Dissertation

The phase behavior of hydrated monoacylglycerols and the design of an x-ray compatible scanning calorimeter

Briggs, Jason

1994

Overview

The purpose of this research project was to identify relationships between the molecular structure of lipid molecules and the phase behavior of these hydrated materials. When dispersed in water, amphiphilic lipids often aggregate into liquid crystalline phases. Because of their well-ordered nature, the various mesophases can be identified and characterized structurally using x-ray diffraction. Temperature-composition phase diagrams were constructed for a series of structurally similar lipid molecules in the temperature range 0$\\sp\\circ$C to ca. 105$\\sp\\circ$C and the hydration range 0% to ca. 60% (w/w) water. The specific molecules investigated were monoacylglycerols of varying hydrocarbon chain length from 14 to 18 carbon atoms. A single cis double bond is located at the 9 or 10 position in the chain for the even and odd numbered chains, respectively. Several liquid crystalline phases were identified in these lipid/water systems at various temperatures and hydration values including lamellar, hexagonal, and cubic mesophases. Lengthening the hydrocarbon chain led to an increased stability of the non-lamellar (cubic and hexagonal) phases with respect to the lamellar phases. This was correlated with a quantifiable increase in the spontaneous monolayer curvature, an important energetic term associated with the stability of mesophases with having interfaces, and with a decrease in the diameter of the water channels that permeate the fully hydrated cubic phases. The ability to control pore size is of interest to researchers studying controlled release properties of various media or to those using lipid mesophase structures as templates for constructing molecular sieves and/or catalysts. Several other mesophase structure parameters were measured as a function of temperature, hydration and lipid structure. Also presented in this Thesis is a progress report on the design of a differential scanning calorimeter that is compatible with x-ray diffraction measurements. The goal was to build a device that has sufficient sensitivity to measure lipid phase transitions at the low temperature scan rates required when using conventional x-ray sources. The prototype has been successful in measuring certain lipid phase transitions both calorimetrically and with x-ray diffraction simultaneously on the same sample.

• Publisher: ProQuest Dissertations & Theses
• Subject: Chemistry / Materials science / Physical chemistry
• ISBN: 9798208818039