UCLA

The use of fluorophores for imaging living systems is a fundamental technique that has led to countless discoveries and driven humankind’s understanding of biology. Through careful design of the structure of organic fluorophores, scientists have assayed aspects of living processes ranging from tracking metabolites in bacteria to diseases in humans. The use of fluorescence will continue to play an integral part in furthering chemistry, biology, and medicine. Fluorine, an element rarely found in biology, has seen a rise in interest for applications in biology. The magnetic resonance of fluorine is driving innovation in developing therapeutics in animal models. The administration of fluorine is done with a class of molecules known as perfluorocarbons, or fluorine-substituted alkyl compounds. As perfluorocarbons phase separate from both aqueous and organic media, these extremely nonpolar compounds are administered as the emulsion form. When stabilized by an amphiphile, droplets of these fluorous solvents are able to be suspended in water and administered through traditional means. The work in this dissertation brings the powerful tool of fluorescence to the perfluorocarbon field by designing fluorous-soluble fluorophores. The interactions of nanomaterials in mammals is closely studied using fluorescence imaging.

Chapter One is a perspective on the field of fluorous chemistry. The fundamental properties of perfluorocarbons, their applications in synthesis and biology are reviewed.

Chapter Two is a review of the structure-property relationships of polymethine dyes. The contributions of heterocycle, polymethine linker, and counterion to photophysical properties are examined and tabulated. As the design of more red-shifted and brighter dyes will allow greater advancements in the ability to visualize processes, understanding how scaffold changes will impact the dye is paramount to propelling the field forward.

Chapter Three details the first truly fluorous-soluble fluorophores. The synthesis and photophysical characterization of fluorous trimethine, pentamethine, and heptamethine dyes are detailed. The comparisons of these dyes in fluorous and organic solvents provided some insights into solvent effects on photophysical properties. The pentamethine cyanine dye was successfully used in imaging experiments in macrophages, zebrafish, and cellular aggregates.

Chapter Four reports on an extension of the concepts developed in Chapter Three. To move into fluorescence imaging in mice, the heterocycle was exchanged for the chromenylium scaffold. Further advancements in fluorous-solubility were made by utilizing a simple counterion exchange strategy, doubling the fluorine content without having to design and synthesize a new dye scaffold. With fluorous-soluble pentamethine and heptamethine chromenylium dyes, their SWIR-emissive properties enabled pairwise imaging in animals to understand the biodistribution of perfluorocarbon emulsions. These studies showed that size is almost exclusively the determining factor in biodistribution, and finer distributions may be achieved by altering the surfactant.

Chapter Five further utilizes the oxygen solubility of perfluorocarbons to achieve photodynamic therapy in xenograft tumors. In collaboration with the McGrath group at the University of Arizona, a fluorous-soluble zinc phthalocyanine was designed. This compound was used in pilot studies for inhibiting the growth of subcutaneous tumors in mice. Further optimizations of the xenograft tumors are necessary before treating with perfluorocarbon emulsions, but initial studies show that growth inhibition is possible.

Chapter Six compiles the results of biodistribution studies done with micelle formulations of four SWIR-emissive polymethine dyes. The four dyes studied here present vastly different accumulations over the 48 hours of imaging, and we hypothesize the dyes are not protected in their micelle formulation upon injection in the bloodstream. Understanding how these micelle formulations differ with respect to pharmacokinetics is key to controlling their biodistribution profiles in future studies.

Chapter Seven is a collection of four vignettes in quests to further understand the interplay between fluorous solubilization, photophysical properties, and dye chemistry. The structure-property relationships of fluorous chain substitution on cyanine dyes, the impact of solvent on fluorescence lifetime, and the impact of the vinylene shift in fluorous chromenylium dyes are discussed. The last section details experimental observations in narrowing down how the trimethine dye is formed during dye reaction. The mechanism for the spontaneous formation of the trimethine dyes using the heterocycle and solvent only is proposed.