8-Hydroxyquinoline-2-Carboxylic Acid as Possible Molybdophore: A Multi-Technique Approach to Define Its Chemical Speciation, Coordination and Sequestering Ability in Aqueous Solution

Abstract

8-hydroxyquinoline-2-carboxylic acid (8-HQA) has been found in high concentrations (0.5–5.0 mmol·dm−3) in the gut of Noctuid larvae (and in a few other lepidopterans), in which it is proposed to act as a siderophore. Since it is known that many natural siderophores are also involved in the uptake and metabolism of other essential elements than iron, this study reports some results on the investigation of 8-HQA interactions with molybdate (MoO42−, i.e., the main molybdenum form in aqueous environments), in order to understand the possible role of this ligand as molybdophore. A multi-technique approach has been adopted, in order to derive a comprehensive set of information necessary to assess the chemical speciation of the 8-HQA/MoO42− system, as well as the coordination behavior and the sequestering ability of 8-HQA towards molybdate. Chemical speciation studies have been performed in KCl(aq) at I = 0.2 mol·dm−3 and T = 298.15 K by ISE-H+ (glass electrode) potentiometric and UV/Vis spectrophotometric titrations. CV (Cyclic Voltammetry), DP-ASV (Differential Pulse-Anodic Stripping Voltammetry), ESI-MS experiments and quantum mechanical calculations have been also performed to derive information about the nature and possible structure of species formed. These results are also compared with those reported for the 8-HQA/Fe3+ system in terms of chemical speciation and sequestering ability of 8-HQA.

Caffeic Acid/Eu(III) Complexes: Solution Equilibrium Studies, Structure Characterization and Biological Activity

“…In the different systems under comparison, we may have ligands with different denticities, different solution conditions, different acid–base properties, but also different metal cations. We may even have competition reactions between other metals and ligands simultaneously present, as protonation reactions and metal hydrolysis compete with the metal complex formation reactions [ 35 , 64 , 65 , 66 , 67 ].…”

“…Due to the complexity of the systems under study, only a multi-analytical-technique approach can provide sufficient knowledge for answering all of these questions; these can be answered by means of investigation of solution equilibria [ 35 ], the correct characterization of the synthesized compounds [ 36 , 37 ], and the assessment of their biological activity [ 38 ]. In our previous works, the above-mentioned effects were mainly examined in the solid phase [ 32 , 34 , 39 , 40 ].…”

Low-dimensional compounds containing bioactive ligands. XXII. First crystal structure, cytotoxic activity and DNA and HSA binding of a zirconium(IV) complex with 8-hydroxyquinoline-2-carboxylic acid

“…One of the important HXQs is 8-hydroxyquinoline-2-carboxylic acid (HQCaH). HQCaH appears to have a significant impact on the biosynthesis regulation of the Noctuid larvae microbiota, due to its excellent chelating properties (Gama et al, 2018;Arena et al, 2020). HQCaH can coordinate as a bidentate chelating ligand via the O atom of the phenol ring and the N atom of the pyridine ring, or as a tridentate chelating ligand that is additionally coordinated through an O atom of the carboxyl group.…”