One-electron reduction and demetallation of copper porphyrins

Journal Article · Thu Nov 12 04:00:00 EST 1992 · Journal of Physical Chemistry

DOI:https://doi.org/10.1021/j100202a091· OSTI ID:563421

Kumar, M; Neta, P ^[1]; Sutter, T P.G.; Hambright, P ^[2]

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1. National Institute of Standards and Technology, Gaithersburg, MD (United States)
2. Howard Univ., Washington, DC (United States)

Reduction of water-soluble Cu{sup II} porphyrins has been studied by {gamma}-radiolysis and pulse radiolysis at various pH values. In neutral and alkaline solutions, the transient species produced by one-electron reduction were identified as the {pi}-radical anions, based on their broad absorption spectra at 600-800 nm, and the two-electron reduction products were either Cu{sup II} phlorins or Cu{sup II} chlorins, depending on pH and on porphyrin structure. Reduction in acidic solution, however, often led to demetallation of these otherwise stable complexes. The pH at which demetallation became apparent was <4 and dependent on phorphyrin structure. Under these conditions, pulse radiolytic reduction gave the spectra of the products of protonation of Cu{sup I} porphyrin. It is concluded that the {pi}-radical anions of Cu{sup II} porphyrins have some Cu{sup I} character, which in acidic solutions results in protonation and demetallation due to the large ionic radius of Cu{sup I}. For comparison, a study of the acid-catalyzed solvolysis of a Mg porphyrin was carried out both by pulse radiolysis and by classical methods. 25 refs., 5 figs.

• Sponsoring Organization: USDOE
• OSTI ID: 563421
• Journal Information: Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 23 Vol. 96; ISSN JPCHAX; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
AQUEOUS SOLUTIONS
COPPER COMPOUNDS
DEMETALLIZATION
PH VALUE
PORPHYRINS
REDUCTION