From Big Medical Encyclopedia

SOLVATION (Latin solvere to dissolve) — the phenomenon which is the cornerstone of process of dissolution and consisting in electrostatic interaction between particles of solute (ions, molecules, macromolecules) and molecules of solvent, and also between colloid particles and particles of suspensions or emulsions and molecules of a dispersion medium. The page is an important condition of dissolution of substances and stability of solutions, suspensions and emulsions, including solutions of biopolymers (proteins, nucleinic to - t, etc.) or bioemulsions (a blood plasma, a lymph, etc.).

S.'s phenomenon is extremely important in processes of digestion, absorption and transport of nutrients, in all processes of a metabolism at the person and animals as any reactions in a live organism can happen only between solvated molecules and ions. Any disturbances of process

of S. can bring to patol. to processes (formation of stones, pathology of a bone tissue and so forth). Knowledge of patterns of S. is necessary during the development of the scientific principles of selection of the solvents used as at synthesis of pharmaceuticals, and their introduction to an organism of the patient. Sometimes selection of solvent at synthesis of pharmaceuticals possible to achieve elimination of racemization (see. Racemic connections ), what essentially affects the mechanism of action, activity and side effects of synthesizable drug. When solvent or a dispersion medium is water, the concept «solvation» is replaced with the term «hydration» (see Hydration). Process, the return S., call desolvation.

For the first time D. I. Mendeleyev in the 60th 19 century pointed to S.'s role in the course of dissolution. The solvate theory was offered them solutions (see). Solvation is the reason of disintegration of molecules electrolytes (see) in solutions on ions, and also a major factor of stability of lyophilic colloids (see) and coarse suspensions. The molecular groups which are formed as a result of S. call solvates, in water solutions or dispersions — hydrates. Formation of solvates happens thanks to van-der-vaalsovym (molecular) forces operating between particles of solute and molecules of solvent (see the Molecule, molecular forces). Communication between them is sometimes so strong that remains also in solid state, at the same time from solutions the firm solvates called by kristallosolvata, e.g. LiClO4 • 4CH3OH, AlBr3 • C6H6, etc. crystallize. A special case of kristallosolvat are crystalline hydrates (see).

S. of ions is fullestly studied. The concept about S. of ions was for the first time entered into scientific practice in 1891 by I. A. Kablukov investigating properties of solutions of hydrogen chloride in non-aqueous solvents. The molecules of solvent having constant dipole moments are attracted to an ion by opposite loaded ends and are guided in electric field of an ion, forming a solvation shell. The so-called inner layer of a solvation shell, next to an ion, contains usually from 2 to 15 molecules of solvent which are rather strongly connected with an ion. Molecules of solvent, more remote from an ion, rather less strongly related, form an enveloping layer of a solvation shell. The number of molecules in a solvation shell of an ion is changeable and depends on many factors (by nature an ion and solvent, on temperature, on concentration of solution, etc.). Owing to the arranged orientation of molecules of solvent in a solvation shell it has a certain structure and differs on properties from other mass of solvent. Solvates can result also from interaction of ions with the dipoles of unpolar molecules of solvent induced under their influence, and also owing to dispersive interaction between particles of solute and molecules of solvent; these types of interactions between particles of solute and molecules of solvent have essential value of hl. obr. in non-polar solvents. With umensheniye:.! polarity of molecules of solvent the aspiration to formation of solvates decreases. As a result of S. of ions their effective (hydrodynamic) radiuses increase that affects the speed of movement of ions in electric field. Small ions are a source of stronger electric fields and therefore are characterized by bigger degree of Page.

Between molecules of solvent and particles of solute the hydrogen bindings playing a huge role in formation of structures of macromolecules and at interaction of biologically important connections can be formed. In this case there are solvates of a certain structure, and S. call specific.

Bibliography: Drakin S. I. A structure of the first solvation shell of ions in solutions and crystal solvates, in book: Probl. solvations and complex formations, under the editorship of G. A. Krestov, etc., page 56, Ivanovo, 1978; Karjakin A. V. both To r and in e N of c about in and G. A. Sostoyaniye of water in organic and inorganic compounds, M., 1973; M e c of l of e r D. Biokhimiya, Chemical changes in living cell, the lane with English, t. 1, page 244, M., 1980; M and puppy K. P. and Poltoratsky G. M. Termodinamika and structure water and nevodeshkh solutions of electrolytes, JT., 1976; P and to and e in A. K. A solvated electron in a radiochemistry, M., 1969; The State and a role of water in biological objects, under the editorship of L. P. Kayushin, page 31, M., 1967; Thermodynamic properties of solutions, under the editorship of A. F. Vorobyov, etc., No. 1, M., 1980; E N of t e l and with S. G. • and T and of e r R. P. Kinetics of reactions in a liquid phase, Quantitative taking note of the environment, M., 1973; Spink of Page N. W a d s of J. Thermochemistry of solutions of biochemical model compounds, J. chern. Thermodyn., v. 7, p. 561, 1975.

V. P. Mishin.