Aim of the present work is to study the effects of oil and drug concentrations on droplets size of a nanoemulsion. Newly introduced oil, palm oil esters (POEs) by Universiti Putra Malaysia researchers was selected for the oil phase of the nanoemulsion, because the oil was reported to be a good vehicle for pharmaceutical use. Nanoemulsions were prepared with different concentrations of oil and drug and their effects on droplets size were studied by laser scattering spectroscopy (Nanophox). The results of droplets size analysis shows the droplets size increase with increasing concentration of oil and drug concentrations. It can be concluded from this study, that oil and drug concentrations have an effect on the droplets size of POEs nanoemulsion system.
Gemini surfactants recently developed by our research group are introduced from the standpoints of their syntheses, aqueous solution properties, and potential applications. Two series of gemini surfactants are introduced in this short review, the first of which is the oleic acid-based gemini surfactants, and the second is the polymerizable gemini surfactants. These gemini surfactants have been developed not only as environmentally friendly materials (the use of gemini surfactants enables the reduction of the total consumption of surfactants in chemical products owing to their excellent adsorption and micellization capabilities at low concentrations) but also as functional organic materials.
Cationic surfactants containing a thioether group in the hydrophobic chain were prepared by the reaction of alkanethiol and bromocholine bromide. The aqueous solution properties of the thio-surfactants were investigated and compared with conventional cationic surfactants. The Krafft temperatures of the thio-surfactants were lower than that of alkyltrimethylammonium bromide. The critical micelle concentrations were determined by the conductivity method, and pyrene and SPQ fluorescence probe methods. A linear relation was observed for the plots of cmc vs. chain length. However, the cmc of the thio-surfactants depended on the position of the thioether group in the hydrophobic alkyl chain. It was found that the thioether group exhibited quenching ability toward SPQ fluorescence. The variation of the surfactant monomer concentration in equilibrium with micelles can be estimated from Stern-Volmer plots.
The adsorption and aggregation behaviors of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) on a hydrophobic graphite surface were examined using a novel molecular dynamics (MD) simulation with the periodic-shell boundary condition (PSBC). Differences in the adsorption behavior of SDS and CTAB molecules were clearly shown on the hydrophobic surface. Unexpectedly, the SDS molecules approached the graphite surface with their hydrophilic head groups. This unexpected approach mode was thought to be due to the aqueous layer on the graphite surface. The hydrophobic moiety of SDS molecules repeatedly adsorbed and desorbed on the graphite surface. In addition, SDS molecules kept moving on the graphite surface; thus, they did not form a stable adsorption layer. In contrast to SDS, the hydrophobic moiety of CTAB molecules approached the graphite surface at the primary step of adsorption. The hydrophobic moieties of CTAB molecules came close to each other, whereas the hydrophilic groups separated from one another. This result suggests that the CTAB molecules form molecular assemblies with a curved structure. The simulation results were consistent with the experimental observations. A clear difference between the adsorption behavior of SDS and CTAB molecules was revealed by MD simulations with PSBC.
The membrane properties of phospholipid mixtures supported on silica were studied by means of a quartz crystal microbalance with dissipation monitoring (QCM-D) technique, in situ soft-contact atomic force microscopy (AFM), and friction force microscopy (FFM). The phospholipids used in this study were di-stearoylphosphatidylcholine (DSPC) and dilauroylphosphatidylcholine (DLPC). The phospholipid films were prepared by a vesicle-fusion method, in which DSPC/DLPC mixed liposomes dispersed in an aqueous medium are adsorbed on silica and their structure is transformed into a bilayer on the substrate. The changes in QCM-D (frequency and dissipation) and friction responses of DSPC single systems (gel state at 25°C) are relatively large compared with those of DLPC single systems (liquid-crystalline state at 25°C) and those of mixed DSPC/DLPC systems. This suggests that (i) the gel-state DSPC liposomes are somewhat flattened on the silica, by keeping their solid-like molecular rigidity, whereas (ii) both the liquid-crystalline DLPC and mixed liposomes experience instantaneous structural transformation at the silica/water interface and form a normally flattened bilayer on the substrate. The friction force response is dependent on the phase state of the phospholipids, and the liquid-crystalline DLPC has a more significant impact on the overall membrane properties (i.e., the degree of swelling and the friction response on the surface) than does the gel-state DSPC.
Novel optically active carbonate-type cationics were designed and synthesized via a green method. A series of n-alkyl N,N-dimethylaminoalkyl carbonates was prepared via a two-step successive carbonate exchange reaction of diphenyl carbonate with 1-alkanol followed by the reaction of the optically active or racemic amino alcohol in the presence of triethylamine. The quaternarization of the N,N-dimethylamino group was carried out using methyl iodide. Furthermore, optically active cationics were prepared by the lipase-catalyzed enantioselective hydrolysis of the racemic cationics. Carbonate-type cationics having an isopropylene linkage showed high hydrolytic stability. They exhibited surfactant properties similar to those of the corresponding racemic cationics. Although no significant differences in the antimicrobial activities were observed owing to the stereochemistry of the cationics, the biodegradability was strongly influenced by the stereochemistry. Some optically active cationics were rapidly biodegraded by activated sludge.
Lamellar lipid layers in the stratum corneum (SC), the outermost layer of the skin, act as a primary permeability barrier to protect the body. The roles of SC lipid composition and membrane structure in skin barrier function have been extensively investigated using ex-vivo SC samples and reconstructed SC lipids in the form of multi-lamellar lipids or liposomes. The primary lipids, especially ceramide, have been found to be highly important. Atopic dermatitis (AD) is a well-known chronic inflammatory skin disease with immunologic and epidermal abnormalities of the permeability barrier; therefore, a comparison of SC lipids in AD skin with those in normal skin is a promising method to explore the mechanisms of skin barrier function. Here, we focused on the effect of sphingoids (ceramide metabolites and a minor component of the SC lipids) and their content/species on skin barrier function. A significant difference in the leakage ratio was observed between model SC lipid liposomes with a different sphingolipid ratio (sphingosine/sphinganine), with a value of 5.43 for normal skin vs. 14.3 for AD skin. This result shows a good concordance with AD mouse experiments. Therefore, an alteration in the composition of minor SC lipids resulting from a ceramide metabolic abnormality can affect the membrane integrity (i.e., skin barrier function). Small angle X-ray scattering (SAXS) measurements revealed no distinct differences in the SAXS pattern between the 3 models, with all models forming a rigid membrane (i.e., a nearly hydrated solid). According to increasing the temperature, the peaks indicated that the lamellar structures decreased in all models and that the lateral packing of lipids decreased, which suggested annealing or melting of the gel to a liquid crystal, although no distinct phase transition was observed through fluorescence anisotropy measurements. Hence, we assume that the altered sphingoid composition triggers local membrane structural changes (i.e., formation of domains or clusters).