Peptide‐Based Hydrogels as a Scaffold for In Situ Synthesis of Metal Nanoparticles: Catalytic Activity of the Nanohybrid System

Abstract

A tripeptide containing an oligo‐methylene group was found to form hydrogels at the two pH extremes (in presence of an acid or a base); however, it does not form a hydrogel at neutral pH. We use this property to obtain a hydrogel of the peptide in the presence of an organic acid, citric acid. The redox potential of citric acid is ideal to reduce Ag+ and Au3+ ions to form the corresponding nanoparticles. Keeping this in mind the hydrogel with citric acid was applied to fabricate silver and gold nanoparticles within the gel phase without the aid of external reducing and stabilising agents. The hydrogels and the peptide nanofiber‐metal nanoparticle based hybrid system were thoroughly characterized by UV‐visible spectroscopy, FEG‐TEM microscopy, FT‐IR spectroscopy, and powder X‐ray diffraction studies. From the FEG‐TEM images it is evident that a considerable amount of Au and Ag nanoparticles are found above the gel nanofibers. Interestingly, the hybrid hydrogel containing silver nanoparticles could be successfully employed as a catalyst in the transformation of p‐nitrophenol to p‐aminophenol and p‐nitroaniline to p‐phenylenediamine. It is also interesting to note that the native hydrogel (without Ag nanoparticles) is unable to act as a catalyst. Moreover, this hybrid hydrogel has been recycled a few times without significant loss of activity, showing the potential of this new nanohybrid system for catalysis.

Palladium-scavenging self-assembled hybrid hydrogels – reusable highly-active green catalysts for Suzuki–Miyaura cross-coupling reactions

“…Unfortunately, the presence of K 2 CO 3 partially destroyed the xerogel network. In terms of other catalytic metal NPs, Banerjee and co-workers have embedded AgNPs and AuNPs in gels to catalyse the reduction of nitroarenes to aminoarenes, but not PdNPs 10…”

Expanding the Functional Scope of the Fmoc‐Diphenylalanine Hydrogelator by Introducing a Rigidifying and Chemically Active Urea Backbone Modification

“…The next functionality tested was the ability of the Fmoc‐FuF hydrogel to reduce metal ions into nanoparticles in situ. We selected to synthesize Au and Ag nanoparticles (AuNPs and AgNPs) in order to demonstrate gel‐mediated nanoparticle synthesis and to test the involvement of the urea group, which was previously associated with metal nanoparticle synthesis . Nanoparticle‐containing Fmoc‐FuF hydrogels were prepared by gelating either 5 × 10 −3 m HAuCl 4 or 10 × 10 −3 m AgNO 3 aqueous solutions (with DMSO at 20% (v/v)) and allowing the nanoparticles to form in the dark in situ.…”

Stimuli responsive dynamic transformations in supramolecular gels

“…A dipeptide hydrogelator H 2 N-ADDAPhe-Phe-COOH (ADDA: 12-amino dodecanoic acid) containing an amine and a carboxylic acid functionality at two opposite terminals was introduced by the Banerjee group. 236 In presence of either HCl or NaOH, the peptide formed self-supportive hydrogels, while it produced white aggregates under neutral conditions. The high pH gel was translucent in nature while the HCl triggered gel was quite transparent.…”