Neralagatta M. Sangeetha

Supramolecular gels: Functions and uses

In recent years there has been immense interest in studying gels derived from low molecular mass gelators (supramolecular, or simply molecular gels). The motivation for this is not only to understand the fundamental aggregate structures in the gels at different length scales, but also to explore their potential for futuristic technological applications. Gels have been made sensitive to external stimuli like light and chemical entities by incorporating a spectroscopically active or a receptor unit as part of the gelator molecule. This makes them suitable for applications such as sensing and actuating. The diversity of gel structural architectures has allowed them to be utilized as templates to prepare novel inorganic superstructures for possible applications in catalysis and separation. Gels derived from liquid crystals (anisotropy gels) that can act as dynamically functional materials have been prepared, for example, for (re-writable) information recording. Supramolecular gels can be important in controlled release applications, in oil recovery, for gelling cryogenic fuels etc. They can also serve as media for a range of applications. This tutorial review highlights some of the instructive work done by various groups to develop smart and functional gels, and covers a wide spectrum of scientific interest ranging from medicine to materials science.

Helical aggregates from a chiral organogelator

A new class of pyrene based organogelators has been discovered, and a chiral gelator of this type has been shown to form helical aggregates upon gelation.

Self-assembling and light-harvesting properties of fluorescent linear condensed aromatic gelators

The self-assembling and photophysical properties of soluble fluorescent linear condensed aromatic gelators are reported. The gels formed by 2,3-alkoxy derivatives are constituted of nanofibers weaving a 3-dimensional supramolecular network and imprisoning the solvent. These nanofibers are efficient light-harvesting systems in which complete energy transfer toward a fluorescent acceptor can be achieved at doping levels below 1 mol % of acceptor.

Ammonium lithocholate nanotubes: stability and copper metallization

Ammonium lithocholate nanotubes (NHLC) have been prepared in alkaline ammonia solutions and exhibited remarkable monodisperse cross-sectional dimensions (external diameter = 52 nm) as shown by cryo-transmission electron microscopy measurements. A classical electroless metallic replication method was used with a single poly(ethylene-imine) PEI layer coating the negatively charged NHLC nanotubes. Short copper rods (external diameter ∼ 80 nm) were observed by scanning electron microscopy that corresponded to the original organic templates. The results obtained in acidic conditions are analyzed in terms of the lifetime of the self-assembled structures and formation of bundles of tubes. Dynamic light scattering measurements and optical observations show that the system in the presence of controlled amounts of hydrochloric acid is stable enough to account for a metallic replication in acidic conditions. An average apparent diffusion coefficient of the organic NHLC assemblies is extracted (∼ 9.8 × 10 nm s) in homogeneous suspensions where bundles have been dispersed by the acidic additions.

Synthesis of both enantiomers of 1-phenylethane-1,2-diol via chirality transfer from bile acid derivatives

Both enantiomers of 1-phenylethane-1,2-diol were synthesized with good to excellent enantioselectivities via selective reduction of the phenylglyoxalates derived from bile acids, followed by reductive cleavage.