title: Counting the monomers in nanometer-sized oligomers by pulsed electron-electron double resonance.
abstract: In a lot of cases active biomolecules are complexes of higher order, thus methods capable of counting the number of building blocks and elucidating their geometric arrangement are needed. Therefore, we experimentally validate here spin-counting via 4-pulse electron-electron double resonance (PELDOR) on well-defined test samples. Two biradicals, a symmetric and an asymmetric triradical, and a tetraradical were synthesized in a convergent reaction scheme via palladium-catalyzed cross-coupling reactions. PELDOR was then used to obtain geometric information and the number of spin centers per molecule in a single experiment. The measurement yielded the expected distances (2.2-3.8 nm) and showed that different spin-spin distances in one molecule can be resolved even if the difference amounts to only 5 A. The number of spins n has been determined to be 2.1 in both biradicals, to 3.1 and 3.0 in the symmetric and asymmetric triradicals, respectively, and to 3.9 in the tetraradical. The overall error of PELDOR spin-counting was found to be 5% for up to four spins. Thus, this method is a valuable tool to determine the number of constituting spin-bearing monomers in biologically relevant homo- and heterooligomers and how their oligomerization state and geometric arrangement changes during function.
authors.affiliation: Institute of Physical and Theoretical Chemistry, Center for Biomolecular Magnetic Resonance, J. W. Goethe-University, Frankfurt am Main, Germany.
authors.forename: Bela E
authors.initials: BE
authors.lastname: Bode
authors.forename: Dominik
authors.initials: D
authors.lastname: Margraf
authors.forename: Jörn
authors.initials: J
authors.lastname: Plackmeyer
authors.forename: Gerd
authors.initials: G
authors.lastname: Dürner
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Prisner
authors.forename: Olav
authors.initials: O
authors.lastname: Schiemann
mesh_terms: D003497:Cyclic N-Oxides / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D020836:Protein Structure, Quaternary; D021241:Spectrometry, Mass, Electrospray Ionization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D003497:Cyclic N-Oxides