Gulmi Chakraborty

Solvent-Induced Molecular Folding and Self-Assembled Nanostructures of Tyrosine and Tryptophan Analogues in Aqueous Solution: Fascinating Morphology of High Order

Hydrophobic derivatives of tyrosine and tryptophan, viz. octyl and dodecyl esters of tyrosine and octyl ester of tryptophan, are synthesized, and the interfacial and bulk properties in aqueous media are investigated as models for the membrane proteins. Molecular modeling by the density functional theory method is carried out to understand the molecular conformation and geometry for the purpose of determining the packing parameters. Water-induced molecular folding of the esters of both tyrosine and tryptophan, as observed using rotating frame nuclear Overhauser effect spectroscopy, indicates that the segregation of the hydrophobic and hydrophilic blocks in water is the key to the development of fascinating interfacial property displayed by the aromatic amino acid esters. The unusually high-order morphology of the aggregates, as observed using high-resolution transmission electron microscopy, is highly uncommon for single-chain amphiphiles and points to the fact that the self-assembly behavior of the present systems resembles that of block copolymers. The study of the growth of mesosized hollow aggregates with internal bilayer structures from tyrosine and tryptophan-based model systems would add to the understanding of biochemistry and biotechnology relevant to the cell membrane. The potential of biocompatible nanostructured motifs as the drug carriers is discussed. The highly functional role played by the aromatic amino acids at the membrane-water interface will be considered with the present amphiphilic models for future perspective.

Synergistic interactions of surfactant blends in aqueous medium are reciprocated in non-polar medium with improved efficacy as a nanoreactor

Organized assemblies in aqueous and non-aqueous media based on mixed surfactants are one of the desired areas for experimental studies and carrying out chemical reactions due to synergistic performance and efficient solvents for various substrates. In this report, a model C–C cross coupling Heck reaction between n-butyl acrylate and 4-iodo-toluene is performed both in micelles and water/oil microemulsion systems as reaction media using a similar set of surfactants, [cetyltrimethylammonium bromide (CTAB) and polyoxyethylene (20) cetyl ether (C16E20)], in their single and mixed states for the first time. In order to explain the possible location and mechanism of reaction in these media, multitechnique approaches are employed to understand the mutual interactions between surfactant(s) and other constituents in pure and mixed states at air–water as well as oil–water interfaces. A synergistic interaction is evidenced experimentally for a mixed CTAB/C16E20 micellar system, which is also supported by theoretical calculations using density functional theory (DFT). The yield of Heck product in different media follows the order water < pure micelle < mixed micelle, which indicates a significant role of the confined environment of the aggregated systems. Further, mixed microemulsions including constituents of the formulations 1-pentanol and n-heptane or n-decane are explored as nanoreactors for carrying out such a reaction. Reaction yield in mixed water-in-oil (w/o) systems as a function of different hydration levels has been correlated with formation and microstructural characteristics of these systems. Further, mixed microemulsions at lower hydration levels produce synergistic performance compared to micelles and individual constituents in terms of reaction yield. These results reveal that the reaction occurs in neither the water nor oil domain, evidently in the micelle/water pseudo-phase and at the palisade layer of the oil/water interface of microemulsions. Moreover, reaction yields in the studied media are rationalized in terms of interaction parameters, spontaneity of micellization, interfacial population of 1-pentanol, and spontaneity of formation of w/o microemulsions.

Interaction of Tyrosine Analogues with Quaternary Ammonium Head Groups at the Micelle/Water Interface and Contrasting Effect of Molecular Folding on the Hydrophobic Outcome and End-Cap Geometry

The surface property of the cationic micelles of cetyltrimethylammonium bromide (CTAB) in an aqueous medium is highly modified in the presence of tyrosineoctyl ester (TYOE) and tyrosinedodecyl ester (TYDE), the models for aromatic amino acid side chains of transmembrane proteins. While the synergistic interaction between the quaternary ammonium head group of CTAB and the π-electron cloud of aromatic amino acid ester is influenced by the relative orientation and the unusual molecular geometry of the latter, this eventually triggers a morphology transition of the spherical micelle to cylindrical/wormlike micelles and imparts a strong viscoelasticity in the medium. Physical characteristics of the elongated micelles have been investigated by high resolution transmission electron microscopy (HRTEM) and the small angle neutron scattering (SANS) technique; the complex fluidic nature of the system is investigated by a dynamic rheological measurement. The intermolecular interactions have been recognized via 1H NMR and 2D nuclear Overhauser effect spectroscopy (NOESY), and the unambiguous geometry of the end-caps of the rods has been ascertained for the first time. While the interplay between lipids and transmembrane proteins is thought to be crucial in controlling the membrane shape of the cells during many vital events such as cellular fission, fusion, and virus entry, the observed tuning of the micellar surface curvature via the cation-π interaction involving tyrosine analogues is thought provoking and opens up an avenue for new physical chemistry research on a vital biological phenomena.