title: Laser-Induced Magnetic Dipole Spectroscopy.
abstract: Pulse electron paramagnetic resonance measurements of nanometer scale distance distributions have proven highly effective in structural studies. They exploit the magnetic dipole-dipole coupling between spin labels site-specifically attached to macromolecules. The most commonly applied technique is double electron-electron resonance (DEER, also called pulsed electron double resonance (PELDOR)). Here we present the new technique of laser-induced magnetic dipole (LaserIMD) spectroscopy based on optical switching of the dipole-dipole coupling. In a proof of concept experiment on a model peptide, we find, already at a low quantum yield of triplet excitation, the same sensitivity for measuring the distance between a porphyrin and a nitroxide label as in a DEER measurement between two nitroxide labels. On the heme protein cytochrome C, we demonstrate that LaserIMD allows for distance measurements between a heme prosthetic group and a nitroxide label, although the heme triplet state is not directly observable by an electron spin echo.
authors.affiliation: Department of Chemistry, University of Konstanz , 78464 Konstanz, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Hintze
authors.affiliation: Department of Chemistry, University of Konstanz , 78464 Konstanz, Germany.
authors.forename: Dennis
authors.initials: D
authors.lastname: Bücker
authors.affiliation: Department of Chemistry, University of Konstanz , 78464 Konstanz, Germany.
authors.forename: Silvia
authors.initials: S
authors.lastname: Domingo Köhler
authors.affiliation: Laboratory of Physical Chemistry, Eidgenössische Technische Hochschule Zürich , 8093 Zürich, Switzerland.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Jeschke
authors.affiliation: Department of Chemistry, University of Konstanz , 78464 Konstanz, Germany.
authors.forename: Malte
authors.initials: M
authors.lastname: Drescher