ASSOCIATION OF ELECTROACTIVE COUNTERIONS WITH POLYELECTROLYTES .6. ELECTROSTATIC AND COORDINATIVE BINDING OF RU-3+ 2+ CENTERS TO A COPOLYMER OF ACRYLIC-ACID AND ACRYLONITRILE/
M. Yoshikawa et Fc. Anson, ASSOCIATION OF ELECTROACTIVE COUNTERIONS WITH POLYELECTROLYTES .6. ELECTROSTATIC AND COORDINATIVE BINDING OF RU-3+ 2+ CENTERS TO A COPOLYMER OF ACRYLIC-ACID AND ACRYLONITRILE/, Journal of physical chemistry, 100(10), 1996, pp. 4199-4204
A random copolymer of acrylic acid and acrylonitrile was prepared in w
hich the functionality on the polymer chain consisted of 93% carboxyli
c acid groups, 4.1% nitrile groups, and 2.9% acid anhydride groups. Th
e nitrile groups were used to coordinate RU(NH3)(5)(2+) centers to the
copolymer. The anionic carboxylate groups produced at pH values above
similar to 3.5 were used to bind Ru(NH3)(6)(3+) counterions to the re
sulting polyanionic copolymer. The electrochemical oxidation or reduct
ion of the two redox centers bound to the copolymer were used to estim
ate diffusion coefficients for the copolymer. Reasonable agreement was
obtained between the values obtained from both electroactive redox gr
oups. The diffusion coefficient exhibited a strong dependence on pH th
at reflected changes in the structure of the copolymer as it was conve
rted from its neutral to its polyanionic form. The rate of the reactio
n between the Ru(NH3)(5)OH22+ complex and the nitrile groups of the co
polymer increased significantly with pH because electrostatic binding
of the cation to the polyanionic copolymer increased the concentration
of the complex in the vicinity of the nitrile groups. Adsorption of t
he copolymer on the surface of the electrodes interfered with the oxid
ation of Ru(NH3)(5)(2)+ groups coordinated to the dissolved copolymer
but not with Ru(NH3)(6)(3+) counterions electrostatically bound to the
polyanion. A possible explanation for the contrasting behavior is sug
gested.