Characterization of Cd Binding Sites on Datura Innoxia Using¹¹³Cd NMR Spectrometry

The interactions between Cd(II) and Datura innoxia cells have been examined using Cd-113 NMR spectroscopy. A series of model solutions containing carboxylate, amine, hydroxyl, sulfhydryl, oxalate, sulfate, and sulfonate functionalities have been utilized to identify the moieties on the cell wall responsible for the observed chemical shifts. Carboxylate groups have been determined to be the dominant functional groups responsible for binding of Cd(II) on the cell wall of D. innoxia at pH less-than-or-equal-to 5. At pH 6, diamine groups have been observed to be involved in the binding of Cd(II) to the biomass. Chemical shift data indicate carboxylate groups could interact with Cd(II) in a 2:1 ratio. The chemical shift of Cd-113 NMR also suggests a rapid exchange equilibrium among Cd(II)-containing species near the cell walls at pH 6.