precursors directly to aqueous micelle solutions. That approach depletes the thermodynamic barrier to chain exchange and thus limits the amount of material added under PMT-control. Here, an ex situ hydrolysis method is developed for TiO2 that mitigates this depletion of water and nearly decouples materials chemistry from micelle control. This enables the widest reported PMT range (M:T = 1.6-4.0), spanning the gamut from sparse walls to nearly isolated pores with ≈2 Å precision adjustment. This high-resolution nanomaterial series exhibits monotonic trends where PMT confinement within increasing wall-thickness leads to larger crystallites and an increasing extent of lithiation, reaching Li0.66 TiO2 . The increasing extent of lithiation with increasing anatase crystallite dimensions is attributed to the size-dependent strain mismatch of anatase and bronze polymorph mixtures.

Ag2CO3-catalyzed cycloaddition of organic azides onto terminal alkynes: A green and sustainable protocol accelerated by aqueous micelles of CPyCl

Using catalytic amount of Ag2CO3 a simple, efficient and copper free green protocol has been developed to synthesize 1,4-disubstituted 1,2,3-triazoles regioselectively. Here, the cationic surfactant, cetylpyridinium chloride (CPyCl) in water provides a micellar media and accelerates the subsequent Ag(I)-catalysed azide-alkyne cycloaddition (AgAAC) reaction by increasing the concentration of reactants in the micellar pseudophase. Our method is found to be environmentally friendly from E-factor measurement. The surfactant, CPyCl is found to be nontoxic.

Surface charge modulation of sulfobetaine micelles by interaction with different anions: A dynamic light scattering study

This work reports a Dynamic Light Scattering study on aqueous micelles formed by tetradecyl dialkylammonium propanesulfonate surfactants (sulfobetaines; with alkyl = methyl, ethyl, n‑propyl and n‑butyl) within a range of surfactant concentrations (0.01–0.40 M) both in pure water and in the presence of various concentrations of NaBr, NaOH and NaClO4 (0.02–0.50 M NaBr; 0.10–1.00 M NaOH; 0.005–0.50 M NaClO4). From values of diffusion coefficients, D, we obtained micellar hydrodynamic radii, Rh, by application of the Stokes-Einstein relation. Plots of D vs. sulfobetaine concentrations can be qualitatively explained with a model based on a linear interaction theory, which allowed to separate thermodynamic and hydrodynamic perturbations to D. Results show that: i) formally neutral sulfobetaine micelles become negatively charged by preferential interaction with strongly interacting, “soft” anions; ii) the surface negative charge increases with the hydrophobicity of the anions; iii) bulkier alkyl substituents on the sulfobetaine head groups lead to less charged, less hydrated aggregates, which result in opposite perturbations to D; (iv) highly hydrated, high charge density hydroxide ions lead to an increase of micellar sizes through a disc-like growth pattern.

Enantioseparation of Selected Imidazole Drugs Using Dual Cyclodextrin-Modified Micellar Electrokinetic Chromatography.

Particular attention has been paid to capillary electrophoresis as versatile and environmentally friendly approach for enantioseparations of a wide spectrum of compounds. Cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) is a method of choice to provide effective separation toward hydrophobic and uncharged stereoisomers. The chiral discrimination of the solutes relies upon the partitioning between a given CD in the aqueous phase and micelles formed from a surfactant. Synergistic combinations of chiral selectors, surfactant, and modifier contribute to successful enantioseparations of the enantiomers. In this chapter, an application of CD-MEKC for the enantioseparation of selected imidazole drugs employing a dual CDs system is described.

Preparation of glycoside polymer micelles with antioxidant polyphenolic cores using alkylated poly(arbutin)s.

This paper describes the synthesis of long-chain-alkylated poly(arbutin)s (poly(Arb)-Rx, where R = alkyl-chain length and x = degree of substitution (DS)) and their aqueous micelle formation. DS was controlled by tailoring the alkyl reagent/main-chain phenol substituent feed ratio. The critical micelle concentrations (CMCs) of poly(Arb)-Rx were determined as 1.3–5.2 mg mL−1 by the surface tension method. Introduction of longer alkyl substituents decreased CMC and also decreased aqueous solubility. In DLS measurement, the average micelle diameters were 225–616 nm, and micelle size decreased with increasing DS because of increased stabilization by hydrophobic alkyl substituents. Transmission electron microscopy indicated that mainly wormlike cylindrical micelles were formed, even with highly hydrophilic polymers. The alkylated polymer exhibited no cytotoxicity, and their antioxidant abilities were evaluated by the β-carotene bleaching method. Only 0.049 mol equivalents of poly(Arb)-C830 to linoleic acid was sufficient to preserve the β-carotene.