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Cite this: Chem. Commun., 2014, 50, 2126 Received 22nd October 2013, Accepted 6th December 2013
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Coordination ligand exchange of a xanthene probe–Ce(III) complex for selective fluorescence sensing of inorganic pyrophosphate† Ekkachai Kittiloespaisan,a Ippei Takashima,b Wansika Kiatpathomchai,c Jirarut Wongkongkatep*a and Akio Ojida*b
DOI: 10.1039/c3cc48101h www.rsc.org/chemcomm
A fluorescence sensing system for inorganic pyrophosphate based on ligand exchange of the Ce(III) complex of a xanthene-type probe is developed. This sensing system is successfully applied to the fluorescence detection of polymerase-catalyzed DNA amplification using loop-mediated isothermal amplification.
From the perspective of supramolecular chemistry, a metal ion is a viable component of fluorescent chemosensors for anion species.1 A remarkable feature of metal ions is metal–ligand coordination interactions, which can serve as the main binding force to capture an anion species even under highly polarized aqueous conditions. Metal ions also play important roles in the mechanism of fluorescence sensing because of their unique properties such as flexible coordination exchange, heavy metal effects, and redox state switching. Such coordination chemistrybased molecular design is exemplified in the recent development of various fluorescent Zn(II) complexes as chemosensors for biologically relevant phosphate anion species.2 However, despite the versatility of coordination chemistry, fluorescent chemosensors for anions exploiting the unique properties of metal ions remain limited.3 Phosphate species are abundant in biological systems where they play many important roles. For example, inorganic pyrophosphate (PPi) is involved in many enzyme-catalyzed biosynthesis and metabolic processes, most of which produce PPi as a hydrolysis product of nucleoside polyphosphates such as ATP. Therefore, a selective fluorescent chemosensor for PPi could serve as a versatile analytical tool to monitor these a
Department of Biotechnology, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok 10400, Thailand. E-mail: [email protected] b Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan. E-mail: [email protected] c National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathumthani 12120, Thailand † Electronic supplementary information (ESI) available: Synthesis of 1, UV and fluorescence titration of 1 with Ce(NO3)3, the ESI mass spectrum of the 1–Ce(III) complex in the presence and absence of PPi. See DOI: 10.1039/c3cc48101h
2126 | Chem. Commun., 2014, 50, 2126--2128
Fig. 1 (a) Schematic illustration of fluorescence sensing of inorganic pyrophosphate (PPi) using the Ce(III) complex of 1. (b) Structure of the xanthene-based chemosensor 1. (c) DLS analysis of the Ce(III) complex of 1.
biological transformations in a convenient and highly sensitive manner.4 However, few fluorescent PPi chemosensors applicable to bioanalytical sensing have been developed.5 We describe herein the design of a fluorescence sensing system for PPi by coordination exchange of the Ce(III) complex (Fig. 1). We found that the Ce(III) complex of xanthene derivative 1 can serve as a selective fluorescent chemosensor for PPi with a large fluorescence enhancement of up to 300-fold. Taking advantage of the high sensing selectivity for PPi among biological phosphate anions, the Ce(III) complex of 1 was successfully applied to detect the enzyme-catalyzed selective amplification of DNA, highlighting the utility of the developed chemosensor in fluorescence biological analysis. It is well known that Ce(III) ions preferably form stable complexes with PPi in aqueous solution. These complexes often precipitate out of aqueous solution because of their low solubility product (Ksp = 7.7 1024 M2).6 Based on this property of Ce(III) ions, we designed a new sensing system for PPi using a Ce(III) complex of a fluorescent chemosensor. It was expected
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that the formation of stable Ce(III)–PPi complexes would facilitate the release of the chemosensor from the Ce(III) complex to induce a change in fluorescence (Fig. 1). As the chemosensor, xanthene-type fluorescent chemosensor 1 bearing two sets of iminodiacetate ligands was designed. Synthesis of 1 is described in the ESI.† When Ce(NO3)3 was titrated into an aqueous solution of 1 (5 mM in 25 mM 2-(N-morpholino)ethanesulfonic acid (MES) buffer–MeOH (1 : 1), pH 6.8), the fluorescence of 1 gradually decreased to less than 1% of its original intensity upon addition of 100 mM of Ce(NO3)3 (Fig. S1, ESI†). Dynamic light scattering (DLS) analysis of the solution showed that the 1–Ce(III) complex formed particles with a mean diameter of 550 nm. Electrospray ionization mass spectrometry (ESI-MS) detected the 1–Ce(III) complex as a high molecular weight complex (m/z C 2000, Fig. S2, ESI†). These results suggest that the 1–Ce(III) complex forms an aggregated polymer through bridging coordination interactions between 1 and Ce(III) ions, as shown in Fig. 1a. Therefore, the large fluorescence decrease of 1 upon complexation with Ce(NO3)3 is ascribed to self-quenching of the xanthene fluorophore in the aggregated state and the quenching effect of the coordinated Ce(III) ions. When PPi was added to a solution of the 1–Ce(III) complex (5 mM of 1, 100 mM of Ce(NO3)3 in 25 mM MES buffer–MeOH (1 : 1), pH 6.8), its fluorescence increased upon addition of over 50 mM of PPi (Fig. 2). The nonfluorescence response in the presence of less than 50 mM of PPi might be due to the complex formation of PPi with the excess of free Ce(III) ions. Upon addition of 100 mM of PPi, the fluorescence reached the original intensity of 1 with over 300-fold of a fluorescence enhancement (F/Fo at 529 nm). ESI-MS showed that 1 mainly exists as the free ligand in the presence of 100 mM of PPi (Fig. S2, ESI†), indicating that coordination exchange occurs between 1 and PPi to form a Ce(III)–PPi complex and release fluorescent ligand 1.‡ The sensing selectivity of the 1–Ce(III) complex for a variety of relevant biological anions was evaluated by fluorescence titration. Fig. 3 summarizes the emission increase ratio (F/Fo at 529 nm) upon addition of various anion species (100 mM). The 1–Ce(III) complex showed a high selectivity for PPi; a large fluorescence enhancement (F/Fo = 318) was only observed upon
Fig. 2 (a) Fluorescence spectral changes of the 1–Ce(III) complex upon addition of PPi (0–200 mM). (b) Change in fluorescence intensity at 529 nm of the 1–Ce(III) complex upon addition of PPi. Conditions: [1] = 5 mM, [Ce(NO3)3] = 100 mM, 25 mM MES (pH 6.8)–MeOH (1 : 1), 25 1C, lex = 500 nm.
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Fig. 3 Fluorescence sensing selectivity of the 1–Ce(III) complex toward various anions (100 mM). Conditions: [1] = 5 mM, [Ce(NO3)3] = 100 mM, 25 mM MES (pH 6.8)–MeOH (1 : 1), 25 1C, lex = 500 nm.
addition of PPi. Other phosphate species including nucleoside polyphosphates such as XTP (X = A, U, C, G) and ADP, and other oxoanions such as carbonate, acetate, sulfate, and pyrosulfate, scarcely induced an increase in fluorescence except for inorganic phosphate (F/Fo = 28) and UTP (F/Fo = 30). The high selectivity of the 1–Ce(III) complex for PPi would be ascribed to the high affinity of Ce(III) for polyanionic PPi, which facilitates the coordination exchange of the 1–Ce(III) complex more than other anions. Taking advantage of the selective PPi sensing properties of the 1–Ce(III) complex, it was applied to the fluorescence detection of DNA polymerase-catalyzed nucleic acid amplification by the loop-mediated isothermal amplification (LAMP) method (Fig. 4). It is known that LAMP can amplify a few copies of DNA to over 109 copies in less than 1 h under isothermal conditions.7 In DNA amplification, PPi is formed as a by-product upon consumption of 2 0 -deoxy NTP (N = A, T, C, G) by DNA polymerase. The fluorescent LAMP assay was conducted using the recombinant plasmid of white spot syndrome virus (WSSV), which is known to cause high motality in penaeid shrimp.8 After the LAMP reaction with the serially diluted plasmid (2, 20, 200, and 1000 copies), fluorescence detection was conducted using a plate reader with a mixture of the reaction samples and the 1–Ce(III) complex under the optimized conditions. The results showed that a greater number of plasmids resulted in a higher fluorescence enhancement, in which the fluorescence of the mixture increased up to 35-fold in the reaction with 1000 copies of the plasmid. A large fluorescence enhancement (over 20-fold) was observed even with 2 copies of the plasmid, clearly demonstrating the higher sensitivity of the present LAMP assay compared to the previously reported methods.9 The large fluorescence enhancement was readily detectable by the naked eye (Fig. 4c), revealing the practical utility of this assay for rapid and convenient detection of the WSSV infection without fluorescence detection equipment. In conclusion, we have demonstrated that coordination exchange of the Ce(III) complex is a useful sensing mechanism for selective fluorescence sensing of PPi. The Ce(III) complex of the xanthene-based chemosensor 1 was successfully applied to the fluorescent LAMP assay with a high sensitivity, demonstrating the
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Notes and references ‡ The precipitate of the Ce(III)–PPi complex was not observed in the solution of the 1–Ce(III) complex after addition of PPi (100 mM). DLS analysis of this solution suggested that the Ce(III)–PPi complex exists as particles with the mean diameter of 1400 nm.
Fig. 4 (a) Mechanism of the fluorescent LAMP assay using the Ce(III) complex of 1. (b) Changes in fluorescence of the 1–Ce(III) complex upon addition of the LAMP reaction solution. Each reaction was conducted in the presence of (A) 0, (B) 2, (C) 20, (D) 200, and (E) 1000 copies of WSSV plasmid DNA. Conditions: [1] = 5 mM, [Ce(NO3)3] = 270 mM, 25 mM MES (pH 6.8)–MeOH (1 : 1), 25 1C, lex = 500 nm. The y-axis indicates the ratio of the fluorescence increase of each sample ((F Fc)/Fo), where F, Fc, and Fo are the fluorescence intensity of the reaction sample, the control reaction sample without plasmid, and the solution of the 1–Ce(III) complex, respectively. (c) Photographs of solutions of the 1–Ce(III) complex upon addition of LAMP reaction solutions.
utility of the present sensing system in biological analysis. We envision that further optimization of the probe structure and screening of metal ions will provide a more sensitive and selective fluorescent sensing system for PPi. A. O. acknowledges the Toray Science Foundation for its financial support. This work was supported by the Platform
2128 | Chem. Commun., 2014, 50, 2126--2128
1 D. Curiel, E. J. Hayes and P. D. Beer, Topics in Fluorescent Spectroscopy, Springer, 2005, vol. 9, p. 59. 2 (a) Y. Kurishita, T. Kohira, A. Ojida and I. Hamachi, J. Am. Chem. Soc., 2012, 134, 18779; (b) H. W. Rhee, S. J. Choi, S. H. Yoo, Y. O. Jang, H. H. Park, R. M. Pinto, J. C. Cameselle, F. J. Sandoval, S. Roje, K. Han, D. S. Chung, J. Suh and J.-I. Hong, J. Am. Chem. Soc., 2009, 131, 10107; (c) H. N. Lee, Z. Xu, S. K. Kim, K. M. K. Swamy, Y. Kim, S.-J. Kim and J. Yoon, J. Am. Chem. Soc., 2007, 129, 3828; (d) E. J. O’Neil and B. D. Smith, Coord. Chem. Rev., 2006, 250, 3068; (e) A. Ojida, Y. Mito-oka, L. Sada and I. Hamachi, J. Am. Chem. Soc., 2004, 126, 2454. 3 (a) M. A. Tetilla, M. C. Aragoni, M. Arca, C. Caltagirone, C. Bazzicalupi, A. Bencini, A. Garau, F. Isaia, A. Laguna, V. Lippolis ´, and V. Meli, Chem. Commun., 2011, 47, 3805; (b) M. A. Hortala L. Fabbrizzi, N. Marcotte, F. Stomeo and A. Tagiletti, J. Am. Chem. Soc., 2003, 125, 20; (c) M. Montalti, L. Prodi, N. Zaccheroni, ´re, L. Douce and R. Ziessel, J. Am. Chem. Soc., 2001, L. Charbonnie 123, 12694; (d) L. A. Cabell, M. D. Best, J. J. Lavigne, S. E. Schneider, D. M. Perreault, M.-K. Monahan and E. V. Anslyn, J. Chem. Soc., Perkin Trans. 2, 2001, 315; (e) P. D. Beer, F. Szemes, V. Balzanni, C. M. Sala, M. G. B. Drew, S. W. Dent and M. Maestri, J. Am. Chem. Soc., 1997, 49, 11864. 4 For a review: S. K. Kim, D. H. Lee, J.-I. Hong and J. Yoon, Acc. Chem. Res., 2009, 42, 23. 5 (a) D.-H. Lee and J.-I. Hong, Bull. Korean Chem. Soc., 2008, 29, 497; (b) W.-H. Chen, Y. Xing and Y. Ping, Org. Lett., 2011, 13, 1362. 6 S. A. Merkusheva, N. A. Skorik, V. N. Kumok and V. V. Serebrennikov, Zh. Neorg. Khim., 1967, 3388. 7 (a) T. Notomi, H. Okayama, H. Masubuchi, T. Yonekawa, K. Watanabe, N. Amino and T. Hase, Nucleic Acids Res., 2000, 28, e63; (b) N. Tomita, Y. Mori, H. Kanda and T. Notomi, Nat. Protocols, 2008, 3, 877. 8 P. J. Walker and J. R. Winton, Vet. Res., 2010, 41, 51. 9 (a) N. Tomita, Y. Mori, H. Kanda and T. Notomi, Nat. Protocols, 2008, 3, 877; (b) E. Kittiloespaisan, A. Ojida, I. Hamachi, Y. SeetangNun, W. Kiatpathomchai and J. Wongkongkatep, Chem. Lett., 2012, 1666.
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Cite this: Chem. Commun., 2014, 50, 2126 Received 22nd October 2013, Accepted 6th December 2013
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Coordination ligand exchange of a xanthene probe–Ce(III) complex for selective fluorescence sensing of inorganic pyrophosphate† Ekkachai Kittiloespaisan,a Ippei Takashima,b Wansika Kiatpathomchai,c Jirarut Wongkongkatep*a and Akio Ojida*b
DOI: 10.1039/c3cc48101h www.rsc.org/chemcomm
A fluorescence sensing system for inorganic pyrophosphate based on ligand exchange of the Ce(III) complex of a xanthene-type probe is developed. This sensing system is successfully applied to the fluorescence detection of polymerase-catalyzed DNA amplification using loop-mediated isothermal amplification.
From the perspective of supramolecular chemistry, a metal ion is a viable component of fluorescent chemosensors for anion species.1 A remarkable feature of metal ions is metal–ligand coordination interactions, which can serve as the main binding force to capture an anion species even under highly polarized aqueous conditions. Metal ions also play important roles in the mechanism of fluorescence sensing because of their unique properties such as flexible coordination exchange, heavy metal effects, and redox state switching. Such coordination chemistrybased molecular design is exemplified in the recent development of various fluorescent Zn(II) complexes as chemosensors for biologically relevant phosphate anion species.2 However, despite the versatility of coordination chemistry, fluorescent chemosensors for anions exploiting the unique properties of metal ions remain limited.3 Phosphate species are abundant in biological systems where they play many important roles. For example, inorganic pyrophosphate (PPi) is involved in many enzyme-catalyzed biosynthesis and metabolic processes, most of which produce PPi as a hydrolysis product of nucleoside polyphosphates such as ATP. Therefore, a selective fluorescent chemosensor for PPi could serve as a versatile analytical tool to monitor these a
Department of Biotechnology, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok 10400, Thailand. E-mail: [email protected] b Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan. E-mail: [email protected] c National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathumthani 12120, Thailand † Electronic supplementary information (ESI) available: Synthesis of 1, UV and fluorescence titration of 1 with Ce(NO3)3, the ESI mass spectrum of the 1–Ce(III) complex in the presence and absence of PPi. See DOI: 10.1039/c3cc48101h
2126 | Chem. Commun., 2014, 50, 2126--2128
Fig. 1 (a) Schematic illustration of fluorescence sensing of inorganic pyrophosphate (PPi) using the Ce(III) complex of 1. (b) Structure of the xanthene-based chemosensor 1. (c) DLS analysis of the Ce(III) complex of 1.
biological transformations in a convenient and highly sensitive manner.4 However, few fluorescent PPi chemosensors applicable to bioanalytical sensing have been developed.5 We describe herein the design of a fluorescence sensing system for PPi by coordination exchange of the Ce(III) complex (Fig. 1). We found that the Ce(III) complex of xanthene derivative 1 can serve as a selective fluorescent chemosensor for PPi with a large fluorescence enhancement of up to 300-fold. Taking advantage of the high sensing selectivity for PPi among biological phosphate anions, the Ce(III) complex of 1 was successfully applied to detect the enzyme-catalyzed selective amplification of DNA, highlighting the utility of the developed chemosensor in fluorescence biological analysis. It is well known that Ce(III) ions preferably form stable complexes with PPi in aqueous solution. These complexes often precipitate out of aqueous solution because of their low solubility product (Ksp = 7.7 1024 M2).6 Based on this property of Ce(III) ions, we designed a new sensing system for PPi using a Ce(III) complex of a fluorescent chemosensor. It was expected
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that the formation of stable Ce(III)–PPi complexes would facilitate the release of the chemosensor from the Ce(III) complex to induce a change in fluorescence (Fig. 1). As the chemosensor, xanthene-type fluorescent chemosensor 1 bearing two sets of iminodiacetate ligands was designed. Synthesis of 1 is described in the ESI.† When Ce(NO3)3 was titrated into an aqueous solution of 1 (5 mM in 25 mM 2-(N-morpholino)ethanesulfonic acid (MES) buffer–MeOH (1 : 1), pH 6.8), the fluorescence of 1 gradually decreased to less than 1% of its original intensity upon addition of 100 mM of Ce(NO3)3 (Fig. S1, ESI†). Dynamic light scattering (DLS) analysis of the solution showed that the 1–Ce(III) complex formed particles with a mean diameter of 550 nm. Electrospray ionization mass spectrometry (ESI-MS) detected the 1–Ce(III) complex as a high molecular weight complex (m/z C 2000, Fig. S2, ESI†). These results suggest that the 1–Ce(III) complex forms an aggregated polymer through bridging coordination interactions between 1 and Ce(III) ions, as shown in Fig. 1a. Therefore, the large fluorescence decrease of 1 upon complexation with Ce(NO3)3 is ascribed to self-quenching of the xanthene fluorophore in the aggregated state and the quenching effect of the coordinated Ce(III) ions. When PPi was added to a solution of the 1–Ce(III) complex (5 mM of 1, 100 mM of Ce(NO3)3 in 25 mM MES buffer–MeOH (1 : 1), pH 6.8), its fluorescence increased upon addition of over 50 mM of PPi (Fig. 2). The nonfluorescence response in the presence of less than 50 mM of PPi might be due to the complex formation of PPi with the excess of free Ce(III) ions. Upon addition of 100 mM of PPi, the fluorescence reached the original intensity of 1 with over 300-fold of a fluorescence enhancement (F/Fo at 529 nm). ESI-MS showed that 1 mainly exists as the free ligand in the presence of 100 mM of PPi (Fig. S2, ESI†), indicating that coordination exchange occurs between 1 and PPi to form a Ce(III)–PPi complex and release fluorescent ligand 1.‡ The sensing selectivity of the 1–Ce(III) complex for a variety of relevant biological anions was evaluated by fluorescence titration. Fig. 3 summarizes the emission increase ratio (F/Fo at 529 nm) upon addition of various anion species (100 mM). The 1–Ce(III) complex showed a high selectivity for PPi; a large fluorescence enhancement (F/Fo = 318) was only observed upon
Fig. 2 (a) Fluorescence spectral changes of the 1–Ce(III) complex upon addition of PPi (0–200 mM). (b) Change in fluorescence intensity at 529 nm of the 1–Ce(III) complex upon addition of PPi. Conditions: [1] = 5 mM, [Ce(NO3)3] = 100 mM, 25 mM MES (pH 6.8)–MeOH (1 : 1), 25 1C, lex = 500 nm.
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Fig. 3 Fluorescence sensing selectivity of the 1–Ce(III) complex toward various anions (100 mM). Conditions: [1] = 5 mM, [Ce(NO3)3] = 100 mM, 25 mM MES (pH 6.8)–MeOH (1 : 1), 25 1C, lex = 500 nm.
addition of PPi. Other phosphate species including nucleoside polyphosphates such as XTP (X = A, U, C, G) and ADP, and other oxoanions such as carbonate, acetate, sulfate, and pyrosulfate, scarcely induced an increase in fluorescence except for inorganic phosphate (F/Fo = 28) and UTP (F/Fo = 30). The high selectivity of the 1–Ce(III) complex for PPi would be ascribed to the high affinity of Ce(III) for polyanionic PPi, which facilitates the coordination exchange of the 1–Ce(III) complex more than other anions. Taking advantage of the selective PPi sensing properties of the 1–Ce(III) complex, it was applied to the fluorescence detection of DNA polymerase-catalyzed nucleic acid amplification by the loop-mediated isothermal amplification (LAMP) method (Fig. 4). It is known that LAMP can amplify a few copies of DNA to over 109 copies in less than 1 h under isothermal conditions.7 In DNA amplification, PPi is formed as a by-product upon consumption of 2 0 -deoxy NTP (N = A, T, C, G) by DNA polymerase. The fluorescent LAMP assay was conducted using the recombinant plasmid of white spot syndrome virus (WSSV), which is known to cause high motality in penaeid shrimp.8 After the LAMP reaction with the serially diluted plasmid (2, 20, 200, and 1000 copies), fluorescence detection was conducted using a plate reader with a mixture of the reaction samples and the 1–Ce(III) complex under the optimized conditions. The results showed that a greater number of plasmids resulted in a higher fluorescence enhancement, in which the fluorescence of the mixture increased up to 35-fold in the reaction with 1000 copies of the plasmid. A large fluorescence enhancement (over 20-fold) was observed even with 2 copies of the plasmid, clearly demonstrating the higher sensitivity of the present LAMP assay compared to the previously reported methods.9 The large fluorescence enhancement was readily detectable by the naked eye (Fig. 4c), revealing the practical utility of this assay for rapid and convenient detection of the WSSV infection without fluorescence detection equipment. In conclusion, we have demonstrated that coordination exchange of the Ce(III) complex is a useful sensing mechanism for selective fluorescence sensing of PPi. The Ce(III) complex of the xanthene-based chemosensor 1 was successfully applied to the fluorescent LAMP assay with a high sensitivity, demonstrating the
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Notes and references ‡ The precipitate of the Ce(III)–PPi complex was not observed in the solution of the 1–Ce(III) complex after addition of PPi (100 mM). DLS analysis of this solution suggested that the Ce(III)–PPi complex exists as particles with the mean diameter of 1400 nm.
Fig. 4 (a) Mechanism of the fluorescent LAMP assay using the Ce(III) complex of 1. (b) Changes in fluorescence of the 1–Ce(III) complex upon addition of the LAMP reaction solution. Each reaction was conducted in the presence of (A) 0, (B) 2, (C) 20, (D) 200, and (E) 1000 copies of WSSV plasmid DNA. Conditions: [1] = 5 mM, [Ce(NO3)3] = 270 mM, 25 mM MES (pH 6.8)–MeOH (1 : 1), 25 1C, lex = 500 nm. The y-axis indicates the ratio of the fluorescence increase of each sample ((F Fc)/Fo), where F, Fc, and Fo are the fluorescence intensity of the reaction sample, the control reaction sample without plasmid, and the solution of the 1–Ce(III) complex, respectively. (c) Photographs of solutions of the 1–Ce(III) complex upon addition of LAMP reaction solutions.
utility of the present sensing system in biological analysis. We envision that further optimization of the probe structure and screening of metal ions will provide a more sensitive and selective fluorescent sensing system for PPi. A. O. acknowledges the Toray Science Foundation for its financial support. This work was supported by the Platform
2128 | Chem. Commun., 2014, 50, 2126--2128
1 D. Curiel, E. J. Hayes and P. D. Beer, Topics in Fluorescent Spectroscopy, Springer, 2005, vol. 9, p. 59. 2 (a) Y. Kurishita, T. Kohira, A. Ojida and I. Hamachi, J. Am. Chem. Soc., 2012, 134, 18779; (b) H. W. Rhee, S. J. Choi, S. H. Yoo, Y. O. Jang, H. H. Park, R. M. Pinto, J. C. Cameselle, F. J. Sandoval, S. Roje, K. Han, D. S. Chung, J. Suh and J.-I. Hong, J. Am. Chem. Soc., 2009, 131, 10107; (c) H. N. Lee, Z. Xu, S. K. Kim, K. M. K. Swamy, Y. Kim, S.-J. Kim and J. Yoon, J. Am. Chem. Soc., 2007, 129, 3828; (d) E. J. O’Neil and B. D. Smith, Coord. Chem. Rev., 2006, 250, 3068; (e) A. Ojida, Y. Mito-oka, L. Sada and I. Hamachi, J. Am. Chem. Soc., 2004, 126, 2454. 3 (a) M. A. Tetilla, M. C. Aragoni, M. Arca, C. Caltagirone, C. Bazzicalupi, A. Bencini, A. Garau, F. Isaia, A. Laguna, V. Lippolis ´, and V. Meli, Chem. Commun., 2011, 47, 3805; (b) M. A. Hortala L. Fabbrizzi, N. Marcotte, F. Stomeo and A. Tagiletti, J. Am. Chem. Soc., 2003, 125, 20; (c) M. Montalti, L. Prodi, N. Zaccheroni, ´re, L. Douce and R. Ziessel, J. Am. Chem. Soc., 2001, L. Charbonnie 123, 12694; (d) L. A. Cabell, M. D. Best, J. J. Lavigne, S. E. Schneider, D. M. Perreault, M.-K. Monahan and E. V. Anslyn, J. Chem. Soc., Perkin Trans. 2, 2001, 315; (e) P. D. Beer, F. Szemes, V. Balzanni, C. M. Sala, M. G. B. Drew, S. W. Dent and M. Maestri, J. Am. Chem. Soc., 1997, 49, 11864. 4 For a review: S. K. Kim, D. H. Lee, J.-I. Hong and J. Yoon, Acc. Chem. Res., 2009, 42, 23. 5 (a) D.-H. Lee and J.-I. Hong, Bull. Korean Chem. Soc., 2008, 29, 497; (b) W.-H. Chen, Y. Xing and Y. Ping, Org. Lett., 2011, 13, 1362. 6 S. A. Merkusheva, N. A. Skorik, V. N. Kumok and V. V. Serebrennikov, Zh. Neorg. Khim., 1967, 3388. 7 (a) T. Notomi, H. Okayama, H. Masubuchi, T. Yonekawa, K. Watanabe, N. Amino and T. Hase, Nucleic Acids Res., 2000, 28, e63; (b) N. Tomita, Y. Mori, H. Kanda and T. Notomi, Nat. Protocols, 2008, 3, 877. 8 P. J. Walker and J. R. Winton, Vet. Res., 2010, 41, 51. 9 (a) N. Tomita, Y. Mori, H. Kanda and T. Notomi, Nat. Protocols, 2008, 3, 877; (b) E. Kittiloespaisan, A. Ojida, I. Hamachi, Y. SeetangNun, W. Kiatpathomchai and J. Wongkongkatep, Chem. Lett., 2012, 1666.
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