Chemistry Reference
In-Depth Information
O particles can also be encapsulated
by a gold shell whose thickness can be accurately controlled [98].
The encapsulation of these gadolinium carbonate particles by a
gold shell induces a decrease in the longitudinal relaxivity with the
increase in the thickness of the gold shell. However, the gold shell
renders the resulting nanoparticles suited for photothermal therapy
[64]. GdO(CO
of a gold layer. Gd
O(CO
)
·H
2
3
2
2
O particles encapsulated in gold shell are able
to combine MRI and therapy as revealed by
)
·H
3
2
2
experiments.
However the exploitation of this attractive feature requires the
reduction of the size of this class of materials.
in vitro
4.3.3.3 Gadolinium metal-organic frameworks (Gd-MOFs)
Metal-organic framework (MOF) designates crystalline hybrid
materials built from metal ion connectors and polydentate bridging
ligands. One-, two- or three-dimensional nanometric structures
can be obtained according to the experimental conditions and to
the nature of the metal ions and the organic ligands. These hybrid
materials exhibit an interesting potential for a large range of
applications (gas purification and separation, catalysis, optical/
magnetic sensors) since their behavior can be accurately tuned by
a judicious choice of building blocks. When the metal ion is Gd
3+
or
2+
, nanoscale MOFs have been proposed as a new class of imaging
probes [128-130]. Although the number of water molecules in
the inner coordination sphere of each gadolinium ion in the MOF
structure, which depends on the nature of the polydendate ligand,
is different for [Gd
Mn
] MOF nanoparticles (bhc for
benzene hexacarboxylate) and for [Gd(H
(bhc)(H
O)
2
2
6
cmp is
(carboxymethyl)iminodi-(methylphosphonic acid)), the longitudinal
relaxivity
cmp)(H
O)] (H
2
2
5
r
and the transverse relaxivity
r
are very similar (
r
=
1
2
1
1.50 mM
−1
s
−1
and
r
= 122.6 mM
−1
s
−1
for [Gd
(bhc)(H
O)
],
r
=
2
2
2
6
1
−1
−1
−1
−1
O)]) [128,
131]. This indicates that the water proton relaxation in these Gd-
MOFs occurs through an outer sphere mechanism. Moreover, the
1.08 mM
s
and
r
= 121.7 mM
s
for [Gd(H
cmp)(H
2
2
2
r
1
values of these MOFs are very low (probably due to the hindered
diffusion of water molecules through the porous MOFs and an
inadequate exchange rate between Gd-coordinated water molecules
and the bulk water) while high values for
are observed whatever
the external magnetic field, in contrast to gadolinium oxide, fluoride,
or carbonate nanoparticles (see Sections 4.3.2, 4.3.3.1, and 4.3.3.2).
These Gd-MOFs are, therefore, better suited for
r
2
T
T2-weighted MRI.
2
