Cationic amino acids linked to Zn(II) phthalocyanines for photodynamic therapy: Synthesis and effects on physicochemical properties

Abstract

Novel Zn(II) phthalocyanines with four and eight moieties of phenylalanine, lysine and arginine which are cationic in physiological medium were synthesized. All new compounds were analyzed by the means of the known spectroscopic techniques (IR, (HNMR)-H-1, MS and UV-vis). The absorbances of phenylalanine, lysine, and arginine substituted Zn(II) phthalocyanines were evaluated with the typical strong absorption bands in the far red spectrum (681-683 nm). The red shifting of appox. 10 nm was observed compared to the absorption of unsubstituted Zn(II) phthalocyanine (ZnPc, 672 nm) in DMSO. The fluorescence maxima showed bathochromic shifts (7-12 nm) as compared to the absorption maxima in organic solvents (DMSO, DMF). Investigations of the physicochemical properties of the new compounds stated the role of the free amino-groups of amino acids contently linked to ZnPc ring to diminish the values. For example, it was observed very low fluorescence quantum yields (0.02-0.07) and also lower fluorescence lifetime values (2.56-2.89 ns) for the new compounds as compared to unsubstituted ZnPc (0.2; 3.99 ns). The singlet oxygen produced in the presence of the studied new Zn(II) phthalocyanines with amino acids showed lower values of the quantum yields (0.2-0.4) than ZnPc (0.67). The free amino groups closed to ZnPc ring is discussed to contribute to a photoinduced electron transfer (PET) effect which quench the singlet excited state and decrease the values of the general physicochemical parameters which are responsible for efficiency of photodynamic therapy.