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

Abstract

An 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.

Cryogels: Morphological, structural and adsorption characterisation

“…However, in this paper [159] the DSC data were not used to estimate any textural characteristic of cryogels.…”

Cryostructuring of Polymeric Systems. 55. Retrospective View on the More than 40 Years of Studies Performed in the A.N.Nesmeyanov Institute of Organoelement Compounds with Respect of the Cryostructuring Processes in Polymeric Systems

“…Certainly, the systems of a “mixed” kind also exist, when the combinations of covalent, ionic, and non-covalent interchain links reside within the common cryogenically-structured polymeric material. For instance, this is often so for the cryogels based on such heterofunctional macromolecular precursors, as proteins [ 163 , 164 , 175 , 207 , 215 , 257 , 259 , 262 , 272 , 306 , 317 , 381 , 386 ] or amphiphilic synthetic copolymers [ 247 , 249 ].…”

“…Rather evident examples, in which similar strictly “personal” approach was employed, are the so-called molecularly-imprinted polymeric matrices and the processes, mainly of analytical-type, where such materials were exploited [ 136 , 137 , 139 , 249 ]. Since the molecular imprinting, as a rule, tunes the polymeric matrix to the recognition of particular molecules, such systems in most cases are characterized by a high selectivity.…”

Ionic and Polyampholyte N-Isopropylacrylamide-Based Hydrogels Prepared in the Presence of Imprinting Ligands: Stimuli-Responsiveness and Adsorption/Release Properties

“…In the presence of the template molecules (rebinding) the memory of the imprinted conformation is recalled by an induced fit or when the suitable stimulus causes the network to shrink. So far, the ability to swell/shrink has been shown useful to modulate the amount of drug loaded and the release rate from stimuli-responsive imprinted networks [ 6 , 7 , 8 , 10 , 11 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. From a theoretical point of view, the study of responsive imprinted gels has contributed to a better understanding of the memorization of conformations in heteropolymer networks and to develop protein-mimicked systems endowed with recognition features [ 11 , 14 ].…”