Bonding mechanisms between aflatoxin B1 and smectite

Bentonites were used in aflatoxin-contaminated feeds and diets to reduce bioavailability of the mycotoxin. The objectives of this study were to test accessibility of smectite interlayer space to aflatoxin adsorption and to investigate bonding mechanisms between adsorbed aflatoxin B1 molecules and smectite. The aflatoxin–smectite complex had a basal spacing greater than 1.2 nm up to 400 °C, which suggests interlayer aflatoxin adsorption. The in-phase carbonyl-stretching band shifted from 1736 cm–1 for monovalent cation (K or Na) to 1687 cm–1 for heavy-metal (Ni or Cu) complexes. At nearly 100% humidity, the cations did not distinctly affect band positions of the adsorbed aflatoxin molecules. We concluded that, under dry conditions, major bonding between adsorbed aflatoxin B1 and smectite was ion-dipole interactions and coordination between exchangeable cations and carbonyl groups. Under humid conditions, H-bonding between carbonyl groups and exchangeable-cation hydration-shell water was the dominant bonding force.