Water-Soluble Quaternized Serotonin Substituted Zinc-Phthalocyanine for Photodynamic Therapy Applications

Abstract

Poor water solubility is the main drawback of phthalocyanine (Pc)-based second generation photosensitizing agents in photodynamic therapy (PDT). To resolve this, we proposed preparation of quaternized serotonin substituted zinc phthalocyanine (q-Ser-ZnPc) since the positive charge on quaternary amines could improve water-solubility and might limit self-interactions of hydrophobic aromatic surface of Pc in aqueous solutions. Briefly, serotonin substituted phthalonitrile was prepared by reaction of 4-nitrophthalonitrile with 5-hydroxytryptamine (Serotonin). Serotonin substituted zinc(II) phthalocyanine (Ser-ZnPc) was prepared by cyclotetramerization of serotonin substituted phthalonitrile. Then, q-Ser-ZnPc was prepared by the quaternization reaction of Ser-ZnPc. The synthesized compounds were characterized by 1H-NMR, UV-Vis, FT-IR, fluorescence, and elemental analysis. Importantly, unlike ZnPc, which is among most widely used second generation photosensitizing agents, we report that q-Ser-ZnPc is actually water-soluble. Besides, q-Ser-ZnPc also absorbs light in the wavelengths corresponding to the therapeutic window. What’s more, q-Ser-ZnPc exhibits a higher fluorescence quantum yield than that of ZnPc. Thus, the material might be useful particularly for image-guided PDT applications.