Identifying the Stoichiometry of Metal/Ligand Complex by Coupling Spectroscopy and Modelling: a Comprehensive Study on Two Fluorescent Molecules Specific to Lead

Abstract

Two new chemosensors for lead (II) were synthesized based on 5-((anthracen-9-ylmethylene) amino)quinolin-10-ol (ANQ): (10-(8-hydroxyquinolin-5-ylimino)methyl)anthracen-9-yl)methyl methacrylate (ANQ-MMA) and ((10-((4-vinylbenzoloxy)methyl)anthracen-9yl)methyleneamino)quinoline-8-ol (ANQ-ST). Complexation of those molecules with Pb 2+ was studied at room temperature using UV-Visible absorption and fluorescence spectroscopies. Thanks to the UVvisible absorption spectroscopy it appeared that ANQ-MMA formed 1:1 and 1:2 complexes with lead (II) and ANQ-ST only 1:1 complex. For both molecules, the fluorescence excitation-emission matrices (EEM) signal intensity increased from 0 to 100 µmol.L-1 of lead (II) followed by a saturation for higher concentrations. The decomposition of the obtained EEMs gave a set of empiric fluorescent components that have been directly linked to the distribution of lead complexes obtained with the UVvisible absorption spectroscopy study. This correlation allowed to evidenced metal/ligand complex stoichiometry and emerge as a new method to identify empiric components. Moreover, the two ligands showed a promising selectivity for Pb 2+ , turning them interesting probes for this hazardous metal.

Influence of the synthesis parameters on the efficiency of fluorescent ion-imprinted polymers for lead detection

“…The impact of the composition of the IIPs was evaluated through fluorescence measurements. In the preliminary study of ANQ-ST, we showed that this polymerizable fluoroionophore answers in a "turnon" mode to the presence of Pb(II) [32]. Its relative fluorescence signal linearly increased upon Pb(II) addition before reaching saturation.…”

“…AgNO3, CaCO3, ZnSO4 and NaNO3 were purchased from Fisher Scientific (Analytical grade), CdSO4, Co(NO3)2 and CuSO4 from Merck (pro analysis grade), Pb(NO3)2 from Carlo Erba (Analytical grade). The functional fluorescent monomer ANQ-ST was prepared according to our previous study [32]. Pb(II) complexation with ANQ-ST was studied at 80°C, the temperature of polymerization, in different solvents: DMSO, DMSO-MeOH (1:1, v-v) and DMSO-ACN(1:1, v/v).…”

“…In a previous study, we reported the preparation of a fluorescent functional monomer, ANQ-ST, for the chelation of Pb(II) with an off-on selective fluorescence answer [32]. ANQ-ST was specially designed by the association of a fluoroionophore combining 5-amino-8-hydroxyquinoline and anthracene, as a ligand for Pb(II) and a fluorescent dye, respectively, with a styrene moiety as a polymerizable group.…”