To gain insight into the protonation state of enzymatic ferryl species we have examined the applicability of Badger's rule to heme and non-heme iron−oxygen bonds. Using density functional theory we have calculated re and νe for the Fe−O bonds of complexes with different axial ligands, iron-oxidation, oxygen-protonation, and spin states. Our results indicate that Badger's rule holds for heme and non-heme oxo and hydroxo complexes. We find that the long Fe−O bonds that have been reported in the crystal structures of the ferryl forms of myoglobin, horseradish peroxidase, cytochrome c peroxidase, and catalase deviate substantially from the values predicted by Badger's rule, while the short Fe−O bonds obtained from X-ray absorption measurements are in good agreement with Badger's rule. In light of our analysis we conclude that the ferryl forms of myoglobin, horseradish peroxidase, and cytochrome c peroxidase are authentic iron(IV)oxos with Fe−O bonds on the order of 1.66 A and pKa's < 4.

Application of Badger's Rule to Heme and Non-Heme Iron−Oxygen Bonds: An Examination of Ferryl Protonation States

Resonance Raman spectra and biological significance of high-valent iron(IV,V) porphyrins

Picosecond transient absorption spectroscopy of diiron(III) μ-oxo bisporphyrins appended to xanthene, (DPX)Fe2O and (DPXM)Fe2O, and dibenzofuran (DPD)Fe2O have been investigated in order to decipher the effect of a spring-loaded cleft on their photophysics and attendant oxidation photocatalysis. The tension of the cofacial pocket is systematically tuned with the bridge span and meso-substitution opposite to the bridge; the distances of the relaxed cofacial pockets and clamped Fe−O−Fe pockets are known from X-ray crystallography (ΔdM-M(relaxed − clamped) = 4.271 A (DPD), 2.424 A (DPXM), 0.208 A (DPX)). The photophysical and chemical properties of these cofacial platforms are compared to the unbridged diiron(III) μ-oxo analogue, (Etio)2Fe2O. Photon absorption by the diiron(III) μ-oxo chromophore prompts Fe−O−Fe photocleavage to release the spring and present a PFeIVO/PFeII pair (P = porphyrin subunit); net photooxidation is observed when oxygen atom transfer to substrate occurs before the spring can reclamp...

Transient Absorption Studies of the Pacman Effect in Spring-Loaded Diiron(III) μ-Oxo Bisporphyrins

Investigation of picosecond optical nonlinearity in porphyrin metal complexes derivatives

Optical self-defocusing, characterized by the non-linear refractive index n2, was investigated by the Z-scan technique in water solutions of two porphyrins (PPhs), negatively charged meso-tetrakis(p-sulfonatophenyl)porphyrin (TPPS4) and positively charged meso-tetrakis(4-N-methyl-pyridiniumyl)porphyrin (TMPyP), in their free base forms and as Fe(III) and Mn(III) complexes. Significant n2 values were observed only for the TMPyP metal complexes, while for the other porphyrins the n2 values were negligible. The effect is explained by the reorientation of the porphyrin molecule due to interaction of its permanent dipole moment perpendicular to the molecular ring plane with the electromagnetic field of the exciting light pulse. The permanent dipole moment is due to the shift of the metal atom out of the molecular plane. The electrostatic interaction between the metal atom and charged substituents increases (repulsion) or decreases (attraction) the shift of the metal atom and consequently affects the dipole moment value. Ligand binding to the metal atoms also increases the out-of-plane metal shift and hence the dipole moment and n2 value. pH changes were shown to modify the Fe(III)-ligand structure, thus changing n2. The experimental data correlate well with the metal shift and dipole moment values calculated for simplified PPh structures by the ZINDO method.

Z‐scan studies and quantum chemical calculations ­of meso‐tetrakis(p‐sulfonatophenyl)porphyrin and ­meso‐tetrakis(4‐N‐methyl‐pyridiniumyl)porphyrin and their Fe(III) and Mn(III) complexes

We report the formation and characterization of (oxoferryl)tetraphenylporphyrin ((TPP)FeIVO) as a result of photodisproportionation of the μ-oxo dimer, (Fe(TPP))2O, obtained on solubilization of Fe(TPP)Cl in an aqueous alkaline TX-100 detergent micelle, under 441.6 nm laser excitation at room temperature and at −50 °C. The other photoproduct is identified as a five-coordinated, high-spin (5cHS) ferrous complex.

Resonance Raman Characterization of (Oxoferryl)tetraphenylporphyrin Formed during Photodisproportionation of (Fe(TPP))2O in a Detergent Micelle at Room Temperature

A. L. Verma

Papers

Resonance Raman Characterization of (Oxoferryl)tetraphenylporphyrin Formed during Photodisproportionation of (Fe(TPP))2O in a Detergent Micelle at Room Temperature