Jayanta Nanda

Pyrene-containing peptide-based fluorescent organogels: inclusion of graphene into the organogel.

The N-terminally pyrene-conjugated oligopeptide, Py-Phe-Phe-Ala-OMe, (Py=pyrene 1-butyryl acyl) forms transparent, stable, supramolecular fluorescent organogels in various organic solvents. One of these organogels was thoroughly studied using various techniques including transmission electron microscopy (TEM), field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), Fourier-transform infrared (FTIR) spectroscopy, photoluminescence (PL) spectroscopy, and rheology. Unfunctionalized and non-oxidized graphene was successfully incorporated into this fluorescent organogel in o-dichlorobenzene (ODCB) to form a stable hybrid organogel. Graphene is well dispersed into the gel medium by using non-covalent π-π stacking interactions with the pyrene-conjugated gelator peptide. In the presence of graphene, the minimum gelation concentration (mgc) of the hybrid organogel was lowered significantly. This suggests that there is a favorable interaction between the graphene and the gelator peptide within the hybrid organogel system. This hybrid organogel was characterized using TEM, AFM, FTIR, PL, and rheological studies. The TEM study of graphene-containing hybrid organogel revealed the presence of both graphene sheets and entangled gel nanofibers. The AFM study indicated the presence of 3 to 4 layers in exfoliated graphene in ODCB and the presence of both graphene nanosheets and the network of gel nanofibers in the hybrid gel system. The rheological investigation suggested that the flow of the hybrid organogel had become more resistant towards the applied angular frequency upon the incorporation of graphene into the organogel. The hybrid gel is about seven times more rigid than that of the native gel.

A new aromatic amino acid based organogel for oil spill recovery

An aromatic amino acid (phenylglycine) based amphiphile with amide and ester groups and a long fatty acyl chain has been found to form organogels selectively in the fuel hydrocarbon solvents including hexane, heptane, cyclohexane, diesel, kerosene and pump-oil at room temperature. Organogels have been well characterized morphologically by field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Morphological studies of these xerogels have revealed the presence of fascinating right-handed twisted nanoribbons (in n-heptane and n-octane). Involvement of different non-covalent interactions among the gelator molecules within the gel matrix has been studied using FT-IR and XRD. The organogel in diesel is mechanically stable with high yield stress (177.8 Pa) and storage modulus (>104 Pa) values, as has been evidenced from the rheological studies. Interestingly, this gelator compound exhibits phase selective gelation properties and the phase selective gelation occurs efficiently and quickly (within 90 s), in oil–water mixtures and the gelator molecule can be recovered and reused several times easily, indicating its applicability in oil spill cleaning.

A Gel‐Based Trihybrid System Containing Nanofibers, Nanosheets, and Nanoparticles: Modulation of the Rheological Property and Catalysis

Wonderful gels: A trihybrid gel was prepared by incorporating graphene oxide and in situ synthesized gold nanoparticles (AuNPs) into an amino-acid-based native gel matrix (see pict). The morphology of this system indicates the presence of three distinctly different nanostructures: nanofibers, nanosheets, and nanoparticles. The catalytic efficiency of this trihybrid system is enhanced relative to that of AuNPs in a dihybrid system.

Multicomponent hydrogels from enantiomeric amino acid derivatives: helical nanofibers, handedness and self-sorting

In this study, chiral helical nanofibers have been obtained from suitable, co-assembling, two oppositely charged amino acid based two component hydrogels. An equimolar mixture of an N-terminally protected amino acid Fmoc-(L/D)Glu (Fmoc: N-fluorenyl-9-methoxycarbonyl, Glu: glutamic acid) and (L/D)Lys (Lys: lysine) can co-assemble to form hydrogels. These hydrogels have been characterised using circular dichroism (CD), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray powder diffraction, fluorescence spectroscopic and rheological studies. CD and AFM studies have been extensively used to examine the chiral/achiral nature of fibers obtained from different hydrogel systems. The equimolar mixture of two L-isomers, {Fmoc-(L)Glu + (L)Lys} in the assembled state, leads to the exclusive formation of left-handed helical nanofibers, whereas an equimolar mixture of two D-isomers, {Fmoc-(D)Glu + (D)Lys}, gives rise to right-handed helical nanofibers. The CD study of the gel obtained from the {Fmoc-(L)Glu + (L)Lys} system is exactly the mirror image of the CD signal obtained from the gel of the {Fmoc-(D)Glu + (D)Lys} system. These results suggest that the molecular chirality is being translated into the supramolecular helicity and the handedness of these fibers depends on the corresponding molecular chirality in the mixture of the two component system. Reversing the handedness of helical fibers is possible by using enantiomeric building blocks. Co-assembly of racemic and equimolar mixtures of all four components, i.e., [{Fmoc-(L)Glu + (L)Lys} + {Fmoc-(D)Glu + (D)Lys}] can also form hydrogels. Interestingly, in this racemic mixture self-sorting has been observed with the presence of almost equal amount of left- and right-handed helical nanofibers. The equimolar mixture of Fmoc-(L)Glu and L-ornithine/L-arginine also produces hydrogel with left-handed helical fibers. Moreover, the straight fiber has been observed from the two component hydrogel {Fmoc-(L)Glu + (L)Lys} system in the presence of Ca2+/Mg2+ ions. This indicates the straight nanofibers are obtained under suitable conditions and acid–base interaction is responsible for making the helical fibers at the nanoscale.

Single amino acid based thixotropic hydrogel formation and pH-dependent morphological change of gel nanofibers

A single amino acid (phenylalanine) based pyrene conjugated low molecular weight hydrogelator has been discovered. This amino acid derivative has been found to form hydrogels in a wide range of aqueous solutions of pH 7.46–14 and the estimated minimum gelation concentration (MGC) in phosphate buffer solution at physiological pH 7.46 is 0.037% (w/v) i.e. 0.85 mM. A transparent hydrogel has been produced in the pH range (7.46–10.5), while a translucent hydrogel has been formed at higher pH. The hydrogel has been characterized by field emission scanning electron microscopy (FE-SEM), fluorescence microscopy, differential scanning calorimetry (DSC), circular dichroism (CD), X-ray diffraction (XRD) and rheological studies. A distinct morphological change of the gel nanofibers from helical to tape-like morphology has been noticed in the FE-SEM studies with an increase in pH. These observations have been supported by a significant decrease of the CD signals and different XRD patterns found with the increase in pH. Interestingly, this hydrogel shows a pH dependent thixotropic property. The thixotropic property of the hydrogel has been examined using rheological experiments. This thixotropic property of the hydrogel has been utilized for the encapsulation of vitamin B12 and an anticancer drug, doxorubicin, in the hydrogel matrix without any heating–cooling cycle and sustained release of these bioactive molecules has been studied at physiological temperature (37 °C) and pH (7.46) over a period of about 3 days.

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.

Organogels from Different Self-Assembling New Dendritic Peptides: Morphology, Reheology, and Structural Investigations

Three new peptide based dendrimers with different generations were synthesized, purified, and characterized. Each of these dendrimers form efficient organogels under suitable conditions and these gels were characterized by field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), atomic force microscopy (AFM), Fourier transformed infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC) and rheology. It has been observed that gel forming propensity increases from first to second generation dendrimer and it decreases from second to third generation. The hydrogen bonding interaction is the main driving force for the formation of aggregated structure that leads to the formation of a fibrillar network, responsible for gelation. The morphology is network type consisting of taped or twisted fibrils spanning throughout the space. DSC measurements show the thermoreversible first-order phase transition. Rheological studies indicate that flow behavior and segmental motion of these gels are different for different peptidic gels, obtained from various generations of dendritic peptides.

Emergent Catalytic Behavior of Self-Assembled Low Molecular Weight Peptide-Based Aggregates and Hydrogels

We report a series of short peptides possessing the sequence (FE)n or (EF)n and bearing l-proline at their N-terminus that self-assemble into high aspect ratio aggregates and hydrogels. We show that these aggregates are able to catalyze the aldol reaction, whereas non-aggregated analogues are catalytically inactive. We have undertaken an analysis of the results, considering the accessibility of catalytic sites, pKa value shifts, and the presence of hydrophobic pockets. We conclude that the presence of hydrophobic regions is indeed relevant for substrate solubilization, but that the active site accessibility is the key factor for the observed differences in reaction rates. The results presented here provide an example of the emergence of a new chemical property caused by self-assembly, and support the relevant role played by self-assembled peptides in prebiotic scenarios. In this sense, the reported systems can be seen as primitive aldolase I mimics, and have been successfully tested for the synthesis of simple carbohydrate precursors.

Peptide based hydrogels for cancer drug release: modulation of stiffness, drug release and proteolytic stability of hydrogels by incorporating D-amino acid residue(s)

Synthetic tripeptide based noncytotoxic hydrogelators have been discovered for releasing an anticancer drug at physiological pH and temparature. Interestingly, gel stiffness, drug release capacity and proteolytic stability of these hydrogels have been successfully modulated by incorporating d-amino acid residues, indicating their potential use for drug delivery in the future.

The Strong Influence of Structure Polymorphism on the Conductivity of Peptide Fibrils

Peptide fibril nanostructures have been advocated as components of future biotechnology and nanotechnology devices. However, the ability to exploit the fibril functionality for applications, such as catalysis or electron transfer, depends on the formation of well-defined architectures. Fibrils made of peptides substituted with aromatic groups are described presenting efficient electron delocalization. Peptide self-assembly under various conditions produced polymorphic fibril products presenting distinctly different conductivities. This process is driven by a collective set of hydrogen bonding, electrostatic, and π-stacking interactions, and as a result it can be directed towards formation of a distinct polymorph by using the medium to enhance specific interactions rather than the others. This method facilitates the detailed characterization of different polymorphs, and allows specific conditions to be established that lead to the polymorph with the highest conductivity.