Hydrated fullerenes (CnHyFn) can be received only in the form of their water solutions (CnFWS - “Fullerene Water Solutions”, where n is the quantity of carbon atoms in the fullerene molecule).

 

The general principle of obtaining CnFWS (i.e. hydrated Cn fullerene solution) is as follows.

The solution of fullerene (e.g., C60) in organic solvent, where it can exist as single molecules, is added to water and sonicated under special conditions. Under the chosen processing conditions, what occurs is the instantaneous substitution of the solvate shell, comprised of molecules of the organic solvent and initially surrounding the С60 molecule with a spherical hydrated (aqueous) one. In such a shell, 6 water molecules take part in the formation of donor-acceptor contacts with symmetrically-located electron-acceptor centres on the fullerene surface and 18 more water molecules via joint hydrogen bonds and, together with 6 molecules on the surface, form the uniform and spherical net around C60 (= hydrated C60 fullerene, C60HyFn). In other words, there is “collapse” of bulk water around the spherical molecule of C60 with the formation of a strong water shell, which fullerene cannot get out of. Now water itself (6+18=24 molecules) has different properties from those of bulk ones. Fullerene cannot be practically removed from this net. For example, it is not extracted from FWS with nonpolar organic solvents and its water shell does not disintegrate upon heating (at least, up to a temperature of 125?C) or under the effect of inorganic and organic coagulants.

 

It is interesting that in heavy water, in D2O, a solution similar to C60FWS cannot be obtained, as heavy water is not capable of forming stable and strong hydrated shells around the C60 molecule.

 

As was pointed out above, for C60HyFn production, a method of fullerene molecule transfer from the organic phase into the water phase is used. Under conditions of ultrasonic cavitation and the heating of the reaction mixture above the boiling point of the azeotropic mixture of the organic solvent with water, what occurs is the substitution of organic molecule, the surrounding fullerene molecules, and water molecules.

 

The organic phase is removed from water solution as an azeotropic mixture with water. The resultant solution undergoes multi-stage additional purification from the residue of organic solvent and other technological impurities. After completion of all the necessary technological procedures, we obtain an aqueous concentrate of C60HyFn, containing only fullerene C60, water and small quantity of inorganic cations.

 

In the process of hydrated fullerenes’ production, much attention is paid to the purity of the resultant solutions. As raw materials, we use fullerene C60 with a purity of at least 99.9%. Water and other components taking part in the technological process preliminarily undergo additional deep purification. The C60HyFn concentration is determined on the basis of the absorption spectrum of its water solution. The coefficient of molar extinction in the maximum absorption band at 343 nm is 68 000 LxM-1xcm-1.

At present, it has been possible to achieve concentrations of hydrated C60 in water solution of about 4 mg/ml, which exceeds C60 solubility in organic solvent, toluene, which is considered to be a good solvent for fullerenes.

 

For biological purposes, solutions of hydrated C60 undergo sterilisation at 100-120?C.