NONIDEALITY OF AQUEOUS-SOLUTIONS OF POLYETHYLENE-GLYCOL - CONSEQUENCES FOR ITS USE AS A MACROMOLECULAR CRYSTALLIZING AGENT IN VAPOR-DIFFUSION EXPERIMENTS

Microisopiestic measurements of the concentrations of polyethylene gly col (PEG 8000) paired with the salts sodium chloride, ammonium sulfate and magnesium sulfate heptahydrate have been made in a sitting-drop a rrangement with PEG in the droplet and salt in the reservoir. Resultin g graphs of the concentrations of PEG and salt that are equivalent wit h respect to the vapor pressure of water are non-linear, do not inters ect their origins, and demonstrate that relatively low (mM) salt conce ntrations are equivalent to relatively high PEG concentrations. The co nsequences of each of these observations for macromolecular crystalliz ation by the vapor-diffusion technique when PEG is employed as the cry stallizing agent are discussed.