Nano Materials from Peptide Mimetics

Singh, Surajit (2025) Nano Materials from Peptide Mimetics. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Surajit Singh (20RS035)) 20RS035.pdf - Submitted Version Restricted to Repository staff only Download (21MB)

Abstract

This thesis entitled as “Nano Materials from Peptide Mimetics” is all about the design, synthesis, characterization, conformational analysis, self-assembly and application of peptide based molecules using proteinogenic and / or non-coded amino acids. The main focus of this thesis is to develop synthetic peptides or Peptide mimetics composed of both genetically coded and non-coded amino acids for studying and understanding the molecular self-assembly processes of these peptides in supramolecular helices, sheets and to study their further aggregation behavior in forming gels or nano-materials like tube, vesicle, fibre, porous structure and their versatile applications in several fields. Here, we have designed and synthesized a stearic acid-appended L-lysine gelator, and also study the conformation and gelation properties which can be changed by appropriate external stimuli. This research presents a novel heat-set supramolecular polymer gel system based on stearic acid-appended L-lysine, β-cyclodextrin (β-CD), and potassium carbonate (K₂2CO₃) in N,N-dimethylformamide (DMF), offering reversible and irreversible gel-sol-gel transitions. The system forms a reversible gel (gelA) at lower temperatures, characterized by nano-fiber morphologies. When heated to 85.7 °C, it transforms into an irreversible gel (gelB) with compact microrod structures driven by supramolecular polymerization facilitated by host-guest interactions between β-CD and the hydrophobic stearic acid chain. K2CO3 plays a crucial role in promoting these non-covalent interactions and stabilizing gelB. Phase transitions were confirmed through various techniques, including rheology, which revealed superior mechanical strength and elasticity of gelB compared to gelA. The gel is highly sensitive to aromatic guest molecules like benzene and toluene, which disrupt the supramolecular polymer and decompose gelB, showcasing its stimuli-responsive properties. Structural analysis using FE-SEM, FT-IR, and PXRD revealed significant microstructural and crystalline differences between gelA and gelB. The study highlights the versatility of this gel system, which can be tuned to undergo microstructural changes and decompose on demand, making it a promising candidate for applications in drug delivery, environmental sensing, and smart materials. These findings contribute to advancing the field of supramolecular chemistry by enabling the design of eco-friendly, functional materials with intelligent response mechanisms. The thesis also represents an engineered tetra-amide macrocycle. Its conformation and anion recognition properties are investigated. The tetra-amide macrocycle, containing the m-amino benzoic acid, 1,3-benzenedicarboxylic acid and m-xylenedinediamine adopts an envelope-like conformation in solid-state, where the m-xylenedinediamine ring is perpendicular with the molecular plain. The tetra-amide macrocycle is able to bind anions such as halides, sulphate and phosphate in DMSO (dimethyl sulphoxide) solution. The stabilities of the fluoride (2.6×10³ M⁻¹) and chloride (5.6×10² M⁻¹) complexes in DMSO is higher than that of bromide (66 M⁻¹) and iodide (52 M⁻¹). SO₄²⁻ complex in DMSO is more stable than the HSO₄⁻, NO₃⁻ and H₂PO₄²⁻ complexes. Using this information, a quantitative evaluation of the stability of the 1 : 1 complex of macrocycle, for which overall binding energy in the order -123.98 kcal/mol for SO₄²⁻ was calculated. The strong binding affinity of the tetra-amide macrocycle toward the SO₄²⁻ ion can be explained on the basis of non-covalant interaction like ion-dipole interaction, hydrogen bonding interaction and size selectivity.

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