Inorganica Chimica Acta 381 (2012) 137–142

Contents lists available at SciVerse ScienceDirect

Inorganica Chimica Acta

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

A highly selective fluorescence-enhanced chemosensor for Al3+ in aqueoussolution based on a hybrid ligand from BINOL scaffold and b-amino alcohol

Ming Dong, Yu-Man Dong, Tian-Hua Ma, Ya-Wen Wang ⇑, Yu Peng ⇑Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, State Key Laboratory of Applied Organic Chemistry and College ofChemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China

a r t i c l e i n f o

Article history:Available online 3 September 2011

Fluorescence Spectroscopy: from SingleChemosensors to Nanoparticles Science –Special Issue

Keywords:FluorescenceChemosensorAluminum ionSelectivityBINOL derivativesAmino alcohol

0020-1693/$ - see front matter � 2011 Elsevier B.V. Adoi:10.1016/j.ica.2011.08.043

⇑ Corresponding authors. Tel.: +86 931 3902316; faE-mail addresses: ywwang@lzu.edu.cn (Y.-W. W

Peng).

a b s t r a c t

A chemosensor (R)-OH bearing an amino alcohol group was synthesized for the highly selective fluores-cent recognition of Al3+ with low limit of detection (16 ppb). ‘‘Turn-on’’ type fluorescence changes wereobserved upon the addition of Al3+ in aqueous solution. The significant enhancement (35.4-fold) of fluo-rescence intensity was ascribed to the complex formation between (R)-OH and Al3+ which denoted as thechelation-enhanced fluorescence (CHEF) process.

� 2011 Elsevier B.V. All rights reserved.

1. Introduction

Aluminum is the third most abundant metal in Earth’s crust andextensively used in modern life, such as food packaging, cookware,drinking water supplies, antiperspirants, deodorants, bleachedflour, antacids and the manufacturing of cars and computers [1–3]. Excess aluminum, however, can induce many health issues,such as Alzheimer’s disease [4] and Parkinson’s disease [5]. Fur-thermore, it is known that 40% of the world’s acidic soils are causedby aluminum toxicity [6,7]. In view of the biological and environ-mental importance of aluminum, considerable effort has been de-voted to the development of optical chemosensors for the faciledetection of Al3+. But, owing to the weak coordination and stronghydration ability of Al(III) in water, it is easily interfered by the var-iation of pH value of solution and the coexistence of interferingions. In comparison with transition metal ions, relatively scarceexamples of fluorescence chemosensors for Al3+ in either organicmedia [8–16] or aqueous solution [17–23] have been reported todate, among which only two examples [8,10] demonstrated signif-icant fluorescence enhancement. Therefore, the design of highlyselective chemosensor for Al3+ with ‘‘turn-on’’ type fluorescencechanges remains highly desirable.

ll rights reserved.

x: +86 931 8912582.ang), pengyu@lzu.edu.cn (Y.

In connection with our continuing research of chemosensorsbased on 1,10-Binaphthyl fluorophore [24,25], we previouslyreported a series of chemosensors for Al3+ based on BINOLderivatives containing b-amino acid moiety, which showedAl3+-selective fluorescent enhancements in pure CH3OH as a sin-gle-channel fluorescent chemosensor, while only (R)-1 could beused as a double-channel fluorescent sensor in CH3OH–water(1:99, v/v) [26]. In this work, we synthesized a conjugate (R)-OHbased on BINOL and b-amino alcohol (Scheme 1), in order to ex-plore whether the change of bonding sites affect selectivity andsensitivity. The further studies indicate that (R)-OH shows moresuperior Al3+-selective fluorescence enhancement (35.4-fold) inCH3OH–water (95:5, v/v) solutions as a single-channel fluorescentchemosensor with lower limit of detection (16 ppb) compared withthe one from previous receptor (R)-1 [26].

2. Experimental

2.1. General

All chemicals were obtained from commercial suppliers andused without further purification. Methanol was distilled frommagnesium prior to use. Column chromatography was performedon silica gel (200–300 mesh). 1H and 13C NMR spectra were mea-sured on the Bruker 400 MHz instruments using TMS as an internalstandard. ESI�MS were determined on a Bruker esquire 6000 spec-trometer. UV–Vis absorption spectra were determined on a Varian

OH OMOMOMOM

NaH,THFOH

OMOMOMOM

CHO

i) n-BuLi, THFTMEDA

ii) DMF

OHOH

CHO

(R)-BINOL (R)-2 (R)-3

(R)-4

HClEtOH

MOMCl0 oC → r.t. −78 oC → r.t.

0 oC

1) D-phenylalaninolEtOH

2) NaBH4

OHOH

NH OH

(R)-OH

Scheme 1. The synthesis of compound (R)-OH.

138 M. Dong et al. / Inorganica Chimica Acta 381 (2012) 137–142

UV-Cary100 spectrophotometer. Fluorescence spectra were re-corded on a Hitachi F-4500 spectrophotometer equipped withquartz cuvettes of 1 cm path length. All pH measurements weremade with a pH-10C digital pH meter.

2.2. Synthesis

Starting from (R)-1,10-bi-2-naphthol (BINOL), (R)-2,20-dihy-droxy-1,10-binaphthyl-3-carbaldehyde was synthesized accordingto a literature procedure [24,25,27].

Fig. 1. (a) Fluorescent spectra of (R)-OH (20 lM) in the presence of different concentratiCH3OH with 20 lM of Al3+, Li+, Na+, K+, Mg2+, Ca2+, Ba2+, Pb2+, Cu2+, Mn2+, Fe2+, Fe3+, Co2+,responses of (R)-OH (20 lM) to various cations in CH3OH at 375 nm. The orange bars reprblack bars represent the emission intensity that occurs upon the subsequent addition of 2Cu2+, Fe2+, Fe3+, K+, Li+, Mg2+, Mn2+, Na+, Ni2+, Pb2+, Hg2+ and Zn2+. (d) Job’s plot at 375 n

2.2.1. (R)-2,20-Bis(methoxymethyloxy)-1,10-binaphthalene ((R)-2)NaH (1.92 g, 80 mmol) was added to DMF (30 mL) on ice bath.

(R)-BINOL ((R)-2,20-dihydroxy-1,10-binaphthyl) (10 g, 34 mmol) inDMF (50 mL) was dropped to this solution for 20 mim. After30 min, MOMCl (Chloromethyl methyl ether) (6.4 g, 80 mmol) wasadded dropwise to the above solution over 20 min. The reactionwas monitored by TLC. After stirring for 1 h, the reaction mixturewas quenched with water and extracted with chloroform(2 � 100 mL). The crude product was purified by flash chromatogra-phy (Pet/EtOAc = 5:1) on silica gel to give 12.4 g of (R)-2 (95% yield).

ons of Al3+ (0–1.0 equiv) in CH3OH. (b) Fluorescence responses of (R)-OH (20 lM) inNi2+, Ag+, Zn2+, Hg2+ and Cd2+. Excitation wavelength was 337 nm. (b) Fluorescenceesent the emission intensity of (R)-OH in the presence of other cations (20 lM). The

0 lM of Al3+ to the above solution. From left to right: none, Ag+, Ba2+, Ca2+, Cd2+, Co2+,m.

Fig. 2. (a) Benesi–Hildebrand plot (kem = 375 nm) of (R)-OH, assuming 1:1 stoichiometry for association between (R)-OH and Al3+ in CH3OH. (b) Normalized response offluorescence signal at 375 nm to changing Al3+ concentrations.

Fig. 4. Fluorescence intensity of (R)-OH (20 lM) in CH3OH–water (95:5, v/v)solution of different pH in the presence of 20 lM Al3+ (kex = 337 nm).

M. Dong et al. / Inorganica Chimica Acta 381 (2012) 137–142 139

1H NMR (CDCl3, 400 MHz): d 3.15 (s, 6H), 4.99 (d, J = 6.6 Hz, 2H), 5.05(d, J = 6.6 Hz, 2H), 7.12–7.37 (m, 6H), 7.56 (d, J = 9.0 Hz, 2H), 7.87 (d,J = 8.1 Hz, 2H), 7.94 (d, J = 9.0 Hz, 2H) ppm; 13C NMR (CDCl3,100 MHz): d 55.8, 95.1, 117.2, 121.2, 124.0, 125.5, 126.2, 127.8,129.4, 129.8, 134.0, 152.6 ppm; ESI�MS: (m/z) 375.1 [M+H]+.

2.2.2. (R)-3-Formyl-2,20-bis(methoxymethyloxy)-1,10-binaphthalene((R)-3)

To a stirred solution of (R)-2 (3.2 g, 8.55 mmol) in THF (30 mL)at �78 �C was added TMEDA (1.55 mL, 10.3 mmol) and then n-BuLi(6.08 mL, 9.67 mmol, 1.6 M in hexane) over 15 min. The mixturewas warmed to 0 �C and stirred for 30 min. After cooling to�78 �C again, DMF (0.76 mL, 10.3 mmol) in THF (40 mL) was addeddropwise over 10 min. The mixture was stirred at the same tem-perature for 30 min and then was warmed to 0 �C and stirred forfurther 40 min. The resulting yellow solution was quenched withsaturated NH4Cl (5 mL). After addition of (1 N) HCl (5 mL), thesolution was extracted with diethyl ether (100 mL), and the com-bined organic layers were washed with saturated NaHCO3

(50 mL) and brine and then dried over MgSO4. The solvent wasevaporated under reduced pressure and the crude product waspurified by flash chromatography (Pet/EtOAc = 15:1) on silica gelto give 2.4 g of (R)-3 (70%). 1H NMR (CDCl3, 400 MHz): d 3.07 (s,3H), 3.20 (s, 3H), 4.64 (d, J = 6.1 Hz, 1H), 4.74 (d, J = 6.1 Hz, 1H),5.03 (d, J = 7.3 Hz, 1H), 5.21 (d, J = 7.3 Hz, 1H), 7.16–7.64 (m, 7H),7.82–8.17 (m, 3H), 8.61 (s, 1H), 10.63 (s, 1H) ppm; 13C NMR (CDCl3,100 MHz): d 56.0, 57.1, 94.5, 100.2, 116.3, 119.4, 124.3, 125.2,125.9, 126.0, 126.8, 126.9, 128.0, 129.0, 129.6, 130.1, 130.2,130.3, 131.0, 133.7, 137.0, 152.8, 153.8, 191.2 ppm; ESI-MS: (m/z)403.1 [M+H]+.

2.2.3. (R)-2,20-Dihydroxy-1,10-binaphthyl-3-carbaldehyde ((R)-4)To an ice-cooled solution of (R)-3 (5.15 g, 12.8 mmol) in EtOH

(80 mL) was added (6 N) HCl (30 mL), and the mixture was stirred

Fig. 3. (a) Fluorescence spectra of free (R)-OH (20 lM) in CH3OH with different propor(20 lM) in CH3OH with different proportions of H2O.

at for 3 h 0 �C. The mixture was extracted with ethyl ether(3 � 100 mL). The combined organic extracts were washed withbrine, dried over MgSO4, and evaporated under reduced pressure.The residue was then dried in vacuo to afford (R)-4 which was di-rectly used for the next step without further purification (95%yield). 1H NMR (CDCl3, 400 MHz): d 5.01 (s, 1H), 7.06–7.44 (m,7H), 7.85–7.99 (m, 3H), 8.33 (s, 1H), 10.13 (s, 1H), 10.60 (s, 1H)ppm; 13C NMR (CDCl3, 100 MHz): d 76.7, 77.0, 77.3, 113.2, 115.1,117.7, 122.1, 123.5, 124.4, 124.9, 125.0, 126.7, 127.8, 128.3,129.2, 130.0, 130.4, 131.2, 133.4, 137.6, 139.1, 151.4, 154.3,196.6 ppm; ESI-MS: (m/z) 315.1 [M+H]+.

2.2.4. Synthesis of (R)-OHA stirred solution of (R)-2,20-dihydroxy-1,10-binaphthyl-3-carb-

aldehyde (31.4 mg, 0.1 mmol), D-phenylalaninol (15.1 mg,

tions of H2O (kex = 337 nm). (b) Fluorescence spectra of (R)-OH (20 lM) with Al3+

Fig. 5. (a) Fluorescence responses of (R)-OH (20 lM) in CH3OH–water (95:5, v/v; pH 7.5) with 20 lM of Al3+, Li+, Na+, K+, Mg2+, Ca2+, Ba2+, Pb2+, Cu2+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+,Ag+, Zn2+, Hg2+ and Cd2+. Excitation wavelength was 337 nm. (b) Fluorescent spectra of (R)-OH (20 lM) in the presence of different concentrations of Al3+ (0–1.0 equiv) inCH3OH–water (95:5, v/v; pH 7.5). (c) Fluorescence responses of (R)-OH (20 lM) to various cations in CH3OH–water (95:5, v/v; pH 7.5) at 375 nm. The red bars represent theemission intensity of (R)-OH in the presence of other cations (20 lM). The black bars represent the emission intensity that occurs upon the subsequent addition of 20 lM ofAl3+ to the above solution. From left to right: none, Ag+, Ba2+, Ca2+, Cd2+, Co2+, Cu2+, Fe2+, Fe3+, K+, Li+, Mg2+, Mn2+, Na+, Ni2+, Pb2+, Hg2+ and Zn2+. (d) Job’s plot at 375 nm.

140 M. Dong et al. / Inorganica Chimica Acta 381 (2012) 137–142

0.1 mmol) in EtOH (10 mL) was heated to reflux for 5 h under N2.Then excess solid NaBH4 (7.6 mg, 0.2 mmol) was added to theintermediate Schiff base solution in portions with gentle and stir-ring while the orange color slowly discharged. After the ethanolwas evaporated under reduced pressure, the residue was purifiedby silica gel column chromatography (Pet/EtOAc = 1:1) to give(R)-OH (41 mg) as a white solid (91% yield). 1H NMR (400 MHz,CDCl3): d 2.78 (dd, J = 10.8, 5.2 Hz, 1H), 2.92 (dd, J = 10.8, 5.2 Hz,1H), 3.02 (br s, 1H), 3.47 (dd, J = 10.8, 5.2 Hz, 1H), 3.68 (dd,J = 10.8, 5.2 Hz, 1H), 4.26 (s, 2H), 4.71 (brs, 1H, –NH–), 7.12 (d,J = 8.4 Hz, 1H), 7.16 (d, J = 8.0 Hz, 2H), 7.21–7.34 (m, 8H), 7.37 (d,J = 8.8 Hz, 1H), 7.68 (s, 1H), 7.80 (d, J = 8.0 Hz, 1H), 7.86 (d,J = 8.0 Hz, 1H), 7.90 (d, J = 8.0 Hz, 1H) ppm; 13C NMR (100 MHz,CDCl3): d 37.0, 50.5, 59.9, 62.3, 113.2, 114.8, 117.7, 123.3, 123.7,124.6, 124.9, 125.6, 126.5, 126.7, 126.9, 127.8, 128.2, 128.4,128.8, 128.8, 129.1 (2C), 129.2 (2C), 129.9, 133.65, 133.72, 137.8,151.6, 154.8 ppm; ESI-MS: (m/z) 450.3 [M+H]+.

Fig. 6. (a) Benesi–Hildebrand plot (kem = 375 nm) of (R)-OH, assuming 1:1 stoichiometrNormalized response of fluorescence signal at 375 nm to changing Al3+ concentrations.

2.3. Analysis

Stock solutions (2 mM) of the perchlorate salts of Li+, Na+, K+,Mg2+, Ca2+, Ba2+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Pb2+, Ag+, Cd2+,Hg2+, Zn2+ and Al3+ in CH3OH were prepared. Stock solutions of host(2 mM) were prepared in methanol. Test solutions were prepared byplacing 20 lL of the probe stock solution into a test tube, adding anappropriate aliquot of each ions stock, and diluting the solution to2 mL with methanol–water (95:5, v/v) solutions. Both the excitationand emission slit widths were 5.0 nm. Solutions were made basic byaddition of 0.1 M NaOH and titrated to acidic pH using 0.05 M HClO4.The pH changes are 5% after the amount of Al3+ increased. Thequantum yields for fluorescence U, which represent the ability oftransferring absorption energy to fluorescence, were determinedby the comparative method which involves the use of well charac-terized standard samples with known quantum yields. The standardchosen should absorb at the excitation wavelength of choice for the

y for association between (R)-OH and Al3+ in CH3OH–water (95:5, v/v; pH 7.5). (b)

M. Dong et al. / Inorganica Chimica Acta 381 (2012) 137–142 141

analyte and emit in a similar region to the analyte. In CH3OH–water,the quantum yields of the samples were measured using a 20 lMaqueous solution of 2-aminopyridine as the standard for solutionsof (R)-OH (quantum efficiency of 0.60 at kexc = 334 nm) [13].

3. Results and discussion

3.1. Complexation studies of (R)-OH with Al3+ in CH3OH solution

Firstly the fluorescence properties of (R)-OH were studied inpure CH3OH solution. All of fluorescence spectra were recordedafter 5 min upon the addition of 1.0 equiv of each of metal ions.As shown in Fig. 1a, when excited at 337 nm, free (R)-OH exhibitssingle fluorescence emission band at 370 nm, which is assigned tothe monomer emission signal. Upon the addition of Al3+, a fluores-cence enhancement was observed with a slightly bathochromicshift from 370 (U = 6.4%) to 375 nm (U = 7.1%) denoted as CHEF(chelation-enhanced fluorescence) [28–31]. The total fluorescenceintensity of (R)-OH was enhanced 4.3-fold when 1.0 equiv of Al3+

was present and further increase in Al3+ concentration led to slightfluorescence quenching. Fluorescence measurements of (R)-OHwith various metal ions revealed excellent selectivity for Al3+

(Fig. 1b and c). All competitive metal ions had no obvious interfer-ence with the detection of the Al3+ ion, which indicated that (R)-OH–Al3+ system was hardly affected by these coexistent ions.These results demonstrated that (R)-OH was highly selective forAl3+ in pure CH3OH solution. Moreover, a 1:1 stoichiometry com-plexation between (R)-OH and Al3+ was obtained by using the Job’splot (Fig. 1d).

As shown in Fig. 2a, the association constant K of the complexwas then calculated to be 2.72 � 104 M�1 with a linear relationshipby Benesi–Hildebrand method (Eq. (1)) [32].

1F � Fmin

¼ 1

KðFmax � FminÞ½Al3þ�þ 1

Fmax � Fminð1Þ

The limit of detection was determined from the fluorescencetitration data [33,34]. According to the results of titration experi-ments, the fluorescent intensity data at 375 nm were normalized be-tween the minimum intensity and the maximum intensity. A linearregression curve was then fitted to these normalized fluorescentintensity data (Fig. 2b), and the point (1.26 lM) at this line whichcrossed the x-axis was considered as the detection limit (34 ppb).

3.2. Complexation studies of (R)-OH with Al3+ in aqueous solution

Considering the practical application, the fluorescence proper-ties of (R)-OH in CH3OH with different proportions of H2O were

Fig. 7. UV–vis absorption spectra of (R)-OH (20 lM) with Al3+ (1.0 equiv) inCH3OH–water (95:5, v/v; pH 7.5).

further examined (Fig. 3). Compared to that in pure CH3OH solu-tion, the fluorescence intensity of free (R)-OH was quenched inCH3OH–water solution. With the addition of H2O up to 10% (v/v),the fluorescence intensity became very low. So the system ofCH3OH-water (95:5, v/v) solutions was selected to study the fluo-rescence properties of (R)-OH with Al3+ in detail.

The effect of pH on the fluorescence intensity at 375 nm forAl3+-(R)-OH complex in CH3OH–water (95:5, v/v) is shown inFig. 4. The response of (R)-OH with Al3+ system exhibited a con-stant between pH 7.0 and 9.0. In subsequent experiments, a pH7.5 solution was used as an ideal condition.

As shown in Fig. 5a, compared to other metal ions examined, onlyAl3+ caused the change of the maximum fluorescence emission bandof probe (R)-OH from 370 nm (U = 1.4%) to 375 nm (U = 4.5%). Thetotal fluorescence intensity of (R)-OH was enhanced 35.4-fold when1.0 equiv of Al3+ was present which is much better than the value ob-tained in pure CH3OH solution and our previous reported result(Fig. 5b) [26]. To validate the selectivity of (R)-OH in practice, thecompetition experiments were also measured by addition of1.0 equiv of Al3+ to the CH3OH–water (95:5, v/v) solutions in thepresence of 1.0 equiv of other metal ions as shown in Fig. 5c. All com-petitive metal ions had no obvious interference with the detection ofAl3+ ion, which indicated the system of (R)-OH–Al3+ was also hardlyaffected by these coexistent ions in CH3OH–water (95:5, v/v) solu-tions. These results suggested that probe (R)-OH displayed an excel-lent selectivity toward Al3+ in CH3OH–water (95:5, v/v) solutions.Moreover, a 1:1 stoichiometry complexation between (R)-OH andAl3+ was obtained by using the Job’s plot (Fig. 5d). As shown inFig.6, the association constant K of the complex was then calculatedto be 2.11 � 105 M�1, and the corresponding detection limit wasfound to be 0.60 lM (16 ppb), both of which are better than the val-ues obtained in pure CH3OH solution.

There was almost no change observed in the UV–vis spectra of(R)-OH (230, 278, 288 and 336 nm) upon the addition of Al3+

(Fig. 7), the interaction between host and guest was only evaluatedby fluorescent spectra.

3.3. The proposed coordination behavior of (R)-OH

To further elucidating the binding site, 1H NMR experimentswere also carried out. As shown in Fig. 8, the signals of Ha, Hb1,

Fig. 8. Partial 1H NMR spectral changes (400 MHz) of (R)-OH (5.0 mM) uponaddition of Al3+ (CD3OD): (a) (R)-OH only; (b) (R)-OH + Al3+ (1.0 equiv).

Fig. 9. The optimized binding mode of (R)-OH�Al3+. The hydrogen atoms areomitted for clarity.

142 M. Dong et al. / Inorganica Chimica Acta 381 (2012) 137–142

Hb2, Hc, Hd1 and Hd2 of (R)-OH were downfield shifted obviouslyupon the addition of Al3+ (1.0 equiv) (Dd = 0.38, 0.31, 0.21, 0.58,0.21, 0.13 ppm, respectively), which indicated that the groups of–OH (BINOL), –NH and –OH (amino alcohol) were the key bindingsites for coordinate with Al3+. In comparison with our previouswork [26], these results implied that the terminal –OH or –COOHwas the main binding site to show the significant selectivity forAl3+. Computational studies have been performed by using thesoftware of HyperChem 8.0 to investigate the possible molecularstructure of (R)-OH�Al3+. The optimized structure is shown inFig. 9. The aluminum ion may be chelated by the counteranion orsolvent to satisfy the need for six-coordination.

4. Conclusion

Fluorescence property of BINOL-b-amino alcohol conjugate(R)-OH has been studied. It still shows Al3+-selective fluorescenceenhancement, which originates from CHEF (chelation-enhancedfluorescence) by coordination association with Al3+ ions. The com-parison of its sensing abilities with previous receptor (R)-1 re-vealed that terminal –OH or –COOH group is the key binding sitefor the high selectivity for Al3+ over other metal ions.

Acknowledgments

This work was supported by NSFC (21001058), the Natural Sci-ence Foundation of Gansu Province of China (1107RJZA192) and

the Fundamental Research Funds for the Central Universities (andlzujbky-2010-38).

References

[1] G.H. Robinson, Chem. Eng. News 81 (2003) 54.[2] E.R. Scerri, The Periodic Table: Its Story and Its Significance, Oxford University

Press, 2007.[3] C. Exley has edited a special issue devoted to ‘‘Aluminium: Lithosphere to

Biosphere (and Back)’’, J. Inorg. Biochem. 99 (2005) 1747.[4] D.P. Perl, A.R. Brody, Science 208 (1980) 297.[5] D.P. Perl, D.C. Gajdusek, R.M. Garruto, R.T. Yanagihara, C.J. Gibbs, Science 217

(1982) 1053.[6] T.P. Flaten, M. Ødegård, Food Chem. Toxical. 26 (1988) 959.[7] R.A. Yokel, Neurotoxicology 21 (2000) 813.[8] S.H. Kim, H.S. Choi, J. Kim, S.J. Lee, D.T. Quang, J.S. Kim, Org. Lett. 12 (2010) 560.[9] D. Maity, T. Govindaraju, Chem. Commun. 46 (2010) 4499.

[10] K.K. Upadhyay, A. Kumar, Org. Biomol. Chem. 8 (2010) 4892.[11] W. Lin, L. Yuan, J. Feng, Eur. J. Org. Chem. (2008) 3821.[12] A.B. Othman, J.W. Lee, Y.-D. Huh, R. Abidi, J.S. Kim, J. Vicens, Tetrahedron 63

(2007) 10793.[13] A. Jeanson, V. Béreau, Inorg. Chem. Commun. 9 (2006) 13.[14] Y. Zhao, Z. Lin, H. Liao, C. Duan, Q. Meng, Inorg. Chem. Commun. 9 (2006) 966.[15] J.-B. Mulon, E. Destandau, V. Alain, E. Bardez, J. Inorg. Biochem. 99 (2005) 1749.[16] J.L. Ren, J. Zhang, J.Q. Luo, X.K. Pei, Z.X. Jiang, Analyst 126 (2001) 698.[17] Y.-W. Wang, M.-X. Yu, Y.-H. Yu, Z.-P. Bai, Z. Shen, F.-Y. Li, X.-Z. You,

Tetrahedron Lett. 50 (2009) 6169.[18] J.-Q. Wang, L. Huang, L. Gao, J.H. Zhu, Y. Wang, X. Fan, Z. Zou, Inorg. Chem.

Commun. 11 (2008) 203.[19] J. Ren, H. Tian, Sensors 7 (2007) 3166.[20] S.M. Ng, R. Narayanaswamy, Anal. Bioanal. Chem. 386 (2006) 1235.[21] M. Arduini, F. Felluga, F. Mancin, P. Rossi, P. Tecilla, U. Tonellato, N.

Valentinuzzi, Chem. Commun. (2003) 1606.[22] C. Jiang, B. Tang, R. Wang, J. Yen, Talanta 44 (1997) 197.[23] L.A. Saari, W.R. Seltz, Anal. Chem. 55 (1983) 667.[24] M. Dong, T.-H. Ma, A.-J. Zhang, Y.-M. Dong, Y.-W. Wang, Y. Peng, Dyes Pigm. 87

(2010) 164.[25] T.-H. Ma, A.-J. Zhang, M. Dong, Y.-M. Dong, Y. Peng, Y.-W. Wang, J. Lumin. 130

(2010) 888.[26] T.-H. Ma, M. Dong, Y.-M. Dong, Y.-W. Wang, Y. Peng, Chem. Eur. J. 16 (2010)

10313.[27] J. Chin, D.C. Kim, H.J. Kim, F.B. Panosyan, K.M. Kim, Org. Lett. 6 (2004) 2591.[28] E.U. Akkaya, M.E. Huston, A.W. Czarnik, J. Am. Chem. Soc. 112 (1990) 3590.[29] M. Chae, J. Yoon, A.W. Czarnik, J. Mol. Recognit. 9 (1996) 297.[30] J.S. Kim, K.H. Noh, S.H. Lee, S.K. Kim, S.K. Kim, J. Yoon, J. Org. Chem. 68 (2003)

597.[31] L. Xue, Q. Liu, H. Jiang, Org. Lett. 11 (2009) 3454.[32] H.A. Benesi, J.H. Hildebrand, J. Am. Chem. Soc. 71 (1949) 2703.[33] M. Shortreed, R. Kopelman, M. Kuhn, B. Hoyland, Anal. Chem. 68 (1996) 1414.[34] A. Caballero, R. Martınez, V. Lloveras, I. Ratera, J. Vidal-Gancedo, K. Wurst, A.

Tarraga, P. Molina, J. Veciana, J. Am. Chem. Soc. 127 (2005) 15666.