Solvent-controlled Novel Cu+ and Cu+/2+ Fluorescent "Turn-ON" Probing

Abstract

A novel Schiff base probe, carbamoyl salicylimine benzothiazole hydrazine, was prepared and measured for its probing ability. High sensitivity was shown for Cu+ and Cu2+. When solvent polarity was regulated through a combination of H2O and acetonitrile, selective sensing of Cu+ or the total amount of Cu+ and Cu2+ was possible. In addition, a linear hypsochromic fluorescent shift of about 30 nm was shown. A binding stoichiometry of 1:1 exists at low concentration. Time-dependent emission measurement showed an exponential decay curve (tau(1) = 2.99 x 10(3) s, 10 equiv of Cu+) and a linear decay line (slope = -0.0216, 5 equiv of Cu+). Interference experiments in 50% acetonitrile in H2O showed that the emission produced by Cu+ and Cu2+ was not disturbed by other metal ions or by acidity or basicity. Peroxynitrite changed the emission trends; Cu+ emission decreased (78%) and Cu2+ fluorescence increased (28-fold). Biothiols, L-cysteine, DL-homocysteine, reduced glutathione, and N-acetyl-L-cysteine affected the complete reversibility of Cu+-induced emission in 50% (v/v) acetonitrile in H2O, relative to partial reversibility of Cu2+ emission. Thus, by regulating the ratio between acetonitrile and H2O, Cu+ and Cu+/2+ can be probed selectively