  The so-called extended law of corresponding states, as proposed by Noro and
Frenkel [J. Chem. Phys. 113, 2941 (2000)], involves a mapping of the phase
behaviors of systems with short-range attractive interactions. While it has
already extensively been applied to various model potentials, here we test its
applicability to protein solutions with their complex interactions. We
successfully map their experimentally determined metastable gas--liquid
binodals, as available in the literature, to the binodals of short-range
square-well fluids, as determined by previous as well as new Monte Carlo
simulations. This is achieved by representing the binodals as a function of the
temperature scaled with the critical temperature (or as a function of the
reduced second virial coefficient) and the concentration scaled by the cube of
an effective particle diameter, where the scalings take into account the
attractive and repulsive contributions to the interaction potential,
respectively. The scaled binodals of the protein solutions coincide with
simulation data of the adhesive hard-sphere fluid. Furthermore, once the
repulsive contributions are taken into account by the effective particle
diameter, the temperature dependence of the reduced second virial coefficients
follows a master curve that corresponds to a linear temperature dependence of
the depth of the square-well potential. We moreover demonstrate that, based on
this approach and cloud-point measurements only, second virial coefficients can
be estimated, which we show to agree with values determined by light scattering
or by DLVO-based calculations.
