New molecular motif for recognizing sialic acid using emissive lanthanide-macrocyclic polyazacarboxylate complexes: deprotonation of a coordinated water molecule controls specific binding.

A new molecular motif--lanthanide-macrocyclic polyazacarboxylate hexadentate complexes, Ln(3+)-ABNOTA--was found to specifically bind to sialic acid with strong emission enhancement and high affinity. The selectivity toward sialic acid over other monosaccharides was one of the highest among artificial receptors. Also, the novel binding mechanism was investigated in detail; binding selectivity is controlled by interactions between sialic acid and both the central metal and a hydroxyl group produced by deprotonation of a coordinated water molecule in the Ln(3+) complex.