(558e) Reversible and Triggerable Self-Assembly of Photoresponsive Catanionic Vesicles

Authors: 
Lee, C. T. Jr., University of Southern California
Peksaglam, Z., University of Southern California
Chmelka, B. F., University of California, Santa Barbara

Photo-responsive catanionic surfactant solutions are compositionally and structurally rich with controllable self-assembly properties and phase behaviors that are triggerable by light. Conventional lipid-type surfactants form vesicles that are often non-equilibrium structures (i.e., they do not form spontaneously and once disrupted cannot be readily reconstituted).  By comparison, aqueous mixtures of cationic and anionic surfactants (“catanionic” mixtures) spontaneously associate into catanionic vesicles under appropriate equilibrium conditions.  Furthermore, reversible assembly and disruption of catanionic vesicles can be achieved by incorporating photo-responsive moieties, such as azobenzene groups, into the hydrophobic regions of cationic and/or anionic surfactants.  Herein we demonstrate that catanionic vesicles with sizes ranging from 50–200 nm can be disrupted and reconstituted with simple light illumination.  Such catanionic vesicles are formed from mixtures of nontoxic, biocompatible photo-sensitive surfactants that can be rapidly “switched” from interfacially-active to interfacially-passive states by exposure to UV light, while subsequent re-exposure to visible light returns the surfactant to the active form.  Thus, under visible light or in dark conditions vesicles form spontaneously, while illumination with UV light causes the surfactant-vesicle aggregates to disassociate.  Depending on the solution conditions (i.e., the cationic/anionic surfactant ratio, overall surfactant concentration, etc.), photo-reversible vesicle-to-mononer, vesicle-to-micelle, or vesicle-to-multilamellar structures are demonstrated.  To understand the spontaneous, reversible, and light-induced surfactant self-assembly into micelles, vesicles, or multilamellar phases, molecular structures, dynamics, guest-host species distributions, and aggregation behaviors of catanionic surfactant systems have been measured using a range of experimental techniques (notably small-angle neutron scattering, cryo-TEM, and NMR measurements).  Furthermore, the application of these photo-responsive surfactant-based vesicles as hosts for membrane proteins, allowing photo-reversible control of membrane protein folding, will be discussed (e.g., membrane proteins are folded in vesicle bilayer and unfolded in micelles).  Finally, the use of these photo-responsive vesicles as drug and gene delivery vehicles will be demonstrated (e.g., vesicle-DNA complexes safely delivered into cells via endocytosis can be exposed to UV illumination to release the DNA from the carrier and more readily allow uptake into the cell nuclei for enhanced gene expression rates).