Electrochemical and spectroscopic studies of model porphyrin, hydroporphyrin complexes for nitrite reductases

Yanming Liu, Marquette University


A number of porphyrin and hydroporphyrin complexes (free bases, iron and nitrosyl complexes) have been studied by various electrochemical techniques, UV-visible, FT-Infrared, resonance Raman spectroscopies and spectroelectrochemistry. The complexes studied in this work are the models for siroheme and heme d$\sb1$ in nitrite reductases. The work has been done on chemical and electrochemical generation and spectroscopic characterization of the reduction products of these model complexes, and elucidation of the reduction mechanisms of heme-bound nitrosyl to ammonia. The redox properties and axial coordination of porphyrin, chlorin, bacteriochlorin and isobacteriochlorin have been compared, and the difference in reduction mechanism for Fe(2,4-DMOEiBC)NO(model for siroheme) and Fe(2,4-dioxo-OEiBC)NO(model for heme d$\sb1$) have been investigated. Experimental results showed that Fe(HP)NO(where HP = porphyrins and hydroporphyrins) reduced in three one-electron steps and the reduction products, Fe(HP)NO$\sp{-}$ and Fe(HP)NO$\sp{2-}$, were stable in THF. Addition of an electron to Fe(HP)NO lead to a strengthening of the Fe-N bond and a weakening of the N-O bond. Nitrosyl reduced to ammonia in the presence of weak acids via hydroxylamine. Isobacteriochlorin displayed an unique electroreduction behavior comparing with porphyrins, chlorins, and bacteriochlorins. The key factor that direct nitrite to different products (ammonia and nitrous oxide) is the basicity of the hydroporphyrin macrocycles.

Recommended Citation

Liu, Yanming, "Electrochemical and spectroscopic studies of model porphyrin, hydroporphyrin complexes for nitrite reductases" (1991). Dissertations (1962 - 2010) Access via Proquest Digital Dissertations. AAI9133799.