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Europium(III) DOTA-derivatives having ketone donor pendant arms display dramatically slower water exchange.

ABSTRACT: A series of new 1,4,7,10-tetraazacyclododecane-derivatives having a combination of amide and ketone donor groups as side-arms were prepared, and their complexes with europium(III) studied in detail by high resolution NMR spectroscopy. The chemical shift of the Eu(3+)-bound water resonance, the chemical exchange saturation transfer (CEST) characteristics of the complexes, and the bound water residence lifetimes (?(m)) were found to vary dramatically with the chemical structure of the side-arms. Substitution of ketone oxygen donor atoms for amide oxygen donor atoms resulted in an increase in residence water lifetimes (?(m)) and a decrease in chemical shift of the Eu(3+)-bound water molecule (??). These experimental results along with density functional theory (DFT) calculations demonstrate that introduction of weakly donating oxygen atoms in these complexes results in a much weaker ligand field, more positive charge on the Eu(3+) ion, and an increased water residence lifetime as expected for a dissociative mechanism. These results provide new insights into the design of paramagnetic CEST agents with even slower water exchange kinetics that will make them more efficient for in vivo imaging applications.

SUBMITTER: Green KN

PROVIDER: S-EPMC3077439 | biostudies-literature | 2011 Mar

REPOSITORIES: biostudies-literature

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Europium(III) DOTA-derivatives having ketone donor pendant arms display dramatically slower water exchange.

Green Kayla N KN Viswanathan Subha S Rojas-Quijano Federico A FA Kovacs Zoltan Z Sherry A Dean AD

Inorganic chemistry 20110209 5

A series of new 1,4,7,10-tetraazacyclododecane-derivatives having a combination of amide and ketone donor groups as side-arms were prepared, and their complexes with europium(III) studied in detail by high resolution NMR spectroscopy. The chemical shift of the Eu(3+)-bound water resonance, the chemical exchange saturation transfer (CEST) characteristics of the complexes, and the bound water residence lifetimes (τ(m)) were found to vary dramatically with the chemical structure of the side-arms. S ...[more]

PMID: 21306137

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Project description:Polymethylated lanthanide 4S4R-M4DOTMA complexes, bearing the ring methyl groups oriented in the SSSS position and the arm methyl groups in the RRRR configuration, exist exclusively as the SAP [Λ(δδδδ)] isomer in solution throughout the lanthanide series. This observation is in contrast to Ln-8S-M4DOTMA, which was recently reported to adopt the SAP [Λ(δδδδ)] isomer in the early lanthanides, while the late lanthanides adopt the TSAP [Δ(δδδδ)] isomer. The methyl groups on the ring and the arm are both oriented in the SSSS configuration for Ln-8S-M4DOTMA ( Dalton Trans. 2016 , 45 , 4673 - 4687 , DOI: 10.1039/C5DT03210E ). Quantum chemical calculations for Pr- and Yb-4S4R-M4DOTMA indicate that the SAP isomer is significantly more stable. The luminescence profiles of Eu-8S-M4DOTMA and Eu-4S4R-M4DOTMA showed similar profiles signifying identical coordination environments. The hydration state, q, of the Eu(III) complexes was q = 0.91-0.95, while Tb-8S-M4DOTMA had q = 0.86. A much lower q value was obtained for Tb-4S4R-M4DOTMA (q = 0.67), which indicates an elongation of the Ln-Ow bond. At 400 MHz, the relaxivity of Gd-8S-M4DOTMA is 5.1 ± 0.1 mM-1 s-1 and 3.9 ± 0.1 mM-1 s-1 at 25 and 37 °C, respectively, whereas the relaxivity of Gd-4S4R-M4DOTMA is 4.6 ± 0.1 mM-1 s-1 at 25 °C and 3.6 ± 0.1 mM-1 s-1 at 37 °C. At 45 MHz, the relaxivity of Gd-8S-M4DOTMA is 5.4 ± 0.1 mM-1 s-1, and the relaxivity of Gd-4S4R-M4DOTMA is 4.5 ± 0.1 mM-1 s-1 at 25 °C. The temperature dependence of the 17O NMR transverse relaxation rate of the Gd complexes revealed a 7-fold increase in the bound water residence lifetime of Gd-8S-M4DOTMA (1/kex = τM = 9.0 ± 0.5 ns and 1/kex = τM = 60 ± 3 ns). The Pr(III) complex of 8S-M4DOTMA crystallized as TSAP isomer with an apical water. The presence of the apical water for the TSAP of Pr-8S-M4DOTMA was further confirmed with the observation that the fluoride ion replaces the bound water from the TSAP isomer of Pr-8S-M4DOTMA. This was shown by the disappearance of the TSAP peaks and appearance of a new set of less shifted resonances, which exchange with the SAP isomer as confirmed by NMR exchange spectroscopy (EXSY).

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Europium(III) DOTA-derivatives having ketone donor pendant arms display dramatically slower water exchange.

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Europium(III) DOTA-derivatives having ketone donor pendant arms display dramatically slower water exchange.

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