Spin-label EPR Spectroscopy
- Brigitte Wiesner
- Dr. Ulrich Scheler
Electron paramagnetic resonance (EPR), also known as electron spin resonance (ESR), is a powerful spectroscopic technique for the study of structure and dynamics of paramagnetic species. Most polymeric materials, however, are diamagnetic and thus do not exhibit EPR signals. The absence of signals from the bulk material provides the opportunity to apply EPR as a selective probe technique, whereby stable paramagnetic species such as nitroxide radicals are introduced artificially. These radicals are called spin labels if they are covalently linked to the macromolecules. Rotational dynamics of such spin labels on time scales between 10 ps and 1 µs can be characterized by the basic, fast and sensitive continuous wave (CW) EPR analyzing the line shape. The rotational dynamics of the spin labels is influenced by the restricted motion of the side group bearing the spin label and local polymer backbone motions at the point of the covalent linking of the spin label.
We are applying the EPR spin-label technique to study local dynamics in polyelectrolyte systems such as polyelectrolyte multilayers (PEM) and polyelectrolyte complexes (PEC). We employ the fact that the EPR line shapes are sensitive to the mobility of the spin label which informs on polymer and label dynamics. The segmental rotational mobility of the spin-labeled macromolecules is determined by simulating and fitting the line shapes of experimental EPR spectra using the EasySpin software.
- Continuous wave (cw) X-band (9.5 GHz) EPR spectrometer EMX-plus (Bruker BioSpin), with digital temperature control unit ER 4141VT (100-500 K)
- DFG: Investigations on the dynamics of polyelectrolyte multilayers by spin-labeling and EPR spectroscopy
4 most important publications
- Lappan, U.; Wiesner, B.; Scheler, U.; Segmental Dynamics of Poly(acrylic acid) in Polyelectrolyte Complex Coacervates Studied by Spin-Label EPR Spectroscopy, Macromolecules 2016, 49, (12), 8616-8621.
- Lappan, U.; Wiesner, B.; Scheler, U.; Rotational Dynamics of Spin-Labeled Polyacid Chain Segments in Polyelectrolyte Complexes Studied by CW EPR Spectroscopy, Macromolecules 2015, 48, (11), 3577-3581.
- Lappan, U.; Wiesner, B.; Scheler, U.; Complex coacervation of polyelectrolytes studied by spin-label EPR spectroscopy, Macromol. Chem. Phys. 2014, 215, (10), 1030-1035.
- Lappan, U.; Wiesner, B.; Zschoche, S.; Scheler, U.; Polyelectrolyte Multilayers Studied by Electron Paramagnetic Resonance (EPR) Spin-Label Technique, App. Magn. Reson. 2013, 44, (1-2), 181-188.