An unexpected bonding interaction between dxy and axial cyanide mediated by porphyrin deformation

Cheng, Richard P.; Lee, Chang-Hung; Chao, Chia-Wei

doi:10.1039/b901116a

Cited by 7 publications

(7 citation statements)

References 15 publications

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“…This ring distortion is evidenced by their absorption spectra, the broad and red-shifted bands. Both features are typical spectral features of nonplanar porphyrins. , The substituent-triggered distortion of porphyrin can entice a displacement of the central metal and the nitrogen atoms of pyrrolic units, where severe ruffling affects the electronic interaction between the metal and the porphyrin macrocycle. − As a result of these perturbations in the electronic structures of porphyrin ring, 1·2CN – and 2·2CN – display additional absorption bands in 400–410 nm. − Particularly, as compared to 1 , the four BTz substituents of 2 on both sides of the porphyrin plane can give rise to more severe ruffling in the axial-binding process of CN – , leading to a more noticeable absorption band at 410 nm.…”

Section: Resultsmentioning

confidence: 99%

Modulation of Axial-Ligand Binding and Releasing Processes onto the Triazole-Bearing Nickel(II) Picket-Fence Porphyrins: Steric Repulsion versus Hydrogen-Bonding Effects

Yoon

Sung

et al. 2015

J. Phys. Chem. B

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N-(p-Methoxycarbonylbenzyl) triazole (BTz) substituents have been introduced to Ni(II) porphyrins (NiPs), in which their modulated axial-coordination processes have been investigated. For this study, the two types of ligands, neutral pyridine versus anionic cyanide, were employed to investigate an effect of BTz substituents. The unique microenvironments given by the BTz substituents provided two different effects on the axial-coordination processes of NiPs on the ground and excited states: (1) steric shielding and (2) donation of hydrogen-bonding sites. The steric shielding diminished the binding affinity of pyridine, while the cooperation of hydrogen bonds extraordinarily strengthened the binding affinity of CN(-). Interestingly, it was observed that the binding of CN(-) with the supporting of BTz substituents accompanied nonplanar distortion of NiPs. Such conformational change perturbed the electronic structure of NiPs, which gave rise to the modulation of coordination processes of NiPs in the excited state. As a consequence, photoinudced ligand binding and releasing processes of four- and six-coordinated NiPs were changed into the dominant photoinduced ligand releasing process.

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Section: Resultsmentioning

confidence: 99%

Modulation of Axial-Ligand Binding and Releasing Processes onto the Triazole-Bearing Nickel(II) Picket-Fence Porphyrins: Steric Repulsion versus Hydrogen-Bonding Effects

Yoon

Sung

et al. 2015

J. Phys. Chem. B

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“…The Fe(III)-CN − interaction is dominated by σ donation from the cyanide lone pair to the metal d z 2 orbital 87–88. It is well-established that π back-bonding in Fe(III)-CN − is very weak and contributes minimally to the bonding interaction 88.…”

Section: Discussionmentioning

confidence: 99%

“…The Fe(III)-CNinteraction is dominated by σ donation from the cyanide lone pair to the metal d z 2 orbital. 87,88 It is well-established that π backbonding in Fe(III)-CNis very weak and contributes minimally to the bonding interaction. 88 Chemical shifts observed in heme 13 CN --ligated proteins are found to be very far upfield, which is consistent with a negative spin density, a consequence of spin polarization through the σ bond.…”

Section: Discussionmentioning

confidence: 99%

Variation and Analysis of Second-Sphere Interactions and Axial Histidinate Character inc-type Cytochromes

Bowman

Bren

2010

Inorg. Chem.

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The electron-donating properties of the axial His ligand to heme iron in cytochromes c (cyts c) are found to be correlated with midpoint reduction potential (E m ) in variants of Hydrogenobacter thermophilus cytochrome c 552 (Ht cyt c 552 ) in which mutations have been made in and near the Cys-X-X-Cys-His (CXXCH) heme-binding motif. To probe the strength of the His-Fe(III) interaction, we have measured 13 C nuclear magnetic resonance (NMR) chemical shifts for 13 CN − bound to heme iron trans to the axial His in Ht Fe(III) cyt c 552 variants. We observe a linear relationship between these 13 C chemical shifts and E m , indicating that the His-Fe(III) bond strength correlates with E m . To probe a conserved hydrogen bonding interaction between the axial His Hδ1 and the backbone carbonyl of a Pro residue, we measured the pK a of the axial His Hδ1 proton (pK a(2) ), which we propose to relate to the His-Fe(III) interaction, reduction potential and local electrostatic effects. The observed linear relationship between the axial His 13 Cβ chemical shift and E m is proposed to reflect histidinate (anionic) character of the ligand. A linear relationship also is seen between the average heme methyl 1 H chemical shift and E m which may reflect variation in axial His electron-donating properties or in the ruffling distortion of the heme plane. In summary, chemical shifts of the axial His and exogenous CN − bound trans to His are shown to be sensitive probes of the His-Fe(III) interaction in variants of Ht cyt c 552 and display trends that correlate with E m .

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“…[20][21][22][23] This term is also successfully related to the isotropic shifts with neat linearity in many metalloporphyrin molecules, but it lacks a connection to the metal-porphyrin bonding interactions and completely neglects the pseudo-contact contributions because in the analyses of 13 C NMR data at a-, b-, and meso-C atoms, the contact shifts were thought to be more considerable than dipolar contributions. [24,25] In our cases, the calculated Fermi contact spin populations (1 ab ) of a-, b-, and meso-C atoms are given in square brackets in Table 2.…”

Section: In Memory Of Ru-jen Chengmentioning

confidence: 97%

Paramagnetic NMR Shifts for Saddle‐Shaped Five‐Coordinate Iron(III) Porphyrin Complexes with Intermediate‐Spin Structure

Chen

2012

Angew Chem Int Ed

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Calculable results: Complex density functional calculations and spin distribution analyses have been performed for planar and saddled iron(III) porphyrin complexes (see picture). The spin populations and the extent of the interactions between the metal and the porphyrin orbitals were determined, which can explain the large change of meso-carbon atom chemical shifts observed for different porphyrin ligands

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An unexpected bonding interaction between dxy and axial cyanide mediated by porphyrin deformation

Cited by 7 publications

References 15 publications

Modulation of Axial-Ligand Binding and Releasing Processes onto the Triazole-Bearing Nickel(II) Picket-Fence Porphyrins: Steric Repulsion versus Hydrogen-Bonding Effects

Modulation of Axial-Ligand Binding and Releasing Processes onto the Triazole-Bearing Nickel(II) Picket-Fence Porphyrins: Steric Repulsion versus Hydrogen-Bonding Effects

Variation and Analysis of Second-Sphere Interactions and Axial Histidinate Character inc-type Cytochromes

Paramagnetic NMR Shifts for Saddle‐Shaped Five‐Coordinate Iron(III) Porphyrin Complexes with Intermediate‐Spin Structure

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