<sup>8</sup>S paramagnetic centres in molecular assemblies: possible effect of their proximity on the water proton relaxivity

Nicolle, Gaëlle M.; Helm, Lothar; Merbach, André E.

doi:10.1002/mrc.1257

Cited by 29 publications

(27 citation statements)

References 29 publications

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“…Dipole-dipole interactions between electron spins of close Gd III centres have been already observed by EPR or proton relaxometry for dinuclear [46] and trinuclear complexes, [47] micelles [48] and dendrimer complexes. [30] Such intramolecular Gd III -Gd III interactions lead to an increase in the electronic relaxation rate, which is unfavourable for relaxivity.…”

Section: Resultsmentioning

confidence: 92%

“…Similar observations were reported for micellar systems with variable Gd III loading. [48] We have also measured proton relaxivities for the three generations of dendrimers as a function of pH between pH 6 and 12 (40 MHz, 40 8C; Figure 4). Below pH 6, the dendrimer complexes are not soluble, probably due to the protonation of the amino functions in the skeleton.…”

Section: Resultsmentioning

confidence: 99%

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Rotational Dynamics Account for pH‐Dependent Relaxivities of PAMAM Dendrimeric, Gd‐Based Potential MRI Contrast Agents

Laus¹,

Sour²,

Ruloff³

et al. 2005

Chemistry A European J

115

118

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The EPTPA5) chelate, which ensures fast water exchange in GdIII complexes, has been coupled to three different generations (5, 7, and 9) of polyamidoamine (PAMAM) dendrimers through benzylthiourea linkages (H5EPTPA = ethylenepropylenetriamine-N,N,N',N'',N''-pentaacetic acid). The proton relaxivities measured at pH 7.4 for the dendrimer complexes G5-(GdEPTPA)111, G7-(GdEPTPA)253 and G9-(GdEPTPA)1157 decrease with increasing temperature, indicating that, for the first time for dendrimers, slow water exchange does not limit relaxivity. At a given field and temperature, the relaxivity increases from G5 to G7, and then slightly decreases for G9 (r1 = 20.5, 28.3 and 27.9 mM(-1) s(-1), respectively, at 37 degrees C, 30 MHz). The relaxivities show a strong and reversible pH dependency for all three dendrimer complexes. This originates from the pH-dependent rotational dynamics of the dendrimer skeleton, which was evidenced by a combined variable-temperature and multiple-field 17O NMR and 1H relaxivity study performed at pH 6.0 and 9.9 on G5-(GdEPTPA)111. The longitudinal 17O and 1H relaxation rates of the dendrimeric complex are strongly pH-dependent, whereas they are not for the [Gd(EPTPA)(H2O)]2- monomer chelate. The longitudinal 17O and 1H relaxation rates have been analysed by the Lipari-Szabo spectral density functions and correlation times have been calculated for the global motion of the entire macromolecule (tau(gO)) and the local motion of the GdIII chelates on the surface (tau(lO)), correlated by means of an order parameter S2. The dendrimer complex G5-(GdEPTPA)111 has a considerably higher tau(gO) under acidic than under basic conditions (tau(298)gO = 4040 ps and 2950 ps, respectively), while local motions are less influenced by pH (tau(298)lO = 150 and 125 ps). The order parameter, characterizing the rigidity of the macromolecule, is also higher at pH 6.0 than at pH 9.9 (S2 = 0.43 vs 0.36, respectively). The pH dependence of the global correlation time can be related to the protonation of the tertiary amine groups in the PAMAM skeleton, which leads to an expanded and more rigid dendrimeric structure at lower pH. The increase of tau(gO) with decreasing pH is responsible for the pH dependent proton relaxivities. The water exchange rate on G5-(GdEPTPA)111(k(298)ex = 150 x 10(6) s(-1)) shows no significant pH dependency and is similar to the one measured for the monomer [Gd(EPTPA)(H2O)]2-. The proton relaxivity of G5-(GdEPTPA)111 is mainly limited by the important flexibility of the dendrimer structure, and to a small extent, by a faster than optimal water exchange rate.

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Section: Resultsmentioning

confidence: 92%

Section: Resultsmentioning

confidence: 99%

Rotational Dynamics Account for pH‐Dependent Relaxivities of PAMAM Dendrimeric, Gd‐Based Potential MRI Contrast Agents

Laus¹,

Sour²,

Ruloff³

et al. 2005

Chemistry A European J

115

118

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“…EPR spectra of Gd III -and mixed Gd III /Y III binuclear complexes clearly show that the two Gd III centres interact intramolecularly, resulting in an enhancement of the electronic relaxation of the Gd III electron spins. [38] Other candidates for the investigation of intramolecular electron-spin interactions include bimetallic azacryptates with Ln III ϪLn III distances of around 3.5 pm. [39] The complex solution equilibria of the ligand OHEC have been studied successfully by potentiometry.…”

Section: Resultsmentioning

confidence: 99%

Structure Comparison of Early and Late Lanthanide(III) Homodinuclear Macrocyclic Complexes with the Polyamine Polycarboxylic Ligand H₈OHEC

et al. 2004

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The solid‐state structures of two new homodinuclear chelate complexes with the late lanthanide(III) ions Yb and Lu, [Na2(Yb2OHEC)].14.5H2O (1), and [Na2(Lu2OHEC)].14.5H2O (2) (H8OHEC = 1,4,7,10,14,17,20,23‐octaazacyclohexacosane‐ 1,4,7,10,14,17,20,23‐octaacetic acid), have been determined by X‐ray crystal structure analysis. Each lanthanide(III) ion is coordinated by eight donor atoms of the ligand and the geometry of the coordination polyhedron approaches a bicapped trigonal prism. These structures are compared with those of the homodinuclear chelate complexes with the same ligand and the mid to early lanthanide(III) ions Gd, Eu, La and also Y. A distinctive structural change occurs across the lanthanide series. The centrosymmetric mid to early lanthanide(III) complexes are all ninefold‐coordinated in a capped square antiprismatic arrangement with a water molecule coordinated in a prismatic position. This structure is maintained in aqueous solution, together with an asymmetric minor isomer. The late lanthanide(III) OHEC complexes not only lack the inner‐sphere water, but the change of coordination sphere also results in a loss of symmetry of the whole complex molecule. The observed change of coordination mode and number of the lanthanide ion may offer a geometric model for the isomerization process in eight‐ and ninefold‐coordinated complex species that are isomers in a possible coordination equilibrium observed by NMR in aqueous solution. This model may also explain the intramolecular rearrangements necessary during water exchange in the inner coordination sphere of the complex [(Gd2OHEC)(H2O)2]2− through a slow dissociative mechanism. Protonation constants of the H8OHEC ligand and complex formation constants of this ligand with GdIII, CaII, CuII and ZnII have been determined by solution thermodynamic studies. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

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“…Hovland and coIn the last decades, nuclear magnetic resonance imaging has evolved as a powerful tool for research and practice in workers prepared a novel Gd(III)-87 complex, which showed high T 1 -relaxivity values in serum albumin solutions, blood and plasma [99]. membered ring formed from the eight amine and bridging ethylene or propylene groups, was synthesized and its properties as a chelator for lanthanides and small transition metals also was studied [100][101][102][103]. For increasing the rotational correlation time compared with conventional DOTA and DTPA and obtaining previously unknown binuclear contrast agents with two closely sited gadolinium ions, H 8 OHEC (1,4,7,10,14,17,20,23-octaazacyclohexacosane-1,4,7,10,14,17,20,23-octaacetic acid) (88), which is a macrocyclic polyaminocarboxylate with a 26-atom-…”

Section: Contrast Agents For Magnetic Resonance Imagingmentioning

confidence: 99%

Medical Applications of Macrocyclic Polyamines

Liang

Wan²,

Li³

et al. 2006

CMC

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Macrocyclic polyamines comprise a special group of heterocycles that bind different guests. Over the past decade, medical interest has focused on macrocyclic polyamines owning to their chemical and biological properties. The discovery and development of the bicyclam AMD3100 highlighted the clinical potential of such compounds in AIDS, cancer and stem-cell mobilization. Many macrocyclic polyamines and their transition metal complexes had the cytotoxic activities to tumors through binding DNA, cleaving DNA, crosslinking DNA, or depleting the endogenous ATP levels of the tumor cells. Furthermore, macrocyclic polyamines also could be labeled with metal ionic radii and have applications in cancer radioimmunotherapy and in vivo magnetic resonance imaging (MRI). The current rational design, and medical applications of macrocyclic polyamines will be reviewed in this manuscript.

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⁸S paramagnetic centres in molecular assemblies: possible effect of their proximity on the water proton relaxivity

Cited by 29 publications

References 29 publications

Rotational Dynamics Account for pH‐Dependent Relaxivities of PAMAM Dendrimeric, Gd‐Based Potential MRI Contrast Agents

Rotational Dynamics Account for pH‐Dependent Relaxivities of PAMAM Dendrimeric, Gd‐Based Potential MRI Contrast Agents

Structure Comparison of Early and Late Lanthanide(III) Homodinuclear Macrocyclic Complexes with the Polyamine Polycarboxylic Ligand H₈OHEC

Medical Applications of Macrocyclic Polyamines

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8S paramagnetic centres in molecular assemblies: possible effect of their proximity on the water proton relaxivity

Cited by 29 publications

References 29 publications

Rotational Dynamics Account for pH‐Dependent Relaxivities of PAMAM Dendrimeric, Gd‐Based Potential MRI Contrast Agents

Rotational Dynamics Account for pH‐Dependent Relaxivities of PAMAM Dendrimeric, Gd‐Based Potential MRI Contrast Agents

Structure Comparison of Early and Late Lanthanide(III) Homodinuclear Macrocyclic Complexes with the Polyamine Polycarboxylic Ligand H8OHEC

Medical Applications of Macrocyclic Polyamines

Contact Info

Product

Resources

About

⁸S paramagnetic centres in molecular assemblies: possible effect of their proximity on the water proton relaxivity

Structure Comparison of Early and Late Lanthanide(III) Homodinuclear Macrocyclic Complexes with the Polyamine Polycarboxylic Ligand H₈OHEC