Alexey V. Donets

Magnetic Resonance and Its Applications

Magnetic resonance and its applications , Magnetic resonance and its applications , کتابخانه دیجیتال جندی شاپور اهواز

“Hydration Shells” of CH2 Groups of ω-Amino Acids as Studied by Deuteron NMR Relaxation

Hydration phenomena play a very important role in various processes, in particular in biological systems. Water molecules in aqueous solutions of organic compounds can be distributed among the following substructures: (i) hydration shells of hydrophilic functional groups of molecules, (ii) water in the environment of nonpolar moieties, and (iii) bulk water. Up to now, the values of hydration parameters suggested for the description of various solutions of organic compounds were not thoroughly analyzed in the aspect of the consideration of the total molecular composition. The temperature and concentration dependences of relaxation rates of water deuterons were studied in a wide range of concentration and temperature in aqueous (D2O) solutions of a set of ω-amino acids. Assuming the coordination number of the CH2 group equal to 7, which was determined from quantum-chemical calculations, it was found that the rotational correlation times of water molecules near the methylene group is 1.5-2 times greater than one for pure water. The average rotational mobility of water molecules in the hydration shells of hydrophilic groups of ω-amino acids is a bit slower than that in pure solvent at temperatures higher that 60 °C, but at lower temperatures, it is 0.8-1.0 of values of correlation times for bulk water. The technique suggested provides the basis for the characterization of different hydrophobic and hydrophilic species in the convenient terms of the rotational correlation times for the nearest water molecules.

Nuclear Quadrupole Resonance

Nuclear quadrupole resonance (NQR) is one of the most sensible tools to study the local structure of materials, electronic density distributions near the nuclei under study, the nature of defects in solids, the mobility of molecules, or their parts, phase transitions and so on. It is very helpful to investigate physical properties of solids, molecular crystals and polymers especially, but can be applied to metals and glasses as well. In liquids quadrupole interactions are averaged to zero and NQR is not applicable.

Nuclear Magnetic Relaxation

In Chap. 1 the concepts of the nuclear magnetic relaxation times (rates) were introduced on the basis of phenomenological considerations, as exemplified by the theory of Bloch.

Covalent-Coupled Paramagnetic Complexes

We have already met the situations when the crystal field model does not lead to correct results. This is the case of the strong crystal field when the interaction of surrounding ions or molecules with a paramagnetic center is comparable with electrostatic interactions of electrons in a ion.

Two-Dimensional NMR Fourier Spectroscopy

Two-dimensional Fourier-transform spectroscopy of nuclear magnetic resonance is one of the capital and most extensive research concepts in the NMR spectroscopy that allows the investigation of complex systems of coupled nuclear spins. Usual one-dimensional spectra are failed to be decoded because of inevitable lineoverlap for large molecules.

Basic Interactions of an Electron in Solids

This part focuses the attention on the approach suitable for studying assemblies of weakly interacting paramagnetic centers. Here we will not consider magnetically ordered systems where ferromagnetic, ferrimagnetic or antiferromagnetic resonance phenomena can be observed, as well as systems with free electrons (metals and semiconductors).

Energy Levels of Paramagnetic Center in Crystal Field

The analysis of the nature of splitting of ion levels under the influence of the crystal field is based on the Wigner theorem and Eq. 10.30.

Magnetic Resonance Quantum Magnetometry

One of the applications of Quantum Radiophysics is quantum magnetometry, based on the phenomenon of magnetic resonance and optical orientation atomic and nuclear moments. Specialists in many fields of physics and engineering face the necessity of the magnetic measurements, but the long-known classical methods do not provide modern requirements to accuracy and reliability of measurements. In the quantum magnetometry the measurement of field magnitude is performed by measuring the frequency of transitions between Zeeman sublevels of the spin system, that can be done with high accuracy by means of radioelectronics. The chapter is devoted to a brief exposition of the physical principles and guidelines of construction of nuclear and atomic quantum magnetometers. The most bright applications of the quantum magnetometry are realized for the measurement of the magnetic field of the Earth (especially its variations in space and time).

Nuclear Magnetic Resonance in Magnetic Materials

Nuclear magnetic resonance in magnetically ordered materials was first observed by Gossard and Portis in the metallic cobalt on \(^{59}\)Co nuclei A. C. Gossard and A. M. Portis, Observation of Nuclear Resonance in a Ferromagnet. Phys. Rev. Lett. 3 (1959) 164–166. Since then numerous studies of different magnetically ordered materials were performed.