ABSTRACT

Carotenoids are naturally-occurring pigments that are essential for the survival of photosynthetic organisms. They act as protective devices against irreversible photodestruction of the photosynthetic apparatus, and they function as light-harvesting pigments. Despite this general knowledge of carotenoid behavior obtained from years of investigations, the excited state spectra and dynamics of these molecules are still not well understood. Many of the assignments of their energy states from spectroscopic data are controversial, and the precise nature of the excited states and the roles they play in controlling the biological functions of carotenoids remain unclear. The overall objective of the project is to elucidate the excited state spectra and dynamics of carotenoids in order to reveal how they carry out their important roles in nature. The planned experiments will analyze systematic series of polyenes and carotenoids obtained either synthetically or from several different photosynthetic organisms. In addition, recombinant proteins refolded with modified chlorophylls, or having undergone site-directed mutagenesis in the vicinity of protein-bound pigments, will be studied. Ultrafast time-resolved spectroscopic methods will be used to measure the spectra and dynamics of the excited states. The experiments will be augmented by theoretical quantum mechanical computations to reveal the excited state configurations which will be correlated with the spectroscopic observables. Kinetic and quantum mechanical models describing the photochemical behavior of carotenoids will be evaluated. Various hypotheses pertaining to the excited state structure and spectral properties of carotenoids will be tested, and a number of issues regarding how carotenoids function will be addressed.

Broader impacts
The subject of the research has broad relevance to several socially important topics including global climate change, biofuels, and the development of alternative solar energy conversion schemes. A critical aspect of this project will be its impact on the training of undergraduate and graduate students which include those from underrepresented groups recruited though several outreach activities in which the PI will continue to participate. In the laboratory of the PI, the students will gain experience in a broad spectrum of experimental approaches including the techniques for the isolation and characterization of complex biological materials, sophisticated molecular spectroscopic methodologies, and kinetic and quantum computational modeling. The students will develop organizational and problemsolving skills by writing reports and publications and making presentations at scientific meetings to obtain valuable critical feedback from experts in the field. In addition, the PI will advance general understanding of the project by incorporating the subject matter directly into the freshman-level General Chemistry and graduate Biological and Physical Chemistry courses and through outreach activities involving the general public. The PI will be giving presentations at various schools where he will speak not only about the scientific content, but also about the broad social impacts of the project. The PI will continue his active role as a mentor in the NSF-sponsored REU program in the Department of Chemistry where a participating student will work directly on the project. Finally, the PI has established collaborative arrangements with internationally-known experts who will interact freely with the students in the group specifically on work related to this project, offer a global perspective on the work, and help bring the studies to fruition as rapidly as possible.

This project is jointly supported by the Molecular Biophysics program in the Division of Molecular and Cellular Biosciences and the Chemical Structure, Dynamics and Mechanism and Chemistry of Life Processes programs in the Chemistry Division

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