Zimmermann Group

Synthesis of isotopically labelled molecules with ¹³C, ²H, ¹⁷O, ¹⁸O, ¹⁵N (Neurotransmitters, Electron-spin-labels for proteins, Quinone-acceptors). Development of new discotic and pyramidic mesophases; Cooperations with the Weizmann-Institute, Dartmouth Medical School, Arrhenius Laboratory, Stockholm; ETH Zürich, FU Berlin and Osaka-Sangyo University.

Asymmetric Hydrogen-Bonding of the Quinone Cofactor in Photosystem I Probed by 13C-Labeled Naphthoquinones

The figure illustrates the case of a special protein-cofactor interaction using the example of the quinone electron acceptor (yellow, QK-A) which functions as a one electron gate in photosynthetic charge separation. The X-ray structure of Photosystem I (1JB0) suggests a single H-bond (marked as broken line in the center of the Figure) connecting the protein backbone (Ala721) and one of the quinone carbonyl groups. Advanced EPR experiments (see pages 9439-9448) enable us to identify and characterize this prominent H-bond in the transient functional chargeseparated intermediate state in even greater detail. The significant H-bond strength may be stabilized by the extended network of H-bonds seen on the other side of the protein backbone.

Another main topic is the synthesis and the characterization by NMR of new series of columnar mesophases particularly of pyramidic liquid crystals. We can prepare crown and saddle isomeres as well as optical isomers of the nona-alkanoyloxi-tribenzocyclononatriene. This is a cooperation with Zeev Luz from the Weizmann Institute of Science in Rehovot / Israel and Philippe Lesot from CNRS Université de Paris-Sud.

Structural formula of the CTV core, (b) numerical convention used for the aromatic carbons, (c) the structure of the crown conformer, (d) the structure of the saddle conformer, and (e) a schematic view of a column made of pyramidic molecules. (f) Pseudorotation of the saddle isomer.