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Molecular Physics
An International Journal at the Interface Between Chemistry and Physics
Volume 111, 2013 - Issue 18-19: Modern EPR Spectroscopy
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Invited Articles

Zero-field splittings in metHb and metMb with aquo and fluoro ligands: a FD-FT THz-EPR study

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Pages 2696-2707 | Received 20 Mar 2013, Accepted 24 May 2013, Published online: 01 Jul 2013
 

Abstract

A combined X-band and frequency-domain Fourier-transform THz electron paramagnetic resonance (FD-FT THz-EPR) approach has been employed to determine heme Fe(III) S = 5/2 zero-field splitting (ZFS) parameters of frozen metHb and metMb solutions, both with fluoro and aquo ligands. Frequency-domain EPR measurements have been carried out by an improved synchrotron-based FD-FT THz-EPR spectrometer. ZFS has been determined by field dependence of spin transitions within the mS = ±1/2 manifold, for all four protein systems, and by zero-field spin transitions between mS = ±1/2 and mS = ±3/2 levels, for metHb and metMb flouro-states. FD-FT THz-EPR data were simulated with a novel numerical routine based on Easyspin, which allows now for direct comparison of EPR spectra in field and frequency domain. We found purely axial ZFSs of D = 5.0(1) cm−1 (flouro-metMb), D = 9.2(4) cm−1 (aquo-metMb), D = 5.1(1) cm−1 (flouro-metHB) and D = 10.4(2) cm−1 (aquo-metHb).

Acknowledgements

This work has been supported and funded by Deutsche Forschungsgemeinschaft (DFG) priority program SPP 1601. B.M. Martins is supported by DFG (MA 3348/2-2). FD-FT THz-EPR has been carried out within the BESSY II user program. We thank Sun Un (CEA, Saclay) for helpful discussions and Dirk Ponwitz (HZB) for technical support.

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