A lyotropic inverse ribbon phase in a branched-chain polyoxyethylene surfactant: pressure effects

Abstract

A centred-rectangular lyotropic inverse ribbon phase, rarely observed in inverse (type II) systems, has been found in the branched-chain polyoxyethylene surfactant tetradecyloctadecyl-tetraoxyethylene ether (C 14 C 16 EO 4 ) in excess water. This phase is stabilised by the application of hydrostatic pressure. The ratio of the 2-D cell parameters, b/a, is observed to be less than √3 (1.732) over the range of temperatures and 10 pressures studied. The constructed pressure -temperature phase diagram shows that, at high temperatures or low pressures, the inverse ribbon phase converts into an inverse micellar cubic phase of spacegroup Fd3m, and at the opposite extreme, a lamellar gel phase was formed. The lattice parameters of the inverse ribbon phase were found to vary with pressure, with the structure becoming increasingly distorted away from 2-D hexagonal symmetry (b/a = √3) with increasing pressure.

Fluorescence characterization of water-driven self-assembled lipids and their temperature-induced phase transitions

“…By comparing the steady-state fluorescence spectra and lifetimes of pyrene in the hexagonal phase of βGlcOC 8 and βMalOC 12 , we concluded that the shorter alkyl chains in the former (C8) interact more with the pyrene molecules. We attributed this observation to the more random and wobbling motion of the longer chains (C12) that give rise to less interaction with pyrene.…”

“…This heterogeneity is important for the biological function of the lipid assembly, giving the lipid a degree of flexibility that is necessary in order to accommodate various molecular sizes. Comparing the long lifetime component for the hexagonal phase of βGlcOC 8 34 and βMalOC 12 33 (11.1 vs. 51 ns), the much longer component in βMalOC 12 implies more isolation of the pyrene molecules in the tail region. This is consistent with the above-mentioned discussion that predicted more interactions between the pyrene molecules and the shorter tails in βGlcOC 8 .…”

“…When dispersed in water, lipids can display not only the lamellar phase, but also a variety of non-lamellar curved liquid crystal phases such as the cubic, the hexagonal and the ribbon phases. [10][11][12] The transition between these possible phases is a result of an abrupt change in the interface curvature. This transition is believed to be governed by competition between the bending elastic-energy of the interface and energies resulting from interfacial separation constraints.…”

“…[33][34][35] Most of the lyotropic phases studied in this work are normal type unless it is stated the inverse kind such as the inverse cubic phase. 12 (98%), D-glucose (96%) and pyrene (99%) were purchased from Sigma-Aldrich. The synthesis of βGlcOC 10 C 6 is described elsewhere.…”

Self-Assembly of Cyclodextrins and Their Complexes in Aqueous Solutions

“…2,3 At concentrations exceeding the critical aggregation concentration (CAC), a high degree of association may even lead to the formation of lyotropic mesomorphs, e.g., lamellar, hexagonal, cubic, and ribbon phases. [4][5][6] The self-assembly properties of substances can be used to develop novel pharmaceutical formulations. Different types of aggregates may be developed into drug delivery systems like micelles, nanoparticles, microspheres, liposomes, and hydrogels to overcome formulation challenges, such as poor aqueous drug solubility, drug permeation through mucus and membrane barriers, and inadequate drug stability, as well as to enhance biological properties of drugs such as to reduce or prevent their side effects.…”