Lanthanide dota-like Complexes Containing a Picolinate Pendant: Structural Entry for the Design of Ln(III)-Based Luminescent Probes

作者：Regueiro Figueroa Martin; Bensenane Bachir; Ruscsak Erika; Esteban Gomez David; Charbonniere Loic J; Tircso Gyula^*; Toth Imre; de Blas Andres; Rodriguez Blas Teresa; Platas Iglesias Carlos

来源：Inorganic Chemistry, 2011, 50(9): 4125-4141.

DOI：10.1021/ic2001915

In this contribution we present two ligands based on a do3a platform containing a picolinate group attached to the fourth nitrogen atom of the cyclen unit, which are designed for stable lanthanide complexation in aqueous solutions. Potentiometric measurements reveal that the thermodynamic stability of the complexes is very high (log K = 21.2-23.5), being comparable to that of the dota analogues. Luminescence life-time measurements performed on solutions of the Eu-III and Tb-III complexes indicate that the complexes are nine coordinate with no inner-sphere water molecules. A combination of density functional theory (DFT) calculations and NMR measurements shows that for the complexes of the heaviest lanthanides there is a major isomer in solution consisting of the enantiomeric pair Lambda(delta delta delta delta) and Delta(lambda lambda lambda lambda), which provides square antiprismatic coordination (SAP) around the metal ion. Analysis of the Yb-III-induced paramagnetic shifts unambiguously confirms that these complexes have SAP coordination in aqueous solution. For the light lanthanide ions however both the SAP and twisted-square antiprismatic (TSAP) isomers are present in solution. Inversion of the cyclen ring appears to be the rate-determining step for the Lambda(delta delta delta delta) <-> Delta(lambda lambda lambda lambda) enantiomerization process observed in the Lu-III complexes. The energy barriers obtained from NMR measurements for this dynamic process are in excellent agreement with those predicted by DFT calculations. The energy barriers calculated for the arm-rotation process are considerably lower than those obtained for the ring-inversion path. Kinetic studies show that replacement of an acetate arm of dota by a picolinate pendant results in a 3-fold increase in the formation rate of the corresponding Eu-III complexes and a significant increase of the rates of acid-catalyzed dissociation of the complexes. However, these rates are 1-2 orders of magnitude lower than those of do3a analogues, which shows that the complexes reported herein are remarkably inert with respect to metal ion dissociation.

• 出版日期2011-5-2