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New Journal of Chemistry
Page 9 of 11
DOI: 10.1039/C7NJ04696K
Journal Name
recovery method with typical 90° pulse width of 3.5
ARTICLE
ꢁ
s, 16
Acknowledgements
experiments of 4 scans. The temperature was controlled with a
Stelar VTC-91 airflow heater equipped with a calibrated
copper-constantan thermocouple (uncertainty of ±0.1 °C).
Variable-temperature 17O NMR measurements were recorded
on a Bruker Avance III spectrometer (11.7 T) equipped with a 5
mm probe and standard temperature control unit. Aqueous
solutions of the complexes containing 2.0% of the 17O isotope
(Cambridge Isotope) were used. The observed transverse
relaxation rates were calculated from the signal width at half-
height.
We are grateful to Università del Piemonte Orientale for
financial support (Ricerca locale 2016). L.T. sincerely
acknowledges the support of Compagnia di San Paolo (CSP-
2014 THERASIL Project).
Notes and references
1
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,
2
3
Conclusions
Bishydrated GdDO3A functionalized derivatives bearing a
suitable substituent on the secondary nitrogen of the
macrocyclic ring have been synthesized and conjugated to a
central unit, resulting in trinuclear complexes. The nature of
the pendant group has a significant influence on the
relaxometric properties of both mononuclear and multinuclear
GdIII complexes. The length and flexibility of the pendant chain
and the presence of a good donor group result in the
perturbation of the inner coordination sphere of the Gd3+ ion,
4
5
N. Bloembergen, L. O. Morgan, J. Chem. Phys. 1961, 34, 842.
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2
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whose hydration state decreases from two to one in GdL1
.
7
8
9
Interestingly, given the relatively low stability of the nine-
membered Gd-N-(CH2)5-CO-Gd ring, the carbonate anion
competes for the coordination of GdIII and, between pH ca. 8-
10, an equilibrium exists between species q = 1 and q = 0. The
greater rigidity of the pendant group in L2 prevents this
process in GdL2 that, therefore, maintains the expected
features of a bishydrated complex. The chemical nature and
electronic effects of the pendant group mainly affect the rate
of water exchange, which is significantly accelerated compared
to that measured for the parent GdDO3A complex.
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,
The length, flexibility and steric hindrance of the linker
connecting the chelates to the central unit affect the rotational
dynamics of the trinuclear complexes, hence their relaxometric
properties, particularly at the fields relevant for MRI. In Gd3L3,
the flexibility of the alkyl chain has two significant
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local rotation about the chain that results in a marked
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effectiveness of the trinuclear complex. In Gd3L4, the lower
,
rotational flexibility entails
a better motional coupling
between local and overall tumbling motion and consequently
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,
Conflicts of interest
There are no conflicts to declare.
Aime, Inorg. Chem. 2013, 52, 7130.
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