Study Of The Interactions Of Silicon With Cadmium Ions And Cell Wall Components By Simulation

Heavy metal pollution in farmland soil reduces crop yield and quality,and also potentially causes the crisis to human health.Formerly,the fact that silicon fertilizer could effectively reduce the residual concentration of heavy metal in crops had been identified at the tissue level.In this paper,molecular dynamics simulation was employed to investigate the effects of the silicified degree of silicic acids[namely the molar ratio of Si?OH?₄ and SiO₂]on the Cd???bound in the aspect of radial distribution functions and mean square displacements.The results demonstrated that Si?OH?₄ bound Cd???through the coordination,while SiO₂ bound Cd???by the adsorption.In particular,when the silicified degree was 0,both the bound Cd???amount and strength were the maximum value,indicating that the silicon had the best efficiency of Cd???bound as Si?OH?₄.By comparing the adsorption energy and electronic transfer of Cd???and Si?OH?₄ adsorption onto the SiO₂ surface through the quantum chemical simulation,we concluded that Cd?II?adsorption onto SiO₂ surface was chemisorption,while the Si?OH?₄ adsorption onto SiO₂ surface was physisorption.Consequently,the adsorption capacity of Cd???on the SiO₂ surface was higher than that of Si?OH?₄ adsorption on the SiO₂ surface.Moreover,the compact hydration layers around Cd???prevented the process of Cd?II?adsorption on the SiO₂ surface,even so,the counter ion Cl^-in the system promoted the adsorption process.Silicon in plants can be crosslinked with the polysaccharide components of cell walls,and silicon was more inclined to crosslink with hemicellulose to form Si-O-C bond,among which glucan in hemicellulose was the most likely one to crosslink with silicic acid.We utilized crosslinking script to analyze the crosslink interaction of mixture system with cellulose and glucan.With the increase of the concentration of silicic acid,the numbers of crosslinking sites of glucan and cellulose both increased.The crosslinking sites of glucan were more incremental than cellulose,indicating that silicic acid was more prone to crosslink with glucan.The crosslinking of different hydroxyl groups of cellulose and glucan at different concentrations of silicic acid was analyzed.The crosslinking sites of cellulose and glucan were dominated by 5-hydroxyl at low concentration of silicic acid.With the increase of the concentration of silicic acid,the crosslinking sites of 5-hydroxyl were gradually saturated,then the crosslinking site of cellulose was mainly distributed on 3-hydroxyl,while the cross-linking sites with glucan were distributed on 2,3,4-hydroxyls.On the silica surface,both cellulose and glucan can crosslink with the hydroxyl groups of silica surface,and the crosslinking of silicic acid with cellulose was more intense than with glucan.We analyzed the mechanism of silicon binding with heavy metal Cd???and crosslinking behavior with the cell wall components from molecular and electronic level,which can provide certain theoretical guidance for the design of silicon fertilizer.