Synthesis, Self-Assembly and Application of Small Peptides

Podder, Debasish (2019) Synthesis, Self-Assembly and Application of Small Peptides. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Debasish Podder (12IP010)) 12IP010.pdf - Submitted Version Restricted to Repository staff only Download (7MB)

Abstract

This thesis entitled “SYNTHESIS, SELF-ASSEMBLY AND APPLICATION OF SMALL PEPTIDES” discussed the design, synthesis, characterization, conformational analysis, self-association and application of small peptides using proteinogenic and / or non-coded amino acids. The main focus of this thesis are (i) design and synthesis of small peptide by coded as well as non-coded amino acids (ii) study their self-assembly behaviour in solid and solution state (iii) design different supramolecular gel by using small peptides (iv) exploring the material properties of foldamers. Here we represents the diverse structure and assembly of two analogues peptides. The tripeptide containing tryptophan, -Aminoisobutyric acid and valine self-assembles through various noncovalent interactions to form tryptophan-zipper like structure by intermolecular hydrogen bonding and - interactions. But the leucine analogue adopts water mediated hydrogen bonded cage like structure. Moreover, by U-tube experiments using pH gradient as the driving force across a liquid chloroform phase, the supramolecular tryptophan-zipper acts as active regular proton transporter. The thesis represents design, synthesis and structure analysis of ɑ-ɑ corner mimetic which bent and close end-to-end like a cyclization reaction to form uniform toroids. Each peptide fragment containing L-leucine, ɑ-aminoisobutyric acid (Aib) and L-tyrosine forms rigid 3₁₀ helical structures stabilized by multiple intramolecular N-H....O hydrogen bonds. Two 3₁₀ helices are connected by the spacer 3- aminomethyl-benzylamine and maintain an angular distance of 120˚ and therefore mimic the ɑ-ɑ corner motif of protein super secondary structure. The individual ɑ-ɑ corner subunits are themselves regularly interlinked through multiple water mediated intermolecular hydrogen-bonding interactions to form the rod like supramolecular structure and toroids. It also describes the effect of topology on the self-assembly and optical propensities of δ luminophores has been investigated. A series of  peptide with dihydropyrimidinone containing amino acid and o, m and p-amino benzoic acid have been designed to study the structure-function relationship and change of optical behavior with changing topology. The X-ray crystallography sheds some light on the conformations, self-assembly and the diverse degree of π-π stacking of adjacent δ peptide molecules. Irrespective of presence of same functional groups, only δ peptide 1 can bind with Fe³⁺. The topology affect the solid state molecular packing and optoelectronic properties of the δ peptides significantly. The thesis also describes an efficient tripeptide based low molecular weight super-organogelators. Four tripeptides with diverse steric crowding at the central amino acid residue were studied. From these series, only sterically less hindered peptide 1 and peptide 3 formed organogel in different saturated hydrocarbons, crude oil, and aromatic solvents. In diesel, the peptides formed gel at 1 wt% i.e. act as super-organogelators. The super-gelators have very high efficiency to solidify only the oil from a biphasic mixture of oil-water. Due to the high solubility of the super-gelators in non-toxic organic solvent ethanol, the solution is easy to handle and just by spraying the ethanol solution over oil-water mixture be able to perform gelling function at room temperature. It also represents the development of engineered hybrid systems by encapsulating nanoparticles in gel scaffolds and their synergistic effects. A series of dipeptides containing aromatic amino acid at the Nterminal and aliphatic amino acid at the C- terminal were synthesised and studied. Among them, only the dipeptide L-Phe-L-Val forms both hydrogelator and organogelator, depending on the N and C terminal protecting groups. The organogel shows bright blue emission under 366 nm UV irradiation. The blue emitting organogel efficiently encapsulate green emission source CdSe quantum dots and red emission source LD 700 perchlorate dye. The resulting organic-inorganic hybrid gel exhibits pure white light emission under 366 nm UV irradiation.

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