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Design Principles and Theory of Paramagnetic Fluorine-Labelled Lanthanide Complexes as Probes for F-19 Magnetic Resonance: A Proof-of-Concept Study

Lookup NU author(s): Professor Andrew BlamireORCiD

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Abstract

The synthesis and spectroscopic properties of a series of CF3-labelled lanthanide(III) complexes (Ln = Gd, Tb, Dy, Ho, Er, Tm) with amide-substituted ligands based on 1,4,7,10-tetraazacyclododecane are described. The theoretical contributions of the F-19 magnetic relaxation processes in these systems are critically assessed and selected volumetric plots are presented. These plots allow an accurate estimation of the increase in the rates of longitudinal and transverse relaxation as a function of the distance between the Ln(III) ion and the fluorine nucleus, the applied magnetic field, and the re-rotational correlation time of the complex, for a given Ln(III) ion. Selected complexes exhibit pH-dependent chemical shift behaviour, and a pK(a) of 7.0 was determined in one example based on the holmium complex of an ortho-cyano DO3A-monoamide ligand, which allowed the pH to be assessed by measuring the difference in chemical shift (varying by over 14 ppm) between two F-19 resonances. Relaxation analyses of variable-temperature and variable-field F-19, O-17 and H-1 NMR spectroscopy experiments are reported, aided by identification of salient low-energy conformers by using density functional theory. The study of fluorine relaxation rates, over a field range of 4.7 to 16.5 T allowed precise computation of the distance between the Ln(III) ion and the CF3 reporter group by using global fitting methods. The sensitivity benefits of using such paramagnetic fluorinated probes in F-19 NMR spectroscopic studies are quantified in preliminary spectroscopic and imaging experiments with respect to a diamagnetic yttrium(III) analogue.

Publication metadata

Author(s): Chalmers KH, De Luca E, Hogg NHM, Kenwright AM, Kuprov I, Parker D, Botta M, Wilson JI, Blamire AM

Publication type: Article

Publication status: Published

Journal: Chemistry: A European Journal

Year: 2010

Volume: 16

Issue: 1

Pages: 134-148

ISSN (print): 0947-6539

ISSN (electronic): 1521-3765

Publisher: Wiley - V C H Verlag GmbH & Co. KGaA

URL: http://dx.doi.org/10.1002/chem.200902300

DOI: 10.1002/chem.200902300

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