Host–Guest Polymer Complexes

Abstract

The discovery of host-guest complexation has resulted in significant advancements in various facets of materials science, including: drug delivery, tissue engineering, etc. Various host molecules such as cyclodextrins (CD), urea, thiourea, cyclo-triphosphazines, pillar [6]arene, cucurbit [6]uril, and calix[4]arene have been identified as undergoing inclusion complexation with a range of guest molecules. Among these host molecules, cyclodextrins are well-known for their complexation capabilities with a variety of guest molecules. Through such complexation, the stability of the guest against thermo-chemical, environmental, light, and air degradation is ensured. In addition, the widespread availability of CD-derivatives (randomly methylated, 2-hydroxypropylated, etc.) has partly contributed to their widespread use in applications extending from textiles to pharmacologics to nuclear waste removal. Another benefit of forming such complexes is that they improve the polymeric properties (for example, mechanical, rheological, and thermal properties) by coalescing the guest polymers from their CD inclusion complexes.While the host-guest complexation occurs predominantly via non-covalent interactions, the underlying mechanism differs among the studied guest molecules, with predominant complexation occurring via hydrogen and ionic bonding, van der Waals and hydrophobic forces/interactions. Even though the mechanisms differ between the chosen host/guest molecules, a common criterion for successful complexation remains lowered Gibbs free energy, which can occur either by an enthalpyor an entropy-driven process. The thermodynamics of the host-guest complexation and associated binding constants are typically characterized using spectroscopy-based techniques such as nuclear magnetic resonance, UV-vis, mass spectrometry, fluorescence-based spectroscopy or calorimetric techniques such as differential scanning and isothermal titration calorimetry [1]. With such a wide range of possibilities in terms of guest and host molecules in host-guest chemistry, the purpose of this special Issue is to provide the latest advancements as well as novel applications of these host-guest compounds.This Special Issue consists of 15 articles, including four comprehensive review articles, written by experts in the field. The first eleven articles are dedicated to the synthesis and characterization of host-guest containing compounds for the fabrication of devices, in particular for biomedical applications. The next four articles are comprehensive review articles discussing the state-of-art synthesis, characterization, and fabrication of various host-guest complexes, including CD-polymer, amylose-polymer, polysaccharide-metal ion, and urea-polymer inclusion complexes. In this series, the first research article reports the synthesis of novel host-guest supramolecular hydrogels comprised of pNIPAm microgels bearing poly[acrylic acid] with attached β-CDs as the host and adamantane-dextrans as the guest molecules. By forming in situ complexation, hydrogel...

Open Linear Polymer Host–Guest Interactions Sensed by Luminescent Silver Nanodots

“…5,6 Not like proteins, linear polymers only act as a host when the polymer chains contain host-like binding groups to construct a polymeric super host−guest matrix. 7,8 Hyperbranched polymers with large cavities in their pseudospherical structures have also been used as a host platform to incorporate versatile guest molecules. 9−11 Otherwise, polymers are cross-linked, such as with disulfide bonds, to form hydrophobic host pockets for the incorporation of hydrophobic guest moieties.…”

“…Host–guest interactions play a particularly important role in molecular sensing and self-assembly. − A close contact between two counterparts, mostly the cavity of a large molecule and its substrate, enables efficient intermolecular interactions between the pair. The extraordinarily high affinity of avidin for biotin as well as the best-fit between crown ether and cations are results of this host–guest complexation. , Not like proteins, linear polymers only act as a host when the polymer chains contain host-like binding groups to construct a polymeric super host–guest matrix. , Hyperbranched polymers with large cavities in their pseudospherical structures have also been used as a host platform to incorporate versatile guest molecules. − Otherwise, polymers are cross-linked, such as with disulfide bonds, to form hydrophobic host pockets for the incorporation of hydrophobic guest moieties . It is plausible that simple linear polymers will not act as a good host, as there have been no reports on this subject.…”