MECHANISM OF THE EXTRACTION OF PROTEINS INTO TWEEN-85 NONIONIC MICROEMULSIONS

Protein extraction into Tween 85 nonionic microemulsions is characteri zed. Apparently, a weak electrostatic interaction is the underlying ex traction mechanism. The extraction of several proteins is examined as a function of protein size and net charge. The proteins that extracted successfully are positively charged. A size-exclusion limit (60 kDa) is also evident in these extractions. Tween 85 and several other nonio nic surfactants possess a net negative charge at neutral pH. Titration measurements are an effective means of quantifying charge on these su rfactants. In Tween 85 microemulsion separations, both the sign and th e magnitude of surfactant charge play a role in extraction. Blends of Neodol 91-2.5 (capable of extracting 0% protein) and Tween 85 (capable of extracting 100% protein) indicate that a minimum net surfactant ch arge of 15 mequiv/mol is required for extraction.