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It has been found that the Cl -and Br -anions change the microstructure of their hydration shells in the temperature range 30-35°C. The effect was observed for simple salt solutions and ternary systems with different organic compounds. Probably this effect can be responsible for the thermoregulation of warm-blooded animals.

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. However, this approach can not clarify the nature of relaxation processes and quantify the relaxation times of various nuclei in different environments. The answers to these questions are given by quantum theory, which allows the calculation of the probability of relaxation transitions. In this chapter the problems of the relaxation in two-and multi-spin systems will be considered using the theory of time-dependent perturbations. Probability Relaxation TransitionsThe interaction of nuclei with the environment (neighboring nuclei, unpaired electrons and etc.) can lead, firstly, to non-equidistant energy levels and, consequently, the splitting of the spectrum of the nuclear magnetic resonance, secondly, to non-radiative transitions of nuclei between different energy states (exchange of energy between different degrees of freedom inside a substance). These non-radiative transitions have usually chaotic character and are a fundamental mechanism of the achievement of an equilibrium (Boltzmann) distribution of nuclei among energy states. These processes, which are the main object of consideration in this chapter, are called as relaxational. In general, the Hamiltonian of the nuclei system can be written aswhere H 0 describes the interaction of nuclei with a constant magnetic field B 0 , H describes their interaction with the environment. In the investigations of nuclear magnetic resonance in the majority of cases one deals with weakly interacting nuclei. Therefore, the Hamiltonians H 0 and H contain terms, taking into account the interaction of an isolated nucleus or a small number of nuclei with the external field B 0

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.

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