EPR studies of weakly coupled oxomolybdenum (V) and low-spin iron (III) porphyrin centers

Raitsimring, Arnold M.; Basu, Partha; Shokhirev, N. V.; Enemark, John H.

doi:10.1007/bf03162041

Cited by 5 publications

(7 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For the averaging, two-dimensional pseudo-random numbers ε uniformly distributed in the unit square were used, , so that the vector is uniformly distributed on a unit sphere. Here The number of points were 2 13 (8192) and 2 14 (16384).…”

Section: Epr Simulationsmentioning

confidence: 99%

EPR Studies of the Dynamics of Rotation of Dioxygen in Model Cobalt(II) Hemes and Cobalt-Containing Hybrid Hemoglobins

et al. 1997

View full text Add to dashboard Cite

Earlier we showed that the shapes of the EPR spectra of cobalt(II) porphyrinate(nitrogen base)(dioxygen) complexes in fluid solution were sensitive to the rate of rotation about the Co−O bond (Walker, F. A.; Bowen, J. H. J. Am. Chem. Soc. 1985, 107, 7632). We have now extended these studies to four metal-substituted hybrid hemoglobins in an attempt to determine whether EPR spectroscopy is sensitive to differences in the mobility of dioxygen in the α and β subunits of the T and R quaternary states. For purposes of this study, [α2(CoO2)β2(FeO2)] and [α2(FeO2)β2(CoO2)] were used as R-state models and [α2(CoO2)β2(Zn)] and [α2(Zn)β2(CoO2)] were used as T-state models. EPR spectra were recorded for samples of each of the above hybrids, equilibrated with 1 atm of O2 gas, as a function of temperature. The “progress toward averaging” of the EPR signals of the Co−O2-containing subunits was measured as the difference in field positions, ΔH, for the midpoint of the low- and high-field extrema of the derivative EPR spectra. A plot of ΔH vs temperature for each hybrid shows that the [α2(Zn)β2(CoO2)] hybrid is unique in averaging more slowly than the other three (all of which behave similarly), indicating more restricted rotation of dioxygen in T-state β-chain pockets than in the heme distal O2-binding pockets of any other form. This finding is consistent with X-ray crystallographic data which show that valine E11 on the distal side of the T-state β-chain pocket partially blocks the dioxygen binding site (Perutz, M. F.; Fermi, G.; Luisi, B.; Shaanan, B.; Liddington, R. C. Acc. Chem. Res. 1987, 20, 309). Simulation of EPR spectra as a function of jump time provides semiquantitative estimates of the rate of dioxygen rotation in these mixed-metal hemoglobin−dioxygen samples; these rates are in the 1 × 108 s-1 range for three of the hybrids at 35−37 °C, and about one-third that value for T-state β(CoO2) centers. These results provide new insight into the highly dynamic nature of dioxygen bound to the metal centers of hemoglobin at physiological temperatures.

show abstract

Section: Epr Simulationsmentioning

confidence: 99%

EPR Studies of the Dynamics of Rotation of Dioxygen in Model Cobalt(II) Hemes and Cobalt-Containing Hybrid Hemoglobins

et al. 1997

View full text Add to dashboard Cite

show abstract

“…At 77 K these molecules display nearly axial spectra due to the pseudo-3-fold axis imposed by the three nitrogen atoms (of the facially coordinated tris(3,5-dimethylpyrazolyl)borate ligand, L) and three oxygen atoms (one oxo oxygen and two from the catechol fragment). Insertion of a diamagnetic metal into the porphyrin core does not change the Mo(V) EPR spectrum . However, when a paramagnetic metal ion is inserted into the porphyrin core, the Mo(V) EPR spectra change dramatically.…”

Section: Resultsmentioning

confidence: 93%

“…From a detailed EPR investigation at multiple frequencies and simulation of the respective spectra, we concluded that, for 4 , where the metal centers are separated by ∼9.4 Å (as determined by computer modeling), the primary interaction is dipolar in nature. The observed spectra could be simulated by considering the intermetal interaction to be primarily dipolar in nature and allowing minor changes in the spectroscopic g values for the molybdenum center . The g values for the molybdenum center in the simulated spectrum of 1 were 1.968, 1.943, and 1.939 (compared to 1.970, 1.968, and 1.925 for LMoO(catechol)).…”

Section: Resultsmentioning

confidence: 99%

“…The g values for the molybdenum center in the simulated spectrum of 1 were 1.968, 1.943, and 1.939 (compared to 1.970, 1.968, and 1.925 for LMoO(catechol)). For 3 , however, the primary interaction is exchange, and the overall features of the spectrum of 3 were simulated by considering a distribution of exchange interactions. , …”

Section: Resultsmentioning

confidence: 99%

“…Molecular modeling data for [Fe(2,3-Mo-TTP)(NMeIm) 2 ]Cl showed that in this system the two metal centers are separated by ∼7.9 Å. From EPR measurements at low temperatures, we concluded that the spin−spin coupling is primarily exchange in nature. , However, in the isomeric [Fe(3,4-Mo-TTP)(NMeIm) 2 ]Cl the two centers are ∼9.4 Å apart, and the spin−spin coupling is dominated by the dipolar interaction. , From a detailed NMR investigation, we showed that in [Fe(2,3-Mo-TTP)(NMeIm) 2 ]Cl one NMeIm is prevented from rotating, even at room temperature, and the other NMeIm is either aligned parallel to the first one or is rotating rapidly . We also found that the molybdenyl substituent had little electronic effect on the porphyrin.…”

Section: Introductionmentioning

confidence: 82%

See 2 more Smart Citations

Oxomolybdenum(V)/Iron(III) Porphyrinate Complexes: Effect of Axial Ligand Plane Orientation on Complex Stability, Reduction Potential, and NMR and EPR Spectra

et al. 1997

View full text Add to dashboard Cite

The compounds {5,10,15-tri-p-tolyl-20-[[2,3-[((hydrotris(3,5-dimethylpyrazolyl)borato)oxomolybdenio)dioxy]phenyl]porphyrinato}bis(2-methylimidazole)iron(III) chloride, Fe(2,3-Mo-TTP)(2MeImH)(2)Cl (1), and {5,10,15-tri-p-tolyl-20-[3,4-[((hydrotris(3,5-dimethylpyrazolyl)borato)oxomolybdenio)dioxy]phenyl]porphyrinato}bis(2-methylimidazole)iron(III) chloride, Fe(3,4-Mo-TTP)(2MeImH)(2)Cl) (2), have been prepared in order to assess the effect of axial ligand plane orientation upon the stability, reduction potential, and NMR and EPR spectra of these novel (porphryinato)iron(III)-Mo(V) systems that possess two S = (1)/(2) metal centers. The proton NMR spectra of 1 and 2 are characteristic of perpendicular orientation of the planes of the axial 2MeImH ligands. These results contrast with those previously reported (Basu, P.; Shokirev, N. V.; Enemark, J. H.; Walker, F. A. J. Am. Chem. Soc. 1995, 117, 9042-9055) for the analogous compounds with NMeIm as the axial base (3, 4) whose (1)H NMR spectra are characteristic of one or both axial ligands in parallel planes. The equilibrium constants (beta(2)) for binding the bulky 2MeImH ligands of 1 and 2 are more than an order of magnitude smaller than those for NMeIm binding to 3 and 4. Three distinct pseudo-Nernstian one-electron couples are observed for 1 and 2 in DMF that can be assigned to the Fe(III/II), Mo(V/IV), and Fe(II/I) reductions, with the Fe(III/II) couple being most positive. The Fe(III/II) and Mo(V/IV) potentials are similar to those for 3 and 4 and only slightly perturbed from those of the individual isolated components. The EPR spectrum of 1 shows features due to Mo(V) and low-spin Fe(III) that are perturbed by weak exchange coupling (2.6 GHz, 0.078 cm(-)(1)) between the two metal centers which are separated by approximately 7.9 Å. The "large g(max)" feature characteristic of the 2MeImH adducts of Fe(III) tetraphenylporphyrinates is shifted toward the Mo(V) signal to 2.85; the anisotropy of the Mo(V) signal is lost, and no molybdenum hyperfine can be detected. The EPR spectrum of 2, which has a metal-metal separation of approximately 9.4 Å, shows an unperturbed "large g(max)" value of 3.41 for the Fe(III) center. The Mo(V) part of the spectrum is slightly perturbed from that of the precursor catecholate complex but is essentially identical to that of 4, which exhibits a rhombic Fe(III) signal.

show abstract

Chemical systems modeling the d1 Mo(V) states of molybdenum enzymes

Young

2016

Journal of Inorganic Biochemistry

View full text Add to dashboard Cite

EPR studies of weakly coupled oxomolybdenum (V) and low-spin iron (III) porphyrin centers

Cited by 5 publications

References 18 publications

EPR Studies of the Dynamics of Rotation of Dioxygen in Model Cobalt(II) Hemes and Cobalt-Containing Hybrid Hemoglobins

EPR Studies of the Dynamics of Rotation of Dioxygen in Model Cobalt(II) Hemes and Cobalt-Containing Hybrid Hemoglobins

Oxomolybdenum(V)/Iron(III) Porphyrinate Complexes: Effect of Axial Ligand Plane Orientation on Complex Stability, Reduction Potential, and NMR and EPR Spectra

Chemical systems modeling the d1 Mo(V) states of molybdenum enzymes

Contact Info

Product

Resources

About