Kinetics of Complex Formation by Macrocyclic Polyaza Polycarboxylate Ligands: Detection and Characterization of an Intermediate in the Eu3+-dota System by Laser-Excited Luminescence

Wu, Shu Ling; Horrocks, William DeW.

doi:10.1021/ic00118a020

Cited by 87 publications

(128 citation statements)

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“…Subseqnent slow base-catalyzed deprotonation of those amines and rearrangement leads to the formation of a final [Ln(DOTA)] − complex where the Ln 3+ ion is trapped "in cage". [8][9][10]27] Evidence for a similar stable intermediate has been reported during formation of the [Ln{DOTA-(gly) 4 }] − complexes as well. [11] Furthermore, an interesting structure that is thought to be the reactive intermediate in the formation of [Ln(DOTAM)] 3+ complexes was characterized recently by X-ray diffraction.…”

Section: }] 3+ Complexessupporting

confidence: 61%

Synthesis and Characterization of DOTA‐(amide)₄ Derivatives: Equilibrium and Kinetic Behavior of Their Lanthanide(III) Complexes

et al. 2007

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Lanthanide complexes of tetraamide derivatives of DOTA are of interest today because of their application as chemical exchange saturation transfer (CEST) agents for magnetic resonance imaging (MRI). The protonation constants of some simple tetraamide derivatives of DOTA and the stability constants of the complexes formed with some endogenous metal ions, namely Mg 2+ , Ca 2+ , Cu 2+ , Zn 2+ , and lanthanide(III) ions, have been studied. These complexes were found to be considerably less stable than the corresponding [M(DOTA)] 2− complexes, largely due to the lower basicity of the tetraamide ligands. The Mg 2+ and Ca 2+ complexes are well described by formation of only ML species at equilibrium while the Zn 2+ and Cu 2+ complexes exhibit one and two additional deprotonation steps above a pH of around 6, respectively. The extra deprotonation that occurs at high pH for the [Zn{DOTA-(amide) 4 }] 2+ complexes has been assigned to an amide deprotonation by 1 H NMR spectroscopy. The first deprotonation step for the Cu 2+ complexes was traced to formation of the ternary hydroxo complexes ML(OH) (by UV/Vis spectrophotometry) while the second step corresponds to deprotonation of an amide group to form ML(OH)H −1 -type complexes. The trends in the stability constants of the [Ln{DOTA-(amide) 4 }] 3+ complexes follow similar trends with respect to ion size as those reported previously for the corresponding [Ln(DOTA)] − complexes, but again, the stability constants are about 10-11 orders of magnitude lower. A kinetic analysis of complex formation has shown that complexes are directly formed between a Ln 3+ cation and fully deprotonated L without formation of a protonated intermediate. [Ln{DOTA-(MeAm) 4 }] 3+ complex formation occurs at a rate that is two to three orders of magnitude slower than those of the corresponding [Ln(DOTA)] − complexes, while the variation in complex formation rates with Ln 3+ ion size is opposite to that observed for the corresponding [Ln(DOTA)] − complexes. The Ce 3+ and Correspondence to: Gyula Tircsó; A. Dean Sherry. Supporting information for this article is available on the WWW under http://www.eurjic.org or from the author. Eu 3+ complexes of DOTA-(MeAm) 4 are kinetically inert with respect to acid-catalyzed dissociation, which suggests that these complexes may potentially be safe for use in vivo.

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Section: }] 3+ Complexessupporting

confidence: 61%

Synthesis and Characterization of DOTA‐(amide)₄ Derivatives: Equilibrium and Kinetic Behavior of Their Lanthanide(III) Complexes

et al. 2007

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“…Kumar et al for Gd(DO3A) and Gd(HP-DO3A) and Kang et al for Gd(DO3MA)). 8,41 Taking into account all possible dissociation pathways the rate of dissociation can be given as: (11) The concentration of the protonated complexes can be calculated with the stability constants of the protonated species according to: (12) Finally, the pseudo-first-order rate constant k d can be expressed with Eqn. 9: (13) As described earlier, k 0 was fixed to zero and the rate constants k 1 and k 2 (k LnLH and k H LnLH from Scheme 2) and protonation constants K 1 and K 2 (K H LnL and K H LnLH from Scheme 2) were fitted to eqn.…”

Section: Kinetics Of Dissociationmentioning

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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“…These intermediate complexes have been identified by various techniques: kinetic measurements [20,22] for Eu 3 + -and Ce 3 + -dota, NMR, [21] absorption spectroscopy, [18,24] luminescence, [31] potentiometry [7,23] and some of their structures have been confirmed by molecular modeling. [31] All of the experimental results published in the literature may be grouped together into two "complexing" mechanisms.…”

Section: Introductionmentioning

confidence: 96%

“…The first complexing mechanism, proposed by Wu and Horrocks, [31] Burai, [32] Brucher, [18] Toth, [24] Jang, [33] Szilagyi, [22] and Chang, [12] and their co-workers, is a three-phase mechanism.…”

Section: Introductionmentioning

confidence: 99%

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Complexing Mechanism of the Lanthanide Cations Eu³⁺, Gd³⁺, and Tb³⁺ with 1,4,7,10‐Tetrakis(carboxymethyl)‐1,4,7,10‐tetraazacyclododecane (dota)—Characterization of Three Successive Complexing Phases: Study of the Thermodynamic and Structural Properties of the Complexes by Potentiometry, Luminescence Spectroscopy, and EXAFS

Moreau

Guillon

Pierrard

et al. 2004

Chemistry A European J

143

186

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Kinetics of Complex Formation by Macrocyclic Polyaza Polycarboxylate Ligands: Detection and Characterization of an Intermediate in the Eu3+-dota System by Laser-Excited Luminescence

Cited by 87 publications

References 3 publications

Synthesis and Characterization of DOTA‐(amide)₄ Derivatives: Equilibrium and Kinetic Behavior of Their Lanthanide(III) Complexes

Synthesis and Characterization of DOTA‐(amide)₄ Derivatives: Equilibrium and Kinetic Behavior of Their Lanthanide(III) Complexes

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

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Kinetics of Complex Formation by Macrocyclic Polyaza Polycarboxylate Ligands: Detection and Characterization of an Intermediate in the Eu3+-dota System by Laser-Excited Luminescence

Cited by 87 publications

References 3 publications

Synthesis and Characterization of DOTA‐(amide)4 Derivatives: Equilibrium and Kinetic Behavior of Their Lanthanide(III) Complexes

Synthesis and Characterization of DOTA‐(amide)4 Derivatives: Equilibrium and Kinetic Behavior of Their Lanthanide(III) Complexes

Equilibrium and Formation/Dissociation Kinetics of Some LnIIIPCTA Complexes

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Synthesis and Characterization of DOTA‐(amide)₄ Derivatives: Equilibrium and Kinetic Behavior of Their Lanthanide(III) Complexes

Synthesis and Characterization of DOTA‐(amide)₄ Derivatives: Equilibrium and Kinetic Behavior of Their Lanthanide(III) Complexes

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