Novel anisotropic supramolecular hydrogel with high stability over a wide pH range

Abstract

The hydrolysis of the carboxylic ester bond, by a base or catalyzed by an enzyme under weak basic conditions, serves as the only path to obtain a novel anisotropic supramolecular hydrogel that is stable over a wide pH range. This result not only expands the molecular scope of supramolecular hydrogelators but also illustrates the design principles for creating pH-stable supramolecular soft materials.

Figure 1

(A) The synthetic route to 2 and 3. (B) The reactions convert the precursor (3) to the hydrogelator (2) at basic condition (pH = 9) to afford gel I or via hydrolysis catalyzed by esterase (1 U/μL, 10 μL) at pH = 7.5 to give gel II (optical images: left, normal; right through a pair of crossed polarizers).

Figure 2

TEM images of the matrices in (A) gel I and (B) gel II (aged for seven days).

Figure 3

(A) Optical images of the gels of 2 immersed in solution with different pHs. (B) Dynamic strain sweeps (at 6.28 rad/s) of aged gels I (400 μL, 0.8 % (w/v)), without treatment and immersed in 1.0 M HCl (20 mL), 1.0 M NaOH (20 mL) and 1.0 M NaCl (20mL) for half an hour. (C) Dynamic frequency sweeps of the corresponding gels I.

Figure 4

(A) Optical images of gel II (formed by the catalysis of esterase) under crossed polarized light at different time points and (B) the corresponding CD spectra.