RG Bioinspired conjugated materials
The research-group „Bioinspired Conjugated Materials“ is aimed to the combination of semiconducting artificial p-systems - especially oligo- or polythiophenes - with biomolecules such as peptides, carbohydrates or nucleosides. Self assembly of the biohybrids allows a controlled arrangement in solution and on surfaces. The resulting nanoarchitectures are typically held together by a wide range of various non-covalent forces. Whereas the “bioblocks” in prior perform polar forces such as directed hydrogen bonds, the (alkylated) π-conjugated oligothiophene is expected to employ mainly van der Waals interaction and π-stacking. Optoelectronic characterization of the novel structures is provided by UV, F, CD spectroscopy, self organizing abilities are investigated by scanning probe microscopy (AFM, STM) and electron microscopy (TEM, SEM) respectively.
The bioconjugates will be useful for a directed design of semiconducting organic materials and specifically recognizing matrix-substrates.
Selected topics of interest:
Synthesis of adenine (A)- and uracil (U)- substituted poly(alkylthiophenes) provided first examples of semiconducting nucleobase-functionalized polythiophenes. In electrochemical experiments selective A…U base-pairing according the known genetic code could be observed during gradual addition of nucleobases to their complementary vested bioconjugates.
A. Emge, P. Bäuerle, Synth. Met. 1997, 84, 213-214
P. Bäuerle, A. Emge, Adv. Mater. 1998, 10, 324-330
A. Emge, P. Bäuerle, Synth. Met. 1999, 102, 1370-1373
For the synthesis of thymidine- (T) and adenosine (A)-functionalized oligothiophenes so-called „click“-chemistry (Huisgen 1,3-dipolar cycloaddition) of nucleosidic azides and ethynylated oligothiophenes was applied. Selective recognition of the nucleobases T and A resulted in ordered superstructures in solution and on surfaces. By means of atomic force microscopy (AFM) fibres up to 30 mm in length could be visualized and a suitable model for the p-stacked assemblies was developed. Efficient base pairing (Watson-Crick and Hoogsteen motifs) was proven by 1H - NMR experiments.
A. Jatsch, A. Kopyshev, E. Mena-Osteritz, P. Bäuerle, Org. Lett. 2008, 10, 961-964.
E. Schillinger, A. Jatsch, S. Schmid, P. Bäuerle, J. Mater. Chem. J. Mater. Chem., 2010, DOI: 10.1039/B926594E: “Biomolecule Assisted Self-Assembly of π-Conjugated Oligomers”.
Peptide- functionalized oligothiophenes
The synthesis of the very first example of a semiconducting oligothiophene substituted with the β-sheet forming peptide sequence Gly-Ala-Gly-Ala-Gly was accomplished by solid phase supported synthesis (SPPS). FTIR experiments confirmed that the β-sheet secondary structure was preserved in the hybrid. STM investigations of the semiconductor-biohybrids lead to visualisation of fibrelike strands, hitherto unknown suprastructures for oligothiophenes, caused by the peptide part of the hybrid.
Extending the concept, a symmetrically substituted semiconducting quaterthiophene equipped with a β-sheet forming peptide sequence (valine-threonine)3 was introduced. The incorporation of “switch” and pseudoproline units facilitates the solid phase supported synthesis. The structurally disturbed system displays new, fiberlike suprastructures with a strictly left-handed helicity. After transformation of the β-ester linkage into the native amide bond, thus reconstructing the peptide backbone, a high tendency for self-organisation of the hybrid could be observed.
H.-A. Klok, A. Rösler, G. Götz, E. Mena-Osteritz, P. Bäuerle, Org. Biomol. Chem. 2004, 2, 3541-3544
E.-K. Schillinger, E. Mena-Osteritz, J. Hentschel, H.-G. Börner, P. Bäuerle, Adv. Mater. 2009, 21, 1562-1567: „Oligothiophene versus ß-sheet peptide: Synthesis and self-assembly of an organic semiconductor-peptide hybride”
First mannose – and glucose functionalized ter (3T)- and quater(4T) - thiophenes are accessible via Sonogashira C–C cross coupling reaction. AFM experiments with the ester-protected glycoconjugates revealed on mica a terrace like multi-layer arrangement with 84% coverage. The thickness of each layer correlates perfectly with their calculated molecular length.
CD – data of the deprotected hybrids implied in polar, aqueous solution the formation of aggregates. Shape and signature of the CD-signal were indicative for the presence of helical arranged chiral superstructures. Thus enantiomeric counterparts display -as depicted here: L- and D-Mannose-functionalized 4T - inverse CD-effects, with appropriate selection of carbohydrates preferred handedness of the performed superstructures can be induced.
S. Schmid, E. Mena-Osteritz, A. Kopyshev, P. Bäuerle, Org. Lett. 2009, 11, 7146-7148: “Self-assembling carbohydrate-functionalized oligothiophenes”. (IF 4.80)
S. Schmid, A. Mishra, P. Bäuerle, Chem. Commun. 2011, 47, 1324-1326: "Carbohydrate-Functionalized Oligothiophenes for Concanavalin A Recognition".