NMR of Liquid 3He in Pores of a Clay Sample

In the present work a new method for studying porous media by nuclear magnetic resonance of liquid ³He has been proposed. This method has been demonstrated by an example of a clay mineral sample. For the first time the integral porosity of the clay sample has been measured. For investigated samples the value of the integral porosity is in the range of 10–30%. The inverse Laplace transform of the ³He longitudinal magnetization recovery curve has been carried out and the distribution of the relaxation times T ₁ has been obtained.     

Size effect in the (PrF3 nanoparticles-3He) system

Spin kinetics of adsorbed and liquid ³He in contact with crystalline nanopowders of the Van Vleck paramagnet PrF₃ at a temperature of 1.5 K has been studied by nuclear magnetic resonance. The correlation between the parameters of the nuclear magnetic relaxation of ³He and the sizes of the sample particles has been found. A qualitative model of the magnetic relaxation of ³He describing the experimental results has been proposed.     

The use of a lyotropic liquid-crystalline medium and residual dipolar coupling constants for determination of the spatial structure of thiacalix[4]arenes in solutions

The possibility of using an approach for the elucidation of the spatial structure of functionalized thiacalix[4]arenes based on the determination the residual dipolar coupling constants between the ¹H and ¹³C nuclei separated by one chemical bond (¹ D _CH) in lyotropic liquid-crystalline media (poly--benzyl-L-glutamate and CDCl₃) is demonstrated for the first time. This approach was used to distinguish between the cone and 1,3-alternate conformations of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(2-oxopropyloxy)-2,8,14,20-tetrathiacalix[4]arene. The results were confirmed by the data from 2D NMR (¹H—¹H) NOESY experiments for these compounds in an isotropic solvent (CDCl₃).     

NMR and AFM investigations of nanocavities on the double rare-earth fluoride crystal surface

Nanocavities with a size of less than 30 nm on the crystal surface of superfine LiYF₄ powders and single crystals of the Van Vleck paramagnet LiTmF₄ were detected by nuclear magnetic resonance (NMR) cryoporometry and atomic-force microscopy (AFM) and liquid³He NMR cryoporometry. NMR investigations show that the nanocavities are evidently present on the surface of the LiYF₄ powder particles. The distribution of nanocavities has two maxima corresponding to the specific porous sizes of 3–5 and 10–15 nm. AFM investigations detect the presence of the nanocavities with sizes in the range 50–300 nm on the surface of powder particles and single crystals. The cases of powder microparticles and of a single crystal differ in the value of the parameter “surface roughness”, which is 14.5 and 11 nm, respectively. The mechanism of creation of nanocavities is proposed and verified by additional investigations with CaF₂ powders.     

Benzopyridosilaazepines and benzopyridosilaazepinones

The Beckmann rearrangement of dihydrosilazatone oximes yields benzopyridosilaazepinones which are isomeric relative to the position of the amide fragment in the central ring. One of these isomers is converted upon thermolysis at 250 °C to the lactam of o-(3-aminopyridyl-4)benzoic acid. The reduction of benzopyridosilaazepinones yields benzopyridosilaazepines.     

Phase diagrams of new lamellar liquid crystalline systems based on 2H NMR spectroscopy data

1. Download : Download high-res image (86KB)
2. Download : Download full-size image