Organized media, which form spontaneously when amphiphiles self-assemble, can exhibit intriguing macroscopic properties reflecting their molecular scale order. Moreover, they can provide microheterogeneous chemical environments that mimic common media, including tissues, soils or aerosols, for scientific investigation and analysis. Variations in the properties of microheterogeneous media can have well-known effects on chemical and physical processes including rate, distribution and yield changes. Reaction properties in a single sample can vary substantially due to local variations in medium properties, complicating process monitoring and characterization. We use multichannel optical spectroscopy and data mining to study the dependence of sample properties on local environments in organized media, then use spectral property variations to characterize complex processes and media.
Our current studies focus on characterizing and utilizing the microheterogeneity of 1-octanol, an aliphatic alcohol considered to self-assemble around solvated water clusters. The utility of 1-octanol as a model biomimetic solvent is reflected in the wide use of the octanol-water partition coefficient in quantitative structure activity relationships constructed to describe a range of chemical, biomedical and environmental phenomena. We are using frequency-domain fluorescence of probes to characterize water clusters in water equilibrated octanol.
Past work in this area focused on characterization and utilization of mixed lipid aggregates, mixtures of long and short chain phospholipids, that exhibit some features of liquid crystals. These features include the ability to align with applied magnetic fields and form reversible water gelators. Consequently, these aggregates, also called bicelles, are useful in important applications, including drug delivery and optically controlled actuators. The effective use of this medium in any application requires a thorough understanding of its physicochemical properties. Our early work using tagged lipids demonstrated that small chain lipid structure is disrupted and reformed during mixed lipid phase transitions.[1] This indicated that the widely held view that bicelles were comprised of bilayer disks at all temperatures was incomplete and suggested the development of extended bilayer networks and perforated lamellae at elevated temperatures. Shortly after our publication, this morphology was observed by X-ray analysis [2]. Our recent analysis of Raman scattering data collected during mixed lipid aggregate phase transitions are also consistent with the evolution of bicelle disks to worm-like micelles and perforated lamellae.
