Spiropyran as a selective, sensitive, and reproducible cyanide anion receptor

Article abstract of DOI:10.1021/ol901399a

A spiropyran derivative (1) behaves as a selective and sensitive cyanide anion receptor in aqueous media under UV irradiation. The receptor can be reproduced just by irradiation with visible light.

Full text of DOI:10.1021/ol901399a

ORGANIC
LETTERS
2009
Vol. 11, No. 15
3482-3485
Spiropyran as a Selective, Sensitive,
and Reproducible Cyanide Anion
Receptor
Yasuhiro Shiraishi,* Kenichi Adachi, Masataka Itoh, and Takayuki Hirai
Research Center for Solar Energy Chemistry, and DiVision of Chemical Engineering,
Graduate School of Engineering Science, Osaka UniVersity, Toyonaka 560-8531, Japan
shiraish@cheng.es.osaka-u.ac.jp
Received June 20, 2009
ABSTRACT
A spiropyran derivative (1) behaves as a selective and sensitive cyanide anion receptor in aqueous media under UV irradiation. The receptor
can be reproduced just by irradiation with visible light.
The cyanide anion (CN-) is an anion extremely toxic to
living organisms.1 It strongly binds to cytochrome-c and
disrupts the mitochondrial electron-transport chain, leading
to decreased oxidative metabolism and oxygen utilization.2
The maximum permissive level of cyanide in drinking water
is therefore set at 1.9 µM by the World Health Organization
(WHO).3 The use of cyanide salts, however, is widespread,
particularly in gold mining, electroplating, and metallurgy.4
Despite increasing levels of monitoring, accidental release
of CN- to the environment does occur. There is thus a strong
need for CN--selective receptors. Several receptors have been
proposed, but many of these rely on a hydrogen-bonding
motif and act only in organic media.5 To overcome this
limitation, reaction-based CN- receptors have been pro-
posed;6-8 however, many of these display relatively poor
selectivity6 and a high detection limit (>1.9 µM)7 in aqueous
media. There are only seven reports of CN- receptors with
high selectivity and sensitivity in aqueous media.8 These
receptors, however, suffer from the biggest problem; they
react with CN- irreversibly and cannot be reused for further
analysis.
Spiropyran derivatives belong to a class of organic
photochromes that have been studied extensively for ap-
plication in optical switches9 and memories.10 These dyes
are converted to the colored merocyanine (MC) form upon
(6) For example, see: (a) Badugu, R.; Lakowicz, J. R.; Geddes, C. D.
Anal. Chim. Acta 2004, 522, 9–17. (b) Badugu, R.; Lakowicz, J. R.; Geddes,
C. D. Dyes Pigm. 2005, 64, 49–55. (c) Badugu, R.; Lakowicz, J. R.; Geddes,
C. D. J. Am. Chem. Soc. 2005, 127, 3635–3641. (d) Lou, X.; Zhang, L.;
Qin, J.; Li, Z. Chem. Commun. 2008, 5848–5850
.
(1) (a) Koenig, R. Science 2000, 287, 1737–1738. (b) Baud, F. Hum.
Exp. Toxicol. 2007, 26, 191–201.
(7) For example, see: (a) Garc´ıa, F.; Garc´ıa, J. M.; Garc´ıa-Acosta, B.;
Mart´ınez-Ma´n˜ez, R.; Sanceno´n, F.; Soto, J. Chem. Commun. 2005, 2790–
2792. (b) Ros-Lis, J. V.; Mart´ınez-Ma´n˜ez, R.; Soto, J. Chem. Commun.
2005, 5260–5262. (c) Hudnall, T. W.; Gabba¨ı, F. P. J. Am. Chem. Soc.
(2) Camerino, P. W.; King, T. E. J. Biol. Chem. 1966, 241, 970–979.
(3) Guidelines for Drinking-Water Quality; World Health Organization:
Geneva, 1996.
2007, 129, 11978–11986
.
(4) (a) Young, C.; Tidwell, L.; Anderson, C. Cyanide: Social, Industrial
and Economic Aspects: Minerals, Metals, and Materials Society: Warrendale,
2001. (b) Ullman’s Encyclopedia of Industrial Chemistry, 6th ed.; Wiley-
VCH: New York 1999.
(8) (a) Chow, C.-F.; Lam, M. H. W.; Wong, W.-Y. Inorg. Chem. 2004,
43, 8387–8393. (b) Jin, W. J.; Ferna´ndez-Argu¨elles, M. T.; Costa-Ferna´ndez,
J. M.; Pereiro, R.; Sanz-Medel, A. Chem. Commun. 2005, 883–885. (c)
Tomasulo, M.; Raymo, F. M. Org. Lett. 2005, 7, 4633–4636. (d) Yang,
Y.-K.; Tae, J. Org. Lett. 2006, 8, 5721–5723. (e) Tomasulo, M.; Sortino,
S.; White, A. J. P.; Raymo, F. M. J. Org. Chem. 2006, 71, 744–753. (f)
Ganesh, V.; Sanz, M. P. C.; Mareque-Rivas, J. C. Chem. Commun. 2007,
5010–5012. (g) Cho, D.-G.; Kim, J. H.; Sessler, J. L. J. Am. Chem. Soc.
(5) For example, see: (a) Miyaji, H.; Sessler, J. L. Angew. Chem., Int.
Ed. 2001, 40, 154–157. (b) Anzenbacher, P. Jr.; Tyson, D. S.; Jurs´ıkova´,
K.; Castellano, F. N. J. Am. Chem. Soc. 2002, 124, 6232–6233. (c) Chung,
Y. M.; Raman, B.; Kim, D.-S.; Ahn, K. H. Chem. Commun. 2006, 186–
188.
2008, 130, 12163–12167
.
10.1021/ol901399a CCC: $40.75
Published on Web 07/15/2009
 2009 American Chemical Society

UV irradiation but revert to the colorless spirocyclic (SP)
form upon visible light irradiation.11 Some spiropyran
derivatives have been proposed for optical sensing of several
analytes, such as cations,12 nucleobases,13 amino acids,14 and
DNA.15 There is, however, no report of a spiropyran-based
anion receptor.
Here, we report that a spiropyran derivative behaves as a
selective and sensitive CN- receptor in aqueous media
(Scheme 1). A simple, popular, and easily preparable
just by irradiation with visible light to the 1-CN- adduct
without any additives.
Figure 1a shows absorption spectra of 116 (20 µM)
measured in a buffered water/MeCN mixture (1/1 v/v; CHES
100 mM, pH 9.3) with 50 equiv of respective anions. As
shown by the red line, without anion and UV irradiation, 1
shows almost no absorption in the visible region. Upon UV
irradiation (334 nm), 1 exhibits a distinctive absorption band
centered at 519 nm, assigned to the generation of MC form,11
with the photostationary state attained after 2 min irradiation.
Addition of anions, except for CN-, to the solution under
UV irradiation does not show a spectral change. In contrast,
addition of CN- leads to a decrease in the 519 nm MC band,
along with an appearance of a blue-shifted band at 421 nm.
The spectral change of 1 upon CN- addition occurs within
25 min under UV irradiation (Figure S1, Supporting Infor-
mation16). As shown in Figure 1b, the solutions obtained
under UV irradiation without anion (B) or with other anions
(C-L) show a pink color, whereas CN- addition (M) creates
an obvious yellow color. This suggests that 1 allows selective
CN- detection. The CN--induced spectral change is unaf-
fected by other anions (Figure S2, Supporting Information16),
indicating that 1 can detect CN- selectively even in the
presence of other anions.
Scheme 1
.
Structure Change of 1 in the Presence of CN- under
UV or Visible Light Irradiation
N-methylated spiropyran derivative (1)11 shows a CN--
selective absorption band under UV irradiation via a nu-
cleophilic addition of CN- to 1 (1-CN- adduct formation).
Figure 2.
Absorption titration of 1 (20 µM) with CN- in water/
MeCN (1/1 v/v; CHES 100 mM, pH 9.3) under UV irradiation at
25 °C. Each spectrum was obtained after stirring the solution for
30 min with UV irradiation. (Inset) Change in absorbance at 421
nm. The line is the nonlinear fitting curve obtained assuming a 1:1
association between 1 and CN-.16
As shown in Figure 2, titration of 1 with CN- under UV
irradiation leads to a decrease in the 519 nm MC band,
associated with the 421 nm band increase. The isosbestic
points at 382 and 472 nm suggest that the reaction of 1 with
CN- produces a single component. Nonlinear fitting of the
data (inset) reveals that 1 reacts with CN- in a 1:1
stoichiometry with the association constant 9.8 × 103 M-1.
The 1:1 reaction is confirmed by ESI-MS (Figure S3,
Supporting Information16); a MeCN solution containing 1
and CN-, when irradiated with UV light, shows a peak at
m/z 348.5, assigned to [1 + CN-] ion.
Figure 1. (a) Absorption spectra of 1 (20 µM) measured with 50
equiv of respective anions (as a n-Bu4N+ salt) in a water/MeCN
mixture (1/1 v/v; CHES 100 mM, pH 9.3) under UV irradiation
(334 nm) at 25 °C. The spectra were obtained after stirring the
solution containing 1 and each anion for 30 min with UV irradiation.
The red spectrum is obtained without anion in the dark. (b)
Photographs of the solutions (A) without anion (dark), (B) without
anion, (C) F-, (D) Cl-, (E) Br-, (F) I-, (G) AcO-, (H) H2PO4-, (I)
HSO4-, (J) ClO4-, (K) NO3-, (L) SCN-, and (M) CN-.
This allows quantitative determination of very low levels of
Quantitative CN- determination can be carried out by
ratiometric analysis. Figure 3 shows change in the ratio of
CN- (>1.7 µM). In addition, the receptor can be reproduced
Org. Lett., Vol. 11, No. 15, 2009
3483

the adjacent indole moiety and shifts downfield as compared
to the SP form. However, in our case, UV irradiation with
CN- leads to upfield shift of Hi (-0.51 ppm). This is because
CN- addition to the spirocarbon of 1 leads to a decrease in
electron density of the indole moiety. These data indicate
that the reaction of 1 with CN- under UV irradiation
produces the spirocycle-opened 1-CN- adduct (Scheme 1).
The blue-shifted absorption band of the 1-CN- adduct
compared to the MC form of 1 is due to the localization of
π-electrons of the molecule. This is confirmed by ab initio
calculations performed within the Gaussian 03 program.16
The lowest singlet electronic transitions of both 1(MC) and
1-CN- are mainly contributed by a HOMO-LUMO transi-
tion, where both transitions have a π,π* character (Table
S1, Supporting Information16). As shown in Figure 5, the
Figure 3. Change in the absorbance ratio (A421/A519) of 1 (10 µM)
with CN- concentration. The titration was performed in water/
MeCN (1/1 v/v; CHES 100 mM, pH 9.3) under UV irradiation at
25 °C (Figure S4, Supporting Information16). The spectra at each
CN- concentration were obtained after stirring the solution for 30
min under UV irradiation.
the 421 and 519 nm absorbance of 1. A linear relationship
in the range of 1.7-300 µM CN- indicates that 1 allows
accurate CN- sensing in this concentration range. The
detection limit, 1.7 µM, is below the WHO guidelines of
drinking water (1.9 µM),3 suggesting that 1 allows sensitive
CN- detection.
The CN--induced absorption change is due to the addition
of CN- to the spirocarbon of 1, leading to a formation of
1
the 1-CN- adduct (Scheme 1). H NMR spectra of 1
obtained in the dark and after UV irradiation with CN-
confirm this. As shown in Figure 4, chemical shift of some
Figure 5. Energy diagrams of HOMO and LUMO orbitals of 1(MC)
and 1-CN- calculated at the DFT level using a B3LYP/6-31+G*
basis set.
HOMO-LUMO gap of 1(MC) is 2.67 eV, whereas the gap
of 1-CN- is 3.29 eV, suggesting that the adduct has a larger
gap than 1(MC) (∆0.62 eV). This is explained by electronic
configuration of the HOMO and LUMO orbitals. The
π-electrons of 1(MC) are distributed over the entire molecule
(Figure 5). In contrast, π-electrons of 1-CN- are localized
on the p-nitrophenolate moiety. This is due to the decrease
(9) (a) Raymo, F. M.; Giordani, S. J. Am. Chem. Soc. 2001, 123, 4651–
4652. (b) Zhu, L.; Wu, W.; Zhu, M.-Q.; Han, J. J.; Hurst, J. K.; Li, A. D. Q.
J. Am. Chem. Soc. 2007, 129, 3524–3526.
(10) (a) Nagashima, S.; Murata, M.; Nishihara, H. Angew. Chem., Int.
Ed. 2006, 45, 4298–4301. (b) Tomozaki, K.; Mihara, H. J. Am. Chem. Soc.
2007, 129, 8345–8352.
Figure 4.
1H NMR chart (270 MHz, 30 °C, CD3CN) of 1 (5 mM)
(11) (a) Berkovic, G.; Krongauz, V.; Weiss, V. Chem. ReV. 2000, 100,
1741–1753. (b) Minkin, V. I. Chem. ReV. 2004, 104, 2751–2776. (c) Raymo,
F. M.; Tomasulo, M. Chem. Soc. ReV. 2005, 34, 327–336.
(12) Inouye, M.; Akamatsu, K.; Nakazumi, H. J. Am. Chem. Soc. 1997,
119, 9160–9165.
measured (a) in the dark, (b) after UV irradiation with 10 equiv of
CN-, and (c) after three cycles of UV/vis light irradiation with 10
equiv of CN- (see Figure 7).
(13) Takase, M.; Inouye, M. Chem. Commun. 2001, 2432–2433.
(14) Shao, N.; Jin, J. Y.; Cheung, S. M.; Yang, R. H.; Chan, W. H.;
Mo, T. Angew. Chem., Int. Ed. 2006, 45, 4944–4948.
(15) Andersson, J.; Li, S.; Lincoln, P.; Andre´asson, J. J. Am. Chem.
Soc. 2008, 130, 11836–11837.
protons of 1 decreases with this process. The biggest change
(-0.73 ppm) is observed for the Hg proton in the ortho
position relative to the phenolate oxygen of 1, indicating that
the reaction of 1 with CN- produces a spirocycle-opened
species.8e As reported,17 olefinic Hi proton of the MC form
is magnetically deshielded due to the ring current effect by
(16) See the Supporting Information.
(17) (a) Parker, W. O., Jr.; Hobley, J.; Malatesta, V. J. Phys. Chem. A
2002, 106, 4028–4031. (b) Machitani, K.; Nakamura, M.; Sakamoto, H.;
Ohata, N.; Masuda, H.; Kimura, K. J. Photochem. Photobiol. A: Chem.
2008, 200, 96–100.
3484
Org. Lett., Vol. 11, No. 15, 2009

in electron density of the indole moiety by the CN- addition,
which is consistent with the upfield shift of the Hi proton
observed by 1H NMR analysis (Figure 4). The lowest singlet
transition energy of 1(MC) is 499 nm (2.48 eV, Table S1,
Supporting Information16), which is similar to λmax of the
1(MC) spectrum (519 nm, Figure 2). In contrast, the
transition energy of 1-CN- (424 nm, 2.92 eV) is much lower
than that of 1(MC) and is similar to λmax of the 1-CN-
spectrum (421 nm). These closely matched results indicate
that the CN- addition to 1 leads to a localization of the
π-electrons; therefore, the adduct requires higher transition
energy than 1(MC), resulting in a blue-shift of the absorption
band (Figure 2).
Figure 7. Change in 421 nm absorbance during sequential UV and
The 1-CN- adduct forms via a nucleophilic addition of
CN- to the positively charged spirocarbon18 of the MC form
of 1, where CN- does not react with the SP form. This is
confirmed by activation energies (Ea) determined by kinetic
absorption analysis.16 The 1-CN- formation during the
reaction of 1 with an excess amount of CN- (50 equiv) under
UV irradiation is explained by first-order kinetics, with the
rate constant 2.44 × 10-3 s-1 (25 °C). An Arrhenius plot of
the kinetic data reveals that Ea for this reaction is 26.9 kJ
mol-1 (Figure 6c). In contrast, kinetic analysis in the dark
visible light irradiations of a water/MeCN solution (1/1 v/v; CHES
100 mM, pH 9.3) containing 1 and 50 equiv of CN- at 25 °C.
change in 421 nm absorbance of a solution containing 1 and
CN-, where UV and visible lights were irradiated sequen-
tially. Visible light irradiation decreases the 421 nm absorp-
tion, but sequential UV irradiation regenerates the band. This
suggests that the 1-CN- adduct, when excited by visible
light, successfully reverts to the SP form with a release of
CN- in a way similar to the MC f SP isomerization.11
Repeated UV and visible light irradiation sequences show
almost the same absorbance change. As shown in Figure 4c,
the sample recovered after three-cycle irradiations shows an
1H NMR spectrum similar to that for the virgin 1 (Figure
4a). These data clearly indicate that 1 reversibly reacts with
CN- and the process is repeatable without significant
degradation of 1.
In summary, we found that a spiropyran derivative behaves
as a selective and sensitive CN- receptor in aqueous media.20
The receptor allows accurate sensing of a very low level of
CN- by simple UV-vis analysis. In addition, the receptor
is reproduced just by visible light irradiation. Convenient
and clean CN- sensing is realized by applying the basic idea
using the spiropyran motif, and the results presented here
may contribute to the development of more useful CN-
receptors.
Figure 6. Energy diagrams for respective reactions, (a) 1(SP) f
1(MC), (b) 1(SP) + CN- f 1-CN-, and (c) 1(MC) + CN-
f
1-CN-, determined by kinetic absorption analysis with 50 equiv
of CN-. The kinetic data and Arrhenius plots are shown in Figures
S5 and S6 (Supporting Information).16
reveals that the rate constant for the reaction between the
SP form of 1 and CN- is 1.75 × 10-5 s-1 (25 °C), which is
much lower than that for the reaction between 1(MC) and
CN-. In addition, Ea for this reaction is 110.2 kJ mol-1
(Figure 6b), which is much higher than Ea for the reaction
between 1(MC) and CN- and is similar to Ea of the thermal
SPfMC isomerization19 (115.1 kJ mol-1, Figure 6a). These
data suggest that the 1-CN- adduct forms via reaction of
the MC form of 1 with CN-, and hence, UV irradiation is
necessary for rapid CN- sensing by the present receptor.
Another significant feature of 1 is that it can be reproduced
just by irradiation with visible light. Figure 7 shows the
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research (No. 21760619) from the
Ministry of Education, Culture, Sports, Science and Technol-
ogy, Japan (MEXT).
Supporting Information Available: Experimental details
and supplementary data (Figures S1-S9, Table S1, and
Cartesian coordinates for compounds). This material is
available free of charge via the Internet at http://pubs.acs.org.
OL901399A
(20) Compund 1 allows selective CN- detection even at neutral pH,
but the sensitivity decreases significantly. This is because the protonation
of CN- (pKa (HCN) ) 9.2) at neutral pH suppresses the nucleophilic
addition of CN- to 1; the association constant between 1 and CN- under
UV irradiation obtained at pH 7.3 (HEPES) is 92 M-1, whereas the constant
(18) Cottone, G.; Noto, R.; Manna, G. L.; Fornili, S. L. Chem. Phys.
Lett. 2000, 319, 51–59.
(19) Suzuki, T.; Oda, N.; Tanaka, T.; Shinozaki, H. J. Mater. Chem.
2006, 16, 1803–1807.
obtained at pH 9.3 is 9.8 × 103 M-1
.
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