N. N. Vylegzhanina

Effects of Protein Solubilization on the Structure of the Surfactant Shell of Reverse Micelles

The influence of protein encapsulation in the water pool of the reverse micelles has been studied by the electron spin resonance (ESR) spin-label technique and electrical conductivity measurements. For this purpose water-sodium-bis(2-ethylhexyl)-sulfosuccinate (AOT)-decane water-in-oil microemulsions with solubilized trypsin were used. The ESR data, obtained with the help of 4-(2-n-undecyl-3-oxyl-4,4,-dimethyloxazolidin-2-yl) butyric acid as a label, show that the protein molecule encapsulated in the water core of a reverse micelle forces a portion of water out from the aqueous core into the hydrophobic shell of a micelle. As a result, changes in the packing of AOT hydrocarbon chains and in the polarity of their microenvironment are induced. The effect of the encapsulated protein depends on the difference in the sizes of the protein molecule and the micelle aqueous core. The perturbations in the dynamic structure of the surfactant shell turn out to be most pronounced when the dimensions of the water cavity are close to the size of the protein molecule. The solubilization of protein in the reverse micelles results in remarkable variations in mass exchange between micelles.

An electron spin resonance study of the soy bean phosphatidylcholine-based reversed micelles

The ESR spectra of l-palmitoyl-2-stearoyl-(n-doxyl)-glycero-3-phosphocholine spin label positional isomers (n = 5, 7, 10, 12 and 16) have been studied in soy bean phosphatidylcholine (SPC)-based microemulsions with various volume fractions of disperse phase over the wide temperature range. The maximum hyperfine splitting 2Amax and the order parametersS were taken as indices of the rotational mobility and the motion spatial restrictions of the labeled lipid chain segments. It is found that the temperaturesTtr at which sharp enhancements of2Amax andS occur depend on concentration and size of the reversed micelles in solutions. To explain this, a plausible model, taking into account capability of the SPC molecule hydrocarbon chains to change a tilt angle with respect to the surface of a polar head group as temperature varies, is proposed. The estimations of the correlation times τsl obtained from the lineshape characteristics of the ESR spectra provided the possibility to suggest that these correlation times characterize the reorientations of the SPC chain axis about the normal to the surface of a polar head group of a reversed micelle.

Effects of solubilized dodecylamine on the microstructure of cetylpyridinium bromide-n-butanol-hexane-water system studied by pulsed-gradient spin echo NMR and ESR spin label methods

The effect of solubilized dodecylamine (DDA) on the structure of the cetylpyridinium bromide-n-butanol-hexane-water microemulsions has been studied by the Fourier-transform pulsed-gradient spin-echo1H nuclear magnetic resonance and the electron spin resonance spin label method. The sample compositions were chosen to examine three different microemulsion structures: oil-in-water, water-in-oil and bicontinuous. In all systems the DDA molecules are shown to be incorporated into the oil-water interface, resulting in essential changes in the microemulsion structure. In the micellar systems the DDA emergence in the interface causes an increase of the micelle size and a redistribution of butanol and water between micelle and bulk phases. In the oil-in-water microemulsions of amine-containing systems the quantity of micellized butanol and water decreases. In the water-in-oil microemulsions the introduction of DDA leads to an increase of butanol and water involved in the micelle formation. The redistribution of butanol and water between polar and organic phases in the microemulsions would be expected to cause changes in the bicontinuous structure.

Dynamic structure of the micelles of gemini alkylammonium surfactants

The dynamic structure of the micelles of gemini (dimeric) alkylammonium surfactants with different lengths of hydrophobic radicals and polymethylene spacer differing in alkyl substituents of the head group and type of counterion are studied by ESR spin probe technique. The use of probes with different localization of spin moiety makes it possible to quantitatively characterize a decrease in micropolarity when going from the surface of micellar aggregates to the core and compare the dynamic structures of the micelles of dimeric and monomeric analogs.

Ethylene glycol and the thermostability of trypsin in a reverse micelle system

The influence of ethylene glycol (EG) on the kinetics of hydrolysis of N-α-benzoyl-L-arginine ethyl ether catalyzed by trypsin encapsulated in sodium bis-(2-ethylhexyl)sulfosuccinate (AOT)-based reverse micelles was studied at different temperatures. Ethylene glycol was shown to shift the range of the trypsin activity in the reverse micelles towards higher temperatures. Infrared spectroscopy showed a stabilizing effect of EG on the secondary structure of the protein in the system of reverse micelles. Electron spin resonance spectroscopy showed that the solubilized protein affected the interactions of EG with the polar head groups of AOT and altered the rigidity of the micellar matrix. The results indicate that EG increases the thermostability of the solubilized enzyme in microemulsion media by two mechanisms.

Effect of Electrolytes on the Catalytic Properties and Sructural Characteristics of Dodecylpyridinium Bromide Micelles

Electrolyte-induced structural rearrangements of dodecylpyridinium bromide micelles affect their catalytic properties in alkaline hydrolysis of phosphonic esters.

Catalytic properties of microheterogeneous systems based on cationic surfactants in transesterification processes

The kinetic parameters of the transesterification processes of carboxylic acid esters under the action of alkylphenolates in aqueous micellar solutions of cetyltrimethylammonium bromide (CTAB) are found. The observed catalytic effect is due to a complex mechanism of the solvent effect, which includes a shift of acid-base equilibria in the nucleophile and the formation of mixed CTAB/alkylphenol micelles. The dynamic structure of these aggregates (size, diffusion mobility, and molecular packing density in a surface layer) has been characterized by spin-probe EPR spectroscopy and high-resolution pulsed-field gradient 1H NMR spectroscopy.

Poly(ethylene glycol) and Phospholipid Packing in the Structure of Reverse Micelles

The influence of water substitution by a substance with a different polarity on the structure of phospholipid monolayer interface in water-in-oil microemulsion has been studied by the Fourier-transform pulsed-gradient spin-echo (FT PGSE)1H nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spin-label methods. For this purpose the soybean phosphatidylcholine-based microemulsion and water soluble poly(ethylene glycol) with molecular weight 400 (PEG400) were used. Self-diffusion coefficients of all microemulsion components obtained by the FT PGSE NMR technique provided information about both the size of reverse micelles and distribution of components between different microemulsion compartments. The maximum hyperfine splitting, 2Amax, in the ESR spectra was used to characterize the degree of the phospholipid hydrocarbon chain mobility. It was shown that PEG400 alters significantly the size of the reverse micelles and the motion of the labeled segments of the lipid tails. A mechanism of PEG400 acting in solution of the phospholipid-based reverse micelles on the basis of the rough decrease of the micelle core polarity was suggested.

Reaction of carboxylic acid esters with phenolates in oil-in-water microemulsions based on cetyltrimethylammonium bromide

A kinetic study of reactions of carboxylic acid esters with phenols activated with alkalis or amines in microemulsions based on cationic surfactants showed that the phenolates formed upon activation exhibit different nucleophilicity depending on the value of the negative charge on the oxygen atom, which is determined by the properties of the phenol, ionizing agent, and solvent.

Investigation of the molecular motion of spin-labeled lysozyme in solution by the use of ESP spectra and electron spin relaxation

The theory of electron spin relaxation in protein solutions taking into account the “two-motion” model of spin label mobility is developed. The relations obtained for the longitudinal and transverse relaxation rates describe the experimental results better than isotropic (“one-motion”) model. The mechanism of longitudinal relaxation in solution of spin-labeled lysozyme is revealed and the correlation time of the inherent motion of spin label is evaluated. The linewidth analysis and study of ESR spectra under viscosity variation were used to obtain the microdynamical parameters characterizing lysozyme molecular mobility. A discrepancy between the correlation time values obtained by viscosity-variation-technique and the results known from other methods is found and ascribed to the manifestation of the intermediate time-scale mobility of protein.