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NMR Characterization of Lanthanide(3+) Complexes of Tetraazatetrakisphosphinato and Tetraazatetrakisphosphonato Ligands
Author(s) -
Pereira Giovannia A.,
Ball Laura,
Sherry A. Dean,
Peters Joop A.,
Geraldes Carlos F. G. C.
Publication year - 2009
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.200900160
Subject(s) - chemistry , lanthanide , cationic polymerization , aqueous solution , ligand (biochemistry) , coordination sphere , micelle , crystallography , vapor pressure osmometry , nuclear magnetic resonance spectroscopy , coordination complex , inorganic chemistry , electron paramagnetic resonance , methylene , stereochemistry , crystal structure , metal , polymer chemistry , medicinal chemistry , organic chemistry , ion , nuclear magnetic resonance , vapor pressure , biochemistry , receptor , physics
The three‐dimensional structures in aqueous solution of the entire series of the Ln 3+ complexes [Ln(DOTP*‐Et)] − (formed from the free ligand P , P′ , P″ , P′′′ ‐[1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetrayltetrakis(methylene)]tetrakis[ P ‐ethylphosphinic acid] (H 4 DOTP*‐Et) were studied by NMR techniques to rationalize the parameters governing the relaxivity of the Gd 3+ complex and evaluate its potential as MRI contrast agent. From the 1 H‐ and 31 P‐NMR lanthanide‐induced‐shift (LIS) values, especially of the [Yb(DOTP*‐Et)] − complex, it was concluded that the [Ln(DOTP*‐Et)] − complexes adopt in solution twisted square antiprismatic coordination geometries which change gradually their coordination‐cage structure along the lanthanide series. These complexes have no inner‐sphere‐H 2 O coordination, and preferentially have the ( R , R , R , R ) configuration of the P‐atoms in the pendant arms. Self‐association was observed in aqueous solution for the tetraazatetrakisphosphonic acid ester complexes [Ln(DOTP*‐OEt)] − (=[Ln(DOTP‐Et)] − ) and [Ln(DOTP*‐OBu)] − (=[Ln(DOTP‐Bu)] − ) at and above 5 m M concentration, through analysis of 31 P‐NMR, EPR, vapor‐pressure‐osmometry, and luminescence‐spectroscopic data. The presence of the cationic detergent cetylpyridinium chloride (CPC; but not of neutral surfactants) shifts the isomer equilibrium of [Eu(DOTP*‐OBu)] − to the ( S , S , S , S ) form which selectively binds to the cationic micelle surface.