Location of paramagnetic defects in detonation nanodiamond from proton spin-lattice relaxation data.

We developed an approach for determining location of intrinsic paramagnetic defects in nanodiamonds from the data of proton spin-lattice relaxation of the surface hydrogen atoms. The approach was applied to the detonation nanodiamond (DND) of the diameter of 5 nm. We found that dangling bonds with unpaired electron spins are located within the near-surface belt at the distance of 0.3-0.9 nm from the DND surface. The NMR data are compared with the results of EPR measurements.

NMR study of microscopic mechanism of water molecules diffusion in natrolite.

The mineral natrolite is a good object for studying the features of the molecular mobility of water molecules in spatially restricted structures by NMR techniques. The microscopic mechanisms of water molecule mobility in channels of monocrystal natural zeolite natrolite (Na16Al16Si24O80·16H2O) have been investigated by broad-line (CW) NMR method. The CW NMR method, which accurately reproduces the shape of a Pake doublets of water molecules, has made it possible to trace diffusion of individual water molecules between specific positions in the crystal lattice as a function of temperature, which is important in understanding diffusion mechanisms in narrow channels of natrolite, where a diameter of the channel is smaller than the diameter of the water molecule. It has been shown that at temperatures higher than 250 K the regular diffusion of water molecules along the Schottky defects located along channels parallel to the c-crystal axis is a main kind of water molecules mobility. At temperature higher than 350 K the diffusion of water molecules in transversal channels of natrolite was observed also. Using the structural data the possible pathways of water molecules diffusion in natrolite channels have been discussed. The relationship between diffusion of water molecules and the dynamics of the zeolite framework and sodium cations is discussed on the basis of the assumption non-Markovian characte of diffusion in natrolite.

Towards Determination of Distances Between Nanoparticles and Grafted Paramagnetic Ions by NMR Relaxation.

We developed an approach for determining distances between carbon nanoparticles and grafted paramagnetic ions and molecules by means of nuclear spin-lattice relaxation data. The approach was applied to copper-, cobalt- and gadolinium-grafted nanodiamonds, iron-grafted graphenes, manganese-grafted graphene oxide and activated carbon fibers that adsorb paramagnetic oxygen molecules. Our findings show that the aforementioned distances vary in the range of 2.7-5.4 Å and that the fixation of paramagnetic ions to nanoparticles is most likely implemented by means of the surface functional groups. The nuclear magnetic resonance data data are compared with the results of electron paramagnetic resonance measurements and density functional theory calculations.

Fitting MAS NMR spectra in crystals with local disorder: Czjzek's vs. Maurer's model for 11B and 71Ga in polycrystalline gallium borate.

A comparative analysis of the Czjzek's and Maurer's models of the joint distribution density of NMR quadrupole parameters has been carried out in view of their application to account for spectra broadening induced by local disorder in crystals. As an example of such an application, we have considered Magic Angle Spinning NMR of 11B and 71Ga isotopes in polycrystalline gallium borate. Computer simulations carried out using both models unambiguously show that in the case of low local disorder the Maurer's model, in contrast to the Czjzek's model, provides satisfactory fits to experimental NMR spectra.

23Na and 27Al NMR Study of Structure and Dynamics in Mordenite.

Temperature dependencies of 27Al and 23Na nuclear magnetic resonance spectra and spin-lattice relaxations in mordenite have been studied in static and magic angle spinning regimes. Our data show that the spin-lattice relaxations of the 23Na and 27Al nuclei are mainly governed by interaction of nuclear quadrupole moments with electric field gradients of the crystal, modulated by translational motion of water molecules in the mordenite channels. At temperatures below 200 K, the dipolar interaction of nuclear spins with paramagnetic impurities becomes an important relaxation mechanism of the 23Na and 27Al nuclei.

Proton Dipolar Spin-Lattice Relaxation in Nano-channels of Natrolite.

The 1H nuclear magnetic resonance (NMR) spectra and the dipolar spin-lattice relaxation time T1D for 1H in the natural natrolite (Na2Al2Si3O10·2H2O) have been measured in the temperature range of 190-390 K. From the temperature transformations of 1H NMR spectra, it follows that at T > 300 K, the diffusion of water molecules along the nano-channels is observed. From experimental T1D data, it follows that the 180° flip motion of the water molecules takes place in natrolite. At low temperature (T < 250 K), the dipolar interaction with paramagnetic impurities as a relaxation mechanism of 1H nuclei becomes significant.

(1)H NMR study of water molecules confined in nanochannels of mordenite.

Behavior of water molecules entrapped in nanochannels of zeolite mordenite has been investigated by (1)H NMR technique. The (1)H spectra and spin-lattice relaxation times in the laboratory and rotating frames, T1 and T1ρ, respectively, as well as the dipolar relaxation time T1D have been measured in the temperature range from 96 to 351K. Diffusion of water molecules along the channels was observed above ~200K. While in bulk liquid the dipolar ordered state of nuclear spins is not formed owing to complete motional average of dipolar interactions, we show that such a state is observed for mobile molecules confined in a restricted geometry. At temperatures below ~140K the relaxation was found to be mainly caused by interaction of (1)H nuclear spins with paramagnetic impurities. Complete lost of the fine structure of (1)H spectra above ~320 K is attributed to isotropic molecular reorientation or/and proton exchange. We show that the dipolar relaxation in mordenite is responsive to slow 180° reorientations of water molecules. The correlation times of nuclear and electron spin fluctuations were determined.

Effect of magic angle spinning on (13)C spin-lattice and spin-spin relaxation in nanodiamonds.

We report on (13)C spin-lattice (R 1) and spin-spin (R 2) relaxation rate dependence on magic-angle-spinning (MAS) rate in highly purified synthetic nanodiamonds. Noticeable slowdown of both relaxation processes and reduction of nuclear spin diffusion coefficient D with increasing MAS rate was obtained. This effect is attributed to suppression of nuclear spin diffusion by MAS. We developed a theoretical approach that describes the MAS rate dependence of R 1, R 2 and D, allows quantitative analysis of the data and shows good compliance with the experiment.

(11)B MAS NMR study of Ga1-xFexBO3 mixed crystals.

Mixed iron-gallium borate crystals Ga1-xFexBO3 have been studied by Magic Angle Spinning (MAS) NMR of (11)B isotope. Experimental MAS NMR spectra have been computer simulated using a laboratory-developed code. The quadrupole parameters and isotropic chemical shift for (11)B are consistent with threefold-coordination of boron atoms. A detailed fitting to the experimental NMR spectra reveals the existence of a certain local disorder in Ga1-xFexBO3 crystals.

Size dependence of 13C nuclear spin-lattice relaxation in micro- and nanodiamonds.

Size dependence of physical properties of nanodiamond particles is of crucial importance for various applications in which defect density and location as well as relaxation processes play a significant role. In this work, the impact of defects induced by milling of micron-sized synthetic diamonds was studied by magnetic resonance techniques as a function of the particle size. EPR and (13)C NMR studies of highly purified commercial synthetic micro- and nanodiamonds were done for various fractions separated by sizes. Noticeable acceleration of (13)C nuclear spin-lattice relaxation with decreasing particle size was found. We showed that this effect is caused by the contribution to relaxation coming from the surface paramagnetic centers induced by sample milling. The developed theory of the spin-lattice relaxation for such a case shows good compliance with the experiment.

(13)C spin-lattice relaxation in nanodiamonds in static and magic angle spinning regimes.

We report on (13)C nuclear spin-lattice relaxation time (T1) dependence on the magic-angle-spinning (MAS) rate in powder nanodiamond samples. We confirm that the relaxation is caused by interaction of nuclear spins with fluctuating electron spins of localized paramagnetic defects. It was found that T1 is practically not affected by MAS for small particles, while for larger particles with lower defect density T1 is different in static and MAS regimes and reveals elongation with increasing MAS rate. This effect is attributed to suppression of nuclear spin diffusion by MAS. We propose an approach that describes T1 dependence on the MAS rate and allows quantitative analysis of this effect.

[Special industrial medicine as a basis for workers' health preservation].

The article covers results and prospects of research in special industrial medicine on improving methodology of complex evaluation of work conditions in major economy branches including medical sphere workers. On the basis of ecologic epidemiologic research, remote effects of occupational and non-industrial hazards in workers and general population were studied, new technologic processes and equipment were assessed, principles for unifying methods to control chemicals in workplace air were defined, regulation methodical documents concordant with WHO, ILO and EC are specified.

Nanodiamond graphitization: a magnetic resonance study.

We report on the first nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) study of the high-temperature nanodiamond-to-onion transformation. (1)H, (13)C NMR and EPR spectra of the initial nanodiamond samples and those annealed at 600, 700, 800 and 1800 ° C were measured. For the samples annealed at 600 to 800 ° C, our NMR data reveal the early stages of the surface modification, as well as a progressive increase in sp(2) carbon content with increased annealing temperature. Such quantitative experimental data were recorded for the first time. These findings correlate with EPR data on the sensitivity of the dangling bond EPR line width to air content, progressing with rising annealing temperature, that evidences consequent graphitization of the external layers of the diamond core. The sample annealed at 1800 ° C shows complete conversion of nanodiamond particles into carbon onions.

Hahn-echo decay for exchange-coupled nuclear spins in solids.

In this paper we present a simple model to calculate the Hahn-echo decay of the exchange-coupled nuclear spins in solids. Satisfactory agreement between the calculated and experimentally observed echo decay of the exchange-coupled spins of T203l and T205l isotopes in thallium chloride TlCl and thallium tantalum sulfide TlTaS(3) is obtained.

Three-pulse spin echo signals from quadrupolar nuclei in magnetic materials.

The time evolutions of the three-pulse spin echo signals from quadrupolar nuclei (63)Cu and (53)Cr in ferromagnetic CuCr(2)S(4):Sb have been investigated at the temperature T=77K. The experimental results were well explained by the developed theory of the time evolutions of the three-pulse echoes. The main assumption of this theory is the assumption that the temporal fluctuations in the electron magnetization lead to the fluctuations in the hyperfine and quadrupole interaction Hamiltonians.

Kubo-Anderson oscillator and NMR of solid state.

The analytical solution for the Kubo-Anderson oscillator with a fluctuating frequency omega for arbitrary distribution function p(omega) has been obtained. The obtained theoretical expression has been applied to consideration of some dynamical problems of solid state NMR, namely (1) dynamical transformation of NMR line shape and spin-echo signal and (2) the temperature transformation of the second moment of NMR line for the case, when the potential barrier for the mobility of magnetic nuclei is a stochastic function of time.

[Complex treatment of venous trophic ulcers of the lower extremities].

Under observation there were 189 patients with trophic ulcers of the lower extremities of venous genesis (CEAP VI class). In 78 patients conservative treatment was used with the low intensity laser radiation. Complex treatment consisted of preliminary preparing the ulcers and the following correction of the venous blood flow was used in 111 patients. 82 patients were treated by traditional methods disregarding the data of ultrasonic diagnosis. Laser therapy of ulcers by our original techniques and correction of the venous blood flow using new technologies and considering the data of duplex scanning was used in 29 patients, the best nearest and long-term results of the treatment being obtained in patients of this clinical group.

Calculation of dipolar correlation function in solids with internal mobility.

A general equation for the dipolar correlation function, to be used to analyze various kinds of independent internal motions, described by some correlation times tau(cm) (m = 1,2 em...k), has been obtained. The obtained expression has been used to analyze the temperature dependencies of different NMR measured values: second moment: spin-lattice relaxation times; amplitude of solid echoes signals.