Unusual coordination and metal-ligand geometry of a vanadyl porphyrin in aqueous solution

Shelnutt, John A.; Dobry, M. M.

doi:10.1021/j100239a008

Cited by 13 publications

(13 citation statements)

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“…Movement of the vanadium atom into the porphyrin plane would most likely cause an expansion of the core. Indeed, the core expands by 0.03 Â as indicated by the shift in I/^Q (3). A similar shift is observed for the pyrrolidine-VO(OEP) complex, suggesting that both complexes have the metal in the porphyrin plane.…”

Section: Effects Of Environment On Vanadium-porphyriη Complexessupporting

confidence: 57%

“…The equilibrium binding constant Κ is 110 at 25° C for phenanthroIine which forms a 1:1 complex (3). The large ring system of the aromatic molecule lies flat on the porphyrin ring where it can displace the ligand(s) and block the metal ligation sites if the ligands are only weakly bound (3,8). On the other hand, strongly bound axial ligands are known to prevent ΤΓ-ΤΓ complex formation (25,26).…”

Section: Effects Of Environment On Vanadium-porphyriη Complexesmentioning

confidence: 99%

“…These metalloporphyrins display complex axial ligation behavior. Spectral shifts occur upon addition of axial I y coordinated ligands in both the resonance Raman spectrum (3^ 5) and in the uv-visible absorption spectrum (1,(3)(4)(5). The spectral shifts may prove to be useful in separation and identification methods based on these techniques.…”

mentioning

confidence: 99%

“…The environments examined include solution studies in non-coordinating and coordinating solvents (3)(4)(5), aqueous surfactant micelles (4,7), se If-aggregates (3,8,9), π-π complexes (10-12), adsorbed onto surfaces (13), and incorporated into wellcharacterized asymétrie sites in proteins (4,5,7). Each of the environments mentioned affect the ligation properties of the metal in the central core of the porphyrin and, in some cases, the dynamical aspects of ligand binding.…”

mentioning

confidence: 99%

“…(2) An novel V(QH)2 porphyrin occurs in certain aqueous environments rather than the usual vanadyl (VO ) porphyrin (3).…”

mentioning

confidence: 99%

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Axial Coordination in Nickel and Vanadium Porphyrins: Transient and Difference Raman Spectroscopy

Shelnutt

Alston

Findsen

et al. 1987

ACS Symposium Series

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Nickel-and vanadium-porphyrin complexes and Ni(II)-reconstituted hemoglobin ( Ni Hb) and myoglobin ( Ni Mb) have been investigated using cw and transient resonance Raman spectroscopy.The state of axial coordination at the metal in these materials can be determined using the characteristic frequencies of the Raman marker lines arising from the porphyrin moiety.The state of axial ligation is highly sensitive to the molecular environment of these geoporphyrin analogs.Whether vanadium porphyrins are 5-or 6-coordinate depends on solvent and π-π aggregation and complexation. Similarly, nickel porphyrins exhibit 4-, 5-, or 6-coordination depending on the molecular environment.Nickel -reconstituted proteins provide well characterized models of hydrophobic cavities such as might exist in a heterogeneous petroleum environment.In the protein cavity a novel 5-coordinate Ni-porphyrin complex is observed. The existence of only one axial ligand is supported by identification of the axial ligand-Ni stretching vibration by isotopic substitution.The frequency of the Ni-ligand mode is consistent with histidine as the fifth ligand. The effects of the T->R change in quaternary structure of the protein environment of the Ni porphyrin are also observed in the Raman spectrum. The photoinitiated ligand-release and ligand-uptake processes in excited states of the Ni porphyrins and Ni-reconstituted proteins were also investigated. Laser excitation (~10-ns duration) of the complexes formed in coordinating solvents induces the release of axial ligands, but does not induce release of the histidine ligand of Ni-reconstituted hemoglobin and myoglobin. The results indicate that the protein matrix controls ligation dynamics by promoting rapid geminate recombination of the ligand.

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Section: Effects Of Environment On Vanadium-porphyriη Complexessupporting

confidence: 57%