Macroscopic Self-Assembly Based on Molecular Recognition: Effect of Linkage between Aromatics and the Polyacrylamide Gel Scaffold, Amide versus Ester

Abstract

The interactions of polyacrylamide- (pAAm-) based gels possessing cyclodextrin (CD) residues (CD-gels) with pAAm-based gels modified with aromatic residues through amide and ester linkages (ArA-gels and ArE-gels, respectively) were investigated to examine the effect of linkage (i.e., amide and ester) between aromatic residues and the pAAm gel scaffold. In the present study, benzyl (Bz), 2-naphthylmethyl (Np), 9-phenanthrylmethyl (Ph), and 1-pyrenylmethyl (Py) residues were chosen as a series of aromatic residues. αCD-gel did not interact notably with the ArA-gels and ArE-gels in water. βCD-gel interacted with the ArA-gels and ArE-gels possessing smaller aromatic residues (i.e., Bz and Np residues) in water to form gel assemblies. γCD-gel showed different tendencies of its interactions with the ArA-gels and with the ArE-gels; γCD-gel interacted with the ArA-gels carrying larger aromatic residues (i.e., Ph and Py residues), while γCD-gel formed stable gel assemblies only with NpE-gel among the ArE-gels examined. This is because γCD residues in γCD-gel included favorably dimeric aromatic residues in the ArA-gels and ArE-gels. Reflection fluorescence spectra for the ArA-gels and ArE-gels possessing fluorescent aromatic residues (i.e., Np, Ph, and Py residues) in the presence of 10 mM γCD were indicative of weak selectivities of γCD toward NpE, PhA, and PyA residues. Such weak selectivities may be largely enhanced in the macroscopic observation of interaction of CD-gels with the ArA-gels and ArE-gels presumably because of multivalency