TY - JOUR
T1 - Nuclear magnetic resonance structural studies of an axially symmetric lanthanide ion chelate in aqueous solution
AU - Sherry, A. D.
AU - Singh, M.
AU - Geraldes, C. F G C
N1 - Funding Information:
This investigation was supported by Grant AT-584 from the Robert A. Welch Foundation and by a NATO Research Grant 0345/82. C. F. G. C. Geraldes acknowledges support from INIC, Portugal, and M. Singh is grateful to Guru Nanak Dev University for a study leave. We thank Professor J. A. Peters for sending a copy of his manuscript prior to publication.
PY - 1986/2/15
Y1 - 1986/2/15
N2 - The complexes of the macrocyclic ligand 1,4, 7-triazacyclononane-N,N′,N″-triacetic acid (NOTA) with the paramagnetic trivalent lanthanide canons have been examined by proton and13C magnetic resonance spectroscopy. Lanthanide-induced shifts (LIS) have been measured for all proton and carbon resonances in nine paramagnetic Ln(NOTA) complexes at 25 and 70°C. At both temperatures the ethylene protons appear as a pair of resonances forming an AA′XX′ splitting pattern (visible only in the Eu(NOTA) spectrum) while the acetate protons remain a singlet. The directions and magnitudes of the 1H and 13C shifts indicate they are dominated by contact interactions in most of the Ln(NOTA) complexes. The 13C spectrum of Pr(NOTA) provides evidence that more than one chelate structure is present in solution. The addition of LiCl to Pr(NOTA) and Eu(NOTA) samples results in significant shifts in the bound 1H and 13C resonances whereas the spectra of Dy(NOTA) and Yb(NOTA) do not change significantly when LiCl is added. These results, along with observed breaks in plots of experimental LIS data versus theoretical pseudocontact and contact shift values, suggest that the early members of the lanthanide ion series form mixed complexes with NOTA in aqueous solution, some with NOTA bound as a hexadentate chelate and some a pentadentate species with one unbound acetate group. The smaller trivalent lanthanide cations (Dy → Yb) appear to form complexes containing only hexadentate chelated NOTA. The contact and pseudocontact contributions to each of the observed LIS have been separated and the resulting pseudocontact shifts for the Dy → Yb complexes agree reasonably well with those calculated using the axial symmetry model. The 1H and 13C relaxation rates determined for three Ln(NOTA) complexes indicate that the smaller lanthanide cations fit into the triazamacrocyclic cavity better than do the larger ions resulting in structurally more rigid Ln(NOTA) complexes.
AB - The complexes of the macrocyclic ligand 1,4, 7-triazacyclononane-N,N′,N″-triacetic acid (NOTA) with the paramagnetic trivalent lanthanide canons have been examined by proton and13C magnetic resonance spectroscopy. Lanthanide-induced shifts (LIS) have been measured for all proton and carbon resonances in nine paramagnetic Ln(NOTA) complexes at 25 and 70°C. At both temperatures the ethylene protons appear as a pair of resonances forming an AA′XX′ splitting pattern (visible only in the Eu(NOTA) spectrum) while the acetate protons remain a singlet. The directions and magnitudes of the 1H and 13C shifts indicate they are dominated by contact interactions in most of the Ln(NOTA) complexes. The 13C spectrum of Pr(NOTA) provides evidence that more than one chelate structure is present in solution. The addition of LiCl to Pr(NOTA) and Eu(NOTA) samples results in significant shifts in the bound 1H and 13C resonances whereas the spectra of Dy(NOTA) and Yb(NOTA) do not change significantly when LiCl is added. These results, along with observed breaks in plots of experimental LIS data versus theoretical pseudocontact and contact shift values, suggest that the early members of the lanthanide ion series form mixed complexes with NOTA in aqueous solution, some with NOTA bound as a hexadentate chelate and some a pentadentate species with one unbound acetate group. The smaller trivalent lanthanide cations (Dy → Yb) appear to form complexes containing only hexadentate chelated NOTA. The contact and pseudocontact contributions to each of the observed LIS have been separated and the resulting pseudocontact shifts for the Dy → Yb complexes agree reasonably well with those calculated using the axial symmetry model. The 1H and 13C relaxation rates determined for three Ln(NOTA) complexes indicate that the smaller lanthanide cations fit into the triazamacrocyclic cavity better than do the larger ions resulting in structurally more rigid Ln(NOTA) complexes.
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U2 - 10.1016/0022-2364(86)90194-0
DO - 10.1016/0022-2364(86)90194-0
M3 - Article
AN - SCOPUS:0011706371
SN - 0022-2364
VL - 66
SP - 511
EP - 524
JO - Journal of Magnetic Resonance (1969)
JF - Journal of Magnetic Resonance (1969)
IS - 3
ER -