Neutral, tridentate Schiff base chelators displaying “turn-on” fluorescence emission signals upon mixing with Zn(II) and Cd(II) salts were identified via high-throughput screening.  Condensation between 2-aminophenol and 1-benzyl-4-formyl-1,2,3-triazole in ethanol at room temperature resulted in a tridentate chelator that displayed fluorescence emission at λ-max = 610 nm when exposed to Zn(II) and λ-max = 590 nm when exposed to Cd(II).  Variation of substituents at the 5-position of the 2-aminophenol subunit among fluoro, chloro, bromo and methyl groups showed emission shifts up to 35 nm along with significant variations in intensity.  Replacement of the 1,2,3-triazole subunit with an analogous imidazole subunit resulted in similar patterns of selectivity towards Zn(II) and Cd(II) salts with fluorescence emission at λ-max = 575 nm and λ-max = 560 nm, respectively. Comparative screening of anilines lacking the <i>ortho</i>-phenol group revealed no selective “turn-on” signals upon exposure to divalent cations, nor did the incorporation of a 2-pyridyl subunit in place of the azole rings.  Competition assays with monovalent and divalent metal cations indicated reversible Zn(II) and Cd(II) coordination.  Titration assays showed emission signal intensity was maximized at a 1:1 chelator:metal binding ratio.  Selected coordination compound analogs were prepared in mmol quantities and characterized by HRMS, NMR and UV-Vis spectroscopy.  XRD analysis of both the Zn(II) and Cd(II) coordination compounds showed a 1:1 binding ratio between the neutral imidazole-containing Schiff base chelator and divalent metal chloride salt.  Details of the high-throughput screening, spectroscopic characterization and structural analysis will be presented.

Phenol-containing tridentate Schiff base chelators with 1,2,3-triazole and imidazole subunits

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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