Bioinspired Systems

2

3

Photosynthesis

Light dependent part Dark part Calvine cycle

synthesis energy reach molecules adenosine triphosphate (ATP) Nicotinamide adenine dinucleotide phosphate(NADPH)

fuel production with CO2 fixation Fuel: carbohydrate(CH2O) Source of carbon: CO2 RUBisCO enzyme

6 CO2 + 6 C5H10O5 + 12 ATP + 12 NADPH + 12 H2O →

6 C6H12O6 + 12 ADP + 12 Pi + 12 NADP+ + 6 H2O

ribose

adenine

nicotinamide

ribose

ribose

ribose

adenine

nicotinamide

Nicotinamide adenine dinucleotide NADH

7

( )

( ) SOCHCOSH

OOCHCOOH

h

h

2222

2222

+→+

+→+

ν

ν

Source of the electrons:

H2O - oxygenic photosynthesis (plants, algae and cyanobacteria)

H2S - anoxygenic photosynthesis (green sulfur, purple bacterias).

Byproducts: oxygen and sulfur

Energy gained by light excitation is used to run reactions that require an input of free energy

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Chloroplast ~5 µm long

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.

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QA, QB, PQ- plastoquinone PQH2- plastoquinol Ph- pheophytin, chlorophyll with no Mg at.

Cyt b6- cytochrome complex, transport of electron from plastoquinol (PQH2) to plastocyanin (CU+1/+2) (PC) A0- monomer chlorophyll A1- quinon (vit. K1) FX- 4Fe-4S Centrum Fd- ferredoxin

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12 H2O → 12 [H2] + 6 O2

4 H2O + 3 ADP + 3 Pi → 4 H+ + 4 e- + O2 + 3 ATP + 2 H2O

4 H+ + 4 e- + 2 NADP+ → 2 NADPH + 2 H+

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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.

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Nature goal is not efficiency and stability!

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Photosynthetic Unit (PSU)

light harvesting proteins (LH): LH1, LH2 and reaction center (RC) consisting of the photosystem II and photosystem I

The sunlight of wavelength between 400-700 nm is captured by light harvesting complex.

Energy transfer LH II→LH I→ RC

A. Damjanovic, I. Kosztin, U. Kleinekathöfer, K. Schulten, Phys. Rev. E 65(2002)031919

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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 470-650 nm green and yellow light that penetrates their ecological niche

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photons are absorbed by the light-harvesting complexes excitons (electron – hole pairs) are transferred to

the RC charge (electron-hole) separation take place

Energy transfer LH II→LH I→ RC

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)031919

LH II

Excitation energy transfer (EET)

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Water decomposition in PS II

H2O H+

H+

Pheo

Q A

Q B

P680

D1 D2

TyrZ

Mn4Ca

Stroma

Lumen

CP43

CP47

O2

Photon

n x Chl + m x Car

Fe

plants, algae cyanobacteria Metaloprotein oxygen evolving complex (OEC) water oxidizing complex (WOC) Mn4O4:Ca

−+•

−+

++→

++→

eHOHOHeHOOH h

2

24

2 442 ν

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

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.

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PSI

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Green algae Chlamydomonas

Cyanobacterium Nostoc sp.

H2 producing heterocyst

Vegetative cells

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PSI

Fusion of hydrogenase to Photosystem I

21 PNAS 2005 vol. 102 no. 47 16911–16912

22 Dalton Trans., 2009, 9990-9996

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Artificial photosynthesis

Calvin Cycle

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What can we mimic from nature?

Light absorption Employ enzyme Active center of enzyme Transition metal catalyst

Holy Grail. We want an efficient and long-lived system for splitting water to H2 and 02 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, 141-145

sunlight + available abundant raw materials (water, carbon dioxide) → converted to oxygen and the reduced organic species that serve as food and fuel.

How to involve light in operation of biocatalytic system?

Nature 414, 589-590 (2001)

Antennas system Semiconductor electrolyte

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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

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Bio-cells

TRENDS in Plant Science 11(2006)543

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Processes at electrode – enzyme interface

Electroactive orientation of enzyme at the surface Stability: no mechanism for repairing enzymes Stability towards O2

33 Chemical Reviews, 2004, Vol. 104, No. 10

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.

Enzyme adsorption on the PG electrode surface

Armstrong et al, Chemical Reviews, 107(2007)4366

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Active center of enzyme

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PSI

Fusion of hydrogenase to Photosystem I

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Biomolecule modification

J. Am. Chem. Soc., 2008, 130 (20), pp 6308–6309

PSI

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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.

H2O PSII PSI Ferrodoxin Hydrogenaze H2 O2

2H+ + 2e H2

H2 H+ + H- 2H+ + 2e

Problems: sensitivity to O2: closed reactors, gen. modification

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The artificial approach to hydrogen evolution

1% H2 in N2 (dotted) and 1% H2 in air (bold), blank graphite electrode under 1% H2 in air (dashed)

1. Use of enzyme’s hydrogenase deposited on electrode (graphite)

2. Synthesis of artificial metal complexes (Fe, Ni, Ru, Ir)

Armstrong et al, JACS 130(2008)424

electrode

H2ase H2ase H2ase

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Artificial system with Hydrognase

Armstrong et al, Chem. Comm. (2009)550 University of Oxford

J. Am. Chem. Soc. 132(2010)9672

H2 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).

Electrochemical tests

DEMS Differential electrochemical mass spectroscopy (with help of Dr.P. Bogdanoff)

0.1M phosphate buffer pH=6, saturated with N2 Light 40 mWcm-2

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ALGAE FARM TO RECYCLE CO2 FOR BIO-HYDROGEN AIRSHIP

Belgian architect Vincent Callebaut has designed a conceptual transport system that would involve airships powered by seaweed (green algae).

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Ca

Mn Mn Mn

Mn

Phil.Trans.R.Soc. B 363(2008)1237

The oxygen-evolving complexes manganese clusters: (Mn ions), (Ca ions).

PSII- oxygen-evolving complexes

Nature Reviews Molecular Cell Biology 5, 971-982 (2004)

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The artificial complexes for water decomposition

ruthenium “blue dimmer effective can lose its catalytic efficiency after a few cycles

(bpy)2(H2O)RuORu(H2O)(bpy)24+

4 Ce(IV) + 2 H2O O2 + 4H+

Ru, Mn, Ir, Co

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How to involve light in operation of biocatalytic system?

Antennas system Semiconductor electrolyte

Nature 414, 589-590 (2001)

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Inorg. Chem. 2005, 44, 6802-6827

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 O2 and its reduction to H2

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-

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Inorg. Chem. 2005, 44, 6852-6864

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Artificial light harvesting systems

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

The best photovoltaic performances have been achieved with polypyridyl complexes of ruthenium or osmium

general formula is cis-X2 bis(2,2’-bipyridyl-4,4’dicarboxylate)-ruthenium(II), where X = Cl-, Br-, I- and SCN-

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Inorg. Chem. 2005, 44, 6841-6851

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Molecular wires: carbon nanotubes

Redox polymer wiring enzyme on anode

enzyme

Nano Lett. 7(2007)3528

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J. Phys. Chem. B, Vol. 113, No. 17, 2009

55 J. Am. Chem. Soc., 2008, 130 (6), pp 2015–2022

NADH electron donor at the photoanode

Overpotential of over 1V

56 Heller et al JACS 124(2002)12962

The anode electrocatalyst film comprises glucose oxidase (Gox), while the cathode electrocatalyst consists of bilirubin oxidase (BOD)

57 PNAS 2005 vol. 102 no. 47 16951–16954

0.1M citrate pH=5

Artificial systems????