Title
Pyrophosphate-Induced Intramolecular Excimer Formation in Dinuclear Zinc(II) Complexes with Tetrakisquinoline Ligands
Author
Yuji Mikata, Risa Ohnishi, Risa Nishijima, Arimasa Matsumoto, Hideo Konno
Year
2018
Journal
Inorganic Chemistry
Abstract
Dinuclear Zn2+ complexes with HTQHPN (N,N,N′,N′- tetrakis(2-quinolylmethyl)-2-hydroxy-1,3-propanediamine) derivatives have been prepared, and their pyrophosphate (PPi, P2O7 4−) sensing properties were examined. The ligand library includes six HTQHPN derivatives with electron-donating/withdrawing substituents, an extended aromatic ring, and six-membered chelates upon zinc binding. Complexation of ligand with 2 equiv of Zn2+ promotes small to moderate fluorescence enhancement around 380 nm, but in the cases of HTQHPN, HT(6-FQ)HPN (N,N,N′,N′- tetrakis(6-fluoro-2-quinolylmethyl)-2-hydroxy-1,3-propanediamine), and HT(8Q)HPN (N,N,N′,N′-tetrakis(8-quinolylmethyl)-2-hydroxy-1,3-propanediamine), subsequent addition of PPi induced a significant fluorescence increase around 450 nm. This fluorescence enhancement in the longwavelength region is attributed to the conformational change of the bis- (quinolylmethyl)amine moiety which promotes intramolecular excimer formation between adjacent quinolines upon binding with PPi. The structures of PPi- and phosphate-bound dizinc complexes were revealed by X-ray crystallography utilizing phenyl-substituted analogues. The zinc complex with HT(8Q)HPN exhibits the highest signal enhancement (IPPi/I0 = 12.5) and selectivity toward PPi sensing (IATP/IPPi = 20% and IADP/IPPi = 25%). The fluorescence enhancement turned to decrease gradually after the addition of more than 1 equiv of PPi due to the removal of zinc ion from the ligand−zinc−PPi ternary complex, allowing the accurate determination of PPi concentrations at the fluorescence maximum composition. The practical application of the present method was demonstrated monitoring the enzymatic activity of pyrophosphatase.
Instrument
FP-6300
Keywords
Fluorescence, Inorganic chemistry, Chemical stability, Ligand binding, Kinetics, Sensors