Photosynthesis. Dark part Calvine cycle. Light dependent part

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1 Bioinspired Systems

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3 Photosynthesis Light dependent part Dark part Calvine cycle synthesis energy reach molecules adenosine triphosphate (ATP) Nicotinamide adenine dinucleotide phosphate(nadph) fuel production with CO 2 fixation Fuel: carbohydrate(ch 2 O) Source of carbon: CO 2 RUBisCO enzyme 6 CO C 5 H 10 O ATP + 12 NADPH + 12 H 2 O 6 C 6 H 12 O ADP + 12 P i + 12 NADP H 2 O nicotinamide ribose adenine ribose 3

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5 Nicotinamide adenine dinucleotide NADH ribose nicotinamide adenine ribose

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7 Energy gained by light excitation is used to run reactions that require an input of free energy Source of the electrons: H 2 O - oxygenic photosynthesis (plants, algae and cyanobacteria) H 2 S - anoxygenic photosynthesis (green sulfur, purple bacterias). Byproducts: oxygen and sulfur H 2 O + CO 2 hν ( CH O) 2 + O 2 H 2 S + CO 2 hν ( CH O) + 2S 2 7

8 ~5 µm long Chloroplast The space separation allows coexistence of different in nature processes like oxidation reduction which generate proton gradient between lumen and stroma space hence proton-motive force for ATP synthesis. 8

9 Q A, Q B, PQ- plastoquinone PQH 2 - plastoquinol Ph- pheophytin, chlorophyll with no Mg at. Cyt b 6 - cytochrome complex, transport of electron from plastoquinol (PQH 2 ) to plastocyanin (CU +1/+2 ) (PC) A 0 - monomer chlorophyll A 1 - quinon (vit. K 1 ) F X - 4Fe-4S Centrum Fd- ferredoxin 9

10 12 H 2 O 12 [H 2 ] + 6 O 2 4 H 2 O + 3 ADP + 3 P i 4 H e - + O ATP + 2 H 2 O 4 H e NADP + 2 NADPH + 2 H + 10

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12 In photosystem II, the missing electron, by light excitation that runs reaction chain, is compensated by the electron taken from water decomposition, with oxygen evolution. Next photons adsorption, hence exited electrons are pumped photosystem I cycle and missing electron comes from phosystem II. 12

13 Nature goal is not efficiency and stability! 13

14 Photosynthetic Unit (PSU) Energy transfer LH II LH I RC light harvesting proteins (LH): LH1, LH2 and reaction center (RC) consisting of the photosystem II and photosystem I The sunlight of wavelength between nm is captured by light harvesting complex. A. Damjanovic, I. Kosztin, U. Kleinekathöfer, K. Schulten, Phys. Rev. E 65(2002)

15 Green Plants chlorophyll a and b (substituted tetrapyrol with helated Mg +2 ion) - light adsorption max. 680 nm carotinoids (protection against photo-damaged by oxidation) - light adsorption max. 500 nm Bacterias Bacteriochlorophyll (BChl) - light adsorption max. 960 nm Bacteriopheophytin (BPh) - light adsorption max. 960 nm Cyanobacteria, Red Algae contain large assemblies called Phycobilisomes - light adsorption nm green and yellow light that penetrates their ecological niche 15

16 Energy transfer LH II LH I RC photons are absorbed by the light-harvesting complexes excitons (electron hole pairs) are transferred to the RC charge (electron-hole) separation take place LH II Excitation energy transfer (EET) a) Förster mechanism induced dipole - induced dipole interaction 5-10 nm B850-B800 (18Å) b) Dexter mechanism hopping of light-generated excitons conductive molecules to be in van der Waals contact carotenoids and bacteriochlorophyl A. Damjanovic, I. Kosztin, U. Kleinekathöfer, K. Schulten, Phys. Rev. E 65(2002)

17 Photon CP47 n x Chl + m x Car D1 H + Q B Fe P680 Q A Pheo Water decomposition in PS II D2 Stroma plants, algae cyanobacteria Metaloprotein oxygen evolving complex (OEC) water oxidizing complex (WOC) Mn 4 O 4 :Ca Lumen CP43 Mn 4 Ca Tyr Z H + O 2 H 2 O Ca Mn O the most efficient anodic electrolysis system known loss of four electrons and four protons from two water molecules formation of oxygen-oxygen bond elimination of one electron at the time leads to formation of a high-energy hydroxyl radical 2H H 2 O O 4hν O + OH + H Complexity of the water splitting is reflected by the fact that even plants find this task difficult: under ambient sunlight in the chloroplasts, the OEC must be resynthesised every half an hour. OEC suffer from the oxygen that it has produced. + H + e + e 17

18 PSI 18

19 Green algae Chlamydomonas Vegetative cells H 2 producing heterocyst Cyanobacterium Nostoc sp. 19

20 PSI Fusion of hydrogenase to Photosystem I 20

21 PNAS 2005 vol. 102 no

22 Dalton Trans., 2009,

23 Artificial photosynthesis 23

24 Calvin Cycle

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28 sunlight + available abundant raw materials (water, carbon dioxide) converted to oxygen and the reduced organic species that serve as food and fuel. Holy Grail. We want an efficient and long-lived system for splitting water to H 2 and 0 2 with light in the terrestrial (AM1.5) solar spectrum at an intensity of one sun. For a practical system, an energy efficiency of at least 10% appears to be necessary. Acc. Chem. Res. 1995,28, What can we mimic from nature? Light absorption Employ enzyme Active center of enzyme Transition metal catalyst 28

29 How to involve light in operation of biocatalytic system? Antennas system Semiconductor electrolyte Nature 414, (2001)

30 Artificial photosynthesis Artificial photosynthesis system must be able to use sun energy to drive thermodynamically uphill reaction of abundant materials to produce a fuel. Lubitz et al, Energy & Environmental Science 1(2008)15 30

31 Bio-cells TRENDS in Plant Science 11(2006)543 31

32 Processes at electrode enzyme interface Electroactive orientation of enzyme at the surface Stability: no mechanism for repairing enzymes Stability towards O 2 32

33 Chemical Reviews, 2004, Vol. 104, No

34 Enzyme adsorption on the PG electrode surface Armstrong et al, Chemical Reviews, 107(2007)4366 A: depicts how a film of protein is formed on a pyrolytic graphite edge electrode by spotting dilute protein onto the surface. B: a scanning electron micrograph of the edge surface of pyrolytic graphite polished with 1 μm R-alumina, rinsed with water, and then sonicated for 10 s in water. Particles of alumina remain on the surface but are removed upon further sonication.

35 Active center of enzyme 35

36 PSI Fusion of hydrogenase to Photosystem I 36

37 Biomolecule modification PSI J. Am. Chem. Soc., 2008, 130 (20), pp

38 Hydrogen evolution by PS I and hydrogenase The hydrogen evolution in biophotolysis process is possible due to activity of hydrogenase enzyme in green algae and cyanobacteria and nitrogenase enzyme in cyanobacteria. H 2 O PSII PSI Ferrodoxin Hydrogenaze H 2 O 2 2H + + 2e H 2 H 2 H + + H - 2H + + 2e Problems: sensitivity to O 2 : closed reactors, gen. modification 38

39 The artificial approach to hydrogen evolution 1. Use of enzyme s hydrogenase deposited on electrode (graphite) 2. Synthesis of artificial metal complexes (Fe, Ni, Ru, Ir) H 2 ase H 2 ase H 2 ase electrode 1% H 2 in N 2 (dotted) and 1% H 2 in air (bold), blank graphite electrode under 1% H2 in air (dashed) Armstrong et al, JACS 130(2008)424 39

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41 Artificial system with Hydrognase Armstrong et al, Chem. Comm. (2009)550 University of Oxford 41

42 H 2 production by a 1:1 mixture of nc-cdte-h2asea (0.25 μm). Rate of H2 production under illumination and in the dark gray in 0.1 M ascorbic acid (ph 4.75). J. Am. Chem. Soc. 132(2010)9672

43 Electrochemical tests DEMS Differential electrochemical mass spectroscopy (with help of Dr.P. Bogdanoff) 0.1M phosphate buffer ph=6, saturated with N 2 Light 40 mwcm -2

44 ALGAE FARM TO RECYCLE CO 2 FOR BIO-HYDROGEN AIRSHIP Belgian architect Vincent Callebaut has designed a conceptual transport system that would involve airships powered by seaweed (green algae). 44

45 PSII- oxygen-evolving complexes Ca Mn Mn Mn Mn Phil.Trans.R.Soc. B 363(2008)1237 The oxygen-evolving complexes manganese clusters: (Mn ions), (Ca ions). Nature Reviews Molecular Cell Biology 5, (2004) 45

46 The artificial complexes for water decomposition ruthenium blue dimmer effective can lose its catalytic efficiency after a few cycles (bpy) 2( H 2 O)RuORu(H 2 O)(bpy) Ce(IV) + 2 H 2 O O 2 + 4H + Ru, Mn, Ir, Co 46

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48 How to involve light in operation of biocatalytic system? Antennas system Semiconductor electrolyte Nature 414, (2001) 48

49 use light absorption and excited-state electron transfer to create oxidative and reductive equivalents for driving relevant fuel-forming half-reactions such as the oxidation of water to O 2 and its reduction to H 2 1. Light absorption, either at a single reaction center chromophore (C) or by excitation of an antenna array 2. Electron-transfer quenching, of a donor-chromophoreacceptor (D-C-A) array either oxidatively, D-C*-A D-C + -A -, or reductively, D-C*-A D + -C - -A. 3. Redox separation by electron transfer, D-C + -A - D + -C-A - or D + -C - -A D + -C-A - Inorg. Chem. 2005, 44,

50 Inorg. Chem. 2005, 44,

51 Artificial light harvesting systems The best photovoltaic performances have been achieved with polypyridyl complexes of ruthenium or osmium adsorption maxima at 380 nm and 518 nm The main optical transition have a metal-to-ligand charge transfer character: exited electron is transferred from the metal center to the π* system of the carboxylate ligand general formula is cis-x 2 bis(2,2 -bipyridyl-4,4 dicarboxylate)-ruthenium(ii), where X = Cl -, Br -, I - and SCN - 51

52 Inorg. Chem. 2005, 44,

53 Molecular wires: carbon nanotubes enzyme Nano Lett. 7(2007)3528 Redox polymer wiring enzyme on anode 53

54 J. Phys. Chem. B, Vol. 113, No. 17,

55 Overpotential of over 1V NADH electron donor at the photoanode J. Am. Chem. Soc., 2008, 130 (6), pp

56 The anode electrocatalyst film comprises glucose oxidase (Gox), while the cathode electrocatalyst consists of bilirubin oxidase (BOD) Heller et al JACS 124(2002)

57 0.1M citrate ph=5 PNAS 2005 vol. 102 no

58 Artificial systems????