Experimental and Molecular Computational Investigation of Bonding Mechanism Between Aflatoxin B1 and Smectite.

Smectite-rich bentonites can be used in aflatoxin-contaminated feeds or diet to reduce toxicity of the mycotoxin. The objectives of this study were to investigate the bonding mechanism between adsorbed aflatoxin B₁ molecules and smectite based on experimental data and molecular mechanic computation. The afaltoxin-smectite complex was synthesized using water as solvent and interlayer adsorption was confirmed with variable-temperature XRD. The stretching vibrations of the two carbonyl bonds of aflatoxin B₁ had greater than 22-cm^-1 red shifts after being adsorbed to Ca-smectite. At nearly 0% humidity, the C=O vibrations in the monovalent cations K- or Na-saturated complexes located more than 30 cm^-1 higher than those in the transition heavy metal Ni-, Mn- or Cu- saturated complexes. Geometry optimization and theoretical IR spectra for aflatoxin and aflatoxin-smectite complexes were performed with density functional theory (DFT) at PCM/B3LYP/DGDZVP level of theory. The experimental spectra were in excellent agreement with theoretical calculations. The calculation allowed accurate assignments of the bands of experimental spectra. We concluded that  the major bonding forces were  ion-dipole interactions and coordinations between the exchangeable cations and the carbonyl groups of aflatoxin B₁ under dry condition, and  H-bonding between the carbonyl group and water in the hydration shell of the exchange cations under wet condition.