Homogeneous Micellar Solutions Research Articles

Nonlinear dynamics in micellar surfactant solutions. II. Diffusion

We discuss diffusion in micellar surfactant solutions in a form appropriate for analyzing experiments that involve large deviations from equilibrium. A general nonlinear dynamical model for inhomogeneous systems is developed that describes the effects of diffusion and micelle kinetics as a set of coupled partial differential equationsfor unimer concentration, micelle number concentration, average micelle aggregation number, and, optionally, the variance of the micelle aggregation number. More specialized models are developed to describe slow dynamics in situations in which the system stays in a state of partial local equilibrium or full local equilibrium. As an illustrative example of a nonlinear transport phenomenon, we discuss a simple model of diffusion from an initially homogeneous micellar solution to a rapidly created absorbing interface with fast unimer adsorption.

Precipitate Deposition around CMC and Vesicle-to-Micelle Transition of Monopotassium Monododecyl Phosphate in Water

Monoalkyl phosphate (MAP) salts are a kind of bivalent anionic surfactants. The difference of properties between half-neutralized monosalt and completely neutralized disalt is very interesting. In this study, the aggregation behavior of monopotassium monododecyl phosphate (MAP-12K) in aqueous solution with an increase in concentration was investigated by surface tension (γ), elemental analysis, gas chromatography, differential scanning calorimetry, steady-state fluorescence, and negative strained transmission electron microscopy techniques. MAP-12K aqueous solution showed some characteristics: (I) Vesicle aggregates were formed at very dilute concentration (1.2 mM). (II) The precipitate of a highly hydrophobic dimer of MAP, which was quaternary neutralized by potassium, was generated only in a certain dilute concentration region (2.7-200 mM) around the critical micelle concentration (cmc = 20 mM). (III) Vesicles spontaneously translate into micelles at the cmc. (IV) In the higher concentration above 200 mM, the solution becomes homogeneous micellar solution. All of these uncommon characteristics are thought to be caused by the generation of the dimer, which is much more hydrophobic than dissolved MAP derivatives, in the complicated chemical equilibria based on the weakly acidic character of MAP. MAP-12K aqueous solution behaves as if it is a binary mixed surfactant solution of hydrophobic dialkyl surfactant and hydrophilic monoalkyl surfactant in spite of a single component solution.

Reconstitution and AFM Observation of Photosynthetic Membrane Protein Assembly in Planar Lipid Bilayers

In purple photosynthetic bacteria, light-harvesting complex 2 (LH2) and the light harvesting-reaction center complex (LH1-RC) play the key roles of capturing and transferring light energy and subsequent charge separation. These photosynthetic apparatuses form a molecular assembly; however, how the assembly influences the efficiency of energy conversion is not yet clear. To address this issue, direct observation of the assembly at the molecular level is necessary to analyze its function. In this study, we reconstituted photosynthetic membrane proteins into artificial lipid bilayers and directly observed their assembly by AFM. The absorption spectra of the reconstituted proteins showed characteristic Qy bands of bacteriochlorophyll a that were identical to those of intact proteins. AFM observation of the reconstituted membranes revealed that LH2 and LH1-RC were successfully assembled into the lipid bilayer, and their observed structures were in good agreement with corresponding crystallographic structures. Specifically, binary proteins, i.e., LH2/LH1-RC and LH2/LH1, which form a densely packed molecular assembly, could be clearly identified at the molecular level by this method of observation. Energy transfer from LH2 to LH1-RC in a reconstituted lipid bilayer was observed by steady-state fluorescence spectroscopy. Enhanced energy transfer was confirmed in the membrane phase compared to that in a homogeneous micellar solution. Such reconstituted molecular assemblies are useful experimental platforms to investigate the relationship between supramolecular arrays and function. [DOI: 10.1380/ejssnt.2011.15]

Effect of salt on the phase behaviour of F68 triblock PEO/PPO/PEO copolymer

We studied the effect of sodium chloride on the phase behaviour of the symmetric triblockcopolymer F68 in water using direct visual observation, viscometry, small-angle x-rayscattering and microscopy. We found that salt has a destabilizing effect. The transitions fromunimer to micellar solution and from micellar solution to BCC micellar crystal occurred some20 °C lower in 1 M NaCl than in the salt-free system. Salt also induced a region of liquid–liquidcoexistence in the phase diagram at F68 concentrations wt%, with the lower critical solution temperature (or critical point) occurring at∼80 °C in 1 M NaCl. At this salt concentration and , liquid–liquid phase separation becomes metastable. A homogeneous micellar solution atthis temperature first separated into coexisting dilute and dense micellar liquids, and thenthe dense liquid would transform into a transparent () and turbid () mesophase. We tentatively identified these as the BCC cubic and lamellar(Lα) phases respectively. A more complex sequence of observations at a Pluronic concentrationof 34 wt% confirms this picture. A phase diagram for F68 in 1 M NaCl consistent with all ofour observations is proposed, as well as a ‘rule of thumb’ for interpreting the effect of salton Pluronic phase behaviour.

ET(30) Values of AOT Reverse Micelles Prepared in Supercritical Ethane

Abstract The ET(30) values in the core region of water/AOT/SC ethane micelles were determined for the first time as functions of pressure and water content of micelles (W0, [H2O]/[AOT]) at 310 K. The ET(30) values increased with increasing W0, but remained independent of pressure after system changed to a homogeneous micellar solution. The ET(30) values ranging from that observed in pure ethanol to 1,3-propanediol were obtained, with increasing W0 from 1 to 8.

Sulfatide prolongs blood-coagulation time and bleeding time by forming a complex with fibrinogen.

Sulfatides (galactosylceramide I3-sulfate), which are found in serum lipoproteins of various mammals, effectively increased prothrombin time (anticoagulant effect) and also effectively prolonged bleeding time (anti-platelet effect). When equal volumes of a homogeneous micellar solution of sulfatide and fibrinogen in phosphate-buffered saline were mixed, an insoluble complex precipitated. Analysis of the precipitated complex showed that the molar ratio of sulfatide to fibrinogen was about 400:1. These results indicate that the sulfatide micelle binds tightly to fibrinogen and thereby interferes with both fibrin gel formation (anticoagulant activity) and platelet function.

Room temperature phosphorescence of palladium(II) — coproporphyrin III complex in a precipitated nonionic surfactant micelle phase: determination of traces of palladium(II)

The palladium(II)—coproporphyrin III complex was distributed and concentrated in the surfactant phase precipitated from a homogeneous micellar solution of Triton X-100 by heating for 20 to 30 min at a temperature above its cloud point. This concentrated complex had strong phosphorescence at room temperature. Based on these findings, the room temperature phosphorimetric determination of 10 −9 M levels of Pd(II) was developed. The detection limit (signal-to-noise ratio = 3) was 2 × 10 −9 M (2.7 ng Pd 2+/15 ml), and the relative standard deviation was 2.1% for 1 × 10 −6 M (1.6 μg Pd 2+/15 ml) (6 determinations).

The physicochemical properties of aqueous mixtures of cationic-anionic surfactants: I. The effect of chain length symmetry

The solution behaviors of equimolar mixtures of cationic-anionic surfactants have been studied by means of the dynamic light scattering technique and surface tension measurements. The surface activity and the micellization properties are different for systems of different hydrophobic chain length symmetry. For systems of lower symmetry (e.g., C 6H 13NC 5H 5Br-C 12H 25SO 4Na mixture), the surface tension at cmc ( γ cmc) is rather high (above 30 mN m −1) and the mixtures form genuinely homogeneous micellar solutions above the cmc. For the systems of high symmetry (e.g., C 8H 17NC 5H 5Br-C 8H 17SO 4Na mixture), γ cmc is very low (about 24 mN m −1, near the value of pure hydrocarbon) and in the apparently homogeneous and clear mixtures slightly above cmc, the aggregates grow slowly and eventually form small droplets; as the concentration is further increased, all these solutions become turbid. We have proposed a new concept of conformation energy of aggregates to account for all these phenomena. Mixtures of octyltriethylammonium bromide and sodium octylsulfate form clear homogeneous micellar solutions in keeping with predictions based upon this concept.

FT-IR study of micelle formation in aqueous sodium n-hexanoate solutions

The application of Fourier transform infrared (FT-IR) spectroscopy to the study of aqueous surfactant solutions is shown to give valuable information concerning the the self-association of such systems. In the case of aqueous sodium n-hexanoate, progressive aggregation and sodium ion binding are demonstrated to commence at a concentration of approximately 0.75 M. A second inflection point is observed at approximately 1.75 M and is interpreted as marking the transition to a homogeneous micellar solution. The variations in previously reported critical micelle concentration values are rationalized in terms of the sensitivity of the techniques to various states of micelle formation. 26 references.