A spectroscopic and quantum chemical calculation method for the characterisation of metal ions complexed with propyl gallate and procyanidins.

ABSTRACT: The deprotonation mechanism for the phenolic hydroxyl and the complexing of metal ions with a commonly used food additive, propyl gallate (PG) were studied theoretically and experimentally. The interaction of procyanidins [PC, epicatechin₁₆ (4 → 8) catechin], and its basic monomeric unit catechin (CA) with metal ions was studied by the fluorescence quenching spectra. The results showed that the 9-OH quinoid PG was formed at higher pH (10.9) by the oxidization of phenolic hydroxyl. The binding affinities (K_a) and stoichiometry of these metal ions with PG were determined. The Al³⁺ in PG-Al complex [Al(PG)(H₂O)₂Cl₂]^- was coordinated at the 8,9-OH doubly deprotonated catechol site with double chloride ions (Cl^-) and double water molecules (H₂O). The fluorescence quenching titration with Sn²⁺, Zn²⁺, Cu²⁺, Al³⁺ and Fe³⁺ revealed that the stoichiometries of metal-bound PC were 1:1, 2:3, 2:3, 2:3 and 1:1, respectively. The presence of bovine serum albumin (BSA) could enhance the complexing strength of PC with metal ions.

SUBMITTER: Zhang L 

PROVIDER: S-EPMC9941574 | biostudies-literature | 2023 Feb

REPOSITORIES: biostudies-literature