Characterization of

Organized Media

The organized media that form spontaneously by self-assembly of lipid mixtures not only exhibit intriguing macroscopic properties because of their molecular scale order they provide a heterogeneous aqueous environment similar to vertebrate cell walls for chemical investigations and analysis. For example, mixed lipid aggregates, mixtures of long and short chain phospholipids, exhibit some features of liquid crystals, including the ability to align with applied magnetic fields. This property makes these aggregates potentially useful in important applications, such as determination of integral membrane protein structures using NMR spectroscopy. The effective use of this medium in any application requires a thorough understanding of the arrangement of lipid molecules in the medium. Our work using tagged lipids demonstrated that small chain lipid structure is disrupted and reformed during mixed lipid phase transitions (tip panel right).  This suggested that the widely held view that bicelles were comprised of bilayer disks was incomplete and suggested the presence of extended bilayer networks similar to the one depicted in the second panel. Shortly after our publication, this morphology was confirmed by the X-ray analysis of van Dam et al.

Their work also shows that several other morphologies are formed during mixed lipid transitions.  One goal of our work developing multivariate fluorescence correlation spectroscopy is to develop methods for making measurements that respond to changes in lipid aggregation in such systems as well as sample composition. 

Related Publications

   •  B.A. Rowe and S.L. Neal, "Fluorescence Probe Study of Bicelle Structure as a Function of Temperature: Developing a Practical Bicelle Structure Model," Langmuir, 2003 19(6) 2039-2048. 

Langmuir, 2003 19(6) 2039-2048.

                                      The Exploratorium, 1994.