Yu. A. Shchipunov

Lecithin organogel: A micellar system with unique properties

Abstract Lecithin self-assembles in nonaqueous media into reversed giant cylindrical micelles when small amounts of water, glycerol or formamide are added. The micellar aggregates, much like the polymer molecules, overlap, interpenetrate, entangle, thus forming a temporal three-dimensional network that brings about viscoelastic properties. For this reason, the micellar system is in a jelly-like state. This review article considers key results on the phase behavior, molecular interactions, properties, structure and dynamics of the lecithin organogels as well as current models for the polymer-like micelles. Much attention is given to rheological behavior. The effects of a shear flow, electric field and added surfactants, that cause a significant change in the structure and properties of the micellar system, are also discussed.

Chitosan-carrageenan gels

Phase behavior of the systems during the formation of polyelectrolyte complexes obtained by mixing of aqueous solutions of chitosan and ι-, κ-, or λ-carrageenan was studied. The gelation was shown to occur throughout the whole bulk solution at chitosan and λ-carrageenan concentrations higher than 0.1 and 0.3 wt %, respectively. At lower polysaccharide concentrations, the polyelectrolyte complexes precipitated. The study was performed at the polysaccharide concentrations not higher than 1 wt %. The gel systems were investigated by the dynamic rheology method. The mechanical characteristics of λ-carrageenan-containing gels were found to be mainly governed by the chitosan content; the viscosity of these gels was independent of temperature. Gels obtained with ι- and κ-carrageenans were sensitive to temperature because of the helix–coil conformational transitions in their molecules. The mechanical strength and stiffness of gels increase in the λ–ι–κ-carrageenan series. This effect was explained by the formation of additional crosslinks by double helixes of ι- and κ-carrageenan molecules.

Carrageenan gels in skim milk: Formation and rheological properties

Phase behavior and mechanical properties of gels of three (kappa-, iota-, and lambda-) carrageenans in skim milk are thoroughly studied. The measurements were performed with the aid of a dynamic rheology in different regimes including determination of frequency dependences of rheological parameters, creep, and critical strain and stress at which the gelled systems are destroyed. Temperature dependences of the rheological parameters were also measured. A set of obtained data allowed to quantitatively characterize the mechanical properties of milk gels and compare the gel-forming properties of various carrageenans. In addition to gels of individual polysaccharides, their mixed gels were studied for the first time. It is shown that kappa-carrageenan formed the most stiff and brittle gels. Its mixing with iota- or lambda-carrageenans made gels softer. This effect is observed when the degree of substitution of kappa-carrageenan was higher than 50% that indicates its prevalent role in the mixed systems. The gelation is explained by the formation of crosslinked structure where the nodes are the casein micelles connected by polysaccharide chains. Their binding occurs due to electrostatic interactions between the sulfo groups of carrageenans and amino groups of kappa-casein. In the case of kappa- or iota-carrageenans, network structure is additionally stabilized due to crosslinking of segments of their molecular chains by the double helices at the gaps between casein micelles.

Self-organization in the chitosan-clay nanoparticles system regulated through polysaccharide macromolecule charging. 2. Films

Formation conditions are studied for bionanocomposite films prepared by mixing cationic chitosan with negatively charged nanoparticles of a synthetic clay (saponite) followed by gradual increasing of the charge of macromolecules by decreasing the pH of a medium. The data on the swelling of the bionanocomposite films in water are used to determine the stoichiometric ratio between the concentrations of macromolecules and nanoparticles that provides the most intense electrostatic interactions stabilizing the films. Their properties and structure are investigated by means of scanning electron microscopy, dynamic thermomechanical analysis, and small-angle X-ray scattering. The films are shown to occur in a glassy state and undergo a number of phase transitions, the temperatures of which depend on the chitosan-to-saponite concentration ratio. In particular, their glass transition temperature increases from 62 to 175°C when passing to the stoichiometric composition. The bionanocomposite films are found to have a layered structure. The layers are, in turn, composed of highly uniform microsized plates 20–30 nm thick. Small-angle X-ray scattering shows a structural order with a periodicity of 1.78 nm. The structure of the bionanocomposite films is discussed.

Nonlinear optical properties of biomineral and biomimetical nanocomposite structures

The transmission of laser femtosecond pulses by spicules of marine glass sponges and monolithic amorphous nanocomposite silica biomaterials synthesized on the basis of natural polysaccharides has been experimentally investigated. The strong non-linear optical properties of these biominerals have been revealed in spectral characteristics of transmitted ultra-short pulses (USP). Comparative analysis of the transmission spectra of USP reveals that spicules exhibit much stronger non-linear optical properties than quartz optical fibers. Recently new monolithic nanocomposite silica biomaterials were synthesized on the basis of various natural polysaccharides and completely water-soluble Si-precursor. The shape of transmitted spectrums through both spicules and new nanocomposite biomaterials demonstrates major changes indicating the broadening with formation markedly strong anti-Stokes component in the output spectrum with generation of supercontinuum spectra. The carried out studies have showed that the nature combination of spongin protein with silicon dioxide extracted from seawater by silicatein protein in glass sponge spicules and monolithic nanocomposite silica biomaterials are biological and biomimetical nanocomposite materials with unique optical properties.

Incorporation of Quantum Dots into a Silica Matrix Using a Compatible Precursor

A method is developed for one-stage incorporation of cadmium-sulfide quantum dots synthesized in the presence of mercaptosuccinic acid into a silica matrix formed from a precursor containing ethylene-glycol residues—tetrakis(2-hydroxyethyl) orthosilica. This precursor has not previously been applied for this purpose. It is more compatible with diverse substances than tetraethoxysilane, which is traditionally used. Moreover, it is advantageous in its unlimited solubility in water; release of ethylene glycol, which does not precipitate quantum dots, rather than alcohol upon hydrolysis; and the feasibility of performing the sol-gel process at any pH value in a range of 2–10 without the addition of acid or alkali and without heating. When the precursor (50 wt %) is added to a dispersion of quantum dots, the system is transformed into a gel in as little as a few minutes. The synthesized hybrid materials are optically transparent. Therewith, the quantum dots incorporated into the silica matrix exhibit luminescence, with their spectral characteristics remaining almost unchanged.

Nanocomposite material with immobilized acid-base dyes conjugated with polysaccharides

Water-soluble acid-base dyes xylenol orange and methyl red are linked by covalent bonds to chitosan macromolecules; neutral dye red is bound to carboxymethyl cellulose to prevent their washing-off from silicate matrix. Dye conjugates were then immobilized by modified sol-gel method using silicate precursor compatible with polysaccharides. Synthesized hybrid nanocomposite materials are optically transparent, which makes it possible to apply them to develop sensors for measuring pH. Spectral characteristics of dyes, their conjugates, and prepared nanocomposites with silicate matrix are studied in detail. It is shown that xylenol orange, which is linked with chitosan by covalent bonds, is the most suitable dye for the development of sensor materials because the conjugation by carboxyl groups, which do not directly bound with chromophore center, does not deteriorate the spectral properties of this dye. In the cases of methyl red and neutral red dyes, undesirable changes in their properties in the course of conjugation are caused by the covalent binding by functional groups, which are auxochromes directly affecting all spectral characteristics of dyes. An increase in the solubility of polysaccharide in water can also positively affect the covalent binding of dyes with chitosan that allows polysaccharide to be used in neutral and alkaline media.

The Effect of Lysophosphatidylcholine and Phosphatidylglycerol on Lecithin Polymer-Like Micelles

The effect of phosphatidylglycerol and lysophosphatidylcholine on the formation, properties, and intermolecular interactions in polymer-like (cylindrical) micelles that arose in nonaqueous lecithin solutions upon the addition of trace amounts of water is studied by the methods of dynamic rheology and IR spectroscopy. It is established that micellar aggregates of lecithin are not changed markedly in the presence of the first phospholipid but are disintegrated into smaller aggregates upon the addition of second phospholipid. The IR spectroscopic studies demonstrate that phosphatidylglycerol and lysophosphatidylcholine do not significantly change intermolecular interactions in polymer-like micelles. Their effect on the structure of micellar aggregates is associated with the variations in the shape of molecules.

Synthesis of monolithic mesoporous silica with a regular structure (SBA-15) and macropores in neutral aqueous solution at room temperature

A monolithic biporous silica material of SBA-15 type has been synthesized by the sol-gel method in a neutral aqueous solution in the presence of glycerol without heating. Synthesis has been performed using P123 triblock copolymer and a novel silica precursor containing ethylene glycol residues.

Lecithin Organogels Containing Poly(ethylene glycol) Monolaurate

The effect of added poly(ethylene glycol) monolaurate (PEGML) on the formation and properties of lecithin organogels composed of polymer-like micelles was studied by the methods of dynamic rheology and the Fourier transform IR spectroscopy. It was established that the addition of even small amounts of PEGML causes a significant decrease in viscosity, whereas the elastic properties of organogels remained almost unchanged. The analysis of the scaling dependences indicated that the formation mechanism of polymer-like lecithin micelles remained also unchanged. Spectral studies revealed that the PEGML molecules affect intermolecular hydrogen bonding during their incorporation into micelles, thus stabilizing micellar structure. This effect is caused by the partial dehydration of the lecithin polar region. This leads to a decrease in the number of hydrogen bonds or their weakening and, as a result, to the disintegration of polymer-like lecithin micelles into shorter micellar aggregates.