Effect of Mixed Pendant Groups on the Solution Properties of 12‐Membered Azapyridinomacrocycles: Evaluation of the Protonation Constants and the Stability Constants of the Europium(<scp>III</scp>) Complexes

Siaugue, Jean‐Michel; Favre‐Réguillon, Alain; Dioury, Fabienne; Plancque, Gabriel; Foos, J.; Madic, C.; Moulin, Christophe; Guy, Alain

doi:10.1002/ejic.200300016

Cited by 13 publications

(23 citation statements)

References 28 publications

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“… a reference (19), b reference (20), c reference (10), d reference(21, 22), e ΔV= 9.74·10 −3 for 506 data pairs, f reference (23), g reference (24), h the log K 6 H for this ligand is 1.40, reference (13). …”

Section: Figures and Tablesmentioning

confidence: 97%

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(S)-5-(p-Nitrobenzyl)-PCTA, a Promising Bifunctional Ligand with Advantageous Metal Ion Complexation Kinetics

et al. 2009

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A bifunctional version of PCTA (3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene-3,6,9,-triacetic acid) that exhibits fast complexation kinetics with the trivalent lanthanide(III) ions was synthesized in reasonable yields starting from N, N′, N″-tristosyl-(S)-2-(p-nitrobenzyl)-diethylenetriamine. pH-potentiometric studies showed that the basicities of p-nitrobenzyl-PCTA and the parent ligand PCTA were similar. The stability of M(NO 2 -Bn-PCTA) (M = Mg 2+ , Ca 2+ , Cu 2+ , Zn 2+ ) complexes was similar to that of the corresponding PCTA complexes while the stability of Ln 3+ complexes of the bifunctional ligand is somewhat lower than that of PCTA chelates. The rate of complex formation of Ln(NO 2 -Bn-PCTA) complexes was found to be quite similar to that of PCTA, a ligand known to exhibit the fastest formation rates among all lanthanide macrocyclic ligand complexes studied to date. The acid catalyzed decomplexation kinetic studies of the selected Ln (NO 2 -Bn-PCTA) complexes showed that the kinetic inertness of the complexes was comparable to that of Ln(DOTA) chelates making the bifunctional ligand NO 2 -Bn-PCTA suitable for labeling biological vectors with radioisotopes for nuclear medicine applications.

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Section: Figures and Tablesmentioning

confidence: 97%

“… a reference (31, 32), b determined by luminescence reference (33, 34), c (19), d reference (10), e reference (21, 22), f reference (25), g I = 0.1 mol/dm 3 Me 4 NNO 3 from reference (26), h reference (35), i I=0.1 M KCl from reference (36), j reference (19), k reference (13). …”

Section: Figures and Tablesmentioning

confidence: 99%

(S)-5-(p-Nitrobenzyl)-PCTA, a Promising Bifunctional Ligand with Advantageous Metal Ion Complexation Kinetics

et al. 2009

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“…[36] ; f literature value of stability constant for Eu(PCTA) are 20.9 and 21.1 from Refs. [19,25] ; g literature value of stability constant for Gd(PCTA) is 21.0±0.5 Ref. [16] ;…”

Section: 87·10 -3mentioning

confidence: 99%

Equilibrium and Formation/Dissociation Kinetics of Some Ln^IIIPCTA Complexes

Tircsó¹,

Sherry

2006

Inorg. Chem.

156

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The protonation constants (K i H ) of 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene-3,6,9,-triacetic acid (PCTA) and stability constants of complexes formed between this pyridine containing macrocycle and several different metal ions have been determined in 1.0 M KCl, 25°C and compared to previous literature values. The first protonation constant was found to be 0.5-0.6 log units higher than the value reported previously and a total five protonation steps were detected (log K i H = 11.36, 7.35, 3.83, 2.12 and 1.29). The stability constants of complexes formed between PCTA and Mg 2+ , Ca 2+ , Cu 2+ and Zn 2+ were also somewhat higher than those previously reported but this difference could be largely attributed to the higher first protonation constant of the ligand. Stability constants of complexes formed between PCTA and the Ln 3+ series of ions and Y 3+ were determined by using an "out-of-cell" potentiometric method. These values ranged from log K = 18.15 for Ce(PCTA) to log K = 20.63 for Yb(PCTA), increasing along the lanthanide series in proportion to decreasing Ln 3+ cation size. The rates of complex formation for Ce(PCTA), Eu(PCTA), Y(PCTA) and Yb(PCTA) were followed by conventional UV-VIS spectroscopy in the pH range pH=3.5 -4.4. First order rate constants (saturation kinetics) obtained for different ligand / metal ion ratios were consistent with rapid formation of a diprotonated intermediate, Ln(H 2 PCTA) 2+ . The stabilities of the intermediates as determined from the kinetic data were 2.81, 3.12, 2.97 and 2.69 log K units for Ce(H 2 PCTA), Eu(H 2 PCTA), Y(H 2 PCTA) and Yb(H 2 PCTA), respectively. Rearrangement of these intermediates to the fully chelated complexes was the rate determining step and the rate constant (k r ) for this process was found to be inversely proportional to the proton concentration. The formation rates (k OH ) increased with a decrease in lanthanide ion size (9.68×10 7 M -1 s -1 , 1.74×10 8 M -1 s -1 , 1.13×10 8 M -1 s -1 and 1.11×10 9 M -1 s -1 for Ce(PCTA), Eu(PCTA), Y(PCTA) and Yb(PCTA), respectively). These data indicate that the Ln(PCTA) complexes exhibit the fastest formation rates among all lanthanide macrocyclic ligand complexes studied to date. The acid catalyzed dissociation rates (k 1 ) varied with cation from 9.61×10 -4 M -1 s -1 , 5.08×10 -4 M -1 s -1 , 1.07×10 -3 M -1 s -1 and 2.80×10 -4 M -1 s -1 for Ce(PCTA), Eu(PCTA), Y(PCTA) and Yb(PCTA), respectively.

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“…42 The overall basicity (∑ log K i H ) of tpptac 3− (N 6 O 3 donor set, 18-membered ring) is comparable to that of structurally related ligands such as pcta 3− and pc2a 2− (N 4 O 3 and N 4 O 2 sets, 12-membered ring). 40,42 The presence of three pyridine rings and the existence of only three aminoacetate groups contribute strongly to a lower overall basicity of tpptac 3− in comparison to that of pyta 4− (N 6 O 4 donor set, 18-membered ring) with a decrease of about 4 log units. A significant change in the overall basicity is observed between the 18-membered macrocyclic ligands tpptac 3− and N-ac 3 [18]aneN 3 O 3 3− .…”

Section: Inorganic Chemistrymentioning

confidence: 99%

Tripyridinophane Platform Containing Three Acetate Pendant Arms: An Attractive Structural Entry for the Development of Neutral Eu(III) and Tb(III) Complexes in Aqueous Solution

et al. 2020

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We report a detailed characterization of Eu 3+ and Tb 3+ complexes derived from a tripyridinophane macrocycle bearing three acetate side arms (H 3 tpptac). Tpptac 3− displays an overall basicity (∑ log K i H ) of 24.5, provides the formation of mononuclear ML species, and shows a good binding affinity for Ln 3+ (log K LnL = 17.5−18.7). These complexes are also thermodynamically stable at physiological pH (pEu = 18.6, pTb = 18.0). It should be noted that the pGd value of Gd-tpptac (18.4) is only slightly lower than that of commercially available MRI contrast agents such as Gd-dota (pGd = 19.2). Moreover, a very good selectivity for these ions over the endogenous cations (log K CuL = 14.4, log K ZnL = 12.9, and log K CaL = 9.3) is observed. The X-ray structure of the terbium complex shows the metal coordinated by the nine N 6 O 3 donor set of the ligand and one inner-sphere water molecule. DFT calculations result in two Eu-tpptac structures with similar bond energies (ΔE = 0.145 eV): one structure in which the water is coordinated to the metal ion and one structure in which the water molecule is farther away from the ion, bound to the ligand with an OH−π bond. By detailed luminescence experiments, we demonstrate that the europium complex in aqueous solution presents a hydration equilibrium between nine-coordinate, dehydrated [Eu-tpptac] 0 and ten-coordinate, monohydrated [Eu-tpptac(H 2 O)] 0 species. A similar trend is observed for the terbium complex. Despite the presence of this hydration equilibrium, the H 3 tpptac ligand sensitizes Eu 3+ and Tb 3+ luminescence efficiently in buffered water at physiological pH. Particularly, the terbium complex displays a long excited-state lifetime of 2.24 ms and an overall quantum yield of 33% with a brightness of 3600 M −1 cm −1 . Such features of Ln 3+ complexes of H 3 tpptac indicate that this platform appears to be particularly appealing for the further development of luminescent lanthanide labels.

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Effect of Mixed Pendant Groups on the Solution Properties of 12‐Membered Azapyridinomacrocycles: Evaluation of the Protonation Constants and the Stability Constants of the Europium(III) Complexes

Cited by 13 publications

References 28 publications

(S)-5-(p-Nitrobenzyl)-PCTA, a Promising Bifunctional Ligand with Advantageous Metal Ion Complexation Kinetics

(S)-5-(p-Nitrobenzyl)-PCTA, a Promising Bifunctional Ligand with Advantageous Metal Ion Complexation Kinetics

Equilibrium and Formation/Dissociation Kinetics of Some Ln^IIIPCTA Complexes

Tripyridinophane Platform Containing Three Acetate Pendant Arms: An Attractive Structural Entry for the Development of Neutral Eu(III) and Tb(III) Complexes in Aqueous Solution

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Effect of Mixed Pendant Groups on the Solution Properties of 12‐Membered Azapyridinomacrocycles: Evaluation of the Protonation Constants and the Stability Constants of the Europium(III) Complexes

Cited by 13 publications

References 28 publications

(S)-5-(p-Nitrobenzyl)-PCTA, a Promising Bifunctional Ligand with Advantageous Metal Ion Complexation Kinetics

(S)-5-(p-Nitrobenzyl)-PCTA, a Promising Bifunctional Ligand with Advantageous Metal Ion Complexation Kinetics

Equilibrium and Formation/Dissociation Kinetics of Some LnIIIPCTA Complexes

Tripyridinophane Platform Containing Three Acetate Pendant Arms: An Attractive Structural Entry for the Development of Neutral Eu(III) and Tb(III) Complexes in Aqueous Solution

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Equilibrium and Formation/Dissociation Kinetics of Some Ln^IIIPCTA Complexes