蒙脱土、高岭土和针铁矿对DNA吸附与解吸特征

采用平衡法研究了蒙脱土、高岭土和针铁矿在不同pH值和不同电解质溶液下的DNA吸附解吸特征.结果表明,在4种电解质体系中,尤其在溶液pH值>5.0时,3种矿物在吸附过DNA后,pH有不同程度上升,但CaCl2电解质体系中含针铁矿溶液的pH开始下降.针铁矿对DNA的吸附率大约为75%～91%,高岭土对DNA的吸附率从pH为3.5时的90%开始下降,至pH 6.0～7.0时的下降至大约18%～50%.在一价电解质体系,当溶液pH值为2.2～5.0时蒙脱土对DNA的吸附率大约为90%开始下降至25%～40%,但在二价电解质体系蒙脱土对DNA的吸附率大约为92%.Freundlich等温吸附方程能更好的拟合针铁矿、蒙脱土和高岭土对DNA的吸附.蒙脱土对DNA相对吸附容量在pH 3.5时大于针铁矿,而pH 5.0时小于针铁矿.以NaOAc为解吸剂,针铁矿、蒙脱土和高岭土上吸附DNA在不同pH时解吸率分别为0.1%～0.4%、63.7%～90.2%和29.7%～87.5%.以NaH2PO4为解吸剂时,这些矿物吸附DNA的解吸率分别为69.6%～78.7%、0.8%～7.0%和0.4%～2.2%.这表明针铁矿吸附DNA时键合作用较大,蒙脱土和高岭土静电引力较大,这是DNA在不同电荷类型矿物表面的吸附差异.

Characteristics of DNA Adsorption and Desorption in Montmorillonite, Kaoline and Goethite

The characteristics of adsorption and desorption of DNA by montmorillonite, kaoline and goethite at different pH values and different electrolytes were studied using a batch method. It showed that there was an obvious increase of solution pH value after adsorption of DNA by the three minerals in four electrolyte systems especially in solution pH>5.0 except as pH of DNA solution by goethite decreased in CaCl₂ electrolyte systems.Percentage of DNA adsorption by goethite was about 75%-91%, and that by kaoline decreased from 90% in solution pH 3.5 to 18%-50% when solution pH was 6.0-7.0, and that by montmorillonite decreased from 95% in solution pH 2.2-5.0 to 25%-40% in solution pH 7.0 in monovalent electrolyte systems and was about 92% in divalent electrolyte systems. Freundlich equation could be used to describe DNA isotherm adsorption by three minerals. Relative absorption capacity of DNA by montmorillonite was greater than that by goethite in solution pH 3.5, where less than that by the solution pH 5.0.The differences of desorption on three minerals were significant while the adsorbed DNA was desorbed with NaOAc solution and NaH₂PO₄ solution. The percentages of DNA desorption when NaOAc as the desorbent in goethite, montmorillonite and kaoline were 0.1%-0.4%, 63.7%-90.2% and 29.7%-87.5% at different pH values, while those were 69.6%-78.7%, 0.8%-7.0% and 0.4%-2.2% when NaH₂PO₄ as the desorbent, respectively. These results implied that the ligand exchange played a more important role in DNA adsorption on goethite, and electrostatic interactions did on montmorillonite and kaoline. This was the differences of DNA adsorption and desorption on different charge minerals surfaces.