Driving forces for DNA adsorption to silica in perchlorate solutions

The adsorption of both plasmid and chromosomal duplex DNA to silica is investigated with the aim of determining the dominant forces involved in the binding reaction. Changes in the initial slopes and plateau values of adsorption isotherms for DNA on microcrystalline silica particles are used to establish the sensitivity of the binding reaction to ionic strength, temperature and pH, and DNA size and conformation. Binding is driven by an increase in entropy, with little or no enthalpic contribution. Adsorption isotherm results indicate that three effects, namely: (i) shielded intermolecular electrostatic forces, (ii) dehydration of the DNA and silica surfaces, and (iii) intermolecular hydrogen bond formation in the DNA-silica contact layer, make the dominant contributions to the overall driving force for adsorption. (C) 1996 Academic Press, Inc.