A Mononuclear Hydroxoiron(<scp>III</scp>) Complex of a Porphinoid Ligand System with Bifacial Steric Hindrance

Buchler, Johann W.; Lay, K. Lam; Lee, Young Jong; Scheidt, W. Robert

doi:10.1002/anie.198204321

Cited by 28 publications

(18 citation statements)

References 7 publications

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“…Furthermore, the distance is longer for Lys heme‐iron coordination in the octaheme tetrathionate reductase from Shewanella oneidensis MR‐1, 2.2 Å[47], and also for the N‐terminal amino coordination in cytochromes f , 2.1 Å[48]. The distance is closer to the Fe‐O distance in Fe‐OH complexes and five coordinate hydroxo‐iron(III) porphyrins ( ≈ 1.9 Å) [49,50].…”

Section: Discussionmentioning

confidence: 99%

The effect of replacing the axial methionine ligand with a lysine residue in cytochrome c‐550 from Paracoccus versutus assessed by X‐ray crystallography and unfolding

et al. 2005

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The structure of cytochrome c‐550 from the nonphotosynthetic bacteria Paraccocus versutus has been solved by X‐ray crystallography to 1.90 Å resolution, and reveals a high structural homology to other bacterial cytochromes c2. The effect of replacing the axial heme‐iron methionine ligand with a lysine residue on protein structure and unfolding has been assessed using the M100K variant. From X‐ray structures at 1.95 and 1.55 Å resolution it became clear that the amino group of the lysine side chain coordinates to the heme‐iron. Structural differences compared to the wild‐type protein are confined to the lysine ligand loop connecting helices four and five. In the heme cavity an additional water molecule is found which participates in an H‐bonding interaction with the lysine ligand. Under cryo‐conditions extra electron density in the lysine ligand loop is revealed, leading to residues K97 to T101 being modeled with a double main‐chain conformation. Upon unfolding, dissociation of the lysine ligand from the heme‐iron is shown to be pH dependent, with NMR data consistent with the occurrence of a ligand exchange mechanism similar to that seen for the wild‐type protein.

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Section: Discussionmentioning

confidence: 99%

The effect of replacing the axial methionine ligand with a lysine residue in cytochrome c‐550 from Paracoccus versutus assessed by X‐ray crystallography and unfolding

et al. 2005

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“…[85] As such, they provide ap otential avenue towards ar ich-but as of yet underdeveloped-receptor chemistry up to enantiorecognition. [86] Much like porphyrins,c alixphyrins are basic and bind protons at their imine functions but, intriguingly,t he corresponding dications are more conjugated and thus more stable than the neutral species. [86b] This again highlights the diverse character of calixphyrins as macrocycles with partial traits of both calixphyrins and porphyrins.I np ractical terms,c oreprotonated calix[4]phyrins form in the presence of acids where acid anions are subsequently hydrogen-bonded to the (protonated) core.I ns uch complexes,f or example, 46,t he pyrrole cycles are tilted significantly out of the mean-plane and, depending on the molecular geometry,t he meso-hydrogen atoms can participate in further stabilization of those salts ( Figure 11).…”

Section: Calix[4]phyrins:p Hlorins Porphomethenes and Porphodimethenesmentioning

confidence: 99%

Molecular Engineering of Free‐Base Porphyrins as Ligands—The N−H⋅⋅⋅X Binding Motif in Tetrapyrroles

Kielmann

Senge

2018

Angew Chem Int Ed

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The core N-H units of planar porphyrins are often inaccessible to forming hydrogen-bonding complexes with acceptor molecules. This is due to the fact that the amine moieties are "shielded" by the macrocyclic system, impeding the formation of intermolecular H-bonds. However, methods exist to modulate the tetrapyrrole conformations and to reshape the vector of N-H orientation outwards, thus increasing their availability and reactivity. Strategies include the use of porpho(di)methenes and phlorins (calixphyrins), as well as saddle-distorted porphyrins. The former form cavities due to interruption of the aromatic system. The latter are highly basic systems and capable of binding anions and neutral molecules via N-H⋅⋅⋅X-type H-bonds. This Review discusses the role of porphyrin(oid) ligands in various coordination-type complexes, means to access the core for hydrogen bonding, the concept of conformational control, and emerging applications, such as organocatalysis and sensors.

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“…The structurally most-related complex characterized is Fe(DBPh 2 ) 2 (NH 3 )(Py), in which (DBPh 2 ) 2 is the macrocyclic equatorial ligand bis(dimethyglyoximato-diphenylborylated) (Vernik and Stynes 1996). In this complex, the Fe-NH 3 axial distance is 2.035(5) Å. Mononuclear hydroxoiron(III) porphyrins are normally unstable (Buchler et al 1982), and the only two examples characterized structurally are pentacoordinated complexes, the hydroxo-iron(III) ␣␥ bis(tert-butyl)-octaethyl-␣␥ dihydroporphyrin (Fe-OH ‫ס‬ 1.89(1) Å) (Buchler et al 1982) and the hydroxoiron(III) meso-tetraphenylporphyrin (Haryono et al 1998). Nevertheless, unambiguous assignment of the sixth axial ligand derives from the H-bond network around the heme group of the present high-resolution crystal structure.…”

Section: Molecular Structure Of the Ammonia Adductmentioning

confidence: 99%

Cleavage of the iron-methionine bond in c-type cytochromes: Crystal structure of oxidized and reduced cytochrome c2 from Rhodopseudomonas palustris and its ammonia complex

et al. 2002

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The three-dimensional structures of the native cytochrome c 2 from Rhodopseudomonas palustris and of its ammonia complex have been obtained at pH 4.4 and pH 8.5, respectively. The structure of the native form has been refined in the oxidized state at 1.70 Å and in the reduced state at 1.95 Å resolution. These are the first high-resolution crystal structures in both oxidation states of a cytochrome c 2 with relatively high redox potential (+350 mV). The differences between the two oxidation states of the native form, including the position of internal water molecules, are small. The unusual six-residue insertion Gly82-Ala87, which precedes the heme binding Met93, forms an isolated 3 10 -helix secondary structural element not previously observed in other c-type cytochromes. Furthermore, this cytochrome shows an external methionine residue involved in a strained folding near the exposed edge of the heme. The structural comparison of the present cytochrome c 2 with other c-type cytochromes has revealed that the presence of such a residue, with torsion angles and of approximately −140 and −130°, respectively, is a typical feature of this family of proteins. The refined crystal structure of the ammonia complex, obtained at 1.15 Å resolution, shows that the sulphur atom of the Met93 axial ligand does not coordinate the heme iron atom, but is replaced by an exogenous ammonia molecule. This is the only example so far reported of an X-ray structure with the heme iron coordinated by an ammonia molecule. The detachment of Met93 is accompanied by a very localized change in backbone conformation, involving mainly the residues Lys92, Met93, and Thr94. Previous studies under typical denaturing conditions, including high-pH values and the presence of exogenous ligands, have shown that the detachment of the Met axial ligand is a basic step in the folding/unfolding process of c-type cytochromes. The ammonia adduct represents a structural model for this important step of the unfolding pathway. Factors proposed to be important for the methionine dissociation are the strength of the H-bond between the Met93 and Tyr66 residues that stabilizes the native form, and the presence in this bacterial cytochrome c 2 of the rare six-residue insertion in the helix 3 10 conformation that increases Met loop flexibility.

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A Mononuclear Hydroxoiron(III) Complex of a Porphinoid Ligand System with Bifacial Steric Hindrance

Cited by 28 publications

References 7 publications

The effect of replacing the axial methionine ligand with a lysine residue in cytochrome c‐550 from Paracoccus versutus assessed by X‐ray crystallography and unfolding

The effect of replacing the axial methionine ligand with a lysine residue in cytochrome c‐550 from Paracoccus versutus assessed by X‐ray crystallography and unfolding

Molecular Engineering of Free‐Base Porphyrins as Ligands—The N−H⋅⋅⋅X Binding Motif in Tetrapyrroles

Cleavage of the iron-methionine bond in c-type cytochromes: Crystal structure of oxidized and reduced cytochrome c2 from Rhodopseudomonas palustris and its ammonia complex

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