Plants, algae and bacteria respond to light in various manners. The effect of light on the growth of plants is called photomorphogenesis and is regulated by the photoreceptor protein named... Show morePlants, algae and bacteria respond to light in various manners. The effect of light on the growth of plants is called photomorphogenesis and is regulated by the photoreceptor protein named phytochrome. Phytochrome is formed in the dark in its inactive red-absorbing (Pr) state and transformed upon absorption of red light to its physiologically active far-red-absorbing state called Pfr. This switching process is linked to a Z-to-E photoisomerization of its open-chain tetrapyrrole cofactor and is transduced to the protein surface modifying the interaction with other proteins in the signal chain. 1H, 15N and 13C cross polarization MAS NMR was used to investigate at atomic resolution both the Pr and Pfr states as well as the two intermediates of the Pfr-to-Pr reaction, Lumi-F and Meta-F. The Pfr state is characterized by a strong hydrogen-bonding at the carbonyl of ring D which leads to an increase in length and strength of the conjugation of the pi-system. The Pfr-to-Pr conversion occurs in two steps: the C15=C16 double bond is photoisomerized in Lumi-F, the rotation around the C14-C15 single bond takes place during the formation of Meta-F. The signal transduction is linked to a change of hydrogen-bonding interaction at the ring D nitrogen with the protein environment. Show less
This thesis focuses on bridging the gap between natural and artificial systems by the structural and structure-function characterization of two kinds of natural photosynthetic antenna systems, a... Show moreThis thesis focuses on bridging the gap between natural and artificial systems by the structural and structure-function characterization of two kinds of natural photosynthetic antenna systems, a pigment-protein complex i.e. the LH2 complex, and the protein-free chlorosome supramolecular light harvesters. Chlorosomes contain the largest numbers of chromophores for any antenna system known in nature and are very efficient ultra-fast light harvesters. They provide an optimal starting point for a novel class of artificial antenna arrays for ultra-rapid feeding of energy into photocatalytic devices. Show less
Photochemically induced dynamic nuclear polarization (photo-CIDNP) is non-Boltzmann nuclear magnetization which can be observed by magic angle spinning NMR spectroscopy as enhanced absorptive or... Show morePhotochemically induced dynamic nuclear polarization (photo-CIDNP) is non-Boltzmann nuclear magnetization which can be observed by magic angle spinning NMR spectroscopy as enhanced absorptive or emissive signals. In solids, photo-CIDNP has been observed since its discovery in 1994 in various photosynthetic reaction centers. In natural photosynthetic charge separation, electron-electron interactions are fine-tuned to lead to highly efficient electron transfer. Nanosecond laser-flash photo-CIDNP magic-angle spinning NMR allows for determination of the nuclear polarizations and hyperfine interactions with atomic selectivity and with a resolution of a few microseconds. The build-up of nuclear polarization in reaction centers of Rhodobacter sphaeroides is found to depend on the presence and lifetimes of the molecular triplet states of the donor and carotenoid. Time-resolved 13C photo-CIDNP MAS NMR spectroscopy is used to map the electronic structure of the donor. In the dark state, maximum electron density is localized in the center of the special pair. In contrast, in the light state, the maximum of the electron spin density is localized at the periphery of the two cofactors. The balance of electron spin density between the two bacteriochlorophyll cofactors is shifted in favor of the L branch of the protein by the ratio of 7:3. We show that the asymmetry is induced by both geometric differences between the two cofactors and non-covalent interactions with the protein. Show less
