Accelerating water exchange for Gd<sup>III</sup>chelates by steric compression around the water binding site

Ruloff, Robert; Tóth, Éva; Scopelliti, Rosario; Tripier, Raphaël; Handel, Henri; Merbach, André E.

doi:10.1039/b207713b

Cited by 94 publications

(100 citation statements)

References 6 publications

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“…The steric strain was usually reached by introduction of one extra methylene group into the backbone (propylene group instead of ethylene bridge) or in one of the pendant arms (i.e. with propionate pendant instead of acetate), [8][9][10][11] or by substitution of ligand backbone by alkyl/aryl group. [12,13] The complexes formed with these new ligands are thermodynamically usually slightly less stable than those of H 4 dota and H 5 dtpa.…”

Section: Introductionmentioning

confidence: 99%

Study of Thermodynamic and Kinetic Stability of Transition Metal and Lanthanide Complexes of DTPA Analogues with a Phosphorus Acid Pendant Arm

et al. 2006

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The thermodynamic and kinetic stabilities of the complexes of phosphonate and phenylphosphinate analogues of H 5 dtpa with selected transition-and lanthanide-metal ions are presented. Both phosphorus-containing ligands form thermodynamically very stable complexes, with stability constants comparable with or even higher than those reported for the parent H 5 dtpa. However, the kinetic inertness of their gadolinium(III) complexes against acid-and metal-assisted decomplexations is surprisingly much lower. The half-life times of gadolinium(III) complexes of the new ligands in the pres-

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Section: Introductionmentioning

confidence: 99%

Study of Thermodynamic and Kinetic Stability of Transition Metal and Lanthanide Complexes of DTPA Analogues with a Phosphorus Acid Pendant Arm

et al. 2006

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“…[1] In order to enhance r 1 , it has been found that: 1) tumbling has to be slowed down by attaching the chelate to macromolecular assemblies, such as proteins, [2,3] dendrimers, [4,5] micellar aggregates [6,7] or polymers; [8] 2) the water-exchange rate has to be increased by promotion of the departure of a coordinated water molecule; this is achieved by the design of optimized chelates such as Gd III complexes of TRITA (1,4,7,10-tetraazacyclotridecane-1,4,7,10-tetraacetic acid), [9] EPTPA (ethylenepropylenetriaminepentaacetic Abstract: We report the study of binuclear Ln III chelates of OHEC (OHEC = octaazacyclohexacosane-1, 4,7,10,14,17,20,23-octaacetate). The interconversion between two isomeric forms, which occurs in aqueous solution, has been studied by NMR, UV/ Vis, EPR, and luminescence spectroscopy, as well as by classical molecular dynamics (MD) simulations.…”

Section: Introductionmentioning

confidence: 99%

Towards Binuclear Polyaminocarboxylate MRI Contrast Agents? Spectroscopic and MD Study of the Peculiar Aqueous Behavior of the Ln^III Chelates of OHEC (Ln=Eu, Gd, and Tb): Implications for Relaxivity

Nicolle¹,

Yerly²,

Böttger³

et al. 2003

Chemistry A European J

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We report the study of binuclear Ln(III) chelates of OHEC (OHEC=octaazacyclohexacosane-1,4,7,10,14,17,20,23-octaacetate). The interconversion between two isomeric forms, which occurs in aqueous solution, has been studied by NMR, UV/Vis, EPR, and luminescence spectroscopy, as well as by classical molecular dynamics (MD) simulations. For the first time we have characterized an isomerization equilibrium for a Ln(III) polyaminocarboxylate complex (Ln(III)=Y, Eu, Gd and Tb) in which the metal centre changes its coordination number from nine to eight, such that: [Ln(2)(ohec)(H(2)O)(2)](2-) r<==>[Ln(2)(ohec)](2-)+2 H(2)O. The variable temperature and pressure NMR measurements conducted on this isomerization reaction give the following thermodynamic parameters for Eu(III): K(298)=0.42+/-0.01, DeltaH(0)=+4.0+/-0.2 kJ mol(-1), DeltaS(0)=+6.1+/-0.5 J K(-1) mol(-1) and DeltaV(0)=+3.2+/-0.2 cm(3) mol(-1). The isomerization is slow and the corresponding kinetic parameters obtained by NMR spectroscopy are: k(298)(is)=73.0+/-0.5 s(-1), DeltaH++(is)=75.3+/-1.9 kJ mol(-1), DeltaS++(is)= +43.1+/-5.8 J K(-1) mol(-1) and DeltaV++(is)=+7.9+/-0.7 cm(3) mol(-1). Variable temperature and pressure (17)O NMR studies have shown that water exchange in [Gd(2)(ohec)(H(2)O)(2)](2-) is slow, k(298)(ex)=(0.40+/-0.02)x10(6) s(-1), and that it proceeds through a dissociative interchange I(d) mechanism, DeltaV( not equal )=+7.3+/-0.3 cm(3) mol(-1). The anisotropy of this oblong binuclear complex has been highlighted by MD simulation calculations of different rotational correlation times. The rotational correlation time directed on the Gd-Gd axis is 24 % longer than those based on the axes orthogonal to the Gd-Gd axis. The relaxivity of this binuclear complex has been found to be low, since 1) only [Gd(2)(ohec)(H(2)O)(2)](2-), which constitutes 70 % of the binuclear complex, contributes to the inner-sphere relaxivity and 2) the anisotropy of the complex prevents water molecules from having complete access to both Gd(III) cages; this decreases the outer-sphere relaxivity. Moreover, EPR measurements for the Gd(III) and for the mixed Gd(III)/Y(III) binuclear complexes have clearly shown that the two Gd(III) centres interact intramolecularly; this enhances the electronic relaxation of the Gd(III) electron spins.

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“…The SolomonBloembergen-Morgan theory predicts maximum proton relaxivity when the water exchange is in a narrow, optimal range, and the rotation and electron spin relaxation are both slow. [4] Recently, the water-exchange rate has been successfully tuned to optimal values in poly(amino carboxylate) [5][6][7][8] and other stable complexes of Gd III . [9] In spite of the continuous work on the understanding of structure-mechanism relationships with regard to electron spin relaxation, it is not yet a straightforward matter to improve this factor through rational molecular design.…”

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confidence: 99%

A Starburst‐Shaped Heterometallic Compound Incorporating Six Densely Packed Gd³⁺ Ions

Livramento

Sour

Borel

et al. 2006

Chemistry A European J

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The heterotritopic ligand [bpy(DTTA)2]8- has two diethylenediamine-tetraacetate units for selective lanthanide(III) coordination and one bipyridine function for selective Fe(II) coordination. In aqueous solution and in the presence of these metals, the ligand is capable of self-assembly to form a rigid supramolecular metallostar structure, [Fe[Gd2bpy(DTTA)2(H2O)4]3]4-. We report here the physicochemical characterization of the dinuclear complex [Gd2bpy(DTTA)2(H2O)4]2- and the metallostar [Fe[Gd2bpy(DTTA)2(H2O)4]3]4- with regard to potential MRI contrast agent applications. A combination of pH potentiometry and 1H NMR spectroscopy has been used to determine protonation constants for the ligand [bpy(DTTA)2]8- and for the complexes [Fe[bpy(DTTA)2]3]22- and [Y2bpy(DTTA)2]2-. In addition, stability constants have been measured for the dinuclear chelates [M2bpy(DTTA)2]n- formed with M = Gd3+ and Zn2+ (log K(GdL) = 18.2; log K(ZnL) = 18.0; log K(ZnHL) = 3.4). A multiple field, variable-temperature 17O NMR and proton relaxivity study on [Gd2bpy(DTTA)2(H2O)4]2- and [Fe[Gd2bpy(DTTA)2(H2O)4]3](4-) yielded the parameters for water exchange and the rotational dynamics. The 17O chemical shifts are indicative of bishydration of the lanthanide ion. The exchange rates of the two inner-sphere water molecules are very similar in the dinuclear [Gd2bpy(DTTA)2(H2O)(4)]2- and in the metallostar (k(ex)298 = 8.1 +/- 0.3 x 10(6) and 7.4 +/- 0.2 x 10(6) s(-1), respectively), and are comparable to k(ex)298 for similar Gd(III) poly(amino carboxylates). The rotational dynamics of the metallostar has been described by means of the Lipari-Szabo approach, which involves separating global and local motions. The difference between the local and global rotational correlation times, tau(lO)298 = 190 +/- 15 ps and tau(gO)298 = 930 +/- 50 ps, respectively, shows that the metallostar is not completely rigid. However, the relatively high value of S2 = 0.60 +/- 0.04, describing the restriction of the local motions with regard to the global one, points to a limited flexibility compared with previously reported macromolecules such as dendrimers. As a result of the two inner-sphere water molecules, with their near-optimal exchange rate, and the limited flexibility, the metallostar has a remarkable molar proton relaxivity, particularly at high magnetic fields (r1 = 33.2 and 16.4 mM(-1) s(-1) at 60 and 200 MHz, respectively, at 25 degrees C). It packs six efficiently relaxing Gd(III) ions into a small molecular space, which leads, to the best of our knowledge, to the highest relaxivity per molecular mass ever reported for a Gd(III) complex. The [bpy(DTTA)2]8- ligand is also a prime candidate as a terminal ligand for constructing larger sized, Fe(II) (or Ru(II))-based metallostars or metallodendrimers loaded with Gd(III) on the surface.

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Accelerating water exchange for Gd^IIIchelates by steric compression around the water binding site

Cited by 94 publications

References 6 publications

Study of Thermodynamic and Kinetic Stability of Transition Metal and Lanthanide Complexes of DTPA Analogues with a Phosphorus Acid Pendant Arm

Study of Thermodynamic and Kinetic Stability of Transition Metal and Lanthanide Complexes of DTPA Analogues with a Phosphorus Acid Pendant Arm

Towards Binuclear Polyaminocarboxylate MRI Contrast Agents? Spectroscopic and MD Study of the Peculiar Aqueous Behavior of the Ln^III Chelates of OHEC (Ln=Eu, Gd, and Tb): Implications for Relaxivity

A Starburst‐Shaped Heterometallic Compound Incorporating Six Densely Packed Gd³⁺ Ions

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Accelerating water exchange for GdIIIchelates by steric compression around the water binding site

Cited by 94 publications

References 6 publications

Study of Thermodynamic and Kinetic Stability of Transition Metal and Lanthanide Complexes of DTPA Analogues with a Phosphorus Acid Pendant Arm

Study of Thermodynamic and Kinetic Stability of Transition Metal and Lanthanide Complexes of DTPA Analogues with a Phosphorus Acid Pendant Arm

Towards Binuclear Polyaminocarboxylate MRI Contrast Agents? Spectroscopic and MD Study of the Peculiar Aqueous Behavior of the LnIII Chelates of OHEC (Ln=Eu, Gd, and Tb): Implications for Relaxivity

A Starburst‐Shaped Heterometallic Compound Incorporating Six Densely Packed Gd3+ Ions

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Accelerating water exchange for Gd^IIIchelates by steric compression around the water binding site

Towards Binuclear Polyaminocarboxylate MRI Contrast Agents? Spectroscopic and MD Study of the Peculiar Aqueous Behavior of the Ln^III Chelates of OHEC (Ln=Eu, Gd, and Tb): Implications for Relaxivity

A Starburst‐Shaped Heterometallic Compound Incorporating Six Densely Packed Gd³⁺ Ions