The iron(II) and cobalt(II) "cap" and "homologous cap" porphyrins. Base and oxygenation equilibriums studies of relevance to hemoglobin cooperativity

Budge, John R.; Ellis, Paul E.; Jones, Robert; Linard, Jack E.; Szymanski, Thomas; Basolo, Fred; Baldwin, Jack E.; Dyer, Robert

doi:10.1021/ja00510a071

Cited by 25 publications

(14 citation statements)

References 8 publications

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“…This is a result of considerable interest since some discussions on cooperativity9•34 have stressed the significance of assumed changes in the Fe-Njm and Fe-Ct separations upon oxygenation. It has been proposed that it is the Fe-N|m bond which is under "tension" in T-state oxyhemoglobin.9 Furthermore, in the very recent studies by Budge et al 38•39 on ligand binding to iron(II) "capped" porphyrins40 in solution, a porphyrin with a larger "cap" possesses a lower affinity for dioxygen. Since the axial base was kept constant, the porphyrin rather than the axial base would appear to be controlling dioxygen affinity in this case.…”

Section: Resultsmentioning

confidence: 99%

Models for the active site of oxygen-binding hemoproteins. Dioxygen binding properties and the structures of (2-methylimidazole)-meso-tetra(.alpha.,.alpha.,.alpha.,.alpha.-o-pivalamidophenyl)porphyrinatoiron(II)-ethanol and its dioxygen adduct

Jameson¹,

Molinaro²,

Ibers³

et al. 1980

J. Am. Chem. Soc.

207

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Section: Resultsmentioning

confidence: 99%

Models for the active site of oxygen-binding hemoproteins. Dioxygen binding properties and the structures of (2-methylimidazole)-meso-tetra(.alpha.,.alpha.,.alpha.,.alpha.-o-pivalamidophenyl)porphyrinatoiron(II)-ethanol and its dioxygen adduct

Jameson¹,

Molinaro²,

Ibers³

et al. 1980

J. Am. Chem. Soc.

207

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“…Aliquots of O2 were then added from a gas manifold16 via a gas-tight valve to the system. When P\/2°2 was less than 10 Torr, a mixture of 0.999% 02 in N2 was used as the titrant. The solution was allowed to stir until equilibrium was attained.…”

Section: Methodsmentioning

confidence: 99%

Oxygenation of iron(II) and cobalt(II) "capped" porphyrins

Linard¹,

Ellis²,

Budge³

et al. 1980

J. Am. Chem. Soc.

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“…To address the nature of steric discrimination against the binding of CO many types of sterically encumbered porphyrins have been synthesized over the past quarter century. Representative examples include “strapped”, − “picnic basket”, − “picket fence”, − “pocket”, − and “capped” − porphyrins as well as hybrids of these different classifications. , The binding of CO and O 2 to these model systems has been studied extensively. However, owing to the difficulty of obtaining crystals of these elaborated porphyrin systems, especially those where O 2 is a ligand, only limited structural data are available.…”

Section: Introductionmentioning

confidence: 99%

“…The capped porphyrin structures will be compared with those known for the C 2 -Cap system, namely H 2 (C 2 -Cap), Fe(C 2 -Cap)(CO)(1-MeIm), and Fe(C 2 -Cap)(Cl), and the C 3 -Cap structure will be compared with that of Co(C 3 -Cap) − ,, systems. …”

Section: Introductionmentioning

confidence: 99%

Structural Characterization of Five Sterically Protected Porphyrins

et al. 1996

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The structures of the sterically protected “pocket” porphyrin H2(α-PocPivP) (1), and the “capped” porphyrins H2(C3-Cap) (2), Fe(C3-Cap)(CO)(1-MeIm) (3), H2(C4-Cap) (4), and Fe(C4-Cap)(Cl) (5) have been determined by single-crystal X-ray diffraction methods. Compounds 1-4 each pack with one independent porphyrin unit and solvate molecules in the unit cell. Compound 5 packs with two crystallographically independent porphyrins and solvate molecules in the unit cell. The structure of 1 is the first of a pocket porphyrin in which there are no ligands bound inside the protected region. This structure reveals that the main form of distortion that occurs when a ligand binds inside the protected region is the lateral movement of the benzene cap relative to a position above the centroid of the porphyrin. In 1 this lateral displacement is 1.86 Å whereas this displacement is 3.30 Å in Fe(β-PocPivP)(CO)(1,2-Me2Im). Comparison of the free-base structure 2 with the FeII carbonyl 3, where the CO ligand is bound under the cap and the 1-MeIm ligand is bound opposite the cap, reveals that there is little lateral distortion in the C3-Cap system, but there is significant vertical expansion of the cap upon coligation to the Fe center. The distance of the cap centroid from the mean porphyrin plane increases 2.37 Å to accommodate the CO ligand, from 3.49 Å in 2 to 5.86 Å in 3. The Fe−C−O angle in 3 is 178.0(13)°. In the structures of the C4-Cap system 4 and 5 there is sufficient space for the binding of small ligands, such as CO and O2, as well as larger ligands. Compound 4 crystallizes with a CHCl3 solvate molecule under the cap. The distances from cap centroid to porphyrin plane in the C4-Cap structures are 7.28, 7.12, and 7.66 Å for 4, 5A, and 5B, respectively. This is significantly greater than the distance of 5.6 Å in Fe(C2-Cap)(CO)(1-MeIm) and 5.86 Å in 3. The relation between these structural changes on ligation and the binding properties of these systems for CO and O2 is explored.

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The iron(II) and cobalt(II) "cap" and "homologous cap" porphyrins. Base and oxygenation equilibriums studies of relevance to hemoglobin cooperativity

Cited by 25 publications

References 8 publications

Models for the active site of oxygen-binding hemoproteins. Dioxygen binding properties and the structures of (2-methylimidazole)-meso-tetra(.alpha.,.alpha.,.alpha.,.alpha.-o-pivalamidophenyl)porphyrinatoiron(II)-ethanol and its dioxygen adduct

Models for the active site of oxygen-binding hemoproteins. Dioxygen binding properties and the structures of (2-methylimidazole)-meso-tetra(.alpha.,.alpha.,.alpha.,.alpha.-o-pivalamidophenyl)porphyrinatoiron(II)-ethanol and its dioxygen adduct

Oxygenation of iron(II) and cobalt(II) "capped" porphyrins

Structural Characterization of Five Sterically Protected Porphyrins

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