Adsorption of Biopolymer at Solid−Liquid Interfaces. 1. Affinities of DNA to Hydrophobic and Hydrophilic Solid Surfaces

Abstract

The extent of adsorption (Γ21) of DNA from aqueous solution on different hydrophobic and hydrophilic solid surfaces has been compared as a function of pH, temperature, ionic strength of the medium, and denaturants. Γ21 at a given surface (except sephadex) increases with an increase of the nucleotide concentration (X2) of DNA in mole fraction units, but it attains a monolayer saturation value Γ2m when X2 attains a value X2m. In most cases Γ21 increases further when X2 ≫ X2m. Various neutral electrolytes like LiCl, KCl, CsCl, KBr, CaCl2, and Na2SO4, surfactants like SDS and Triton-X 100, the denaturing action of heat, and the addition of acid and alkali have been observed to play an important role during the study of the adsorption of DNA on charcoal powder. Further, a comparative study has been performed to examine the relative affinity of DNA toward different types of solid surfaces. The significant role of different types of surfaces in controlling the adsorption process has been explained in terms of Gibbs' surface excess quantities. The experimental results have been interpreted in terms of maximum work due to the free energy change of DNA adsorption on various solid surfaces and more quantitatively in terms of the standard free energy change (ΔG°) for the saturation of the surface by DNA as a result of the change in the nucleotide concentration in the bulk from zero to unity in mole fraction units.