title: A Bis-Manganese(II)-DOTA Complex for Pulsed Dipolar Spectroscopy.
abstract: High-spin gadolinium(III) and manganese(II) complexes have emerged as alternatives to standard nitroxide radical spin labels for measuring nanometric distances by using pulsed electron-electron double resonance (PELDOR or DEER) at high fields/frequencies. For certain complexes, particularly those with relatively small zero-field splitting (ZFS) and short distances between the two metal centers, the pseudosecular term of the dipolar coupling Hamiltonian is non-negligible. However, in general, the contribution from this term during conventional data analysis is masked by the flexibility of the molecule of interest and/or the long tethers connecting them to the spin labels. The efficient synthesis of a model system consisting of two [Mn(dota)](2-) (MnDOTA; DOTA(4-) =1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) directly connected to the ends of a central rodlike oligo(phenylene-ethynylene) (OPE) spacer is reported. The rigidity of the OPE is confirmed by Q-band PELDOR measurements on a bis-nitroxide analogue. The Mn(II) -Mn(II) distance distribution profile determined by W-band PELDOR is in reasonable agreement with one simulated by using a simple rotamer analysis. The small degree of flexibility arising from the linking MnDOTA arm appears to outweigh the contribution from the pseudosecular term at this interspin distance. This study illustrates the potential of MnDOTA-based spin labels for measuring fairly short nanometer distances, and also presents an interesting candidate for in-depth studies of pulsed dipolar spectroscopy methods on Mn(II) -Mn(II) systems.
authors.affiliation: Ecole Normale Supérieure-PSL Research University, Département de Chimie, Sorbonne Universités-UPMC Univ Paris 06, CNRS UMR 7203 LBM, 24 rue Lhomond, 75005, Paris, France.
authors.forename: Paul
authors.initials: P
authors.lastname: Demay-Drouhard
authors.affiliation: Institute for Integrative Biology of the Cell (I2BC), Department of Biochemistry, Biophysics and Structural Biology, Université Paris-Saclay, CEA, CNRS UMR 9198, Gif-sur-Yvette, F-91198, France.
authors.forename: H Y Vincent
authors.initials: HY
authors.lastname: Ching
authors.affiliation: Goethe-University Frankfurt am Main, Institute of Physical and Theoretical Chemistry and, Center for Biomolecular Magnetic Resonance, Max von Laue Str. 7, 60438, Frankfurt am Main, Germany.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Akhmetzyanov
authors.affiliation: Institut de Chimie Moléculaire et des Matériaux O'Orsay, Université Paris-Sud, UMR CNRS 8182, Université Paris-Saclay, 91405, Orsay, France.
authors.forename: Régis
authors.initials: R
authors.lastname: Guillot
authors.affiliation: Institute for Integrative Biology of the Cell (I2BC), Department of Biochemistry, Biophysics and Structural Biology, Université Paris-Saclay, CEA, CNRS UMR 9198, Gif-sur-Yvette, F-91198, France.
authors.forename: Leandro C
authors.initials: LC
authors.lastname: Tabares
authors.affiliation: Ecole Normale Supérieure-PSL Research University, Département de Chimie, Sorbonne Universités-UPMC Univ Paris 06, CNRS UMR 7203 LBM, 24 rue Lhomond, 75005, Paris, France. helene.bertrand@ens.fr.
authors.forename: Hélène C
authors.initials: HC
authors.lastname: Bertrand
authors.affiliation: Ecole Normale Supérieure-PSL Research University, Département de Chimie, Sorbonne Universités-UPMC Univ Paris 06, CNRS UMR 7203 LBM, 24 rue Lhomond, 75005, Paris, France. clotilde.policar@ens.fr.
authors.forename: Clotilde
authors.initials: C
authors.lastname: Policar
keywords: EPR spectroscopy; gadolinium; manganese; pulsed electron-electron double resonance; spin labels