Interactions of alpha-tocopherol with biomembrane models: binding to dry lecithin reversed micelles.

The state of alpha-tocopherol (Vitamin E) in solutions of dry lecithin reversed micelles dispersed in an apolar medium has been investigated as a function of the Vitamin E to surfactant molar ratio (RVE) at fixed surfactant concentration by FT-IR, 1H NMR and SAXS with the aim to emphasize the role played by anisotropic intermolecular interactions and confinement effects as driving forces of its partitioning between apolar bulk solvent and polar nanodomains and of mutual Vitamin E/reversed micelle effects. It has been found that its binding strength to reversed micelles, triggered by steric and orientational constrains, is mainly regulated by specific interactions between the hydrophilic groups both of Vitamin E and surfactant. Moreover, the RVE dependence of the Vitamin E distribution constant and of the micellar size suggest that the inclusion of increasing amounts of Vitamin E in reversed micelles involves substantial changes in the structural and dynamical properties of the micellar aggregates. The occurrence of mutual effects and the partitioning of Vitamin E between hydrophilic/hydrophobic interfaces and apolar domains allow to infer some important biological implications concerning the capacity of Vitamin E to scavenge free radicals arising from hydrophilic and/or hydrophobic domains, possible variations of its local reactivity respect to that observed in bulk as well as its significant influence on the stability of biomembranes.

Spectrophotometric investigation of the binding of vitamin E to water-containing reversed micelles.

The distribution constants of vitamin E partitioned between apolar organic phase and water-containing reversed micelles of sodium bis (2-ethylhexyl) sulfosuccinate (AOT), didodecyldimethylammonium bromide (DDAB), soybean phosphatidylcholine (lecithin) and tetraethylene glycol monododecyl ether (C12E4) have been evaluated by a spectrophotometric method. The results suggest that in the presence of domains from apolar organic solvent to surfactant and to water, vitamin E is partitioned between the micellar palisade layer and the organic solvent and also that its binding strength to reversed micelles depends mainly by specific interactions between the head group of vitamin E and that of the surfactant. Moreover, in addition to the advantageous interactions between vitamin E and water, the dependence of the distribution constants upon the molar ratio R (R=[water]/[surfactant]) indicates a competition between water and vitamin E for the binding sites at the water/surfactant interface. The biological implications of the preferential location and confinement of vitamin E in water-containing reversed micelles are discussed.

Interactions of tryptophan and serotonin with biomembrane models: binding to reversed micellar systems of ionic and non ionic surfactants.

The interactions of Tryptophan (TRP) and Serotonin (5-HT), with water-containing sodium bis (2-ethylhexyl) sulfosuccinate (AOT), didodecyldimethylammonium bromide (DDAB) and tetraethylene glycol monododecyl ether (C12E4) reversed micelles have been investigated by UV absorption spectroscopy. Our results suggest that independently of the nature of the surfactant and the amount of the water encapsulated into the micellar core, TRP and 5-HT are solubilized in the micellar phase, preferring to be located in a shallow region constituted by the hydrated surfactant head groups. This is due to the amphiphilic nature of TRP and 5-HT and the biological implications are discussed.

Interactions of melatonin with membrane models: portioning of melatonin in AOT and lecithin reversed micelles.

The interaction of melatonin with water containing either sodium bis (2-ethylhexyl) sulfosuccinate (AOT) or soybean phosphatidylcholine (lecithin) reversed micelles has been investigated by UV absorption spectroscopy, at a molar ratio of melatonin:surfactant 1:800 for AOT and 1:400 for lecithin reversed micelles, and by varying the water:surfactant molar ratio (R). Our results suggest that in the presence of domains from apolar organic solvent to surfactant and to water, melatonin positions itself in the micellar phase, with a preferential location in the surfactant polar head group domain, independent of the nature of the surfactant and the amount of water encapsulated into the micellar core. Effects are due to the hydrophilic and lipophilic moieties of melatonin. The effectiveness of melatonin as an electron donor and free radical scavenger has been recently recognized. While supporting the hypothesis that melatonin may provide antioxidant protection without the benefit of receptors, present findings may suggest that the molecule could easily scavenge aqueous as well as lipophilic radicals.

The structure and the stereochemistry of atractyliretin.

The nor-kaurane diterpene Atractyliretin was obtained by acid hydrolysis of Atractyloside, a toxic substance isolated from ATRACTYLIS GUMMIFERA L (Compositae). On the basis of spectral (IR, (1)H-NMR, (13)C-NMR and MS) analysis and chemical degradation its structure and stereochemistry was identified as 4.