DIMERIZATION OF ALUMINUM PHTHALOCYANINE CHLORIDE IN ORGANIC AND AQUA-ORGANIC MEDIUM

Abstract

Aluminum phthalocyanine chloride (AlClPc) is a photoactive macroheterocyclic compound, which, in its monomeric form, is used as a photosensitizer (PS) in photodynamic therapy and diagnostics. In this paper, its physicochemical properties were studied in organic (N, N-dimethylformamide, DMF) and aqua-organic (DMF-aqua) media. It has been shown that the hydrophobic properties of AlClPc prevent its widespread use in various pharmacological compositions due to its tendency to aggregate in aqueous solutions, which leads to the formation of non-fluorescent aggregates and a decrease in its photodynamic activity. The geometry and electronic structure of AlClPc in the monomeric and dimerized (H- and J-aggregates) states were studied using quantum-chemical calculations with the help of the electron density functional theory (DFT) method. Different types of orientation during the dimerization of AlClPc molecules are presented: “back to back”, “head to head”, “head to back”, as well as mixed-oriented types. It has been proven that both in DMF and DMF-aqua media, the preferred orientation is “back to back”, without sacrificing the monomeric geometry of the constituent molecules in the dimer. It is shown that in an aqueous organic solvent the AlClPc molecule is easily hydrated with the formation of a coordination bond between the Al atom of the AlClPc molecule and the O atom of the aqua molecule. The bond length is 2.23 Å, and the hydration energy is 16.84 kcal/mol. Hydration promotes the formation of dimers, in which two aqua molecules play the role of "bridges" between two AlClPc molecules. In such dimer, each aqua molecule has two bonds: one coordination bond between its O atom and the Al atom of one of the AlClPc molecules and one hydrogen bond between its H atom and the N atom of another AlClPc molecule. Based on the calculated data obtained, the AlClPc dimers in the DMF medium were assigned to H-aggregates, and in the DMF-water medium, to J-aggregates, respectively.