Determination of high-spin iron(III)-nitroxyl distances in spin-labeled porphyrins by time-domain EPR

Journal of Magnetic Resonance
M H RakowskyS S Eaton

Abstract

Continuous wave EPR spectra of the nitroxyl signals for four spin-labeled high-spin (h.s.) Fe(III) porphyrins showed partially resolved splittings at temperatures near 4 K. Axial ligands were fluoride, chloride, or bromide. As temperature was increased to 20 to 30 K the iron-nitroxyl splitting collapsed due to increasing rates of iron relaxation. Electron spin-echo (ESE) spectroscopy showed that above about 6 K collapse of the iron-nitroxyl spin-spin splitting caused a dramatic increase in the nitroxyl phase memory relaxation rates. Electron spin relaxation rates were determined for Fe(tetratolylporphyrin)X, X = F, Cl, Br, in toluene solution by ESE or inversion recovery at 4.5 to 6 K and by analysis of the temperature-dependent contributions to the continuous wave EPR linewidths between about 10 and 120 K. Above about 10 K iron relaxation rates increase in the order X = F < Cl < Br, which is the order of increasing zero-field splitting. Saturation recovery data for two spin-labeled h.s. iron(III) porphyrins between about 15 and 120 K and for two additional spin-labeled h.s. iron(III) porphyrins between about 85 and 120 K demonstrated that interaction with the h. s. iron enhanced the electron spin relaxation rate of the spin la...Continue Reading

References

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Citations

Dec 16, 2011·Journal of Magnetic Resonance·Deborah G MitchellGareth R Eaton
Jun 15, 2007·Free Radical Biology & Medicine·Guo-Ping YanSteven E Bottle
Jul 23, 2013·Biophysical Journal·Deborah G MitchellGareth R Eaton
Jun 5, 2012·Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy·Maria Jerzykiewicz
May 10, 2016·The Journal of Physical Chemistry. a·Andreas Meyer, Olav Schiemann
Oct 8, 2014·Journal of the American Chemical Society·Zhongyu YangWayne L Hubbell
May 17, 2012·The Journal of Physical Chemistry Letters·Petra LuedersMaxim Yulikov

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