Complexation of Amino Acids with Cadmium and Their Application for Cadmium-Contaminated Soil Remediation

The interaction of amino acids with toxic heavy metals influences their immobilization and bioavailability in soils. However, the complexation ability of amino acids with Cd has not been well studied. The complexes of amino acids and cadmium were investigated by density functional theory (DFT) calculations and Fourier transform infrared spectrometry (FTIR) analyses. The complex structures were found to be [COc, COc] for fatty amino-cadmium and PheCd(2+), [COc, COc, COs] for GluCd2+ and ThrCd(2+), respectively. The complex energy of these conformers followed the order PheCd(2+)> AlaCd(2+) > LeuCd(2+) > GluCd(2+) > GlyCd(2+) > ThrCd(2+). Importantly, all of the complex energy values were less than zero, indicating that these complexes could be easily dissolved in water. The Cd2+ concentration decreased with increasing amino acid concentration in aqueous solution. The complex stability constants (log beta) followed the order PheCd(2+)> AlaCd(2+) > LeuCd(2+) > GluCd(2+) > GlyCd(2+) > ThrCd(2+), consistent with the order of the calculated complex energy values. The Cd removal efficiencies by Thr, Glu, Gly, Ala, Leu, and Phe were 38.88%, 37.47%, 35.5%, 34.72%, 34.04%, and 31.99%, respectively. In soil batch tests, the total Cd concentration in soil decreased in the presence of amino acids, while the Cd concentration in water increased from 231.97 mu g/L to 652.94~793.51 mu g/L. The results of sequential extraction showed that the acid-extractable fraction and the reducible fraction of Cd sharply decreased. Consequently, the significant features of amino acids along with their biocompatibility make them potentially applicable chelators in Cd-contaminated soil remediation processes.

Automated summary

The study investigated complex structures and stability of amino acid-Cd complexes using DFT calculations and FTIR analyses, revealing that amino acids can reduce Cd concentration in soil. Results showed a positive correlation between amino acidCd removal efficiency and stability constants with complex energy.