Chromogenic and fluorogenic signaling of sulfite by selective deprotection of resorufin levulinate

Article abstract of DOI:10.1021/ol102298b

A new sulfite-selective probe system based on resorufin was investigated. Levulinate of resorufin exhibited a prominent chromogenic and turn-on type fluorogenic signaling toward sulfite ions in aqueous media based on the selective deprotection of the levulinate group. The sulfite-selective signaling was possible in the presence of commonly encountered anions.

Full text of DOI:10.1021/ol102298b

ORGANIC
LETTERS
2010
Vol. 12, No. 24
5624-5627
Chromogenic and Fluorogenic Signaling
of Sulfite by Selective Deprotection of
Resorufin Levulinate
Myung Gil Choi, Jiyoung Hwang, Suyoung Eor, and Suk-Kyu Chang*
Department of Chemistry, Chung-Ang UniVersity, Seoul 156-756, Korea
skchang@cau.ac.kr
Received September 24, 2010
ABSTRACT
A new sulfite-selective probe system based on resorufin was investigated. Levulinate of resorufin exhibited a prominent chromogenic and
turn-on type fluorogenic signaling toward sulfite ions in aqueous media based on the selective deprotection of the levulinate group. The
sulfite-selective signaling was possible in the presence of commonly encountered anions.
Sulfites are widely used as preservatives in food and
beverages,1 and the development of analytical methods for
the determination of sulfite levels is important for consumer
safety.2 Sulfites are known to be associated with allergic
reaction and food intolerance symptoms. The most frequent
sulfite-induced symptoms are of the asthmatic and allergic
type, such as difficulty in breathing, wheezing, and hives,
as well as gastrointestinal distress.3 Sulfites are potentially
toxic, and the acceptable daily intake is strictly regulated as
0.7 mg/kg of body weight.4
Hence, the development of convenient methods for sulfite
analysis is important for food safety and quality control.5
Sulfites in food and beverages are determined by conven-
tional methods, such as titrimetry,6 chromatography,7 elec-
trochemistry,8 capillary electrophoresis,9 and flow injection
analysis.10 However, conventional methods for sulfite analy-
ses usually require troublesome sample pretreatment and
reagent preparation and are either time-consuming or require
complicated instruments unsuited for routine analysis.11 For
this reason, more convenient tools, such as optical sensors12
and chromoreactands,13 have attracted much research interest.
Signaling by selective chemical transformation of chemo-
dosimeters or chemical probes has been uniquely employed
for the construction of many sophisticated signaling sys-
tems.14 Representative examples of this approach are Cu2+
signaling by the hydrolysis of rhodamine hydrazide15 and
hydrogen peroxide visualization by boronate deprotection of
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10.1021/ol102298b  2010 American Chemical Society
Published on Web 11/17/2010

fluorescein and resorufin.16 Other successfully designed
systems are probes for the signaling of fluoride,17 cyanide,18
sulfide,19 phosphate,20 Cu2+,21 and Hg2+ ions.22
The levulinyl group is frequently used as a protection tool
for the hydroxyl group in nucleotides, peptides, and sug-
ars.23,24 Ono et al. have reported that levulinate-protected
phenol moieties could be easily and selectively deprotected
by sulfites under mild and neutral conditions.25 On the basis
of this report, we attempted to construct a novel sulfite-
selective probe, which yielded naked-eye detectable chro-
mogenic and fluorogenic signaling. The resorufin fluorophore
was chosen as a signaling handle for this purpose as in other
signaling systems for the detection of fluoride,17 DNA
hybridization,26 and hydrolase.27 Levulinate of resorufin was
prepared by reaction of resorufin sodium salt with levulinyl
chloride in good yield (75%) (Scheme 1).
Figure 1. UV-vis spectra of probe 1 in the presence of common
anions. [1] ) 1.0 × 10-5 M, [An-] ) 1.0 × 10-3 M. In HEPES
buffered (pH 7.0, 10 mM) H2O-CH3CN (98:2, v/v), measured after
20 min of each mixing.
Scheme 1. Synthesis of a Sulfite-Selective Probe 1
sulfite by the naked eye. The change in absorption profile was
quite large, as has been reported in other resorufin-based
signaling systems via the deprotection to resorufin. With sulfite,
the absorbance ratio A571/A359 at the two characteristic wave-
lengths of 571 and 359 nm increased over 320-fold. Other
common anions were relatively nonresponsive, and A571/A359
values varied in a limited range between 0.76 (for iodide) and
1.32 (for hydrogen phosphate) (Figure S1, Supporting Informa-
tion).
Next, the fluorogenic signaling behavior of 1 toward sulfite
was measured. Levulinate 1 showed a weak emission at 584
nm. However, upon treatment with 100 equiv of sulfite,
intense emission appeared at 588 nm (Figure 2). The
First, the chromogenic signaling behavior of resorufin le-
vulinate 1 was investigated in aqueous solution containing a
minimal amount of acetonitrile as a solubilizer (H2O:CH3CN
) 98:2, v/v) at pH 7.0 (HEPES buffer, 10 mM). Levulinate 1
revealed moderate UV-vis absorptions at 359 and 456 nm.
Upon interaction with 100 equiv of sodium sulfite, a strong
absorption band centered at 571 nm was developed (Figure 1).
Concomitantly, a prominent pink color, which is a characteristic
of resorufin, developed that allowed colorimetric detection of
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Commun. 2009, 4838.
Figure 2. Fluorescence spectra of probe 1 in the presence of
common anions. [1] ) 5.0 × 10-6 M, [An-] ) 5.0 × 10-4 M. In
HEPES buffered (pH 7.0, 10 mM) H2O-CH3CN (98:2, v/v),
measured after 20 min of each mixing. λex ) 487 nm.
(22) (a) Yang, Y.-K.; Yook, K.-J.; Tae, J. J. Am. Chem. Soc. 2005, 127,
16760. (b) Song, K. C.; Kim, J. S.; Park, S. M.; Chung, K.-C.; Ahn, S.;
Chang, S.-K. Org. Lett. 2006, 8, 3413. (c) Lee, M. H.; Cho, B.-K.; Yoon,
J.; Kim, J. S. Org. Lett. 2007, 9, 4515.
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Synthesis, 3rd ed.; John Wiley & Sons: New York, 1999; p 168
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.
fluorescence enhancement factor I/Io observed at 588 nm was
large (57-fold), and the solution revealed a dramatic color
change from dark to deep pink under illumination with a
UV lamp. Other common anions were relatively nonrespon-
sive, and I/Io at 588 nm varied in a limited range between
J. Am. Chem. Soc. 2009, 131, 8496
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Org. Lett., Vol. 12, No. 24, 2010
5625

1.08 (for fluoride) and 1.88 (for perchlorate) (Figure S2,
Supporting Information).
The chromogenic and fluorogenic signaling are due to
sulfite-induced selective deprotection of resorufin levulinate
1 (Scheme 2). The cleavage of levulinate was effected by
nm grew at increasing rates (Figure S4, Supporting Informa-
tion). In spectra taken 20 min after addition of sulfite, the
absorbance increased steadily to about 20 equiv of sulfite
(Figure 4). From this concentration-dependent signaling
Scheme 2. Sulfite-Selective Signaling Mechanism
initial attack of sulfite to the carbonyl carbon at the 4-position
of levulinate with the formation of a tetrahedral intermediate
and subsequent intramolecular cyclization leading to cleavage
of the ester function.25 Thus generated resorufin exhibited
its characteristic chromogenic and fluorogenic signaling
behaviors.
Figure 4. Concentration-dependent chromogenic signaling of sulfite
by probe 1. [1] ) 1.0 × 10-5 M. In HEPES buffered (pH 7.0, 10
mM) H2O-CH3CN (98:2, v/v), measured after 20 min of each
mixing.
behavior, the detection limit28 of 1 for the analysis of sulfite
was estimated as 4.9 × 10-5 M (4.0 ppm) in aqueous 2%
acetonitrile solution.
The suggested sulfite-induced transformation was evi-
denced by NMR, UV-vis, and fluorescence measurements.
1
The H NMR spectrum of 1 in the presence of 20 equiv of
Practical applicability of the sulfite signaling by 1 was
ascertained by competition experiments with commonly
encountered anions. The signaling of 1 toward sulfite was
not affected by the presence of 5 equiv of coexisting
representative anions, and the interference from other anions
expressed as the ratio A1+Sulfite+Anion/A1+Sulfite at 571 nm varied
in a limited range from 0.94 for iodide to 1.04 for fluoride
(Figure 5 and Figure S3, Supporting Information). These
observations imply that the designed levulinate 1 could be
used as a selective and efficient signaling probe for the sulfite
ions in aqueous environment.
sulfite was almost identical to that of resorufin with additional
residual peaks of sulfonate byproduct around 2.1, 2.6-2.7,
and 3.0-3.2 ppm (Figure 3). The UV-vis and fluorescence
1
Figure 3
.
Partial H NMR spectra of 1 only, 1 + sulfite, and
resorufin + sulfite. [1] ) [resorufin] ) 5.0 × 10-3 M, [Na2SO3] )
1.0 × 10-1 M. In D2O-CD3CN (50:50, v/v).
spectra of the 1-sulfite system, obtained by the interaction
of 1 (1.0 × 10-5 M) with 100 equiv of sulfite, were almost
identical to those of resorufin itself.
Quantitative analytical behavior of 1 for the analysis of
sulfite was investigated by UV-vis measurement using a
series of solutions having different amounts of analyte. As
the concentration of sulfite increased, the absorbance at 571
Figure 5. Competition experiments for a 1-sulfite system in the
presence of coexisting anions. [1] ) 1.0 × 10-5 M. [Sulfite] ) 2.0
× 10-4 M. [An-] ) 1.0 × 10-3 M. In HEPES buffered (pH 7.0, 10
mM) H2O-CH3CN (98:2, v/v), measured after 20 min of each
mixing.
5626
Org. Lett., Vol. 12, No. 24, 2010

In summary, we have devised a new sulfite-selective probe
by utilizing the sulfite-selective deprotection of levulinate.
With the representative signaling moiety of resorufin, a
pronounced sulfite-selective chromogenic and fluorogenic
signaling system was realized. The developed system could
be used as a convenient and practical signaling tool for the
optical determination of sulfites in routine chemical analytes
in aqueous environment.
Acknowledgment. This work was supported by a fund
from the Korea Research Foundation of the Korean Govern-
ment (2010-0008631) and Seoul Science Fellowship (MGC)
in 2010.
Supporting Information Available: Experimental details,
NMR spectra, and additional chemosignaling behavior of 1
are reported. This material is available free of charge via
the Internet at http://pubs.acs.org.
(28) Shortreed, M.; Kopelman, R.; Kuhn, M.; Hoyland, B. Anal. Chem.
1996, 68, 1414.
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