Yu. F. Zuev

Time domain dielectric spectroscopy. A new effective tool for physical chemistry investigation

The general principles of time domain dielectric spectroscopy (TDS) are summarized. The methods of data treatment and presentation, and different TDS methods which enable one to obtain the permanent spectrum of ε* (ω) in the frequency range of 105–1010 are given. The examples of TDS application for the investigation of dielectric properties in samples of different nature and structure are considered in this review.

A Fourier transform pulsed-gradient spin echo nuclear magnetic resonance self-diffusion study of microemulsions and the droplet size determination

Abstract Self-diffusion of all components in two different microemulsions has been studied by the Fourier-transform pulsed-gradient spin echo 1 H nuclear magnetic resonance technique. The analysis of hydrodynamic and direct droplet-droplet interactions in microemulsions allows the simultaneous application of the Stokes-Einstein equation for surfactant and oil. The result of this analysis is a simple relation connecting self-diffusion coefficients of components and the size of droplets. It is shown that because of partial solubilization of water in oil the droplet radius can be significantly different from the expected radius.

Self-diffusion in microemulsions and micellar size

Self-diffusion of all components of two different microemulsions have been measured. Application of Stokes-Einstein equations for surfactant and oil gives a simple relation connecting their size and self-diffusion coefficients. Using the measured self-diffusion coefficients and dimensions of oil molecules known from elsewhere, the size of the surfactant droplets was estimated. This approach turns out to be advantageous in practical determination of droplet size in microemulsions.

Time domain dielectric spectroscopy with nonuniform signal sampling

The hardware and software designs for fast measurement of dielectric properties of different substances over a wide range of characteristic times (10−5–10−10 s) by means of time domain dielectric spectroscopy (TDS) are presented. The characteristic feature of the described installation is the nonuniform time sampling of measured signals, which enables one to cover a wide range of characteristic times with a single measurement. Comparative results for an aqueous solution of lysozyme obtained on the traditional apparatus and on the described one are presented.

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.

Tissue-specific rhamnogalacturonan I forms the gel with hyperelastic properties.

Rhamnogalacturonans I are complex pectin polysaccharides extremely variable in structure and properties and widely represented in various sources. The complexity and diversity of the structure of rhamnogalacturonans I are the reasons for the limited information about the properties and supramolecular organization of these polysaccharides, including the relationship between these parameters and the functions of rhamnogalacturonans I in plant cells. In the present work, on the example of rhamnogalacturonan I from flax gelatinous fibers, the ability of this type of pectic polysaccharides to form at physiological concentrations hydrogels with hyperelastic properties was revealed for the first time. According to IR spectroscopy, water molecules are more tightly retained in the gelling rhamnogalacturonan I from flax fiber cell wall in comparison with the non-gelling rhamnogalacturonan I from primary cell wall of potato. With increase in strength of water binding by rhamnogalacturonan I, there is an increase in elastic modulus and decrease in Poisson’s ratio of gel formed by this polysaccharide. The model of hyperelastic rhamnogalacturonan I capture by laterally interacting cellulose microfibrils, constructed using the finite element method, confirmed the suitability of rhamnogalacturonan I gel with the established properties for the function in the gelatinous cell wall, allowing consideration of this tissue- and stage-specific pectic polysaccharide as an important factor in creation of gelatinous fiber contractility.

Sodium dodecyl sulfate self-diffusion in premicellar and low-concentrated micellar solutions in the presence of a background electrolyte

The Fourier transform pulsed field gradient NMR method is employed to investigate the self-diffusion of surface active sodium dodecyl sulfate ions in premicellar and low-concentrated micellar solutions at different NaCl concentrations in a system. The self-diffusion coefficient of the surfactant is found to markedly decrease in the premicellar region. An analysis of the experimental data carried out using a model implying the presence of sodium dodecyl sulfate monomers, dimers, and micelles in the system made it possible to determine the self-diffusion coefficients of the monomers and dimers, as well as the corresponding sizes of kinetic units.

Time domain treatment of TDS data for the lumped-capacitance method

Abstract An equation is obtained connecting the dielectric response function with the quantities directly registered by the lumped capacitance method. The response function calculated for n -butanol is represented.

Association of sodium dodecyl sulfate in aqueous solutions according to chemical shifts in 1H NMR spectra

Proton chemical shifts of different atomic groups in sodium dodecyl sulfate (SDS) have been studied by 1H NMR spectroscopy as functions of surfactant concentration in aqueous solutions. Three surfactant concentration ranges of the chemical shifts have been revealed. The first range corresponds to the premicellar solutions, the second one is in the vicinity of critical micelle concentration (CMC1), and the third range corresponds to high surfactant concentrations, at which intermicellar interactions play a significant role. The parameters of SDS association (CMC1 and CMC2) determined based on the concentration dependences of the chemical shifts are in satisfactory agreement with the data available from the literature. The concept of critical dimerization concentration (CDC) has been introduced for the first concentration range. The values of CDC and dimerization constant K2(210 × 60 dm3/mol) have been estimated within the framework of the two-state model.

Self-assembly and secondary structure of beta-casein

The secondary structure alterations during isothermal and temperature guided beta-casein micellization were studied by dynamic light scattering, circular dichroism and Fourier transform infrared spectroscopy techniques. Micelle formation induced by the increase in the protein concentration at constant temperature is accompanied by the formation of a small number of additional peptide hydrogen bonds, preliminary assigned to the intraprotein beta-structure. The heating results in more pronounced but qualitatively different changes consisted in dehydration of the peptide groups and disruption of the polyproline II helix segments with the subsequent conversion to the random conformation and the beta-turns. Nevertheless, in both cases the total number of residues involved in the transition is very few and cannot be regarded as a decisive factor for casein micellization.