Salt-Induced Disintegration of Lysozyme-Containing Polyelectrolyte Complex Micelles

The salt-induced disintegration of lysozyme-filled polyelectrolyte complex micelles, consisting of positively charged homopolymers (PDMAEMA(150)), negatively charged diblock copolymers (PAA(42)-PAAm(417)) and lysozyme, has been Studied with dynamic light scattering (DL) and small-angle neutron scattering (SANS). These measurements show that, from 0 to 0.2 M NaCl, both the hydrodynamic radius (R(h)) and the core radius (R(core)) decrease with increasing salt concentration. This suggests that the micellar structures rearrange. Moreover, from similar to 0.2 to 0.4 M NaCl the light-scattering intensity is constant. In this salt interval, the hydrodynamic radius increases, has a maximum at 0.3 M NaCl, and subsequently decreases. This behavior is observed in both a lysozyme-containing system and a system without lysozyme. The SANS measurements on the lysozyme-filled micelles do not show increased intensity or a larger core radius at 0.3 M NaCl. This indicates that from 0.2 to 0.4 M NaCl another structure is formed, consisting of just the diblock copolymer and the homopolymer, because at 0.12 M NaCl the lysozyme-PAA(42)-PAAm(417) complex has disintegrated. One may expect that the driving force for the formation of the complex in this salt range is other than electrostatic.