S. G. Vasil’ev

Water metabolism in cells of Saccharomyces cerevisiae of races Y-3137 and Y-3327, according to pulsed-field gradient NMR data

The self-diffusion of water in cells of Saccharomyces cerevisiae of races Y-3137 and Y-3327 is studied by means of pulsed-field gradient (PFG) NMR. Three types of water are detected that differ by their self-diffusion coefficients (SDCs): free, intercellular, and intracellular. It is found that the self-diffusion of intercellular and intracellular water is restricted. The size and permeability of the cells of yeasts with different cultivation times (24 and 48 h) is determined by analyzing the dependences of the self-diffusion coefficients of intracellular water on the interval between pulses of the magnetic field gradient.

An NMR study of a water-methanol solution sorbed in MF-4SK sulfonated cation-exchange membranes

Concentration dependences of self-diffusion coefficients (SDCs), self-diffusion activation energies for water and methanol, and chemical shifts of the protons of the hydroxyl groups δOH simultaneously in an external water-methanol solution and the solution sorbed in MF-4SK membranes have been studied by NMR. It has been revealed that the SDC of pure methanol and pure water sorbed in an MF-4SK membrane is 3–5 times lower than that outside the membrane. It has been found that, in the presence of a small amount of methanol, the SDC of water in the membrane is 1.5–2 times higher than the SDC of pure sorbed water. At a solution concentration of 0.1–0.5 mole fraction, the SDC values of water and methanol in the membrane vary only slightly and are about 6 × 10−6 and 4 × 10−6 cm2/s, respectively. It has been determined that the δOH value in the membrane is 100–200 Hz higher than that in the external solution. The observed increase in δOH and decrease in SDC in the membrane suggest that the state of the solution in the MF-4SK sulfonated cation-exchange membrane has significantly changed compared to the external solution. The effect of the implanted carbon phase (CP) on the SDC of water and methanol and δOH of the solution sorbed in the MF-4SK membranes containing the CP has been studied. It has been revealed that at a methanol mole fraction of up to 0.5, the introduction of 23 wt % CP decreases the SDC of the solution components by no more than 10–20%. At a methanol mole fraction of 0.25–0.5, the self-diffusion activation energies for methanol and water in the external and membrane solutions decrease by 5–7 kJ/mol.

An NMR study of sorption-diffusion properties of MF-4SK-carbon composite membranes in aqueous methanol solutions

The distribution of water and methanol and their self-diffusion coefficients (SDCs) in carbon-doped MF-4SK perfluorinated membranes have been studied by NMR. It has been shown that at a concentration of 12–35 wt % in the external solution, the methanol concentration inside the membrane is higher by a factor of 1.4–2 than that in the external solution and increases with increasing the carbon phase content. It has been found that SDC values for water and methanol in the membrane decrease with an increase in the C phase content. In a membrane with 23 wt % C, the SDC of methanol is reduced by a factor of 1.6. It has been shown that the SDC of methanol in these membranes is below that of water by a factor of 1.5. The activation energies of self-diffusion of water and methanol have been determined. It has been found that they remain almost unaffected by the C content and have close values of 19–20 kJ/mol, which are 2–4 kJ/mol above the activation energy of self-diffusion of pure water in these membranes.

Dynamics and relaxation of multiple quantum NMR coherences in a quasi-one-dimensional chain of nuclear spins 19F in calcium fluorapatite

Multiple quantum experiments on nuclear magnetic resonance on spins of 19F in calcium fluorapatite have been performed. It has been shown that more than 97% of the observed signal refers to the multiple quantum coherences of the zeroth and plus/minus second orders. The dependences of the intensities of these coherences on the time of the preparation period of the multiple quantum NMR experiment have been obtained. The dipole relaxation of multiple quantum coherences on the evolution period of the multiple quantum nuclear magnetic resonance experiment has been studied. A probe providing short radio-frequency pulses with the duration up to 0.3 μs has been developed for experiments. The experimental results show that the studied system can be used for the transmission of quantum information and the study of the decoherence process in strongly correlated multispin clusters.

Electron and nuclear spin dynamics in plastically deformed silicon crystals enriched in isotope 29Si

Paramagnetic defects of a new type with a concentration of about 1015 cm−3 are shown to be generated during the plastic deformation of isotope-rich (72%, 76% 29Si) silicon crystals at a temperature of 950°C. The electron paramagnetic resonance (EPR) spectra of these defects are anisotropic and have a significant width (up to 1 kOe). The nonuniform broadening of the EPR lines is caused by the variation of the internal magnetic field in correlated defect clusters. The nuclear magnetic resonance (NMR) spectra of the deformed crystals consist of Pake doublets split by nuclear spin-spin interaction. The broadening of the NMR spectra is caused by nuclear dipole-dipole relaxation.

Features of rubber swelling in transformer oil, according to NMR data

NMR spectroscopy, NMR relaxation, and NMR with a pulsed magnetic field gradient methods are used to study the swelling of the elastomers based on ethylene-propylene rubber, butadiene-nitrile rubber, and fluororubber SKF-26 in transformer oil. Components corresponding to the fractions of oil and polymer network are identified. It is shown that the affinity of the polymers toward transformer oil displays an increase in the orderly sequence of ethylene-propylene rubber, fluororubber, and butadiene-nitrile rubber; the stability of the polymers towards carbon tetrachloride falls in the same sequence. Based on an analysis of the spin–spin relaxation time depending on the degree of swelling, it is found that fluororubber elastomers are characterized by the formation of a polymer network that prevents further sorption, In contrast, elastomer based on ethylene-propylene rubber gives no indication of the formation of a rigid polymer network.

High-temperature carbonization of humic acids and a composite of humic acids with graphene oxide

Humic acids (HAs) isolated from high-moor peat have been studied by magic-angle spinning solid-state nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetry (TG), and Raman spectroscopy. A composite of HAs with graphene oxide (GO) has been prepared for the first time, and the thermal carbonization (900°C) of both HAs and the HA–GO composite has been carried out. With the use of mass spectrometry, it has been found that CO2 and H2O molecules are mainly released from HAs into the gas phase at a low temperature (to 150°C). At higher temperatures, carbon monoxide and different low-molecular-weight hydrocarbons also begin to be released. From microscopic examinations, it follows that HA forms small agglomerates with sharply outlined edges as a result of carbonization, whereas the composite forms only large aggregates.

Hydrodynamic characteristics of branched polystyrenes with varying content of a highly branched fraction

The branched polymers containing different amounts of the highly branched fraction are synthesized by the radical copolymerization of styrene and divinylbenzene under conditions of the reversible inhibition by 2,2,6,6-tetramethylpiperidine-1-oxyl. The branched polystyrenes are studied by size-exclusion chromatography combined with static light scattering, viscometry, and pulsed-field gradient nuclear magnetic resonance. The branched polymers prepared by living radical polymerization (in the presence of 2,2,6,6-tetramethylpiperidine-1-oxyl) feature reduced intrinsic viscosities and increased self-diffusion coefficients compared with their linear analogs. As the content of the highly branched fraction in the synthesized polymers grows, the Zimm contraction factor in toluene solution decreases to g′ = 0.13. The Kuhn-Mark-Houwink parameters for these polymers in toluene solution (a = 0.43) confirm the nonlinear architecture of macromolecules.

Structure and hydration processes in perfluorinated bilayer cation-exchange membranes

Based on perfluorinated polymers MF-4SK and F-4KF bilayer composite ion-exchange membranes are studied by using the magic-angle-rotation NMR, electrochemical impedance spectroscopy, scanning electron microscopy, and electron-probe microanalysis. It is shown that the contact of the polymers includes an interlayer, approximately 5 μm thick. The NMR data point to slow water-molecules-exchange between hydrate-complexes of sulfo- and carboxyl-groups.