One-electron transfer reactions involving zinc and cobalt porphyrins in aqueous solutions

Journal Article · Thu Nov 26 04:00:00 EST 1981 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j150624a030· OSTI ID:5879915

Neta, P

Zn and Co complexes of the water soluble porphyrins (P) TPPS (tetra(4-sulfonatophenyl)porphyrin), TAPP (tetra(4-(N,N,N-trimethylamino)phenyl)porphyrin), and TMPyP (tetra(4-N-methylpyridyl)porphyrin) were studied by steady-state and pulse radiolysis. ZnP are reduced with e/sub aq//sup -/ (k approx. = 10/sup 10/ M/sup -1/s/sup -1/), (CH/sub 3/)/sub 2/COH (k = 8 x 10/sup 7/-2 x 10/sup 9/ M/sup -1/s/sup -1/), and (CH/sub 3/)/sub 2/CO/sup -/ (k = 1 x 10/sup 9/-7 x 10/sup 9/ M/sup -1/s/sup -1/) to yield the anion radicals ZnP/sup -/. The rate of reduction increases in the order ZnTPPS < ZnTAPP < ZnTMPyP. All the anion radicals exhibit broad absorption maxima around 700 to 730 nm. These porphyrins are also oxidized by Br/sub 2//sup -/ (k approx. = 10/sup 9/ M/sup -1/s/sup -1/) and by CH/sub 2/CHO (k approx. 10/sup 8/M/sup -1/s/sup -1/) to yield the cation radicals ZnP/sup +/. The latter radicals exhibit broad absorptions at 650 to 700 nm. One-electron reduction of Co/sup III/P by e/sub aq//sup -/ (k approx. 10/sup 10/M/sup -1/s/sup -1/) or (CH/sub 3/)/sub 2/ CO/sup -/ (K approx. 10/sup 9/M/sup -1/s/sup -1/) yields Co/sup II/P. Br/sub 2//sup -/ and CH/sub 2/CHO oxidize Co/sup II/P rapidly (k approx. 10/sup 9/M/sup -1/s/sup -1/) into Co/sup III/P. All ZnP/sup -/ studied transfer an electron to all three Co/sup III/P. The rate constants vary between 10/sup 7/ and 10/sup 9/ M/sup -1/s/sup -1/ and are affected by the redox potentials and by the electrostatic change of the reacting species. The effect of charge is much smaller than expected for multiply charged species and indicates that the reactants are influenced only by one or two charges at the site of interaction. Rate constants for one-electron oxidation of Co/sup II/TPPS by ZnP/sup +/ (k approx. = 10/sup 8/ to 10/sup 9/ M/sup -1/s/sup -1/) follow a similar pattern.

• Research Organization: Univ. of Notre Dame, IN
• OSTI ID: 5879915
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 85:24; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400201 -- Chemical &amp; Physicochemical Properties
400301* -- Organic Chemistry-- Chemical &amp; Physicochemical Properties-- (-1987)
400600 -- Radiation Chemistry
AQUEOUS SOLUTIONS
CARBOXYLIC ACIDS
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
COBALT COMPLEXES
COMPLEXES
DATA
DECOMPOSITION
DISPERSIONS
ELECTRON TRANSFER
EXPERIMENTAL DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
KINETICS
MIXTURES
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PORPHYRINS
RADIATION CHEMISTRY
RADIATION EFFECTS
RADIOLYSIS
REACTION KINETICS
REDOX REACTIONS
SOLUTIONS
TRANSITION ELEMENT COMPLEXES
ZINC COMPLEXES