Absolute reaction rate and kinetics of protein adsorption at solid-liquid interfaces.

Extents of adsorption of bovine serum albumin from aqueous solution to the surface of alumina, silica, carbon and chromium powder have been studied as function of time for various values of bulk protein concentration, pH, ionic strength and temperature. The rates of adsorption in all cases have been observed to fit in the first order rate equation with two different rate constants Ka1 and Ka2. Effects of addition of SDS, CTAB and neutral salts on values of Ka1 and Ka2 have also been studied. Using Arrhenius equation the activation energy values Ea1 and Ea2 have been evaluated from the values of Ka1 and Ka2 at three different temperatures, respectively. The corresponding values of enthalpy of activation (delta H*), entropy of activation (delta S*), and free energy of activation (delta G*) have been evaluated using Eyring's equation of absolute reaction rate. The mechanism of protein adsorption has been discussed in the light of basic principles of absolute reaction rate. It has been found that for Ka1 the delta H*1 greater than T delta S*1 and for Ka2 T delta S*2 greater than H*2, i.e. the anchorage and binding of protein to the surface are enthalpy controlled processes whereas the surface denaturation as well as rearrangement and folding is an entropy controlled process. The role of diffusion on rate of adsorption has also been discussed.