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O
O
OH
OH
O
O
O
O
O
O
2RNH
2
+
N
N
N
N
O
N
O
RHN
N
NHR
OH
OH
O
O
O
O
HO
HO
HO
N
OH
HO
N
NHR
EDC+NH
S
N
N
N
N
RNH
2
+
O
O O
O
O
O O
O
OH
OH
OH
OH
O
O
OH
OH
O
O
N
N
N
N
EDC+NHS
OH
NHR
RNH
2
+
HO
HO
N
N
N
N
O
O
HO
HO
O
O
N
SCN
RHN
C
S
COOH
COOH
RNH
2
+
N
N
HOOC N
N COOH
HOOC N
N COOH
COOH
HOOC
COOH
HOOC
COOH
HOOC
HOOC
COOH
N
SCN
N
N
N
N
RHN
C
RNH
2
+
S
N
N
N
N
COOH
HOOC
HOOC
COOH
Scheme 4.4
Reaction of DTPA, DOTA, and DTPA- and DOTA-analogues with
amine groups.
surface and DTPA (Schemes 4.1, 4.4, 4.5). Despite a low amount of
gadolinium chelates immobilized on nanoparticles (four gadolinium
ions per nanoparticle), a strong positive and negative contrast
enhancement is observed. This increase in relaxivity is consistent
with the increase in rotational correlation time, which results from
both the increase in molecular weight and maximum compactness
of the SiO
structure as compared to organic molecules. Indeed,
the rigid nature of the inorganic nanoparticle tends to prevent the
Gd
2
3+
chelate from freely rotating or even folding back. Since the
propensity of nanoparticles to be internalized in cells is higher
than in the case of the molecules, the immobilization of gadolinium
chelates onto nanoparticles is attractive because an efficient
