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Despite the promising application of liposomes in wool dyeing, little is known about the mechanism of liposome interactions with the wool fiber and dyestuffs. The kinetics of wool dyeing by two dyes, Acid Green 27 (hydrophobic) and Acid Green 25 (hydrophilic), were compared in three experimental protocols:  (1) without liposomes, (2) in the presence of phosphatidylcholine (PC) liposomes, and (3) with wool previously treated with PC liposomes. Physicochemical interactions of liposomes with wool fibers were studied under experimental dyeing conditions with particular interest in the liposome affinity to the fiber surface and changes in the lipid composition of the wool fibers. The results obtained indicate that the presence of liposomes favors the retention of these two dyes in the dyeing bath, this effect being more pronounced in case of the hydrophobic dye. Furthermore, the liposome treatment is accompanied by substantial absorption of PC by wool fibers with simultaneous partial solubilization of their polar lipids (more evident at higher temperatures). This may result in structural modification of the cell membrane complex of wool fibers, which could account for a high level of the dye exhaustion observed at the end of the liposome dyeing process.

Phosphatidylcholine (PC) liposomes were able to be reconstituted inside the pig stratum corneum (SC), the outermost layer of the skin. In addition, these vesicles protected the SC tissue against the octyl glucoside surfactant (OG) effect. These abilities were examined using high-resolution low-temperature scanning electron microscopy and freeze-substitution transmission electron microscopy. The treatment of the SC with OG led to the breaking of the corneocyte envelopes and to disorganization in the intercellular lipid structure. Previous incubation of SC with PC liposomes reduced the alterations induced by the OG, this protection being associated with the incorporation of about 10% of PC to the SC. Intact PC vesicles were found in the intercellular lipid domain of the SC samples treated first with PC liposomes and second with OG, after washing in water. The OG/PC molar ratio incorporated in these SC samples corresponded to that in which the transition micelle−lamellae occurs by dilution. Hence, the presence of PC vesicles inside the SC is explained by the incorporation of an OG/PC micellar system and the subsequent reconstitution in PC vesicles by continuous dilution during washing.

Sucrose, maltose, leucrose, maltotriose, and β-D-dodecylmaltoside fatty acid esters with acyl chains having 12 to 18 carbon atoms were enzymatically synthesized and their surface properties −critical micelle concentration, surface tension in water, and interfacial tension between water and xylene− were evaluated. The synthesized esters present critical micelle concentration (CMC) values in the range 2−250 μM with surface tension values ranging from 24.5 to 36.5 mN/m, and interfacial tension values from 1.0 to 9.4 mN/m depending on the compound. For the same acyl chain, CMC values were in the order maltotriose < leucrose < maltose < sucrose. The longest the fatty acid displays the lowest CMC, showing a decrease of one order of magnitude when the chain length was increased by six carbon atoms. β-D-dodecylmaltoside monoesters exhibited high efficiency as water-in-oil emulsifiers. All the newly synthesized di- and trisaccharide-based surfactants displayed better surface-active properties and higher solubility compared with similar monosaccharide esters.

Thermotropic physicochemical techniques such as differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and electron paramagnetic resonance (EPR) were applied to liposomes made up of internal wool lipids. These vesicles can be regarded as a model of wool membranes. Differences in fluidity obtained from EPR allow us to deduce a high rigidity of the polar external section of the vesicle in contrast to the high fluidity of the hydrophobic internal section, which accounts for the thermotropic properties of the liposome. The coincidence of the thermotropic changes obtained with the EPR, FTIR, and DSC techniques allows us to infer a reversible phase transition temperature in the range of 30−40 °C, indicating a transition from a mixture of hexagonal gel−liquid crystal state to a single liquid crystal state.

The aggregation state of the microfilm produced by the glycoprotein (GP) excreted by a new Gram-negative species, Pseudoalteromonas antarctica NF3, on a support of phosphatidylcholine (PC) liposomes was examined by transmission electron microscopy (TEM). Image analysis profiles of digitized freeze-fracture TEM micrographs show that the outer covering film (PC:GP weight ratio 8:2) consisted in a multilayer structure formed by 9−10 layers. The periods of the average distance of the pattern ordering in layers were of about 2.3 nm, and the thickness of the complete film was of about 25 nm. The fact that the protective effect against sodium dodecyl sulfate of PC liposomes prepared in the presence of GP sharply increased with respect to that obtained when liposomes were only outwardly coated by this compound indicates that in the first case the GP multilayer structure also affected the inner monolayer of liposomes. Image analysis of freeze-fracture TEM showed that the coatings present in these two types of liposomes had the same structure despite that the number of external layers in the first case was almost the half than that in the second.

The ability of an exopolymer of glycoproteic character (GP) excreted by a new Gram-negative species Pseudoalteromonas antarctica NF3, to coat phosphatidylcholine (PC) liposomes and to protect these bilayers against the action of the sodium dodecyl sulfate (SDS) surfactant was investigated. Transmission electron microscopy micrographs of freeze fractured liposome/GP aggregates reveal that the addition of GP to liposomes led to the formation of a film (polymer adsorbed onto the bilayers) that tightly coated PC bilayers. The complete coating was achieved at a PC:GP weight ratio of about 9:1. Higher GP amounts resulted in a growth of this film, which exhibited at the highest GP proportion (50% of GP in weight) a multilayered structure. An increasing resistance of PC liposomes to be affected by SDS at both subsolubilizing and solubilizing levels occurred as the proportion of GP in the system rose, although this protective effect was more effective at low GP proportions (PC:GP weight ratios from 9:1 to 8:2). Although a direct dependence was found between the growth of the enveloping structure and the resistance of the coated liposomes to be affected by SDS, the best protection occurred when this structure was a thin film (thickness of about 20−25 nm for a PC:GP weight ratio ranging from 9:1 to 8:2).

The mechanisms governing the interaction of equimolecular mixtures of nonylphenol polyethoxylated with 10 mol of ethylene oxide (NP(EO)10) and sodium dodecyl sulfate (SDS) with phosphatidylcholine (PC) liposomes were investigated. Permeability alterations were detected as a change in 5(6)-carboxyfluorescein (CF) released from the interior of vesicles and bilayer solubilization was detected as a decrease in the static light scattered by liposome suspensions. At the subsolubilizing level, a maximum bilayer/water partitioning of surfactant mixture was reached at 30−50% CF release, which correlated with the increased presence of SDS in the bilayers. However, transition stages between 60% CF release and 100% light scattering corresponded to the increased presence of NP(EO)10 in these structures. The surfactant mixture showed throughout the interaction a much higher affinity with bilayers and a higher ability to saturate and solubilize these structures than that reported for the anionic component. A direct dependence was established in the initial interaction steps (effective molar ratio of surfactant to phospholipid in bilayers (Re) lower than 0.190) between the growth of vesicle fluidity and the maximum bilayer/water partitioning of the surfactant mixture (K). These parameters also depended on the surfactant saturation of the outer vesicle leaflet. A linear dependence was also established during solubilization between the decrease in both the surfactant−PC aggregate size and the scattered light of the system and the composition of these aggregates (Re). The fact that the free surfactant concentration at subsolubilizing and solubilizing levels was respectively lower than and similar to the critical micelle concentration (cmc) of the surfactant mixture indicates that permeability alterations and solubilization were determined respectively by the action of the surfactant monomer and by the formation of mixed micelles. This finding supports the generally admitted assumption, for single surfactants, that the concentration of free surfactant must reach the cmc for solubilization to occur and highlights the influence of the negative synergism of this surfactant mixture on the free surfactant concentration needed to saturate or solubilize liposomes.

The subsolubilizing interactions of three alkyl sulfates (chain lengths C10, C12, and C14), with liposomes modeling the stratum corneum lipid composition, were investigated. Liposomes were formed from a lipid mixture containing by weight 40% ceramides, 25% cholesterol, 25% palmitic acid and 10% cholesteryl sulfate. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients (K) were determined by monitoring the increase in the fluorescence intensity of liposomes due to the 5(6)-carboxyfluorescein (CF) released from the interior of vesicles. The free surfactant concentration was always lower than the critical micelle concentration. At the two interaction levels studied (50% and 100% CF release) the tetradecyl sulfate showed the highest ability to release the CF trapped in the liposomes (lowest Re values) and the highest degree of partitioning into the bilayers (highest K values). Whereas stratum corneum liposomes were more resistant to the action of alkyl sulfates than were phosphatidylcholine (PC) liposomes, the degree of partitioning of these surfactants into stratum corneum bilayers was always greater than that reported for PC ones.