From colorimetric chemosensors to metal nanoparticles using two new tyrosine Schiff-base ligands for Cu 2+ detection

Two new tyrosine Schiff-base ligands 1 and 2 bearing an indole or a thianaphthene moiety were synthesized and characterized by elemental analysis, ¹H NMR, IR spectroscopy (KBr discs), MALDI-TOF-MS spectrometry, UV-Vis and fluorescence emission spectroscopy. The sensing ability towards Ca ²⁺, Zn ²⁺, Cd ²⁺, Cu ²⁺, Ni ²⁺, Hg ²⁺ and Al ³⁺ metal ions was explored in absolute ethanol. Both compounds showed colorimetric properties in the presence of Cu ²⁺ ions, changing their colour from light yellow to purple (1) and dark pink (2). The minimal amount of Cu ²⁺ that compounds 1 and 2 could quantify was ca. of 8 ppm. In order to obtain new nanomaterials based on the reported systems, new gold and silver nanoparticles were successfully synthesized by self-reduction of compound 1 in an aqueous alkaline environment. The nanoparticle formation was demonstrated by UV-Vis and fluorescence emission spectroscopy, dynamic light scattering and transmission electron microscopy (TEM). TEM images of AgNPs and AuNPs showed sizes of 12 ± 3.5 nm with monodispersed distribution, and 7.50 ± 6 nm with asymmetric average distribution, respectively. In the case of gold nanoparticles the polydisperse distribution suggested some nanoparticle aggregation.