THE FORMATION AND VOLTAMMETRIC BEHAVIOR O F MESO-TETRA (4-SULFOPHENYL) PORPHYRIN DIMER IN AQUEOUS-SOLUTION

The dimerization of meso-tetra(4-sulfophenyl) porphyrin (TPPS) in aque ous solution is studied by electrochemical methods. In weak acidic sol ution, TPPS dimerizes easily and its characteristic peaks can be seen in either visible absorption spectra or cyclic voltammogram. With the known dissociation constants K3, K4 and the dimerization formation con stant K(D) of TPPS the amount of dimer at different pH was calculated, and it reaches its maximum at about pH 5. This result agrees with our experimental data in HOAc-NaOAc. Then the model of the dimer is propo sed as H3P+-H2O-H3P+, i.e., two monomers are linked together by the hy drogen bond between TPPS and H2O. In addition, the factors influencing the formation of the dimer, including the TPPS concentration, the pH value of the solution, the formation of metal complexes, etc., were in vestigated and explained.