Precipitation of a water soluble ABC triblock methacrylic polyampholyte: Effects of time, pH, polymer concentration, salt type and concentration, and presence of a protein

The solution behavior of a low molecular weight ABC triblock methacrylic polyampholyte with the structure (dimethylaminoethyl methacrylate)(8)-(methyl methacrylate)(12)-(methacrylic acid)(16) was investigated by turbidimetry. The variation of the optical density at 420 nm of dilute polyampholyte solutions with time, pH, polymer concentration, salt type and concentration, and presence of a protein was explored. Polyampholyte precipitation was fast and occurred around the isoelectric pH. The size of the aggregates increased with increasing salt concentration and was independent of polyampholyte concentration. High salt concentrations suppressed polyampholyte precipitation. The precipitation in the presence of various electrolytes at a concentration of 0.2 M was insensitive to the anion type for a series of potassium halides and also to the divalent sulfate anion, but was greatly increased by the divalent calcium cation and was completely suppressed by the anionic surfactant sodium dodecyl sulfate. The polyampholyte formed insoluble complexes with a basic protein, chicken egg lysozyme in the pH region between the isoelectric points of the two reactants. The results of this study will be useful for designing the extraction of solutes, such as heavy metals and proteins, via polyampholyte electrostatic complexation; moreover, they will facilitate the development of efficient strategies for polyampholyte recovery and recycling.