A novel supermolecular tetrameric vanadate-selective colorimetric and "off-On" sensor with pyrene ligand

Article abstract of DOI:10.1021/ol200846a

Tris(2-((ethylimino)methyl)pyren-1-ol)amine (1) was synthesized and introduced as the first tetrameric vanadate fluorescence sensor, the entire binding of which was successfully accomplished in two steps with distinct colorimetric changes and "off-on" fluorescent enhancement.

Full text of DOI:10.1021/ol200846a

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ORGANIC
LETTERS
2011
Vol. 13, No. 10
2742–2745
A Novel Supermolecular Tetrameric
Vanadate-Selective Colorimetric and
“OffÀOn” Sensor with Pyrene Ligand
Ying Zhou,† Ji Young Jung,‡ Hye Ryeong Jeon,† Youngmee Kim,† Sung-Jin Kim,† and
Juyoung Yoon*,†,‡
Department of Chemistry and Nano Sciences and Department of Bioinspired Science
(WCU), Ewha Womans University, Seoul 120-750, Korea
jyoon@ewha.ac.kr
Received April 1, 2011
ABSTRACT
Tris(2-((ethylimino)methyl)pyren-1-ol)amine (1) was synthesized and introduced as the first tetrameric vanadate fluorescence sensor, the entire
binding of which was successfully accomplished in two steps with distinct colorimetric changes and “off-on” fluorescent enhancement.
The development of molecular recognition and sensing
systems for anions has received considerable attention in
recent years.1 In contrast to the sensing of pyrophosphate
or phosphate ions,1a,2 which has been an especially active
area of research because of their biological significance, the
recognition of transition metal oxoanions, such as vana-
date, has not been widely studied.3 In fact, the significance
of vanadate has been well documented in areas of bio-
chemistry, medicine, and catalysis.4 Most of these studies
concentrated on the role of vanadate as a phosphate
analogue, allowing it to act both as an inhibitor of phos-
phate-metabolizing enzymes as well as an activator of
others.5
The main difficulty in studying the interaction of vana-
date with organic ligands by way of fluorescent sensor is
the tendency of VV to hydrolyze, forming both mono- and
polynuclear species in aqueous solution.6 For example,
aqueoussolutions ofvanadium salts often contain multiple
species such as mono-, di-, tetra-, and pentanuclear com-
pounds. Therefore, it is challenging to obtain a proper
receptor to detect the binding of different vanadate species
by colorimetric and fluorescent changes.
† Department of Chemistry and Nano Sciences.
‡ Department of Bioinspired Science (WCU).
ꢀ~
ꢀ
(1) (a) Martı
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This paper reports tris(2-((ethylimino)methyl)pyren-1-ol)-
amine (1) as a receptor of tetrameric vanadate to sense the
(5) (a) Yamaki, R. T.; Paniago, E. B.; Carvalho, S.; Howarth, O. W.;
Kam, W. J. Chem. Soc., Dalton Trans. 1997, 4817. (b) Zhang, X.;
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r
10.1021/ol200846a
Published on Web 04/22/2011
2011 American Chemical Society

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binding process by both distinct colorimetric and fluorescent
changes for the first time. During the titration, 1 was
immediately able to bind V1 (monomeric, VO43À), V4
(tetrameric, V4O124À), and V5 (pentameric, V5O155À) simul-
taneously, and the color of the solution 1 changed from pink
to yellow, with a strong yellow-green fluorescence. Interest-
ingly, the equilibrium of oligomeric vanadates shifted toward
V4 slowly, because 1 preferentially binds V4 over V1 and V5,
and the situation reached the maxium point after 8 h of the
addition of monovanadate. The color of solution 1 changed
from yellow to orange, with a strong yellow fluorescence
emission. Therefore, the entire sensing process of vanadate
was successfully indicated by the colorimetric and fluorescent
changes of 1 in two steps.
absorption band centered at 548 nm with three peaks at
350, 393, and 432 nm. As 0À3 equiv of (n-Bu4N)2 HVO4
3
(V1) was added to the solution of 1, the peaks around 350
and 550 nm decreased while the peaks at 393 and 481 nm
increased significantly, with two isosbestic points at 364
and 512 nm (Figure 1a). However, the increase did notstop
after it reached the maximum point with 3 equiv of V1. The
intensities of peaks at 393 and 481 nm increased slowly and
finally stopped increasing 1 h after the addition (Figure 1a,
inset). As shown in Figure 1b, the color of solution
1 immediately changed from pink to yellow when 3 equiv
of (n-Bu4N)2 HVO4 was added and changed slowly from
3
yellow to orange within 1 h.
Scheme 1. Synthetic Route for Compound 1 and Crystal
Structure of 1 (a) along the b-Axis and (b) along the c-Axis
Figure 1. (a) UVÀvis changes of 1 (1 Â 10À5 M, DMSO) upon
the addition of 3 equiv of (n-Bu4N)2 HVO4 after 5 min. Inset:
3
UVÀvis changes of 1 (1 Â 10À5 M, DMSO) after addition of
3 equiv of (n-Bu4N)2 HVO4 for 1 h. (b) Pictures of compound
1 upon the addition of 7 equiv of (n-Bu4N)2 HVO4 after 5 min
3
3
(left); compound 1 (middle); compound 1 upon the addition of
7 equiv of (n-Bu4N)2 HVO4 after 10 h (right).
3
Scheme 1 explains the synthetic route of compound 1.
Compounds P1ÀP3 were synthesized with improved yield
by a modification of the previously reported procedure.7
The condensation of P3 with tris(2-aminoethyl)amine pro-
duced the target compound 1, which was rapidly purified by
filtration, in a high yield of 70%. The structure of 1 was
characterized by NMR spectroscopy and confirmed by
X-ray crystallography. As shown in Scheme 1, a basket
framework is formed in 1 by the introduction of tris(2-
aminoethyl)amine group, and three hydroxyl groups face
outward the center of the “basket” due to the steric effect.
The absorption and fluorescence properties of 1 were
tested in DMSO. Compound 1 exhibited an major
The fluorescence spectrum of 1 in DMSO exhibited
characteristic emission bands of the pyrene monomer at
390, 410, 437 nm as well as a small peak at 607 nm, with a
pink color emission. (Figure 2a) Upon titration with V1, the
fluorescence of both of the monomer and the peak at 607 nm
quenched while a peak at 508 nm, assigned to the emission
of the pyrene excimer,8 and a shoulder peak at 564 nm
appeared, which confirmed the stacking of pyrene. With the
addition of 7 equiv of V1 to solution 1, the intensity of the
major peak at 513 nm, with a 5 nm red-shift, increased
significantly with 30-fold enhancement (Figure 2b). The
solution fluorescence color changed from pink to yellow-
green (Figure 2a). After it reached the maximum point,
(7) (a) Demerseman, P.; Einhorn, J.; Gourvest, J. F.; Royer, R.
J. Heterocycl. Chem. 1985, 22, 39. (b) Zhou, Y.; Wang, F.; Kim, Y.;
Kim, S.-J.; Yoon, J. Org. Lett. 2009, 11, 4442. (c) Zhou, Y.; Kim, H. N.;
Yoon, J. Bioorg. Med. Chem. Lett. 2010, 20, 125. (d) Zhou, Y.; Won, J.;
Lee, J. Y.; Yoon, J. Chem. Commun. 2011, 47, 1997.
(8) (a) Xu, Z.; Singh, N. J.; Lim, J.; Pan, J.; Kim, H. N.; Park, S.; Kim,
K. S.; Yoon, J. J. Am. Chem. Soc. 2009, 131, 15528. (b) Wang, F.;
Nandhakumar, R.; Moon, J. H.; Kim, K. M.; Lee, J. Y.; Yoon, J. Inorg.
Chem. 2011, 50, 2240.
Org. Lett., Vol. 13, No. 10, 2011
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tetrameric (V4, V4O124À), respectively. With the addition
of 1, four different vanadate species,9 V1 at À528 ppm, V2
at À558 ppm, V4 at À578 ppm, and pentameric (V5,
V5O155À) at À585 ppm, appeared at the 51V NMR
(Figure 3). As 1 increased (equivalents of 1 are related to
the concentration of V1), the V1, V2 and V5 peaks disap-
peared, while the V4 peak became the major peak, indicating
that the equilibrium of oligomeric vanadates shifts toward
V4 during the titration. This scenario was achieved by
reaching the maxium point by adding 1 equiv of 1.
Figure 2. (a) Fluorescence pictures of compound 1 after the
addition of 7 equiv of (n-Bu4N)2 HVO4 for 5 min (left); com-
3
pound 1 without (n-Bu4N)2 HVO4 (middle); compound 1 after
the addition of 7 equiv of (n-Bu4N)2 HVO4 for 10 h (right). (b)
3
3À5
Fluorescence changes of 1 (1Â 10 M, DMSO) upon the
addition of 0À7 equiv of (n-Bu4N)2 HVO4 (tested within 10
3
min), Inset: kinetics upon addition of 50 equiv of V1 to 1 in
DMSO, excitation at 335 nm. (c) Fluorescence changes of 1 (1 Â
10À5 M, DMSO) after adding of 7 equiv of (n-Bu4N)2 HVO4
(tested from 1 to 9 h). Inset: kinetics upon addition of 50 equiv of
V1 to 1 in DMSO, excitation at 335 nm, slit 1.5 nm/3 nm.
3
no additional V1 was added to the solution. As time
progressed, the peak at 513 nm quenched (Figure S3 in
Supporting Information), while the peak at 564 nm in-
creased with 50-fold enhancement and an isosbestic point
at 541 nm (Figure 2c). Eight hours later, the major peak
finally red-shifted to 568 nm, and an orange-colored solu-
tion with a yellow emission was formed (Figure 2a).
As it is well-known, the solution of vanadate contains
monovanadate in equilibrium with its oligomers. Accord-
ing to the changes in UVÀvis and fluorescence spectra, it
presumed that there are two steps for 1 to sense the
vanadate ions and form the stable vanadate complexes.
The 51V NMR titration of 1 was carried out, and the
results proved the binding affinity of 1 toward V1, V4, and
V5. The 2 mM vanadate stock solution shows three peaks
at À527, À556, and À577 ppm, which can be assigned to
monomeric (V1, VO43À), dimeric (V2, V2O74À), and
Figure 3. Proposed binding mechanism of compound 1 with
different vanadate species and 51V NMR spectra of vanadate
(2 mM) with compound 1 (0.5 mM) in DMSO-d6; equivalents
of 1 are related to the concentration of V1. NMR spectra explain
preferential binding of 1 with V4 over V1 and V5.
To identify the time influence in the binding mode, the
51V NMR of 2 mM vanadate stock solution with 0.5 mM
1 was tested at different time points: 2 min, 2 h, 8 h, and 24
(9) (a) Aureliano, M. J. Inorg. Biochem. 2000, 80, 141. (b) Bhattacharyya,
S.; Martinsson, A.; Batchelor, R. J.; Einstein, F. W. B.; Tracey, A. S.
Can. J. Chem. 2001, 79, 938. (c) Mba, M.; Pontini, M.; Lovat, S.; Zonta,
€
C.; Bernardinelli, G.; Kundig, P. E.; Licini, G. Inorg. Chem. 2008, 47,
8616.
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Org. Lett., Vol. 13, No. 10, 2011

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h after the addition (Figure 4). The results showed that, in
the presence of 1, the V4 and V5 peaks increased immedi-
ately and the peak of V2 decreased significantly. This
implies that 1 binded V1, V4, and V5 at the same time, in
other words, compounds 2, 3, and 4coexistatthe first stage
(Figure 3). As the three hydroxyl groups of 1 turned from
facing outside to facing inside to bind V1, V4, and V5, it
could explain the increase of the fluorescence peak at 508
nm, assigned to the emission of the pyrene excimer in
addition to a shoulder peak at 564 nm. Eight hours later,
V2 disappeared and V1 and V5 decreased dramatically,
which suggested compound 1 mainly binds V4 and creates
an equilibrium of oligomeric vanadates that slowly shifts
toward V4 (Figure 3). This corresponded to the increase of
the fluorescence peak at 564 nm and the fluorescent color
changefrom yellow-green toyellow. Bothfluorescenceand
51V NMR titration indicated 1:1 complex final formation
between 1 with V4 (V4O124À), as even the binding interac-
tion of 1 to V4 (Ka = 2.43Â 104 MÀ1) was slightly weeker
than that of 1to V5 (Ka =3.14Â 105 MÀ1) in the first step.10
In conclusion, tris(2-((ethylimino)methyl)pyren-1-ol)-
amine (1) was synthesized as a receptor for tetrameric
vanadate, and for the first time, the entire binding process
was successfully accomplished by the distinct colorimetric
and “offÀon” fluorescent changes of 1 in two steps. First, 1
immediately binds V1, V4, and V5 simultaneously. The
color of solution 1 changed from pink to yellow, emiting a
strong yellow-green fluorescence with 30-fold enhance-
ment. Then, the equilibrium of oligomeric vanadates
shifted toward V4 slowly because 1 preferentially binds
to V4, and the situation reached the maxium point 8 h after
the addition of monovanadate. The color of solution 1
changed from yellow to orange, with a 50-fold enhance-
ment of yellow fluorescence emission. The entire sensing
process of vanadate (V4, V4O124À) was successfully de-
tected by the colorimetric and fluorescent changes of 1 in
two steps. The good selectivity and unique fluorescence
changes of 1 toward V4, coupled with visual detection by
the naked eye, hasproven 1 to be a promising candidate for
practical applications as a good probe. Work toward this
goal is currentlly underway in our laboratory.
Acknowledgment. This work was supported from the
National Research Foundation (NRF) (2010-0018895),
the Converging Research Center Program through the
Ministry of Education, Science and Technology
(2010K001202) and WCU program (R31-2008-000-
10010-0). Mass spectral data were obtained from the
Korea Basic Science Institute (Daegu) on a Jeol JMS 700
high resolution mass spectrometer.
Supporting Information Available. Experimental pro-
cedures and characterization data of compounds. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(10) (a) Association constants were obtained using the computer
program ENZFITTER, available from Elsevier-BIOSOFT, 68 Hills
Road, Cambridge CB2 1LA, U.K. (b) Conners, K. A. Binding Con-
stants, The Measurement of Molecular Complex Stability; Wiley: New
York, 1987.
Figure 4. 51V NMR spectra of vanadate (2 mM) with 1 (0.5 mM)
in DMSO-d6.
Org. Lett., Vol. 13, No. 10, 2011
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