Investigation of Tetramethyltribenzotetraazachlorin Association in Binary Mixtures of Polar Solvents and in Colloidal Solutions of Nonionic Surfactant

The phenomena of association often occurs in concentrated solutions of porphyrins and their analogues, where high content of a substance leads to specific and nonspecific intermolecular interactions, changing their physico-chemical and spectral properties. Photochemical properties of porphyrin solutions including tetraazachlorins strongly depend on the degree of aggregation. The association suppresses the fluorescence and ability of these compounds to initiate formation of singlet oxygen, which is the basis for photodynamic therapy. Understanding the factors of tetraazachlorins aggregation in solution is important for selection of appropriate materials, preventing it, and for creation on their basis of pharmaceutical preparations containing tetraazachlorins as active components. In this paper we investigate the behavior of metal-free tetramethyltribenzotetraazachlorin (H(2)TBTAC) in binary mixtures of polar solvents and in colloidal solutions of nonionic surfactants. The phenomenon of H(2)TBTAC association in solutions of nonionic surfactant is studied by means of UV-VIS spectroscopy. The influence of the conditions and time of storage solutions on the association of H(2)TBTAC immobilized in a matrix of nonionic surfactant is substantiated. We describe the probable mechanism of H(2)TBTAC association due to the formation of associates of a higher level. They are characterized by a significant decrease in the intensity of the absorption and broadening of the main absorption bands, it is noticed for the main Q-band maximum. Associates especially in the presence of water have the electronic spectrum, which differs from that of the monomeric form of the disappearance of the main Q-band maximum at 748 nm, and the change in the form of electronic spectrum in the range 550-650 nm and 670-780 nm. The reversibility of the association was observed when co-solvent (DMSO) in an amount of more than 40% vol. was added to aqueous solutions of Pluronic F-68 containing H(2)TBTAC. We have hypothesized a face-to-face aggregation to take place in the investigated solutions. The specific solvation of tertiary nitrogen atoms of tetraazachlorin agregates with proton-donor solvents (especially water) leads to the formation H-association of H(2)TBTAC in binary solution. When H(2)TBTAC is immobilized in colloidal solutions of nonionic surfactants degree of tetraazachlorin association depends on the hydrophilic-lipophilic properties of the high-molecular substance. The lower HLB increases the content of monomeric form in the solution.