Polyoxyethylene Chain Research Articles

Evidence for surfactant solubilization of plant epicuticular wax.

The solubilization of isolated, reconstituted tomato (Lycopersicon esculentum Mill.) fruit and broccoli (Brassica oleracaea var. botrytis L.) leaf epicuticular waxes (ECW) by nonionic octylphenoxypolyethoxy ethanol surfactant (Triton X-100) was demonstrated in a model system by TLC and fluorescence analysis using pyrene as a fluorescent probe. ECW was solubilized at or above the surfactant critical micelle concentration; solubilization increased with an increase in micelle concentration. As shown by the fluorescence quenching of pyrene, surfactant solubilization of the ECW increased rapidly for the first 12 h, then approached a plateau, increased linearly with an increase in temperature (22--32 degrees C), and decreased linearly with the log of the polyoxyethylene chain length (range 5--40 oxyethylenes). These data are discussed in relation to surfactant effects on phytotoxicity and performance of foliar spray application of agrochemicals.

Phase Behavior of Heptaethylene Glycol Dodecyl Ether and Its Aqueous Mixture Revealed by DSC and FT-IR Spectroscopy

The phase behavior of heptaethylene glycol dodecyl ether (C12E7) and its aqueous mixture was investigated by means of differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) spectroscopy in the temperature range from −20 to 70 °C. Phase boundaries among various phases including mesomorphic phases were determined on the basis of DSC thermograms, from which the binary phase diagram of this mixture system was constructed. According to the phase diagram, the mixture with the composition of 31 wt % H2O exhibits the following phase sequence with increasing temperature: solid → H1 (normal hexagonal) → V1 (normal bicontinuous-type cubic) → Lα (lamellar) → liquid. FT-IR measurements for the mixture with this composition revealed the following features concerning the conformational structure of the C12E7 molecule and the interaction between the surfactant and D2O in each phase. In the solid phase, the polyoxyethylene (POE) chain of the surfactant molecule has a rather extended structure with a trans-rich conformation, in contrast to the case of pure C12E7, in which a helical structure is dominant. When the solid phase transforms to the H1 phase, the hydrogen-bond interaction between C12E7 molecules and between C12E7 and water are both weakened, and the fraction of gauche-conformer in the POE chain increases, whereas the alkyl chain adjacent to the POE chain remains, taking a rather trans-zigzag conformation. The enhanced fraction of gauche-conformer in the POE chain suggests that the POE chain has a helical structure in this phase. The increase in temperature within the H1 region causes a conformational change in both the POE chain and the alkyl chain of the surfactant to a more disordered structure. Among the phases of V1, Lα, and liquid, no significant difference is seen in the conformational structure and interaction with water molecules of the surfactant.

Interfacial Behavior of Mixed Systems of Glycerylether-Modified Silicone and Polyoxyethylene-Modified Silicone

Undecylglycerylether-modified silicone (GES; the glycerylether-type surfactant with a silicone segment and alkyl chains (carbon number, 11) as the hydrophobic portion) forms a molecular aggregate (M.A.) with a small amount of water. This M.A. is similar to the reversed hexagonal liquid crystal formed by α-mono long-chain alkylglycerylether (3-isooctadecyloxy-1,2-propanediol; GE). From the investigation of the phase behavior in the water/GES/polydimethylsiloxane (PDMS) ternary system, a wide three-phase region of water (W)+M.A.+oil (O) was observed. As this M.A. is insoluble in PDMS and easily orients in the interface between water and PDMS, the high water content silicone W/O emulsion using GES as a surfactant is well stabilized. However, as the PDMS content increased this W/O emulsion became less stable. In order to improve this stability, mixtures of GES and polyoxyethylene-modified silicone (PS) were applied to the silicone emulsion as co surfactant. By application of a PS with a methyl group at the end cap of the polyoxyethylene chain (PSM), the emulsion became most stable at a GES/PSM ratio of 1 : 2, and at the same time, the interfacial tension between the oil phase and the water phase became minimal. The reason for this was studied by the measurement of spin–lattice relaxation times (T1) of the alkyl chains of GES in the GES/PS/water system by 13C NMR. We assumed that the W/O silicone emulsions were stabilized by the efficient orientation of the aggregates in the interface between the silicone phase and the water phase by using PSM as a cosurfactant.

The cross-sectional headgroup area of nonionic surfactants; the influence of polydispersity

In this work, we have measured surface tension as a function of concentration of pure and technical nonionic ethoxylated surfactants. Critical micelle concentration(CMC) values, surface tension at the CMC and the cross-sectional headgroup areas are compared. It is shown that the CMC does not depend significantly on the polydispersity of the polyoxyethylene chain. However, the surfactant headgroup area, as determined from the surface tension plots, is much smaller for polydisperse surfactants than for homologue pure surfactants. This is proposed to be due to selective adsorption of the shorter polyoxyethylene species at the surface. For the same reason, the surface tension at the CMC is lower for technical surfactants than for homologue pure species.

Study of the structure of Triton X-100 micelles in polyacrylamide aqueous solution by 2D heteronuclear Overhauser enhancement spectroscopy

Two-dimensional nuclear Overhauser enhancement (2D NOESY) and two-dimensional heteronuclear Overhauser enhancement (2D HOESY) experiments were performed on Triton X-100 (TX-100-polyacrylamide (PAAM) aqueous solution at concentrations of 104 gl(-1) TX-100 and 40 gl(-1) PAAM. The absence of the NOESY cross peaks between the protons of TX-100 and PAAM and their presence among TX-100 molecules significantly imply that interaction among the protons of TX-100 molecules is far stronger than that between the protons of TX-100 molecules and PAAM even at very high concentration. There are no HOESY cross peaks of protons of the system with either the carbonyl or the carboxylic carbon nuclei of PAAM. Therefore, there is no evidence for either hydrophobic (by 2D NOESY) or hydrophilic interaction (by 2D HOESY) between TX-100 and PAAM in aqueous solution. The appearance of cross correlation peaks between hydrophobic protons and hydrophilic carbon nuclei and Vice versa of the same pairs of groups in the 2D HOESY map gives strong evidence for the coiled and folded feature of the loosely packed hydrophilic chain of TX-100 upon micellization. This suggests that the conformation of the hydrophilic polyoxyethylene chain remains unchanged as the concentration of TX-100 increases even up to about 104 gl(-1). Copyright (C) 2001 John Wiley & Sons, Ltd.

Study of the structure of Triton X‐100 micelles in polyacrylamide aqueous solution by 2D heteronuclear Overhauser enhancement spectroscopy

Two-dimensional nuclear Overhauser enhancement (2D NOESY) and two-dimensional heteronuclear Overhauser enhancement (2D HOESY) experiments were performed on Triton X-100 (TX-100–polyacrylamide (PAAM) aqueous solution at concentrations of 104 g l−1 TX-100 and 40 g l−1 PAAM. The absence of the NOESY cross peaks between the protons of TX-100 and PAAM and their presence among TX-100 molecules significantly imply that interaction among the protons of TX-100 molecules is far stronger than that between the protons of TX-100 molecules and PAAM even at very high concentration. There are no HOESY cross peaks of protons of the system with either the carbonyl or the carboxylic carbon nuclei of PAAM. Therefore, there is no evidence for either hydrophobic (by 2D NOESY) or hydrophilic interaction (by 2D HOESY) between TX-100 and PAAM in aqueous solution. The appearance of cross correlation peaks between hydrophobic protons and hydrophilic carbon nuclei and vice versa of the same pairs of groups in the 2D HOESY map gives strong evidence for the coiled and folded feature of the loosely packed hydrophilic chain of TX-100 upon micellization. This suggests that the conformation of the hydrophilic polyoxyethylene chain remains unchanged as the concentration of TX-100 increases even up to about 104 g l−1. Copyright © 2001 John Wiley & Sons, Ltd.

Small-Angle Neutron-Scattering Studies of Nonionic Surfactant Vesicles

Small-angle neutron-scattering (SANS) studies have been performed on potential drug delivery vesicles formed from 1,2-di-O-octadecyl- and 1,2-di-O-hexadecyl-rac-glycerol-3-(ω-methoxydodecaethylene glycol) (2C18E12 and 2C16E12, respectively). The 2C18E12 vesicles are shown to be delimited by single bilayers 55 Å thick, while the 2C16E12 vesicles are more likely delimited by twin bilayers (with lamellae thicknesses of 104 Å). For both types of surfactant the molecular interfacial areas occupied in the vesicle bilayers are calculated to be ∼100 Å2. Through model fitting of the SANS data, approximating the vesicle lamellae as infinite sheets, it is shown that the lamellae have undulating (rather than perfectly flat) surfaces, with a small proportion of the surfactant's polyoxyethylene chains intermixed with the hydrocarbon chains, and a rather low level of headgroup hydration (of the order of 1 H2O per oxyethylene unit). In the presence of 0.15 M NaCl (used as a crude approximation to human blood plasma), the 2C18E12 vesicle lamellae are completely unaffected, while the 2C16E12 vesicles have mean lamellae thicknesses that are reduced by ∼20%, possibly because the salt causes changes in the relative proportions of unilamellar and bilamellar vesicles in the samples.

Conformational Dependence of Triton X-100 on Environment Studied by 2D NOESY and 1H NMR Relaxation

Conformation of Triton X-100 (TX-100) in the bulk and in aqueous solutions at concentrations higher and lower than the critical micellar concentration (cmc) was studied by NMR relaxation, two-dimensional nuclear Overhauser enhancement spectroscopy (2D NOESY), and molecular simulation by HYPERCHEM. Results show that motion of TX-100 in dilute solution (0.5 cmc) is in the extreme narrowing condition. Molecules are in the single molecular state with an extended polyoxyethylene chain. In forming micelles, these hydrophilic polyoxyethylene chains, staying in the exterior of the micellar core, coil, bend, and align along the surface of the TX-100 micellar core, forming a layer thick in dimension and loose in structure around the micellar core with a certain number of water molecules included. This hydrophilic layer is in contact with the solvent, water, keeping the micellar solution stable. The micelle is spherical at 10 cmc. Motions of all of the protons of TX-100 in the bulk, even of those on the polyoxyethyl...

SOLUBILIZATION OF OIL IN DISCONTINUOUS CUBIC LIQUID CRYSTAL IN POLY(OXYETHYLENE)n OLEYL ETHER SYSTEMS

The structural change of the discontinuous cubic (I1) phase upon addition of oil (heptane, decane, and hexadecane) is investigated by small-angle x-ray scattering. In polyoxyethylene oleyl ether (C18.1EOn) systems having long polyoxyethylene chain (n =19.2, 30.1, and 50.8), the I 1 phase is formed in a wide concentration range. Only in C18.1EOnEO19.2EOn systems, the structure of the I1 phase changes from body-centered to face centered cubic lattice upon addition of oil. According to the analysis of the change in effective cross-sectional area, the solubilization of hexadecane increases the repulsion between polyoxyethylene chains, while solubilization of heptane makes it decrease. The solubilization of decane keeps the repulsion constant. Since the repulsion hampers the curvature change due to the solubilization, the solubilization capacity is in the order, heptane>decane>hexadecane. The oil penetration and nonpenetration into the palisade layer are also discussed in term of the change in the effective volume of the lipophilic part in the surfactant molecule.

Modelling of detergency of oxyethylated alcohols

Detergency of narrow and broad range distributed oxyethylated alcohols was correlated with various structural (average degree of oxyethylation and distribution parameter of the polyoxyethylene chain) and physicochemical parameters (refractive index, surface tension at critical micelle concentration, cloud point, hydrophile lipophile balance, molar volume and temperature). Statistically valid equations were derived which permit calculation of the detergency of oxyethylates. Distribution parameter of the polyoxyethylene chain, cloud point, hydrophile lipophile balance and the surface tension at critical micelle concentration are the most important descriptors needed for such a prediction. © 2000 Society of Chemical Industry

Optical behavior of an associating polymer under shear flow

Flow birefringence and dichroism experiments are used to study the behavior of solutions of a hydrophobic ethoxylated urethane with a molecular weight of 35 000 g/mol and a C16 hydrophobic end cap in a concentration range around C*. Relaxation experiments after step shear have shown the existence of two relaxation processes. The first relaxation process with a characteristic time, τshort≈0.1 s, independent of concentration, has been attributed to the lifetime of an end group in a micelle and subsequent relaxation through a Rouse process. The second relaxation process (τlong≈300 s), has been attributed to the relaxation of aggregates of polyoxyethylene chains. They induce a small dichroism in the solutions and damped oscillations in start-up shear flows at low-shear rates. Upon cessation of steady-shear flow, the two relaxations are still observed, the amplitude of the short time one increasing with shear rate. The origin of this long-time relaxation, which is not observed in classical rheological measurements, is attributed to the presence of organic impurities remaining from the chemical modification of the polymer. Extensive purification of the polymer leads to the disappearance of these impurities and consequently of the long relaxation process.

Modulation of interaction of polycations with negative unilamellar lipid vesicles

Interactions of small unilamellar negative vesicles composed of diphosphatidylglycerol (cardiolipin, CL 2−), 20 mol%, and phosphatidylcholine (egg yolk lecithin, EL), 80 mol%, with various cationic polymers (CP) derived from poly(4-vinylpyridine) (PVP) were studied in water and water–salt solutions by means of photon correlation spectroscopy, microelectrophoresis, conductometry, and fluorescence techniques. The linear charge density and hydrophilic lipophilic balance of CPs were varied by quaternization of PVP with various amounts of different alkyl bromides (ethyl-(2), heptyl-(7), dodecyl-(12), cetyl-(16)). Substantial differences were observed in the behavior of exhaustingly N-ethylated PVP (CP2) and PVP N-ethylated to 50 mol% (CP2(50)) or 30 mol% (CP2(30)). All of them adsorb to the CL 2−/EL vesicle membrane, neutralizing the surface negative charge and causing aggregation of the vesicles. However, CP2, a polycation with a maximum linear charge density, strongly enhances transfer of the negative lipid ions from the inner to outer bilayer leaflet, while CP2(50) and CP2(30) do not. Adsorbed CP2 does not disturb integrity of the vesicle membrane and can be completely removed from the surface of aggregated vesicles by adding a simple salt (NaCl) or a negative linear polyelectrolyte (polyacrylic acid (PAA) sodium salt). Such removal is followed by release of the original vesicles. In contrast to that, adsorbed CP2(50) or CP2(30) produce some leak through the lipid bilayer and cannot be completely desorbed either by increasing ionic strength or adding an excess of PAA. The probable reason of these differences is discussed. PVP partially N-alkylated with dodecyl or cetyl bromides (3 mol%) and then completely N-ethylated (CP2,12 and CP2,16), also having a maximum linear charge density, adsorbs to the negative vesicle surface as a result of both electrostatic binding and hydrophobic interaction. Bulky hydrocarbon pendant groups incorporate into the inner bilayer compartment. Similarly to CP2(50) and CP2(30), CP2,12 and CP2,16 cannot be removed from the surface either by adding the simple salt, or an excess of PAA. However, in contrast to CP2(50) and CP2(30), the polycations with the bulky hydrocarbon pendant groups do not cause any leak through the vesicle membrane. Finally, we have succeeded to prepare the ternary vesicles also composed of 20 mol% of CL 2−, but partially replacing EL for polyoxyethylene 20 cetyl ether (Brij 58) (up to 30 mol%). The CL 2−/EL/Brij vesicle carries a hydrophilic corona formed by polyoxyethylene chains exposed into water, while hydrophobic cetyl radicals are incorporated in the lipid bilayer. The CL 2−/EL/Brij vesicles adsorb all studied CPs similar to the binary CL 2−/EL vesicles. This means that polyoxyethylene corona is permeable for polycationic species restricting neither electrostatic binding nor incorporation of bulky hydrocarbon groups of CP2,16 into the membrane. However, the corona effectively stabilizes the CP-vesicle complexes against aggregation when the membrane surface is neutralized.

Mixing Effect of Polyoxyethylene-Type Nonionic Surfactants on the Liquid Crystalline Structures

An effective cross-sectional area per surfactant molecule at hydrophobic interfaces of aggregates, aS, in hexagonal (H1) and lamellar (Lα) liquid crystals was calculated in homogeneous and mixed polyoxyethylene dodecyl ether systems as a function of polyoxyethylene (EO) chain length by means of small-angle X-ray scattering. The aS increases with increasing the EO chain length. The aS in the mixed surfactant system is considerably smaller than that in the single surfactant system, even if the average EO chain length is the same. The reduction of aS is larger than that predicted by ideal mixing of the surfactants. Moreover, if the EO chain lengths of the surfactants are more separated, the aS is smaller. The shapes of surfactant self-organizing structures may be governed by the balance of the attractive and the repulsive forces acting at the hydrophobic interfaces of the aggregates. According to this consideration, the mixing effect of surfactants with the different EO chain lengths on the aS in the Lα phase was discussed. It is considered that the surfactant molecules are tightly packed in the aggregates since the reduction in repulsion force takes place in the excess EO chain part of the hydrophilic surfactant longer than the short EO chain of the lipophilic one. The lower surface tensions and the better stability of macroemulsions and the large solubilizing capacity of microemulsions result from the mixing effect.

Glucopyranoside Recognition by Polypyridine-Macrocyclic Receptors Possessing a Wide Cavity with a Flexible Linkage.

New polypyridine-macrocyclic receptors for glucopyranosides were designed and synthesized. The artificial receptors possess a terpyridine skeleton as a hydrogen-bonding site and a flexible polyoxyethylene chain as a bridge for the macrocyclic structure, in which the cavity of the receptors is large enough to incorporate pyranosides. The receptors showed high affinities for n-octyl beta-(D)-glucopyranoside, and selective binding of the receptors was observed between epimeric pyranosides. The results obtained in this paper demonstrated versatility of the terpyridine skeleton as a hydrogen-bonding site for saccharides.

Analysis of ethoxylated fatty amines. Comparison of methods for the determination of molecular weight

AbstractSpecific lengths of the fatty and polyoxyethylene chains of ethoxylated fatty amines are critical to their performance in specific applications, and thus the ability to characterize these surfactants accurately is crucial. Normal‐phase high‐performance liquid chromatography (HPLC) and matrixassisted laser desorption ionization‐time of flight (MALDI‐TOF) mass spectrometry methods were developed to determine with accuracy the molecular weight and degree of ethoxylation of ethoxylated fatty amines. Ethoxylated fatty amines were analyzed using these methods, and comparison was made to molecular weight determinations using proton nuclear magnetic resonance (NMR), neutralization equivalent weight, and hydroxyl value methods. Molecular weight results from normalphase HPLC analyses were in very good agreement with MALDI‐TOF results, typically varying less than one ethylene oxide unit. A reversed‐phase HPLC method was developed to determine concentrations of polyethylene glycols (PEG) and fatty homologs. PEG interfered with molecular weight determinations by NMR, neutralization equivalent weight, and hydroxyl value methods. PEG caused no interference with molecular weight determinations by normal‐phase HPLC and MALDI‐TOF methods.

Thermosensitive networks based on high molecular weight polyoxyethylene and N -isopropylacrylamide

γ- and UV-irradiation was successfully used for the preparation of mixed networks on the basis of high molecular weight polyoxyethylene (POE) and/or N-isopropylacrylamide and poly(N-isopropylacrylamide) (PNIPAAm). These gels preserve the swelling transition temperature of the pure PNIPAAm and shrink faster above this temperature due to the hydrophilic POE chains. It was found that in a collapsed state these gels retain alkaline organic salts from aqueous solutions.

The length of the polyoxyethylene chain in the Triton X detergents modulates the apparent activation of neurosteroid sulfatase in bovine brain

The effect of the Triton X series on the solubilization and enzyme activity of neurosteroid sulfatase (NSS) in the bovine midbrain was investigated. Triton X-100 and X165 stimulated NSS activity in the bovine midbrain, while Triton X-305 did not. This apparent activation was attributed to the action of the detergents, and not to the latency of the enzyme or the removal of some inhibitory substance from the microsomes. The maximum stimulation was obtained when the length of the polyoxyethylene chain of the detergent was 16.

The Physicochemical Behavior of Phytosterol Ethoxylates

In this work the physicochemical behavior of a series of phytosterol ethoxylates in water is presented. The influence of the length of the polyoxyethylene chain is studied. The surfactant solutions have been examined by means of birefringent microscopy, surface tension, self-diffusion1H NMR, dynamic and static light scattering, and rheology. The surfactants with a hydrophilic chain of 10 oxyethylene units or more gave a micellar region. The CMC values were generally very low and a reverse relationship between the CMC value and the polyoxyethylene chain length was obtained. The time required to reach equilibrium surface tension was very long, more than 150 min. For the hydrophobic surfactants large lamellar regions appeared while for the more hydrophilic surfactants cubic and hexagonal structures were present which remained stable up to temperatures of 100°C. In the micellar region prolate aggregates were formed which showed “ghostlike” behavior, consisting of cross-linked micelles with very fast relaxation times.

Solution behavior of a surfactant aldehyde–the oxidation product of an alcohol ethoxylate

It has previously been shown that alcohol ethoxylates readily undergo autoxidation and that one of the major oxidation products is the surfactant aldehyde, i.e. an ethoxylate carrying a –CH 2CHO group at the terminal end of the polyoxyethylene chain. In this work the cloud point, phase behavior and aggregation characteristics of the surfactant aldehyde produced by oxidation of C 12H 25(OCH 2CH 2) 5OH (C 12E 5) are determined and compared with the values obtained with the parent surfactant. It was found that the physico–chemical behavior of the two species was very similar, which indicates that a considerable portion of the aldehyde group is in hydrated state, i.e. the surfactant aldehyde consists of a mixture of aldehyde in carbonyl form and the corresponding geminal diol. The cloud point of the surfactant aldehyde decreased rapidly with time, even when it was stored at low temperature. Also the parent surfactant and its homologue C 12E 6 exhibited a decrease in cloud point during storage. For instance, a 1% aqueous solution of C 12E 6 showed a cloud point decrease from 62 to 32°C after 4 months storage at 40°C. Such a change in solution behavior can have important practical implications.

Interfacial activity of narrow‐range alcohol oxyethylates

AbstractSurface and interfacial tension isotherms for narrow‐range distribution ALFOL 1214 alcohol oxyethylates were determined and compared with those obtained for broad‐range alcohol oxyethylates. Various adsorption parameters were estimated. The effectiveness of surface tension reduction decreases when the length of polyoxyethylene hydrophile increases. Micellization is observed at log cmc ranging from −4.7 to −3.3. Effects of the length and distribution of the polyoxyethylene chain on cmc are very small. A minimum of Amin/Nav0.5 is obtained for Nav=8, where Amin and Nav denote the minimum interfacial area occupied by a statistical molecule at the saturated interface and the average degree of oxyethylation, respectively. The interface becomes saturated at pC20=−5.61±0.35, where pC20 denotes the logarithm of concentration required to obtain the surface pressure equal to 20 mNm−1. The highest and lowest values of the surface excess at saturation and the free energy of adsorption, respectively, are obtained for an average degree of oxyethylation equal to 8. Parameters are correlated with the average degree of oxyethylation and the oxyethylene chain distribution parameter according to empirical second‐order polynomials. Small differences in adsorption abilities at the water/air interface are only observed for narrow‐ and broad‐range distributed oxyethylates. The differences become important for adsorption at the hexadecane/water interface. The lowest values of interfacial tension are obtained for narrow‐range oxyethylates with Nav=7 and 8. The Krefeld fabric detergency tests indicated that the best detergency was observed for alcohol oxyethylates with Nav=5–7. Narrow‐range oxyethylates exhibit somewhat better washing abilities than the broad‐range products. No relationship between detergency of alcohol oxyethylates and their abilities to adsorb at the water/air and water/hydrocarbon interfaces is observed.