We are involved in the design and synthesis of compounds with two or more paramagnetic sites at well-defined distance. These compounds are used quasi as molecular rulers in the development and evaluation of EPR techniques such as DEER, RIDME, cw-EPR techniques - techniques that allow to obtain information on the structure of molecules or molecular aggregates through determining distances between deliberately chosen specific sites of the molecule or molecules. The techniques cover a distance range of about 2-8 nm and can be applied to molecules in an amorphous state and even in a living cell, what makes the techniques of utmost usefullness for gaining insight into the structure and dynamics of biopolymers, e.g. DNA/RNA and peptides or proteins in their native state and natural environment. Presently, we focus on the investigation and development of Gd(III), Mn(II), and Cu(II) complexes as spin labels, also in combination with other radicals, and work on the synthesis of appropriate molecular rulers which are water soluble.

This project is performed in tight collaboration with Prof. Dr. G. Jeschke and Dr. M. Yulikov at the ETH Zürich, Prof. Dr. D. Goldfarb at the Weizmann Institute of Science, Rehovot, Israel, and Prof. Dr. Song-I Han and Prof. Dr. M. Sherwin at the University of California, Santa Barbara, CA, USA. We are contributing to the Priority Progamme (Schwerpunktprogramm) SPP 1601, funded by the German Science Foundation (DFG).

Gd(III), Mn(II), and Cu(II) complexes as spin labels
Besides making appropriate molecular rulers, there is lots to do in respect to ligand tuning and enabling the complex ligand or the ready-made complex to highly selective bioconjugation under mild reaction conditions - targets that need creative and organic synthesis loving coworkers. The application of the spin labels on peptides and proteins as well as in-cell studies will be performed in collaboration with Prof. Dr. M. Drescher at the University of Konstanz and Prof. Dr. E. Bordignon at the Ruhr University Bochum.

Complexes for dynamic nuclear polarization (DNP)
The bis(metal-complex)es used to explore the EPR-based techniques are also of interest as dynamic nuclear polarization (DNP) agents to investigate solid and cross effect in DNP NMR spectroscopy, as shown by the recent results of a cooperation with Dr. B. Corzilius at the Goethe Universität Frankfurt am Main.

Organic building blocks with metal organic frameworks
Metal organic frameworks are porous frameworks consisting of organic compounds, such as dicarboxylic acids that are linked through individual metal ions or units containing more than one metal ion. Many applications of these materials are expected, e.g. separation, adsorption, catalysis, ion conductivity. The frameworks are formed in a process of selfassembly. A research project in cooperation with Prof. P. Behrens at the Leibniz Universität Hannover, led to the discovery of a class of metal organic frameworks which we named PIZOFs (porous interpenetrated zirconium organic frameworks). The PIZOFs have large and well accessible pores and are highly resistant against hydrolysis. The interior of their pores can be widely varied through the substituents present at the organic building blocks or postsynthetically attached to the organic units of the framework. This allows a fine tuning of the pore environment for a specific application. This project has been funded through the Priority Progamme (Schwerpunktprogramm; SPP 1362) of the German Science Foundation (DFG).