Water-soluble quaternized mercaptopyridine-substituted zinc-phthalocyanines: Synthesis, photophysical, photochemical and bovine serum albumin binding properties Mahmut Durmus ¸ a, * , Hanifi Yaman a , Cem Göl a , Vefa Ahsen a, b , Tebello Nyokong c a Gebze Institute of Technology, Department of Chemistry, PO Box 141, Gebze, 41400 Kocaeli, Turkey b TUBITAK-Marmara Research Center, Materials Institute, PO Box 21, Gebze, 41470 Kocaeli, Turkey c Department of Chemistry, Rhodes University, Grahamstown 6140, South Africa article info Article history: Received 3 January 2011 Received in revised form 4 February 2011 Accepted 7 February 2011 Available online 8 March 2011 Keywords: Phthalocyanine Quaternization Water soluble Photosensitizer Bovine serum albumin Photodynamic therapy abstract The synthesis and characterization of the new zinc phthalocyanine derivatives, tetra- (non-peripheral, 5) and octa-(peripheral, 6) substituted with 2-mercaptopyridine and their respective quaternized deriva- tives (8 and 9) are reported. Photochemical and photophysical properties of the new complexes are compared with those of the previously reported peripherally tetra-substituted complexes 7 and 10. The quaternized compounds exhibit excellent solubility in water, making them potential photosensitizers for use in photodynamic therapy (PDT) of cancer. Spectroscopic, aggregation, photophysical and photo- chemical properties of these complexes are also investigated and compared. Photophysical (fluorescence quantum yields and lifetimes) and photochemical (singlet oxygen and photodegradation quantum yield) properties of these phthalocyanine photosensitizers are very important for the assessment of these complexes as PDT agents. In this study, the effects of the position of the substituents and quaternization of the substituents on the photophysical and photochemical parameters of the zinc phthalocyanines are also reported. This study also showed that the water-soluble quaternized zinc phthalocyanines strongly bind to blood plasma proteins such as bovine serum albumin (BSA). Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Phthalocyanines (Pcs) are remarkable macrocyclic compounds having magnificent physical and chemical properties [1]. Metal- lophthalocyanines (MPc) have been investigated in detail for many years due to their wide applications in many fields, mostly in terms of their uses as blue-green dyes and catalysts [2,3]. They have also found different applications in many fields ranging from industrial [4], technological [5,6] to medical [7,8]. Most metal ions can be engaged in the Pc macrocyle’s cavity; therefore, a large number of different MPc complexes have been synthesized. When the central metal is diamagnetic and non-transitional, MPc derivatives are photoactive and may be employed in photosensitization [9,10]. In this regard, it is worth emphasizing the Pcs’ application as photo- sensitizers in the photodynamic therapy (PDT) of tumours. High triplet state quantum yields and long triplet lifetimes are required for efficient sensitization by MPc complexes. The photophysical properties of the Pc dyes are strongly influenced by the presence and nature of the central metal ion. MPcs containing transition metals give short triplet lifetimes. Closed shell and diamagnetic ions, for example Zn 2þ , Ga 3þ and Si 4þ , give Pc complexes excellent properties such as high triplet yields and long lifetimes [11e 13]. ZnPcs in particular have been extensively studied because of d 10 configuration of the central Zn 2þ ion results in optical spectra that are not complicated by additional bands, as in transition-metal Pc complexes. ZnPcs have intensive red-visible region absorption and high singlet and triplet yields, making them valuable photosensi- tizers for PDT applications. In PDT applications, the drug is injected into the patient’s blood stream, and since the blood itself is a hydrophilic system, water solubility plays a very important role for a potential photosensitizer in PDT [14e17]. The advantages of MPcs bearing cationic substitu- ents over those with neutral and anionic substituents are numerous [18], for examples: (i) they are able to improve water solubility and prevent aggregation [19]; aggregation seriously compromises the PDT value of the photosensitizer, (ii) they are more efficient as PDT agents [20] and also improve cell uptake [21], (iii) they are selec- tively localized in the cell mitochondria and cause apoptosis [22]. * Corresponding author. Tel.: þ90 262 6053075; fax: þ90 262 6053101. E-mail address: durmus@gyte.edu.tr (M. Durmus ¸ ). Contents lists available at ScienceDirect Dyes and Pigments journal homepage: www.elsevier.com/locate/dyepig 0143-7208/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.dyepig.2011.02.007 Dyes and Pigments 91 (2011) 153e163