Kinetics of adsorption of DNA at solid-liquid interfaces

Abstract

We have investigated the mechanistic aspect of DNA adsorption at different hydrophobic and hydrophilic solid-liquid interfaces as a function of bulk DNA concentration, pll, ionic strength, temperature. In all cases of DNAadsorption at solid-liquid interfaces, initial rate of adsorption is controlled by diffusion process and the steady value of extent of adsorption (Γ e 2 ) is attained after nearly six hours. The rates of adsorption in all eases fit the first order rate equation with two kinetic constants k 1 and k 2 . Using the Arrhenius equation, the activation energies E 1 * and E 2 * for DNA adsorption have been evaluated. The corresponding values of enthalpy of activation (ΔH # ), entropy of activation (ΔS # ), and free energy of activation (ΔG # ) have been evaluated using Eyring's equation of absolute reaction rate. It has been found that T a v ΔS # > ΔH # for both the kinetic steps, so adsorption of DNA at charcoal-water and silica-water interface is solely entropy-controlled. But in case of BaSO 4 -water interface, adsorption of DNA is enthalpy-controlled. Free energy of activation, ΔG # 1 and ΔG # 2 vary within 65 to 75 and 70 to 80 kJ mol - 1 , respectively, and these values are comparable with adsorption of different proteins at solid-liquid interfaces.