Y.-Y. Ren et al. / Journal of Alloys and Compounds 501 (2010) 42–46
43
6−
Fig. 1. Photograph of 0.05 mol L−1 Ln(PTA)3 complexes in water solutions under
excitation by a standard laboratory UV lamp (ꢁex = 254 nm), Ln = Tb and Eu from left
to right.
Fig. 2. Crystal structure of Na6[Tb(PTA)3]·16.5H2O.
(m, ꢀ(C C, in Py)), 1365.8 (s, ꢀ(C O)), 467.4 (w, ꢀ(Eu–O)). The elemental analy-
sis results for Na6[Tb(PTA)3]·16.5H2O are: found (calcd for Na6TbC24H39N3O34.5) C
23.12 (23.66), H 3.28 (3.23), N 3.38 (3.45). IR (KBr): ꢀ = 3441.5 (s, ꢀ(COO–H)), 1625.6
(s, ꢀ(C O)), 1557.2 (m, ꢀ(C N, in Py)), 1436.6 (m, ꢀ(C C, in Py)), 1366.8 (s, ꢀ(C O)),
455.7 (w, ꢀ(Tb–O)), 405.3 (w, ꢀ(Tb-O)).
Diffraction intensities for the complex were collected at 20 ◦C on a Siemens R3m
diffractometer with the v-scan technique. Lorentz-polarization and absorption cor-
rections were applied [10]. The structures were solved with the direct method and
all non-hydrogen atoms, and the organic hydrogen atoms were generated geomet-
rically (C–H 0.96 Å), the aqua hydrogen atoms were located from difference maps
and refined with isotropic displacement factors. Analytical expressions of neutral-
atom scattering factors were employed, and anomalous dispersion corrections were
incorporated [13]. Both the crystal data and the data details [14] were collected and
refined for the complex, and drawings were produced with SHELXTL [15].
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6−
2.3. Labeling of BSA with Eu(PTA)3 and Tb(PTA)3
Fig. 3. UV absorption spectra for (a) Eu(PTA)36−, (b) Tb(PTA)3 and (c) H3PTA in
aqueous solutions (5.0 × 10−5 mol L−1).
6−
Na6Eu(PTA)3, Na6Tb(PTA)3 and N-hydroxysuccinimide (NHS) were dried in vac-
uum for 24 h in a desiccator in the presence of P2O5. Then, 0.7 mg of NHS and 1 mg
of 1-ethyl-3−(3−dimethylaminopropyl) carbodiimide hydrochloride (EDC) were
added to the solution of 5 mg of Na6Eu(PTA)3 in 800 L of ethanol and 200 L water,
and the solution was shaked for 24 h at 37 ◦C in the dark. The ethanol was removed
by vacuum evaporation. The product was directly used for BSA labelling without
molecules. As shown in Fig. 2, The Tb3+ atom coordinated in a
tri-capped trigonal prism geometry with three nitrogen atoms [Tb
(1)–N (1) 2.531 (7) Å] in pyridine rings and six carboxylate oxygen
atoms [Tb (1)–O (1) 2.425 (4) Å] from three different PTA3− ligands.
The coordination number of the central Tb3+ atom is 9, reach-
ing its coordination-saturated state. Therefore, the lattice water
molecules only form donor hydrogen bonds with the carboxylate
oxygen atoms. Every lanthanide ion is wrapped thoroughly by three
PTA3− ligands, and this kind of structure may be beneficial to good
luminescence properties and long lifetime.
6−
further purification. Since Ln(PTA)3 (Ln = Eu or Tb) and NHS are equimolar, and
6−
the three non-coordinated carboxyl groups from Ln(PTA)3 (Ln = Eu or Tb) have
equal chemical activity, it was proposed that only one carboxyl group of the lan-
thanide complex is esterified in the intermediate compound, NHS-Ln(PTA)3 (Ln = Eu
or Tb). NHS-Ln(PTA)3 (Ln = Eu or Tb) was added to 1 mg BSA in 100 L 50 mmol L−1
carbonate buffer of pH 9.6. After shaking for 4 h at 37 ◦C in the dark, the solution was
dialyzed three times against 4 L of 0.01 mol L−1 PBS buffer at 4 ◦C for 48 h.
2.4. Physical measurements
Elemental analysis for the samples was carried out with an Elementar vario
EL elemental analyzer. UV absorption spectra were recorded on Hitachi U-2900
UV–vis recording spectrophotometer in the region of 200–400 nm. IR spectra in the
region of 4000–400 cm−1 were recorded on a Bruker infrared spectrophotometer
by conventional KBr method. The 1H NMR spectra were recorded on a USA Var-
ian UNITYINOVA-500 spectrometer (500 MHz). The excitation and emission spectra
for the complexes were measured on a Shimadzu RF-5301PC spectrofluophotome-
ter at room temperature. The emission spectra of BSA labelled the complexes were
recorded on a Hitachi F-7000 spectrofluophotometer at room temperature.
3.2. UV absorption spectra
UV absorption spectra for dilute H3PTA and Ln(PTA)36− (Ln = Eu
and Tb) aqueous solutions were determined at the same conditions,
the maximum absorption wavelengths and molecular absorption
coefficients are given in Table 1. The absorptions for Ln(PTA)3
(Ln = Eu and Tb) dilute solutions are stronger than that of H3PTA
6−
ligand (Fig. 3), which is attributed to the metal coordination effect.
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3. Results and discussion
The absorption spectra for Ln(PTA)3
(Ln = Eu and Tb) aqueous
solutions mainly consist of one strong absorption band at 281 nm,
which is due to → * absorption from the PTA3− ligand. The
lanthanide complexes and the organic ligand showed the same
maximum absorption wavelength at 281 nm, which was attributed
to that the coordination oxygen atoms from the ligands have no p
3.1. Crystal structure
The crystal structure of Na6[Ln(PTA)3]·16.5H2O consists
of mononuclear Na6[Ln(PTA)3] molecules and lattice water