| Abstract
| - The macrocyclic ligand DO2A(1,4,7,10-tetraazacyclododecane-1,7-bis(acetic acid)) wasprepared and used as abuilding block for four new macrocyclic ligands having mixed side-chainchelating groups. These ligands andtheir complexes with MgII, CaII, andLnIII were studied extensively by potentiometry,high-resolution NMR, andwater proton relaxivity measurements. The protonation constants ofall compounds compared well with those ofother cyclen-based macrocyclic ligands. All CaIIcomplexes were found to be more stable than thecorrespondingMgII complexes. Trends for the stabilities of theLnIII complexes are discussed and compared withliteraturedata, incorporating the effects of water coordination numbers,LnIII contraction, and the nature of the sidechainsand the steric hindrance between them. 1H NMRtitrations of DO2A revealed that the first and secondprotonationstake place preferentially at the secondary ring nitrogens, while thethird and fourth involved protonation of theacetates. 17O NMR shifts showed that theDyDO2A+ complex had two inner-sphere water molecules.Waterproton spin−lattice relaxation rates for the GdDO2A+complex were also consistent with water exchange betweenbulk water and two inner-sphere GdIII coordinationpositions. Upon formation of the diamagnetic complexesofDO2A (CaII, MgII, LaIII, andLuIII), all of the macrocyclic ring protons becamenonequivalent due to slowconformational rearrangements, while the signals for the acetateCH2 protons remained a singlet.
- The macrocyclic ligand DO2A (R = H) was used as abuilding block for four new macrocyclic ligands having mixed side-chainchelating groups. These ligands and their complexes withMgII, CaII, and lanthanide(III)(LnIII) ions were studied by potentiometry, high-resolutionNMR, and water proton relaxivity measurements. Trends for thestabilities of the LnIII complexes are discussed,incorporating the effects of water coordination numbers,LnIII contraction, and the nature of the side chains andthe steric hindrance betweenthem.
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