DOTP complexes

Fig. 17. Gd-aqueous proton radial distribution function for the aqueous solution of the Gd(III)(DOTP) complex (after Borel, A. Helm, L. Merbach, A.E. Chemistry - A European Journal 2001, 7, 600-610).

H and NMR studies of the diamagnetic [La(DOTP)] and [Lu(DOTP)] complexes revealed a high degree of stereochemical rigidity in these compounds [91]. In addition, [Ln(DOTP)] complexes possess a remarkable thermodynamic stability with long-lived coordinate bonds rendering them extremely... 

Similar to other cyclen-based macrocycles (e.g. DOTA), two enantiomeric forms defined by a clockwise or counter-clockwise spiraling of the methyl-enephosphonate arms may be envisaged for [Ln(DOTP)] complexes. However, unlike DOTA complexes, [Ln(DOTP)] complexes are believed to exist in solution as one enantiomeric pair. An isomeric form of [Tm(DOTP)] corresponding to the minor isomer observed for [Yb(DOTA)] (8-coordinate SAP geometry) was inferred by comparison of the paramagnetic shifts of the two species... 

Stability constants for [Ln(dotp)] complexes have been determined log K ranges from 27.6 (La) to 29.6 (Lu) (dotp = 1,4,7,10-tetraazaccyclododecane-l,4,7,10-tetrakis(methylenephosphonic acid). In view of its use as a cation-shift reagent, it is notable that Na-NMR studies show NH4+ and K+ compete effectively with Na" " for the binding sites on [Tm(dotp)] . Ca " " and Mg also complex with [Tm(dotp)]. ... 

In principle, lanthanide complexes of alkyl- (phosphinates) or alkoxy- (phosphonate esters) DOTP derivatives may give rise to 32 stereoisomers, existing as 16 enantiomeric pairs, which are indistinguishable by NMR spectroscopy. The isomers originate from chiral elements inherent in these complexes, including the R or S configuration at each phosphorus and the helicity defined by the pendant arm orientations (AIA). Various Ln3+ complexes of phosphinate and phosphonate ester ligands derived from 1,4,7,10-tetraazacyclododecane (cyclen) have been described in the literature [104-107]. 

NMRD studies of Gd3+ complexes of DOTPME and DOTPMB indicate q< 1 suggesting that the inner coordination sphere of these complexes is obstructed due to the steric encumbrance of the alkoxy substituents [ 104]. In a multinuclear NMR study of Ln3+ complexes (Ln = La, Gd, Dy, Tm and Yb) with a fluorinated ethyl ester analog of DOTP (F-DOTPME), the 19F NMR spectra reveal up to 16 resonances, which demonstrate that these complexes exist in aqueous solution as a mixture of stereoisomers [105]. [Gd(F-DOTPME)] afforded a water proton relaxivity typical of non-hydrated complexes. 170 NMR of the Dy 1 complex confirmed the lack of a bound water molecule. 

The average lifetime of water molecules in the second coordination shell can be obtained from the MD simulation and was found to be in the range of 20-25 ps for the poly(amino-carboxylate) complexes and 56 ps for the polyamino-phosphonate based [Gd(DOTP)]5- [97]. These residence times are long if compared to those of second sphere water around the aqua ions of lan-... 

Gd-complexes of TETA and DOTP have no inner sphere water molecule and therefore the NMRD profiles reflect directly the second- and outer-sphere relaxivity accessible also from calculations based on the molecular dynamics simulations (Fig. 8). The experimental NMRD profile of [Gd(TETA)]- could be reproduced by drastically changing the electronic relaxation parameters from those... 

DOTP ligand are arranged in a propeller-like fashion above the basal plane made up of the four N donor atoms which encompass the R(lll) ion, thereby generating a C4 symmetry axis in these complexes (fig. 40). Four of the residual negative charges are localized on the phos-... 

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