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The m ethod of preparation of highly stable reproducible C60 fullerene aqueous colloid solution is described. The structural organization of C6o fullerenes in aqueous solution was studied and analyzed in detail using various techniques such as chemical analysis, U V /V IS spectroscopy, atomic force and scanning tunneling microscopy, dynamic light scattering, and zeta potential methods.

The contributions of various physical factors to the energetics of complexation of aromatic drug molecules with C(60) fullerene are investigated in terms of the calculated magnitudes of equilibrium complexation constants and the components of the net Gibbs free energy. Models of complexation are developed taking into account the polydisperse nature of fullerene solutions in terms of the continuous or discrete (fractal) aggregation of C(60) molecules. Analysis of the energetics has shown that stabilization of the ligand-fullerene complexes in aqueous solution is mainly determined by intermolecular van der Waals interactions and, to lesser extent, by hydrophobic interactions. The results provide a physicochemical basis for a potentially new biotechnological application of fullerenes as modulators of biological activity of aromatic drugs.

In this work, we report that the surface hydroxylation of C 60 molecules is the most likely mechanism for pristine C 60 fullerenes/C 60 fullerene aggregate stabilization in water, being independent of the method of C 60 fullerene aqueous solution preparation. ■ INTRODUCTIONNanocarbon materials are used in a wide variety of biomedical applications, including biosensorics, targeted drug delivery, chemotherapy, cellular imaging, and diagnostics. 1 For example, the pristine C 60 fullerenes as a unique class of carbon allotropes are able to penetrate the cell membrane, 2,3 to exhibit antioxidant properties, 4,5 and, being nontoxic (at least at low concentration), 6 to exert specific health effects (e.g., antibacterial, 7 antitumor, 8 and drug carrier 9 ).Biomedical applications require a dispersal of C 60 fullerene in a solvent, with aqueous dispersions being preferred because of biocompatibility, safety, or environmental concerns. Although pristine C 60 fullerenes have extremely low water solubility, they can form stable colloid solutions containing individual C 60 fullerenes as well as C 60 fullerene aggregates (clusters) in water when subjected to extended mixing, sonication, or solvent exchange 10−16 (to be further referred to as a C 60 fullerene aqueous colloid solution (C 60 FAS)). However, the origin of stabilization of such particles in water still remains poorly investigated.At least two approaches have been suggested in order to explain the stability of fullerene particles in water solutions. One of them 17 postulates the formation of a water shell around C 60 molecules stabilized simultaneously by the H-bonding network between the water molecules and charge transfer from water to the C 60 fullerene. Another one 18 suggests that the sonication process induces the covalent attachment of water hydroxyls to C 60 fullerene carbons, resulting in the formation of alcohol moieties that enable C 60 fullerene dissolution. The problem here is that the properties of C 60 FAS (including biological properties) as well as the mechanism of water solubility may depend on the method of preparation of C 60 fullerene aqueous solution. 13,16,17 Indeed, these two approaches differ by the underlying method of C 60 FAS preparation although the sonication step is presented in both methods. The question therefore arises as to whether the mechanism of solubility of C 60 fullerene in water depends on the method of C 60 FAS preparation. This question has been investigated in this article. ■ EXPERIMENTAL SECTIONSample Preparation. For the preparation of C 60 FAS, we used a saturated solution of pure C 60 fullerene (purity >99.99%) in toluene with a C 60 molecule concentration corresponding to maximum solubility near 2.9 mg/mL and the same amount of distilled water in an open beaker. The two phases that formed were treated in an ultrasonic bath. The procedure was continued until the toluene had completely evaporated and the water phase became yellow. Filtration of the aqueous solution allowed us to separate the product from un...

In the present work we develop a novel approach for quantification of the energetics of C60 fullerene aggregation in aqueous media in terms of equilibrium aggregation constant KF. In particular, it is shown that the experimental determination of the magnitude of KF is possible only within the framework of the 'up-scaled aggregation model', considering the C60 fullerene water solution as a solution of fullerene clusters. Using dynamic light scattering (DLS) data we report the value, K(F) = 56,000 M(-1), which is in good agreement with existing theoretical estimates and the results of energetic analyses. It is suggested that the proposed 'up-scaled model' may be used in any instances of non-specific aggregation resulting in formation of large spherical particles. The measurement of the translational diffusion coefficient and the dimensions of the light scattering particles using a DLS approach with respect to C60 fullerene aggregates is found to contain significant systematic errors originating from the interaction effect that is well-known for micellar solutions. As a result, corrections to the equations associated with DLS data are proposed.