title: pH influence on the complexation site of Al(III) with protocatechuic acid. A spectroscopic and theoretical approach.
abstract: Electronic spectroscopy techniques with the aid of quantum chemical calculations, and notably the Time-Dependent Density Functional Theory, can be used to probe the structure of metal complexes in solution. Here, we report the characterization of Al(III)-protocatechuate in aqueous solution, at pH=6.5. The exploitation of the UV-vis spectra of the system by chemometric methods highlights the formation of a single complex of stoichiometry 1:1. From different structural hypothesis, the comparison of theoretical and experimental spectra shows that Al(III) forms a monodentate complex with the carboxylate function. This hypothesis is confirmed by the calculation of the complexation reaction pathways. Previous studies report the formation of a chelate involving the ortho-dihydroxyl group, at pH=3.5. These results illustrate the important dependence of the protonation state of the carboxylic function on the Al(III) fixation site on the studied ligand.
authors.affiliation: LASIR, CNRS UMR8516, Université des Sciences et Technologies de Lille, Bât C5, 59 655 Villeneuve d'Ascq Cedex, France. jean-paul.cornard@univ-lille1.fr
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Cornard
authors.forename: Christine
authors.initials: C
authors.lastname: Lapouge
authors.forename: Erwan
authors.initials: E
authors.lastname: André
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D004583:Electrons; D006863:Hydrogen-Ion Concentration; D062385:Hydroxybenzoates / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics
chemical_list: D056831:Coordination Complexes; D062385:Hydroxybenzoates; C009091:protocatechuic acid; D000535:Aluminum