Measuring Nanometer Scale Distances by high-field Pulse Electron Paramagnetic Resonance Using Mn(II) Spin-Labels
Final Report Abstract
In this project the high spin MnII ions were investigated with respect to their properties as paramagnetic centers for nanometer distance measurements; either between two manganese ions or between a manganese ion and a nitroxide spin label. For this purpose Mn-Mn and Mn- Nitroxide molecules have been synthesized, with different distances between both paramagnetic centers and with different ligand spheres of the Mn II ion, resulting in different zero field splitting parameters. Multi-frequency (34-260 GHz) high field (1-9.2T) EPR spectroscopy has been used to determine the zero field splitting parameters and pulsed dipolar EPR spectroscopy methods, such as PELDOR (Pulsed Electron Electron Double Resonance) and RIDME (Relaxation Induced Dipolar Modulation Enhancement) were tested for their performance with respect to distance determination with MnII ions as spin labels. The wellcharacterized model compounds allowed to draw the following conclusions: 1) MnII ions with low zero field splitting parameters have superior performance for pulsed dipolar spectroscopy because they allow better selection of the central ms=1/2 to ms=-1/2 transition for EPR detection and pumping. This simplifies pulse length optimizations as well as the spin Hamiltionian calculations for a quantitative understanding of the observed transitions. Additionally it could be shown numerically that complications and artifacts in the dipolar evolution signal caused by mixing of spin sublevels can be strongly reduced if the Zeeman splitting is much larger compared to the zero field splitting. 2) Distances between two MnII ions and between MnII and a nitroxide spin label could be obtained with very good accuracy with PELDOR (DEER) at high magnetic fields (≥ 1 T). Artifacts related to the pseudosecular term in the dipolar Hamiltionian do not seriously obscure the distances derived from Tikhonov regularization of the dipolar evolution function if pump and probe frequency are well separated. Modulation depths are very small, so high sensitivity is required to measure the distances precisely. RIDME experiments at high magnetic fields (≥ 3 T) can be also used to extract nanometer distance information between two MnII ions. As the flips of the second MnII ion are in this case induced by relaxation, much larger efficiencies can be achieved compared to PELDOR. On the other hand higher harmonics of the dipolar coupling were observed, resulting from multiquantum relaxation effects. These contributions could be partially removed by using soft pulses. At lower frequencies ESEEM (electron spin echo envelope modulation) effects obscured the dipolar evolution function demonstrating that high magnetic fields are necessary to perform this experiment properly.
Publications
- (2014) High-field pulse EPR nanometre-scale distance measurements of paramagnetic centres, FrenchBic, 28 October – 1 November 2014, Anglet, France
Ching, V., Demay-Drouhard, P., Bertrand, H., Policar, C., Un, S., Tabares, L.
- (2014) Pulsed Electron-Electron Double Resonance Spectroscopy on a High-Spin Mn2+ Ion coupled with a nitroxide radical. 36th Discussion Meeting of the GDCh-Division of "Magnetic Resonance" (FGMR), 29 September – 4 October 2014, Berlin, Germany
Akhmetzyanov, D., Plackmeyer, J., Endeward, B., Denysenkov, V., Prisner, T.
- (2014) Pulsed Electron-Electron Double Resonance Spectroscopy on a High-Spin Mn2+ Ion non-covalently attached to a Nitroxide Radical. Modern Development of Magnetic Resonance (MDMR), 23 – 27 September 2014, Kazan, Russia
Akhmetzyanov, D., Plackmeyer, J., Endeward, B., Denysenkov, V., Prisner, T.
- (2014) Pulsed Electron-Electron Double Resonance Spectroscopy on a High-Spin Mn2+ Ion non-covalently attached to a Nitroxide Radical. Rocky Mountain EPR Symposium, 13 – 17 July 2014, Copper Mountain, Colorado, USA
Akhmetzyanov, D., Plackmeyer, J., Endeward, B., Denysenkov, V., Prisner, T.
- (2015) Measuring Nanometer-Scale Distances by High-Field Pulsed Electron-Electron Double Resonance Using MnII Spin Labels, PhD Thesis, Université Pierre et Marie Curie, Paris
Paul Demay-Drouhard
- (2015) Mn(II)- Mn(II) Nanometre-Scale Distance Measurements By High-Field pulse EPR, 13th International Symposium on Applied Bioinorganic Chemistry ISABC13, 12 – 15 June, NUI Galway, Ireland
Ching, V., Demay-Drouhard, P., Bertrand, H., Policar, C., Un, S., Tabares, L.
- (2015) Nanometric distance measurements between Mn(II)DOTA centers, Phys. Chem. Chem. Phys., 17, 23368 – 23377
Ching, V., Demay-Drouhard, P., Bertrand, H., Policar, C., Tabares, L., Un, S.
(See online at https://doi.org/10.1039/c5cp03487f) - (2015) Pulsed electron–electron double resonance spectroscopy between a high-spin Mn2+ ion and a nitroxide spin label, Phys. Chem. Chem. Phys., 17, 6760 – 6766
Akhmetzyanov, D., Plackmeyer, J., Endeward, B., Denysenkov, V., Prisner T.
(See online at https://doi.org/10.1039/c4cp05362a) - (2015) Pulsed EPR Dipolar Spectroscopy with High-Spin Mn2+ Ions. 37th Discussion Meeting of the GDCh- Division of "Magnetic Resonance" (FGMR), 7 – 10 September 2015, Darmstadt, Germany
Akhmetzyanov, D., Ching, V., Endeward, B., Demay-Drouhard, P., Plackmeyer, J., Denysenkov, V., Un, S., Tabares, L., Bertrand, H., Policar, C., Prisner, T.
