Visible-light induced reactions in lamellar phospholipid assemblies

Abstract

Cyanine photosensitizers are visible-light absorbing dyes commercially useful in photography and available in a variety of structures with tunable redox, absorptivity and excited state properties. The areas of research described in this dissertation all utilize cyanine dyes to photosensitize various processes to visible-light within the confines of lamellar phospholipid assemblies. In Chapter III, an efficient three component, liposome-bound photochemical molecular device for transfer of energy and electrons is described. A porphyrin (free base or metallated) serves as the energy donor, a cyanine functions as the energy acceptor/electron acceptor and Ph₃BnB- acts as an electron donor. In Chapter IV, the first example of visible-light sensitized bilayer polymerization is presented. Sensitizing the polymerization of two-dimensional lipid assemblies to visible-light is part of a current research effort to exploit the properties of polymerized supramolecular structures. Extending the polymerization sensitivity of such amphiphile aggregates to lower energy visible-light creates possibilities for applications where UV photolysis would not be useful. Applications of liposomes as drug delivery vehicles thus far have relied upon such release mechanisms as pH sensitivity or target specific interactions to empty the liposome contents to the cell. Chapter V describes a new system for the successful destabilization of liposomes at pH 4.5 via visible-light sensitive polymerization of lipids. Visible-light sensitized polymerization induces the release of liposome aqueous contents providing temporal and spatial control over the release event and lower energy irradiation with more tissue penetration than UV photolysis.