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Photoinduced Charge and Energy Transfer in Complexes of C-Type Cytochromes with Water-Soluble Porphyrins
442a
Tuesday, February 14, 2017
2170-Pos Board B490 The Picosecond Kinetics of Non-Photochemical Quenching in Leaves in the Presence of Open and Closed Reaction Centers Herbert van Amerongen, Shazia Farooq. Laboratory of Biophysics, Wageningen University, Wageningen, Netherlands. When the photosynthetic apparatus of plants becomes saturated in high light, a protective mechanism, called non-photochemical quenching (NPQ), is switched on. This is particularly important when the reaction centers (RCs) of photosystem II (PSII) are closed because in that case enhanced chlorophyll triplet formation might occur, leading to the production of singlet oxygen, which can lead to severe damage or even death of the plant. NPQ provides an additional decay channel for chlorophyll excited states, thereby shortening the excited-state lifetime and lowering the probability that excitations end up in a closed RC. However, the exact mechanism of NPQ is still unknown and also the rate of NPQ has never been determined. It is therefore not known whether this rate depends on the state of the RCs, i.e. whether they are open or closed. We have designed a new setup on which it is now possible to measure spectrally-resolved picosecond fluorescence on leaves with either open or closed RCs in the presence and absence of NPQ. We have measured remarkable differences for leaves with open and closed RCs, which are in disagreement with the current views on NPQ and the results will be presented. 2171-Pos Board B491 Mimicking Natural Photosynthsis: Ultrafast Charge Transfer in PpcA Ru(bpy)3 Complexes Matthew O’Malley. James Madison University, Harrisonburg, VA, USA. Converting light energy into its electrochemical equivalent requires precise control and fine tuning of relevant kinetic and thermodynamic parameters, including primary charge separation. To this end, we developed a series of 22 cysteine mutants of PpcA, a 3-heme cytochrome from Geobacter sulfurreducens as a model system to study short distance photo-induced electron transfer. These proteins were successfully expressed in E.coli and isolated for covalent labeling with Ru(bpy)2(bpy-Br). Protein purity and successful posttranslational modifications were confirmed with HPLC-MS. Time-resolved nanosecond and ultrafast transient absorbance characterization was performed at Argonne National Laboratory (ANL) and identified 6 constructs with apparent photo-induced charge transfer time constants of 20 ps or faster, including 2 constructs with 1-2 ps time constants. The latter is a significant result as up to this point only natural photosynthetic systems demonstrated such a fast initial charge separation, while all artificial covalent constructs exhibited charge transfer rates 3 or more orders of magnitude slower. To understand molecular principles responsible for such a dramatic acceleration of electron transfer rates, we conducted small- and wide angle X-ray scattering data collection at the Advanced Photon Source at ANL. Further, we are currently attempting to obtain X-ray crystallographic and NMR structures of the ultrafast constructs. Finally, we performed triplicate 250-300 ns all-atom molecular dynamics simulations of all 6 ultrafast constructs. Based on the obtained results we conclude that that photo-induced ultrafast charge transfer requires van der Waals contact between heme vinyl groups and photosensitizers while contacts with propionates or short covalent donor-acceptor distances play a much less significant role. 2172-Pos Board B492 Photoinduced Charge and Energy Transfer in Complexes of C-Type Cytochromes with Water-Soluble Porphyrins Oleksandr Kokhan, Daniel R. Marzolf, C. Alexander Hudson, Aidan M. McKenzie. Chemsitry and Biochemistry, James Madison University, Harrisonburg, VA, USA. Due to their rich and tunable spectral and redox properties as well as relatively simple synthesis protocols, water-soluble porphyrins are promising candidates as photosensitizers for artificial photosynthesis. Quenching of porphyrin static fluorescence by monoheme horse heart cytochrome (cyt) c is a well-known phenomenon. It is attributed to the fast charge separation (CS), though the CS state has not been observed. Similarly, we found quenching of static fluorescence of porphyrins in the presence of PpcA, a 3-heme c-type cytochrome from the cyt c7 family from Geobacter sulfurreducens. In this report using ultrafast visible transient absorbance spectroscopy we demonstrate that the excited state of proteinbound zinc tetraphenyl sulfonated porphyrin (ZnTPPS) decays with an apparent time constant of about 200 ps in the presence of cyt c and approximately 20 ps in the presence of PpcA. However, the spectral changes are dominated by the fea-
tures of porphyrin singlet and triplet states. Only a small fraction of photosensitizer excited state energy is retained in the CS state suggesting a competing energy transfer mechanism. Unbound fraction of ZnTPPS shows triplet quenching as a second order process with similar low CS state yields for both cyt c and PpcA. Heteronuclear NMR and all-atom molecular dynamics simulations reveal the likely surface binding sites for ZnTPPS. However, small angle X-ray scattering measurements demonstrate propensity of ZnTPPS to induce formation of protein multimers under experimental conditions typical for our experiments. There results demonstrate an unexpected complexity of ZnTPPS binding interactions and photochemistry with c-type cytochromes and suggest the presence of a competing dominant energy transfer process. 2173-Pos Board B493 Optical and Electrochemical Properties of Synthetic Chlorophyll Oligomers Connected with Amide Bond Tomohiro Tatebe, Hitoshi Tamiaki. Ritsumeikan University, Kusatsu, Japan. Chlorophylls are photosynthetically active pigments and frequently form various dimers in photosynthetic apparatuses. To mimic such supermolecules, we have already synthesized chlorophyll dyads linked with an amide bond and here report their optical and electrochemical properties in a solution. The Soret and Qy bands of the synthetic dimers were broader and shifted to a longer wavelength, respectively, in CH2Cl2 than those of the corresponding monomer. In addition, new CD peaks were observed at the red-sides of these absorption bands in the dimers. The oxidation potentials were reduced by the dimerization. These changes were invisible in amino-linked chlorophyll dimers and ascribable to the intermolecularly stacking chlorin p-systems in the present dimers. Similar observation in chlorophyll trimers will be discussed. 2174-Pos Board B494 Dephasing Times in the Phycobiliprotein Antenna Complexes PE545 and PE555 Maria I. Mallus, Suryanarayanan Chandrasekaran, Ulrich Kleinekatho¨fer. Dept. of Physics & Earth Sciences, Jacobs University Bremen, Bremen, Germany. Since long-lived quantum coherence have not only been observed in the FennaMatthews-Olson (FMO) complex of green sulfur bacteria but also in the phycoerythrin 545 (PE545) photosynthetic antenna system, the interest in these systems has been increased significantly. Moreover, similar results have been found for the PE555 complex in which the two alpha-beta monomers are rotated compared to the PE545 structure leading to a water filled channel. By now, all three complexes have been investigated by a sequential combination of molecular dynamics (MD) simulations, calculations of vertical excitation energies along the trajectory and quantum dynamics for the exciton transfer [1-3]. A comparison of the obtained spectral densities and dynamics will be provided. An interesting property for the systems is the dephasing time which can give an estimate for how long quantum coherences might survive in the respective system. In a first step, the relationship between dephasing time and energy gap fluctuations of the individual pigments has been determined [4]. For the above mentioned complex but also additional exciton and charge transfer systems it can be confirmed that that an inverse proportionality exists between dephasing time and average gap energy fluctuation. Interestingly, an interestingly very similar behavior has been found for all these systems. In a subsequent step, the relationship between dephasing time and excitonic energy gap fluctuations for entire complexes including the respective inter-molecular couplings has been studied. [1] C. Olbrich, J. Str€umpfer, K. Schulten, U. Kleinekatho¨fer, J. Phys. Chem. Lett. 2, 1771 (2011). [2] M. Aghtar, J. Str€umpfer, C. Olbrich, K. Schulten, U. Kleinekatho¨fer, J. Phys. Chem. Lett. 5, 3131 (2014). [3] S. Chandrasekaran, K. R. Pothula, U. Kleinekatho¨fer, J. Phys. Chem. B, DOI: 10.1021/acs.jpcb.6b05803 (2016). [4] M. I. Mallus, M. Aghtar, S. Chandrasekaran, G. L€udemann, M. Elstner, U. Kleinekatho¨fer, J. Phys. Chem. Lett. 7, 1102 (2016). 2175-Pos Board B495 Using a Light-Driven Proton Pump Protein to Develop a ReductionOxidation Reaction Cell U-Ting Chiu, Ling Chao. National Taiwan University, Taipei, Taiwan. Bacteriorhodopsin (BR) is a membrane protein found in the halophilic archaea Halobacterium salinarum, which is characterized as a light-driven proton pump. BR has a wide range of absorption wavelength in visible light, high thermal stability and a broad range of pH tolerability, which render the possibility of using it for bioelectronic applications. Here, we developed a novel device utilizing BR as a photoactive agent to generate steady currents through the continuous reduction-oxidation reaction of proton under light illumination.
Tuesday, February 14, 2017
2170-Pos Board B490 The Picosecond Kinetics of Non-Photochemical Quenching in Leaves in the Presence of Open and Closed Reaction Centers Herbert van Amerongen, Shazia Farooq. Laboratory of Biophysics, Wageningen University, Wageningen, Netherlands. When the photosynthetic apparatus of plants becomes saturated in high light, a protective mechanism, called non-photochemical quenching (NPQ), is switched on. This is particularly important when the reaction centers (RCs) of photosystem II (PSII) are closed because in that case enhanced chlorophyll triplet formation might occur, leading to the production of singlet oxygen, which can lead to severe damage or even death of the plant. NPQ provides an additional decay channel for chlorophyll excited states, thereby shortening the excited-state lifetime and lowering the probability that excitations end up in a closed RC. However, the exact mechanism of NPQ is still unknown and also the rate of NPQ has never been determined. It is therefore not known whether this rate depends on the state of the RCs, i.e. whether they are open or closed. We have designed a new setup on which it is now possible to measure spectrally-resolved picosecond fluorescence on leaves with either open or closed RCs in the presence and absence of NPQ. We have measured remarkable differences for leaves with open and closed RCs, which are in disagreement with the current views on NPQ and the results will be presented. 2171-Pos Board B491 Mimicking Natural Photosynthsis: Ultrafast Charge Transfer in PpcA Ru(bpy)3 Complexes Matthew O’Malley. James Madison University, Harrisonburg, VA, USA. Converting light energy into its electrochemical equivalent requires precise control and fine tuning of relevant kinetic and thermodynamic parameters, including primary charge separation. To this end, we developed a series of 22 cysteine mutants of PpcA, a 3-heme cytochrome from Geobacter sulfurreducens as a model system to study short distance photo-induced electron transfer. These proteins were successfully expressed in E.coli and isolated for covalent labeling with Ru(bpy)2(bpy-Br). Protein purity and successful posttranslational modifications were confirmed with HPLC-MS. Time-resolved nanosecond and ultrafast transient absorbance characterization was performed at Argonne National Laboratory (ANL) and identified 6 constructs with apparent photo-induced charge transfer time constants of 20 ps or faster, including 2 constructs with 1-2 ps time constants. The latter is a significant result as up to this point only natural photosynthetic systems demonstrated such a fast initial charge separation, while all artificial covalent constructs exhibited charge transfer rates 3 or more orders of magnitude slower. To understand molecular principles responsible for such a dramatic acceleration of electron transfer rates, we conducted small- and wide angle X-ray scattering data collection at the Advanced Photon Source at ANL. Further, we are currently attempting to obtain X-ray crystallographic and NMR structures of the ultrafast constructs. Finally, we performed triplicate 250-300 ns all-atom molecular dynamics simulations of all 6 ultrafast constructs. Based on the obtained results we conclude that that photo-induced ultrafast charge transfer requires van der Waals contact between heme vinyl groups and photosensitizers while contacts with propionates or short covalent donor-acceptor distances play a much less significant role. 2172-Pos Board B492 Photoinduced Charge and Energy Transfer in Complexes of C-Type Cytochromes with Water-Soluble Porphyrins Oleksandr Kokhan, Daniel R. Marzolf, C. Alexander Hudson, Aidan M. McKenzie. Chemsitry and Biochemistry, James Madison University, Harrisonburg, VA, USA. Due to their rich and tunable spectral and redox properties as well as relatively simple synthesis protocols, water-soluble porphyrins are promising candidates as photosensitizers for artificial photosynthesis. Quenching of porphyrin static fluorescence by monoheme horse heart cytochrome (cyt) c is a well-known phenomenon. It is attributed to the fast charge separation (CS), though the CS state has not been observed. Similarly, we found quenching of static fluorescence of porphyrins in the presence of PpcA, a 3-heme c-type cytochrome from the cyt c7 family from Geobacter sulfurreducens. In this report using ultrafast visible transient absorbance spectroscopy we demonstrate that the excited state of proteinbound zinc tetraphenyl sulfonated porphyrin (ZnTPPS) decays with an apparent time constant of about 200 ps in the presence of cyt c and approximately 20 ps in the presence of PpcA. However, the spectral changes are dominated by the fea-
tures of porphyrin singlet and triplet states. Only a small fraction of photosensitizer excited state energy is retained in the CS state suggesting a competing energy transfer mechanism. Unbound fraction of ZnTPPS shows triplet quenching as a second order process with similar low CS state yields for both cyt c and PpcA. Heteronuclear NMR and all-atom molecular dynamics simulations reveal the likely surface binding sites for ZnTPPS. However, small angle X-ray scattering measurements demonstrate propensity of ZnTPPS to induce formation of protein multimers under experimental conditions typical for our experiments. There results demonstrate an unexpected complexity of ZnTPPS binding interactions and photochemistry with c-type cytochromes and suggest the presence of a competing dominant energy transfer process. 2173-Pos Board B493 Optical and Electrochemical Properties of Synthetic Chlorophyll Oligomers Connected with Amide Bond Tomohiro Tatebe, Hitoshi Tamiaki. Ritsumeikan University, Kusatsu, Japan. Chlorophylls are photosynthetically active pigments and frequently form various dimers in photosynthetic apparatuses. To mimic such supermolecules, we have already synthesized chlorophyll dyads linked with an amide bond and here report their optical and electrochemical properties in a solution. The Soret and Qy bands of the synthetic dimers were broader and shifted to a longer wavelength, respectively, in CH2Cl2 than those of the corresponding monomer. In addition, new CD peaks were observed at the red-sides of these absorption bands in the dimers. The oxidation potentials were reduced by the dimerization. These changes were invisible in amino-linked chlorophyll dimers and ascribable to the intermolecularly stacking chlorin p-systems in the present dimers. Similar observation in chlorophyll trimers will be discussed. 2174-Pos Board B494 Dephasing Times in the Phycobiliprotein Antenna Complexes PE545 and PE555 Maria I. Mallus, Suryanarayanan Chandrasekaran, Ulrich Kleinekatho¨fer. Dept. of Physics & Earth Sciences, Jacobs University Bremen, Bremen, Germany. Since long-lived quantum coherence have not only been observed in the FennaMatthews-Olson (FMO) complex of green sulfur bacteria but also in the phycoerythrin 545 (PE545) photosynthetic antenna system, the interest in these systems has been increased significantly. Moreover, similar results have been found for the PE555 complex in which the two alpha-beta monomers are rotated compared to the PE545 structure leading to a water filled channel. By now, all three complexes have been investigated by a sequential combination of molecular dynamics (MD) simulations, calculations of vertical excitation energies along the trajectory and quantum dynamics for the exciton transfer [1-3]. A comparison of the obtained spectral densities and dynamics will be provided. An interesting property for the systems is the dephasing time which can give an estimate for how long quantum coherences might survive in the respective system. In a first step, the relationship between dephasing time and energy gap fluctuations of the individual pigments has been determined [4]. For the above mentioned complex but also additional exciton and charge transfer systems it can be confirmed that that an inverse proportionality exists between dephasing time and average gap energy fluctuation. Interestingly, an interestingly very similar behavior has been found for all these systems. In a subsequent step, the relationship between dephasing time and excitonic energy gap fluctuations for entire complexes including the respective inter-molecular couplings has been studied. [1] C. Olbrich, J. Str€umpfer, K. Schulten, U. Kleinekatho¨fer, J. Phys. Chem. Lett. 2, 1771 (2011). [2] M. Aghtar, J. Str€umpfer, C. Olbrich, K. Schulten, U. Kleinekatho¨fer, J. Phys. Chem. Lett. 5, 3131 (2014). [3] S. Chandrasekaran, K. R. Pothula, U. Kleinekatho¨fer, J. Phys. Chem. B, DOI: 10.1021/acs.jpcb.6b05803 (2016). [4] M. I. Mallus, M. Aghtar, S. Chandrasekaran, G. L€udemann, M. Elstner, U. Kleinekatho¨fer, J. Phys. Chem. Lett. 7, 1102 (2016). 2175-Pos Board B495 Using a Light-Driven Proton Pump Protein to Develop a ReductionOxidation Reaction Cell U-Ting Chiu, Ling Chao. National Taiwan University, Taipei, Taiwan. Bacteriorhodopsin (BR) is a membrane protein found in the halophilic archaea Halobacterium salinarum, which is characterized as a light-driven proton pump. BR has a wide range of absorption wavelength in visible light, high thermal stability and a broad range of pH tolerability, which render the possibility of using it for bioelectronic applications. Here, we developed a novel device utilizing BR as a photoactive agent to generate steady currents through the continuous reduction-oxidation reaction of proton under light illumination.