Lanthanide-induced shift data are presented for cyclopropanecarboxylic acid (CPCA) binding to nine lanthanide-nota (nota is the axially symmetric macrocyclic triaza ligand 1,4,7-triazacyclonionane-N,N′N″-triacetic acid) chelates at pH 6, 25 °C and 70 °C. The contact and pseudocontact contributions to the observed proton and carbon shifts have been separated by linear regression analysis. Plots of the data in two linear forms show a break at Dy in the lanthanide series. Possible sources of this break are discussed with the help of measured proton and carbon relaxation rates of CPCA bound to five different lanthanide chelates, and comparison with similar data for CPCA bonding to the lanthanide-ethylenediaminetetraacetate chelates. This work shows that the pseudocontact shifts induced by Ln(nota) chelates in the CPCA 1H and 13C nuclei conform to the axial symmetry model, making these chelates potentially very useful as conformational probes in biological systems.
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