8-Hydroxyquinoline Based Multipodal Systems: Effect of Spatial Placement of 8-Hydroxyquinoline on Metal Ion Recognition

The complexation behaviors of tetrapod 1,2,4,5-tetrakis(8-hydroxyquinolinoxymethyl) benzene (1) and dipod 1,2-bis(8-hydroxyquinolinoxymethyl)benzene (2) have been determined by fluorescence spectroscopy in CH3CN–H2O (4:1) buffered at pH 6.9 [HEPES 10 mM] and by 1H NMR in CD3CN-CDCl3 (1:1) mixture. Tetrapod 1 can recognize Ag+(10–40 μM) even in the presence of (500 μM) of alkali and alkaline earth metal ions. However, transition metal ions interfere in the estimation of Ag+. Dipod 2 shows poor selectivity towards Ag+. The 1H NMR based titrations of podands 1 and 2 against AgNO3 show characterstic changes in chemical shifts in quinoline, methylene and aromatic protons. The spectral fitting of fluorescence and 1H NMR titration data has been used to evaluate the stoichiometries of complexes and their complexation constants.