Antara Dasgupta

Effect of the head-group geometry of amino acid-based cationic surfactants on interaction with plasmid DNA.

The interaction between DNA and different types of amino acid-based cationic surfactants was investigated. Particular attention was directed to determine the extent of influence of surfactant head-group geometry toward tuning the interaction behavior of these surfactants with DNA. An overview is obtained by gel retardation assay, isothermal titration calorimetry, fluorescence spectroscopy, and circular dichroism at different mole ratios of surfactant/DNA; also, cell viability was assessed. The studies show that the surfactants with more complex/bulkier hydrophobic head group interact more strongly with DNA but exclude ethidium bromide less efficiently; thus, the accessibility of DNA to small molecules is preserved to a certain extent. The presence of more hydrophobic groups surrounding the positive amino charge also gave rise to a significantly lower cytotoxicity. The surfactant self-assembly pattern is quite different without and with DNA, illustrating the roles of electrostatic and steric effects in determining the effective shape of a surfactant molecule.

Hydrogelation of a Naphthalene Diimide Appended Peptide Amphiphile and Its Application in Cell Imaging and Intracellular pH Sensing

This study reports the self-assembly and application of a naphthalene diimide (NDI)-appended peptide amphiphile (PA). H-bonding among the peptide moiety in conjunction with π-stacking between NDI and hydrophobic interactions within the alkyl chain are the major driving forces behind the stepwise aggregation of the PA to form hydrogels. The PA produced efficient self-assemblies in water, forming a nanofibrous network that further formed a self-supportive hydrogel. The molecule followed a three-step self-assembly mechanism. At a lower concentration (50 μM), it forms extremely small aggregates with a very low population of the molecules. With an increase in concentration, spherical aggregates are formed above 450 μM concentration. Importantly, this water-soluble conjugate was found to be nontoxic, cell permeable, and usable for cell imaging. Moreover, the aggregation process and consequently the emission behavior are highly responsive to the pH of the medium. Thus, the pH responsive aggregation and emission behavior has an extended biological application for assessing intracellular pH. The biocompatibility and intracellular pH determining capability suggest it is a promising candidate for use as a supramolecular material in biomedical applications.