Macroscopic Reaction Vessel

Transcription

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2 Macroscopic Reaction Vessel Organic molecule of life 2H 2 O Sunlight O 2 + 4H + + 4e +CO 2

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4 Solar Energy Biology adopted the perfect solution to the energy problem O 2 photosynthesis light reactions dark reactions CO 2 2H 2 O 4H + + 4e CH 2 O Organic CO 2 molecules Energy respiration O 2 combustion biomass food fossil fuels

5 5 Billion Year Clock Oxygenic atmosphere & Ozone layer H 2 O splitting Big Bang of Evolution

6 Photosynthetic water splitting is The Engine of Life

7 Photosystem II (PSII) is the enzyme found in plants, algae and cyanobacteria which uses solar energy to split water into molecular oxygen and reducing equivalents

8 Plants and Green Algae

9 Redox scale ev -1 Red. Electron transfer in Photosystem II P680* Pheo - H + PQ A 0 PQ B Oxid. +1 P680 + H 2 O Tyr z (Y Z ) P680 + is highly oxidising Em ~ 1.3eV at ph 7

10 Water splitting reaction is a four photon process 2H 2 O + 2PQ O 2 + 2PQH 2 Light (4hv) PSII

11 Oxygen emission induced by flashes Joliot & Kok ~1969

12 S-state cycle Kok & Joliot dark stable state

13 Photosystem II (PSII) Water splitting rapid turnover of D1 a repair process

14 PSII 1994 SP EM 1995 From Black Box to Atomic Resolution EC X-ray 1998 Cyanobacterial PSII Plant PSII

15 PSII Dimeric Core of T. elongatus Duncan, Nield, Barber (2001) unpublished

16 46,630 atoms 5138 amino acids

17 X-ray Collaborators Kristina Ferreira Tina Iverson Karim Maghlaoui So Iwata Also Joanna Kargul James Murray

18 Mn 4 -Ca cluster Mn 4 -Ca cluster Per monomer 19 protein subunits 16 intrinsic + 3 extrinsics 35 transmembrane helices 57 cofactors Ferreira et al Science 303(2004) Pdf coordinates ref. 1S5L.

19 Comparison of the purple photosynthetic bacterial reaction centre with photosystem II H M D2 L Cyt D1 Bacterial RC D1/D2 PSII monomer 4 subunits 19 subunits

20 Comparison of bacterial RC and D1/D2 of PSII R. sphaeroides R. viridis D2 D1 PS II

21 Extinsics important for producing 3D crystals PsbO P

22 Lumenal view of PSII monomer within the dimer

23 Side view of cofactors, chlorophylls and carotenoids 14Chls 6Chls 16Chls 7 Carotenoidsb

24 CP43 CP47 14 Chls 16 Chls 13 conserved

25 CP43 Chls + CP47 Chls

26 Electron transport cofactors Active Branch Protective Branch

27 Non-haem iron and quinones bicarbonate ligand

28 Diffusion pathway for PQ/PQH 2 from the Q B pocket to the lipid environment of the membrane PsbJ PsbE PsbN PsbD (D2) PQ

29 Lumenal view of PSII monomer within the dimer PQ/PQH 2

30 Electron transport cofactors Active Branch Protective Branch

31 P680 Chlorophylls

32 Oxygen Evolving Centre Anomalous diffration for Mn (1.89A) and Ca (2.25A) bicarbonate?

33 Cubane-like Mn 3 CaO 4 cluster linked to a 4th Mn by a mono-μ-oxo bond Amino acid ligands D1 protein 1 CP43

34 A de D E B C cd E ab D1 protein

35 Large loops of CP43 and CP47 FFESFPVIL GGETMRFWD CP43 CP47

36 Water Splitting-Oxygen Evolving Catalytic Site A344

37 Resolution in the 3.0 t0 3.5 Å region Is the Ca 2+ in the approx right position? Yes it is based on replacement by Sr 2+ (Kargul et al 2007 BBA) Where is Chloride in the OEC? (Murray et al 2008 Energy and Environ.)

38 Anomalous diffraction at 0.7Å Srr Kargul et al (2007) BBA ALA 344 GLU 189 ASP 170 Mn4 Mn ASP 342 GLU 333 CP43 GLU 354 HIS 332

39 Is the Ca 2+ in the approx right position? Yes it is based on replacement by Sr 2+ (Kargul et al 2007 BBA) Where is Chloride in the OEC? (Murray et al 2008 Energy and Environ.)

40 Anomalous difference map for bromide at 0.92 Å Murray et al 2008

41 What about channels at the water oxidation site? Light (4hv) PSII 2H 2 O O 2 + 4H + + 4e In Out Out P680 +

42 H + exit/h 2 O entry seems to be across PsbO P680 H + H 2 O D158 D222 D223 D224 H228 E229 H228 E312 K317 e - D224 E65 D158 D61 OEC His 190

43 H+

44 Oxygen channel? H + Murray & Barber J. Struct. Biol.

45 Possible oxygen channel Murray & Barber J. Struct. Biol.

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47 Does the structure help understand the mechanism of water splitting? 2H 2 O O 2 + 4H + + 4e

48 Diagrammatic representation of the water splitting centre

49 With two substrate water molecules bond Ca 2+ Mn4

50 S 4 Highly electrophilic oxo (or oxyl radical) H H Cl O Ca O O Mn V O Nucleophilic attack O Mn IV Mn IV MnIV O

51 Fe 2+ Cu + Mn 2+ Ca 2+ Y/W e - 2e - O 2 e - 3e - O 2 e - H + H + Fe 4+ =O HO-Cu 2+ 3H + Mn 5+ =O HO-Ca 2+ 3H + 2H 2 O 2H 2 O Cyt oxidase PSII

52 Victor Batista, Gary Brudvig and coworkers (Yale) H +, e - H +, O 2 DFT-QM/MM S-State Cycle H +, e - 2 H 2 O H +, e - e -

53 Chemically feasible?

54 Carbon monoxide dehydrogenase Fe 1 Fe 2 Fe 3 Ni Fe 4 CO O H H Fe 4 S x Ni - cluster CO + H 2 O CO 2 + 2H + + 2e

55 Mishra, Christou et al Chem.Commun 2005 *

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57 Model based on QM/MM calculations by Basita, Brudvig and colleagues in Yale Imperial Yale

58 Sproviero, Gascon, McEvoy, Brudvig, Batista, (2008) J. Am. Chem. Soc. 130, This structure fitted the polarised EXAFS spectra of Yano et al (2006) Science 314, 821. Mn 3 CaO 4 -cubane with the 4 th Mn linked to the cubane by one of its bridging oxygens remains a feasible working model

59 Leonardo s Dream

60 Our dream 2H 2 2H 2 O O 2 Solar energy

61 From Natural to Artificial Photosynthesi s Q A Q B Acceptor N N Tyr P 680 N Ru N NH N N Me EtO 2 C N N O N N Mn O Mn N Mn O O O Mn O N Hammerstrom & Styring U. of Uppsala Me Me

62 Design of an artificial water splitting system O H B O Fe Mn V H Cl O Daniel O Nocera MIT Ca O O O IV MnIVMn Mn IV O

63 Kanan/Nocera Colbalt/phosphate based electrochemical catalyst

64 Solar Energy (100,000TW) Solar Energy (100,000TW) O 2 O 2 One hour of solar = annual global energy consumption 2H 2 O 2H 2 2H 2 O 2H 2 Energy Total global Energy Total (14TW) global (14TW) O 2 O 2 If a leaf can do it we can do it If a leaf can do it we can do it even better! Its only chemistry It s just chemistry

65 Nature is miserably inefficient in converting light to useable energy and surely science properly appliedcould do better

66 Starch Photograph of Lord George Porter OM FRS

67 Jules Verne s Dream (1875) I believe that water will one day be used as a fuel, because the hydrogen and oxygen which constitute it, used separately or together, will furnish an inexhaustible source of heat and light. I therefore believe that, when coal deposites are oxidised, we will heat ourselves by means of water. Water is the fuel of the future

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