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Air-water Interface (air-water + interface)

Distribution by Scientific Domains

Chemistry	60%

Selected Abstracts

Solubilities and surface activities of phthalates investigated by surface tension measurements

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2001
Marianne Thomsen
Abstract Aueous solutions of DEP (di-ethyl), DnBP (di- n -butyl), DnH(6)P (di- n -hexyl), and DEHP (di-[2-ethyl-hexyl])phthalates have been investigated by use of surface tension measurements at temperatures between 10 and 35°C. A tensiometric approach allows for the determination of unimeric solubilities and ,G°, which is the standard Gibbs free energy change, for the dissolution of phthalates in water. The unimeric solubility of the phthalates increase with decreasing temperature. The ,G° shows a linear increase with increasing phthalate alkyl chain length. The contribution of enthalpy (,H°) and entropy (,S°) to ,G° were calculated from the temperature-dependent solubilities. The contributions of both ,H° and ,S° are negative and increase in magnitude with increasing alkyl chain length, suggesting hydrophobic interactions between phthalates and water. The ability of different phthalates to lower the surface tension decreases with increasing alkyl chain length, whereas the relative affinity for adsorption in the air-water interface increases drastically for long-chain phthalates. Despite the low surface activity of phthalates compared with that of common surfactants, they show significant affinity for adsorption in air-water interfaces of natural surface waters. This property, combined with their low solubilities, may affect the fate of these compounds within the natural environment, because they form emulsions above unimeric saturation in aqueous media. [source]

Adsorption and rheological properties of biopolymers at the air-water interface

AICHE JOURNAL, Issue 7 2006
Rosa Baeza
Abstract Dynamics of adsorption and viscoelasticity of biopolymers (,-lactoglobulin (,-lg) + polysaccharides (PS)) at 20 °C and pH 7 have been studied. Protein concentration in the bulk phase was 0.1 wt %, and the concentration of polysaccharides (xanthan gum, ,-carrageenan, and propylenglicol alginate with different degrees of esterification and viscosity) was varied from 0.1% to 0.5 wt %. The results reveal a significant effect of surface-active and non surface-active polysaccharides on the dynamics of the formation and viscoelasticity of adsorbed films at the air-water interface. The rate of diffusion of the biopolymers increased in the mixed systems, but the effect was more significant at the highest concentration of polysaccharide (0.5 wt %). The rate of rearrangement of the adsorbed films decreased in the presence of polysaccharides as compared to the protein film. Competitive adsorption, complexation and limited thermodynamic incompatibility between ,-lactoglobulin and polysaccharide would explain the observed effects. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source]

Physicochemical characterization of branched chain polymeric polypeptide carriers based on a poly-lysine backbone

BIOPOLYMERS, Issue 3 2003
I. B. Nagy
Abstract A systematic study is reported on the physicochemical characteristics of two branched chain polymers (based on a poly- L -lysine backbone) with a general formula poly[Lys-(DL -Alam - Xi)], where X = Orn (OAK) or N -acetyl-Glu (Ac-EAK) and m , 3, using surface pressure and fluorescence polarization methods. These data are compared with those of the linear poly(L -Lys) from which OAK and Ac-EAK are derived. These two polymers show a moderate surface activity, able to form stable monomolecular layers at the air-water interface. Poly(L -Lys), the most hydrophilic, has the lowest surface activity. The interaction of these polymers with phospholipid bilayers either neutral or negatively charged was studied with vesicles labeled with two fluorescent probes: ANS and DPH. Results indicate that these polymers are able to accommodate in their internal structure, mainly through electrostatic interactions, a certain amount of ANS marker molecules, but fluorescence increases of the ANS-polypeptide complexes were so low that its influence in further polarization measurements could be discarded. After interaction with liposomes, these polymers induce an increase in the polarization of the probes, thus indicating a rigidification of the bilayers. Electrostatic forces seem to be very important in this interaction; cationic polymers are clearly more active, with PG-containing liposomes, than Ac-EAK. Moreover, in these assays poly(L -Lys) behaves as the more active compound. This fact is probably due to its major ability to form ,-helical structures that could insert easily in the bilayers. These results indicate that the polymeric structures studied can be used as carriers for biologically active molecules, because their interactions with bilayers remain soft and have a positive effect on the stability of the membranes. © 2003 Wiley Periodicals, Inc. Biopolymers 70: 323,335, 2003 [source]