Dynamics and thermodynamics of axial ligation in metalloporphyrins. 6. Axial lability of nitrogenous bases in low-spin ferric complexes and the role of five-coordinate transient species

Jd, Satterlee; Gn, La Mar; Tj, Bold

doi:10.1021/ja00446a019

Cited by 53 publications

(33 citation statements)

References 8 publications

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“…The logarithm of ν 1/2 is plotted against T -1 as this has often been found to yield a linear plot for a paramagnetic species in the absence of chemical exchange. [68,69] The temperature profile (regions I-III) corresponds to an exchange process between two paramagnetic species A and B, one of which is significantly less populated (P A ϾϾ P B ) and thus impossible to observe directly. [5,61,68] The dynamic process is slow in region I and the observed dependence may therefore be attributed solely to paramagnetic broadening and extrapolated into regions II and III.…”

Section: Conformational Flexibility Of Nickel(ii) Benziporphyrinsmentioning

confidence: 99%

“…[68,69] The temperature profile (regions I-III) corresponds to an exchange process between two paramagnetic species A and B, one of which is significantly less populated (P A ϾϾ P B ) and thus impossible to observe directly. [5,61,68] The dynamic process is slow in region I and the observed dependence may therefore be attributed solely to paramagnetic broadening and extrapolated into regions II and III. [68] The analysis concentrated on region II, which corresponds to the slow-exchange limit between A and B.…”

Section: Conformational Flexibility Of Nickel(ii) Benziporphyrinsmentioning

confidence: 99%

“…[5,61,68] The dynamic process is slow in region I and the observed dependence may therefore be attributed solely to paramagnetic broadening and extrapolated into regions II and III. [68] The analysis concentrated on region II, which corresponds to the slow-exchange limit between A and B. The pre-exchange lifetime for A (τ A ) was obtained experimentally by de- [70][71][72] Benziporphyrin macrocycles are generally more flexible than regular porphyrins, as can be judged from the puckered structures observed in the solid state for free bases and their complexes.…”

Section: Conformational Flexibility Of Nickel(ii) Benziporphyrinsmentioning

confidence: 99%

“…[73] Coordination imposes a steric constraint on the geometry of the ligand and leads to two directly detectable stereoisomers with the butadiene fragment oriented towards [(VPH 2 usual temperature dependence that is characteristic of a dynamic process. [67][68][69] This behavior can be interpreted in terms of a conformational equilibrium in which one of the forms is present at a very low concentration. [5,61,68] The conformational equilibrium presented in Scheme 5 may contribute to this mechanism providing that the concentration of [ (Figure 9).…”

Section: Two Coordination Modes Of Vacataporphyrinmentioning

confidence: 99%

“…[67][68][69] This behavior can be interpreted in terms of a conformational equilibrium in which one of the forms is present at a very low concentration. [5,61,68] The conformational equilibrium presented in Scheme 5 may contribute to this mechanism providing that the concentration of [ (Figure 9). All resonances of the coordinated imidazole are clearly discernible and have been assigned by line width analysis and selective deuteration.…”

Section: Two Coordination Modes Of Vacataporphyrinmentioning

confidence: 99%

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NMR Studies of Paramagnetic Metallocarbaporphyrinoids

Pacholska‐Dudziak

Latos‐Grażyński

2007

Eur J Inorg Chem

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Carbaporphyrinoids provide a suitable macrocyclic platform for organometallic investigations that provide unique opportunities for modifying a macrocyclic structure. Alteration of a coordination core is a route of choice for stabilizing unusual metal ion oxidation states and coordination geometries. This microreview presents the general characteristic of paramagnetic metallocarbaporphyrinoids, with a focus on NMR studies. NMR spectroscopy of paramagnetic molecules can be considered as a powerful probe of several intriguing aspects of the molecular and electronic structures, structural rearrangements, and reactivity, including oxidation and oxygenation, of this fascinating class of compounds. The chosen

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Section: Conformational Flexibility Of Nickel(ii) Benziporphyrinsmentioning

confidence: 99%

Section: Conformational Flexibility Of Nickel(ii) Benziporphyrinsmentioning

confidence: 99%

Section: Conformational Flexibility Of Nickel(ii) Benziporphyrinsmentioning

confidence: 99%

Section: Two Coordination Modes Of Vacataporphyrinmentioning

confidence: 99%

Section: Two Coordination Modes Of Vacataporphyrinmentioning

confidence: 99%

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NMR Studies of Paramagnetic Metallocarbaporphyrinoids

Pacholska‐Dudziak

Latos‐Grażyński

2007

Eur J Inorg Chem

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Iron Porphyrin Chemistry

Walker¹,

Simonis²

2005

Encyclopedia of Inorganic Chemistry

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This article reviews most aspects of the chemistry of iron porphyrins, from Fe(0) to Fe(V), including occurrence and roles of natural iron porphyrins (hemes) and their synthetic analogs, structures and electron configurations of iron porphyrins of all oxidation and spin states, π electron configuration of the porphyrin ring, synthesis of metal‐free porphyrins and other related macrocycles, insertion of iron into free‐base porphyrins and related macrocycles, the properties, reactions, uses and biological relevance of iron(0), ‐(I), ‐(II) porphyrins (the latter with S = 0, 1, and 2 spin state possibilities), of iron(II) porphyrin π‐cation radicals, of iron(III) porphyrins (with S = 1/2, 3/2, and 5/2 spin state possibilities), of iron(III) porphyrin and corrole π‐cation radicals, of iron(IV) porphyrins (including five‐ and six‐coordinate ferryl (FeO) 2+ , iron(IV) phenyl, carbene and hydrazine complexes, and the bis‐methoxide complex) and a comparison of iron(IV) porphyrins to iron(III) porphyrin π‐cation radicals, of iron(IV) porphyrin π‐cation radicals, and of the possible existence of iron(V) porphyrins. Included in the Fe(II) part are sections on addition of ligands to four‐coordinate iron(II) porphyrins, including equilibrium binding constants, photodissociation of ligands from PFeL 2 complexes, binding of small molecules (O 2 , CO, NO, HNO) to 5‐coordinate iron(II) porphyrins and design of porphyrin ligands that will mimic the active sites of heme proteins such as myoglobin and hemoglobin, the cytochromes P450 and nitric oxide synthases, and the nitrophorins and guanylyl cyclases. Included in the iron(III) part are sections on both 5‐ and 6‐coordinate high‐spin complexes and their similarities and differences, bridged or through‐space magnetically coupled complexes of high‐spin iron(III) porphyrins with other metal complexes as possible models for cytochrome oxidase and the assimilatory sulfite reductases, coupled oxidation of hemes by hydrogen peroxide or its equivalent, and the relationship of this reactivity to the reactions of heme oxygenase, iron(III) porphyrins as reduction catalysts, and photochemistry of iron(III) porphyrins, possible electron configurations of low‐spin iron(III) porphyrins, the phenomenon and possible electronic consequences of ruffling of the porphinato core in iron(III) porphyrins, the preferred orientation of planar axial ligands bound to low‐spin iron(III) porphyrins, NO complexes of iron(III) porphyrins, reduction potentials, equilibrium constants and rates of axial‐ligand addition and exchange, kinetics of axial‐ligand rotation and porphyrin ring inversion, kinetics of reduction and autoreduction of iron(III) porphyrins, electron self‐exchange between low‐spin iron(III) and iron(II) porphyrins, synthetic ferriheme proteins, and synthesis of five‐coordinate low‐spin iron(III) porphyrins having σ‐alkyl or σ‐aryl groups as axial ligands. The iron(IV) and iron(IV) cation radical sections discuss the high‐valent states of cytochromes P450 and related enzymes.

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