Journal
MACROMOLECULAR RAPID COMMUNICATIONS
Volume 41, Issue 1, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/marc.201900421
Keywords
Spherical polyelectrolyte brushes; proteins; ITC; thermodynamics; enthalpy-entropy compensation (EEC)
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Funding
- Deutsche Forschungsgemeinschaft via the International Research Training Group 1524
- National Science Foundation Research Triangle Materials Research Science and Engineering Center (NSF MRSEC) [DMR-11211107]
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A thermodynamic study of the adsorption of Human Serum Albumin (HSA) onto spherical polyelectrolyte brushes (SPBs) by isothermal titration calorimetry (ITC) is presented. The SPBs are composed of a solid polystyrene core bearing long chains of poly(acrylic acid). ITC measurements done at different temperatures and ionic strengths lead to a full set of thermodynamicbinding constants together with the enthalpies and entropies of binding. The adsorption of HSA onto SPBs is described with a two-step model. The free energy of binding Delta Gb depends only weakly on temperature because of a marked compensation of enthalpy by entropy. Studies of the adsorbed HSA by Fourier transform infrared spectroscopy (FT-IR) demonstrate no significant disturbance in the secondary structure of the protein. The quantitative analysis demonstrates that counterion release is the major driving force for adsorption in a process where proteins become multivalent counterions of the polyelectrolyte chains upon adsorption. A comparison with the analysis of other sets of data related to the binding of HSA to polyelectrolytes demonstrates that the cancellation of enthalpy and entropy is a general phenomenon that always accompanies the binding of proteins to polyelectrolytes dominated by counterion release.
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