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We present molecular dynamics simulations of cardiolipin (CL) and CL monohydroperoxized derivative (CLOOH) monolayers to investigate the initial steps of phospholipid oxidation induced by methylene blue (MB) photoexcitation under continuous illumination. We considered different MB atomic charge distributions to simulate the MB electronic distribution in the singlet ground and triplet excited states. Simulation results allied to experimental data revealed that initial CL photooxidation probably occurs via a type II mechanism, to produce lipid hydroperoxide by singlet oxygen attack to the alkyl chain unsaturations. The resulting hydroperoxide group prefers to reside near the aqueous interface, to increase the membrane surface area and to decrease lipid packing. Interestingly, MB orientation changes from nearly parallel to the water–monolayer interface in the ground state to normal to the interface in its triplet excited state. The latter orientation favors oxidative chain reaction continuity via a type I mechanism, during which the hydrogen atom must be transferred from the hydroperoxide group to triplet MB. Taken together, the present results can be extrapolated to improve our understanding of how oxidation progresses in lipidic biomembrane, which will lead to the formation of oxidized species with shortened chains and will cause severe photodamage to self-organized systems.

The interaction of sodium dodecyl sulfate (SDS) in aqueous solution with poly(N-vinyl-2-pyrrolidone) (Mw = 55 000 g/mol) in the presence of poly(ethylene glycol) (Mw = 8000 g/mol) is investigated by electrical conductivity, zeta potential measurements, viscosity measurements, fluorescence spectroscopy, and small-angle X-ray scattering (SAXS). The results indicate that SDS−polymer interaction occurs at low surfactant concentration, and its critical aggregation concentration is fairly dependent on polymer composition. The polymer-supported micelles have average aggregation numbers dependent on surfactant concentration, are highly dissociated when compared with aqueous SDS micelles, and have zeta potentials that increase linearly with the fraction of PVP at constant SDS concentration. The analysis of the SAXS measurements indicated that the PVP/PEG/SDS system forms surface-charged aggregates of a cylindrical shape with an anisometry (length to cross-section dimension ratio) of about 3.0.

Sodium dodecyl (lauryl) sulfate (SLS)/water/decanol systems at a fixed water/SLS molar ratio of 144.0 (10 wt % SLS in water) and varying decanol/SLS molar ratios (Md) were studied through small-angle X-ray scattering (SAXS). Results from the distance and electron distribution functions retrieved from the SAXS curves show an increase in the maximum dimension of the spheroidal micelles with Md ratios of up to 0.18. At Md = 0.20, the micelle symmetries change from spherical to cylindrical, with an anisotropy (ratio between the longest and the shortest dimension) close to 1.8, according to bending energy requirements. Micellar aggregates self-assemble into cylinder-like particles with Md ratios of up to 0.40, where a cylinder → disk shape transformation is observed. The cylinder → disk transition occurs at nearly the same Md as that of the nematic cylindrical → nematic discotic liquid−crystalline phase transition in more concentrated systems. The transformation also agrees with bending energy requirements for the polar/apolar interface in mixed micelles. Furthermore, the amount of bound water per polar head remains the same in both the more diluted and the more concentrated systems.

Concentrated micellar solutions of the binary system sodium lauryl sulfate−water and the ternary system sodium lauryl sulfate−water−decanol have been studied by X-ray diffraction in the vicinity of the isotropic (I)−type I hexagonal (Hα) liquid-crystal phase transitions. Results show how decanol affects the I → Hα phase transition. In the binary system there is a close packing of micelles in a local hexagonal order in the I phase, and the Hα phase has a behavior typical of finite/hard objects. In contrast, in the ternary system the close packing is relaxed through a micellar growth, and the Hα phase has a behavior typical of infinite/flexible objects. An intriguing phase sequence Hα−nematic cylindrical (Nc) with an increase in the decanol content is also investigated, and it is attributed to a combined effect of micellar growth and change in rigidity with decanol addition.