Pii: S0040-4039(98)01492-0

A luminescent ruthenium(ll) bipyridyl receptor with pendant boronic acids is synthesized and shown to bind phosphorylated sugars in water. The association constant for fructose-6-phosphate is log K a = 3.1 M "1 at 298 °K. The receptor simultaneously binds saccharide/phosphate with positive cooperativity. © 1998 Elsevier Science Ltd. All rights reserved. Recent designs of anion receptors have included acyclic ruthenium(II) bipyridyl derivatives, such as 1, which bind phosphate anions in polar aprotic solvents by a combination of electrostatic interactions and hydrogen bonding with the receptor amide residues.l, 2 This paper describes the luminescent ruthenium(II) bipyridyl receptor 2 which contains pendant boronic acids. Since boronic acids form covalent complexes with the diol groups in saccharides, 3,4 we reasoned that 2 would act as a heteroditopic receptor capable of binding saccharides, 5 and phosphate groups at two adjacent sites (Figure 1). Here we report the synthesis of 2 and show that it is capable of: (a) binding and sensing phosphorylated sugars in aqueous solution, and (b) binding saccharides and phosphate ions with positive cooperativity. 6 Figure Phosphate ,~ Binding S i te Saccharide , . ~ -~ .~e (on )2 Binding Site Heteroditopic binding of saccharide and phosphate by racemic receptor 2. Compounds 11 and 27 were prepared in straightforward fashion by treating Ru(bpy)2Cl2.2H20 with the appropriate bipyridyl ligand in ethylene glycol. Compound 2 exhibits the optical properties expected for a ruthenium(II) bipyridyl derivative (MLCT absorption band at 479 nm in water (e = 1.1 x 104 M-I cm-l), emission at 637 nm). The electronic absorption spectrum of 2 in aqueous solution hardly changes upon treatment with phosphorylated sugars. However, the emission intensity increases with fructose-6-phosphate producing the largest change (Figure 2) 8. Titration of 2 with fructose-6-phosphate in a range of solvents produces isotherms that fit nicely to a 1:1 binding model. 9 The association constants listed in Table 1 were extracted from the luminescence titration curves by iterative curve fitting methods. 10 The 1:1 binding stoichiometry was confirmed by: (i) 31p NMR titration experiments in water which showed a peak due to the 2/fructose-6-phospbate complex in slow exchange and 1.2 ppm upfield of free fructose-6-phosphate, and (ii) 0040-4039/98/$ see front matter © 1998 Elsevier Science Ltd. All rights reserved. PII: S0040-4039(98)01492-0