Bimetallic Ruthenium(II) Polypyridyl Complexes Bridged by a Boron Dipyrromethene (BODIPY): Synthesis, Spectroscopic and Plasmid DNA Photoreactions and The Impact of the 515 nm Effect in Photosynthesis: Model System Using ?-Carotene Acid Complexes

Date of Award

2019

Degree Name

M.S. in Chemistry

Department

Department of Chemistry

Advisor/Chair

Advisor: Shawn Swavey

Second Advisor

Advisor: Mark Masthay

Abstract

The projects described in this thesis were focused on studying two aspects of singlet oxygen. The first is the ability of singlet oxygen to be generated by photosensitizers for use in photodynamic therapy and the second is the ability of singlet oxygen to be quenched with ?-carotene.Photodynamic therapy (PDT) is a medical technique which utilizes a photosensitizing drug, light of a certain wavelength and molecular oxygen to generate singlet oxygen, a toxic oxidizing species. When present, singlet oxygen will rapidly react with surrounding biomolecules, causing cellular damage that ultimately leads to cell death. To the ends of creating a photosensitizer for PDT, a new pi-extended dipyrrin containing isoquinolpyrrole has been synthesized by solvent free reactions with trifluoroacetic acid (TFA) as a catalyst. The borondipyrrin (Bodipy) of the isoquinolpyrrole was synthesized by standard procedures followed by synthesis of the bis-ruthenium(II) Bodipy analog. The spectroscopic properties of this complex show the typical intra-ligand charge transfer transitions (ILCT) along with the Ru(?) to ligand(?*) metal to ligand charge transfer (MLCT) transitions. An intense transition at 608 nm with molar absorptivity greater than 100,000 M-1 cm-1 associated with the ??* transition of the Bodipy core is observed. In acetonitrile solutions the bis-Ru(II)-Bodipy complex generates significant singlet oxygen when irradiated with low energy light. In aqueous solutions the complex is capable of photo-nicking plasmid DNA when irradiated within the photodynamic therapy (PDT) window of 600 to 850 nm.?-carotene (?C) is an orange pigment present in the photosynthetic reaction center (PRC) of green plants, where it plays a vital role in photosynthesis: It quenches singlet oxygen before it damages chlorophyll and other components of the PRCs. During photosynthesis, ?C temporarily converts from its native orange-450 state to a pink-515 state via the so-called 515nm Effect. Because of the differences between the electronic structures of orange-450 and pink-515, my working hypothesis was that pink-515 will quench singlet oxygen less efficiently than orange-450. This hypothesis has not been tested to date because orange-450 and pink-515 states are both present during photosynthesis, making deconvolution of their relative quenching efficiencies effectively impossible. The objective of this research was to characterize the relative efficiencies with which "native orange" ?C (?max = 450 nm), "acid-blue" ?C complexes (?max = 700 nm), and the transient "515nm-pink" (?max = 515 nm) ?C species generated during photosynthesis quench singlet oxygen and harvest blue and green light, with a view to understanding the impact of the 515 nm Effect on photoprotective and light-harvesting roles of ?C in photosynthesis. Through studies with the singlet oxygen substrate DBPF it was found that the "acid-blue" ?C was less efficient in quenching singlet oxygen than the "native-orange" ?C, but not to the extent that we expected. These experiments were not conclusive as there was a large standard deviation in each set of data. We plan to repeat these experiments with a singlet oxygen detector (Ocean Optics NIRQuest) to obtain clean and more conclusive data. To date, we have been able to generate a singlet oxygen signal at 1,270 nm using the device but have not yet fully optimized the experimental parameters.

Keywords

Chemistry, Inorganic Chemistry, Physical Chemistry, photosensitizer, photodynamic therapy, PDT, carotenoids

Rights Statement

Copyright © 2019, author

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