Dynamic light scattering evidence of a `fragileʹ character of protein aqueous solutions

Dynamic light scattering has been used to measure the mutual diffusion coefficient Dm of bovine serum albumin as a function of temperature at different protein concentrations. A deviation from the Arrhenius behaviour is observed, at each protein concentration investigated, corresponding to a characteristic temperature TA, whose value is found to be dependent on the protein concentration itself. In the whole temperature range, the dependence of Dm on T is well represented by a Vogel–Fulcher–Tamman law. The results are discussed in the framework of the so-called strong/fragile classification scheme for glass-forming liquids, connected to the peculiar properties of the water–protein system.