Studies on the kinetics of formation and dissociation of the cerium(III)-DOTA complex

Brücher, Ernő; Laurenczy, Gábor; Makra, Zsolt

doi:10.1016/s0020-1693(00)84060-8

Cited by 69 publications

(104 citation statements)

References 3 publications

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“…3 Based on these data, the dissociation of the complexes in vivo can occur through one of the following pathways (Scheme 2): 1) spontaneous dissociation characterized by the rate constant k LnL , 2) proton assisted dissociation characterized with the protonation constants K H LnHL and K H LnH2L and rate constants k LnHL and k H LnHL , 3) ligand assisted dissociation characterized by the stability constant of mixed ligand complexes K LLnL* and rate constant k LLnL* , and 4) metal-ion catalyzed dissociation characterized by the stability of dinuclear complexes K LnLM and rate constant k LnLM . The rate of the dissociation is directly proportional to the total concentration of the complex: (7) where the k d is a pseudo-first-order rate constant. Taking into account of all possible dissociation pathways according to Scheme 2 the total concentration of the complex [LnL] t can be expressed as: (8) In the systems Ln(III) ion and octa-or nonadentate macrocyclic ligands the probability of a ligand exchange reaction is very low as formation of ternary complex (LLnL*) is unlikely.…”

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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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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“…[8][9][10] A recently published report on the thermodynamic stability and kinetics of [Ln{DOTA-(gly) 4 }] − complex formation demonstrated that both the basicity of the amide ligands and the stability of the complexes are several orders of magnitude lower than for their [Ln(DOTA)] − analogues. [11] It was also shown that spontaneous dissociation of [Eu{DOTA-(gly) 4 }] − occurs somewhat faster than [Eu (DOTA)] − , but that acid-catalyzed dissociation of the protonated intermediate [Eu{H 4 DOTA-(gly) 4 }] 3+ seems to occur more slowly than for its protonated [Eu(H 2 DOTA)] + analog.…”

Section: Introductionmentioning

confidence: 99%

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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“…Propane-1,3-diamine, dioxaand trioxadiamines, aza-and diazacrown ethers, 1-(bromomethyl)-3-bromobenzene, l-proline, 2-isobutyrylcyclohexanone, BINAP, cesium carbonate, potassium carbonate, sodium tert-butoxide, CuI were purchased from Aldrich and used without further purification, Pd(dba) 2 was synthesized according to the method described, [31] 1-(bromomethyl)-3-iodobenzene was obtained from commercially available m-iodotoluene by a standard bromination with NBS in CCl 4 . Dioxane was distilled over NaOH followed by the distillation over sodium under argon, acetonitrile was distilled over CaH 2 , DMF, EtCN, dichloromethane and methanol were used freshly distilled.…”

Section: Methodsmentioning

confidence: 99%

“…The reaction mixture was refluxed for 8 h, after cooling the reaction mixture down to room temperature the reaction mixture was diluted with CH 2 Cl 2 (10 ml), the solution was filtered, evaporated in vacuo, dissolved in CH 2 Cl 2 (10 ml), and additional precipitate was separated. After evaporating the solvent, the residue was chromatographed on silica gel using a sequence of eluents: CH 2 3,3'- (1,4,10,…”

Section: 16-bis(3-iodobenzyl)-141013-tetraoxa-716-diazacyclooctmentioning

confidence: 99%

“…It has been widely used in the coordination studies with various metal cations including rare earth metals and lanthanides. [1][2][3][4] Well-studied are other tetrasubstituted tetraazamacrocycles like cyclen and cyclam (1,4,8,11-tetraazacyclotetradecane) with phosphonate, [5][6][7][8][9][10] amide, [11] nitrile, [12] primary and tertiary amino groups. [13,14] In many cases additional donor atoms are present in C-substituted macrocycles like cyclam [15,16] or crown ethers.…”

Section: Introductionmentioning

confidence: 99%

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Copper-catalyzed amination in the synthesis of polyoxadiamine derivatives of aza- and diazacrown ethers

Yakushev¹,

Averin²,

Anokhin³

et al. 2014

MHC

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Studies on the kinetics of formation and dissociation of the cerium(III)-DOTA complex

Cited by 69 publications

References 3 publications

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

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

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

Copper-catalyzed amination in the synthesis of polyoxadiamine derivatives of aza- and diazacrown ethers

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Studies on the kinetics of formation and dissociation of the cerium(III)-DOTA complex

Cited by 69 publications

References 3 publications

Equilibrium and Formation/Dissociation Kinetics of Some LnIIIPCTA Complexes

Equilibrium and Formation/Dissociation Kinetics of Some LnIIIPCTA Complexes

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

Copper-catalyzed amination in the synthesis of polyoxadiamine derivatives of aza- and diazacrown ethers

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

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

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