Study On The Interactions And Mechanisms Of DNA With Clay Minerals

Supergene environment are rich in enzyme, DNA （Deoxyribonucleic Acid） and otherbiological active substance, clay minerals, organic matter and other nonliving matter. Theseextracellular DNA are closely linked with clay minerals in soil and it can persist in naturalenvironment for long periods.In order to reveal the dynamic mechanism of DNA/clay mineralinterface reaction system and its migration, enrichment and gene transfer rule, we firstlyselected montmorillonite and layered double hydroxide as clay mineral representation, takingsalmon sperm DNA and herring testis DNA as DNA material and then studied the adsorptionand desorption properties of DNA on clay mineral.Secondly, DNA-LDH nanohybirds weresimulatively prepared, and the surface microstructure changes of these clays were analyzed byXRD,FTIR,TG-DSC and SEM. Finally, through a simplified model, we discussed theinterface reaction characteristics of DNA and clay mineral, which had different charge typesand layers structure. The results were shown as below：1.Cationic surfactant, anionic surfactant and poly hydroxyl iron and aluminum was usedto prepare organic and inorganic montmorillonite（MMT）.The values of equilibriumadsorbance were in order of HTDM-MMT> MMT>SDS-MMT>Fe/Al-MMT. After organicmodification, HDTMA promote DNA adsorption, with the adsorbance of61.04μg·mg^-1.However, as a result of being carpeted with SDS on external surface, the SDS-MMT adsorbedless DNA with the adsorbance of26.88μg·mg^-1. When pH values were5.0～9.0, the amountsof DNA adsorption on organic modified MMT declined far less than original MMT with theincrease of pH value. The kinetics of adsorption indicated that the main step which controlledDNA adsorption on modified MMT is chemical adsorption. The differences of desorption onorganic and inorganic modified MMT are very significant while the DNA adsorbed wasdesorbed with NaOAc and NaH2PO4solution. It implied that adsorption intensity greatlyenhanced in the presence of poly hydroxyl Fe/Al and SDS. These results showed that thestructure, the electronegativity and the characteristics of the surface were the key factors thataffect DNA adsorption on differently modified MMT.2. Except adsorption, the main interaction between DNA and LDH has turned out to beintercalation. Size expansion of the basal spacing （003） from0.76nm in LDH to2.30nmwas observed in the resulting DNA-LDH nanohybrids and it gave peaks corresponding toC=O (1534cm^-1and1488cm^-1) in skeleton and bases, C–O stretching vibration (1228 cm^-1), and P–O symmetrical stretching vibration (1096cm^-1) functional groups of DNA,indicating that DNA were intercalated into the LDH by the ion exchange. However, thedisplacement of NO－3was not fully complete （partial intercalation of DNA）.Those DNAoutside LDH interlayers was absorbed on the surface of LDH. The cyclic voltammetric curvesshowed that DNA in the composites exhibited a very similar peaks, which is corresponding tothe two reduction current peaks （EP=－1.2mV and EP=－2.4mV） of free DNA.Itsuggested that both Cd²⁺and Pb²⁺cannot insert the groove of DNA to associate with base pairsor other groups when DNA was bound on LDH. The results showed that, on the one hand,both Cd²⁺and Pb²⁺were absorbed on the external surface of LDH for immobilization, on theother hand, the layer of LDH provided ideal space for DNA by the action of protecting DNAmolecules from Cd²⁺and Pb²⁺.3. According to the experiment, simulation system of two kinds of mechanism will bedesigned: One is a surface adsorption model of DNA, which is suitable for DNA adsorptionby montmorillonite and modified montmorillonite; another is interlayer intercalation model ofDNA, which is suitable for intercalation of DNA into the layers of LDH.