Phos-tag chemistry

Abstract

Recently, we found that an alkoxide-bridged dinuclear zinc(II) complex of 1,3-bis[bis(pyridin-2-ylmethyl) amino]propan-2-olate acts as a novel phosphate capture molecule under physiological conditions. The dizinc(II) complex forms a stable 1:1 complex with a phosphate monoester dianion in aqueous solutions. The X-ray crystal analysis of the 1:1 dizinc(II) complex with a p-nitrophenyl phosphate dianion disclosed that each phosphate oxygen anion binds to a zinc(II) at the fifth coordination site and that the two zinc(II) ions are separated by a distance of 3.6 A. Thus, the dizinc(II) complex having a vacancy on the two zinc(II) ions is suitable for the access of a phosphate monoester dianion. In an aqueous solution, the dizinc(II) complex strongly binds to the phenyl phosphate dianion (Kd=2.5×10-8 M) at a neutral pH. The anion selectivity indexes against SO42-, CH3COO-, Cl-, and the diphenyl phosphate monoanion at 25°C are 5.2×103, 1.6×104, 8.0×105, and >2×106, respectively. In addition, the 1:1 formation of the dizinc(II) complex and an inorganic phosphate dianion (HOPO32-) was clearly detected by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) based on a characteristic mass shift and a total-charge change of the phosphate (from -2 to +1). This finding introduced a new procedure for the analysis of phosphorylated compounds using the dizinc(II) complex as an MS probe. Therefore, we termed the dinuclear metal complex Phos-tag as a phosphate-binding tag molecule.