Complexation Mechanism of Bovine Serum Albumin and Poly(allylamine hydrochloride)

Abstract

The mechanism of aggregation of bovine serum albumin (BSA) by poly(allylamine) hydrochloride (PAH) is investigated as a function of the mixing ratio r defined as the ratio of the number of BSA molecules and PAH chains present in the solution, under pH conditions of strong binding between the two partners. It is found that as r increases the turbidity first increases, passes through a maximum at a value r max before decreasing again. For small and large values of r, one forms small aggregates in the 10 nanometer size range, whereas at r max , the size of the aggregates becomes of the order of micrometers. The structure of the aggregates appears to be independent of the history of the systems but depends only on the value of r despite the strong BSA/ PAH binding. The desaggregation of the large aggregates formed at r max by the addition of BSA or PAH is shown to be an isenthalpic process and is thus entirely entropically driven. Moreover, we prove that r max corresponds to the state of the system where both the PAH chains and the BSA molecules interact one with each other, both with their maximum number of interaction points per molecule. This explains the independence of r max on the BSA or PAH concentration in the solution and why it varies linearly with the molecular weight of the polyelectrolyte. Moreover, we show that at r max , all the BSA and PAH molecules present in the solution are involved in the aggregates. At small (respectively large) values of r, the aggregates appear positively (respectively negatively) charged, corresponding to a charge excess at the surface of the aggregates. Finally, it is found that the protein/polyelectrolyte interaction is endothermic, indicating that the BSA/PAH binding must thus be entropically driven. The binding enthalpy of BSA molecules with PAH chains for r < r max is of the order of 400 kJ‚mol -1 of BSA molecules for solutions containing less than 0.1M of NaCl. The effect of the salt concentration of the solution on the binding process is also briefly discussed.

Controlled Release of Dexamethasone from Microcapsules Produced by Polyelectrolyte Layer-by-Layer Nanoassembly

“…The binding of PDDA with the dexamethasone core and between PDDA and gelatin A is an entropically driven process such as that known to govern interactions between polyelectrolytes and proteins or between nucleic acids and proteins (24,25), whereas the interaction between the two polyions PSS and PDDA is a mildly exothermic interaction (26,27). The inter- 4 10-14 (PDDA/gelatin A) 4 25-35 (PDDA/gelatin B) 4 45-55 (PSS/gelatin A) 4 50-60 action between PDDA and the drug cores and gelatin is associated with a loss of chain conformational entropy of the polyion combined with a release of counterions from the protein and the polyelectrolyte during the formation of charge/ charge interactions between the two macromolecules and between the core and the charged polymer (25). The loss of configurational entropy of the polymer chains is compensated for by a gain in entropy associated with the release of the counterions producing a positive enthalpy.…”

Entering and Exiting the Protein−Polyelectrolyte Coacervate Phase via Nonmonotonic Salt Dependence of Critical Conditions

“…47 However, these effects do not influence the consideration of chain configurational entropy presented above. The competition between loss of chain configurational entropy and gain of counterion entropy has been discussed 48 for a more closely related serum albumin-polycation system. Resolution among these manifold effects is not possible at present.…”

Protein‐Enabled Synthesis of Monodisperse Titania Nanoparticles On and Within Polyelectrolyte Matrices

“…Changes in protein conformation upon adsorption onto polyelectrolyte surfaces have been previously studied for globular proteins that exhibit an organized secondary structure in solution. [49,54,55,[62][63][64] This has revealed that polyelectrolyte LbL multilayers can create a favorable environment for the incorporated proteins, which results in the preservation of their secondary structure and activities. [63,65,66] In some cases, however, the secondary structure of globular proteins were altered upon deposition on polyelectrolyte films and resulted in a decrease in a-helix content with an increase in b-sheet content.…”