An azophenol-based chromogenic pyrophosphate sensor in water

Article abstract of DOI:10.1021/ja034689u

A new azophenol-based colorimetric sensor shows a selective detection for pyrophosphate in aqueous solution. Copyright

Full text of DOI:10.1021/ja034689u

Published on Web 06/06/2003
An Azophenol-based Chromogenic Pyrophosphate Sensor in Water
Dong Hoon Lee,† Ja Hyun Im,† Seung Uk Son,† Young Keun Chung,† and Jong-In Hong*,†,‡
Department of Chemistry, College of Natural Sciences, Seoul National UniVersity, Seoul 151-747, Korea, and
Center for Molecular Design and Synthesis, KAIST, Daejon 305-701, Korea
Received February 17, 2003; E-mail: jihong@plaza.snu.ac.kr
Scheme 1. Synthetic Strategy for Sensor 1‚2Zna
The development of receptors and sensors for biologically
important anions is emerging as a research area of great importance.1
Pyrophosphate anion (PPi), in particular, participates in several
bioenergetic and metabolic processes.2,3 Therefore, the detection
of PPi has been the main focus of several research groups. While
PPi analysis such as ion chromatography remains important, there
is mounting incentive to find alternative means of analysis, including
those based on the use of selective chemosensors.1b,4 Particularly
useful would be systems that can recognize PPi in an aqueous
a Conditions: (a) i. aq. NaOH, MeOH, rt, ii. p-nitroaniline, NaNO2, aq.
HCl, acetone, 0 °C. (b) Zn(NO3)2, H2O, MeOH.
solution and signal its presence via an optical signal. Until now,
very few examples of optical sensors for PPi in aqueous solution
have been reported.5,6 In this communication, we present a new
chromogenic PPi sensor based on an azophenol-Dpa (bis(2-
pyridylmethyl)amine) system, which shows a high sensitivity and
selectivity for PPi over other anions in aqueous solvent of a wide
pH range.7
A color-inducing p-nitrophenylazo group can be easily introduced
on the para position of the phenolic moiety of 2,6-bis[(bis(2-
pyridylmethyl)amino)methyl]phenol (H-bpp).8 Zn2+ complexation
with bis(2-pyridylmethyl)amine (Dpa) moiety generates an anion-
binding site through the formation of a well-known phenoxo-bridged
dinuclear metal complex (Scheme 1).9 Compound 1 was obtained
in an overall yield of 38% from 2,6-dimethylphenol.10a Sensor 1‚
2Zn, the dinuclear Zn2+ complex of compound 1, is easily formed
by the addition of a methanolic solution of 1 to an aqueous solution
of 2 equiv of Zn(NO3)2.
7.4) at 25 °C.11 These results suggest that sensor 1‚2Zn has high
selectivity for PPi over other anions.
Similar results are obtained in an aqueous solvent of 100 mM
HEPES buffer (pH 7.4) at 25 °C. The addition of PPi also makes
a color change from yellow (λmax ) 417 nm) to red (λmax ) 463
nm). In 100 mM HEPES buffer, sensor 1‚2Zn shows the reduced
affinity for PPi (Ka ) (8.3 ( 1.8) × 107 M-1), compared with 10
mM HEPES buffer system.
The novel binding mode for PPi-1‚2Zn is illustrated in Figure
2, which was unambiguously elucidated by an X-ray analysis. The
X-ray structure of the complex reveals that the two sets of oxygen
anions on each P of PPi bind to the dinuclear zinc complex by
bridging the two metal ions to give rise to the two hexacoordinated
Zn2+ ions in 1‚2Zn.12a The binding mode for HPO42--1‚2Zn
should be the same as that of HPO42--H-bpp.9c-f Despite this,
First, the effect of anions (sodium salts) on the absorption
spectrum of 1‚2Zn (30 µM) was examined in an aqueous solution
of 10 mM HEPES buffer (pH 7.4) (HEPES ) 2-[4-(2-hydroxy-
ethyl)-1-piperazinyl]ethanesulfonic acid) at 25 °C (Figure 1). In
the absence of an anion guest, the absorption spectrum of sensor
1‚2Zn is characterized by an intense band centered at 417 nm.
Sensor 1‚2Zn does not show any obvious spectral change upon
2-
HPO4 does not make a large UV-vis absorption change upon
complexation with 1‚2Zn. Instead, only PPi induces the selective
red-shift of λmax of 1‚2Zn because weakening the bond between
p-nitrophenylazo phenolate oxygen and Zn2+ induces more negative
charge character on the phenolate oxygen and thus the bathochromic
shift of λmax of 1‚2Zn occurs. As revealed by previous works,9c-f
2-
HPO4 does not coordinate in tetradentate fashion as PPi does.
-
addition of H2PO4 as well as other monovalent anions such as
2-
This explains why HPO4 does not alter λmax of 1‚2Zn. Stronger
CH3CO2-, F-, HCO3-, Cl- even up to an excess of 100 equiv.
Moreover, no detectable spectral change is observed upon addition
coordination of PPi to dinuclear zinc complex enables sensor 1‚
2-
2Zn to show color changes and higher selectivity over HPO4
2-
of dibasic anions HPO4 and citrate. However, the addition of
(Figure 3). Hexacoordination of Zn2+ ions is clearly reflected in
the extremely high Ka of PPi-1‚2Zn in water (Ka ) 6.6 × 108
M-1). It is worthwhile noting that PPi binds 1‚2Zn over 103-fold
4-
P2O7 (PPi) causes bathochromic shifts from 417 nm (λmax) to
465 nm. It is remarkable that the degree of absorption changes is
no longer affected by the addition of more than 1 equiv of PPi. As
expected from the UV-vis absorption data, color change occurs
by the addition of PPi to the solution of 1‚2Zn from yellow to red.
Job’s plot for the binding between 1‚2Zn and PPi shows a 1:1
stoichiometry (inset of Figure 1a).11 Even in the presence of 10
equiv of HPO42-, sensor 1‚2Zn shows a similar detection ability
for PPi. It is surprising that the apparent association constant (Ka)
was determined as (6.6 ( 1.2) × 108 M-1 for PPi-1‚2Zn by a
standard algorithm for competitive binding in the presence of excess
more tightly than HPO4 does.9e
2-
A control sensor, mononuclear 2‚Zn does not show λmax and color
changes upon the addtion of PPi. This result means that the
cooperative action of two Zn2+-Dpa is needed for the selective
sensing of PPi.5d Finally, to check the working pH, the effect of
the pH value of the medium on the PPi sensing was checked. UV-
vis absorption changes shown in Figure 1b occur in the wide pH
range of 6.5-8.3 with a similar tendency.10b This result shows that
even if the external pH is disturbed, sensor 1‚2Zn can still detect
PPi.
2-
HPO4 in a pure aqueous solvent of 10 mM HEPES buffer (pH
In summary, we have developed a new azophenol-based colo-
rimetric sensor, which shows a selective coloration for PPi with
† Seoul National University.
‡ Center for Molecular Design and Synthesis, KAIST.
9
7752
J. AM. CHEM. SOC. 2003, 125, 7752-7753
10.1021/ja034689u CCC: $25.00 © 2003 American Chemical Society

C O M M U N I C A T I O N S
Figure 3. Color changes of sensor 1‚2Zn in 10 mM aqueous HEPES buffer
solution (pH 7.4), [1‚2Zn] ) 60 µM, [anion] ) 60 µM; from left to right:
no anion, PPi, citrate, HPO42-, H2PO4-, acetate, F-.
00137-0) is gratefully acknowledged. D.H.L., J.H.I., and S.U.S.
thank the Ministry of Education for the BK 21 fellowship.
Supporting Information Available: Experimental procedure and
selected spectral data for compounds 1, 2, 1‚2Zn, and 2‚Zn, UV-vis
absorption data (PDF). X-ray crystallography data (CIF). This material
is available free of charge via the Internet at http://pubs.acs.org.
References
(1) (a) Brzo´zka, Z. In ComprehensiVe Supramolecular Chemistry; Atwood,
J. L., Davies, J. E. D., MacNicol, D. D., Vo¨gtle, F., Suslick, K, S., Eds.;
Pergamon: Oxford, 1996; pp 187-212 (b) Chemosensors of Ion and
Molecular Recognition; Desvergne, J.-P., Czarnik, A. W., Eds.; Kluwer:
Dordrecht, 1997; Vol 492. (c) Schmidtchen, F. P.; Berger, M. Chem. ReV.
1997, 97, 1609-1646. (d) Beer, P. D. Acc. Chem. Res. 1998, 31, 71-80.
(e) Supramolecular Chemistry for Anions; Binachi, K., Bowman-James,
K., Garcia-Espana, E., Eds.; New York, 1997. (f) Lehn, J.-M. Supramo-
lecular Chemistry, Concepts and PerspectiVes; VCH: Weinheim, 1995.
(2) Limpcombe, W. N.; Stra¨ter, N. Chem. ReV. 1996, 96, 2375-2434.
(3) (a) McCarty, D. J. Arthritis Rheum. 1976, 19, 275-285 (b) Caswell, A.;
Guilland-Cumming, D. F.; Hearn, P. R.; McGuire, M. K.; Russell, R. G.
Ann. Rheum. Dis. 1983, 42 (suppl 1), 27-37. (c) Doherty, M. Ann. Rheum.
Dis. 1983, 42(suppl 1), 38-44.
(4) (a) Kubo, Y.; Maeda, S.; Tokita, S.; Kubo, M. Nature. 1996, 382, 522-
523. (b) Niikura, K.; Metzger, A.; Anslyn, E. V. J. Am. Chem. Soc. 1998,
120, 8533-8534. (c) Lavigene, J. J.; Anslyn, E. V. Angew. Chem., Int.
Ed. 1999, 38, 3666-3669. (d) Fabbrizzi, L.; Licchelli, M.; Rabioli, G.;
Taglietti, A. Coord. Chem. ReV. 2000, 205, 85-108. (e) Zhong, Z.; Anslyn,
E. V. J. Am. Chem. Soc. 2002, 124, 9014-9015.
(5) PPi sensors in aqueous solution: (a) Vance, D. H.; Czarnik, A. W. J.
Am. Chem. Soc. 1994, 116, 9397-9398. (b) Czarnik, A. W. Acc. Chem.
Res. 1994, 27, 302-308. (c) Mizukami, S.; Nagano, T.; Urano, Y.; Odani,
A.; Kikuchi, K. J. Am. Chem. Soc. 2002, 124, 3920-3925. (d) Fabbrizzi,
L.; Marcotte, N.; Stomeo, F.; Taglietti, A. Angew. Chem., Int. Ed. 2002,
41, 3811-3814.
(6) PPi sensors in MeOH and aqueous CH3CN: (a) Nishizawa, S.; Kato, Y.;
Teramae, N. J. Am. Chem. Soc. 1999, 121, 9463-9464. (b) Anzenbacher,
P. Jr.; Jurs´ıkova´, K.; Sessler, J. L. J. Am. Chem. Soc. 2000, 121, 9350-
9351.
Figure 1. (a) Absorbance change of sensor 1‚2Zn (30 µM) upon addition
of PPi (Sodium salt): [PPi] ) 0, 2, 4, 6, 8, 11, 14, 17, 20, 23, 26, 29, 32
µM. The spectra were measured in an aqueous solvent of 10 mM HEPES
buffer (pH 7.4) at 25 °C. (Inset) the Job’s plot examined between 1‚2Zn
and PPi. (b) UV-vis spectra of sensor 1‚2Zn (30 µM) in an aqueous solvent
10 mM HEPES buffer (pH 7.4) at 25 °C in the presence of various anions
(30 µM).
(7) To the best of our knowledge, our system is the first colorimetric sensor
for PPi in water that holds several advantages when compared to previous
systems for the following reasons. Our system does not have any
competing simple inorganic anions, as measured by UV-vis studies, unlike
the Kikuchi system5d which also responds to citrate anions. Furthermore,
our system operates in a wide pH range, unlike the previous systems.5a,d
(8) (a) Lee, D. H.; Lee, K. H.; Hong, J.-I. Org. Lett. 2001, 3, 5-8. (b) Lee,
D. H.; Lee, H. Y.; Lee, K. H.; Hong, J.-I. Chem. Commun. 2001, 1189-
1189. (c) Lee, K. H.; Lee, H. Y.; Lee, D. H.; Hong, J.-I. Tetrahedron
Lett. 2001, 42, 5447-5449.
(9) (a) Suzuki, M.; Kanatomi, H.; Murase, I. Chem. Lett. 1981, 1745-1748.
(b) Munch, B. P.; Bradley, F. C.; Boyle, P. D.; Papaefthymiou, V.; Que,
L., Jr. J. Am. Chem. Soc. 1987, 109, 7993-8003. (c) Jin, S. S.; Sung, N.
D.; Hynes, R. C.; Chin, J. Inorg. Chem. 1996, 35, 7472-7473. (d) Torelli,
S.; Belle, C.; Gautier-Luneau, I.; Pierre, J. L.; Saint-Aman, E.; Latour, J.
M.; Le Page, L.; Luneau, D. Inorg. Chem. 2000, 39, 3526-3536. (e) Han,
M. S.; Kim, D. H. Angew. Chem., Int. Ed. 2002, 41, 3809-3811. (f)
Molenveld, P.; Engbersen, J. F. J.; Reinhoudt, D. N. Chem. Soc. ReV.
2000, 29, 75-86.
Figure 2. (Left) Binding mode. (Right) PPi-1‚2Zn with the partial atom
labeling scheme (30% probability level).12
(10) See the Supporting Information for: (a) detailed syntheses (b) pH
high affinity in aqueous solution in a wide pH range.13 This system
shows good selectivity for PPi even in the presence of a strong
competitor such as HPO42-. In addition, the novel binding mode
for PPi-1‚2Zn was unambiguously confirmed by an X-ray analysis.
For biochemical and analytical applications, work is directed toward
the development of fluorescent sensors capable of detecting PPi at
lower concentrations.
dependence of sensor 1‚2Zn.
(11) Binding Constants, The Measurement of Molecular Complex Stability;
Conners, K. A., Ed.; John Wiley and Sons: New York, 1987; pp 175-
183.
(12) (a) Although refinement of the structure has been unsatisfactory (R1 )
0.14) due to the disorder of solvents and cation molecule, it clearly shows
the connectivity of the complex that we are interested in. (b) Some atoms
are omitted for clarity
(13) Naked eye detection for PPi is optimized under the condition of [1‚2Zn]
) 60 µM.
Acknowledgment. Support of this work by a grant from the
Basic Research Program of the KOSEF (Grant No. R02-2002-000-
JA034689U
9
J. AM. CHEM. SOC. VOL. 125, NO. 26, 2003 7753