A colorimetric sensor for the recognition of biologically important anions

Article abstract of DOI:10.1007/s10847-010-9815-3

A colorimetric anion sensor 1 based on 3-phthaloyl-N-4-nitrophenylhydrozone was synthesized and characterized. The binding ability evaluated by UV-vis experiment reveals that 1 can selectively recognize fluoride. Further insights into the nature of interactions between sensor 1 and anions were investigated by H NMR titrations experiments. In addition, the color changes induced by fluoride can provide a way of detection by 'naked-eye'.

Full text of DOI:10.1007/s10847-010-9815-3

J Incl Phenom Macrocycl Chem (2011) 69:69–73
DOI 10.1007/s10847-010-9815-3
ORIGINAL ARTICLE
A colorimetric sensor for the recognition of biologically important
anions
•
•
•
Weiwei Huang Xudong Yu Hai Lin
Huakuan Lin
Received: 5 July 2008 / Accepted: 27 May 2010 / Published online: 11 June 2010
Ó Springer Science+Business Media B.V. 2010
Abstract A colorimetric anion sensor 1 based on
3-phthaloyl-N-4-nitrophenylhydrozone was synthesized
and characterized. The binding ability evaluated by UV–vis
experiment reveals that 1 can selectively recognize fluo-
ride. Further insights into the nature of interactions
between sensor 1 and anions were investigated by H NMR
titrations experiments. In addition, the color changes
induced by fluoride can provide a way of detection by
‘naked-eye’.
and acetate play important roles in biological, industrial,
and environmental process [6–8]. For example, fluoride is
essential in a variety of biological processes such as pre-
venting children’s dental caries and treating osteoporosis
[9]. Acetate plays an important role in enzymes and anti-
bodies [10], because carboxylates are critical components
in numerous metabolic processes [11]. Thus, there is a need
to develop receptors which can selectively recognize bio-
logically important fluoride ion or acetate ion.
It is well-known that amides [7], (thio)ureas [12], and
ammonium [13] derivatives are particularly effective in the
reaction with anions through the formation of hydrogen
bond between the active N–H and anions. Furthermore,
with the strong inducement of the anions, proton transfer
often takes place in the host–anions reaction [14]. In this
paper, we prepared a highly selective sensor for fluoride
ion with dramatic color changes from colorless to red. On
the contrary, no detectable color changes were observed
when adding AcO-, H2PO4-, Cl-, Br- and I- ions, even in
a large amount to the solution. These results suggest that
sensor 1 can distinguish F- from many other anions.
Keywords Anion recognition ꢀ Fluoride ꢀ Acetate ꢀ
Sensor
Introduction
The design and synthesis of efficient sensors that can rec-
ognize anions selectively through electrochemical or opti-
cal responses is an increasingly important field in
supramolecular chemistry in recent years [1–5]. Colori-
metric sensor is more noticeable for it can detect anions by
naked eye with reliable calibration stability. Anions such as
fluoride, chloride, bromide, iodide, dihydrogenphosphate
Experimental
Materials
All reagents for synthesis obtained commercially were
used without further purification. In the titration experi-
ments, all the anions were added in the form of tetrabu-
tylammonium (TBA) salts, which were purchased from
Sigma-Aldrich Chemical, stored in a vacuum desiccator
containing self-indicating silica and dried fully before
using. DMSO was dried with CaH2 and then distilled in
reduced pressure.
W. Huang ꢀ X. Yu ꢀ H. Lin (&)
Department of Chemistry, Nankai University, Tianjin 300071,
People’s Republic of China
e-mail: hklin@nankai.edu.cn
H. Lin
Key Laboratory of Functional Polymer Materials
of Ministry of Education, Nankai University, Tianjin 300071,
People’s Republic of China
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J Incl Phenom Macrocycl Chem (2011) 69:69–73
General method
washed with saturated sodium chloride solution for three
times and then recrystallized by ethanol. H NMR (400 Hz,
CDCl3); 5.88 (2H, s), 7.27 (1H, s), 7.67 (2H, d, J = 8 Hz),
7.74 (1H, s), 8.20 (2H, d, J = 8 Hz).
H NMR spectra were recorded on a Varian UNITY Plus-
400 MHz Spectrometer at the Key Laboratory of Func-
tional Polymer Materials of Ministry of Education, Nankai
University. UV–vis spectroscopy titrations were performed
on a Shimadzu UV2450 Spectrophotometer at 298 K.
Elemental analysis for C, H, and N were carried out on a
PerkinElmer 240C element analyzer at the Institute of
Elemento-Organic Chemistry, Nankai University.
Preparation of 1,3-phthaloyl-N-4-nitrophenylhydrozone
A solution of 4-nitrophenylhydrozone (0.5 mmol) in dry
CHCl3 was added dropwise to the mixture of m-phthaloyl
chloride (0.5 mmol), 1 mL triethylamine and 20 mL CHCl3
over a period of 10 min. After continuous stirring for about
24 h, the mixture was filtered and the precipitate was re-
crystallized by CHCl3. H NMR (400 Hz, DMSO-d6): 7.75
(1H, t), 8.01–8.04 (4H, m), 8.17 (2H, d, J = 7.2 Hz), 8.31–
8.36 (4H, m), 8.53 (1H, s), 8.62 (2H, d, J = 7.2 Hz), 12.37
(2H, s). Elemental analysis calcd. for C22H16N6O6: C, 57.39;
N, 18.25; H 3.5. Found: C, 57.42; N, 18.24; H, 3.5.
A series of DMSO solutions having same host concen-
tration and different anion concentrations were prepared,
respectively. The affinity constants Ks were obtained by the
determination of absorption of the series of solutions and
analysis of obtained absorption values with non-linear least
square calculation method for data fitting.
Synthesis
Preparation of m-phthaloyl chloride (Scheme 1)
Results and discussion
0.33 g (2.0 mmol) m-phthalic acid, 5 mL SOCl2 chloride
(60 mmol), 3 drops of DMF were refluxed in CHCl3 for
8 h. Then SOCl2 and CHCl3 were evaporated and the
residue were dried in vacuum, faint yellow solid was
acquired, m.p. 41–42 °C. It is directly used for further
reaction without purification.
Colorimetric experiments
In the naked-eye colorimetric experiments (see Fig. 1),
sensor 1 underwent a dramatic color change from almost
colorless to red upon the addition of F-, while there were
no noticeable color changes when adding other anions such
as AcO-, H2PO4-, Cl-, Br-, I-. It clearly suggested that 1
showed the selective recognition for F-.
Preparation of 4-nitrophenylhydrozone
4-Nitrobenzaldehyde (0.33 mmol) in 20 mL methanol was
added dropwise to rapidly stirring anhydrous hydrazine
(2.0 mmol, 64 g). After stirring, the mixture was refluxed
for 3 h. After cooling, the acquired yellow precipitate was
UV–vis titrations
In order to study the binding selectivity of sensor 1, UV–
vis experiments of sensor 1 with different anions in the
form of tetrabutylammonium salts were performed in
DMSO at 298.2 0.1 K. Obviously spectra changes were
observed after adding F- to the solution (see Fig. 2).
However, no detectable optical responses were observed
when adding AcO-, H2PO4-, Cl-, Br- and I- ions, even in
a large amount to the solution. These results suggest that
sensor 1 can distinguish F- from many other anions.
NH2
Cl
Cl
CHO
NO2
N
O
O
NH2NH2
Methanol, 3 h
CH3Cl, 24 h
NO2
NO2
O2N
O
O
N
Fig. 1 Color changes observed for sensor 1 in DMSO solution
(2 9 10-5 M) upon addition anions as TBA salts: from left to right: 1
only, 1 ? F-, 1 ? AcO-, 1 ? H2PO4-, 1 ? Cl-, 1 ? Br- and
1 ? I-
N
N
N
H
H
Scheme 1 General synthetic routes to the target sensor 1
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J Incl Phenom Macrocycl Chem (2011) 69:69–73
71
1.2
1.0
0.8
0.6
0.40
0.38
0.36
0.34
0.32
0.30
0.28
0.26
0.24
0.22
2.0
1.5
1.0
0.5
0.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0.4
-
1+F-
[host]/([host]+[AcO ])
100 equiv
0 equiv
1+AcO-
1,1+ H2PO4-, C1-, Br-, I-
0.2
0.0
300
400
500
600
700
Wavelength
300
400
500
600
700
Wavelength
Fig. 2 UV–vis spectra of 1 (2 9 10-5 M) in the presence of
10 equiv. of F-, or AcO-, H2PO4-, Cl-, Br- and I-
Fig. 4 Evolution of the UV–vis spectrum of sensor
1
(2.0 9 10-5 M) during the titration with AcO- in DMSO. Inset
Job’s plot for complexation of sensor 1 with AcO- determined by
1.0
0.65
UV–vis in DMSO, [1] ? [anion] = 2.0 9 10-3
M
0.60
0.55
0.50
0.45
FHF-
(f)
0.5
0.40
0.0
0.2
0.4
0.6
0.8
1.0
(e)
(d)
-
[host]/([host]+[F ])
25 equiv
0 equiv
(c)
(b)
(a)
0.0
300
400
500
600
700
Wavelength
Fig. 3 Evolution of the UV–vis spectrum of sensor
1
(2.0 9 10-5 M) during the titration with F- in DMSO. Inset Job’s
plot for complexation of sensor 1 with F- determined by UV–vis in
16
15
14
13
12
11
10
9
8
7
ppm
DMSO, [1] ? [anion] = 2.0 9 10-3
M
Fig. 5 Partial H NMR spectra of 1 (1.0 9 10-2 M) in DMSO-d6
upon the addition of F-. (a) 0 equiv.; (b) 0.2 equiv.; (c) 1 equiv.; (d)
3 equiv.; (e) 5 equiv.
Then to explore more about the applicability of the
sensor 1 for fluoride, Fig. 3 shows the UV–vis spectral
changes of 1 during the titration with fluoride ions. The
presence of fluoride resulted in an increasing of intensity of
the absorbance at 495 nm gradually and the centered bands
of sensor 1 at 255 nm developed, accompanied significant
color changes from colorless to red. The presence of ace-
tate ion has induced similar changes in UV–vis spectrum
(see Fig. 4). However, other anions including Cl-, Br-, I-,
H2PO4- did not cause noticeable spectral changes or color
changes, even in the presence of a large amount of them.
sensor 1 and anions. From Fig. 5, after the addition of
fluoride anion, the signal of –NH at 12.36 ppm gradually
broadened and disappeared, a new broad resonance at 15.
10 ppm appeared clearly, which was ascribed to the FHF-
dimer [15, 16] and it indicated the deprotonation of Ha (see
Fig. 5). H NMR titrations suggested that sensor 1 formed
hydrogen bonds with F- at first, then as increasing the
concentration of F-, the sensor 1 displayed the complete
deprotonation eventually.
The interaction of sensor 1 with AcO- was also studied
(see Fig. 6). Upon the addition of 5 equiv. of AcO-, the –
NH had a down shift from 12.36 to 12.55 ppm, which
indicated that a classic hydrogen bonding formed between
1 and AcO-.
H NMR titrations
H NMR titrations carried out in DMSO-d6 give some
creditable evidence for the complex system formed by
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J Incl Phenom Macrocycl Chem (2011) 69:69–73
The affinity constants of sensor 1 for the studied anionic
species are calculated and listed in the Table 1 below.
Discussion
(a)
(b)
As clearly shown in Table 1, the order of binding affinity of
-
1 with anions in DMSO is F- [ AcO- ꢃ H2PO4
* Cl- * Br- * I-. The recognition ability of sensor 1
for F- was the most remarkable. Two main reasons for
preferring F- were that fluoride has a relatively strong
basicity and its shape is more complemented with two –NH
of sensor 1 (Scheme 2).
16
14
12
10
8
ppm
Fig. 6 Partial H NMR spectra of 1 (1.0 9 10-2 M) in DMSO-d6
upon the addition of ACO-. (a) 0 equiv.; (b) 10 equiv.
According to the results from UV–vis titrations and H
NMR titrations, the proposed mode for the host–guest
bonding in solution was depicted in Scheme 2. In the
structure, anions such as F- and AcO- combined sensor 1
via N–Hꢀꢀꢀ anion hydrogen bonds.
Table 1 Affinity constants of sensor 1 with anions in DMSO at
298.2 0.1 K
Anions (M-1
)
F-
AcO-
H2PO4 Cl- Br- I-
-
In our UV–vis titration studies, we found when the
concentration of sensor 1 is 2 9 10-5 M in DMSO, the
limit of [F-] detection (LOD) is 1 9 10-4 M before the
host–guest binding reaction reaching an equilibrium. So we
hope sensor 1 may be applied in detection of micro
amounts of fluoride ion.
log Kass
3.04 0.15 1.51 0.03 ND
ND ND ND
ND cannot determined
Determination of the binding constant
and stoichiometry
Compared with the previous research in literature [2],
the sensor 1 showed significant color changes upon addi-
tion of fluoride ion. The process of sensing can literally be
observed through the ‘naked-eye’ for the sharply color
changes from colorless to red.
Continuous variation method was used to determine the
stoichiometric ratios of the host and anion guest [17]. Job’s
plot [18, 19] of sensor 1 and F- in DMSO (see Fig. 3)
showed the maxima was at a molar fraction of 0.5. This
result indicated that the sensor 1 binded F- anion guest
with a 1:1 ratio. Similar results could also be obtained for
AcO- (see Fig. 4).
Conclusions
In summary, we have presented a colorimetric charge-neu-
tral sensor 1, which could recognize fluoride among the
anions investigated. The whole process can be observed by
the ‘naked-eye’, for its sharply color changes from colorless
to red. This outstanding property is also bolstered by UV–vis
and H NMR titrations experiments. It is expected to be
applied for detection of biologically important anions in real
life for its easy synthesis and highly selective sensing ability.
For a complex of 1:1 stoichiometry, the relation in Eq. 1
could be derived easily, where X is the absorption intensity,
and CH or CG is the concentration of the host or the anion
guest correspondingly [20].
X ¼ X0 þ ðXlim ꢁ X0ÞfCH þ CG þ 1=Kass ꢁ ½ðCH þ CG
2
1=2
þ 1=KassÞ ꢁ 4 CHCGꢂ g=2CH
ð1Þ
Scheme 2 The proposed 1-F-
binding mode
NO2
NO2
O2N
O2N
F-
O
O
O
O
N N
N N
N N
N N
H
H
H
F-H
NO2
excess F-
O2N
O
O
N N-
N- N
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J Incl Phenom Macrocycl Chem (2011) 69:69–73
73
Acknowledgment This project was supported by the National
Natural Science Foundation of China (20371028, 20671052).
charge neutral PET chemosensors. Org. Lett. 4, 2449–2452
(2002)
12. Kim, T.H., Swager, T.M.: A fluorescent self-amplifying wave-
length responsive sensory polymer for fluoride ion. Angew.
Chem. Int. Ed. 42, 4803–4806 (2003)
13. Copper, C.R., Spencer, N., James, T.D.: Selective fluorescence
detection of fluoride using boronic acids. Chem. Commun. 1365–
1366 (1998)
14. Huang, W.W., Lin, H., Cai, Z.S., Lin, H.K.: A novel anthracene-
based receptor: highly sensitive fluorescent and colorimetric
receptor for fluoride. Talanta 81, 967–971 (2010)
References
1. Martinez-Manez, R., Sancenon, F.: Chemodosimeters and 3D
inorganic functionalised hosts for the fluoro-chromogenic sensing
of anions. Coord. Chem. Rev. 250, 3081–3093 (2006)
2. Tzeng, B.C., Chen, Y.Y., Wu, C.C., Hu, C.C., Changa, Y.T.,
Chena, C.K.: Anion-recognition studies of a Re(I)-based square
containing the dipyridyl-amide ligand. New J. Chem. 31, 202–
209 (2007)
3. Gale, P.A., Garcia-Garrido, S.E., Garric, J.: Anion receptors
based on organic frameworks: highlights from 2005–2006. Chem.
Soc. Rev. 37, 151–190 (2008)
´
15. Descalzo, A.B., Rurack, K., Weisshoff, H., Martınez-Man˜ez, R.,
Marcos, M.D., Amoros, P., Hoffmann, K., Soto, J.: Rational
´
´
design of a chromo- and fluorogenic hybrid chemosensor material
for the detection of long-chain carboxylates. J. Am. Chem. Soc.
127, 184–200 (2005)
´
16. Boiocchi, M., Boca, L.D., Gomez, D.E., Fabbrizzi, L., Licchelli,
4. Wei, L.H., He, Y.B., Wu, J.L., Wu, X.J., Meng, L.Z., Yang, X.:
Two thiourea-based colorimetric sensors for anions: structure and
binding study. Supramol. Chem. 16, 561–567 (2004)
5. Gunnlaugsson, T., Glynn, M., Tocci, G.M., Kruger, P.E., Pfeffer,
F.M.: Anion recognition and sensing in organic and aqueous
media using luminescent and colorimetric sensors. Coord. Chem.
Rev. 250, 3094–3117 (2006)
6. Bianehi, B., Bowaman, J.K.: In: Garcia-Espana, E. (ed.) Supra-
molecular Chemistry of Anions. Wiley-VCH, New York (1997)
7. Martinez-Manez, R., Sancenon, F.: Fluorogenic and chromogenic
chemosensors and reagents for anions. Chem. Rev. 103, 4419–
4476 (2003)
8. Nguyen, B.T., Anslyn, E.V.: Indicator-displacement assays. Co-
ord. Chem. Rev. 250, 3118–3127 (2006)
9. Kim, S.K., Yoon, J.: A new fluorescent PET chemosensor for
fluoride ions. Chem. Commun. 7, 770–771 (2002)
10. Gale, P.A.: Anion and ion-pair receptor chemistry: highlights
from 2000 and 2001. Coord. Chem. Rev. 240, 191–221 (2003)
11. Gunnlaugsson, T., Davis, A.P., O’Brien, J.E., Glynn, M.: Fluo-
rescent sensing of pyrophosphate and bis-carboxylates with
M., Monzani, E.: Nature of urea-fluoride interaction: incipient
and definitive proton transfer. J. Am. Chem. Soc. 126, 16507–
16514 (2004)
17. Kim, J.S., Shon, O.J., Yang, S.H., Kim, J.Y., Kim, M.J.: Chro-
mogenic indoaniline armed-calix[4]azacrowns. J. Org. Chem. 67,
6514–6518 (2002)
18. Thangadural, T.D., Singh, N.J., Hwang, I.C., Lee, J.W., Chan-
dran, R.P., Kim, K.S.: Analytic approach for anion differentiation
using chromo-fluorogenic receptors. J. Org. Chem. 72, 5461–
5464 (2007)
19. Linn, M.M., Poncio, D.C., Machado, V.G.: An anionic chromo-
genic sensor based on the competition between the anion and a
merocyanine solvatochromic dye for calix[4]pyrrole as a receptor
site. Tetrahedron Lett. 48, 4547–4551 (2007)
20. Bourson, J., Pouget, J., Valeur, B.: Ion-responsive fluorescent
compounds. 4. Effect of cation binding on the photophysical
properties of a coumarin linked to monoaza- and diaza-crown
ethers. J. Phys. Chem. 97, 4552–4557 (1993)
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