Institut für Organische Chemie
Keywords: Membranes, synkinesis, bolaamphiphiles, chiral assemblies, porphyrins, carbohydrate lipids.
Takustr. 3, D-14195 Berlin; Tel. +49 30 838-55394, Fax -55589. E-mail: email@example.com
The group is working on the non-covalent synthesis ("synkinesis") of small and large molecular assemblies in bulk water and on surfaces (e.g., silicon wafers, polymers). Synthetic bolaamphiphiles with two different head groups, e.g. carbohydrates and amino acids, are applied to build up helical and tubular structures in bulk water and on various solid surfaces ("bola landscapes"). Bolaamphiphilic porphyrin assemblies functionalize these systems to form photochemical redox systems. Solid state NMR spectroscopy and various electron microscopic techniques are used to characterize the assemblies' interactions and stereochemistry.
Promotion: TU Braunschweig (1968); Habil.: TU Braunschweig (1974); Postdoc Rockefeller U., NY (1966-68); Professor: FU Berlin (since 1978).
Dr. U. Siggel, Max Vollmer Inst. (TU Berlin); Prof. E. Tsuchida (Waseda U., Tokyo); Prof. W. Stehlik (Institut für Physik FU Berlin); Dr. Mike Eaton (CellTech, Windsor, England).
DFG, BMFT, Fonds der Chemischen Industrie.
The general aims of the work are threefold: (1) to understand the molecular interactions between the major bioorganic molecules in a membrane-type environment, e.g., amino acid-carbohydrate, porphyrin-amino acid, metalloporphyrin-ascorbic acid etc., (2) to apply regio- and stereoselective interactions of major natural products in the synkinesis of complex, hopefully useful molecular assemblies, and (3) to learn how to disrupt lipid membranes, e.g., in vesicles, under biological conditions in order to deliver entrapped materials, e.g., nucleic acids.
Our special field of bioorganic supramolecular chemistry has been described in a recent book by J. Fuhrhop and J. Köning. lt develops our philosophy and provides many examples of intelligent synkineses of extraordinary micellar, vesicular, fibrous and tubular membranes as well as surface monolayers and designed holes within crystals1.
Here we summarize four concrete recent results in order to supply some insight into our scientific approach and methodology:
1. N-Octyl-D-gluconamide is insoluble in cold water, but dissolves very well above 80 °C. When the amide hydrogen bonds disintegrate upon cooling a micellar quadruple helix is formed, which can be observed and analyzed in detail by electron microscopy (Fig. 1a)2. Addition of the enantiomeric fiber leads to the rearrangement of the fibers to platelets3. A solid state NMR procedure has been developed to establish molecular conformations in supramolecular assemblies4.
Fig. 1 (a) and (b) N-Octylgluconamide forms quadruple helical fibers in water which have been characterized by electron micrographs. (c) Four molecular conformations have been assigned by 13C-NMR solid state spectroscopy in solution, 3D crystals, crystallites and the fibers.
2. A porphyrin with tetracationic northern and southern edges and hydrophobic eastern and western edges forms molecular monolayers in bulk water5. Its cationic surfaces bind redox-active counterions, e.g., ascorbate. The photochemically excited state of the porphyrin monolayer takes up electrons from the ascorbate. These monolayers can be combined with rigid diamide monolayers6. Porphyrin fibers with high curvature7,8,9 have also been produced (not shown).
Fig. 2 Cationic porphyrin monolayers can form the basis of redox-active monolayer landscapes on solid surfaces.
3. A covalent combination of four carotenoid molecules ("bixin") and a porphyrin forms vesicles spontaneously (Figure 3). It is active in charge separation processes and can be combined with the cationic monolayer given above.
Fig. 3. Structure of a synthetic bolaamphiphilic carotene porphyrin.
4. A steroid-based hydrophobic hole in a fixed monolayer adsorbs water-soluble compounds, e.g. glucose (quartz balance) (Figure 4).
Fig. 4. Hydrophobic gaps of nanometer dimensions with a steroidal base bind saccharides. Water does not wash them away.
Several other systems, e.g., nucleotides, steroids and porphyrin fibers, are applied to arrange well-defined and complex supramolecular assemblies. For a successful book on organic synthesis based on lectures see reference 10.