ИСТИНА

Fullerenes attract the attention in many fields. They are used in the production of composites and catalysts. Of much value are their applications for the immobilization of medicines. Fullerenes form colloidal solutions (dispersions) in aqueous media. These aqueous fullerene dispersions (AFDs) [1] can also be applied to one of the most promising and innovative directions, drug delivery. At cell and macro levels, their aqueous solutions are powerful antioxidants that adsorb free radicals and prevent aging and various pathologies like cancer, cardiovascular diseases, etc. As well, fullerene clusters of certain size may create an antiviral cell barrier. However, such uses are still limited because AFDs, which are of prime importance for solving these problems, are not fully characterized and difficultly regulated. The parameters of AFDs that are required in many fields are their light-absorption, thermophysical, and size-related properties. In our opinion, photothermal spectroscopy can be used successfully in determining these properties due to their intrinsic capabilities. It is strongly necessary for biomedical purposes to know concentration of fullerenes in solutions and size of colloidal particles. Nowadays, there are not many articles that deal with the investigation of AFDs by photothermal spectroscopy [2]. The aim of this study is to estimate the possibilities of thermal-lens spectroscopy (TLS) for monitoring AFDs. Another goal is the determination of ultra-low concentrations and size of fullerenes in aqueous media. Dependence of the steady-state thermal-lens signal from fullerenes in various media was obtained, showing wide linear ranges of calibration curves and high sensitivity for AFDs in all the cases. Another aim is to carry out experiments of kinetics of coagulation of AFDs using strong acids and increasing ionic strength. The time-resolved curves are used for determining the thermophysical parameters of AFDs. Putting together the data from thermal-lens experiments and state-of-the-art spectrochemical methods like these UV/Vis/IR spectroscopy allows to us corroborate the hypothesis about the conjectural structure of AFDs. The data of TLS on the size parameters of AFDs are backed up by other state-of-the-art methods like dynamic light scattering (DLS) and small-angle neutron scattering. The method comparison shows that DLS has some significant drawbacks like the problem of scattering on large particles and do not show satisfactory results in all instances. From our evaluation of thermal-lens experiment, the estimation of size of AFDs is in good concordance with DLS data. Acknowledgements This work was supported by the Russian Foundation for Basic Research, grants nos. 12-03-00653-а and 12-03-31569-mol_a and the Ministry of Science and Technology of Russian Federation, contract no. 16.740.11.0471 and by the grant for Leading Scientific Schools in Russia. Reference. 1. McHedlov-Petrossyan, N.O., Klochkov V.K., and Andrievsky G.V., Colloidal dispersions of fullerene C60 in water: some properties and regularities of coagulation by electrolytes. Journal of the Chemical Society, Faraday Transactions, 1997. 93(24): p. 4343-4346. 2. Volkov, D.S., et al., Quantification of nanodiamonds in aqueous solutions by spectrophotometry and thermal lens spectrometry. Journal of Analytical Chemistry, 2012. 67(10): p. 842-850.