Ion-macromolecule interactions studied with model polyurethanes

Abstract

HypothesisThe solubility and self-assembly of macromolecules in solution can be tuned by the presence of different salts. Natural proteins have been long manipulated with the aid of salts, and natural silk is processed in the gland tip across a gradient of different salts which modifies its solubility. Hence, the comprehensive understanding of the role of ion-macromolecule interactions should pave the way towards a biomimetic processing of macromolecules. ExperimentsA model polyurethane catiomer (PU+) with high density of hydrogen donors and acceptors (similar to proteins) has been designed and synthesized in order to study ion-macromolecule interactions by means of dynamic light scattering (DLS), infrared spectroscopy (FTIR) and nuclear magnetic resonance (13C NMR). FindingsThe PU+ solubility in the presence of different salts exhibited a reversed anion Hofmeister series (i.e., the anion ability to precipitate the PU+ was F−<Cl−<Br−<NO3−<CH3COO−<H2PO4−<H2CO3−<I−<ClO4−<SCN−). The ordering of this series was found to be predicted, for the first time, by the Born-Landé-Ephraim-Fajans-Bjerrum model used here to estimate the degree of macromolecule-ion pairing in water solution. This work also helps understanding the role of cations and anions nature on their interaction with macromolecules backbone.