the first events of photosynthesis. the design of a biosolar cell rienk van grondelle

The First Events Of Photosynthesis.

The Design Of A BioSolar Cell

Rienk van Grondelle

Photosynthesis Stores About 8x The Total World’s Energy Need

Waar vindt de fotosynthese plaats?

The Photosynthetic Membrane

Top-view of the Photosystem II-LHCII supercomplex

Peripheral Light-Harvesting Complex II of Plants.

Binds 50% of all Chlorophyll on this planet

From Photosynthesis to Artificial Photosynthesis

The major design principles of photosynthesis

1. ExcitonsThe effective energy storage in antenna complexes is possible due to the presence of light-harvesting pigments (chlorophylls, carotenoids, bilins) with long-lived excited states and a high cross-section for light absorption.

The elementary excitation of the antenna is described by the wavefuction n, which correspond to excitation of the n-th pigment. Quantum mechanics dictates that when neighbouring pigments are coupled because they are closeby, the excited state of the complex is given by a superposition of such wavefunctions, i.e. c1n1+c2n2+…, where one elementary excitation is shared between a number of molecules.

Such a collective excitation (denoted ‘exciton’) is different from independently excited molecules n1, n2,… due to correlations (‘coherences’) between them given by c1*c2…… Such coherences can be produced if the electronic Hamiltonian contains off-diagonal terms, i.e. Hn2n1. In this coherent state one molecule ‘knows’ about the excitation of its neighbours.

This dramatically changes the spectrum of a pigment aggregate as well as the energy transfer dynamics. In natural antenna complexes these features produce more efficient light absorption, faster conversion from short- to long-wavelength spectral bands, and increase the irreversible trapping of excitations by the RC.

Transfer rates between two Chl molecules (as a function of the

energy gap and interaction energy between them) calculated according to modified Redfield (A) and Förster (B) expressions.

The specific non-monotonous dependence of the rates on the

energy gap and interaction energy is determined by the

shape of exciton-phonon spectral density for Chl.

Relaxation in the Exciton Manifold of LH2

k-th exciton state

Bottleneck

Relaxation between one-exciton states (k,r) and (p,s), where kr and ps for coherence transfer or decay, or k=r and p=s for population transfer, is given by the term nmcnkcnpcmrcmsJkp<vnvm>.

Peripheral Light-Harvesting Complex II of Plants.

Binds 50% of all Chlorophyll on this planet

4 nm

Energy Transfer in PE545; a peripheral light-harvesting complex from cryptophyte algae

From Photosynthesis to Artificial Photosynthesis

The major design principles of photosynthesis

2. Quantum Coherence

From Photosynthesis to Artificial Photosynthesis

The major design principles of photosynthesis

3. High pigment/protein ratio: ultrafast (< 1 ps) energy transfer

Plant PSI

>30% of the mass is

pigment!!!!

Mg-Mg-distance about 1 nm

Couplings of 20-200 cm-1

20 ps trapping time

From Photosynthesis to Artificial Photosynthesis

The major design principles of photosynthesis

4. Long exciton lifetimes when the Reaction Center is absent or no ‘concentration quenching’.

Antenna lifetime

LH1 ~1 ns

LH2 ~1 ns

CP47 ~4 ns

LHC II ~2 ns

Chlorosome ~200 ps

Chl a aggregates < 20 ps

Stark

++

++

0

0

+++

??

From Photosynthesis to Artificial Photosynthesis

The major design principles of photosynthesis

5. The Supra Molecular Organization

1950’s

20 nm

2004

Architecture and constituents of a spherical chromatophore vesicle from R. sphaeroides constructed from AFM/LD data (37, 39)

Şener M. K. et.al. PNAS 2007;104:15723-15728

©2007 by National Academy of Sciences

52nm

From Photosynthesis to Artificial Photosynthesis

The major design principles of photosynthesis

6. Multiple Pathways for Energy Transfer and Many Entries into the Reaction Center

Chls at 3-4 nm transfer excitations in ~10 ps!!!

The RC-LH gap: Förster vs. Marcus

Chlorophylls at 3-4 nm transfer excitations into the RC in ~ 10 ps.

**

e-

e-

And electrons out of the RC in ~1 second!!!!!!

From Photosynthesis to Artificial Photosynthesis

The major design principles of photosynthesis

7. Multiple Pathways for Light-Driven Charge Separation

3 ps

1 ps

Zinth cs.

In The Bacterial RC Charge Separation Originates From The Special Pair

In RCs of green plantsThere is NO special pair

Experimental Evidence For Two Paths in the PS2 RC

Romero et al,submitted

~1

09V

/m (

ne

t e

lec

tric

fie

ld)

BPhe

acc. BChl

L(a)

L(b)

L(c)

L(e)M(d)

+ +

+

+

-

- -

-

-

+

-

-20%

0%

20%

-5 0 5Height (Å) below/above atom

Rel

ativ

e de

nsity

cha

nge

MgNCmacCper

Pigments in The Active Branch of the RC

Scherz et al, 2010

From Photosynthesis to Artificial Photosynthesis

The major design principles of photosynthesis

8. Photoprotection in LHCII

3Chl-> 3Car

Peterman et al, 1995

DCMU1 minP AL

Fo

Fm

Fm’

NPQ

To Regulate The Energy Flow The Light-Harvesting Antenna Has The Ability To Switch Off!!!

Non-Photochemical Quenching

Fluorescence Yield

Time

Chl 1

Chl 2

Car T

kQ kT

kR

Annihilation

Chl 1

Chl 2

Q

k1

γ

γ

kT

K

Lhc2 quenching:

Target Analysis With a Real Annihilation Model

Car*

Chl a Lut1

Qy S1

NPQ

a611

a612

a610

Neo

Lut1

A

B

Is LHCII a Switch??????

Principles

• Excitons\• Quantum Coherence• Concentration• Spatial Organization• Supramolecular Organization• Multiple entries to catalytic center• Multiple ET pathways• Photoprotection

Acknowledgements

• Vladimir Novoderezhkin, Alexander Doust, Jan Dekker, Chantal van der Weij-de Wit, Ivo van Stokkum, Bruno Robert, Alessandro Marin, Tjaart Krueger, Natalia Pawlowicz, Sandrine d’Haene, Henny van Roon, Maxime Alexandre, Thomas Cohen Stuart, Cosimo Bonetti, Rudi Berera, John Kennis, Neil Hunter, Marcus Wendling, Eli Romero, Christian Ilioalia, Mariangela DiDonato, Manolis Papagiannakis, Mikas Vengris, Delmar Larson, Herbert van Amerongen, Marloes Groot, Miguel Palacios, Raoul Frese, Greg Scholes, Roberta Croce, Andy Stahl, Graham Fleming, Leonas Valkunas, Andy Pascal, Lavanya Premvardhan, Gert van der Zwan, Sacha Ruban, Peter Horton, Jos Thieme, etc etc