Pradyot Koley

Multilayer vesicles, tubes, various porous structures and organo gels through the solvent-assisted self-assembly of two modified tripeptides and their different applications

A set of two modified tripeptides containing conformationally rigid m-aminobenzoic acid (m-ABA) as a template at the C-terminal self-assemble to form diverse micro- and nanostructure materials such as nanovesicles, nanotubes, giant microvesicles, macroporous vesicular structures including macroporous films, macro- and mesoporous materials, and organo gels—depending upon the solvent polarity. A balanced participation of the hydrogen bonding and the π–π interactions mainly between aromatic rings of m-ABA is crucial for this morphological diversity. Insertion of an aromatic amino acid instead of an aliphatic one in the peptide sequence drastically changes the morphology of the nanostructures formed from a particular solvent system. Interestingly these short hydrophobic peptides form salt-responsive multilayer vesicular structures from methanolic solutions, where the diameter of the vesicles increases with an increase of concentration. The most important property of these multilayer vesicular structures is the encapsulation of a potent natural hydrophobic drug curcumin and of a fluorescent dye rhodamine B, which can be effectively released in presence of biocompatible metal ions. Moreover, the encapsulation efficiency and release profile of drug and other biologically important guest molecules have been successfully quantified. We have developed a simple modified peptide based organogelator from chloroform, where the xerogel shows the striking property of adsorbing dye rhodamine B from water, which can be utilized in water purification by removing the toxic dye from waste water. Short peptide based macroporous vesicular structures including macroporous films have been successfully fabricated through controlled self-assembly employing solvents with different chloroform–petroleum ether ratios. Furthermore, the mesoporous structures prepared from toluene can efficiently absorb I2.

Design and Self‐Assembly of a Leucine‐Enkephalin Analogue in Different Nanostructures: Application of Nanovesicles

An opioid (leucine-enkephalin) conformational analogue forms diverse nanostructures such as vesicles, tubes, and organogels through self-assembly. The nanovesicles encapsulate the natural hydrophobic drug curcumin and allow the controlled release through cation-generated porogens in membrane mimetic solvent.

pH-sensitive morphological transition from nanowire to nanovesicle of a single amino acid-based water soluble molecule

Employment of single amino acid-based molecules for the construction of various nanostructures is a challenging issue. Moreover, it is fascinating to see the controlled fabrication of specific nanostructures from the self-assembly of molecular building blocks through the fine tuning of pH of the solution. The present study demonstrates pH-responsive nanostructural transformation of single amino acid-based nanostructures from nanowires to nanovesicles. The molecules have been developed by coupling the carboxyl group of natural amino acids with the amino group of unnatural m-aminobenzoic acid (m-ABA), such as NH2–Xx–m-ABA–CO2H, where Xx are amino acids Phe, Tyr, Gly, and Pro. The presence of m-aminobenzoic acid helps in self-assembly through insertion of conformational constraints in the peptide backbone and also through aromatic π–π interactions. The insertion of m-aminobenzoic acid also induces proteolytic stability in the nanostructures. The formation of nanowires has been observed at acidic pH (pH 4.2–6.0), while both nanowires and nanovesicles are formed simultaneously at nearly neutral pH (pH 6.4). With an increase in the pH of the solution, only one nanoscopic species, i.e., nanovesicles have been formed exclusively, and these nanovesicles are stable within the range of pH 7.0–9.1. A further increase in pH (pH 10) triggers the disruption of nanovesicular structures that starts at the peripheral wall of the vesicles and is completed after total disintegration at pH 11. Studies show that alkali metal salt KCl can also disrupt these nanovesicles efficiently. These peptide-based nanovesicles can encapsulate a potent drug curcumin, which can be effectively released through the disruption of the vesicles either in presence of KCl or alkaline pH. Single crystal X-ray diffraction analysis indicates the sheet-mediated self-assembly in the formation of different nanostructures. Studies also show that the tyrosine-based peptide nanovesicles are elegant hosts for in situ preparation and stabilization of silver nanoparticles.

Design of supramolecular β-sheet forming β-turns containing aromatic rings and non-coded α-aminoisobutyric acid and the formation of flat fibrillar structures through self-assembly

Single crystal X-ray diffraction studies show that the three designed tripeptides Boc-Leu-Aib-m-NA-NO2 (I), Boc-Phe-Aib-m-NA-NO2 (II) and Boc-Pro-Aib-m-ABA-OMe (III) (Aib, α-aminoisobutyric acid; m-NA, m-nitroaniline; m-ABA, m-aminobenzoic acid; Boc, t-butyloxycarbonyl) containing aromatic rings in the backbones adopt β-turn structures that are self-assembled through intermolecular hydrogen bonds and van der Waals interactions to create layers of β-sheets. Solvent-dependent NMR titration and CD studies show that the β-turn structures of the peptides also exist in the solution phase. The field emission scanning electron microscopic and transmission electron microscopic images of the peptides in the solid state reveal fibrillar structures of flat morphology that are formed through β-sheet mediated self-assembly of the preorganised β-turn building blocks.

Overlapping Double Turn Conformations Adopted by Tetrapeptides Containing Non-Coded α-Amino Isobutyric Acid (AIB) and Formation of Tape-Like Structures Through Supramolecular Helix Mediated Self-Assembly

Single crystal X-ray diffraction studies and solvent dependent (1)H NMR titrations reveal that a set of four tetrapeptides with general formula Boc-Xx(1)-Aib(2)-Yy(3)-Zz(4)-OMe, where Xx, Yy and Zz are coded L-amino acids, adopt equivalent conformations that can be described as overlapping double turn conformations stabilized by two 4-->1 intramolecular hydrogen bonds between Yy(3)-NH and Boc C=O and Zz(4)-NH and Xx(1)C=O. In the crystalline state, the double turn structures are packed in head-to-tail fashion through intermolecular hydrogen bonds to create supramolecular helical structures. Field emission scanning electron microscopic (FE-SEM) images of the tetrapeptides in the solid state reveal that they can form flat tape-like structures. The results establish that synthetic Aib containing supramolecular helices can form highly ordered self-aggregated amyloid plaque like human amylin.