Recent progress on fluorescent chemosensors for metal ions

Inorganica Chimica Acta 381 (2012) 2–14

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Inorganica Chimica Acta

journal homepage: www.elsevier .com/locate / ica

Review

Recent progress on fluorescent chemosensors for metal ions

Yongsuk Jeong a, Juyoung Yoon a,b,⇑a Department of Bioinspired Science (WCU), Ewha Womans University, Seoul 120-750, Republic of Koreab Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Republic of Korea

a r t i c l e i n f o

Article history:Available online 17 September 2011

Fluorescence Spectroscopy: from SingleChemosensors to Nanoparticles Science –Special Issue

Keywords:Fluorescent chemosensorsCu2+ sensorHg2+ sensorZn2+ sensorPb2+ sensorCd2+ sensor

Yongsuk Jeong was bornMaster course in Prof. Juy

Juyoung Yoon was bornat UCLA and at Scripps Rescurrently a professor of Dgations of fluorescent che

0020-1693/$ - see front matter � 2011 Elsevier B.V. Adoi:10.1016/j.ica.2011.09.011

⇑ Corresponding author at: Department of ChemisWomans University, Seoul 120-750, Republic of Kore+82 2 3277 2384.

E-mail address: [email protected] (J. Yoon).

a b s t r a c t

The recognition and sensing of the biologically and environmentally important metal ions has emerged asa significant goal in the field of chemical sensors in recent years. Among the various analytical methods,fluorescence has been a powerful tool due to its simplicity, high detection limit and application to bioi-maging. This review highlights the fluorescent chemosensors for metal ions, which have been recentlydeveloped from our laboratory. This review was categorized by target metal ions, such as Cu2+, Hg2+,Zn2+, Pb2+, Cd2+, Vanadate, Ag+ and Au3+. Selectivity and sensitivity for these metal ions were achievedby introducing various ligands to core fluorophores, such as, rhodamine, fluorescein, pyrene, anthracene,naphthalimide, coumarin, and BODIPY.

� 2011 Elsevier B.V. All rights reserved.

in Anyang, Korea in 1985. She receivoung Yoon’s laboratory in Ewha Wo

in Pusan, Korea in 1964. He receivedearch Institute, he joined the facultyepartment of Chemistry and Nano Smosensors, molecular recognition an

ll rights reserved.

try and Nano Science, Ewhaa. Tel.: +82 2 3277 2400; fax:

ed B.S. degree from Department of Chemistry of Ewha Womans University. She is on amans University.

his Ph.D. (1994) from The Ohio State University. After completing postdoctoral researchat Silla University in 1998. In 2002, he moved to Ewha Womans University, where he iscience and Department of Bioinspired Science. His research interests include investi-d organo EL materials.

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Y. Jeong, J. Yoon / Inorganica Chimica Acta 381 (2012) 2–14 3

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32. Fluorescent chemosensors for metal ions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.1. Chemosensors for Cu2+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2. Chemosensors for Hg2+/CH3Hg+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.3. Chemosensors for Zn2+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.4. Chemosensors for Pb2+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.5. Chemosensors for Cd2+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.6. Chemosensor for vanadate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.7. Chemosensors for noble metal ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3. Conclusions and future perspectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

OO

O

O

O

OOO

Cu2+

OO

OO

O

Dynamic Excimerλem = 477 nm

Static Excimerλem = 447 nm

OOO

Cu2+

1

Fig. 1. Proposed binding mode of compound 1 with Cu2+.

1. Introduction

The recognition and sensing of the biologically and environmen-tally important metal ions has emerged as a significant goal in thefield of chemical sensors in recent years [1,2]. Several methods, suchas high performance liquid chromatography, mass spectrometry,and atomic absorption spectroscopy, have been developed to ana-lyze the concerned targets. However, these methods suffer eitherfrom extensive, time consuming procedures or the use ofsophisticated instrumentation. Fluorescence has been a powerfultool due to its simplicity, high detection limit and application to bioi-maging [3]. More specifically, the fluorogenic methods in conjunc-tion with suitable probes are preferable approaches to measurethese analytes since fluorimetry is rapidly performed, nondestruc-tive, highly sensitive, suitable for high-throughput screening appli-cations, and most importantly, can afford real information on thelocalization and quantify of the targets of interest. In this current re-view, we focus on the fluorescent chemosensors for metal ions,which have been recently developed from our laboratory. This re-view was categorized by target metal ions, such as Cu2+, Hg2+,Zn2+, Pb2+, Cd2+, Vanadate and precious metal ions (Ag+ and Au3+).Selectivity and sensitivity for these metal ions were achieved byintroducing various ligands to core fluorophores, such as, rhoda-mine, fluorescein, pyrene, anthracene, naphthalimide, coumarin,and BODIPY.

2. Fluorescent chemosensors for metal ions

2.1. Chemosensors for Cu2+

Among various metal ions, copper ion plays a critical role as acatalytic cofactor for a variety of metalloenzymes, including super-oxide dismutase, cytochrome c oxidase and tyrosinase. However,under overloading conditions, copper can cause neurodegenerativediseases (e.g., Alzheimer’s and Wilson’s diseases) probably due toits involvement in the production of reactive oxygen species[4,5]. Owing to its biological importance, fluorescent chemosen-sors, which can monitor Cu2+ in living cells, have attracted muchattention in recent years [6].

Our group also contributed for Cu2+ selective fluorescentchemosensors by utilizing a new binaphthyl derivative, whichbears two pyrene groups and crown other unit (1) [7]. In the ab-sence of Cu2+, this probe showed strong excimer emission(kmax = 477 nm) in CH3CN. On the contrary a unique blue shiftwas observed upon the addition of Cu2+. When Cu2+ was addedto the CH3CN solution, probe 1 displayed a large fluorescentenhancement with about 40 nm blue shift, which was attributedto the formation of a static pyrene excimer (Fig. 1). From the fluo-rescence titration, the association constant of 1 with Cu2+ was ob-served to be 6.56 � 104 M�1.

New rhodamine derivatives 2 and 3 bearing binaphthyl groupwere synthesized as selective fluorescent and colorimetric sensorsfor Cu2+ (Fig. 2) [8]. Highly selective ‘‘Off–On’’ type fluorescentchanges were observed upon the addition of Cu2+ among the vari-ous metal ions in CH3CN–HEPES buffer. Probe 2 displayed a 380-fold increase in its emission upon the addition 8.0 equiv. of Cu2+

and the value of log K for the binding of 2 and Cu2+ was calculatedas 4.93. For probe 2, a carbonyl oxygen as well as crown ether oxy-gens can provide a nice binding pocket for Cu2+. On the other hand,the values of logK1:1 logK1:2 for the binding of 3 and Cu2+ weredetermined as 4.19 and 4.83, respectively. A chemo-sensing of 3with Cu2+ was successfully applied to the microfluidic system, too.

We recently reported naphthalimide derivative 4 which is linkedby a piperazine ring as a selective fluorescent chemosensors for Cu2+

in aqueous solutions [9]. Free 4 in polar solvents displayed a dy-namic excimer emission (Fig. 3), which resulted from a naphthali-mide dimer formed in the excited state; whereas, the 4/Cu2+ (1:1)complex display a static excimer emission arising from a naphthal-imide dimer in the ground state. The method of continuous varia-tions was used to explain the final stoichiometry of the 4-Cu2+

complex which indicated the formation of a 4/Cu2+ (1:2) complexshowing naphthalimide monomer emission. Significantly, the fluo-rescence responses of 4 to Cu2+ in aqueous solutions(CH3CN:HEPES = 1:1, v/v) induced a selective increase in monomeremission whereas other metal ions produced a negligible change.The dissociation constant (Kd) of 4 with Cu2+ was determined to be3.4 � 10�4 M.

N

O

N

NN

ON

O

N

N

N O

NO

N

N

NO

O O O

O O O

OHHO

23

Fig. 2. Structures of 2 and 3.

N

OHNCu2+ (1 equiv.)

CH3CN

N

O

N

OHN NH

Cu2+

N

O

N

HN

ONH

Cu2+N

O

O

Cu2+ (1 equiv.) CH3CN

static excimerdynamic excimer

monomer

Cu2+

N

O NH

4

Fig. 3. Proposed mechanism of stepwise binding mode of 4 with Cu2+.

4 Y. Jeong, J. Yoon / Inorganica Chimica Acta 381 (2012) 2–14

A rhodamine-pyrene derivative 5 has been synthesized as aratiometric and ‘‘off-on’’ sensor for the detection of Cu2+ inCH3CN–HEPES buffer (0.02 M, pH 7.4) (4:6, v/v) [10]. When Cu2+

was added to the solution, a significant decrease of the fluores-cence intensity of 424 nm and a new fluorescence emission bandcentered at 575 nm, which was attributed to the Cu2+ induced ringopening of the spirolactam moiety (Fig. 4). In addition, the absor-

ON N

N

O

N

HO

Cu2

ON N

N

O

N

(HO)2B

Cu2+

5

6

Fig. 4. Proposed binding mod

bance at 424 nm decreased sharply, while the ones at 356 nmand 557 nm increased significantly, which induced a color changefrom primrose yellow to pink. The nonlinear fitting of the titrationcurve and the data of Job’s plot from absorption spectra assumed a1:1 stoichiometry for the 5-Cu2+ complex with an association con-stant of 2.5 � 104 M�1.

The first example of boronic acid-linked fluorescent and colori-metric chemosensor for copper ions was reported recently [11].The monoboronic acid-conjugated rhodamine probe 6 (Fig. 4) dis-played a highly selective fluorescent enhancement with Cu2+

among the various metal ions in 20 mM HEPES (0.5% CH3CN) atpH 7.4. Upon addition of Cu2+ to this solution, a pink color(kmax = 556 nm) was developed and the resulting species exhibitedstrong orange fluorescence (kmax = 572 nm). These absorption andemission changes were attributed to the Cu2+-induced spirolactamring opening process as shown in Fig. 4. The association constant of6 for Cu2+ was determined to be 2.8 � 103 M�1. Furthermore, thismonoboronic acid-conjugated rhodamine probe was applied to de-tect copper ions in mammalian cells and zebra fish.

New BODIPY derivatives (7 and 8) were synthesized as ‘‘Off–On’’fluorescent chemosensor and fluorescent chemodosimeter for Cu2+

(Fig. 5) [12]. Compound 8 showed a highly selective CHEF (chelationenhanced fluorescence) effect only with Cu2+ among the metal ionsexamined. The fluorescence emission intensity of 8 reached itsmaximum when 5 equiv. of Cu2+ was added, and a gradual decreasein its emission intensity as well as a red-shift (�9 nm) were ob-served as the concentration of Cu2+ increased. A similar red shiftand an absorbance decrease of 8 were also observed in its UV spec-tra. A small amount of water comes from copper perchlorate-hy-

ON N

O

N N

O

+

ON N

O

N N

BO

OH

H

es of 5 and 6 with Cu2+.

N NB

FF

N

OO

O O

N NB

FF

N NB

FF

N

OOOO

N

OOHH

8 7

Cu2+

fast

Fig. 5. Proposed mechanism of recognition/reactivity of compound 7and 8 towards Cu2+.


drate as well as tightly bound Cu2+ in the binding site promotedhydrolysis of acetyl groups in 8 resulting in 7-Cu2+. These resultsdemonstrated that this compound can be utilized as a selectivefluorescent chemodosimeter for Cu2+ (see Fig. 6).

We reported a small library of fluorophore-triazine tripod fluo-rescent system, which can accommodate a combination of threedifferent functional groups, such as fluorophore (BODIPY), ligand(or ligands) and auxiliary group [13]. The binding properties ofthese tripod fluorescent systems were determined using Ag+,Ca2+, Cd2+, Co2+, Cu2+, Cs+, Hg2+, K+, Mg2+, Mn2+, Na+, Ni2+, Pb2+

and Zn2+ ions (2 eq.) to evaluate the metal ion binding propertiesof these compounds in acetonitrile. For different ligands, com-pound 9 (Fig. 5) bearing one 2-methylpyridine binding unitdisplayed a highly selective fluorescent quenching effect with onlyCu2+ among the metal ions examined. Compound 10 bearing onedi-(2-picolyl)amine (DPA) unit also displayed a large and selective

N NB

FF

O

N

N

N

ClHN

N

N NB

FF

O

N

N

N

Cl N

N

N

N

NBF

F

9 10

12

N NB

FF

O

N

N

N

N N

N

N

N

N

Fig. 6. Structures of c

CHEQ (chelation enhanced fluorescence quenching) effect withCu2+, even though there were relatively small CHEQ effectswith Hg2+, Pb2+ and Zn2+. Compound 13 bearing two signal BODIPYunits and one DPA unit displayed a large CHEQ effect with Cu2+,and relatively small CHEQ effects with Hg2+, Pb2+ and Zn2+. Com-pound 11 bearing two 2-methylpyridine binding units displayeda highly selective fluorescent quenching effect with only Cu2+,and compound 12 bearing two DPA binding units displayed largeCHEQ effects with Co2+, Cu2+ and Ni2+.

Two 4,5-disubstituted-1,8-naphthalimide derivatives 14 and 15were synthesized as ratiometric fluorescent sensor and colorimetricsensors for Cu2+ [14]. In 100% aqueous solutions of 14, Cu2+ induceda fluorescent enhancement centered at 478 nm at the expense of thefluorescent emission of 14 centered at 534 nm. 15 senses Cu2+ bymeans of a colorimetric (primrose yellow to pink) method with athorough quench in emission attributed to the deprotonation of

N NB

FF

O

N

N

N

HN

HN

NN

N

N

N

OO

NNN

N

NB F

F

11

13

ompounds 9–13.


the secondary amine conjugated to the naphthalimide fluorophore.14-Cu2+ and 15-Cu2+ were further applied to sense cyanide in ratio-metric way via colorimetric and fluorescent changes.

A new naphthalimide-calix [4] arene was synthesized as atwo-faced and highly selective fluorescent chemosensor for Cu2+

or F� [15]. This chemosensor displayed a selective fluorescencequenching effect only with Cu2+ among the various metal ions(Fig. 8). From the fluorescent titrations, the association constantof 16 with Cu2+ in acetonitrile was calculated to be 6.1 �104 M�1. Similar high selectivity for Cu2+ in the presence of 10%aqueous system (CH3CN:water = 9:1, v/v) was also observed forthe fluorescent study. The weak and red-shift emission wasrecorded for 16 with Cu2+, this unique change can be attributedto the deprotonation of naphthalimide NH in the presence of Cu2+.

A new cavitand derivative 17 bearing four coumarin groups(Fig. 7) was also synthesized and studied as a Cu2+ selectivefluorescent chemosensor [16]. Compound 17 in acetonitrile-chloro-form (4:1, v/v) showed unique large CHEQ effect only with Cu2+

among the metal ions examined. The job plot using the fluorescencechanges indicated a 1:4 binding for compound 17 with Cu2+. Fromthe fluorescence titration experiments, the Kd value with Cu2+

was observed to be �3 lM. The binding of this complex with dicar-boxylates was further demonstrated via the fluorescent changes.

A new fluorescent chemosensor based on the fluorescein deriv-ative which effectively recognized Cu2+ in nanomolar range at pH7.4 [17]. Compound 18 (Fig. 9) displayed a large CHEQ effect withCu2+ and the dissociation constants of complex 18 with Cu2+ wascalculated to be 26 nM. Furthermore, the usefulness of the titlefluorescent chemosensor 18 as a sensor was demonstrated bymonitoring Cu2+ ion uptake by copper binding proteins such astransferrin and amyloid precursor protein, respectively. This highlysensitive Cu2+-selective chemosensor can be suitable for manyother biological applications possibly including in vivo experi-

HN

OH

NO O

HN

N

HN

OH

NO O

N6

NN

6

14 15

Fig. 7. Structures of compounds 14 and 15.

OHOH OO

HNNH

N OO

16

OOO

RH

O

N

O

O

Cu2+

Fig. 8. Strructures of 1

ments. Later, we also utilized Cu2+ complex of this fluoresceinderivative for the detection of cyanide in aqueous solution [18].

Sulfur containing anthracene derivatives (Fig. 9) were synthe-sized as fluorescent chemosensors for Cu2+ [19]. Compound 19 dis-played a highly selective CHEQ effect only with Cu2+ among themetal ions examined whereas compound 20, 1,8-isomer, showedquite different emission patterns, a large CHEF effect along witha red-shift (� 40 nm) upon the addition of Cu2+.

Conjugated polymer based sensors have been extensively stud-ied because their absorption, emission, and redox characteristicsare sensitive to environmental perturbations [20]. Among them,polydiacetylenes (PDAs) have attracted significant attention fortheir unique chromatic properties [21]. We recently synthesizednew azide- and alkyne- functionalized polydiacetylene (PDA-aa)vesicles (Fig. 10) and applied them as a new method for visual detec-tion of Cu2+ [22]. In the presence of ascorbic acid, Cu2+ can be reducedto Cu+, which catalyzed the click reaction between the two func-tional groups. After incubation with Cu2+ and ascorbic acid, PDA-aa solution changed its color from blue to red, which was attributedto conformational transition of the conjugated backbone. Othermetal ions were explored but only induced negligible color changes.

2.2. Chemosensors for Hg2+/CH3Hg+

Mercury is one of the most prevalent toxic metals in the envi-ronment, and gains access to the body orally or dermally. The USEPA (Environmental Protection Agency) standard for the maximumallowable level of inorganic Hg in drinking water is 2 ppb [23]. Dueto the high toxicity of mercury, considerable attention has beendevoted to the development of new fluorescent chemosensors forthe detection of mercury and mercuric salts [24].

We recently reported two rhodamine hydrazone derivativesbearing thiol and carboxylic acid groups, respectively, as selectivefluorescent and colorimetric chemosensors for Hg2+ [25]. Thering-opening process of spirolactam induced large fluorescentenhancement and colorimetric change upon the addition of Hg2+.In CH3CN-H2O (1:99, v/v) solution, about 10-fold and 50-foldenhancements in fluorescent intensities of 21 and 22 were ob-served upon the addition of 100 equiv. Hg2+ (Fig. 11). By monitor-ing the fluorescence of microchannel containing 21/22 with Hg2+, alinear response was observed in the range of 1 nM–1 lM with thedetection limits of 1 nM for 21 and 4.2 nM for 22, respectively. TheJob’s plots indicated the 2:1 stoichiometry for the binding of 21and Hg2+ and the 1:1 stoichiometry for the binding of 22 andHg2+. Both chemosensors were also successfully applied to visual-ize Hg2+ accumulated in the nematode C. elegans, which was previ-ously exposed to nanomolar concentrations of Hg2+.

OO

O O

R RRHH H

O

N

O

N

O

N

O

O

O

O

O

O

17, R = CH2CH2Ph

Cu2+ Cu2+Cu2+

6 and 17–4Cu2+.

O

COOHCl Cl

HO O

N NHO2C

HO2C

CO2H

CO2HS

S

S S

18 19 20

Fig. 9. Structures of 18–20.

HN N N

O

HN

O

N N

HN

O

N N

N3

Cu2+ ascorbic acid

7

7

7 3

3

3

HN N N

O

HN

O

N N

HN

O

N N

7

7

7 3

3

3

NN

N

PDA-aa

Fig. 10. PDA-aa vesicle functionalized with azide and alkyne groups and the detection of Cu2+ using click chemistry.


A rhodamine-based sensor 23 (Fig. 11) bearing histidine groupwas also reported for the detection of Hg2+ [26]. Two carbonyl oxy-gens as well as imidazole nitrogen in probe 23 provided a nicebinding pocket for Hg2+. In 0.02 M pH 7.4 HEPES:EtOH (1:9, v/v),the addition of 100 equiv. Hg2+ induced over 100-fold increase influorescence due to the spiro-lactam ring opening. In contrast, noresponses were observed when other metal ions were added. Fromthe fluorescence titrations, the association constant of 23 with Hg2+

was calculated to be 2.0 � 103 M�1. Probe 23 was also further ap-plied to detect Hg2+ in the cell.

Rhodamine derivatives 24 and 25 (Fig. 12) bearing mono andbis-boronic acid groups displayed selective fluorescent and colori-metric changes for Hg2+ in CH3CN–HEPES buffer (pH 7.4, 10 mM)(9:1, v/v) [27]. Two boronic acid derivatives displayed selectiveand large fluorescent enhancements and distinct color changes

with Hg2+. The association constants of 24 and 25 with Hg2+ werecalculated as 3.3 � 103 M�1 and 2.1 � 104 M�1, respectively. Bis-boronic probe 25 displayed about 9-fold tighter binding withHg2+ compared to mono-boronic probe 24, which can be attributedto an additional boronic acid moiety of 25.

Two new rhodamine derivatives (26 and 27) bearing ureagroups were synthesized as Hg2+ selective fluorescent and colori-metric chemosensors (Fig. 13) [28]. The dimeric system 27 showeda highly selective fluorescent enhancement and colorimetricchanges upon the addition of Hg2+ in acetonitrile, on the contrary,compound 26 showed a poorer selectivity toward Hg2+. The associ-ation constants of 26 and 27 with Hg2+ were calculated as2.9 � 104 M�1 and 3.2 � 105 M�1, respectively.

A new rhodamine 6G derivative bearing spirothiolactone ring28 (Fig. 14) showed a very high selectivity towards the Hg2+ ion

ON N

N

O

N

SH

ON N

N

O

N

COOH

O

N

O

NN

NH

O

NH2

21 22 23

N

NH


O

N

O

NN

NH

(HO)2B

O

N

O

NN

N

(HO)2B

(HO)2B

24 25


O NH

NH

S

O

O NN

Se

O

28 29



over other metal ions in the CH3CN–HEPES buffer (0.01 M, pH 7.4)(1:99, v/v) [29]. An enhancement of up to 200-fold ‘‘Off–On’’ typefluorescence for 28 was observed after the addition of the Hg2+. Aunique 2:1 binding mode (28:Hg2+) was confirmed by electro-spray-ionization mass spectroscopy (ESIMS), the Job’s plot, andX-ray crystal structure data. The spirothiolactone ring-openedstructure, as well as the coordination of the two sulfur atoms toHg2+, was clearly confirmed. Probe 28 was also successfully appliedto visualize Hg2+ accumulated in the nematode C. elegans.

Methylmercury species, which can readily pass through biolog-ical membranes, are much more toxic than inorganic mercury spe-cies [30]. Based on the high affinity between mercury andselenium, we designed a fluorescent chemodosimeter 29 (Fig. 14)based on rhodamine B selenolactone for inorganic mercury andmethylmercury species [31]. The fluorescence enhancement andUV-vis spectral change induced by mercury/methylmercury spe-

ON N

N

ONH

NH

NO2

O

ON

N

O

O

N

26

Fig. 13. Structures of rhodamine B urea derivatives (26 an

cies were attributed to deselenation reaction. The fluorescenceintensity of 29 was linearly proportional to the Hg2+ concentrationof 0–30 nM. Job’s plot indicated the binding mode of 1:1 stoichi-ometry between 29 and Hg2+. This sensor was successfully appliedto detect inorganic mercury/methylmercury species in cells andzebrafish.

As other approach, we synthesized an anthracene derivative,which bears azathiacrown ligand on the 1,8-positions of anthra-cene framework [32]. The fluorescent chemosensor 30 (Fig. 15) di-played extreme selectivity for Hg2+ in aqueous solution atphysiological pH and it showed a selective large CHEQ effect withHg2+ (Ka = 1.95 � 105 M�1). The anthracene moiety in host 30 actsnot only as a fluorescence source but also as a template for intro-ducing the binding selectivity. These results suggest that the rigidcapping of azacrown ligand onto a fluorophore framework may beemployed successfully in the creation of selective chemosensors.

We further extended this similar strategy to acridine deriva-tives, which bear immobilized azacrown or azathiacrown ligands

N

NH

O NN

N

OHN

NHO

HNO

O

N

N

NH

NHO

NO

N

HN

HN O

NO

Hg2+

27

d 27) and a proposed binding mode of 27 with Hg2+.


(Fig. 15) [33]. Compound 31 and 32 displayed large CHEF effectswith Hg2+ and Cd2+ among the metal ions examined at pH 7.4.The association constants of compound 31 with Hg2+ and Cd2+

were calculated to be 1.18 � 105 and 4.48 � 103 M�1, on the otherhand, the association constants of compound 32 with Hg2+ andCd2+ were calculated to be >108 and 3.28 � 104 M�1, respectively.These results explain that cooperative binding from an immobi-lized ligand and nitrogen on acridine can provide such selectivity.The practical use of these probes was demonstrated by their appli-cations to the detection of Hg2+ and Cd2+ ions in mammalian cells.

Two new selenium moieties were also introduced to the the1,8-positions of anthracene framework [19]. Compound 33 and34 (Fig. 15) displayed highly selective CHEF (chelation enhancedfluorescence) effects only with Hg2+ among the metal ions exam-ined in acetonitrile chloroform (4:1, v/v). The association constantswere calculated as 3.6 � 104 and 4.4 � 104 M�1, respectively. Thejob plots indicated 1:1 binding between host 33/34 and Hg2+. Eventhough pyridine moiety in 34 contains additional nitrogen for thebinding with Hg2+, the association constants turned out to be verysimilar.

Two binaphthyl-azacrown-anthracene fluorophores (35 and 36,Fig. 15) were synthesized as selective fluorescent chemosensors forHg2+ in CH3CN–0.01 M HEPES (pH 7.4) (4:1, v/v) [34]. Both of thesecompounds showed large fluorescence enhancements with Hg2+

even though there were moderate fluorescent enhancements withZn2+ and Cu2+. Furthermore, fluorescent emissions from thebinaphthyl and anthracene groups using different excitation wave-lengths showed different patterns with these metal ions. All threemetal ions, such as Hg2+, Zn2+ and Cu2+, showed CHEF effects wheneither 336 nm or 390 nm were used as the excitation wavelength.On the other hand, Zn2+ induced CHEF effects and Cu2+ inducedlarge CHEQ effects when 290 nm was used as the excitation wave-length. The different CHEF and CHEQ effects in the dual emissionchanges from a binaphthyl group and a second fluorophore canprovide more precise detections of their metal ions.

We synthesized other tripod fluorescent systems 33 and 34(Fig. 16), which bear a triazine core for combining three differentfunctional groups, such as fluorophore (BODIPY), ligand and auxil-iary group [35]. To confirm about the auxiliary subunit effect, the

N

S S

NS S

SeSeN

SeSe

30

3433

N

X X

NX XN

31: X= O32: X= S

O

O

ON

O

(R)-35: R = H(R)-36: R = CN

R


fluorescent emission changes in compounds 33 and 34 with Hg2+

(10 eq.) were productively compared (Fig. 16); a quenching effectwith compound 33, and an enhancement and a slight red shift withcompound 34. The large chelation enhanced fluorescence (CHEF)effect of compound 34 upon the addition of Hg2+ can be explainedby the blocking of the PET mechanism.

Another BODIPY derivative bearing piperazine group 39(Fig. 16) was also synthesized and characterized by X-raycrystallography [36]. Among the various metal ions, 39 showed aselective CHEQ effect with Hg2+ in CH3CN-water (95:5, v/v). Fromthe fluorescence titration experiments, the association constantof 1 with Hg2+ was observed to be 2800 M�1, respectively [11].The job plots using the fluorescence changes indicated 1:1 bindingfor 1 with Hg2+.

2.3. Chemosensors for Zn2+

Many of the enzymes available in the human body as well as insea organisms contain zinc as a very essential element and manypathological processes such as cerebral ischemia, Alzheimer’s dis-ease, infantile diarrhea involve intracellular zinc detection[37,38]. Accordingly, its cellular imaging with high sensitivityand selectivity over biologically abundant cations has been activelystudied [39].

We recently reported a simple and effective fluorescent sensor40 (Fig. 17) based on the hyrazone-pyrene [40]. This probe dis-played a highly selective fluorescent enhancement with Zn2+, andapplication of this probe to detect the intrinsic Zn2+ ions presentin pancreatic-cells was successfully demonstrated. The absence ofany significant change in absorption spectra upon the addition ofZn2+ indicated that large fluorescence enhancement with Zn2+

can be attributed to the blocking of the PET process from nitrogenin the hydrazone moiety to pyrene.

An NBD based TRPEN chemosensor 41 was also synthesized re-cently [41]. Compound 41 displayed a red-to-yellow color changeand a selective fluorescence enhancement in the presence of Zn2+

with a slight wavelength change. The addition of Zn2+ to 41 in100% aqueous solution (0.1 M HEPES, pH 7.2) caused a large CHEF,which was explained by photoinduced electron transfer (PET) andinternal charge transfer (ICT) mechanisms. The dissociation con-stant (Kd) of 41 with Zn2+was calculated as 1.3 ± 0.13 lM. The prac-tical use of this probe was demonstrated by its application to thebiologically relevant detection of Zn2+ ions in pancreatic b-cells.

Even though DPA-based receptors have higher affinities for Zn2+

over alkali and alkaline-earth metal ions, they show similar affini-ties for most of transition and heavy metal (HTM) ions. Recently,we reported a new strategy called ‘receptor transformer’. We syn-thesized an amide- containing DPA receptor for Zn2+, combinedwith a naphthalimide fluorophore (42, Fig. 18) [42]. Compound42 binds Zn2+ in an imidic acid tautomeric form of the amide-

N NB

FF

O

N

N

N

A N

N

N

HN Cl

HN N

37 : A =

38 : A =

N NB

FF

N

N

39

Fig. 16. Structures of compounds 37–39.

OHHC

N NH2

N

NO

N

NO2

N

N

NN

40 41

Fig. 17. Structure of compounds 40 and 41.


DPA receptor in aqueous solutions with the highest affinity(Kd = 5.7 nM), while most other HTM ions are bound to the chemo-sensor in an amide tautomeric form (Fig. 18). Due to this differentialbinding mode, 42 showed excellent selectivity for Zn2+ over mostcompetitive HTM ions, and an enhanced fluorescence (22-fold) aswell as a red-shift in emission from 483 nm to 514 nm was ob-served with Zn2+. Interestingly, the 42/Cd2+ complex (Kd = 48.5 nM)showed an enhanced (21-fold) blue-shift in emission from 483 nmto 446 nm. We demonstrated that 42 could discriminate in vitro andin vivo Zn2+ and Cd2+ with green and blue fluorescence, respectively.Finally, 42 was successfully applied to detect zinc ions during thedevelopment of living zebrafish embryos.

New 4- or 8-substituted-7-hydroxycoumarin derivatives 43–45(Fig. 19) were recently reported as fluorescent sensors for metal ionsin HEPES buffer solutions (20 mM, pH 7.4) containing 1% DMSO [43].Probe 43, which has an iminodiacetic acid diethyl ester ligand at the8-position, displayed a selective and large fluorescenceenhancement with Zn2+ even though there was a small fluorescenceenhancement with Cd2+ and fluorescence quenching effects withCu2+ and Ni2+. The association constant of probe 43 with Zn2+ wascalculated as 1.7 � 104 M�1. Among the metal ions examined, probe44, which has an iminodiacetic acid group at the 4-position, showedlarge fluorescence enhancements only with Zn2+ and Cd2+. As com-pared to probe 43, probe 44 displayed less selectivity for Zn2+ over

O

N

N

N

M2+

NONO O

HN

N

ON

N

M2+

aqueous solution

42 42-M2+

amide tautomer

Fig. 18. Different binding modes of 42 with Zn

OO OH

N

O

O

O O

43

OO

NHO

OH

O O

44

Fig. 19. Structures of c

Cd2+, however, the fluorescent changes for other metal ions wererelatively reduced. The association constants were calculated as4.2 � 105 M�1 for Zn2+, and 1.3 � 104 M�1 for Cd2+, respectively.Two carboxylate oxygens vs phenolate could be the reason for thelarger association constants of probe 44 compared to those of probe43. Probe 45, in which DPA ligand was introduced at the 4-position,showed large fluorescence enhancements with Zn2+ and Cd2+ andfluorescence quenching effects with Cu2+ and Hg2+. From the fluo-rescence titrations, the association constants were calculated as1.4 � 105 M�1 for Zn2+, and 1.2 � 104 M�1 for Cd2+, respectively.

2.4. Chemosensors for Pb2+

Lead is a poisonous metal and its poisoning mostly comes fromingestion of contaminated food or water. Long-term exposure tolead or its salts can damage nervous connections (especially inyoung children) and cause blood and brain disorders [44]. In2005, we reported a rhodamine-B derivative 46 as a fluorescentchemosensor for Pb2+ (Fig. 20) [45]. A single crystal of compound46 was characterized using X-ray crystallography, which for thefirst time represented the unique spirolactam-ring formation.Upon the addition of Pb2+ to a colorless solution of 46 in acetoni-trile, both a pink color and the fluorescence characteristics of rho-damine B appeared. Because both changes disappeared upon theaddition of excess cyclen or ethylenediamine, it is believed thatthe complexation of 46 with Pb2+ is reversible.

Recently, we have developed a new PDA-based chemosensorsystem for the detection of Pb2+ in aqueous solution [46]. UV irra-diation of the mixtures of both DA monomers (47:PCDA = 1:9) in-duced the formation of stable and blue-colored PDA molecules 48(Fig. 21). 48 displayed a selective and clear blue-to-red transitiononly with Pb2+ in HEPES (10 mM, pH 7.4) among various metalions. The blue-to-red transition of the PDAs was also accompaniedby the enhancement of fluorescence. The fluorescence spectra ofthe PDAs 48 showed a gradual increase in the presence of 0–9 lM Pb2+ with the detection limit of 0.8 ppm.

NO O

N

N

ON

N

Zn2+

N

O

H H

Zn2+

aqueous solution

42-Zn2+

imidic acid tautomer

2+ over other metals in aqueous solution.

OH

45

O

O

OH

NN

N

ompound 43–45.

O NN

N

O

NN

N

Pb2+

O NN

O

NN

NN

46

Fig. 20. Proposed binding mechanism for the fluorescence enhancement of 46 upon addition of Pb2+.


2.5. Chemosensors for Cd2+

A new anthracene derivative as a reverse PET chemosensor formetal ions was synthesized in 2001 [47]. An anthryl tetra acid 49(Fig. 23) showed large fluorescence quenching effects in 100%aqueous solution (pH 7.0) with metal ions via photoinduced elec-tron transfer. Unlike other metal ions, the addition of Cd2+ inducedan additional broad, red-shifted band yielding the composite spec-trum with kmax 435 nm. Based on the NMR experiments, uniquechelatoselective fluorescence perturbation in the presence of Cd2+

was attributed to the electrophilic aromatic cadmination at the9-position of anthracene. On the contrary, chemosensor 50(Fig. 22) displayed a selective CHEF effect with Cd2+ among the me-tal ions examined at pH 10 [48].

2.6. Chemosensor for vanadate

We recently reported tris(2-((ethylimino)methyl)pyren-1-ol)a-mine 51 as a first optical sensor of tetrameric vanadate and uniquebinding process was proposed by both distinct colorimetric andfluorescent changes (Fig. 23) [49]. During the titration, 51 was sup-posed to bind V1 (monomeric, VO4

3�), V4 (tetrameric, V4O124�),

and V5 (pentameric, V5O155�) simultaneously, and the color of

the solution 51 changed from pink to yellow, with a strong yel-low-green fluorescence. Interestingly, the equilibrium of oligo-meric vanadates shifted towards V4 slowly, since 51preferentially binds V4 over V1 and V5. and the situation reachedthe maximum point after 8 h of the addition of monovanadate. Thecolor of solution 51 changed from yellow to orange, with a strong

HOO

HNO O

HOO

UV

11

7

11

7

11

7

11

7

HO

N

N N

O

NH

N

11

7

NN

47

Fig. 21. Self-assemble and polymer

yellow fluorescence emission. Therefore, the two step recognitionprocesses of vanadate with 51 were successfully indicated by thecolorimetric and fluorescent changes (Fig. 23).

2.7. Chemosensors for noble metal ions

Noble metals, such as gold, silver, platinum and palladium, arewidely used to prepare dental materials, catalysts, fuel cells, jew-elry, and anticancer drugs. However, their frequent use can resultin a high level of residual noble metal ions, which may result inthe contamination of water systems and soil and therefore causea health hazard. In this regards, selective sensing methods wouldbe very useful for real-time monitoring of these metal ions in envi-ronmental and biological samples.

In 2002, we reported two fluorescence sensors 52 and 53 withan anthracene-functionalized pyrazole receptor for Ag+ (Fig. 24)[50]. Compound 52 displayed fluorescence quenching effects withAg+ and Cu2+ ions in CHCl3–ethanol (7:3, v/v). The association con-stants for Ag+ and Cu2+ were calculated to be 1.25 � 105 and1.34 � 105 M�1, respectively. Compound 53 displayed a selectivefluorescent quenching effect only with Ag+ ion, and its associationconstant was calculated as 2.44 � 103 M�1, which means that 52binds with Ag+ about 100-fold more strongly than 53. The overallfluorescent emission change of 53 was ca. 20-fold and that of the52 was 0.3-fold, which can be attributed to the additional Ag+–pinteraction in the case of 53 (Fig. 24).

We also reported two fluorescein derivatives 54 and 55 bearingmorpholine and thiomorpholine substituents, respectively for thedetection of Ag+ (Fig. 26) [51]. Chemosensors 54 and 55 showed

HOO O

HOO

HOO

48

10 10 10 10

7 7 7 7

HN

N

NN

ization of monomer 47 and 48.

N

N

CO2H

CO2H

CO2H

CO2H5049

NN

CO2HHO2C

HO2C CO2H

Fig. 22. Structure of compounds 49 and 50.

N NN N

N N

NN

52

53

Ag+ N NN NAg+

Ag+N

NN

NAg+

Fig. 24. Proposed binding modes of 52 and 53 with Ag+.


high binding selectivity towards Ag+ ions and showed completelydifferent fluorescent and colorimetric changes upon the additionof Ag+. Chemosensor 54 showed a selective CHEF effect with Ag+

at pH 7.4 (0.01 M HEPES:DMSO = 95:5, v/v). On the other hand,the fluorescence of chemosensor 55 showed a selective CHEQ ef-fect and a light yellow to pink color change took place upon theaddition of Ag+. Two different binding modes are explained inFig. 25. The data from the fluorescence titration experiments gaveassociation constants of 3.5 � 103 M�1 and 3.2 � 109 M�2 for 54and 55, respectively, with Ag+.

Two naphthalimide derivatives 56 and 57 were reported re-cently (Fig. 26) [52]. Probe 56 can detect Ag+ with a selective fluo-rescence enhancement (�14-fold) and high association constant(Ka = 1.24 � 105 M�1) in CH3CN–H2O (50:50, v/v; 0.5 M HEPES buf-fer at pH 7.4) solution. Furthermore, Ag+ could be detected at leastdown to 1.0 � 10�8 M. On the other hand, the reference compound57 without the carbonyl group did not show a strong binding with

OV VO O

O OO O

V2

VO

OOO

V1

OOO

OHO

V

V

O

O

O

O

O

N

N

N

N

HO

51

HOHO

Fig. 23. Propose binding mechanism of comp

Ag+, which suggests that the carbonyl group between the 1,8-naphthalimide and [15] aneNO2S2 plays an important role for theselective fluorescence enhancement.

In 2011, we synthesized a bis-pyrene derivative 58 bearing twopyrenes and reported as a ratiometric fluorescent chemosensor forsilver ions at physiological pH (Fig. 27) [53]. Compound 58 showeda selective fluorescence change only with Ag+ in DMSO-HEPES (pH7.4, 1:1, v/v), although there was a relatively smaller quenching ef-fect with Hg2+. In the absence of metal ions, a strong excimer emis-sion was observed at 463 nm, along with a monomer emission at399 nm. upon the addition of Ag+, the excimer peak was signifi-cantly reduced with the enhancement of the monomeric peak.

OV V

OOO

V VO

OO

V4

V

V

V

O

O

O

O

O

O

O

O

OO

V5

NN

N

N

OO

OV

O

N

NN

N

O O

OOV VO

O

OOVV

O

OO

O

N

NN

N

OO

O

OV VO

O

OOV

VO

OO O

VO

OO-

ound 51 with different vanadate species.

O

CO2

Cl

O O

Cl

N N

O O

HH

54Fluorescent

Yellow Solution

O

CO2

Cl

HO O

Cl

N

O

N

O

Ag+Ag+

High FluorescentYellow Solution

O

CO2

Cl

O O

Cl

N N

S S

HH

55Fluorescent

Yellow Solution

Ag+ O

CO2

Cl

O O

Cl

S

N N

S

PET

Ag+ Ag+

Less FluorescentPink Solution

Fig. 25. Proposed binding modes of 54 and 55 with Ag+.

NO O

NH

S O

OS

N

O

NO O

NH

S O

OS

N

56 57

Fig. 26. Structures of compound 56 and 57.


The 1:1 stoichiometry of the 53-Ag+ complex was confirmed andthe association constant of 58 with Ag+ was calculated as3.2 � 105 M�1.

A rhodamine-alkyne derivative 59 as the first fluorescent andcolorimetric chemodosimeter for Au3+ was reported recently(Fig. 28) [54]. Probe 59 displayed a selective fluorescence enhance-ment (over 100-fold) and colorimetric change (from colorless topink) with Au3+ in EtOH–HEPES buffer (0.01 M, pH 7.4) (1:1, v/v).

N NN N

Ag+

58

Fig. 27. Proposed binding

The product was isolated and characterized as the oxazolecarbal-dehyde of 55. There was also a large enhancement (�6-fold) inthe UV absorption (kmax = 562 nm) of probe 59 upon the additionof Au3+. The rate constant for the conversion of 59 (5 lM) to 60was measured in the presence of Au3+ (10 equiv.), and estimatedto be Kobs = 4.5 (±0.20) � 10�4 s�1. The detection limit was esti-mated to be 63 ppb in EtOH–water (1:1, v/v). Finally, probe 59was successfully applied to the cell imaging of Au3+.

3. Conclusions and future perspectives

Due to the biologically and environmentally importance, detec-tion of metal ions has emerged as a significant goal in the field ofchemical sensors in recent years. Certainly fluorescence has beenproven to be the most powerful tool due to its simplicity, highdetection limit and application to bioimaging. In this review, wefocused our recent contributions to this field. This review was cat-egorized by target metal ions, such as Cu2+, Hg2+, Zn2+, Pb2+, Cd2+,Vanadate, Ag+ and Au3+. Selectivity and sensitivity for these metalions were achieved by introducing various ligands to core fluoro-phores, such as, rhodamine, fluorescein, pyrene, anthracene, naph-thalimide, coumarin, and BODIPY.

Generally, there are three different approaches to design fluo-rescent chemosensors. The most popular way involves the use ofsensors in which the binding sites and signaling subunits are

N N

N NAg+

mode of 58 with Ag+.

59

O

N

O

Et2N NEt2 OEt2N NEt2

O

N

CHO

60

Au3+

Fig. 28. Au3+-induced transformation from 59 to 60.


linked covalently. A coordination complex-based displacement ap-proach has also been used. A third method is known as a chemod-osimeter approach. These types of sensors rely on the occurrenceof specific, most often irreversible chemical reactions. In thisreview, these three approaches are adopted to design variouschemosensors. Especially, second approach was used for the detec-tion of cyanide from Cu2+ complex of chemosensors [14,18,55]. Inaddition, metal complexes can be further used as fluorescentchemosensors for biologically important anionic species, such aspyrophosphate [55], ATP [57], UTP [56].

We believe fluorescent chemosensors will be developed intelli-gently with aid of molecular recognition, supramolecular chemis-try and ligand engineering. Nowadays, specific and sensitivefluorescent chemodosimeters are actively reported utilizing con-ventional organic reactions. Application to biology and environ-mental science is another driving force for researchers of thisfield in the future.

Acknowledgment

This work was supported by National Research Foundation(NRF) Grant (2011-0020450), WCU (R31-2008-000-10010-0) andby the Converging Research Center Program through the Ministryof Education, Science and Technology(2011K000720). J.Y. also dee-ply thanks to previous and present group members.

References

[1] H.N. Kim, M.H. Lee, H.J. Kim, J.S. Kim, J. Yoon, Chem. Soc. Rev. 37 (2008) 1465.[2] (a) D.T. Quang, J.S. Kim, Chem. Rev. 110 (2010) 6280;

(b) A.P. de Silva, H.Q.N. Gunaratne, T. Gunnlaugsson, A.J.M. Huxley, C.P. McCoy,J.T. Rademacher, T.E. Rice, Chem. Rev. 97 (1997) 1515;(c) J.S. Kim, S.Y. Lee, J. Yoon, J. Vicens, Chem. Commun. (2009) 4791;(d) J.F. Zhang, Y. Zhou, J. Yoon, J.S. Kim, Chem. Soc. Rev. 40 (2011) 3416.

[3] (a) X. Chen, Y. Zhou, X. Peng, J. Yoon, Chem. Soc. Rev. 39 (2010) 2120;(b) R. Martinez-Manez, F. Sancenon, Chem. Rev. 103 (2003) 4419;(c) Z. Xu, X. Chen, H.N. Kim, J. Yoon, Chem. Soc. Rev. 39 (2010) 127;(d) Z. Xu, S.K. Kim, J. Yoon, Chem. Soc. Rev. 39 (2010) 1457;(e) S.-K. Ko, X. Chen, J. Yoon, I. Shin, Chem. Soc. Rev. 40 (2011) 2120;(f) S.K. Kim, H.N. Kim, Z. Xiaoru, H.N. Lee, H.N. Lee, J.H. Soh, K.M.K. Swamy, J.Yoon, Supramol. Chem. 19 (2007) 221;(g) X. Chen, X. Tian, I. Shin, J. Yoon, Chem. Soc. Rev. 40 (2011) 4783;(h) Y. Zhou, Z. Xu, J. Yoon, Chem. Soc. Rev. 40 (2011) 2222.

[4] G. Multhaup, A. Schlicksupp, L. Hesse, D. Beher, T. Ruppert, C.L. Masters, K.Beyreuther, Science 271 (1996) 1406.

[5] R.A. Lovstad, BioMetals 17 (2004) 111.[6] E.L. Que, D.W. Domaille, C.J. Chang, Chem. Rev. 108 (2008) 1517.[7] E.J. Jun, H.N. Won, J.S. Kim, K.H. Lee, J. Yoon, Tetrahedron Lett. 47 (2006) 4577.[8] X. Chen, M.J. Jou, H. Lee, S. Kou, J. Lim, S.-W. Nam, S. Park, K.-M. Kim, J. Yoon,

Sens. Actuators B 137 (2009) 597.[9] Z. Xu, J. Yoon, D.R. Spring, Chem. Commun. 46 (2010) 2563.

[10] Y. Zhou, W. Fang, Y. Kim, S. Kim, J. Yoon, Org. Lett. 11 (2009) 4442.[11] K.M.K. Swamy, S.-K. Ko, S.K. Kwon, H.N. Lee, C. Mao, J.-M. Kim, K.-H. Lee, J. Kim,

I. Shin, J. Yoon, Chem. Commun. (2008) 5915.[12] X. Qi, E.J. Jun, L. Xu, S.-J. Kim, J.S.J. Hong, Y.J. Yoon, J. Yoon, J. Org. Chem. 71

(2006) 2881.[13] X. Qi, S.K. Kim, S.J. Han, L. Xu, A.Y. Jee, H.N. Kim, C. Lee, Y. Kim, M. Lee, S.-J. Kim,

J. Yoon, Supramol. Chem. 21 (2009) 455.[14] Z. Xu, J. Pan, D.R. Spring, J. Cui, J. Yoon, Tetrahedron 66 (2010) 1678.[15] Z. Xu, S. Kim, H.N. Kim, S.J. Han, C. Lee, J.S. Kim, X. Qian, J. Yoon, Tetrahedron

Lett. 48 (2007) 9151.[16] Y.J. Jang, B.-S. Moon, J.H. Park, J.Y. Kwon, Y.J. Yoon, K.D. Lee, J. Yoon,

Tetrahedron Lett. 47 (2006) 2707.[17] (a) E.J. Jun, J.-A. Kim, K.M.K. Swamy, S. Park, J. Yoon, Tetrahedron Lett. 47

(2006) 1051;

(b) S. Kou, H.N. Lee, D. van Noort, K.M.K. Swamy, S.H. Kim, J.H. Soh, K.-M. Lee,S.-W. Nam, J. Yoon, S. Park, Angew. Chem., Int. Ed. 47 (2008) 872.

[18] S.-Y. Chung, S.-W. Nam, J. Lim, S. Park, J. Yoon, Chem. Commun. (2009) 2866.[19] Y.J. Lee, D. Seo, J.Y. Kwon, G. Son, M.S. Park, J.H. Sho, H.N. Lee, K.D. Lee, J. Yoon,

Tetrahedron 62 (2006) 12340.[20] H.N. Kim, Z. Guo, W. Zhu, J. Yoon, H. Tian, Chem. Soc. Rev. 40 (2011) 79.[21] (a) X. Chen, S. Kang, M.J. Kim, J. Kim, Y.S. Kim, H. Kim, B. Chi, S.-J. Kim, J.Y. Lee, J.

Yoon, Angew. Chem., Int. Ed. 49 (2010) 1422;(b) X. Chen, J. Lee, M.J. Jou, J.-M. Kim, J. Yoon, Chem. Commun. 23 (2009) 3434;(c) K.M. Lee, X. Chen, W. Fang, J.-M. Kim, J. Yoon, Macromol. Rapid. Commun.32 (2011) 497;(d) X. Chen, J. Yoon, Dyes Pigm. 89 (2011) 194;(e) K.M. Lee, J.H. Moon, H. Jeon, X. Chen, H.J. Kim, S. Kim, S.-J. Kim, J.Y. Lee, J.Yoon, J. Mater. Chem. (2011), doi:10.1039/c1jm12818c.

[22] Q. Xu, K.M. Lee, F. Wang, J. Yoon, J. Mater. Chem. 21 (2011) 15214.[23] Mercury Update: Impact on Fish Advisories, EPA Fact Sheet EPA-823-F-01-011,

EPA, Office of Water, Washington, DC, 2001.[24] (a) E.M. Nolan, S.J. Lippard, Chem. Rev. 108 (2008) 3443;

(b) Z. Guo, W. Zhu, M. Zhu, X. Wu, H. Tian, Chem. Eur. J. 16 (2010) 14424.[25] H.N. Kim, S.-W. Nam, K.M.K. Swamy, Y. Jin, X. Chen, Y. Kim, S.-J. Kim, S. Park, J.

Yoon, Analyst 136 (2011) 1339.[26] S.K. Kwon, H.N. Kim, J.H. Rho, K.M.K. Swamy, S.M. Shanthakumar, J. Yoon, Bull.

Korean Chem. Soc. 30 (2009) 719.[27] S.K. Kim, K.M.K. Swamy, S.-Y. Chung, H.N. Kim, M.J. Kim, Y. Jeong, J. Yoon,

Tetrahedron Lett. 51 (2010) 3286.[28] J.H. Soh, K.M.K. Swamy, S.K. Kim, S. Kim, S.-H. Lee, J. Yoon, Tetrahedron Lett. 48

(2007) 5966.[29] X. Chen, S.-W. Nam, M.J. Jou, Y. Kim, S.-J. Kim, S. Park, J. Yoon, Org. Lett. 10

(2008) 5235.[30] ATSDR, Toxicological Profile for Mercury, US Department of Health and Human

Services, Atlanta, GA, 1999.[31] X. Chen, K.-H. Baek, Y. Kim, S.-J. Kim, I. Shin, J. Yoon, Tetrahedron 66 (2010)

4016.[32] J.Y. Kwon, J.H. Sho, Y.-J. Yoon, J. Yoon, Supramol. Chem. 16 (2004) 621.[33] H.N. Lee, H.N. Kim, K.M.K. Swamy, M.S. Park, J. Kim, H. Lee, K.-H. Lee, S. Park, J.

Yoon, Tetrahedron Lett. 49 (2008) 1261.[34] K.S. Kim, E.J. Jun, S.K. Kim, H.J. Choi, J. Yoo, C.-H. Lee, M. Ho Hyun, J. Yoon,

Tetrahedron Lett. 48 (2007) 2481.[35] X. Qi, S.K. Kim, S.J. Han, A.Y. Jee, H.N. Kim, C. Lee, Y. Kim, M. Lee, S.-J. Kim, J.

Yoon, Tetrahedron Lett. 49 (2008) 261.[36] X. Qi, S.K. Kim, E.J. Jun, L. Xu, S.-J. Kim, J. Yoon, Bull. Korean Chem. Soc. 28

(2007) 2231.[37] M.P. Cuajungco, G.J. Lees, Neurobiol. Dis. 4 (1997) 137.[38] D.W. Choi, J.Y. Koh, Annu. Rev. Neurosci. 21 (1998) 347.[39] (a) Z. Xu, J. Yoon, D.R. Spring, Chem. Soc. Rev. 39 (2010) 1996;

(b) X. Lu, W. Zhu, Y. Xie, X. Li, Y. Gao, F. Li, H. Tian, Chem. Eur. J. 16 (2010) 8355.[40] Y. Zhou, H.N. Kim, J. Yoon, Bioorg. Med. Chem. Lett. 20 (2010) 125.[41] Z. Xu, G.-H. Kim, S.J. Han, M.J. Jou, C. Lee, I. Shin, J. Yoon, Tetrahedron 65 (2009)

2307.[42] Z. Xu, K.-H. Baek, H.N. Kim, J. Cui, X. Qian, D.R. Spring, I. Shin, J. Yoon, J. Am.

Chem. Soc. 132 (2010) 601.[43] K.M.K. Swamy, M.J. Kim, H.R. Jeon, J.Y. Jung, J. Yoon, Bull. Korean Chem. Soc. 31

(2010) 3611.[44] H.L. Needleman, Human Lead Exposure, CRC Press, Boca Raton, FL, 1992.[45] J.Y. Kwon, Y.J. Jang, Y.J. Lee, K.M. Kim, M.S. Seo, W. Nam, J. Yoon, J. Am. Chem.

Soc. 127 (2005) 10107.[46] K.M. Lee, X. Chen, W. Fang, J.-M. Kim, J. Yoon, Macromol. Rapid Commun. 32

(2011) 497.[47] M. Choi, M. Kim, K.D. Lee, K.-N. Han, I.-A. Yoon, H.-J. Chung, J. Yoon, Org. Lett. 3

(2001) 3455.[48] S.K. Kim, J.H. Lee, J. Yoon, Bull. Korean Chem. Soc. 24 (2003) 1032.[49] Y. Zhou, J.Y. Jung, H.R. Jeon, Y. Kim, S.-J. Kim, J. Yoon, Org. Lett. 13 (2011)

2742.[50] J. Kang, M. Choi, J.Y. Kwon, E.Y. Lee, J. Yoon, J. Org. Chem. 67 (2002) 4384.[51] K.M.K. Swamy, H.N. Kim, J.H. Soh, Y. Kim, S.-J. Kim, J. Yoon, Chem. Commun.

(2009) 1234.[52] Z. Xu, S. Zheng, J. Yoon, D.R. Spring, Analyst 135 (2010) 2554.[53] W. Fang, R. Nandhakumar, J.H. Moon, K.M. Kim, J.Y. Lee, J. Yoon, Inorg. Chem.

50 (2011) 2240.[54] M.J. Jou, X. Chen, K.M.K. Swamy, H.N. Kim, H.-J. Kim, S.-G. Lee, J. Yoon, Chem.

Commun. (2009) 7218.[55] X. Chen, S.-W. Nam, G.-H. Kim, N. Song, Y. Jeong, I. Shin, S.K. Kim, J. Kim, S. Park,

J. Yoon, Chem. Commun. 46 (2010) 8953.[56] (a) S.K. Kim, D.H. Lee, J.-I. Hong, J. Yoon, Acc. Chem. Res. 42 (2009) 23;

(b) M.J. Kim, K.M.K. Swamy, K.M. Lee, A.R. Jagdale, Y. Kim, S.-J. Kim, K.H. Yoo, J.Yoon, Chem. Commun. (2009) 7215;(c) H.N. Lee, K.M.K. Swamy, S.K. Kim, J.-Y. Kwon, Y. Kim, S.-J. Kim, Y.J. Yoon, J.Yoon, Org. Lett. 9 (2007) 243;(d) H.N. Lee, Z. Xu, S.K. Kim, K.M.K. Swamy, Y. Kim, S.-J. Kim, J. Yoon, J. Am.Chem. Soc. 129 (2007) 3828;(e) X. Chen, M.J. Jou, J. Yoon, Org. Lett. 11 (2009) 2181;(f) X. Huang, Z. Guo, W. Zhu, Y. Xie, H. Tian, Chem. Commun. 41 (2008) 5143;(g) Z. Guo, W. Zhu, H. Tian, Macromolucules 43 (2010) 739.

[57] K.M.K. Swamy, S.K. Kwon, H.N. Lee, S.M. Shanthakumar, J.S. Kim, J. Yoon,Tetrahedron Lett. 48 (2007) 8683.

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