Action of Humicola lanuginosa lipase on mixed monomolecular films of tricaprylin and polyethylene glycol stearate

The hydrolysis catalyzed by Humicola lanuginosa lipase (HLL) of pure tricaprylin (TC) or stearate of polyethylene glycol 1500 (PEG-St) as well as their mixtures spread as monomolecular films were studied. The catalytic transformation of the two substrates TC or PEG-St into their respective reaction products was detected by measuring simultaneously the decrease in the film area and the surface potential using the "zero order" trough at constant surface pressure. A kinetic model describing the enzymatic hydrolysis was developed. The surface concentrations of the two substrates and their respective reaction products as well as the values of the global kinetic constants of hydrolysis were determined. The experimentally obtained global kinetic constants of the catalytic action of HLL against TC and PEG-St present in mixed monolayers of TC/PEG-St are approximately the same as in the case of pure monolayers. These obtained results give some indications that the activity of enzyme is not significantly affected by the different molecular environments in the mixed monolayers

Interfacial behavior of lipid nanocapsules spread on model membrane monolayers

The lipid nanocapsules (LNCs) spread at the air–water interface (A/W) undergo destabilization and disaggregation leading to formation of a triglyceride (TG) surface film. The kinetics of reorganization and formation of TG surface film were followed by measuring either the change of surface pressure at constant area or the surface area at constant surface pressure. From the obtained experimental data were determined the effectiveness of TG spreading and the rate of LNC disaggregation at A/W interface covered with preformed model membrane monolayers of DPPC, Curosurf®, and mucus. Partial LNC stabilization due to their interaction with the model membrane monolayers was observed and characterized by atomic force microscopy (AFM). The obtained results demonstrated that the LNCs spread on mucus surface layer, which models the epithelial surface were more stable than if they were spread either on DPPC or Curosurf® surface layers, which emulate the alveolar surface

Mechanical and electrochemical effects on surface convection and on emulsification new criteria

Theoretical and experimental studies of surface instability for charged and polarized interfaces between two immiscible liquids are reviewed. A linear analysis of stability shows the role of mechanical and electrochemical para meters for the onset of interfacial convection. Three cases are studied: 1) For the restored Boltzman distribution in bulk phases, the stability is only governed by the interfacial tension through the composition between mechano-chemicaland electrical contributions to the surface free energy; 2) for the non-restored Boltzman distribution, the stability is also governed by the discontinuity of mechanical quantities (density-viscosity) associated with the discontinuity of electrochemical and electrical quantities (dielectric constant-solute concentration-diffusion coefficient, potential drop); and 3) for concentrated charged and dipolar monolayers, the convection criteria of stability are directly related to the discontinuity of mechanical quantities (density-viscosity) associated with the discontinuity of electrochemical quantities (dielectric constant). Additional experiments on emilsification and demulsification were performed in order to verify this last theoretical prediction. © 1984.link_to_subscribed_fulltex

Optimizing multiplex SNP-based data analysis for genotyping of Mycobacterium tuberculosis isolates.

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