Confinement of 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin in novel poly(vinylpyrrolidone)s modified with aromatic amines

Polymeric derivatives of the biocompatible poly(vinylpyrrolidone) bearing discrete amounts of aromatic amines have been synthesized. The interaction of 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin with a series of these copolymers (P10, P25, P50, P75, and P100, the numbers referring the molar percentage of incorporation of aromatic amines in the copolymers) has been analyzed regarding shifts of the absorption bands and shift of the transition pH between the di-anionic and the tetra-anionic forms of 5,10,15,20-tetrakis-(4- sulfonatophenyl)-porphyrin. The interaction between the dye and poly(vinylpyrrolidone) has also been studied as a control. The incorporated aromatic amines increase the hydrophobic properties of the resulting polymers and provide specific interactions with the tetra-anionic form of 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin. Thus, P10 was soluble in water, P25 was dispersible in the form of polydisperse nanoparticles, and P50, P75, and P100 are insoluble in water. However, low polydisperse nanoparticles of mean size of 175 nm were formed by pouring 1 volume of a solution of P25 in DMSO into 9 volumes of water. These nanoparticles are permeable to 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin. Both P10 and P25 nanoparticles produce strong binding to 5,10,15,20-tetrakis-(4-sulfonatophenyl)- porphyrin, stabilize the tetra-anionic form of the dye in a wide range of pH, and prevent the undesirable self-aggregation both in the form of H- and J-aggregates. It was shown that the affinity of the 5,10,15,20-tetrakis-(4- sulfonatophenyl)-porphyrin for P10 is stronger than for chitosan, which gives insights concerning the possible stability of the complex in biological systems.