Surprising Impact of Donor Charge on the Water Exchange Rates of Gd(III) AAZTA Derivatives

Lorenzo Tei; Loredana Leone; Daniela Lalli; Mauro Botta; Carlos Platas-Iglesias

doi:10.1002/ejic.202300730

Surprising Impact of Donor Charge on the Water Exchange Rates of Gd(III) AAZTA Derivatives

Lorenzo Tei, Loredana Leone, Daniela Lalli, Mauro Botta, Carlos Platas-Iglesias

Dipartimento di Scienze e Innovazione Tecnologica

Risultato della ricerca: Contributo su rivista › Articolo in rivista › peer review

Abstract

We report the synthesis of three new heptadentate ligands derived from H₄AAZTA (6-amino-6-methylperhydro-1,4-diazepinetetraacetic acid) that contain a dimethyl-amide group (AAZTA-MA)³⁻, two dimethyl-amide groups (AAZTA-BMA)²⁻ or two acetylglycine groups (AAZTA(Gly)₂)⁴⁻. The corresponding Gd(III) complexes were investigated using ¹H NMR relaxometry and ¹⁷O NMR chemical shifts and transverse relaxation rates. A computational DFT study was also performed to aid the analysis of the NMR data. The Gd(III) complexes contain two water molecules coordinated to the metal ion. In contrast to the prevailing trend, the amide derivatives discussed in this context exhibit comparatively rapid water exchange rates that do not align with the changes in the overall electric charge of the complexes: k_ex²⁹⁸=14.4×10⁶ s⁻¹, 14.5×10⁶ s⁻¹ and 9.56×10⁶ s⁻¹ for [Gd(AAZTA-MA)(H₂O)₂], [Gd(AAZTA-BMA)(H₂O)₂]⁺ and [Gd(AAZTA(Gly)₂(H₂O)₂]⁻, respectively. The analysis of the data and the computational work suggest that the relatively fast water exchange rates could be linked to the occurrence of associatively activated mechanisms, which is somewhat unexpected for nine-coordinated complexes.

Lingua originale	Inglese
Numero di articolo	e202300730
Rivista	European Journal of Inorganic Chemistry
Volume	27
Numero di pubblicazione	11
DOI	https://doi.org/10.1002/ejic.202300730
Stato di pubblicazione	Pubblicato - 12 apr 2024

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10.1002/ejic.202300730

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title = "Surprising Impact of Donor Charge on the Water Exchange Rates of Gd(III) AAZTA Derivatives",

abstract = "We report the synthesis of three new heptadentate ligands derived from H4AAZTA (6-amino-6-methylperhydro-1,4-diazepinetetraacetic acid) that contain a dimethyl-amide group (AAZTA-MA)3−, two dimethyl-amide groups (AAZTA-BMA)2− or two acetylglycine groups (AAZTA(Gly)2)4−. The corresponding Gd(III) complexes were investigated using 1H NMR relaxometry and 17O NMR chemical shifts and transverse relaxation rates. A computational DFT study was also performed to aid the analysis of the NMR data. The Gd(III) complexes contain two water molecules coordinated to the metal ion. In contrast to the prevailing trend, the amide derivatives discussed in this context exhibit comparatively rapid water exchange rates that do not align with the changes in the overall electric charge of the complexes: kex298=14.4×106 s−1, 14.5×106 s−1 and 9.56×106 s−1 for [Gd(AAZTA-MA)(H2O)2], [Gd(AAZTA-BMA)(H2O)2]+ and [Gd(AAZTA(Gly)2(H2O)2]−, respectively. The analysis of the data and the computational work suggest that the relatively fast water exchange rates could be linked to the occurrence of associatively activated mechanisms, which is somewhat unexpected for nine-coordinated complexes.",

keywords = "MRI, gadolinium, hydrates, ligand effects, relaxivity",

author = "Lorenzo Tei and Loredana Leone and Daniela Lalli and Mauro Botta and Carlos Platas-Iglesias",

note = "Publisher Copyright: {\textcopyright} 2024 The Authors. European Journal of Inorganic Chemistry published by Wiley-VCH GmbH.",

year = "2024",

month = apr,

day = "12",

doi = "10.1002/ejic.202300730",

language = "English",

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journal = "European Journal of Inorganic Chemistry",

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T1 - Surprising Impact of Donor Charge on the Water Exchange Rates of Gd(III) AAZTA Derivatives

AU - Tei, Lorenzo

AU - Leone, Loredana

AU - Lalli, Daniela

AU - Botta, Mauro

AU - Platas-Iglesias, Carlos

PY - 2024/4/12

Y1 - 2024/4/12

N2 - We report the synthesis of three new heptadentate ligands derived from H4AAZTA (6-amino-6-methylperhydro-1,4-diazepinetetraacetic acid) that contain a dimethyl-amide group (AAZTA-MA)3−, two dimethyl-amide groups (AAZTA-BMA)2− or two acetylglycine groups (AAZTA(Gly)2)4−. The corresponding Gd(III) complexes were investigated using 1H NMR relaxometry and 17O NMR chemical shifts and transverse relaxation rates. A computational DFT study was also performed to aid the analysis of the NMR data. The Gd(III) complexes contain two water molecules coordinated to the metal ion. In contrast to the prevailing trend, the amide derivatives discussed in this context exhibit comparatively rapid water exchange rates that do not align with the changes in the overall electric charge of the complexes: kex298=14.4×106 s−1, 14.5×106 s−1 and 9.56×106 s−1 for [Gd(AAZTA-MA)(H2O)2], [Gd(AAZTA-BMA)(H2O)2]+ and [Gd(AAZTA(Gly)2(H2O)2]−, respectively. The analysis of the data and the computational work suggest that the relatively fast water exchange rates could be linked to the occurrence of associatively activated mechanisms, which is somewhat unexpected for nine-coordinated complexes.

AB - We report the synthesis of three new heptadentate ligands derived from H4AAZTA (6-amino-6-methylperhydro-1,4-diazepinetetraacetic acid) that contain a dimethyl-amide group (AAZTA-MA)3−, two dimethyl-amide groups (AAZTA-BMA)2− or two acetylglycine groups (AAZTA(Gly)2)4−. The corresponding Gd(III) complexes were investigated using 1H NMR relaxometry and 17O NMR chemical shifts and transverse relaxation rates. A computational DFT study was also performed to aid the analysis of the NMR data. The Gd(III) complexes contain two water molecules coordinated to the metal ion. In contrast to the prevailing trend, the amide derivatives discussed in this context exhibit comparatively rapid water exchange rates that do not align with the changes in the overall electric charge of the complexes: kex298=14.4×106 s−1, 14.5×106 s−1 and 9.56×106 s−1 for [Gd(AAZTA-MA)(H2O)2], [Gd(AAZTA-BMA)(H2O)2]+ and [Gd(AAZTA(Gly)2(H2O)2]−, respectively. The analysis of the data and the computational work suggest that the relatively fast water exchange rates could be linked to the occurrence of associatively activated mechanisms, which is somewhat unexpected for nine-coordinated complexes.

KW - MRI

KW - gadolinium

KW - hydrates

KW - ligand effects

KW - relaxivity

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DO - 10.1002/ejic.202300730

M3 - Article

SN - 1434-1948

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JO - European Journal of Inorganic Chemistry

JF - European Journal of Inorganic Chemistry

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ER -

Surprising Impact of Donor Charge on the Water Exchange Rates of Gd(III) AAZTA Derivatives

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