Poulami Jana

Fabrication of Hollow Self-Assembled Peptide Microvesicles and Transition from Sphere-to-Rod Structure

This paper presents the construction of hollow peptide microspheres and the mechanism of transition of microspheres to rod-like vesicles at low concentration. The tripeptides Boc-Phe-Maba-Phe-OMe 1 and Boc-Phe-Maba-Tyr-OMe 2, each of them containing a rigid m-aminobenzoic acid (Maba) template at the central position, forms microspheres at a concentration of 1.6 mM in methanol. At low concentration, these vesicular structures are fused through neck formation, and this leads to sphere-to-rod transition of vesicles. Sizes of these microspheres increase with increasing concentration. We have successfully characterized this transition by fluorescence spectroscopy, DLS, and electron microscopic study. The scanning electron microscopy clearly shows that these spheres are hollow. One important property of these microvesicular structures is the encapsulation of a potent anticonvulsant and mood stabilizing drug carbamazepine, which holds future promise to use these microvesicles as delivery vehicles.

Photo-induced charge-transfer complex formation and organogelation by a tripeptide

A terminally protected tripeptide Boc–Phe–Phe–Tyr–OMe 1 and picric acid form a photo induced charge-transfer complex and organogels. The interactions between stacked aromatic units play a key role in the assembly process. UV light (366 nm) has been used as a source of energy to cleave and homogenize π-stacking in the supramolecular arrangement of peptide 1 and picric acid. CD, FT-IR, NMR and powder X-ray diffraction studies exhibit distinct structural changes before and after light irradiation. Field emission scanning electron microscopy of the xerogels reveal a morphological change caused by photo induced charge-transfer complex formation. The fluorescence spectroscopy as well as confocal microscopy studies show that these charge-transfer complexes have a significant red emission at 672 nm.

Sonication-responsive organogelation of a tripodal peptide and optical properties of embedded Tm3+ nanoclusters

The sonication induced organogelation of a tripodal peptide has been investigated. The tripodal peptide does not form a gel in organic solvents after heating, cooling and ageing. Ultrasound has been used as a source of energy to tune the molecular assembly and organogelation. CD, NMR and fluorescence spectroscopies indicate distinct structural changes before and after sonication. FE-SEM and AFM of the xerogels reveal the nanofibrillar morphology. Moreover, the sonication responsive organogelation has been used to fabricate novel lanthanide nanocrystal decorated fibers. This gelation selectively quenches the viable emissions from the nanocryatsls as well the FRET observed between Tm3+/Yb3+-doped LiYF4 nanocrystals and ketocyanine dye occurring near 550 nm without affecting the NIR emissions of the nanocrystals.

Mesoporous vesicles from supramolecular helical peptide as drug carrier

The self-assembly of a hydrophobic pentapeptide has been investigated in an attempt to develop a drug delivery vehicle. The peptide forms a supramolecular helical column through intra- and intermolecular hydrogen bonding interactions and an interdigitated helical bundle structure in the solid state. In methanol solution, the peptide forms mesoporous vesicles, where the diameters of the vesicles vary with the concentration in direct proportion. The most important property of these mesoporous vesicular structures is the encapsulation of a potent bacteriostatic antibiotic, sulfamethoxazole. Moreover, at pH 6.2, the drug loaded vesicles can effectively release the encapsulated drug slowly, which holds future promise for use of the microvesicles as drug cargo.

Fabrication of nanoporous material from a hydrophobic peptide

A pentapeptide containing hydrophobic residues self-assembles to form nonporous materials in solid state. The X-ray crystallography reveals that there is no pore in the crystal and the peptide exhibits supramolecular helical architecture prompted by the formation of intra- and intermolecular hydrogen bonds. But the phase-selective gelation of the peptide from xylene–water leads to the formation of nanoporous material with different internal diameter. The field emission scanning electron micrographs (FE-SEM) show that the average pore size is in the range of 20 to 50 nm. Moreover, the nanoporous xerogel can efficiently adsorb I2 and remove organic dyes from wastewater.

Hierarchical self-assembly of naphthalene bisimides to fluorescent microspheres and fluoride sensing

Donor acceptor π–π stacking and hydrogen bond mediated self-assembly of two synthetic naphthalene bisimides containing L-amino acids are illustrated. The solution studies exhibit a blue shift in UV/vis spectrum with increasing concentration for both phenylalanine and tyrosine-appended naphthalene bisimides. The single crystal X-ray reveals that both the Phe and Tyr side chains are in the trans position in the reported naphthalene bisimides 1 and 2. In higher order packing, the bisimide 2 molecules self-assemble through intermolecular hydrogen bonds between side chain Tyr –OH and ester –CO, and donor acceptor π–π stacking interactions between the electron deficient central naphthalene moiety and side chain tyrosine ring to generate a staircase architecture. Atomic force microscopy revealed microsphere morphology with diameters of 200–300 nm for bisimides 1 and 2. The microspheres have significant green emission upon excitation at 400 nm. Moreover these two naphthalene bisimides can be used as turn on fluoride sensor in aqueous medium.

Porous Organic Material from Discotic Tricarboxyamide: Side Chain Core interactions

The benzene-1,3,5-tricarboxyamide containing three l-methionine (1) self-assemble through 3-fold amide-amide hydrogen bonds and π-π stacking to fabricate one-dimensional nanorod like structure. However, the tyrosine analogue (2) carrying multiple H-bonding side chains lost the C3 symmetry and 3-fold amide-amide hydrogen bonds and developed a porous structure. The porous material exhibits ten times more N2 sorption (155 cc/g) than the columnar one, indicating that side chain-core interactions have a drastic effect on structure and function.

Insights into self-assembling nanoporous peptide and in situ reducing agent

A tripeptide containing an Aib (α-amino isobutyric acid) residue self-assembles to form porous nanomaterials in solid state. In spite of having a hollow nanotubular structure, the self-assembly nature of the peptide is different, which leads to the formation of pores with different internal diameters. The single-crystal X-ray diffraction study reveals that the peptide forms continuous hydrogen-bonded poly-disperse nanopores (3, 5 and 8 membered) starting from the β-turn conformation as an associating sub-unit. The field emission scanning electron micrograph (FESEM) shows that the average pore sizes are in the range of 20 to 200 nm, although a few large pores are also visible. Moreover, the peptide 1 acts as an in situ reducing agent to synthesize hexagonal gold nanoparticles (GNP).

CdS quantum dots doped with a peptide matrix: structural and photoelectrochemical properties

Luminescent CdS quantum dots have been embedded on the tapes or matrices obtained by the self-assembly of two synthetic short peptides. The X-ray crystallography reveals that both the peptides exhibit a turn-like structure in the solid state and form an intermolecular hydrogen bonded dimer. In higher order assembly, the tripeptide forms a β-sheet like structure by noncovalent interactions. The dipeptide analogue forms a rhombus like 2D matrix in higher order packing through intermolecular hydrogen bonding and π-stacking interactions. Moreover, these self-assembled peptides are used to immobilize luminescence CdS quantum dots. Photoluminescence measurement of the CdS–peptide 1 quantum dots shows a considerably enhanced emission intensity compared to the CdS–peptide 2 conjugate which shows a little increase compared with free CdS.

Luminescent nanoparticles from tripeptide–CdS conjugate

Self-assembly of two synthetic tripeptides containing ω-amino acids and α-aminoisobutyric acid is used to fabricate luminescent nanoparticles by doping with CdS quantum dots. The X-ray crystallography reveals that both the peptides exhibit an unusual turn structure in the solid state where N-terminal γ-aminobutyric acids prefer to adopt a gauche–gauche conformation. In higher order assembly, these peptides form a continuous hydrogen-bonded four-member nanoporous architecture. From methanol solution, the peptides form polydisperse nanospheres. The field emission scanning electron micrographs (FE-SEM) show that the average size of the nanospheres is in the range of 25 to 30 nm. Moreover, these peptide nanospheres can be efficiently doped with CdS quantum dots and exhibit optoelectronic properties.