title: EPR characterization of Mn(ii) complexes for distance determination with pulsed dipolar spectroscopy.
abstract: The four Mn(ii) complexes Mn-DOTA, Mn-TAHA, Mn-PyMTA, and Mn-NO3Py were characterized by electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR), and relaxation measurements, to predict their relative performance in the EPR pulse dipolar spectroscopy (PDS) experiments. High spin density localization on the metal ions was proven by ENDOR on1H, D,14N, and55Mn nuclei. The transverse relaxation of the Mn(ii) complexes appears to be slow enough for PDS-based spin-spin distance determination. Rather advantageous ratios of T1/Tmwere measured allowing for good relaxation induced dipolar modulation enhancement (RIDME) performance and, in general, fast shot repetitions in any PDS experiment. Relaxation properties of the Mn(ii) complexes correlate with the strengths of their zero field splitting (ZFS). Further, a comparison of Mn(ii)-DOTA and Gd(iii)-DOTA based spin labels is presented. The RIDME technique to measure nanometer-range Mn(ii)-Mn(ii) distances in biomolecules is discussed as an alternative to the well-known DEER technique that often appears challenging in cases of metal-metal distance measurements. The use of a modified kernel function that includes dipolar harmonic overtones allows model-free computation of the Mn(ii)-Mn(ii) distance distributions. Mn(ii)-Mn(ii) distances are computed from RIDME data of Mn-rulers consisting of two Mn-PyMTA complexes connected by a rodlike spacer of defined length. Level crossing effects seem to have only a weak influence on the distance distributions computed from this set of Mn(ii)-Mn(ii) RIDME data.
authors.affiliation: Laboratory of Physical Chemistry, Department of Chemistry and Applied Bioscience, ETH Zurich, Vladimir Prelog Weg 2, 8093 Zurich, Switzerland. maxim.yulikov@phys.chem.ethz.ch.
authors.forename: Katharina
authors.initials: K
authors.lastname: Keller
authors.affiliation: Max Planck Institut for Chemical Energy Conversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany. anton.savitsky@cec.mpg.de and Institute of Physical Chemistry and Chemical Physics, Slovak University of Technology in Bratislava, Faculty of Chemical and Food Technology, Radlinského 9, 81237 Bratislava, Slovak Republic.
authors.forename: Michal
authors.initials: M
authors.lastname: Zalibera
authors.affiliation: Faculty of Chemistry and Center for Molecular Materials (CM2), Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany. godt@uni-bielefeld.de.
authors.forename: Mian
authors.initials: M
authors.lastname: Qi
authors.affiliation: Faculty of Chemistry and Center for Molecular Materials (CM2), Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany. godt@uni-bielefeld.de.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Koch
authors.affiliation: Faculty of Chemistry and Center for Molecular Materials (CM2), Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany. godt@uni-bielefeld.de.
authors.forename: Julia
authors.initials: J
authors.lastname: Wegner
authors.affiliation: Faculty of Chemistry and Center for Molecular Materials (CM2), Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany. godt@uni-bielefeld.de.
authors.forename: Henrik
authors.initials: H
authors.lastname: Hintz
authors.affiliation: Faculty of Chemistry and Center for Molecular Materials (CM2), Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany. godt@uni-bielefeld.de.
authors.forename: Adelheid
authors.initials: A
authors.lastname: Godt
authors.affiliation: Laboratory of Physical Chemistry, Department of Chemistry and Applied Bioscience, ETH Zurich, Vladimir Prelog Weg 2, 8093 Zurich, Switzerland. maxim.yulikov@phys.chem.ethz.ch.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Jeschke
authors.affiliation: Max Planck Institut for Chemical Energy Conversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany. anton.savitsky@cec.mpg.de.
authors.forename: Anton
authors.initials: A
authors.lastname: Savitsky
authors.affiliation: Laboratory of Physical Chemistry, Department of Chemistry and Applied Bioscience, ETH Zurich, Vladimir Prelog Weg 2, 8093 Zurich, Switzerland. maxim.yulikov@phys.chem.ethz.ch.
authors.forename: Maxim
authors.initials: M
authors.lastname: Yulikov