Association of Small Molecule Cosolutes with Water-Soluble Polymers. Effects of Polymer Binding on the Reactivity of Water-Soluble Porphyrins

Article abstract of DOI:10.1021/j100297a045

The tetraanionic porphyrin, 1, associates strongly with poly(vinylpyrrolidone) (PVP) in dilute buffered aqueous solutions.The equilibrium constant for association of 1 with PVP in pH 3 acetate at 298 K is 1.4 x 1E7 M^-1 for M = 48000 PVP.Chelation of Cu²⁺ by the porphyrin is slowed dramatically in the presence of PVP.The rate expression is K<1>_b2+>/(k' + k 2+>), which fits a mechanism in which only free porphyrin, <1>_f, coordinates to Cu²⁺ (<1>_b is the concentration of polymer-bound porphyrin).The palladium(II) porphyrin, 2, also associates with PVP.The palladium(II) porphyrin, 2, also associates with PVP.The efficient quenching of the phosphorescence of 2 by methylviologen, MV²⁺, in aqueous solution is completely inhibited upon association of 2 with PVP.The lack of reactivity of 1 and 2 bound to PVP indicates that the porphyrin microenvironment involves little contact with the bulk aqueous solution.