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Excitation Energy Transfer In Photosynthetic Membranes

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Information about Excitation Energy Transfer In Photosynthetic Membranes

Published on June 16, 2008

Author: acidflask

Source: slideshare.net

Description

Term project for PHYS 598NSM (K. Schulten, Fall 2004).
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Excitation Energy Transfer in Light Harvesting Complex II Jiahao Chen December 15, 2004 PHYS 598 NSM

Plants as Transducers Light energy  Chemical potential energy The light harvesting process threshold of photochemistry M. Kamen, Primary Processes in Photosynthesis , Academic Press: NY, 1963 . This study Light harvesting ~ 0.5 – 100 ps

Light energy  Chemical potential energy

The light harvesting process

threshold of photochemistry

Light Harvesting Complex II Most common photosynthetic protein in plants Energy funneled to reaction center Trimeric in vivo Study monomer properties Components: chlorophyll a (pink), chlorophyll b (grey), protein (cyan). LHC-II from spinach. PDB code 1RWT. Liu et. al. , Nature , 428 , 2004 , 287-292.

Most common photosynthetic protein in plants

Energy funneled to reaction center

Trimeric in vivo

Study monomer properties

Components: chlorophyll a (pink), chlorophyll b (grey), protein (cyan).

Objectives Quantum and Statistical Physics How long does it take to harvest energy? Chemical Biology What is the efficiency of light harvesting?

Quantum and Statistical Physics

How long does it take to harvest energy?

Chemical Biology

What is the efficiency of light harvesting?

The Origin and Nature of Excitation Light absorption Photon  exciton electronic excited state Ground state hole electron exciton Excited state occupied orbital empty orbital photon

Light absorption

Photon  exciton

electronic excited state

How Energy is Transferred Coulomb interaction Coherent/Resonant Incoherent/Hopping Two mechanisms Dexter Förster Range <5 Å 5-12Å Different Spin Correlations! hole electron D onor A cceptor Dexter D onor A cceptor Förster

Coulomb interaction

Coherent/Resonant

Incoherent/Hopping

Two mechanisms

Dexter

Förster

Range

<5 Å

5-12Å

F örster Theory Approximations Time-dependent first-order perturbation theory  Fermi’s Golden Rule (Transition) Dipole-dipole interactions only Optically accessible states only Förster formula

Approximations

Time-dependent first-order perturbation theory  Fermi’s Golden Rule

(Transition) Dipole-dipole interactions only

Optically accessible states only

Förster formula

How to Quantify Efficiency Mean passage time Average time needed to traverse the entire protein Quantum yield Fraction of excitons that make it from start to end Assume dissipation to be the only competing process

Mean passage time

Average time needed to traverse the entire protein

Quantum yield

Fraction of excitons that make it from start to end

Assume dissipation to be the only competing process

Computational Procedure Atomic coordinates Distances between centers of mass: R ij Identity: chlorophyll a v. b Transition dipole strength, f Orientation: k factor Förster rate: k ij Quantum yield,  Mean passage time:  results PDB literature parameters

Dipole-dipole couplings in LHC-II

Energy transfer rates for LHC-II (II) Fastest route Energy ends up sloshing between this pair

Results Strongest dipole couplings lead to fastest transition rates Light harvesting efficiency: 98.7% Excitons have half-life of 50 transitions! Excitons can travel long distances before decaying Mean passage time: 13.52 ps Average transition time: 0.97 ps

Strongest dipole couplings lead to fastest transition rates

Light harvesting efficiency: 98.7%

Excitons have half-life of 50 transitions!

Excitons can travel long distances before decaying

Mean passage time: 13.52 ps

Average transition time: 0.97 ps

Conclusions Numerical evidence support model of antenna complexes funneling energy to a reaction center Pair that excitation prefers to move in one direction Chl b (650 nm)  Chl a (670 nm) transition Pair that excitation prefers to end up at Directional preference in exciton transfer rates

Numerical evidence support model of antenna complexes funneling energy to a reaction center

Pair that excitation prefers to move in one direction

Chl b (650 nm)  Chl a (670 nm) transition

Pair that excitation prefers to end up at

Directional preference in exciton transfer rates

Acknowledgements TCBG Klaus Schulten Melih Şener Martínez Group Todd Martínez Hanneli Huddock

TCBG

Klaus Schulten

Melih Şener

Martínez Group

Todd Martínez

Hanneli Huddock

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