220
D.-W. ZHANG ET AL.
Relaxation time of complexes were measured referring to lit- one exothermic peak for the ligand at 278◦C. The complexes
erature[8] by an inversion-recovery pulse sequences on a Bruker have an endothermic peak between 98◦ and 115◦C. The corre-
AC-80 NMR spectrophotometer, using the INVREC. Au pro- sponding TG curves show that the weight loss is equal to two
gram at 90◦ pulse width t p (90◦) = 2.8us.
water molecule or four water molecules. The results are in ac-
cordance with the composition of the complexes as determined
by elemental analyses. Three exothermic peaks appear around
355–557◦C. The initial temperature of decomposition is greater
than 278◦C, which indicates that the thermal stability of the
complexes is higher than that of the free ligand which decom-
posed at 278◦C, showing that there may be large conjugation in
the chelate ring in the complexes.
RESULTS AND DISCUSSION
The Composition and General Character of Complexes
All of the complexes are easily soluble in water, DMF, and
DMSO; slightly soluble in ethanol; insoluble in acetone, chlo-
roform, and Et2O; quite stable at room temperature and nor-
mal pressure; and not sensitive to light. Elemental analyses and
empirical formula are shown in Table 1. The elemental analy-
ses show that the formulas of the complexes are REL · nH2O
(RE = La, Tb, n = 2; RE = Eu, Gd, n = 4). Elemental analysis
was in good agreement with the structures, respectively. The
molar conductivities of the complexes are around 12.1–33.0
S·cm2·mol−1 in DMF (Table 1), showing that all complexes are
non-electrolytes in DMF.[9]
Relaxivity of the Complexes
The relaxivity mainly consists of two components: the in-
nersphere and outersphere relaxivity. The high relaxivity is fa-
vorable of tissue imaging. The relaxivity (R1) of complexes
and Gd(DTPA)2– used are compared and given in Table 4. The
results showed that the spin-lattice relaxivity of GdL is larger
than that of Gd(DTPA)2−. Measurement of the relaxation time
of GdL is showed in Figure 2.
Infrared Spectra
The main stretching frequencies of the IR spectra of the lig-
ands and their complexes are tabulated in Table 2. It can be
found that the characteristic absorption peaks of all complexes
are similar. In the spectra of H3L, the carboxylic ν(COOH) ap-
pears at 3500 cm−1, the peak is absent in the complexes, but there
is a broad peak at around 3218–3487 cm−1 in the complexes.
The peak at around 1571–1582 cm−1 is assigned to δHOH, which
shows that there is the coordinating H2O in the complexes. The
CONCLUSION
Non-ion complexes of GdL derivative from diethylene tri-
amine pentaacetic acid and o-hydroxybenzoyl hydrazine are
prospective MRI contrast agent with high spin-lattice relaxivity
and stability, low cost, good solubility and stability to light.
REFERENCES
1. Caravan, P.; Ellison, J. J.; McMurry, T. J.; Lauffer, R. B. Gadolinium(III)
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carboxylic ν(C
of free ligands is at 1707 cm−1, which does
O)
not appear in the complexes. However, two new vibrations of
CO2− for νas and νs show themselves at 1550 and 1398 cm−1
the ꢀν(νas-νs) of which is approximately equal to 152 cm−1
,
.
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6. Geigy, J. R. French Patent 1,548,888, 1968.
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Thermal Analyses
Some data of thermal analyses are listed in Table 3. The
DTA curves of the ligand have an endothermic peak at 183◦C,
but there is no weight lost on the corresponding TG curves,
showing that this is a phase transition process, which is the
same as the melting point of the ligand. In addition, there is
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Zhang, Ding-Wa
