Molecular Interactions in Lyotropic Reverse Hexagonal Liquid Crystals: A Dielectric Spectroscopy Study

Abstract

A dielectric study of reverse hexagonal mesophases (HII) is presented. Conducted in the frequency range 0.01-1 MHz and temperature range 293<T<319 K, the study reveals complex molecular behavior in and around the interfaces of the mesoscopic structures of the gel. There exist three clearly defined dielectric relaxations related to separate moieties in the interface, as well as a temperature-activated dc conductivity. A critical temperature, T0=307 K, is noted in the results and related to the dehydration of the glycerol monooleate (GMO) head groups. Effectively, this represents a breakdown of the interfacial layer of water. The consequences of this act are clearly visible in the change in behavior of the fitting parameters for all processes. A physical picture emerges whereby at T0=307 K, the "loosening " of the GMO heads accentuates the dangling motion of the phosphatidylcholine (PC) tails, evidenced by counterion motion along the PC head. Furthermore, it precipitates the percolation of the large TAG molecules that are intercalated in the GMO and PC tails.

Interactions of biomacromolecules with reverse hexagonal liquid crystals: Drug delivery and crystallization applications

“…Structural flexibility and stability is essential for a drug delivery system and tuning its physical properties (such as viscosity) and composition. Dielectric spectroscopy analysis of this system showed a critical temperature, T 0 = 307 K, related to the dehydration of the GMO head groups [26]. Effectively, this represented a breakdown of the interfacial layer of water.…”

“…In addition, it was shown that phosphatidylcholine (PC) can be embedded into the ternary GMO/TAG/water system [23][24][25][26]. PC was incorporated into the ternary mesophases, as it is known that phospholipid-based structures possess relatively high thermal stability, and enhance transdermal drug permeation [27][28][29] and transmembrane transport across the digestive tract [30,31].…”

“…3A and B). Furthermore, it precipitates the percolation of the large TAG molecules that are intercalated in the GMO and PC tails [26].…”

“…The perturbation of the PC heads leads to greater dangling, enabling diffusive movement of the TAG molecule through the tails (from Ref. [26] with permission). (C) ESEM micrographs of H II mesophase of GMO/tricaprylin/PC (63, 7, 10 wt.%, respectively) containing 20 wt.% water at 14°C and magnification 8000Â (from Ref.…”

Recent Developments in Lyotropic Liquid Crystals as Drug Delivery Vehicles

“…This enabled expanding conditions to obtain stable H II mesophases at room temperature. In addition, it was shown that phosphatidylcholine (PC) can be embedded into the ternary GMO -TAG -water system (Ben Ishai et al, 2009 ;Libster et al, 2007Libster et al, , 2008Libster et al, , 2009a. PC was incorporated into the ternary mesophases because it is known that phospholipid -based structures possess relatively high thermal stability and enhance transdermal drug permeation (Kurosaki et al, 1991 ;Touitou et al, 1994 ;Spernath and Aserin, 2006 ) and transmembrane transport across the digestive tract (Brondsted et al, 1995 ;Liu et al, 1999 ).…”