Octaethylene Glycol Research Articles

An Azobenzene-Based Single-Component Supramolecular Polymer Responsive to Multiple Stimuli in Water.

One of the most appealing features of supramolecular assemblies is their ability to respond to external stimuli due to their noncovalent nature. This provides the opportunity to gain control over their size, morphology, and chemical properties and is key toward some of their applications. However, the design of supramolecular systems able to respond to multiple stimuli in a controlled fashion is still challenging. Here we report the synthesis and characterization of a novel discotic molecule, which self-assembles in water into a single-component supramolecular polymer that responds to multiple independent stimuli. The building block of such an assembly is a C3-symmetric monomer, consisting of a benzene-1,3,5-tricarboxamide core conjugated to a series of natural and non-natural functional amino acids. This design allows the use of rapid and efficient solid-phase synthesis methods and the modular implementation of different functionalities. The discotic monomer incorporates a hydrophobic azobenzene moiety, an octaethylene glycol chain, and a C-terminal lysine. Each of these blocks was chosen for two reasons: to drive the self-assembly in water by a combination of H-bonding and hydrophobicity and to impart specific responsiveness. With a combination of microscopy and spectroscopy techniques, we demonstrate self-assembly in water and responsiveness to temperature, light, pH, and ionic strength. This work shows the potential to integrate independent mechanisms for controlling self-assembly in a single-component supramolecular polymer by the rational monomer design and paves the way toward the use of multiresponsive systems in water.

Binding isotherms of surfactants used in detergent formulations to bovine serum albumin

Protein-surfactant interactions are the focus of extensive research due to their many applications in food technology and detergent industry. In this work, we investigate the interaction between bovine serum albumin (BSA) and five relevant surfactants to the cleaning industry, which differ in head group charge, namely: sodium alkyl ether sulphate (C12-C14 AE3S), Cocoamidopropyl amine-oxide (CapAO), alkyl dimethyl amine oxide (C12C14AO), octaethylene glycol monodecyl ether (C10EO8) and didecyldimethylammonium chloride (DDAC). The results collected with fluorescence emission spectroscopy highlight zwitterionic and nonionic surfactants have the lowest affinity for the protein, as their interaction does not result in protein denaturation. Instead, higher and mutually close binding constants are found for AE3S (anionic) and DDAC (cationic) due to the presence of electrostatic interactions between the surfactant heads and the charged residues of BSA. AE3S leads to irreversible protein unfolding. The case of DDAC is more complex and has been studied through a combination of fluorescence, DLS, PGSE-NMR and zeta-potential measurements. At low concentration DDAC binding neutralizes negatively charged residues present in BSA, causing a reversible flocculation of BSA after the isoelectric point (23 DDAC molecules per protein). Further DDAC adsorption, at 70 DDAC molecules per protein, leads to an excess of positive charge on the protein which restores electrostatic repulsions between BSA-surfactant complexes.

Unfolding and partial refolding of a cellulase from the SDS-denatured state: From β-sheet to α-helix and back

Globular proteins are typically unfolded by SDS to form protein-decorated micelle-like structures. Several proteins have been shown subsequently to refold by addition of the nonionic surfactant octaethylene glycol monododecyl ether (C12E8). Thus SDS converts β-lactoglobulin, which has mainly β-sheet secondary structure, into a state rich in α-helicality, while addition of C12E8 leads to refolding and recovery of the original β-sheet structure. Here we extend these studies to the large β-sheet-rich cellulase Cel7b from Humicola insolens whose enzymatic activity provides a very sensitive refolding parameter. The enzymes widespread usage in the detergent industry makes it an obvious model system for protein-surfactant interactions. SDS-unfolding and subsequent refolding using C12E8 were investigated at pH 4.2 using near- and far-UV circular dichroism (CD), small-angle X-ray scattering (SAXS), isothermal titration calorimetry (ITC), size-exclusion chromatography (SEC) and activity measurements. The Cel7b:SDS complex can be described as a random configuration of 3–4 connected core-shell structures in which the protein is converted to a mainly α-helical secondary structure. Addition of C12E8 recovers almost all the secondary structure, part of the tertiary structure, about 50% of the activity and dissociates part of the protein population completely from detergent micelles. The lack of complete refolding may be due to charge neutralisation of Cel7b by SDS, kinetically trapping the enzyme into aggregated structures. In support of this, aggregates did not form when C12E8 was first mixed with Cel7b followed by addition of SDS. Formation of such aggregates may be a general phenomenon hampering quantitative refolding from the SDS-denatured state.

Molecular dynamics study of solubilization of cyclohexane, benzene, and phenol into mixed micelles composed of sodium dodecyl sulfate and octaethylene glycol monododecyl ether.

Molecular dynamics calculations of a mixed micelle composed of sodium dodecyl sulfate (SDS) and octaethylene glycol monododecyl ether (C12 E8 ) were performed for six compositions (SDS/C12 E8 = 100/0, 80/20, 60/40, 40/60, 20/80, and 0/100) to investigate the composition dependence of the mixed micelle structure and solubilization of cyclohexane, benzene, and phenol molecules by the micelle. The radial density distribution of the hydrophilic polyoxyethylene (POE) group of C12 E8 as a function of distance from the micelle center is very sharp for micelles with high SDS content because the POE group captures a Na+ ion in solution and wraps around it to form a compact crown-ether-like complex. The hydrophobic dodecyl groups of SDS and C12 E8 were separately distributed in the mixed micelle core. ΔG(r) evaluated for each solute showed that despite the structural changes of the micelle the binding strength of the solute molecules to the micelle did not change significantly. © 2019 Wiley Periodicals, Inc.

A general modular approach for the solubility tagging of BODIPY dyes

We describe a general and practical strategy for the direct one-step incorporation of a tunable solubility module at the boron atom of F-BODIPY dyes. The tethering reaction uses easy-to-handle reagents, has broad functional group compatibility and proceeds under mild conditions without requiring any pre-functionalization of the starting F-BODIPY to yield the solubility-tagged O-BODIPY derivative in 51–86% yield. The module can be introduced at the end of the synthetic route without perturbing the fluorophore scaffold, thus minimizing difficulties in product isolation. Its orthogonal geometrical arrangement with respect to the plane of the BODIPY chromophore hampers intermolecular aggregation processes that quench fluorescence, while the covalent attachment to the boron atom has a minimal effect on the absorption properties. Fully water-soluble and hydrolytically stable BODIPYs were prepared by incorporating either neutral (tetra- and octaethylene glycol chains) or zwitterionic (sulfobetaine) hydrophilic tags in the module. The new dyes are valuable live cell imaging probes that ameliorate the undesired partitioning into lipophilic compartments that is often observed for standard BODIPYs. This strategy can be readily adapted to the general and highly practical post-synthetic introduction of new functionalities into F-BODIPY dyes, including phase-tagging, by appropriately choosing the nature of the chemical tags attached to the module.

Micellar size changing in the systems of octaethylene glycol mono(n-dodecyl) ether without and with poly(acrylic acid)

Aqueous octaethylene glycol mono(n-dodecyl) ether (C12E8) solutions, in the absence and presence of poly(acrylic acid) (PAA) are studied by means of viscosity, pH, refractive index, static fluorescence and dynamic light scattering measurements. At high surfactant concentrations, these properties present inflection points. They are different by the classical critical points (critical micelle concentration and critical interaction concentrations) of such systems and appear at almost the same surfactant concentration, irrespective of the polymer presence. The results are interpreted in terms of micellar size and shape changes. Some images collected with two microscopes prove these changes and the coexistence of various shaped aggregates.

Markov Chain Modeling of Surfactant Critical Micelle Concentration and Surface Composition.

A Markov chain (MC) model has been used to model the following binary surfactant mixtures: linear alkylbenzenesulfonate (LAS4)/octaethylene glycol monododecyl ether (C12E8) at 10 and 25 °C, LAS6/acidic sophorolipid (AS), C12Betaine/C12Maltoside, sodium lauryl ether sulfate (SLES2)/C12E8, and rhamnolipid (R1)/LAS6. The critical micellar concentration and the composition of the adsorbed layer, for each system, can be modeled using the same monomer reactivity ratio values, g1 and g2. This implies that the interactions between the surfactants in the bulk solution and at the interface are the same, within error. For the LAS4/C12E8 system at 25 °C, the ranges of g1 and g2 values which can model both sets of data are within 0.03-0.05 and 1.55-2.10, respectively; g1 ≪ g2 implies that C12E8 is significantly more surface active than LAS4. The MC model indicates a negative change in the free energy upon mixing for all of the surfactant systems, consistent with the literature. The interfacial mixing behavior of LAS4/SLES2 is inferred from the results of the MC analysis of the LAS4/C12E8 and SLES2/C12E8 systems, which share a common surfactant partner in C12E8, and the prediction is in line with the published data.

Improvement in the Predicted Partitioning of Alcohol and Polyethylene Oxide Groups Between Water and Octanol (logP) in Molecular Dynamics Simulations

Molecular dynamics simulations can be applied to explore the complex liquid phase behavior of lipid-based formulations and the gastrointestinal tract lumen. In order for the results from these simulations to be of value, the manner in which molecules interact with both aqueous and oil phases present needs to be as correct as possible. An existing molecular dynamics force field, GROMOS 53a6, was demonstrated to poorly reproduce the partitioning of straight-chain alcohol and short-chain polyethylene glycol (PEG) molecules between octanol and water phase (logP), with the molecules too hydrophobic. Force field parameters for Lennard-Jones interactions between CH2 and CH3 with water oxygen were adjusted to reproduce the experimental octanol logP, with all other Lennard-Jones and force field parameters left untouched. This parameter set, called 53a6DBW, was subsequently used to recalculate straight-chain alcohol and short-chain PEG molecules, with significant improvement in the values obtained. Simulations of a nonionic surfactant in water, octaethylene glycol monocaprylate, were also performed to observe the aggregation behavior. 53a6DBW demonstrated significant improvements in water interactions with the PEG chains, well hydrating the PEG groups, and allowing the formation of micelles. Further improvements and evaluation of the improved parameter set are ongoing.

Modification of Oil–Water Interfaces by Surfactant-Stabilized Carbon Nanotubes

In this research, simulation results for using carbon nanotubes (CNTs) to deliver surfactants to an oil–water interface are reported. Two different surfactants were considered, the anionic sodium dodecyl sulfate (SDS) and the nonionic octaethylene glycol monododecyl ether (C12E8). The surfactants were first allowed to adsorb on the CNT surface in an aqueous environment. It was found that the capacities of SDS and C12E8 to adsorb on the CNT were 2.62 and 2.43 molecules/nm2, respectively. The electrostatic effect of the anionic surfactant and the steric effect of the nonionic surfactant negatively affected the adsorption process. On the oil–water interface, the surfactant molecules quickly desorbed from the CNT to distribute on the interface, leading to the reduction of the oil–water interfacial tension. At a low surfactant concentration, the CNT also remained on the interface, reducing further the interfacial tension. When the surfactant interfacial concentration reached the value corresponding to the bulk...

Location of Solvated Probe Molecules Within Nonionic Surfactant Micelles Using Molecular Dynamics

An iconic textbook that pharmaceutical scientists encounter in undergraduate courses is “Martin’s Physical Pharmacy and Pharmaceutical Sciences.” Within the chapter on Colloids, a figure indicates the location of solubilization of molecules within spherical, nonionic surfactant micelles. The surfactant consists of polyethylene glycol (PEG) hydrophilic headgroups and alkane chains for the hydrophobic tail. The figure shows benzene and toluene within the alkane core, salicylic acid (2-hydroxybenzoic acid) at the interface between the core and PEG chains, and then para-hydroxybenzoic acid (4-hydroxybenzoic acid) located between the PEG chains. Molecular dynamics simulations of octaethylene glycol monododecyl ether micelles were performed with a series of probe molecules, including those within the Martin’s figure, to determine their solubilization location. Relative placement of molecules within the micelle was correct; however, some specifics were different. In particular, benzene and toluene are excluded from the core, and 4-hydroxybenzoic acid prefers to maintain contact with the core. A series of molecules containing 6 carbon atoms were also studied to determine the effects of cyclization (moves out of core), polar functionalization (anchored to interface), and aromatization (excluded from central core). Molecular dynamics was found to be a useful tool for gaining insight into interactions important in solubilization of molecules.

Oil-water interfaces with surfactants: A systematic approach to determine coarse-grained model parameters.

In order to investigate the interfacial region between oil and water with the presence of surfactants using coarse-grained computations, both the interaction between different components of the system and the number of surfactant molecules present at the interface play an important role. However, in many prior studies, the amount of surfactants used was chosen rather arbitrarily. In this work, a systematic approach to develop coarse-grained models for anionic surfactants (such as sodium dodecyl sulfate) and nonionic surfactants (such as octaethylene glycol monododecyl ether) in oil-water interfaces is presented. The key is to place the theoretically calculated number of surfactant molecules on the interface at the critical micelle concentration. Based on this approach, the molecular description of surfactants and the effects of various interaction parameters on the interfacial tension are investigated. The results indicate that the interfacial tension is affected mostly by the head-water and tail-oil interaction. Even though the procedure presented herein is used with dissipative particle dynamics models, it can be applied for other coarse-grained methods to obtain the appropriate set of parameters (or force fields) to describe the surfactant behavior on the oil-water interface.

Dynamic surface tension and adsorption mechanism of surfactin biosurfactant at the air-water interface.

The dynamic adsorption of the anionic biosurfactant, surfactin, at the air-water interface has been investigated in this work and compared to those of two synthetic surfactants: the anionic sodium dodecylbenzenesulfonate (SDBS) and the nonionic octaethylene glycol monotetradecyl ether (C14E8). The results revealed that surfactin adsorption at the air-water interface is purely controlled by diffusion mechanism at the initial stage of the adsorption process (i.e., [Formula: see text]), but shifts towards a mixed diffusion-barrier mechanism when surface tension approaches equilibrium (i.e., [Formula: see text]) due to the development of an energy barrier for adsorption. Such energy barrier has been found to be a function of the surfactin bulk concentration (increases with increasing surfactin concentration) and it is estimated to be in the range of 1.8-9.5kJ/mol. Interestingly, such a trend (pure diffusion-controlled mechanism at [Formula: see text] and mixed diffusion-barrier mechanism at [Formula: see text]) has been also observed for the nonionic C14E8 surfactant. Unlike the pure diffusion-controlled mechanism of the initial surfactin adsorption, which was the case in the presence and the absence of the sodium ion (Na+), SDBS showed a mixed diffusion-barrier controlled at both short and long time, with an energy barrier of 3.0-9.0 and 3.8-18.0kJ/mol, respectively. Such finding highlights the nonionic-like adsorption mechanism of surfactin despite its negative charge.

Adsorption at the Air-Water Interface in Biosurfactant-Surfactant Mixtures: Quantitative Analysis of Adsorption in a Five-Component Mixture.

The composition of the air-water adsorbed layer of a quinary mixture consisting of three conventional surfactants, octaethylene glycol monododecyl ether (C12E8), dodecane-6-p-sodium benzene sulfonate (LAS6), and diethylene glycol monododecyl ether sodium sulfate (SLE2S), mixed with two biosurfactants, the rhamnolipids l-rhamnosyl-l-rhamnosyl-β-hydroxydecanoyl-β-hydroxydecanoyl, R2, and l-rhamnosyl-β-hydroxydecanoyl-β-hydroxydecanoyl, R1, has been measured over a range of compositions above the mixed critical micelle concentration. Additional measurements on some of the subsets of ternary and binary mixtures have also been measured by NR. The results have been analyzed using the pseudophase approximation (PPA) in conjunction with an excess free energy, GE, that depends on the quadratic and cubic terms in the composition. The compositions of the binary, ternary, and quinary mixtures could all be fitted to two sets of interaction parameters between the pairs of surfactants, one for micelles and one for adsorption. No ternary interactions or ternary corrections were required. Because the system contains two strongly anionic surfactants, the PPA can be extended, in practice, to ionic surfactants, contrary to the prevailing view. The values of the interaction parameters show that the quinary mixture, SLE2S-LAS6-C12E8-R1-R2, which is known to be a highly effective surfactant system, is characterized by a sequence of strong surface but weak micellar interactions. About half of the minima in GE for the strong surface interactions occur well away from the regular solution value of 0.5.

Refolding of SDS-Unfolded Proteins by Nonionic Surfactants

The strong and usually denaturing interaction between anionic surfactants (AS) and proteins/enzymes has both benefits and drawbacks: for example, it is put to good use in electrophoretic mass determinations but limits enzyme efficiency in detergent formulations. Therefore, studies of the interactions between proteins and AS as well as nonionic surfactants (NIS) are of both basic and applied relevance. The AS sodium dodecyl sulfate (SDS) denatures and unfolds globular proteins under most conditions. In contrast, NIS such as octaethylene glycol monododecyl ether (C12E8) and dodecyl maltoside (DDM) protect bovine serum albumin (BSA) from unfolding in SDS. Membrane proteins denatured in SDS can also be refolded by addition of NIS. Here, we investigate whether globular proteins unfolded by SDS can be refolded upon addition of C12E8 and DDM. Four proteins, BSA, α-lactalbumin (αLA), lysozyme, and β-lactoglobulin (βLG), were studied by small-angle x-ray scattering and both near- and far-UV circular dichroism. All proteins and their complexes with SDS were attempted to be refolded by the addition of C12E8, while DDM was additionally added to SDS-denatured αLA and βLG. Except for αLA, the proteins did not interact with NIS alone. For all proteins, the addition of NIS to the protein-SDS samples resulted in extraction of the SDS from the protein-SDS complexes and refolding of βLG, BSA, and lysozyme, while αLA changed to its NIS-bound state instead of the native state. We conclude that NIS competes with globular proteins for association with SDS, making it possible to release and refold SDS-denatured proteins by adding sufficient amounts of NIS, unless the protein also interacts with NIS alone.

Liquid Chromatography-Tandem Mass Spectrometric Analysis of Octaethylene Glycol Monodecyl Ether in Rat Plasma and its Application to Pharmacokinetic Studies.

Alcohol ethoxylates (AEs) are a major class of non-ionic surfactants, which are widely used in household, institutional and industrial cleaners, and they are considered as an alternative of nonylphenol. In this study, a rapid, sensitive and reliable bioanalytical method was developed for the determination of octaethylene glycol monodecyl ether (C10E8, an AE) in rat plasma using liquid chromatography-tandem mass spectrometry (LC-MS-MS). Chromatographic separation was performed on a reversed-phase C18 column (2.1 mm × 50 mm, 2.1 μm). The mobile phase consisted of 0.1% formic acid in distilled water and 0.1% formic acid in acetonitrile (40:60% v/v). The flow rate was 0.3 mL/min. For mass spectrometric detection, the multiple reaction monitoring (MRM) mode was used; the MRM transitions were m/z 511.5 → m/z 133.1 for C10E8 and m/z 423.3 → m/z 133.1 for hexaethylene glycol monodecyl ether (internal standard) in the positive ion mode. A calibration curve was constructed within the range of 2-2,000 ng/mL; the intra- (n = 5) and inter-day (n = 3) precision and accuracy were within 10%. The LC-MS-MS method was specific, accurate and reproducible, and this method was successfully applied in a pharmacokinetic study of C10E8 in rats. C10E8 was intravenously (1 mg/kg, n = 6) and orally (10 mg/kg, n = 7) administered to rats. The kinetic parameters were analyzed based on a noncompartmental statistical model using the pharmacokinetic modeling software (WinNonlin). The oral bioavailability of C10E8 was 34.4%.

Thermally-induced lateral assembly of a PEG-containing amphiphile triggering vesicle budding.

A macrocyclic amphiphile consisting of a thermo-responsive octaethylene glycol chain with hydrophobic aromatic and aliphatic units undergoes lateral self-assembly in a liquid-disordered-state phospholipid bilayer membrane upon heating, which further leads to vesicle budding.

Measurements of surface concentration and charge number per adsorbed molecule for a thiolipid monolayer tethered to the Au(111) surface by a long hydrophilic chain

The charge number per adsorbed molecule and surface concentration of 2,3-di-O-phytanyl-sn-glycero-1-octaethyleneglycol-D,L-α-lipoic acid ester (DPOL) at a Au(111) electrode surface was investigated by chronocoulometry using two different film deposition methods. First, a known amount of the thiolipid was transferred from the air-water interface of a Langmuir trough onto the gold electrode surface via a Langmuir-Blodgett (LB) deposition. The charge density measurements for this monolayer system were used to determine the charge number per adsorbed DPOL molecule (electrosorption valency). The observed electrosorption valency values of the adsorbed DPOL film were much lower than the expected number of transferred electrons for a simple reductive desorption process. In the second deposition method, charge densities were measured for the electrode covered by a self-assembled DPOL monolayer. The electrosorption valency values determined from the LB DPOL film were used to calculate the packing density of the DPOL molecules within the self-assembled monolayer. The surface concentration of the molecules within the thiol monolayer with octaethylene glycol chains gave similar results to a related thiolipid with tetraethylene glycol chains (DPTL). This new finding indicates that both of these molecules (DPTL and DPOL) assume a brush conformation in densely packed self-assembled monolayers.

Self-assembly in dilute mixtures of non-ionic and anionic surfactants and rhamnolipd biosurfactants

The self-assembly of dilute aqueous solutions of a ternary surfactant mixture and rhamnolipid biosurfactant/surfactant mixtures has been studied by small angle neutron scattering. In the ternary surfactant mixture of octaethylene glycol monododecyl ether, C12E8, sodium dodecyl 6-benzene sulfonate, LAS, and sodium dioxyethylene monododecyl sulfate, SLES, small globular interacting micelles are observed over the entire composition and concentration range studied. The modelling of the scattering data strongly supports the assumption that the micelle compositions are close to the solution compositions. In the 5-component rhamnolipid/surfactant mixture of the mono-rhamnose, R1, di-rhamnose, R2, rhamnolipids with C12E8/LAS/SLES, globular micelles are observed over much of the concentration and composition range studied. However, for solutions relatively rich in rhamnolipid and LAS, lamellar/micellar coexistence is observed. The transition from globular to more planar structures arises from a synergistic packing in the 5 component mixture. It is not observed in the individual components nor in the ternary C12E8/LAS/SLES mixture at these relatively low concentrations. The results provide an insight into how synergistic packing effects can occur in the solution self-assembly of complex multi-component surfactant mixtures, and give rise to an unexpected evolution in the phase behaviour.

Determination of Rice Storage Time with Colorimetric Sensor Array

Aroma of rice greatly affects palatability as well as consumer acceptability and is one of the main factors of rice quality. In this work, gas chromatography mass spectrometry (GC-MS) was used to investigate the volatile organic compounds (VOC) of rice samples with different storage time. It was found that the compounds of benzaldehyde, 2-fluoro-5-methylaniline increased remarkably during storage, while hexanal, octaethylene glycol and monododecyl ether continuously decreased. And then, colorimetric sensor array composed of 12 sensitive dyes were used for rice sample discrimination. A CCD camera was employed to capture the images of colorimetric sensor array, and the difference map of sensor array before and after exposure VOC was obtained. The red (R), green (G), and blue (B) components images were extracted from the difference map. Moreover, the images were further processed and turned into digital data for subsequent analysis. Recently harvested rice and that stored for 6 and 12 months samples were distinguished with three dimensional spaces personal computer assistant cluster trend. Linear discriminant analysis (LDA) model based on PCA scores was used to discriminate the storage time of rice samples, and the result indicates 85 % of samples were correctly identified.

Aqueous solutions of didecyldimethylammonium chloride and octaethylene glycol monododecyl ether: Toward synergistic formulations against enveloped viruses

Micellization of di-n-decyldimethylammonium chloride, [DiC10][Cl], and octaethylene glycol monododecyl ether, C12E8, mixtures have been investigated by surface tension and conductivity measurements. From these results, various physicochemical and thermodynamic key parameters (e.g. micellar mole fraction of [DiC10][Cl], interaction parameter, free energy of micellization, etc.) have been evaluated and discussed in detail. The results prove high synergistic effect between the two surfactants. Based on these results, the virucidal activity of an equimolar mixture of [DiC10][Cl] and C12E8 has been investigated. A marked synergism was observed on lipid-containing deoxyribonucleic and ribonucleic acid viruses, such as herpes virus, respiratory syncytial virus, and vaccinia viruses. In contrast, Coxsackievirus (non-enveloped virus) was not inactivated. These results support that the mechanism is based on the extraction of lipids and/or proteins from the envelope inside the mixed micelles. This extraction creates ⿿holes⿿ the size of which increases with concentration up to a specific value which triggers the virus inactivation. Such a mixture could be used to extend the spectrum of virucidal activity of the amphiphiles virucides commonly employed in numerous disinfectant solutions.