Abstract
One-electron and multi-electron reduction of the three isomeric free-base porphyrins derived from TMPyP [tetrakis(N-methylpyridyl)porphyrin] in aqueous solutions under various conditions have been studied by spectrophotometric pulse radiolysis and γ-radiolysis. Similar experiments were carried out with TPyP (tetrapyridylporphyrins) in acidic solutions. Significant differences were found in the behaviour of the three isomers, in the stability of their one-electron and two-electron reduction products and in the effect of pH. An exceptionally stable radical was formed upon one-electron reduction of the ortho isomer, TM2PyP [tetrakis(N-methyl-2-pyridyl)porphyrin], at high pH. The stability of this radical is due to inhibition of protonation, a necessary step in the decay of the radical to final reduction products. Protonation is probably inhibited by the positive charges on the 2-pyridyl groups, which are very close to the meso positions of the porphyrin, and by steric effects of the ortho N-methyl groups, which inhibit deformation of the porphyrin ring and thus retard protonation. Somewhat stable radicals were also found in strongly acidic solutions of TM2PyP and T2PyP.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call