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Unformatted text preview: Dextrin-Microencapsulated Porphyrin Luminescent Properties P RISCILLA P AIVA L UZ , C L ´ AUDIO R OBERTO N ERI , AND O SVALDO A NTONIO S ERRA Chemistry Department of FFCLRP, University of S˜ao Paulo, Ribeir˜ao Preto, Brazil Photophysical properties of porphyrins in aqueous solutions are strongly affected by aggre- gation. One possible solution to this problem is to encapsulate the porphyrin into polymeric spheres, to provide an environment where the photosensitizer can be administered in its monomeric form in such treatments as photodynamic therapy. Here we report the microen- capsulation of the meso-tetrakis(4-sulphonatophenyl) porphyrin (TPPS 4 ) photosensitizer by the ultrasonic spray-drying technique. The encapsulated TPPS 4 was morphologically characterized by scanning electron microscopy, and its photophysical properties were studied and compared with those of a physical blend of dextrin and TPPS 4 . We successfully encapsulated TPPS 4 into dextrin microspheres, and the encapsulated photosensitizer displays higher luminescence in- tensity than that of the prepared physical blends. Key words: microencapsulation; spray-drying; porphyrin; luminescence; photodynamic therapy Introduction Photodynamic therapy (PDT) is an efficient ther- apeutic modality for the treatment of a variety of oncological, cardiovascular, dermatological, and oph- thalmic diseases. PDT is based on the use of photo- sensitizers, which are preferentially taken up and/or retained by diseased tissue. 1–3 Activation of the photo- sensitizer upon absorption of light at the appropriate wavelength takes the drug from its ground state ( 1 PS) to an excited singlet state 1 PS ∗ (F IG . 1). From this state, the drug may decay directly back to the ground state by emitting fluorescence, which is a property that can be used clinically for photodetection. However, to obtain a therapeutic photodynamic effect, the photosensitizer must undergo electron spin conversion to its triplet state ( 3 PS ∗ ). In the presence of oxygen, the excited molecule can react directly with a substrate by proton or electron transfer, to form radicals or radical ions that can interact with oxygen to produce oxygenated prod- ucts (type I reaction). Alternatively, the energy of the excited photosensitizer can be directly transferred to oxygen to form singlet oxygen (type II reaction), which is the most damaging species generated during PDT. 4 , 5 The generation of cytotoxic species leads to irreversible Author for correspondence: Prof. Dr. Osvaldo Antonio Serra, Chem- istry Department of FFCLRP, University of S˜ao Paulo, Bandeirantes Av. 3900, 14040-901 Ribeir˜ao Preto, Brazil. [email protected] destruction of the treated tissues. Compared with cur- rent treatments, including surgery, radiation therapy, and chemotherapy, PDT is advantageous because it is an effective and selective method of destroying dis- eased tissues without damaging surrounding healthy tissues....
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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.
- Spring '10