Ashesh Garai

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.

Optical and electronic properties of polyaniline sulfonic acid–ribonucleic acid–gold nanobiocomposites

Finely fibrillar polyaniline sulfonic acid (PSA)/ribonucleic acid (RNA) hybrids are developed by wrapping PSA with RNA from a mixture of aqueous PSA (P) and RNA (R) solutions of different compositions. FTIR spectra suggest H-bonding and π-π interactions in the hybrids and dedoping of self doped PSA during hybrid formation. UV-vis spectra exhibit a blue shift of the π-band to polaron band transition of PSA from 870 to 581 nm due to dedoping. The PR hybrids show enhanced PL-properties when excited at 540 nm relative to PSA which also exhibits rectification behavior in current (I)-voltage (V) curves. Gold nanoparticles (Au NPs) grown on these PR hybrids by the reduction of Au(3+) by PSA show different morphologies with varying composition. FTIR spectra of the nanobiocomposites indicate that Au NPs are stabilized by the co-ordination of the nitrogen atoms of -N=Q=N- bonds of PSA (Q = quinonoid ring). The intensity of the Au plasmon band gradually decreases with time but the PL-intensities of the PAu/PRAu nanocomposites increase with time. The PL-intensity of the nanocomposites is higher than that of PSA and PR hybrids. The DC-conductivity of the PR hybrids increases by an order of magnitude on addition of Au NPs. I-V curves of the nanobiocomposites show negative differential resistance (NDR) in PSA rich systems with a stable NDR ratio of 7 in the PRAu21 and PRAu11 hybrids. Possible reasons from the accumulation of charges on the Au NPs and its stabilization through the π-clouds of RNA bases are discussed. The PRAu11 system also exhibits rectification properties with a rectification ratio of 14.