Mammea A/AA (MA) potency as ratiometric absorbance based molecular probe: Cations detection and quantification ability

Abstract

MA is a phenyl coumarin extracted from the bark of the stem of Mammea Africana. This compound exhibits two absorption peaks in the region between 300 and 550 nm, whose relative wavelength positions, their absolute absorbances and the ratio of their absorbances depend on the molecular environment. In this work, this property was exploited for the first time to detect and quantify metal ions in aqueous solution. Alkali (Mg2+, Na+, Ca2+, K+), transition (Zn2+, Fe2+, Co2+, Cu2+) and heavy (Hg2+, Pb2+, Sn2+) metal ions were considered. We found that the MA spectroscopic response depends on the nature and class of the cations in solution, indicating a binding interaction. Our method applied to the detection and quantification of cations in different mineral waters, allowed us to obtain the concentrations of different cations with good accuracy. A theoretical calculation using DFT methods provided the geometrical structures of the organometallic complexes, which revealed that the metal ions are chelated by MA at the carbonyl site of the coumarin moiety. In addition, calculation of electronic transitions by TDDFT as well as analysis of MOs showed that the photophysics of complexes involving MA and a metal cation is governed by intra-ligand, ligand-to-metal and metal-to-ligand electron transfer.