Computational Studies on the Interaction of Aflatoxins with a few Metal Ions

Abstract

Aflatoxins (AF) are toxic secondary metabolites produced by aspergillus fungi, pose significant health risks due to their contamination in food products, particularly maize and peanuts. This study investigates the interactions of the most toxic variant, AFB1 along with its reduced form AFB2 and hydroxylated metabolite AFM1 with metal ions (Zn²⁺ and Fe²⁺) using the DFT/B3LYP/6-31G+(d,p) computational method implemented in Gaussian 16W. The Conductor-like Polarizable Continuum Model (CPCM) with water as the solvent was employed to analyze solvation effects. Before complexation with metal ions, all the variant of aflatoxins (B1, B2, G1, G2, M1 and M2) were optimized using the same computational method. It is well known than metal ions (Zn2+ and Fe2+) influence aflatoxin stability, reactivity, and toxicity. Geometrical parameters, thermodynamic properties, spectral analysis and NBO charge distributions were analyzed to understand metal coordination effects. Several complexes of metal ion (Zn2+ and Fe2+) with aflatoxin (B1, B2 and M1) are optimized. The most stable structure for each complexation is assigned as structure A. The aflatoxin complexes with Zn²⁺ and Fe²⁺ exhibited negative ∆G and ∆H values, confirming spontaneous complexation and an exothermic process. The change in entropy, ∆S for Zn2+-aflatoxin complexes show lower value compared to Fe2+-aflatoxin complexes which reflects Zn2+ aflatoxin complexes are thermodynamically favored. NBO analysis revealed strong donor acceptor interactions with Zn2+-aflatoxin complexes demonstrating greater electronic stability than Fe2+-aflatoxin complexes. The absorption maxima, λmax for the most stable complexes of Zn2+-AFB1 and Fe2+-AFB1 are 318.51 nm and 324.39 nm respectively. The nature of transition for Zn2+-AFB1 complexes are n→π* and π →π* along with ligand to metal charge transfer (LMCT) while for Fe2+-AFB1 complexes are n→π*, π →π*, d→d along with metal-to-ligand charge transfer (MLCT). IR spectral analysis further supported the strong complex formation with Zn²⁺ which coordination significantly weakening C=O bonds, whereas Fe²⁺ interactions cause shifting of frequency depending on the binding site. This computational study explores metal- aflatoxin interactions, highlighting the structural and thermodynamic effects of Zn²⁺ and Fe²⁺ coordination. Zn²⁺ forms stronger, more stable complexes, significantly altering molecular geometry and electron distribution compared to the Fe2+-aflatoxin. These findings contribute to understanding aflatoxin reactivity and potential metal-based detoxification strategies, paving the way for further experimental validation.