F. Tian et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 179 (2017) 194–200
195
good specificity, high recognition ability and strong choice ability. The
2.2. Material
Eu(III) complexes with some aminopolycarboxylic acid ligands can be
used as fundamental fluorescence probes due to the obvious photo-re-
sponsive property. In order to make these fundamental fluorescence
probes have better recognition ability and strong choice ability, it is nec-
essary to pointedly modify the dtpa ligand by using some targeting
compounds to detected object.
Diethylenetriamine pentaacetic acid (dtpa) and guanine (Gu) (A.R.,
Beijing SHLHT Science & Trade Co., Ltd., China) were purchased and
used to synthesize the dtpa-bis(guanine) ligand. Adenine (Ad), hypo-
xanthine (Hy), xanthine (Xa) and uric acid (Ur) (A.R., Beijing SHLHT Sci-
ence & Trade Co., Ltd., China) were purchased and used to be target
client. Eu(NO3)3·6H2O (99.999%, Yuelong Rare Earth Co., Ltd., China)
was obtained to prepare the EuIII-dtpa-bis(guanine) complex as fluores-
cent probe. Anhydrous acetic anhydride and DMF (analytical purity,
Shenyang Chemical Reagent Plant, China) were purchased and used as
solvent. Pyridine and Triethylamine (analytical purity, Shenyang Chem-
ical Reagent Plant, China) were obtained and used as acid-binding-
agent. Tris (hydroxyl-methyl) aminomethane (Tris) and HCl (analytical
purity, Shenyang Chemical Reagent Plant, China) were used to prepare
the Tris-HCl (pH = 7.4 and [Tris-HCl] = 50 mmol L−1) buffer solution
in order to maintain the ionic strength and adjust the solution acidity.
In this paper, the structure of dtpa was modified by guanine and
formed a new ligand dtpa-bis(guanine). The Eu3+ ion can form a
nine-coordinate EuIII-dtpa-bis(guanine) complex with the new ligand
dtpa-bis(guanine) [35–37]. In the EuIII-dtpa-bis(guanine) complex as
fluorescence people, two guanines at the two ends (up and down),
like the two arms. When the EuIII-dtpa-bis(guanine) encounters the ad-
enine, whose molecular structure and chemical composition are similar
to that of guanine, these two arms (guanines) can capture the adenine
tightly. Because of the change of ligands from water to adenine
forming the new coordination bond, the fluorescence intensity of
EuIII-dtpa-bis(guanine) was changed obviously. Due to the highly
chemical similarity, the EuIII-dtpa-bis(guanine) complex can com-
bine with adenine exclusively. Thus, as adenine fluorescence probe
the EuIII-dtpa-bis(guanine) complex not only have the characteris-
tics of high sensitivity, high accuracy and low detection concentra-
tion, but also the advantages of strong targeting, high recognition
ability and choice ability. Subsequently, by means of fluorescence
spectrum, it was found that the fluorescence emission intensity
was significantly enhanced, when the adenine was introduced to
the EuIII-dtpa-bis(guanine) solution. While the other base com-
pounds, such as guanine, xanthine, hypoxanthine and uric acid,
were added to the EuIII-dtpa-bis(guanine) solution, the fluorescence
emission intensity was hardly changed. Meanwhile, in this work, the
effects and interferences of guanine, hypoxanthine, xanthine and
uric acid were also studied. It was found that the EuIII-dtpa-
bis(guanine) complex as fluorescence probe can detect adenine
with specificity and not be affected by other base compounds. There-
fore, the sensitivity and specificity of the EuIII-dtpa-bis(guanine)
complex in the adenine detection could be confirmed.
2.3. Synthesis of Diethylenetriamine Pentaacetic Acid Dianhydride (dtpaa)
It must be pointed out that the diethylenetriamine pentaacetic acid
dianhydride (dtpaa) is demand for the start of all experiments and its
synthesis procedure is described in Scheme 1. Diethylenetriamine
pentaacetic acid (dtpa) (7.80 g, 0.02 mmol) was dissolved in acetic an-
hydride (8.00 mL, 0.08 mmol) and pyridine (10.00 mL, 0.12 mmol) as
acid-binding agent under anhydrous condition. The mixed solution
was stirred for one day under heat-refluxing at 65 °C. Afterwards, the
reaction mixture was cooled down to room temperature, and the sol-
vent was removed by reduced pressure filter. The residue washed
twice by acetic anhydride and anhydrous diethyl ether. Finally, the res-
idue was dried to give 6.50 g white powder under vacuum (52 kpa) at
80 °C with yield of 83%. FT-IR (KBr, cm−1): 1642.41, 1772.10, 1821.08,
2341.42, 2820.47 and 2979.80. 1H NMR (500 MHz, DMSO): d = 2.593
(t, 4H), 2.748 (t, 4H), 3.300 (s, 2H), 3.705 (s, 8H) and 11.013 (s, 1H).
2.4. Synthesis of dtpa-bis(guanine)
Dtpa-bis(guanine) ligand was synthesized by the aminolysis reac-
tion between dtpaa and guanine and the synthesis procedure is shown
in Scheme 1. Dtpaa (1.96 g, 55 mmol) was dissolved in DMF (50 mL)
and Trithylamine as base under anhydrous condition. Subsequently, the
guanine was added to the mixed solution slowly. The mixed solution
was stirred 24 h under heat-refluxing at 100 °C. The mixture was then
cooled down to room temperature. After the solvent was removed by vac-
uum filter, the white solid was obtained. The white solid was evaporated
to dryness under vacuum (52 kpa) at 50 °C to give 2.30 g white powdery
solid with yield of 92%. FT-IR (KBr, cm−1): 1668, 1710, 2691, 2854, 2908,
3119 and 3321. 1H NMR (500 MHz, DMSO): d = 2.010 (m, 2H), 2.717 (s,
2H), 2.807 (d, 2H), 2.460 (t, 8H), 3.254 (s, 4H), 3.301 (s, 6H), 7.503 (d, 2H),
7.973 (s, 2H) 8.010 (s, 2H) and 11.012 (s, 3H).
2. Experimental
2.1. Apparatus
Fourier Transform-Infrared (FT-IR) spectra were taken in KBr disks
on a Nicolet 5700 FTIR spectrometer. NMR spectra were conducted
with an Agilent Technologies Plus-400MR spectrometer with DMSO-
d6, D2O and NaOH-d1 as the solvent and tetramethysilane (TMS) as in-
ternal standard. Fluorescence determination experiments were carried
out by fluorophotometer (Cary 300, Varian Company, USA) and the
UV–vis absorption spectra were recorded with an UV–Vis spectropho-
tometer (Cary 50, Varian Company, USA).
Scheme. 1. The structure and synthetic route of the dtpa-bis(guanine) ligands.