Submitted to: Annual Experimental Nuclear Magnetic Resonance Conference
Publication Type: Abstract only
Publication Acceptance Date: 1/14/2001
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Polyaspartate is used in water treatment, detergents, and as a soil additive to improve crop yields. The ability of polyaspartate to complex metal ions is thought to play a role in its performance in these applications. 1H spectra of the methylene protons on L- and D-aspartic acid in D2O showed multiplicity changes, followed by broadening and then coalescence as metal concentrations increased. Exchange equilibrium betwee aspartic acid and metals was established at lower concentrations for certain metals. A 1H spectrum exhibiting coalescence at a low concentration of a given metal implies that binding to aspartic acid is more specific for that metal. The specificity of binding increased from alkali metals (no apparent interaction) to alkaline earths, to transition metals (strongest interaction). Vandium was particularly favored. The methylene protons on polyaspartate are conformationally broadened. However, 13C spectra of polyaspartate in D2O showed evidence for metal binding and a similar specificity trend. The chemical shift of the free carbonyl group decreases when metals are added. At a given low metal concentration, the magnitude of the shift correlates to the specificity: for example, V and Mn were preferred over Al and especially Ca. At higher metal concentrations the magnitude of the shift remains constant.