Electron transfer reactions involving porphyrins and chlorophyll a

Journal Article · Wed Jun 20 04:00:00 EDT 1979 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00507a031· OSTI ID:6227552

Neta, P; Scherz, A; Levanon, H

Electron transfer reactions involving porphyrins (P) and quinones (Q) have been studied by pulse radiolysis. The porphyrins used were tetraphenylporphyrin (H/sub 2/TPP), its tetracarboxy derivative (H/sub 2/TCPP), the sodium and zinc compounds (Na/sub 2/TPP and ZnTPP), and chlorophyll a (Chl a). These compounds were found to be rapidly reduced by electron transfer from (CH/sub 3/)/sub 2/CO/sup -/. Reduction by (CH/sub 3/)/sub 2/COH was rapid in aqueous solutions but relatively slow in i-PrOH solutions. Transient spectra of the anion radicals were determined and, in the case of H/sub 2/TCPP/sup -/., a pK = 9.7 was derived for its protonation. Electron-transfer reactions from the anion radical of H/sub 2/TCPP to benzoquinone, duroquinone, 9,10-anthraquinone 2-sulfonate, and methylviologen occur in aqueous solutions with rate constants approx. 10/sup 7/-10/sup 9/ M/sup -1/ s/sup -1/ which depend on the pH and the quinone reduction potential. Reactions of Na/sub 2/TPP/sup -/., ZnTPP/sup -/., and Chl a/sup -/. with anthraquinone in basic i-PrOH solutions occur with rate constants approx. 10/sup 9/ M/sup -1/ s/sup -1/. The spectral changes associated with these electron-transfer reactions as observed over a period of approx. 1 ms indicated, in some cases, the formation of an intermediate complex (P...Q/sup -/.). 8 figures, 2 tables.

• Research Organization: Univ. of Notre Dame, IN
• OSTI ID: 6227552
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 101:13; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ALKALI METAL COMPOUNDS
ANIONS
ANTHRAQUINONES
AROMATICS
BENZOQUINONES
CARBOXYLIC ACIDS
CHARGED PARTICLES
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
CHLOROPHYLL
DECOMPOSITION
ELECTRON TRANSFER
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
IONS
KINETICS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PH VALUE
PHYTOCHROMES
PIGMENTS
PORPHYRINS
PULSE TECHNIQUES
QUINONES
RADIATION CHEMISTRY
RADIATION EFFECTS
RADIOLYSIS
REACTION KINETICS
REDUCTION
SODIUM COMPOUNDS
ZINC COMPOUNDS