Monomerization and photodynamic activity of Zn(II) tetraalkyltetrapyridinoporphyrazinium derivatives in AOT reverse micelles Carlos A. Suchetti, Edgardo N. Durantini * Departamento de Quı ´mica, Universidad Nacional de Rı ´o Cuarto, Rı ´o Cuarto, Agencia Postal Nro. 3, X5804BYA Rı ´o Cuarto, Co ´ rdoba, Argentina Received 11 April 2006; accepted 20 April 2006 Available online 8 June 2006 Abstract Monomerization and photodynamic activity of cationic Zn(II) tetraalkyltetrapyridinoporphyrazinium derivatives bearing N-alkyl chains of different length (ZnPc 1 R: eCH 3 , ZnPc 2 R: e(CH 2 ) 11 CH 3 , ZnPc 3, R: e(CH 2 ) 15 CH 3 ) were evaluated in n-heptane/sodium bis(2-ethylhexyl)- sulfosuccinate (AOT)/water micellar system. Absorption and fluorescence spectroscopic studies of these sensitizers were analyzed in n-heptane/ AOT (0.1 M)/water system by varying the amount of water dispersed in the reverse micelles (W 0 ¼ [H 2 O]/[AOT]). Under these conditions, the absorbance of the monomeric Q-band (w686 nm) of ZnPcs 1e3 increases rapidly until W 0 w 30 and then the increase becomes steady. These results were also confirmed by fluorescence studies. Analysis of the Q-band at different AOT concentrations, keeping W 0 ¼ 30 as constant, was carried out to determine the binding constant (K b ) between these sensitizers and AOT reverse micelles. The values of K of 210, 150 and 34 were found for ZnPcs 1, 2 and 3, respectively. Photodynamic activity of these sensitizers was evaluated in AOT system using 9,10-dimethylanthracene (DMA). The photooxidation rate of DMA sensitized by these phthalocyanines follow the order: ZnPc 1 > ZnPc 2 w ZnPc 3. As shown by spec- troscopic and photodynamic studies, the AOT reverse micellar system very effectively inhibits the aggregation of phthalocyanines, promoting the formation of photoactive monomeric species. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Phthalocyanine; Micelles; AOT; Photodynamic effect; Photosensitizer 1. Introduction Solubilization of substrates in micellar aggregates plays an important role in biological and industrial processes [1]. In mi- croheterogeneous systems, a solute can be located in a variety of microenvironments namely the organic surrounded solvent, the water pool or at the micellar interface. Among the surfac- tants capable of forming these aggregates, sodium bis(2-ethyl- hexyl)sulfosuccinate (AOT) is the one mostly used since solutions of AOT in nonpolar solvents have the remarkable ability to solubilize a large amount of water [1]. Microhetero- geneous systems such as reverse micelles are frequently used as an interesting model to mimic the water pockets that are of- ten found in various bioaggregates such as proteins, enzymes and membranes [2,3]. Also, AOT reverse micelles form suit- able and variable reaction media depending on water-to-sur- factant ratio for the study of different types of organic and enzymatic reactions. Thus, water-soluble and water-insoluble compounds can be dissolved simultaneously in reverse mi- celles, which simulate a biomimetic microenvironment [4]. Phthalocyanine derivatives exhibit a high absorption coeffi- cient (3 > 10 5 M 1 cm 1 ) in the visible region of the spectrum, mainly in the phototherapeutic window (600e800 nm) and a long lifetime of triplet excited state to produce efficiently O 2 ( 1 D g ) [5]. Based on these properties, one of the most recent and promising applications of phthalocyanine in medicine is in the detection and cure of tumors. Photodynamic therapy (PDT) is an innovative treatment for several types of cancer * Corresponding author. Tel.: þ54 358 4676157; fax: þ54 358 4676233. E-mail address: edurantini@exa.unrc.edu.ar (E.N. Durantini). 0143-7208/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.dyepig.2006.04.004 Dyes and Pigments 74 (2007) 630e635 www.elsevier.com/locate/dyepig