ИСТИНА

Unique properties of fullerenes, especially endohedral metallofullerenes (EMFs) and their dispersions find increasingly wide acceptance in basic science and applied technologies. During the last decade, they are in demand in up-to-date energy systems and fine-chemical and drug synthesis. Recently, much attention has been paid to their use in medicine e.g. for drug delivery into cells or for attaching various substances to cell membrane surface, MRI contrast agent, radiopharmaceuticals. Here, one of the difficulties is the synthesis of non-toxic watersoluble fullerene compounds that can be introduced into human body. In this regard, aqueous dispersions (AFD) of unmodified (pristine) fullerenes and EMFs are of importance. Nonetheless, AFDs show certain difficulties and often call for a chemical modification or the use of the toxic organic solvents. In addition, the aggregation properties of AFDs have not been studied in full. Currently, there is a lack of sufficient methodology for accurate identification and aggregation, size, surface alteration etc. characterization. Thus, the aim of this study is to develop approaches to the analysis of the fullerene aqueous dispersions. AFDs of Y@C 82 and Gd@C 82 were prepared according to the procedure of solvent-exchange protocol and dispergation with a surfactant. Total organic carbon analyzer was used for the determination of carbon in AFDs. ICP-OES was used for trace metal analysis with direct input of the AFD samples. The crucial aspects of the AFD production is the residual amount of the organic solvents. Headspace GC/MS procedure was applied for estimating this hazardous content. In the case of organic solvent-polluted samples, we used the step of SPE purification. Concentration of the residual organic solvent (benzene, toluene, o-xylene etc.) was no higher than 0.1 ppb. The content of fullerenes and EMFs in their aqueous dispersions at a very low level (ppm) makes the use of classical methods of chemical analysis almost impossible. Thus, to solve this problem, low concentrations of fullerenes and EMFs were determined using thermal-lens spectrometry. To prove the state of the unmodified fullerene and EMFs in AFDs, their UVvisible absorption spectra as well as the spectra of the toluene extracts were recorded; the data show that the majority of fullerene and EMFs in AFDs is not chemically modified. Furthermore, MALDI confirmed the unmodified state of fullerenes and EMFs in their AFD: we did not observe the m/z peaks more than fullerene molecular ion signals. An important parameter (as the cell membrane is able to pass a very limited size of the molecule clusters or aggregates into the cell) is the distribution of fullerene and EMF cluster size, which was implemented by DLS and HRTEM. The average clusters diameter was estimated ca. 100 nm for C 60 , C 70 , and Y@C 82 . The cluster stability was estimated by zeta potentials. The concentration of EMF was determined by ICP-OES. We used analytical wavelengths Y 324.228 nm, Gd 358.496 nm, and Bi 223.061 nm was selected as an internal standard. Another interesting application of EMF is MRI agents. For the Gd@C 82 the characteristic of potency to decrease the nuclear spin relaxation rates of water protons was measured. Its effect on the proton relaxation rate is 60-fold higher than that of the commercial contrast-enhancing agent “Magnevist” commonly used in MRI.