Oxidation triggers extensive conjugation and unusual stabilization of two di-heme dication diradical intermediates: role of bridging group for electronic communication

Abstract

Synthetic analogs of diheme enzyme MauG have been reported. Unlike the bis-Fe(iv) state in MauG, the 2e-oxidation stabilizes two ferric hemes, each coupled with a porphyrin π-cation radical.

Intermacrocyclic Interaction Triggers Facile One‐Pot Synthesis of a Chlorin–Porphyrin Heterodimer

“…The spectral pattern between Pd 2 DEPR⋅I 3 and Cu 2 DEPR⋅I 3 is very much similar, but the low‐energy bands in the NIR region are more redshifted in Cu 2 DEPR⋅I 3 (Figure ). Moreover, the lowering of the Soret band intensity in M 2 DEPR⋅I 3 indicates the reduction of the overall aromaticity of the complex because of its extensive π‐conjugation through the bridge –. ESI‐MS spectra show the molecular ion peaks at m / z= 1334.6537 for [Cu 2 DEPR] + and at m / z= 1422.6019 for [Pd 2 DEPR] + supporting that three protons were removed as a result of intramolecular oxidative fusion (Figures S8 and S9 in the Supporting Information).…”

Through Bridge Spin Coupling in Homo‐ and Heterobimetallic Porphyrin Dimers upon Stepwise Oxidations: A Spectroscopic and Theoretical Investigation

“…Interestingly, meso protons are shifted from large upfield to large downfield after 2e‐oxidation. Compared to Fe 2 ‐PD ⋅ 2ClO 4 , [9h] two bridging −C H protons in CuFe‐PD ⋅ 2ClO 4 shifted more to the downfield regions while meso protons are shifted upfield. The proton resonances follow similar spectral pattern as observed for homobimetallic complex Fe 2 ‐PD ⋅ 2ClO 4 (Figure 8), however, the numbers of methylene and meso signals are just half in CuFe‐PD ⋅ 2ClO 4 .…”

“…1 H NMR spectra of the complexes have been recorded using crystalline samples and are displayed in Figures 7 and 8. 1 H NMR spectrum of Fe 2 ‐PD produces eight methylene proton signals between 36.4 to 46.7 ppm, two upfield‐shifted meso signals at −68.2 and −52.0 ppm in 1 : 2 intensity ratio while a highly downfield shifted signal at 112.2 ppm observed for the bridging −C H proton [9h] . In the spectrum of heterobimetallic complex CuFe‐PD, eight methylene proton signals are observed between 28.1 to 49.5 ppm, two upfield shifted meso signals at −68.3 and −52.2 ppm in 1 : 2 intensity ratio and two highly downfield shifted bridging signals at 112.3 and 119.2 ppm in 1 : 1 intensity ratio.…”

“…Previously, 2e‐oxidations of homobimetallic porphyrin dimers produce stable dication diradical complexes in which substantial conjugation between two porphyrin macrocycles is exhibited also through the bridge [9,10] . However, unlike the bis‐Fe(IV) state in MauG, the two‐electron oxidation generate stable dication diradical complex which is indeed a viable alternative for storing two oxidizing equivalents in dihemes [9h] . Very recently, we briefly reported [9c] in a communication that the spin coupling models in the dication diradicals are different between manganese and iron which also responsible for large variations in their reactivities.…”

Status of Inorganic Chemistry Research in India

“…Their group has also contributed to the model bioinorganic chemistry of non-heme enzymes (Sankaralingam et al, 2017). Rath and co-workers have investigated the bioinorganic chemistry of multi-heme proteins and enzymes using synthetic models (Sil et al, 2016, (Kumar et al, 2019. Paine and co-workers have been involved in model bio-mimetic chemistry involving iron and cobalt .…”