The design of luminescent lanthanide complexes is of great importance in the development of biological labelling systems providing effective alternatives to radioisotopes, and for their application as light triggered sensors and materials. Our approach involves the controlled formation of mixed-ligand Eu(III) and Tb(III) complexes based on specific molecular recognition such that a biological molecular recognition event may be detected. The strategy is based on design of lanthanide systems with controlled coordination around the metal ion. Enhancement of the emission is based on intramolecular energy transfer which is much more efficient than the FRET mechanism. Our design is based on the arrangement of two different ligands around the metal ion (Figure 1). (Fig. 1352) A multidentate non-absorbing ligand (NAL) is chosen to form a stable, coordinatively unsaturated complex with the metal, allowing one or two water molecules to occupy the vacant binding sites. Formation of the luminescent ternary complex is achieved by displacement of the remaining inner sphere water molecules upon recognition between the LnNAL chelate and a strongly absorbing, strongly binding light harvesting centre (LHC). This strategy allows flexibility in choosing the antenna ligand. The chromophore, which governs the input energy of light, need not be included in the structure of the encapsulating ligand. Complicated syntheses are avoided and the system can be optimised can be optimised for maximum emission output. We have chosen DTPA-AM<sub>2</sub> ligands as our NAL ligands and simple aromatic carboxylic acids as LHCs to test the design. The DTPA-AM<sub>2</sub> chelates the metal in an octandentate manner via the 3 nitrogen donors of the diethylenetriamine backbone, the two amide carbonyls and the three remaining carboxylate groups. The amide nitrogen atoms are not involved in coordination and are free to form a binding cavity, ideal for LHC recognition. The binding of the LnNAL chelate by the acid moiety is followed by monitoring the emission of the europium ion, triggered by intramolecular energy transfer from the LHC> Electrospray mass spectrometry data and NMR spectroscopic studies provide additional evidence of the controlled formation of ternary complexes. Specificity of molecular recognition is observed between EuDTPA-bis(ethylamide) and picolinic acid, phthalic acid and benzoic acid binding units, forming mixed ligand species in 1:1, 1:1 and 1:2 stoichiometries respectively.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:657663 |
| Date | January 2002 |
| Creators | Meason, Linette L. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12641 |
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