Publikationsserver der RWTH Aachen University
Pinzettenförmige Moleküle mit Wasserstoffbrücken-Donor-Akzeptor-Einheiten : potentielle Kandidaten zur Anwendung in der dynamisch kombinatorischen Chemie
Abstract
dc:descriptionThe presented thesis discusses the synthesis of receptors and receptor libraries containing molecules with labile side chain functionalities. These molecules are able to interact with guest species via hydrogen bonding. Building blocks for the libraries are tweezer-type molecules, which are obtained by coordinative metal-ligand-interactions or covalent aryl-ester-bonds. The formation of dynamic libraries should be possible by interchanging the labile side chains. The synthesis of dynamic mixtures with supramolecular metal complexes as components, which are able to bind anions via hydrogen-bonding is described in the first part of the thesis. Therefore, tweezer-type Mo(VI)-dioxocatecholate- and tripodal hydroxychinolinate-complexes are prepared. The tweezer-type Mo(VI)-dioxocatecholate complexes are ideal for the binding of planar ("two-dimensional") guests like nitrate. NMR-spectroscopy shows that the mixture of different stereoisomeres (which are produced by complex formation) by addition of nitrate during 18 weeks transforms into one single pair of enantiomers. Probably nitrate favors binding to one of the three different pairs of enantiomers and shifts the equilibrium to the most favored receptor/substrate complex (concept of dynamic combinatorial chemistry). NMR-spectroscopy shows that the hydroxychinolinate complexes are formed as mixtures of diastereomers, which are in equilibrium. ESI-MS reveals that the complexes are able to bind spherical anions like chloride, bromide and iodide and that they distinguish between the differently sized anions. The second part of the thesis reports the synthesis of arylester linked tweezer-type molecules which are based on biphenol, resorcin or catechol. The attached side chains are peptide- or urea-derivatives. HPLC-analysis shows that the side chains can be exchanged by others at 384 K. This reveals that the receptors are able form dynamic combinatorial libraries. By the use of different aromatic units (as backbone) one can orientate the side chains in different angles to each other. Biphenol acts as a molecular hinge and allows a conformative adjustment during the host-guest-interaction (induced fit). By x-ray-analysis of some representative receptor-molecules the tweezer-type nature of the binding units is confirmed. Moreover it is seen that the derivatives are able to interact by hydrogen-bonding with other molecules, complicated two- or three-dimensional hydrogen-bridged networks are formed. Some of the tweezer-type receptors lead to the networks even in solution. The bisurea-derivatives of catechol and resorcin are low molecular weight organic gelators. Association contstants for the binding of nitrate to the tweezer-type receptors are obtained by NMR-spectroscopy. Correlating the different structures of the receptors and the obtained free enthalpies of complexation, an additive effect of the hydrogen bonds on the free enthalpy of complexation is observed. Every additional hydrogen bond increases d GHG for the binding of nitrate in chloroform by approximately 2-3 kJ×mol-1. It is also recognized that this interaction is not only influenced by the number of hydrogen bonds which can occur but also by the geometry of the whole molecule. This work presents the synthesis of a new class of molecules, which are able to interact with anionic guests by hydrogen-bonding. Using labile side chain functionalities, the molecules are able to form dynamic combinatorial libraries.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2002
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Zauner, Jeanette
- Contributors dc:contributor
-
- Albrecht, Markus
Subjects
dc:subject × 5Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- ger
Identifiers
dc:identifier.*- OAI identifier oai:identifier
- oai:publications.rwth-aachen.de:57221