CATIONIC PORPHYRINS IN WATER - H-1-NMR AND FLUORESCENCE STUDIES ON DIMER AND MOLECULAR-COMPLEX FORMATION

Three kinds of cationic porphyrins have been employed to study intermolecular interaction of these porphyrins in water. Fluorescence behavior of 4,4′,4″,4‴-(21H,23H-porphine-5,10,15,20-tetrayl)tetrakis[1- octylpyridinium] tetrachloride (TOPyP) is essentially the same as that of 4,4′,4″,4‴-(21H,23H-porphine-5,10,15,20-tetrayl)tetrakis[1- methylpyridinium] tetrachloride (TMPyP), which has been assumed to form a dimer in water even at very low concentrations (>2 × 10-7 M). In contrast with these cationic porphyrins, 4,4′,4″,4‴-(21H,23H-porphine-5,10,15,20-tetrayl) tetrakis[trimethylphenylammonium] tetrachloride (TAPP) shows the fluorescence spectrum having well-resolved Q(0-0) and Q(0-1) bands. The self-association of TAPP is detectable at higher TAPP concentrations and/or in the presence of NaCl. 1H NMR clearly indicates the formation of the TAPP aggregates where the monomer-aggregates exchange rates are fast. TMPyP and TOPyP form molecular complexes with proflavin (PFl) that are more stable than the TAPP-PFl complex. The continuous variation method for the absorption spectral change indicates the 2:1 complex of TMPyP and/or TOPyP and PFl and the 1:1 complex of TAPP and PFl. These cationic porphyrins also form molecular complexes with bovine serum albumin (BSA) at pH 5.3, the stoichiometries being 4:1 and 2:1 for the TMPyP- and TAPP-BSA complexes, respectively. All the experimental results cannot provide the direct evidence for the dimer model of TMPyP but can be interpreted reasonably in terms as that both TMPyP and TOPyP form the dimers in water even at very low concentrations while TAPP exists predominantly as its monomer. A dipole-induced dipole interaction seems to play an important role in the formation of the dimers and other molecular complexes of TMPyP and TOPyP. © 1990 American Chemical Society.