Abstract
A 1-naphthaleneacetic acid-appended phenylalanine-derivative (Nap-F) forms a stable hydrogel with a minimum gelation concentration (MGC) of 0.7% w/v (21 mM) in phosphate buffer of pH 7.4. Interestingly, Nap-F produces two-component [Nap-F + H = Nap-F(H), Nap-F + K = Nap-F(K) and Nap-F + R = Nap-F(R)], three-component [Nap-F + H + K = Nap-F(H-K), Nap-F + H + R = Nap-F(H-R) and Nap-F + K + R = Nap-F(K-R)] and four-component [Nap-F + H + K + R = Nap-F(H-K-R)] hydrogels in water with all three natural basic amino acids (H = histidine, K = lysine and R = arginine) at various combinations below its MGC. Nap-F-hydrogel forms a nice entangled nanofibrillar network structure as evidenced by field emission scanning electron microscopy (FE-SEM). Interestingly, lysine-based co-assembled two- (Nap-F(K)), three- (Nap-F(H-K) and Nap-F(K-R)) and four-component (Nap-F(H-K-R)) xerogels exhibit helical nanofibrillar morphology, which was confirmed by circular dichroism spectroscopy, FE-SEM and TEM imaging. However, histidine and arginine-based two-component (Nap-F(H) and Nap-F(R)) and three-component (Nap-F(H-R)) co-assembled xerogels exhibiting straight nanofibrillar morphology. In their co-assembled states, these two-, three- and four-component supramolecular hydrogels show promising esterase-like activity below their MGCs. The enhanced catalytic activity of helical fibers compared to obtained straight fibers (other than lysine-based assembled systems) suggests that the helical fibrillar nanostructure is involved in ordering the esterase-like although all supramolecular assemblies are chemically different from one another.