17O NMR and Density Functional Theory Study of the Dynamics of the Carboxylate Groups in DOTA Complexes of Lanthanides in Aqueous Solution

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• 作者：Florian Mayer ; Carlos Platas-Iglesias ; Lothar Helm ; Joop A. Peters ; Kristina Djanashvili
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：January 2, 2012
• 年：2012
• 卷：51
• 期：1
• 页码：170-178
• 全文大小：406K
• 年卷期：v.51,no.1(January 2, 2012)
• ISSN：1520-510X

文摘

The rotation of the carboxylate groups in DOTA (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) complexes of several lanthanide ions and Sc³⁺ was investigated with density functional theory (DFT) calculations and with variable temperature ¹⁷O NMR studies at 4.7鈥?8.8 T. The data obtained show that the rotation is much slower than the other dynamic processes taking place in these complexes. The exchange between the bound and unbound carboxylate oxygen atoms for the largest Ln³⁺ ions (La³⁺鈫扴m³⁺) follows a pathway via a transition state in which both oxygens of the carboxylate group are bound to the Ln³⁺ ion, whereas for the smaller metal ions (Tm³⁺, Lu³⁺, Sc³⁺) the transition state has a fully decoordinated carboxylate group. The activation free energies show a steady increase from about 75 to 125鈥?35 kJ路mol^鈥? going from La³⁺ to Lu³⁺. This computed trend is consistent with the results of the ¹⁷O NMR measurements. Fast exchange between bound and unbound carboxylate oxygen atoms was observed for the diamagnetic La-DOTA, whereas for Pr-, Sm-, Lu-, and Sc-DOTA the exchange was slow on the NMR time scale. The trends in the linewidths for the various metal ions as a function of the temperature agree with trends in the rates as predicted by the DFT calculations.