Physicochemical Analysis of Mixed Micelles of a Viologen Surfactant: Extended to Water-in-Oil (w/o) Microemulsion and Cucurbit[8]uril-Assisted Vesicle Formation

A systematic study of the self-assembly process of a viologen-containing surfactant in aqueous medium is reported. Dodecyl-ethyl-viologendibromide (DDEV) is mixed in different proportions with dodecyltrimethylammonium bromide (DTAB), and the physicochemical properties of micellization are evaluated in order to find a suitable combination which does not interfere with the micellar properties of DTAB but introduces the characteristic properties of viologen. In this process, 1% doping of DDEV with DTAB was found to be the most appropriate, as negligible changes were observed in the physicochemical behavior of this system with respect to that of pure DTAB. The 1% DDEV-doped DTAB mixed micellar system showed the characteristic two-step reduction process for the viologen units at the interface as revealed by CV experiments. 1% mixing of DDEV with DTAB also allowed us to prepare stable w/o microemulsions containing viologen units at the interface which is otherwise unattainable with pure viologen surfactants. The charge-transfer capability of the viologen unit to the electron-rich 2,6-dihydroxynaphthalene (DHN) moiety inside the macrocyclic host, cucurbit[8]­uril (CB[8]) is also evaluated for this system, and surprisingly even at this very low concentration, the ternary complex of DDEV-DHN@CB[8] transformed the micellar assembly to uniform vesicles. All of these properties have been further extended to other tetraalkylammonium surfactants, and similar effects were observed

Dual Self-Sorting by Cucurbit[8]uril To Transform a Mixed Micelle to Vesicle

A systematic study on the cucurbit[8]­uril (CB[8]) assisted transformation of a mixed micellar system of CTAB and a viologen surfactant to vesicles is depicted. The micelle to vesicle transformation is assisted by a charge transfer complex mediated ternary complexation between the viologen group of the surfactant, CB[8], and 2,6-dihydroxynaphthalene. In the presence of CB[8], both the surfactants formed U-shaped binary inclusion complexes inside the CB[8] cavity, and no selective binding is observed. Upon addition of DHN, CB[8] showed two different self-sorting mechanisms. The U-shaped binary complex with CTAB breaks down, and CB[8] moves toward the viologen headgroup of the other surfactant to form a stable ternary complex. In the case of the viologen surfactant, CB[8] moved toward the headgroup leaving the hydrophobic tail free in order to form the ternary complex. The mechanistic detail of this micelle to vesicle transformation is revealed through methodical studies using ¹H and DOSY NMR, ESI-MS, ITC, and other instrumental techniques

Self-Assembly of Peptide-Amphiphile Forming Helical Nanofibers and in Situ Template Synthesis of Uniform Mesoporous Single Wall Silica Nanotubes

A lysine based peptide amphiphile (PA) is designed and synthesized for efficient water immobilization. The PA with a minimum gelation concentration (MGC) of 1% w/v in water shows prolonged stability and can also efficiently immobilize aqueous mixtures of some other organic solvents. The presence of a free amine induced pH dependency of the gelation as the PA could form hydrogel at a pH range of 1–8 but failed to do so above that pH. Various spectroscopic and microscopic experiments such as steady state fluorescence, NMR, IR, CD, and FESEM reveal the presence of hydrophobic interaction, hydrogen bond, and π–π stacking interaction in the self-assembly process. The self-aggregation has been correlated with the design of the molecule to show the involvement of supramolecular forces and the hierarchical pathway. While the L analogue formed left-handed helical nanofibers, the other enantiomer showed opposite helicity. Interestingly the equimolar mixture of the isomers failed to form any fibrous aggregate. Although fibers formed at a subgel concentration, no helical nature was observed at this stage. The length and thickness of the fibers increased with increase in the gelator concentration. The nanofibers formed by the gelator are used as a template to prepare mesoporous single wall silica nanotubes (SWSNTs) in situ in plain water without the requirement of any organic solvent as well as any external hydrolyzing agent. The SWSNTs formed are open at both ends, are few micrometers in length, and have an average diameter of ∼10 nm. The BET isotherm showed a type IV hysteresis loop suggesting mesoporous nature of the nanotubes

Cyclo[4]carbazole, an Iodide Anion Macrocyclic Receptor

A novel preorganized and rigid iodide anion macrocyclic receptor, cyclo[4]­carbazole (<b>Cy­[4]­C</b>), is reported here. The structure of <b>Cy­[4]­C</b> was confirmed by single-crystal X-ray analysis. The binding affinity of <b>Cy­[4]­C</b> for iodide anion was investigated by UV–vis and ¹H NMR spectroscopic techniques. The crystal structure of the complex between <b>Cy­[4]­C</b> and chloroform also provided evidence for the recognition ability of <b>Cy­[4]­C</b> toward iodide anion. Furthermore, the 1:1 complexation stoichiometry between <b>Cy­[4]­C</b> and iodide anion was confirmed by high-resolution mass spectrometry and molecular modeling

Cyclo[4]carbazole, an Iodide Anion Macrocyclic Receptor

A novel preorganized and rigid iodide anion macrocyclic receptor, cyclo[4]­carbazole (<b>Cy­[4]­C</b>), is reported here. The structure of <b>Cy­[4]­C</b> was confirmed by single-crystal X-ray analysis. The binding affinity of <b>Cy­[4]­C</b> for iodide anion was investigated by UV–vis and ¹H NMR spectroscopic techniques. The crystal structure of the complex between <b>Cy­[4]­C</b> and chloroform also provided evidence for the recognition ability of <b>Cy­[4]­C</b> toward iodide anion. Furthermore, the 1:1 complexation stoichiometry between <b>Cy­[4]­C</b> and iodide anion was confirmed by high-resolution mass spectrometry and molecular modeling