Recognition and Visual Detection of ADP and ATP Based on a Dinuclear Zn(II)-complex with Pyrocatechol Violet in Water

The new fluorescent dinuclear complex [Zn2L(S)] 1, (asymmetric ligand, L = 5,8-Bis{[bis(acetate)amino] methyl} quinoline, S = solvent) was synthesized and studied in-depth as a receptor for nucleoside polyphosphates in 100% aqueous solution at physiological pH. The Zn-receptor 1 shows turn-on fluorescence and high selectivity to adenosine 5'-diphosphate (ADP) and adenosine 5'-triphosphate (ATP) over other phosphorylated anions including guanosine 5'-tripohosphate (GTP), citidine 5'-tripohosphate (CTP) and pyrophosphate. On the basis of the spectroscopic tools (H-1,P-31 NMR, UV-vis, fluorescence) and DFT calculations, the Zn-receptor binds ADP with high affinity (log K = 5.12) through three-point recognition involving cooperative coordination bonds and a hydrogen bond. The Zn-receptor 1 is an order of the magnitude more selective for ADP than ATP. ADP can be selectively detected in water even in the presence of coexisting species in blood plasma and urine with a detection limit of 30 mu mol L-1 using a naked-eye detection system based on the complex between Zn-receptor 1 and pyrocatechol violet.