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Laboratory | Chemistry


Biological High-Field Magnetic Resonance

Published on 27 November 2017
EPR equipment is part of the Saclay Biophysics platform 
certified IBiSA and are an integral part of the
Paris-South node of FRISBi infrastructure .

HFEPR is a powerful biophysical tool for investigating the magnetic centers within biological systems. The position and bonding of radicals and metal ions as well as the structure of the bio-macromolecules can be established using an array of HFEPR techniques.

Team Leader

Sun UN
01 69 08 28 42




High magnetic-field and high frequency electron paramagnetic resonance

The group specializes in the application of high magnetic-field and high frequency electron paramagnetic resonance (HFEPR) techniques for solving physical, chemical and biological problems. This involves a wide range of activities that include design and construction of instruments, computational and synthetic chemistry, as well as biochemistry and molecular biology. We have been involved in projects ranging from environmental chemistry to large proteins to molecular magnets with collaborators worldwide.

Major biochemical focus

One major biochemical focus has been on the characterization of radicals and Mn(II) centers in proteins. Both of these areas are strongly tied to research in oxidative stress and photosynthesis. The list of Mn(II) proteins that we are studying has been steadily growing and include those involved in the regulation and transport of manganese in cells as well as many other important biological functions ranging from regulation of oxidative stress and bacterial virulence to breakdown of organic molecules. We have extended our methodology to characterizing these paramagnetic centers inside intact viable cells.


We have extensive experience in the synthesis of Mn(II) complexes that help us understand the EPR spectroscopy of Mn(II) containing proteins. Some of these complexes are also functional mimics and provide valuable frameworks for examining the mechanisms of Mn(II) proteins and the design principles required for metal based drugs that mimic these enzymes. To complement HFEPR measurements, we use quantum chemical methods to calculate structures and magnetic spin parameters from first principles and molecular biology to not only test the spectroscopic measurements and quantum calculations, but also to probe aspects of enzyme function.

Pulse Electron Double Resonance

Recently, we have been interested in using HFEPR PELDOR (Pulse Electron Double Resonance) to determine the structure and structural changes of bio-macromolecules. By measuring the magnetic dipole coupling between unpaired electrons, precise nanometer scale distances can be obtained. Paramagnetic centers can be endogenous to the biological system or introduced as spin labels, and we have begun developing new spin labels and spectroscopic protocols for various applications.

Figure 1. Spectres RPE haut champ de Superoxyde Dismutases à Manganèse(II)  dans trois états différents. Le spectre de la protéine native est montré en rouge. Il existe deux sites différents au niveau desquels les ligands exogènes interagissent avec la protéine. Lorsque le ligand est dans le site distal, le centre Mn(II) reste pentacoordonné et donne le spectre vert. Par contre, dans le site proximal, le ligand coordonne le Mn(II) ce qui produit un centre hexacoordonné et donne un signal caratéristique à six lignes étroites (spectre bleu).
© Sun UN / CEA