The esterification of carboxylate functionalities present in the cell walls of Datura innoxia results in a decrease in metal uptake by as much as 40%, depending on the metal studied. These findings suggest that carboxylate groups are important in metal ion adsorption to this biomaterial. Base hydrolysis of the native plant material resulted in a slight increase in metal ion uptake for Cu2+ and Sr2+ and a decrease in uptake for Cd2+. These results are attributed to the hydrolysis of esters native to the plant material, which increases the carboxylate content but also results in conformational changes in the macromolecules that comprise the cell fragments. Both the esterified product and the hydrolyzed material were examined via infrared spectroscopy. A peak occuring at 1735 cm-1 (attributed to the carbonyl stretch) confirmed the esterification process. The infrared spectra of the hydrolyzed samples indicate further ionization of carboxylate groups or hydrolysis of esters native to D. innoxia.

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The excitation spectra associated with the 7F0↦5D0 transition of Eu+3 has been used to examine the binding sites on cell wall fragments of Datura innoxia. Both native and esterified cell wall fragments were each examined at pH 5 and pH 2 to determine the contributions to metal ion sorption from both the carboxylate and sulfonate functional groups. The excitation spectra have been de-convoluted into the individual groups responsible for metal ion uptake. At least four unique binding sites can be described as being responsible for metal ion uptake. The higher affinity sites involve carboxylates in the binding of Eu+3 in a tridentate (3:1 ligand-to-metal ratio) configuration.

The use of frontal affinity chromatography for the study of metal-biomaterial interactions is described. Both normal frontal affinity chromatography and a modification of this methodology were used to generate metal binding isotherms to a biomaterial. This modification enabled the acquisition of binding isotherms with extended concentration ranges at the expense of time-dependent binding information. Comparison between normal and modified mode was made by using a well-defined commercial resin. Similar performance of these two modes was obtained. The biomaterial investigated was composed of cell fragments from the plant Datura innoxia which were immobilized within a polysilicate matrix. The application of a regularized least-squares method indicated the existence of two classes of sites on this biosorbent involved in the binding of Ag(+). A total metal-ion binding affinity order at solution pH 3-5 was determined to be Cu(2+) > Cd(2+) ≈ Ag(+) > Ca(2+).