Electrochemical and Spectral Studies on the Reductive Nitrosylation of Water-Soluble Iron Porphyrin

Abstract

The reaction of iron(III) (meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (Fe(III)TMPyP) with nitric oxide (NO) was studied by electronic absorption spectroscopy, ESR, and electrochemical and spectroelectrochemical techniques in aqueous solutions with pH from 2.2 to 12.0. Fe(III)TMPyP has been found to undergo a reductive nitrosylation in all pHs, and the product of nitric oxide binding to the porphyrin has been determined as iron(II) porphyrin nitrosyl complex ([Fe(II)(NO)TMPyP]). The rate of the reductive nitrosylation exhibits a tendency to get faster with increase in pH. An intermediate species was observed around neutral pH by spectroelectrochemical technique and was proposed to be the iron(II) nitrosyl complex of the mu-oxo dimeric form of FeTMPyP, which is known to be a predominant in neutral solutions.

Nitric oxide transfer from the NO-donor S-nitroso-N-acetylpenicillamine to monomers and dimers of water-soluble iron-porphyrins

“…This is also observed in the presence of SDS micelles, but no spectral modifications occur in the presence of CTAB or C 12 E 9 . These spectral changes are due to the nitrosylation of the iron-porphyrin and is characteristic of NO-Fe(II)porphyrin [26,27].…”

“…The absorbance of the Soret band increases, and the Qbands at 598 and 630 nm vanish giving rise to a Q-band at 552 nm. These changes are also due to formation of NO-Fe(II)TMPyP [27]. FeTMPyP, undergoes reductive nitrosylation in the presence of C 12 E 9 , in addition to nitrosylating in buffer and in the presence of CTAB micelles.…”

“…Several studies concerning the interaction of nitric oxide with iron-porphyrins [24,25], including soluble iron-porphyrins has recently appeared [26][27][28]. In these studies, NO gas was used to obtain the nitrosylated porphyrins.…”

Spectroelectrochemical investigation of the pH dependent aggregation state of iron TAP

“…This suggests that complete reduction of the pH 4 species was not achieved. A Soret band at 442 nm was observed by Natalia et al [17] for monomeric Fe II TMPyP in methanol. The failure to completely eliminate the 406 nm band (Fig.…”

Reduction of (chloro)-μ-nitrido-bis[(tetra-tert-butyl-phthalocyaninato)iron(IV)] with organic N-bases

“…It should be noted that the N-bridged diiron complex retains its binuclear structure during the reaction in the presence of reducing agent in contrast to iron m-oxodimers of porphyrin or phthalocyanine which have undergone decomposition with the monomeric species formation in similar reaction [40]. Furthermore, it was important to confirm that the resulting complex actually have biscoordination of the ligand.…”