EPR and ENDOR study of selected porphyrin- and phthalocyanine-copper complexes

Greiner, Steven P.; Rowlands, D. L.; Kreilick, Robert W.

doi:10.1021/j100202a012

Cited by 43 publications

(37 citation statements)

References 4 publications

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“…3A, black line) essentially coincides with the spectrum of a typical copper porphyrin monomer as reported in the literature 20,21 and shown for a copper porphyrin monomer ( P1 Cu ) with the same side groups as present in c -P10 Cu2 in the ESI† of this paper (Fig. S20): the interaction of the unpaired electron of copper with its nuclear spin of 3/2 results in four lines, two of which are clearly resolved at the low-field side of the spectrum (out-of-plane or z orientation).…”

Section: Resultssupporting

confidence: 83%

Exploring template-bound dinuclear copper porphyrin nanorings by EPR spectroscopy

et al. 2016

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Section: Resultssupporting

confidence: 83%

Exploring template-bound dinuclear copper porphyrin nanorings by EPR spectroscopy

et al. 2016

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“…In the program, provision was made for noncollinear principal axes of the g tensor and the Co hf tensor [51] and an orientationally dependent linewidth variation as described earlier [52]. ENDOR frequencies are best interpreted by a nucleus-specific spin Hamiltonian containing the hf, the quadrupole, and the nuclear Zeeman interactions [8,9,34,[39][40][41][42][43]. First-order expressions for the ENDOR transition frequencies will approximately hold along g tensor principal directions, if the principal axes of the hf and quadrupole tensors are collinear and, at other orientations, if the hf or Zeeman interaction dominates the nuclear spin Hamiltonian. For a situation where the magnetic field is aligned along one of the principal axes of the g tensor (for example, g^), which also happens to coincide with principal axes of the hf (Az) and quadrupole (Qz) tensors, the ENDOR transition frequencies are given by:…”

Section: Discussionmentioning

confidence: 99%

“…In the Co(II) complexes studied here, the g anisotropy dominates the spectra and one obtains hf tensor components for the various hf-coupled nuclei along the principal axes of the g tensor. From this information one can, in principle, obtain the location of the nuclei around the spin-carrying metal center (distance greater than 0.2 nm) [34,38] by use of the point-dipole approximation as demonstrated earlier for axially ligated Cu(II) and Co(II) complexes [39][40][41][42][43]. More recently cw and pulsed multifrequency EPR and ENDOR studies of Co(II) tetraphenylporphyrin complexes (CoTPP) with imidazol and pyridine as axial ligands as well as their superoxo complexes have been published [8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

Probing the surrounding of a cobalt(II) porphyrin and its superoxo complex by EPR techniques

2001

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Octaethylporphyrinato-cobalt(II), Co(II)OEP, was studied by electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) in frozen solutions of methanol, tetrahydrofuran and pyridine diluted into chloroform. Oxygenation led to the respective paramagnetic superoxo complexes Co(III)OEP • py • O. The EPR spectra demonstrate strong differences in the axial ligation states ((base-on)/(base-off)) and ease of the oxygenation process. Additional ENDOR studies with partial orientation selection along the principal g tensor axes are performed for resolution of the 'H, 4115N and 59 Co hyperfine coupling constants. This allows a comparison of the electron spin density distribution of the superoxo complex and its precursor. The data are interpreted in the framework of a more rigorous and detailed theoretical configuration interaction model than previously presented in the literature. The theoretical treatment shows that the structure of the superoxo complex is best described in a three-orbital model with contributions from the cobalt 3d, 4s, and oxygen it orbitals. The analysis reproduces the experimental g and Co hyperfine data yielding the relative energies of the MO's and the MO coefficients for the description of the spin density distribution in the Co(II) complex and its superoxo complex. To demonstrate the generality of the approach and possible applications, a comparison is made with the vitamin B, 2 , system. Furthermore, it provides detailed insight into the electronic and geometric changes resulting from axial ligation and oxygenation of the Co(II)OEP complex; this information can be used for predictions of the catalytic activity.

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“…Thus, the two coordinated nitrogens of His are altered with H 2 O 2 treatment, and the geometry is relaxed slightly, resulting in a lower Cu(II) hyperfine coupling (an A z value of 420 MHz) compared with the pure tetragonal axial symmetric systems, viz. copper tetraphenylporphyrin and copper phthalocyanin with A z values of 631 and 637 MHz, respectively (36). However, in the presence of HCO 3 Ϫ , there was only a minimal change in the spectra, indicating that the active site geometry was not affected greatly under these conditions.…”

Section: Epr/endor Of Hcomentioning

confidence: 97%

Direct Probing of Copper Active Site and Free Radical Formed during Bicarbonate-dependent Peroxidase Activity of Bovine and Human Copper,Zinc-superoxide Dismutases

Karunakaran

Zhang

Crow

et al. 2004

Journal of Biological Chemistry

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Using X-band electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) spectroscopy at liquid helium temperatures, the Cu(II) coordination geometry at the active site of bovine and human copper,zinc-superoxide dismutases (bSOD1 and hSOD1) treated with H 2 O 2 and bicarbonate (HCO 3 ؊ ) was examined. The time course EPR of wild type human SOD1 (WT hSOD1), W32F hSOD1 mutant (tryptophan 32 substituted with phenylalanine), and bSOD1 treated with H 2 O 2 and HCO 3 ؊ shows an initial reduction of active site Cu(II) to Cu(I) followed by its oxidation back to Cu(II) in the presence of H 2 O 2 . However, HCO 3 ؊ induced a Trp-32-derived radical from WT hSOD1 but not from bSOD1. The mutation of Trp-32 by phenylalanine totally eliminated the Trp-32 radical signal generated from W32F hSOD1 treated with HCO 3 ؊ and H 2 O 2 . Further characterization of the free radical was performed by UV irradiation of WT hSOD1 and bSOD1 that generated tryptophanyl and tyrosyl radicals. Both proton ( 1 H) and nitrogen ( 14 N) ENDOR studies of bSOD1 and hSOD1 in the presence of H 2 O 2 revealed a change in the geometry of His-46 (or His-44) and His-48 (or His-46) coordinated to Cu(II) at the active site of WT hSOD1 and bSOD1, respectively. However, in the presence of HCO 3 ؊ and H 2 O 2 , both 1 H and 14 N ENDOR spectra were almost identical to those derived from native bSOD1. We conclude that HCO 3 ؊ -derived oxidant does not alter significantly the Cu(II) active site geometry and histidine coordination to Cu(II) in SOD1 as does H 2 O 2 alone; however, the oxidant derived from HCO 3 ؊ (i.e. carbonate anion radical) reacts with surface-associated Trp-32 in hSOD1 to form the corresponding radical.Pioneering research from Fridovich and co-workers (1-4) has demonstrated a unique peroxidase activity from bovine SOD1 (bSOD1) 1 that was dependent on bicarbonate levels in phosphate buffers. The peroxidase activity was proposed to result as shown in Equations 1 and 2.The oxidant, E-Cu(II)-⅐ OH, derived from bSOD1 is able to oxidize several small anionic ligands, viz. azide, formate, and others (3-8), that gain access to the active site through a narrow channel as shown in Fig. 1. It has been proposed that the bicarbonate (HCO 3 Ϫ ), a ubiquitous anion present in high concentrations (ϳ25 mM) in biological systems, may enter the active site and be oxidized to form the carbonate anion radical, CO 3 . , which can diffuse out and oxidize other substrates in the bulk solution (3, 11-13) as shown in Equation 3.Previously, we reported that HCO 3 Ϫ enhances the peroxidase activity of human Cu,Zn-SOD (hSOD1) in a concentration-dependent manner, causing protein aggregation through Trp-32-derived oxidation products (14).Recently, Elam et al. (15) proposed an alternative mechanism for HCO 3 Ϫ -mediated peroxidase activity and inactivation of SOD1 via an enzyme-associated peroxycarbonate (HCO 4 Ϫ ) intermediate, which apparently oxidized the histidine coordinated to Cu(II) at the active site causing its inactivation (15). It was propose...

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EPR and ENDOR study of selected porphyrin- and phthalocyanine-copper complexes

Cited by 43 publications

References 4 publications

Exploring template-bound dinuclear copper porphyrin nanorings by EPR spectroscopy

Exploring template-bound dinuclear copper porphyrin nanorings by EPR spectroscopy

Probing the surrounding of a cobalt(II) porphyrin and its superoxo complex by EPR techniques

Direct Probing of Copper Active Site and Free Radical Formed during Bicarbonate-dependent Peroxidase Activity of Bovine and Human Copper,Zinc-superoxide Dismutases

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