Toward Time-Resolved Circular Dichroism Spectroscopy of Photosynthetic Proteins: Accessing Excitonic States

Valentyn Stadnytskyi, Purdue University


The focus of this thesis is the study the physical properties and functions of photosynthetic proteins and biomimetic artificial systems that are responsible for electron and energy transfer, and could facilitate the development of biomimetic, renewable energy sources. In particular, transient absorption and circular dichroism spectroscopy, and structure based quantum mechanical simulations have been used to determine triplet state energy transfer in the Fenna-Matthews-Olson antenna protein complex and the effective dielectric constant deep within cytochrome b6f and bc1 proteins complexes. ^ The Fenna-Matthews-Olson protein complex was one of the first proteins crystallized. Since then, a substantial study of its properties has been conducted. The protein became a model system for a lot of theoretical and experimental work because of strongly bound pigments that form the excitonic states, which play a major role in efficient energy transfer, photo-protection, charge separation and electron transfer. However, it is often difficult or even impossible to access those pigments with conventional spectroscopic tools. ^ In this work, I implemented novel time-resolved circular dichroism spectroscopic tools in nanosecond and femtosecond time domains. The first time-resolved circular dichroism spectra have been obtained and provide very rich and unique information even at room temperature. The measured transient circular dichroism spectra have uniquely identified the previously observed 11 microsecond component and assigned it to a new transition. ^ The low-temperature absorbance and circular dichroism spectroscopy coupled with structure-based excitonic simulation have been applied to study new Fenna-Matthews-Olson mutants that reveal incredible details about the excitonic energy landscape of the FMO protein. ^ The proof-of-concept femtosecond transient circular dichroism spectrometer has been built, and the first round of experiments using it appear promising. ^ This novel circular dichroism tools will be used to study photosynthetic proteins such as Fenna-Matthews-Olson antenna protein complex and Photosystem I intrinsic charge separation via direct probing and(or) excitation of strongly coupled pigments.^




Sergei Savikhin, Purdue University.

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