The analysis of iron K-edge XAFS for hemoproteins is a subject of maturity in bioinorganic chemistry. The analysis of the in situ iron K-edge EXAFS reported here for 40% [Fe(TMPP)] 2 O adsorbed on BP as a function of solution pH and applied potential has benefit from this precedence. The results that clearly emerge are that d(Fe-N p ) is longer for the oxidized than for the reduced states. The range of d(Fe-N p ) for the oxidized macrocycles (2.05-2.08 A) is typical of high-spin Fe III , whereas the corresponding range for the reduced macrocycle (2.01-2.04 A) is smaller and typical of either high- and/or intermediate-spin Fe II . The μ-oxo dimer structure, [Fe(TMPP)] 2 O, is maintained from pH 5-11 for the oxidized material. At lower solution pH values (1.2-3.1), the smaller value of d(Fe-N p ) suggests the presence of a diaquo complex, [FeTMPP(OH 2 ) 2 ] + , whereas at higher pH values, i.e., 13, the dihydroxy species appears to predominate.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry