17O NMR  INVESTIGATION OF WATER CLUSTERS IN WATER – ELECTROLYTE SYSTEM

G.A.Kalabin1, L.E.Rzaeva2, V.S.Erofeeva2, A.V.Rokhin2, D.F.Kuschnarev2

1Peoples’ Friendship University of Russia, 8/5 Podolskoye Shosse, 113093 Moscow, Russia
2Irkutsk State University,1 K.Marx Street, 664003 Irkutsk, Russia

The 17O chemical shifts (δ17O) and relaxation rates (v½) values of water have been measured in aqueous solutions with various salts C+A¯, where C+ = Na+ , K+, NH4+ and A¯ = Cl¯, Br¯, I¯, NO3¯. The effects of the electrolytes on 17O parameters together with some predicted hydration structures from computational date of classical molecular dynamic have been discussed. The most interesting results for K+/water complexes are discovered. As an example, the dependence between relaxation rate 17O of some nitrates in solution with concentration (C, mol/L, abscissa axis) have been shown.

It may be concluded, that Na+ is the structure-formed (positively hydrated) cation irrespective of a counter ion. The cation K+ has binary properties (structure-forming and structure-destroying). It has been observed water clusters which consist of about 28 or 80 molecules water for a system with anion NO3¯ (and about 14, 28 or 112 – with anions Cl¯ and I¯). The cation NH4+ is realizing the isomorphous-like replacement of water molecules irrespective of a counterion.