Mark Masthay, Ph.D.
β-carotene (βC) 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 (1O2 , a toxic oxidizing species generated during photosynthesis) before the 1O2 damages chlorophyll and other components of the PRCs. During photosynthesis, βC 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, I hypothesize that pink–515 will quench 1O2 less efficiently than orange–450. This hypothesis has not been tested to date because orange–450 and pink–515 states are both inherently present during photosynthesis, making deconvoluation of their relative 1O2–quenching efficiencies affectively impossible. The object of this research was to chemically model βC’s pink state with blue βC– acid complexes, which are chemically similar to pink βC, created by reacting βC with trichloroacetic acid (TCA), in order to test this hypothesis. βC’s efficiency at deactivating 1O2 was characterized by measuring the rate of degradation of 1,3-diphenylisobenzofuran (DPBF), which has a high reactivity towards 1O2 and is used to detect the amount of 1O2 in a solution. Our DPBF–based results to date indicate that native orange βC and blue βC–TCA complexes quench 1O2 with roughly equal efficiency, with the native orange βC showing slightly more efficiency in ability to quench 1O2. In future studies, we intend to confirm our DPBF–based results by monitoring the impact of βC and βC–TCA complexes on the 1270 nm (near– infrared) emission of 1O2 using a cooled photomultiplier tube. The results from this research will further the understanding of the 515nm Effect and βC’s role in photosynthesis and could facilitate the development of solar energy devices with greater long-term stability.
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Hoody, Lauren A., "The Impact of the 515nm Effect on 1O2 Quenching in Photosynthesis: Model System Studies Using β-Carotene–Acid Complexes" (2018). Honors Theses. 160.