Soapwort (Saponaria officinalis L.) Extract vs. Synthetic Surfactants-Effect on Skin-Mimetic Models.

Our skin is continuously exposed to different amphiphilic substances capable of interaction with its lipids and proteins. We describe the effect of a saponin-rich soapwort extract and of four commonly employed synthetic surfactants: sodium lauryl sulfate (SLS), sodium laureth sulfate (SLES), ammonium lauryl sulfate (ALS), cocamidopropyl betaine (CAPB) on different human skin models. Two human skin cell lines were employed: normal keratinocytes (HaCaT) and human melanoma cells (A375). The liposomes consisting of a dipalmitoylphosphatidylcholine/cholesterol mixture in a molar ratio of 7:3, mimicking the cell membrane of keratinocytes and melanoma cells were employed as the second model. Using dynamic light scattering (DLS), the particle size distribution of liposomes was analyzed before and after contact with the tested (bio)surfactants. The results, supplemented by the protein solubilization tests (albumin denaturation test, zein test) and oil emulsification capacity (using olive oil and engine oil), showed that the soapwort extract affects the skin models to a clearly different extent than any of the tested synthetic surfactants. Its protein and lipid solubilizing potential are much smaller than for the three anionic surfactants (SLS, ALS, SLES). In terms of protein solubilization potential, the soapwort extract is comparable to CAPB, which, however, is much harsher to lipids.

Surface activity of saponin from Quillaja bark at the air/water and oil/water interfaces.

Surface activity of Sigma's Quillaja bark saponin (QBS) was studied by means of dynamic interfacial tension and surface dilational rheology at three fluid/fluid interfaces with the polarity of the non-aqueous phase increasing in the order: air/water, tetradecane/water and olive oil/water. The equilibrium interfacial tension isotherms were fitted to the generalized Frumkin model with surface compressibility for the air/water and tetradecane/water interfaces, whereas the isotherm for the third interface displays a more complex shape. Upon fast compression of a drop of concentrated "Sigma" QBS solution immersed in olive oil, a clearly visible and durable skin was formed. On the other hand, no skin formation was noticed at the air/water interface, and only a little at the tetradecane/water interface. Addition of a fatty acid, however, improved slightly the skin-formation ability of the QBS at the latter interface. The surface behavior of the QBS from Sigma was compared with that from Desert King, Int. ("Supersap"), employed in a recent study by Stanimirova et al. [22]. The two products exhibit different areas per molecule in the saturated adsorbed layer (0.37nm(2) vs. 1.19nm(2) for "Sigma" and "Supersap", respectively). Also their surface rheology is different: although both QBSs form predominantly elastic layers, for "Sigma" the surface storage modulus, εr=103mNm(-1), while for "Supersap" εr=73mNm(-1) at 10(-3)moll(-1) (i.e., around their cmc). The two saponin products exhibit also different ionic character, as proven by the acid-base titration of their aqueous solutions: QBS from Sigma is an ionic surfactant, while the "Supersap" from Desert King is a non-ionic one.

Surfactant mixtures at the oil-water interface.

We report the structural study of mixed monolayers of partially deuterated N,N'-di-hexadecyl-(d33)-4,13-diaza-18-crown-6 ether (d-ACE16) and palmitic acid (PA) at the oil-water interface, in order to understand the mechanism of metal ion transport through Permeation Liquid Membrane (PLM) devices. The composition of the mixed monolayers remains constant with increasing spread amount and the saturation of the interface is achieved at a relatively low spread amount. The excess PA material is accommodated in the oil phase, playing an important role in equilibrating the interfacial concentration of ACE-16. The presence of PA increases the surface concentration of ACE-16 at low spread amount and facilitates its dissolution into the oil phase at the high spread amount. The result suggests a dynamic exchange between the bulk phase and the interface ensuring a continuous turnover which reflects their relevance in PLM devices. The conclusions regarding the role of a fatty acid in regulating the surface concentration of the alkylated azacrown ether and its dominant role in the bulk transport of metal ions through the membrane are consistent with the results of macroscopic studies reported earlier.

Biosurfactant-protein mixtures: Quillaja Bark Saponin at water/air and water/oil interfaces in presence of ß-lactoglobulin.

The adsorption kinetics of mixtures of a biosurfactant Quillaja Bark Saponin (QBS) with a globular protein, ß-lactoglobulin (ß-LG) at the water/air and water/tetradecane interfaces was investigated by measuring dynamic interfacial tension with axisymmetric drop shape analysis (ADSA) and maximum bubble pressure (MBP) techniques. With bulk concentration of ß-LG fixed at 10(-7) M, the most pronounced synergistic effects in the rate of the QBS adsorption at both interfaces were observed at low biosurfactant concentrations (5 × 10(-7)-1 × 10(-5) M). The synergistic effect due to a protein-biosurfactant complex formation is clearly noticeable, yet less pronounced than, e.g., previously studied QBS/lysozyme mixtures. The surface pressures attained at water/oil interface are higher than in the water/air system, although, at high biosurfactant/protein ratios, the presence of ß-LG decelerates adsorption of the QBS/ß-LG complex onto the water/tetradecane interface. In analogy to mixtures of synthetic surfactants with proteins, the adsorbed layer gets dominated by QBS at higher biosurfactant concentrations, although the presence of ß-LG affects the surface pressures attained even at QBS/ß-LG ratios as high as 10(4). The synergistic effects are much less noticeable in foamability and emulsion formation/stability, as probed by the modified Bikerman's and dynamic light scattering (DLS) techniques, respectively.

Stabilization of alkylated azacrown ether by fatty acid at the air-water interface.

The adsorbed amount of partially deuterated dihexadecyl-diaza-18-crown-6 ether (d-ACE16) in the presence of different chain length fatty acids as a function of surface pressure was determined by neutron reflectometry technique. The highest adsorbed amount of the azacrown ether was observed for the mixture of ACE16 with hexadecanoic (palmitic) acid, pointing to the importance of chain length matching between the two species for optimum stabilization of the mixed monolayer. The contrast variation technique was used to estimate the contribution to the total adsorbed amount from stearic acid and ACE16. It was found that the mixed Langmuir monolayer is stable against dissolution up to a surface pressure of 20 mN m(-1). Above this pressure, however, the spread and adsorbed amounts start to deviate, indicative of partial dissolution into the aqueous subphase. The consequences of this behavior for the transport of metal ions through the interfaces of permeation liquid membranes (PLMs) are discussed.

Azacrown ether-copper(ii)-hexanoate complexes. From monomer to 1-D metal organic polymer.

The synthesis and characterisation of two new Cu(ii)-hexanoate-azacrown ether species are described. The first monomeric complex is a "classical" macrocyclic Cu(ii) complex with two monodentate axially coordinated carboxylates serving as counterions. The second is an adduct of the former complex with the copper(ii) hexanoate paddlewheel dimer, Cu(2)(hexanoate)(4), forming an infinite 1-D chain of alternating monomer-dimer units. The electronic and magnetic properties of both species are discussed based on UV-vis, IR, X-ray and EPR studies combined with the DFT calculations. The UV-vis titration results prove that complex and the polymeric species are in equilibrium in toluene solution.

The interaction of azacrown ether with fatty acid in nonpolar solvents and at the organic-aqueous interface.

In the paper, we show that lipophilic azacrown ether (22DD) in solvents of low to intermediate polarity forms the complexes with fatty acids, like lauric or palmitic acid. Due to the weak acid-base properties of the azacrown ether-fatty acid system, no proton transfer between the two molecules was observed, as shown by IR and 1H NMR studies. The Job plot exhibits double maximum, suggesting the coexistence of two 22DD-fatty acid complexes, of 1:1 and 1:2 stoichiometry, respectively. Their stability constants were calculated by taking into account the dimerization of fatty acid in toluene. The diffusion coefficients for the free molecules and their complexes were measured with diffusion-ordered spectroscopy (DOSY) NMR in order to prove the close spatial proximity of the molecules. Interfacial tension measurements at the water-toluene interface showed that due to the presence of two decyl chains, 22DD adsorbs at the interface much stronger than dodecanoic (lauric) acid does. The shape of the adsorption isotherm for the mixture of 22DD and lauric acid suggests that the two molecules also interact at the interface in a similar manner as in the bulk of low to intermediate polarity solvents. As a result of the affinity of the fatty acid to strongly surface-active azacrown ether, the interface might be enriched with fatty acid molecules, which without 22DD shows little adsorption at the liquid-liquid interface.

Heme-protein active site models via self-assembly in water.

[structure: see text] Water-soluble models of heme-protein active sites are obtained via the self-assembly of cationic porphyrins 1 and tetrasulfonato calix[4]arene 2 (K(1.2)() = 10(5) M(-)(1)). Selective binding of ligands either outside or inside the cavity of assemblies 1.2 via coordination to the zinc center has been observed. Small ligands such as 4-methylpyridine and 1-methylimidazole are encapsulated, while the bulkier caffeine is bound outside. Assemblies Co-1.2, in which the Zn porphyrin moiety has been replaced by a Co(II) porphyrin, can act as O(2) carriers.