Paper BI+AS-WeA8
Interactions between Calix-6-arene Sulfonates and Poly (Allylamine Hydrochloride) : A Stoichiometric Complexation Able to Release Proteins Bound to the Polyelectrolyte
In the framework of our research, aimed to understand the fundamental mechanisms of interactions between polyelectrolytes and proteins or between polyelectrolytes and ions either in the adsorbed state on surfaces or in solution, we describe here the interaction between calix-6-arene sulfonate (C6S) and poly (allylamin hydrochloride), PAH. At pH = 7.4, the C6S molecules carry 6 negative charges owing to their sulfonate groups whereas the polyelectrolyte is positively charged. Electrophoretic mobility experiments show that neutral particles are formed when the amount of negative charges coming from C6S matches the amount of positive charge from PAH (two chain lengths have been investigated). These particles display sizes in the µm range and are subjected to sedimentation after long term equilibration. Hence, coacervation occurs and this process is irreversible, since addition of either an excess of PAH or C6S does not change the solution turbidity and the particle size distribution. At smaller C6S/PAH stoichiometries, where C6S is totally removed from the unbound state in solution, the particles are positively charged and smaller in size (hydrodynamic radius between 50 and 150 nm). Therefore, the neutral particles obtained at the charge equivalence may result from aggregation of smaller C6S-PAH aggregates. Moreover, H-NMR experiments show that the C6S molecules are tightly bound to the polymer. We show then that one can make use this strong interaction in competition experiments to release quantitatively bovine serum albumin (BSA) that has been bound to PAH molecules in a previous step. These BSA-PAH aggregates are spontaneously dissociated and replaced by C6S-PAH particles which sediment, the supernatant only containing proteins in their native secondary conformation.