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Macrocyclization of N,N '-propylenebis(3-formyl-5-tert-butylsalicylaldimine): a ratiometric fluorescence chemodosimeter for Zn-II
SUDHANSHU DAS, JAYDEEP ADHIKARY, PRATEETI CHAKRABORTY, TONMOY CHAKRABORTY,
Published in ROYAL SOC CHEMISTRY
2016
Volume: 6
   
Issue: 101
Pages: 98620 - 98631
Abstract
Addition of 1,3-propane diamine to 2,6-diformyl-4-tert-butyl phenol in ethanol produces a site-selective imination product N, N'-propylenebis(3-formyl-5-tert-butylsalicylaldimine), an acyclic side-off compartmental ligand (H2L). In the presence of zinc nitrate the ligand goes on hydrolysis in 50 : 50 water-acetonitrile medium and forms a partially hydrolyzed ligand (H2L') which slowly metallates to generate a macrocyclic dinuclear zinc(II) complex (1), as characterized by single crystal X-ray analyses. The formation of H2L' is believed to occur through the cleavage of an imine bond of the acyclic compartmental ligand (H2L) in the presence of zinc nitrate which acts as a Lewis acid. The formation of H2L' has been monitored by means of H-1 NMR and further confirmed by HRMS spectroscopic studies. The interactions of H2L with nickel(II) and copper(II) nitrate produce dinuclear complexes 2 and 3 (reported in Inorg. Chem. Commun. 2012, 15, 266-268) respectively, which are formed with unchanged ligand. Various spectroscopic techniques have been used to further characterize the complexes. H2L hardly exhibits yellowish green fluorescence emission at 523 nm when excited at 437 nm in 1 : 1 water-acetonitrile. Upon addition of Zn2+, a new fluorescence emission band at 481 nm appears, the intensity of which slowly enhances. Thus, the ligand H2L is a ratiometric fluorescence chemodosimeter for the selective detection of Zn2+ ions. On addition of Ca-II, Mg-II, Na-I and K-I in the same concentrations as that of Zn2+, the emission band at 523 nm is slightly enhanced, whereas the addition of paramagnetic metal cations like Cu-II, Fe-II, Ni-II, Co-II, and Mn-II resulted in quenching of fluorescence. The quenching effect is also observed in the presence of Cd-II, a d(10) metal cation exhibiting similar coordination properties to Zn-II. The ZnII ion selectivity has also been studied in the presence of other biologically relevant metal ions in 50 : 50 water-acetonitrile.
About the journal
JournalRSC Advances
PublisherROYAL SOC CHEMISTRY
ISSN2046-2069