Sudip Malik

Nanoparticle-Induced Controlled Biodegradation and Its Mechanism in Poly(ε-caprolactone)

Poly(epsilon-caprolactone) (PCL)/layered silicate nanocomposites have been prepared via solution route. Two different organically modified nanoclays were used to compare the variation in properties based on organic modifications. The nanostructures, as observed from wide-angle X-ray diffraction and transmission electron microscopy, indicate intercalated and partially exfoliated hybrids depending on the nature of organic modification in nanoclay. The nanohybrids exhibit significant improvement in thermal and mechanical properties of the matrix as compared to neat polymer. The nanoclays act as nucleating agent for the crystallization of PCL. The biodegradability of pure PCL and its nanocomposites have been studied under controlled conditions in enzyme, pure microorganism (fungi), compost, Ganges water, and alkaline buffer solution. The rate of biodegradation of PCL has enhanced dramatically in nanohybrids and depends strongly on the media used. Scanning confocal, electron, and atomic force microscopes have used to demarcate the nature of biodegradation of pristine PCL and its nanocomposites. The change in biodegradation is rationalized in terms of the crystallization behavior and organic modification in nanoclays of the nanohybrids vis-a-vis the neat polymer. The extent of compatibility was measured quantitatively through the interaction parameter for two different nanoclays to compare and establish the reason for variation in their properties in nanohybrids. A biodegradation mechanism has been revealed for PCL and its nanocomposites through enzyme activity in varying pH environment.

Assemblies of perylene diimide derivatives with melamine into luminescent hydrogels

We report unique and spontaneous formation of hydrogels of perylene derivatives with melamine. The luminescent gel network is formed by H-type aggregation of the perylene core, supramolecularly cross-linked by melamine units. As a result of controlled aggregation in the extended nanofibers, strong exciton fluorescence emission is observed.

Self healing hydrogels composed of amyloid nano fibrils for cell culture and stem cell differentiation

Amyloids are highly ordered protein/peptide aggregates associated with human diseases as well as various native biological functions. Given the diverse range of physiochemical properties of amyloids, we hypothesized that higher order amyloid self-assembly could be used for fabricating novel hydrogels for biomaterial applications. For proof of concept, we designed a series of peptides based on the high aggregation prone C-terminus of Aβ42, which is associated with Alzheimers disease. These Fmoc protected peptides self assemble to β sheet rich nanofibrils, forming hydrogels that are thermoreversible, non-toxic and thixotropic. Mechanistic studies indicate that while hydrophobic, π-π interactions and hydrogen bonding drive amyloid network formation to form supramolecular gel structure, the exposed hydrophobic surface of amyloid fibrils may render thixotropicity to these gels. We have demonstrated the utility of these hydrogels in supporting cell attachment and spreading across a diverse range of cell types. Finally, by tuning the stiffness of these gels through modulation of peptide concentration and salt concentration these hydrogels could be used as scaffolds that can drive differentiation of mesenchymal stem cells. Taken together, our results indicate that small size, ease of custom synthesis, thixotropic nature makes these amyloid-based hydrogels ideally suited for biomaterial/nanotechnology applications.

Graphene oxide/polyaniline nanostructures: transformation of 2D sheet to 1D nanotube and in situ reduction

The formation of unique polyaniline nanotubes has been reported in presence of graphene oxide (GO) which plays crucial dual role as dopant and soft template, simultaneously. GO in nanotubes is in situ reduced to reduced GO with restoration of electrical conductivities and enhanced thermal stabilities.

Facile Decoration of Polyaniline Fiber with Ag Nanoparticles for Recyclable SERS Substrate

Facile synthesis of polyaniline@Ag composite has been successfully demonstrated by a simple solution-dipping method using high-aspect-ratio benzene tetracarboxylic acid-doped polyaniline (BDP) fiber as a nontoxic reducing agent as well as template cum stabilizer. In BDP@Ag composite, BDP fibers are decorated with spherical Ag nanoparticles (Ag NPs), and the population of Ag NPs on BDP fibers is controlled by changing the molar concentration of AgNO3. Importantly, Ag-NP-decorated BDP fibers (BDP@Ag composites) have been evolved as a sensitive materials for the detection of trace amounts of 4-mercaptobenzoic acid and rhodamine 6G as an analyte of surface-enhanced Raman scattering (SERS), and the detection limit is down to nanomolar concentrations with excellent recyclability. Furthermore, synthesized BDP@Ag composites are applied simultaneously as an active SERS substrate and a superior catalyst for reduction of 4-nitrothiophenol.

In situ preparation of fluorescent polyaniline nanotubes doped with perylene tetracarboxylic acids

Herein, we report an easy preparation of polyaniline (PANI) nanotubes in the presence of perylene tetracarboxylic acid acting as a dopant. These tubes are crystalline and fluorescent in nature as a result of controlled confinement of dopant molecules in the tubes.

Aggregation induced chirality in a self assembled perylene based hydrogel: application of the intracellular pH measurement

With the aim of controlling helicity of self-assembled fibers, a pair of water soluble perylene derivatives has been designed and synthesized. Intermolecular hydrogen bonding interactions and π-π stacking, combined with the effect of molecular chirality, have been found to guide the aggregation that eventually led to gelation in water upon decreasing pH. This work has demonstrated a new paradigm of simple and non-toxic perylene derivatives for biological applications.

Supramolecular hydrogels of adenine: morphological, structural and rheological investigations

Hydrogelation of adenine has been tested here with three isomers of benzene tricarboxylic acid. Upon cooling the homogeneous solution, adenine formed an instantaneous gel with one isomer while the other two did not. Hydrogels were thermoreversible in nature and were characterized with the help of 1H-NMR, FE-SEM, TEM, AFM, PL, XRD, FT-IR and rheological analyses. 1H-NMR studies showed the formation of molecular interaction between adenine and 1,3,5-benzenetricarboxylic acid (1,3,5-B) to form a supramolecular complex that led to the production of gel with a large volume of water. The morphological investigation of dried gel revealed the network of nanofibers that assembled further into belt-like thick fibers. FT-IR and X-ray studies showed that in the gel adenine and 1,3,5-B were mainly assembled through hydrogen bonding interactions into a layered structure, and the interlayer distance was 1.52 nm. The gel network formed as a result of controlled aggregation between adenine and 1,3,5-B was stable even after large deformation under rheological investigations.

Charge-Transfer-Induced Fluorescence Quenching of Anthracene Derivatives and Selective Detection of Picric Acid.

2,6-Divinylpyridine-appended anthracene derivatives flanked by two alkyl chains at the 9,10-position of the core have been designed, synthesized, and characterized by NMR, MALDI-TOF, FTIR, and single-crystal XRD. These anthracene derivatives are able to recognize picric acid (2,4,6-trinitrophenol, PA) selectively down to parts per billion (ppb) level in aqueous as well as nonaqueous medium. Fluorescence emission of these derivatives in solution is significantly quenched by adding trace amounts of PA, even in the presence of other competing analogues, such as 2,4-dinitrophenol (2,4-DNP), 4-nitrophenol (NP), nitrobenzene (NB), benzoic acid (BA), and phenol (PH). The high sensitivity of these derivatives toward PA is considered as a combined effect of the proton-induced intramolecular charge transfer (ICT) as well as electron transfer from the electron-rich anthracene to the electron-deficient PA. Moreover, visual detection of PA has been successfully demonstrated in the solid state by using different substrates.

Benzene tetracarboxylic acid doped polyaniline nanostructures: morphological, spectroscopic and electrical characterization

The in situ preparation of polyaniline nanotubes via assembly of an aromatic dopant acid is a challenging task at present in polymer chemistry. Here, we report the formation of PANI nanostructures doped with benzene 1,2,4,5-tetracarboxylic acid (BTCA), which simultaneously acts as a dopant acid as well as a structure-directing agent to produce high aspect ratio nanotubes having more or less uniform diameter. The diameter of the fibers is intricately tuned by changing the ratio of BTCA to aniline. The effect of dopant concentration in the polymer composites has been investigated with the help of 1H-NMR, UV-Vis and IR studies. It has also been demonstrated that the dopant acid plays an important role in the fiber formation, particularly in the nanotube formation. A comparative investigation with other tetracarboxylic acids has been made in the light of the variation of diameter. The outer diameter (OD) of PANI nanotubes depends on the size of the dopant tetracarboxylic acid under identical reaction conditions and it follows the order ODPTCA > ODNTCA > ODBTCA. Furthermore, it has been found that the conductivities of the BTCA–PANI nanotubes depend on the BTCA to aniline molar ratios, and the low temperature charge transports in these composites predominantly follow the three dimensional variable range hopping mechanism.