ELECTROSTATIC AND VAN-DER-WAALS CONTRIBUTIONS TO PROTEIN ADSORPTION -COMPARISON OF THEORY AND EXPERIMENT

Electrostatic and van der Waals interactions are important in many col loidal phenomena and as such have been studied and described extensive ly. In a previous paper (Langmuir 1993, 9, 962), we described a model for the adsorption equilibrium constant of proteins at charged surface s based on these effects, calculated using molecular properties of the proteins. Here, we compare the predictions of this model to experimen tally determined equilibrium constants obtained using total internal r eflectance fluorescence (TIRF) spectroscopy. With this Surface-sensiti ve technique, equilibrium constants were obtained over 4 orders of mag nitude as the ionic strength was varied over a decade and a half. Lyso zyme adsorbed preferentially compared to chymotrypsinogen A at low ion ic strengths while the opposite trend was observed at high ionic stren gths. The model, in its various degrees of complexity, is able to pred ict the trend observed in equilibrium constant with varying ionic stre ngth, to predict the values approximately, and to discern differences between the behaviors of the proteins studied. The utility of this mod el in understanding the interplay between charge and size-dependent fo rces is demonstrated, as is its potential for predictive calculations.