Complexation of zinc(II) and other divalent metal ions by the fluorophore 2-methyl-8-(toluene-p-sulfonamido)-6-quinolyloxyacetic acid in 50% aqueous ethanol
1997
Rodopoulos, T. | Pittet, P.A. | Mahadevan, I. | Lincoln, S. | Ward, A. | Duckworth, P. | Kurucsev, T. | Hendrickson, K. | Forbes, I. | Zalewski, P.
A potentiometric and fluorescence study of the complexation of divalent metal ions (M<sup>2+</sup>) by the fluorophore 2-methyl-8-(toluene-p-sulfonamido)-6-quinolyloxyacetic acid (H<inf>2</inf>L) in 50% (v/v) aqueous ethanol at 298.2 K and I = 0.10 mol dm<sup>-3</sup> (NaClO<inf>4</inf>) showed that the [ML] and [ML<inf>2</inf>]<sup>2-</sup> complexes are characterised by log(β<inf>1</inf>/dm<sup>3</sup> mol<sup>-1</sup>) and log(β<inf>2</inf>/dm<sup>6</sup> mol<sup>-2</sup>) values of 8.12 ± 0.20 and 17.06 ± 0.11, respectively, when M<sup>2+</sup> = Co<sup>2+</sup> and corresponding values of < 8 and 15.73 ± 0.03 when M<sup>2+</sup> = Ni<sup>2+</sup>, 11.96 ± 0.02 and 21.40 ± 0.03 when M<sup>2+</sup> = Cu<sup>2+</sup>, 9.65 ± 0.02 and 19.11 ± 0.06 when M<sup>2+</sup> = Zn<sup>2+</sup> and 8.44 ± 0.50 and 15.38 ± 0.40 when M<sup>2+</sup> = Cd<sup>2+</sup>. In the cobalt(II) system, [CoL<inf>3</inf>]<sup>4-</sup>, where log(β<inf>3</inf>/dm<sup>9</sup> mol<sup>-3</sup>) = 25.56 ± 0.11, was also detected. The pK<inf>a</inf> values for H<inf>3</inf>L<sup>+</sup> are 1.87 ± 0.10, 3.72 ± 0.03 and 10.01 ± 0.02. These data are discussed together with the fluorescence characteristics of HL<sup>-</sup>, [ZnL] and [ZnL<inf>2</inf>]<sup>2-</sup>.
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