Ganesh Shanmugam

2,2,2-Trifluoroethanol disrupts the triple helical structure and self-association of type I collagen.

Collagen, a fibrous structural protein, is a major component of skin, tendon, bone, and other connective tissues. Collagen is one of the dominant biomaterials used for tissue engineering and drug delivery applications. 2,2,2-Trifluoroethanol (TFE) has been used as a co-solvent in the preparation of collagen based biomaterials, which are used for tissue engineering applications. However, the basic knowledge about the structural behavior of collagen in TFE is necessary for an adequate application of collagen as a carrier system. In this work, the effect of TFE on the structure and self-association of collagen has been studied in detail using different spectroscopic methods such as circular dichroism (CD), Fourier transform infrared (FTIR), and UV-Vis absorption. The results obtained from CD and FTIR suggest that collagen transform its structure from triple helix to predominantly unordered conformation with increasing concentration of TFE. Thermal melting studies reveal that the stability of collagen triple helix decreases even at low concentration of TFE. Turbidity measurements indicate that TFE, at higher concentrations, inhibits the collagen fibril formation which arises due to the self-association of collagen molecules. TFE has conventionally been known to promote the ordered structures in proteins and peptides. Destabilization of collagen triple helix by TFE is first of its kind information on the effect of TFE to disrupt the native conformation of proteins.

Role of Intramolecular Aromatic π-π Interactions in the Self-Assembly of Di-l-Phenylalanine Dipeptide Driven by Intermolecular Interactions: Effect of Alanine Substitution.

Although the role of intermolecular aromatic π-π interactions in the self-assembly of di-l-phenylalanine (l-Phe-l-Phe, FF), a peptide that is known for hierarchical structure, is well established, the influence of intramolecular π-π interactions on the morphology of the self-assembled structure of FF has not been studied. Herein, the role of intramolecular aromatic π-π interactions is investigated for FF and analogous alanine (Ala)-containing dipeptides, namely, l-Phe-l-Ala (FA) and l-Ala-l-Phe (AF). The results reveal that these dipeptides not only form self-assemblies, but also exhibit remarkable differences in structural morphology. The morphological differences between FF and the analogues indicate the importance of intramolecular π-π interactions, and the structural difference between FA and AF demonstrates the crucial role of the nature of intramolecular side-chain interactions (aromatic-aliphatic or aliphatic-aromatic), in addition to intermolecular interactions, in deciding the final morphology of the self-assembled structure. The current results emphasise that intramolecular aromatic π-π interaction may not be essential to induce self-assembly in smaller peptides, and π (aromatic)-alkyl or alkyl-π (aromatic) interactions may be sufficient. This work also illustrates the versatility of aromatic and a combination of aromatic and aliphatic residues in dipeptides in the formation of structurally diverse self-assembled structures.

Hydrogelation Induced by Change in Hydrophobicity of Amino Acid Side Chain in Fmoc‐Functionalised Amino Acid: Significance of Sulfur on Hydrogelation

Although a few Fmoc-functionalised amino acids (Fmoc-AA) are capable of forming hydrogels, the exact levels of hydrophobicity, hydrogen bonding, and ionic nature of the Fmoc-AA gelator required for hydrogel formation remains uncertain. Here, the role of hydrophobicity of amino acid side chain, particularly in the formation of hydrogel, was studied by using Fmoc-norleucine (Fmoc-Nle) and its simple sulfur analogues such as Fmoc-methionine (Fmoc-M) in which the γCH2 of Fmoc-Nle is replaced by sulfur. Results indicate that Fmoc-M forms thermally reversible hydrogels in water (pH ca. 6.8), whereas Fmoc-Nle fails to display any gelation under similar conditions. The result suggests that substitution of the sulfur atom likely reduces the hydrophobicity of the alkyl side chain in Fmoc-Nle to the optimum level, which is sufficient to induce supramolecular hydrogelation in Fmoc-M. The difference in the self-association behaviour of Fmoc-M and Fmoc-Nle emphasise the importance of weak noncovalent interaction between side chains (in addition to the hydrogen-bond and aromatic interactions) to stabilise supramolecular self-assembly of Fmoc-functionalised compounds. The current observations provide a lead to the design of new sulfur-based low molecular weight gelators for various potential applications.

Selective binding and dynamics of imidazole alkyl sulfate ionic liquids with human serum albumin and collagen – a detailed NMR investigation

The interaction of ionic liquid (IL) with protein is now becoming important as it stabilizes the protein due to the selective cation-anion combination of the IL. The binding and dynamics of the green solvents such as imidazole alkyl sulfate based ILs, viz., 1-butyl-3-methylimidazolium alkyl [where alkyl = hydrogen, methyl, octyl and dodecyl] sulfate, with two distinct model proteins, namely human serum albumin (HSA) and collagen in aqueous solution, have been investigated with the aid of solution nuclear magnetic resonance (NMR). Interactions of ILs with HSA and collagen have been probed at the atomistic level through NMR determined parameters, such as 1H line-shapes, selective and non-selective spin-lattice relaxation times (T1SEL & T1NS) and spin-spin relaxation times (T2). Furthermore, saturation transfer difference (STD) NMR has been used to monitor the spatial proximities of ILs with HSA and collagen. The results indicate that despite the type of protein (HSA or collagen), STD NMR of protein-IL mixtures exhibits responses only from the anionic part of the selected ILs. Also, a combination of T1SEL and T1NS measurements indicates the genuine protein-IL interaction. Furthermore, it was observed that the global binding affinity between IL and proteins is enhanced with an increase in alkyl chain length of the anionic portion of the IL. The present study thus highlights the role of the anionic part of ILs in the interaction with the selected proteins. The outcome of the present study provides an opportunity to design new ILs with a judicious choice of anionic and cationic parts for targeted functionalities.