Shibaji Basak

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.

Charge-Transfer Complex Formation in Gelation: The Role of Solvent Molecules with Different Electron-Donating Capacities

A naphthalenediimide (NDI)-based synthetic peptide molecule forms gels in a particular solvent mixture (chloroform/aromatic hydrocarbon, 4:1) through charge-transfer (CT) complex formation; this is evident from the corresponding absorbance and fluorescence spectra at room temperature. Various aromatic hydrocarbon based solvents, including benzene, toluene, xylene (ortho, meta and para) and mesitylene, have been used for the formation of the CT complex. The role of different solvent molecules with varying electron-donation capacities in the formation of CT complexes has been established through spectroscopic and computational studies.

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.

Selective binding of hydrogen chloride and its trapping through supramolecular gelation.

A pyridine containing amino acid based gelator forms gel in aqueous media in the presence of hydrochloric acid and the chloride ion is found to be very selective for gelation. The gelator is successfully applied for the detection and trapping of hydrogen chloride gas and this indicates its probable application for removing hazardous HCl gas from the environment.

Amino acid-based amphiphilic hydrogels: metal ion induced tuning of mechanical and thermal stability

A phenylalanine based gelator was found to form a hydrogel in phosphate buffer solution. Addition of metal ions to this hydrogel dramatically increases the thermal stability and mechanical strength.

AgI-Induced Switching of DNA Binding Modes via Formation of a Supramolecular Metallacycle

The histidine derivative L1 of the DNA intercalator naphthalenediimide (NDI) forms a triangular AgI complex (C2). The interactions of L1 and of C2 with DNA were studied by circular dichroism (CD) and UV/Vis spectroscopy and by viscosity studies. Different binding modes were observed for L1 and for C2, as the AgI complex C2 is too large in size to act as an intercalator. If AgI is added to the NDI molecule that is already intercalated into a duplex, higher order complexes are formed within the DNA duplex and cause disruptions in the helical duplex structure, which leads to a significant decrease in the characteristic CD features of B-DNA. Thus, via addition of a metal we show how a classic and well-known organic intercalator unit can be turned into a partial metallo insertor. We also show how electrochemical impedance spectroscopy (EIS) can be used to probe DNA binding modes on DNA films that are immobilized on gold surfaces.

Luminescent Naphthalene Diimide-Based Peptide in Aqueous Medium and in Solid State: Rewritable Fluorescent Color Code

This study convincingly demonstrates a unique example of the self-assembly of a naphthalene diimide (NDI)-appended peptide into a fluorescent J-aggregate in aqueous media. Moreover, this aggregated species shows a remarkable yellow fluorescence in solid state, an unusual phenomenon for NDI-based compounds. The aggregated species has been characterized using transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy, X-ray diffraction, time-correlated single proton counting (TCSPC), UV–vis, and photoluminescence studies. TEM images reveal cross-linked nanofibrillar morphology of this aggregated species in water (pH 7.4). TCSPC study clearly indicates that the aggregated species in water has a higher average lifetime compared to that of the non-aggregated species. Interestingly, this NDI-based peptide shows H+ ion concentration-dependent change in the emission property in water. The fluorescence output is erased completely in the presence of an alkali, and it reappears in the presence of an acid, indicating its erasing and rewritable property. This indicates its probable use in authentication tools for security purposes as a rewritable fluorescence color code. This NDI-appended peptide-based molecule can be used for encryption of information due to erasing and rewritable property of the molecule in the aggregated state in aqueous medium.