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Unformatted text preview: Fluorescent Studies on Cooperative Binding of Cationic Pheophorbide- a Derivative to Polyphosphate O LGA R YAZANOVA , a I GOR V OLOSHIN , a I GOR D UBEY , b L ARISA D UBEY , b AND V ICTOR Z OZULYA a a B. Verkin Institute for Low Temperature Physics and Engineering of NAS of Ukraine, Department of Molecular Biophysics, Kharkov, Ukraine b Institute of Molecular Biology and Genetics of NAS of Ukraine, Kyiv, Ukraine The cooperative binding of a novel water-soluble cationic derivative of pheophorbide- a (CatPheo- a ) to inorganic polyphosphate (PPS) in buffered aqueous solutions was studied by means of polarized fluorescence spectroscopy in a wide range of molar phosphate-to-dye ratios (P/D). Under low P/D values, CatPheo- a forms extended stacking associates on the PPS matrix, while under high P/D the dye binds to PPS in the dimer form. The CatPheo- a self-association is accompanied by 40-fold dye fluorescence quenching and a substantial increase in the fluorescence polarization degree. The fluorescent titration data were used for determination of cooperative binding parameters by Schwarzs method. Key words: pheophorbide- a ; polyphosphate; polarized fluorescence; cooperative binding; stacking association Introduction In the last two decades considerable interest and re- search efforts in life sciences have been focused on the study of photophysical properties of porphyrin dyes, which can be used in molecular biology and medicine as photosensitizers. 13 The pheophorbide- a (Pheo- a ) is an anionic porphyrin derivative which can be eas- ily prepared from chlorophyll. 4 It is used in photody- namic therapy 2 , 5 of tumors and psoriasis because of its high photosensitizing activity in vitro and in vivo . 69 The photophysical properties of Pheo- a were inves- tigated earlier. 10 , 11 It is known that Pheo- a is selec- tively accumulated in tumor cells, being incorporated into their nuclei, mitochondria, and lysosomes. 12 The dye has a high extinction coefficient in the red re- gion of spectrum, where the transparency of tissues to light increases considerably. It was established that the photodynamic activity of Pheo- a is predominantly determined by monomeric dye molecules. However, the dimerization 13 or aggregation of the dye in water- Address for correspondence: Olga Ryazanova, B. Verkin Institute for Low Temperature Physics and Engineering of NAS of Ukraine, 47 Lenin ave., 61103, Kharkov, Ukraine. Voice: + 38-057-3410934; fax: + 38-057- 3450593. ryazanova@ilt.kharkov.ua containing solutions strongly reduces its photodynamic activity. Natural Pheo- a contains a carboxylic group, and its anionic character prevents it from efficient in- teraction with negatively charged nucleic acids....
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This note was uploaded on 07/11/2010 for the course SPECTOGRAP 545 taught by Professor Gdf during the Spring '10 term at AIB College of Business.

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fulltext40 - Fluorescent Studies on Cooperative Binding of...

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