Table 2.
Intermediates characterized in the reactions of O2 with M-HPCD enzyme-substrate complexes.a
| Intermediateb | Metal Oxidation State (System Spin State) |
λmax (nm) (ε, M−1cm−1) |
Proposed Assignment |
Ref |
|---|---|---|---|---|
| Fe-HPCAInt1 (I) | hs-Fe(II) (S = 2) | – | [Fe(II)(OOR)] | [29, 36] |
| H200N-Fe-HPCAInt1 (G) | hs-Fe(III)/radical (S = 2) | 395 (3,200), 610(1,100) |
[Fe(III)(SQ•)(OO(H))] | [33, 36] |
| H200N-Fe-HPCAInt2 (I) | hs-Fe(II) (S = 2) | – | [FeII(OOR)] | [33, 36] |
| H200N-Fe-4NCInt1 (C) | hs-Fe(III)/radical (S = 2) | 506 (~10,000), 630 (~1,200) |
[Fe(III)(4NC)(O2•−)] | [33, 37] |
| H200N-Fe-4NCInt2 (G) | hs-Fe(III)/radical (S = 2) | 405 (~15,000), 675 (~1,000) |
[Fe(III)(SQ•)(OO(H)] | [33, 37] |
| Y257F-Fe-HPCAInt1 (B) | hs-Fe(II) (S = 2) | – | [Fe(II)(HPCA)(O2)] | [38] |
| Y257F-Fe-HPCAInt2 (H) | hs-Fe(II) (S = 2) | 425 (~10,500) | [Fe(II)(Q)(OO(H))] | [38] |
| Mn-HPCAInt1 (D or G) | hs-Mn(III)/radical (S = 5/2) | – | [Mn(III)(HPCA)(O2•−)] or [Mn(III)(SQ•)(OO(H))] |
[9] |
| Mn-HPCAInt2 (I) | hs-Mn(II) (S = 5/2) | – | [Mn(II)(OOR)] | [9] |
| wt/H200N-Co-4NCInt (E) | ls-Co(III) (S = 1/2) | 390 (~7,000), 526 (~13,000) |
[Co(III)(4NC)(O2•−)] | [39] |
a
Abbreviations used: HPCA, homoprotocatechuate; 4NC, 4-nitrocatechol; SQ• semiquinone; Q, quinone; O2•− superoxide radical anion; hs, high-spin; ls, low-spin.
b
Labels in this column refer to structures in Scheme 3.