Interaction of porphyrins with PAMAM dendrimers in aqueous solution

Anionic 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and 5,10,15,20-tetrakis(4-phosphonatophenyl)porphyrin (TPPP) are bound to PAMAM dendrimer, generation 5 (G5, 128 amine terminal groups), and cationic 5,10,15,20-tetrakis(N-methylpyridynium-4-yl)porphyrin (TMPyP) and 5,10,15,20-tetrakis(α-triphenylphosphonio-p-tolyl)porphyrin (TPPTP) to PAMAM dendrimer, generation 4.5 (G4.5, 128 carboxyl terminal groups). A positive charge of G5 induces preferably the formation of H-dimers with the face-to-face arrangement of the anionic porphyrin units. Protonation of the porphyrin rings within H-dimers occurs at pH below 2.5 and is followed by changing the aggregate structure. TPPS forms edge-to-edge aligned J-aggregates with a highly ordered structure. The structure of J-aggregates formed from TPPP is more random. Whereas TMPyP is bound to G4.5 as monomer, TPPTP aggregates on the G4.5 surface. TPPTP aggregates dissociate at pH below 3 due to protonation of the porphyrin ring.