Monolayer kinetic model of formation of β-cyclodextrin-β-carotene inclusion complex.

The carotenoids are sensitive molecules and their chemical integrity must be preserved from pro-oxidant elements which could affect and decrease their physiological benefits. The encapsulation based on the inclusion of the carotenoids into cage molecules is a promising approach for preserving over time of the intrinsic properties of the carotenoids. It is well known that cyclic oligosaccharide β-cyclodextrin (CD) as a cage molecule possesses strong inclusion ability to β-carotene (C) and as a result of the hydrophobic interactions forms an inclusion complex.

Properties of mixed monolayers of clinical lung surfactant, serum albumin and hydrophilic polymers.

It is now established that the surface activity of the clinically used lung surfactant is reduced by serum proteins and can be restored by adding the hydrophilic polymers. The mechanisms of lung surfactant inactivation by serum proteins and restoring effect by the hydrophilic polymers remain not completely understood. In this paper the state and rheological dilatational properties of surface films formed from clinical lung surfactant Exosurf, Survanta, Curosurf and Alveofact in the presence of serum albumin (BSA) and hydrophilic polymers polyvinylpyrrolidone (PVP), polyethylene glycol (PEG) and Dextran were studied.

Savinase proteolysis of insulin Langmuir monolayers studied by surface pressure and surface potential measurements accompanied by atomic force microscopy (AFM) imaging.

The mechanism of the enzymatic action of Savinase on an insulin substrate organized in a monolayer at the air-water interface was studied. We followed two steps experimental approach classical surface pressure and surface potential measurements in combination with atomic force microscopy imaging. Utilizing the barostat surface balance, the hydrolysis kinetic was followed by measuring simultaneously the decrease in the surface area and the change of the surface potential versus time.

Hydrolysis of mixed monomolecular films of tricaprylin/dilauroylphosphatidylcholine by lipase and phospholipase A₂.

The purpose of this article was to describe the kinetics of the enzymatic action of one or more enzymes on mixture of substrates organized in 2D structures in order to mimic some situations existing in biological or industrial systems. Hydrolysis of the mixed monomolecular films of tricaprylin/dilauroylphosphatidylcholine (TC8/DiC12PC) by Thermomyces lanuginosus lipase (TLL) and phospholipase A₂ (PLA₂) was studied by measuring the decrease of the surface area and change of the surface potential at barostatic conditions. The decrease of the surface area detects the transition of the substrate into reaction products and their solubilization while the change of the surface potential detects the contribution of dipole moment of the molecules remaining at the interface during the hydrolysis.

Enzymatic proteolysis of alpha gliadin monolayer spread at the air-water interface.

The mechanism of the enzymatic hydrolysis under the proteolytic enzyme action of a plant protein alpha gliadin organized as a model monolayer system at the air/water interface was studied. The advantage of the monolayer technique is the ability to control and modify easily the interfacial organization of the molecules and the possibility to optimize the conditions for the hydrolysis. Enzymatic hydrolysis was studied by using a traditional barostat surface balance.

Comparative study of lipolysis by PLA2 of DOPC substrates organized as monolayers, bilayer vesicles and nanocapsules.

The water-soluble lipolytic enzymes act at the interface of insoluble lipid substrates, where the catalytical step is coupled with various interfacial phenomena as enzyme penetration, solubilization of reaction products, loss of mechanical stability of organized assemblies of phospholipids molecule, etc. One biologically relevant example is the enzymatic hydrolysis of DOPC by PLA(2), which results in cleavage of phospholipids molecules into water insoluble lipolytic products, namely oleic acid and lysophospholipid. In general, the enzymatic activity depends on the substrate organization and molecular environment of the catalytic reaction.

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.

Interfacial properties of adsorbed films made of a PEG2000 and PLA50 mixture or a copolymer at the dichloromethane-water interface.

Adsorption kinetics of films of poly(ethylene glycol) (PEG2000) studied by the dynamic pendant drop method showed that PEG2000 was more tensioactive at the dichloromethane (DCM)-water interface than at the air-water interface. When initially solubilized into DCM, PEG2000 segments would form an adsorbed layer with hydrophobic segments buried into the polymer chains turned toward the organic phase. Compression of this layer, accompanied by viscoelastic effects, led to expulsion of some hydrophilic tails toward the water phase.

Reorganization of lipid nanocapsules at air-water interface. I. Kinetics of surface film formation.

The size, the electrical properties and the behaviour at air-water interface of lipid nanocapsules (LNC) with various compositions were investigated. Two populations of LNC are presented in the suspension after the preparation: with (LNC II) and without (LNC I) phospholipid molecules. After the spreading at air-water interface, a rapid disaggregation of LNC I, located in the vicinity of interface, occurs leading to formation of surface film.

Reorganization of lipid nanocapsules at air-water interface 3. Action of hydrolytic enzymes HLL and pancreatic PLA2.

The action of the hydrolytic enzymes humicola lanuginosa lipase (HLL) and pancreatic phospholipase A2 (PLA2) on monolayers formed from lipid nanocapsules (LNC) and model monolayers containing their components, Labrafac, Solutol and Lipoid, is studied by simultaneous measuring the changes in the film area and the surface potential in the "zero order" trough at constant surface pressure (pi). The kinetic models describing the hydrolysis by HLL of the Labrafac, Solutol and their mixtures have been proposed. By using the developed theoretical approach together with the experimental results the surface concentrations of the substrates, hydrolysis products and values of the global kinetic constants were obtained.

Reorganization of lipid nanocapsules at air-water interface: Part 2. Properties of the formed surface film.

The state, electrical and dilatational rheological properties of surface films formed at air-water interface from lipid nanocapsules (LNC) with various compositions as well as model monolayers formed by the LNC constituents-Labrafac, Solutol and Lipoid are investigated. These nanocapsules constitute potential drug delivery systems where lypophilic drug will be loaded in their core. The study of the model Labrafac/Solutol (Lab/Sol) mixed monolayers shows behavior close to the ideal.

[Phenomenon of formation of structures in the dense fraction of the enteric milieu when its pH is changed].

Morphological study of the dog duodenum and ileum contents revealed that the food particles of less than 2 mm size constituted not more than 30% of the total volume of the chyme dense fraction. The main part of the dense fraction consists of the gel structures precipitating in the enteral milieu during changes of its pH due to acid content of the stomach. Histochemical reactions of these structures reveal presence of mucopolysaccharides, proteins and lipids.