Title: Gadolinium(III) complexes of mono- and diethyl esters of monophosphonic acid analogue of DOTA as potential MRI contrast agents: solution structures and relaxometric studies
Authors: Lebduskova, Petra ×
Hermann, Petr
Helm, Lothar
Toth, Eva
Kotek, Jan
Binnemans, Koen
Rudovsky, Jakub
Lukes, Ivan
Merbach, Andre E #
Issue Date: 2007
Publisher: Royal soc chemistry
Series Title: Dalton transactions issue:4 pages:493-501
Abstract: Two new macrocyclic DOTA-like chelates containing one phosphonate pendant arm were synthesised as potential contrast agents for MRI ( magnetic resonance imaging). The chelates bind to the lanthanide(III) in an octadentate manner, via four nitrogen atoms, three carboxylate and one phosphonate oxygen atoms. Solution structures of [Ln(do3apO(Et2))(H2O)] and [Ln(do3ap(OEt))(H2O)](-) were studied using P-31 and H-1 NMR spectroscopy and SAP (square-antiprismatic)/TSAP ( twisted square-antiprismatic) isomerism was observed. Depending on the nature of the lanthanide( III) ion, the lanthanide( III) complexes of H(4)do3ap(OEt) are present in solution as up to four different diastereoisomers observable with NMR. The TSAP isomer is the most abundant at the beginning of the lanthanide series and, with a decrease of the ionic radius of lanthanide( III) ions, both TSAP and SAP forms were observed. A second interconversion (SAP <-> TSAP') becomes important at the end of the series (TSAP' means the TSAP species without a coordinated water molecule). The remaining axial coordination site is occupied by one water molecule for the Gd3+-complex. The calculated fraction of the TSAP isomer in the gadolinium( III) complexes increases in the order [Gd(DOTA)(H2O)](-) < [Gd(do3ap(OEt2))(H2O)] < [Gd(do3ap(OEt))(H2O)](-) < [Gd(do3ap)(H2O)](2-). Gadolinium( III) complexes of phosphorus-containing chelates, generally, have the advantage of a relatively fast water exchange rate due to a greater sterical demand of the phosphorus acid moiety and of the presence of the second-sphere water shell, which also contributes to the overall relaxivity. The [Gd(do3ap(OEt2))(H2O)] and [Gd(do3ap(OEt))( H2O)](-) complexes were studied by variable-temperature O-17 NMR and H-1 NMRD. The experimental data were evaluated simultaneously with commonly used equations based on Solomon-Bloembergen-Morgan approximation, extended by a contribution of the second coordination sphere. The water exchange rates were found to be strongly dependent on the TSAP/SAP isomeric ratio and the overall charge of the complex: the monoanionic [Gd(do3ap(OEt))(H2O)](-) complex with TSAP molar fraction equal to 0.36 has the water exchange rate of 20 x 10(6) s(-1) (tau(M) = 50 ns) while neutral [Gd(do3apO(Et2))(H2O)] complex with TSAP molar fraction 0.28 has an exchange rate equal to 4.4 x 10(6) s(-1) (tau(M) = 227 ns).
ISSN: 1477-9226
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Molecular Design and Synthesis
× corresponding author
# (joint) last author

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