Thermoresponsive Copolymer Cryogel Possessing Molecular Memory: Synthesis, Energetics of Collapse and Interaction with Ligands

Abstract

AbstractAn imprinted thermoresponsive cryogel of copolymer of N‐isopropylacrylamide and N‐[3‐(N,N′‐dimethylamino)propyl]acrylamide was synthesized in a frozen (−10 °C) aqueous medium in presence of a molecular template, the drug substance ibuprofen. A reversible volume phase transition upon heating (thermotropic collapse) of the swollen cryogel was studied by high‐sensitivity differential scanning calorimetry. In the absence of ligands, the transition temperature, enthalpy, and width were 82.5 °C, 9.8 J · g−1 and 32.2 °C, respectively. Significant changes in the transition parameters were observed in presence of the template ligand (ibuprofen): with increasing ligand concentration the transition temperature decreased down to 30 °C, the enthalpy passed through a minimum, and the transition width notably reduced. The binding constants of ibuprofen by the cryogel subchains in the collapsed and swollen states were 119 and 5 M−1, respectively. This implies a preferential binding of ibuprofen by the shrunken cryogel. The excess absorption of ibuprofen by the cryogel related to its collapse amounted to 0.327 mmol · g−1 while for all other ligands that were structural analogs of ibuprofen this parameter did not exceed 0.016 mmol · g−1. Consequently, the imprinted cryogel possessed a selective molecular memory toward the template ligand. magnified image