Photosensitizing properties of supramolecular systems based on chlorine е6 I. V. Klimenko1, A.V. Lobanov2 1Emanuel Institute of Biochemical Physics, Rus. Ac. Sci., Kosygin str. 4, Moscow, Russia 2Semenov Institute of Chemical Physics, Rus. Ac. Sci., Kosygin str. 4 Moscow, Russia *E-mail: inna@deom.chph.ras.ru

INTRODUCTION One of the most important tasks during the new medicines creation applied at photodynamic therapy is the research of physico-chemical properties of the novel porphyrine containing objects, such as the water-soluble derivative of chlorophyll - chlorine e6 (Ce6), which belongs to the group of second generation photosensitizers (PS). Ce6 is absolutely non-toxical PS and at the same time anticancer immune response modifier which is strongly activating system of cell-mediated immunity and, especially, K cells, distinguishing and destroying tumor cells. It has the following spectral and power characteristics: the maximum of Ce6 absorption is in area of 660±5 nm that corresponds to area of the greatest optical transparency for biological tissue, and a quantum yield of singlet oxygen reaches 0.7 [1]. 1. Parkhats M. V., Galievsky V. A., A. S. Stashevsky A. S., Trukhacheva T. V., Dzhagarov B. M. Dynamics and efficiency of the photosensitized singlet oxygen formation by chlorin e6: the effects of the solution pH and polyvinylpyrrolidone. Optics and Spectroscopy, 2009, v. 107, № 6, p. 974–980. Nowadays a number of PS based on Ce6 is applied in clinical practice in Russia [2], but searches of other, more effective medicines and ways of their receiving continue now. 2. Akopov A.L., Kazakov N.V., Rusanov A.A., Karlson A., The mechanisms of photodynamic action for treating of cancer patients. Photodynamic therapy and photodiagnostics, 2015, №2, p. 9-16

Purposes of research - To collect spectral data of optical absorption and fluorescence of different supramolecular systems with the purpose of the optimum excipient selection - To study the influence of various excipients on spectral characteristic of this supramolecular systems. - To define the influence of intermolecular interactions on aggregation behavior of chlorine e6 in solutions. - To determine efficiency of data of supramolecular systems in generation of singlet oxygen.

Objects of research: We studied optical absorption and fluorescence of supramolecular systems based on chlorine e6 (Ce6 ) (2•10-5 М) in different excipients such as poly- N vinylpyrrolidone (PVP), polyethyleneglycol (PEG), bovine serum albumin (BSA), Triton X-100 (TX-100) PEG PVP Chlorine e6 ТХ-100 BSA

Research methods - Absorption spectra (200-900 nm) were recorded with TU-1901 UV-Vis spectrophotometer from Beijing Purkinje General Instruments Co Ltd. Poorly resolved spectra were analyzed by decomposing the spectra into their Gaussian constituents. The fluorescence spectra in the range of 550-800 nm were recorded with Fluorat-02-Panorama set-up (Lumex). The excitation wavelength was 410 nm. All measurements were conducted at 20 0С in standard K10 quartz cuvettes with optical path lengths of 1 cm. Registration of singlet oxygen was carried out by the method of "chemical traps". 1,3-diphenylisobenzofuran was used as a "trap".

Fig.1. Optical absorption spectra of Ce6 (2•10-5 М) in aqueous solution

Fig.2. Optical absorption spectra of supramolecular systems based on Ce6 (210-5 М) in the region of the Soret band: 1. Ce6 in aqueous solution, 2. Ce6 -BSА, 3. Ce6 -PEG, 4. Ce6 -ТХ-100, 5. Ce6 -PVP

Fig. 3. Optical absorption spectra of supramolecular systems based on Ce6 (210-5 М): 1. Ce6 in aqueous solution, 2. Ce6 -BSА, 3. Ce6 -PEG, 4. Ce6 -ТХ-100, 5. Ce6 -PVP

Fig. 4. Fluorescence spectra of supramolecular systems based on Ce6 (210-5 М): 1. Ce6 in aqueous solution, 2. Ce6 -BSА, 3. Ce6 -PEG, 4. Ce6 -ТХ-100, 5. Ce6 -PVP

RESULTS - When studying spectral properties of all presented supramolecular systems on the base of Ce6 the "blue" shift in the region of the peak Cope wasn't revealed. It testifies the identical hydrophobic nature of all systems, similar to hydrophobic nature of Ce6. - On the basis of optical density drop in the region of the peak Cope for all systems it is possible to speak about the formation of singlet oxygen in all presented supramolecular systems. The hypochromic effect is the result of the strengthening of intermolecular interactions and the formation of molecular complexes. - The spectral changes in the Q band region, connected with the bathochromic shift of a long wave absorption band of a sensitizer, and essential reduction of half-width demonstrate the disaggregation of the Ce6 molecules, their interaction with excipients in solutions and formation of a molecular complex. The appearance of molecular complex band of the porphyrine with TX-100, BSA and PVP at 615 nm is the confirmation of this. -The specific characteristic of fluorescence spectra of all supramolecular systems is their overlap with Q band of absorption spectra, that allows to consider the formed molecular associates and complexes as donors of photoexcitation energy for Ce6 molecules. It is revealed that addition of all studied excipients in Ce6 aqueous solution leads to the increase of fluorescence intensity of Ce6. The greatest increase in intensity of fluorescence is observed at addition of PVP. - As a part of the supramolecular complexes Ce6 is an effective photosensitizer of singlet oxygen generation with a quantum yield 0.53 (Ce6-PVP), 0.50 (Ce6-PEG), 0.62 (Ce6-TH-100) and 0.56 (Ce6-BSA).

CONCLUSION Thus, the study of spectral and fluorescent characteristics of various supramolecular systems on the basis of chlorine e6 allow to conclude prospects of further researches for search of new sensitizers in photodynamic therapy The obtained results allow to develop promising method of controlled aggregation of photosensitizers in the composition of supramolecular complexes to create medicines of predictable photodynamic activity.