DOI: 10.1002/chem.201100734 A Zinc-Sensing Glucose-Based Naphthyl Imino Conjugate as a Detecting Agent for Inorganic and Organic Phosphates, Including DNA Atanu Mitra, [a] Vijaya Kumar Hinge, [a] Ankit Mittal, [a] Snehasis Bhakta, [a] Philippe Guionneau, [b] and Chebrolu P. Rao* [a] Owing to the importance of zinc and phosphate in biology and human health, [1] sensing such species is always impor- tant and continues to intrigue chemists to emerge with better receptor designs. [2] Our recent report on sensing of Zn 2 + in blood serum milieu by a calixarene derivative [2h] prompted us to employ biologically benign receptor systems and to investigate if these receptors can also extend their sensitivity towards anions (especially phosphates). In this regard, water-soluble and biologically benign [3] carbohy- drate-based fluorescent sensors [4] would be of great rele- vance to explore their in vitro and in vivo applications. Among the derivatives of phosphate, adenosine-mono/di/tri- phosphate (AMP, ADP, ATP), DNA, and their hydrolytic species are important. [5] Therefore, it is essential to monitor the presence of phosphate related species in solution. [6] If a receptor can sense both the zinc and the phosphate group, it would be doubly advantageous. [5e] Therefore, herein we in- vestigate the primary detection of Zn 2 + by switch-on fluo- rescence using 1-(d-glucopyranosyl-2’-deoxy-2’-iminometh- yl)-2-hydroxynaphthalene conjugate L and the successive detection of phosphates by the corresponding zinc complex through fluorescence quenching (switch-off). To demon- strate the bio-suitability of L, titrations were carried out using nucleotides and DNA. To our knowledge, this is the first carbohydrate-based receptor system shown to be sensi- tive towards a cation followed by an anion, including biomo- lecular systems. Conjugate L has been synthesized by a one-pot condensa- tion of the neutralized C2-deoxy-C2-amino-glucose with 2- hydroxy-1-naphthaldehyde and his structure has been char- acterized (see SI 01 in the Supporting Information). [7] Con- jugate L has been crystallized in a non-centrosymmetric tri- clinic system by layering methanol on to a concentrated so- lution in DMSO and the structure was determined by single crystal XRD (for crystal and metric data see SI 02 in the Supporting Information). Conjugate L exhibits a preformed ONO core that is suitable for metal ion binding (Scheme 1). An intramolecular hydrogen bond present between the phe- nolic O4  H···N1-imino orients the naphthyl moiety almost perpendicular to the mean plane of the carbohydrate moiety (see SI 02b in the Supporting Information). In the lattice, molecules form columns by interacting through two strong hydrogen bonds per each L and also by exhibiting hydro- phobic p–p interactions with a centroid to centroid distance of 4.878 . The columnar structure formed in the lattice clearly exhibits hydrophobic (6 ) and hydrophilic (7 ) re- gions alternatively (see SI 02c in the Supporting Informa- tion). The selectivity of L has been demonstrated by titration against seven biologically and ecologically relevant metal ions, such as, Na + ,K + , Ca 2 + , Mg 2 + , Zn 2 + , Cd 2 + , and Hg 2 + in methanol using fluorescence spectroscopy. In dry metha- nol, L exhibits approximately a 140-fold enhancement in the emission intensity against Zn 2 + , while none of the alkali and alkaline earth or Group XII metal ions show appreciable change under similar experimental conditions (Figure 1). To check the effect of the solvent on the selectivity of L, fluorescence titrations were carried out in aqueous metha- nol. As the ratio of water increases, the number of folds of fluorescence enhancement decreases owing to the quenching by water (ca. (60  7)-fold at 1:4 and ca. (8  2)-fold at 1:1), thus suggesting that L can be used even in 1:1 mixture of aqueous methanol for sensing Zn 2 + (see SI 03 in the Sup- [a] A. Mitra, V. K. Hinge, A. Mittal, S. Bhakta, Prof. C. P. Rao Department of Chemistry Indian Institute of Technology Powai, Mumbai - 400076 (India) Fax: (+ 91) 22-2576-7152 E-mail: cprao@iitb.ac.in [b] Prof. P. Guionneau CNRS, UniversitØ de Bordeaux, ICMCB 87 avenue du Dr. A. Schweitzer Pessac, 33608 (France) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201100734. Figure 1. Fluorescence titration of L with metal ions: a) Spectral traces obtained during the titration with Zn 2 + . b) Bar diagram showing the rela- tive fluorescence intensity (I 0 is the initial intensity and I is the intensity after adding different metal ions) in methanol and the inset shows the same in aqueous alcoholic solutions. # 2011 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim Chem. Eur. J. 2011, 17, 8044 – 8047 8044