Sudipta Ray

Fabrication of Luminescent CdS Nanoparticles on Short‐Peptide‐Based Hydrogel Nanofibers: Tuning of Optoelectronic Properties

The pH-induced self-assembly of three synthetic tripeptides in water medium is used to immobilize luminescent CdS nanoparticles. These peptides form a nanofibrillar network structure upon gelation in aqueous medium at basic pH values (pH 11.0-13.0), and the fabrication of CdS nanoparticles on the gel nanofiber confers the luminescent property to these gels. Atomic force microscopy, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy clearly reveal the presence of CdS nanoparticles in a well-defined array on the gel nanofibers. This is a convenient way to make organic nanofiber-inorganic nanoparticle hybrid nanocomposite systems. The size of the CdS nanoparticles remains almost same before and after deposition on the gel nanofiber. Photoluminescence (PL) measurement of the CdS nanoparticles upon deposition on the gel nanofibers shows a significant blue shift in the emission spectrum of the nanoparticles, and there is a considerable change in the PL gap energy of the CdS nanoparticles after immobilization on different gel nanofibrils. This finding suggests that the optoelectronic properties of CdS nanoparticles can be tuned upon deposition on gel nanofibers without changing the size of the nanoparticles.

Smart oligopeptide gels: in situ formation and stabilization of gold and silver nanoparticles within supramolecular organogel networks

Tripeptide with redox active chemical entities based smart organogels have been used for in situ formation and stabilization of gold and silver nanoparticles within the supramolecular gel networks and the gold nanoparticles are aligned in arrays along the gel nanofibers of peptide 1-toluene gels.

Synthesis of multiple shaped gold nanoparticles using wet chemical method by different dendritic peptides at room temperature

Gold nanoparticles of various shapes including pentagonal, hexagonal, prismatic, branched (multipods), spherical and oval have been prepared by using different generations of peptidic dendrons as templates at room temperature without adding any external reducing or stabilizing agents. Each peptide based dendron molecule (G1, G2 or G3) contains a redox active tyrosine (Tyr) moiety and a free –NH2group at the N-terminus and as a result of that each peptide-dendron molecule can be used to reduce AuCl4− to Au0 and stabilize the nascent gold nanoparticles (GNPs) by the NH2group present in the molecule at room temperature. Not only the shapes but also the sizes of these particles can be tuned by using this chemical methodology involving different peptidic dendrons in water-methanol (4:1) at pH 11. The first generation dendritic peptide produces various shaped GNPs, while the second-generation peptide-dendron molecule leads to the exclusive formation of hexagonal gold nanoparticles and the third generation dendritic peptide gives rise to branched nanoparticles at a certain dendron concentration (5.88 × 10−6 M). In this procedure no external reducing agents or stabilizing agents nor relatively high temperature are required to produce various anisotropic gold nanoparticles. Nanoparticles with different shapes exhibit their characteristic surface plasmon resonance peaks. TEM images vividly demonstrate the specific morphology of gold nanoparticles with different shapes obtained by using different generations of peptide-based dendrons. Corresponding dark field luminescence spectra provide an insight into the shape dependence of the optical properties.

Supramolecular β-Sheet and Nanofibril Formation by Self-assembling Tripeptides Containing an N-terminally Located γ-Aminobutyric acid Residue

Three terminally protected tripeptides Boc–γ-Abu–Val–Leu–OMe 1, Boc–γ-Abu–Leu–Phe–OMe 2 and Boc–γ-Abu–Val–Tyr–OMe 3 (γ-Abu = γ-aminobutyric acid) each containing an N-terminally positioned γ-aminobutyric acid residue have been synthesized, purified and studied. FT-IR studies of all these peptides revealed that these peptides form intermolecularly hydrogen bonded supramolecular β-sheet structures. Peptides 1, 2 and 3 adopt extended backbone β-strand molecular structures in crystals. Crystal packing of all these peptides demonstrates that these β-strand structures self-assemble to form intermolecularly H-bonded parallel β-sheet structures. Peptide 3 uses a side chain tyrosyl –OH group as an additional hydrogen bonding functionality in addition to the backbone CONH groups to pack in crystals. Transmission electron microscopic studies of all peptides indicate that they self-assemble to form nanofibrillar structures of an average diameter of 65 nm. These peptide fibrils exhibit amyloid-like behavior as they bind to a physiological dye Congo red and show a characteristic green-gold birefringence under polarizing microscope.