Effect of molecular characteristics of DNA on its adsorption and binding on homoionic montmorillonite and kaolinite.

Adsorption or binding of DNA by montmorillonite or kaolinite, homoionic to Ca2+, was not affected by base composition, blunt or cohesive ends. Fitting data to both Freundlich and Langmuir adsorption isotherms showed that the amount of lower molecular mass DNA adsorbed and bound by both clay minerals was higher than that of the higher molecular mass DNA. The relevance of phosphate groups for the adsorption of DNA by clay minerals was investigated by adding sodium metaphosphate before and after the addition of DNA to clay minerals: DNA was partially not adsorbed even at low concentrations of sodium metaphosphate. The fact that the observed DNA was partially desorbed by washing with double-distilled H2O indicated that bonds with different degrees of strength were formed between DNA molecules and clay minerals. The higher molecular mass DNA could interact with a larger number of binding sites on the external surface of clay mineral than the lower molecular mass DNA. The number of external surface binding sites was higher on kaolinite than on montmorillonite.