Mutual and self-diffusion of charged porphyrines in aqueous solutions

► Self and mutual diffusion coefficients of charged porphyrines in aqueous dilute solutions. ► Complementary molecular mechanics studies. ► Effect of association in diffusion of charged porphyrines. We have investigated the diffusion properties for an ionic porphyrin in water. Specifically, for the {tetrasodium tetraphenylporphyrintetrasulfonate (Na 4TPPS) + water} binary system, the self-diffusion coefficients of TPPS 4− and Na +, and the mutual diffusion coefficients were experimentally determined as a function of Na 4TPPS concentration from (0 to 4) · 10 −3 mol · dm −3 at T = 298.15 K. Absorption spectra for this system were obtained over the same concentration range. Molecular mechanics were used to compute size and shape of the TPPS 4− porphyrin. We have found that, at low solute concentrations (