Metal chelation by a plant lignan, secoisolariciresinol diglucoside

Secoisolariciresinol diglucoside (SDG) is a polyphenolic phytoestrogen which is particularly abundant in flaxseed. As a diphenolic compound, SDG is expected to function as a metal chelating ligand. The affinity of SDG for metal cations was determined using a mass spectrometric approach. Experiments yielded equilibrium constants in aqueous solution for SDG center dot Ca2+, SDG center dot Cu2+, SDG center dot Pb2+, SDG center dot Ni2+, SDG center dot Fe2+ and SDG center dot Ag+ of 20.34, 5.99, 4.26, 2.77, 2.46 and 1.90, respectively. These values are consistent with those determined for plant phenolics. Semiempirical calculations for the SDG metal complexes yield an insight into their likely structures.