Dynamic Surface Properties of α-Lactalbumin Fibril Dispersions.

The dynamic surface properties of aqueous dispersions of α-lactalbumin (ALA) amyloid fibrils differ noticeably from the properties of the fibril dispersions of other globular proteins. As a result, the protocol of the application of ALA fibrils to form stable foams and emulsions has to be deviate from that of other protein fibrils. Unlike the fibrils of ß-lactoglobulin and lysozyme, ALA fibrils can be easily purified from hydrolyzed peptides and native protein molecules. The application of the oscillating barrier method shows that the dynamic surface elasticity of ALA fibril dispersions exceeds the surface elasticity of native protein solutions at pH 2. ALA fibrils proved to be stable at this pH, but the stability breaks at higher pH levels when the fibrils start to release small peptides of high surface activity. As a result, the dynamic surface properties of ALA coincide with those of native protein solutions. The ionic strength strongly influences the adsorption kinetics of both fibril dispersions and native protein solutions but have almost no impact on the structure of the adsorption layers.

Thermodynamic properties of gaseous BaSnO2 and Ba2 O2 studied by Knudsen effusion mass spectrometry.

RATIONALE: BaSnO3 is an interesting technical and industrial ceramic, with uses in many areas of electronic technology. Currently, there is great interest in this ceramic material because of its potential as a transparent conductive oxide. Due to its good chemical stability, it is also used as a surface processing material in the synthesis of electroluminophores. When heated, the stannates of alkaline earth metals can pass into the vapor phase with or without dissociation. Until the present investigation, gaseous salts where SnO plays the role of an anion-forming oxide had been unknown. The formation enthalpy of gaseous Ba2 O2 also needed to be determined. METHODS: Knudsen effusion mass spectrometry was used to determine the partial pressures of vapor species, equilibrium constants and enthalpies of the studied gas-phase reactions, as well as the formation and atomization enthalpies of gaseous BaSnO2 and Ba2 O2 : a mixture of BaO and SnO2 was evaporated from a platinum effusion cell. For the evaporation of gold (pressure standard), a molybdenum effusion cell was used. A theoretical study of gaseous BaSnO2 and Ba2 O2 was performed by several quantum chemistry methods. RESULTS: Ba, BaO, Ba2 O2 , SnO and BaSnO2 were found to be the main species in the vapor over the BaO-SnO2 mixture in the temperature range of 1680-1920 K. The standard formation enthalpies of gaseous BaSnO2 and Ba2 O2 were determined on the basis of the equilibrium constants of the studied gas-phase reactions. Energetically favorable structures of these gaseous species were found and vibrational frequencies were evaluated in the harmonic approximation. The formation enthalpy of gaseous Ba2 O2 was clarified; in addition, the formation enthalpies of gaseous SrSnO3 and CaSnO3 were estimated. CONCLUSIONS: The thermal stability of gaseous BaSnO2 was confirmed by Knudsen effusion mass spectrometry. The reaction enthalpies of gaseous BaSnO2 from gaseous barium and tin oxides were theoretically evaluated and the obtained values were found to be in reasonable agreement with the experimental ones.