Untangling Excitation Energy Transfer for the LHC-II complex from Full First-Principles Calculations.

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1 Untangling Excitation Energy Transfer for the from Full First-Principles Calculations. Joaquim Jornet-Somoza, Joseba Alberdi-Rodríguez, Bruce Milne, Xavier Andrade, Miguel A. L. Marques, Fernando Nogueira, Micael J. T. Oliveira, Angel Rubio nano-bio spectroscopy group ψk-conference. Donostia-San Sebastián. 10 Septembre 2015

2 LHC-II Complex: Light Absorption Process Role: >50% of light energy captured by green plants Trimeric Complex (PDB: 1WRT) ~ atoms ( ~ 7000 belong to chromophores) robust structure crystallisation. Challenge: role of individual chromophores & energy transfer mechanism are not well understood. LHC-II PS-II At low light levels the quantum efficiency of this process approaches unity.

3 LHC-II Complex Stroma Chromophore Network Lumen 6 Chlorophyll b: 3 Stroma + 3 Lumen 8 Chlorophyll a: 5 Stroma + 3 Lumen 4 Carotenoids: Photoprotection Role

4 Real-space time-propagation TDDFT calculations octopus Features: Real-space grid Parallelization in domains & states Pseudopotential approx. Excited states obtained from Time Dependent Density Functional Theory (TDDFT). Real-time propagation of the electronic states: parallelisation in KS orbitals. no need of virtual states. PBE xc functional and Averaged Density Self interaction (ADSIC-PBE-TDDFT). Absorption Spectra from real-time propagations TDDFT GS KS-System ĥ KS ψ i (r)=ε i ψ i (r) n(r)= N i=1 ψ i(r) 2 TD KS-System ψ i (r,δt)=e iκz ψ i (r,0) d(t)= grid r=1 ẑn(r,t) Polarisability α(ω)= 1 κ dt e iωt [d(t) d(0)] Dipole Strength Function S(ω)= 2ω π Iα(ω)

5 Absorption Spectra Chlorophyll s Network D.Siefermann-Hamms, Biochim. Biophys. Acta, 1985, 811, 325 Absorption Experimental Monomer Dimer Trimer ω (ev) Q-band Soret-band Monomer Chl s Network (2025 atoms, 1440 CPUs, 11s/iter, iter = 40fs) Aggregated Chl s Network (6075 atoms, 5120 CPUs, 30s/iter, iter = 40fs) Good agreement on Q-band. (ΔE ~ 0.05eV) Red shifted Soret-band (ΔE ~ 0.35 ev) Only minor inter-monomer perturbations. Absorption process is governed by intramonomer interactions.

6 Objective: to compute the contribution of the individual chromophores for any observable on complex systems. Principle: split the global density on fragments belonging to each subsystem. Compute the expected value on the local domain. Local Dipole Analysis The local electronic densities are obtained by performing a division of the ground-state density based on the Bader charge-topological approach. Local absorption spectra computed from dynamic polarisability for each local electronic density.

7 hν- Fingerprint: Chlorophyll Network All chlorophyll molecules are included as well as the ligand of Mg. Local domains: atoms belonging to porphyrin rings

8 Chlorophyll a Absorption Spectra 611a 610a Isolated Chl + ligand Chl s inside Chromophore Network 612a 602a 614a 604a 613a 603a General red-shift due to electrostatic effect Hidden peak apparition attributed to oscillator strength transfer

9 Chlorophyll b Absorption Spectra Low interacting Chlb: enhancement of Q-band peak Isolated Chl + ligand Chl s inside Chromophore Network 608b 601b 609b 605b-606b-607b cluster strong nonelectrostatic interaction 607b 606b 605b

10 Spectrum Information Stroma Soret band Lumen Qy band Stromal absorption spectrum presents a red-shift in front of Lumen side. Q-band of LHC-II is dominated by Chla s excitations. Soret-band splitting due to different contributions of Chla and Chlb.

11 Excitation Energy Transfer Avergaged Peak Maxima Stroma Soret Shift Chlorophyll label Stroma Lumen 602a 603a 610a 611a 612a 601b 608b 609b 604a 613a 614a 605b 606b 607b ω / ev Lumen Qy Shift Energy transfer pathways determined by excitation frequency gradients: energy transfer after an excitation in the Q-band region should take place following an energy descent path from lumen to stroma. Blue light absorption in stromal side can be transferred down to the center of the complex where 605b-606b-607b cluster is located.

12 Summary and We have demonstrated that the electrostatic and non-electrostatic effects of the environment as well as specific Chl Chl interactions are essential for theoretical investigations of systems of this type. Local analysis of the contribution of each Chl has been introduced and shown to be a powerful tool for use in studying interchromophore interactions and site-specific contributions. Ongoing studies using our real-space TDDFT method on the Chl network aim to quantify the proposed coupling between chromophores and distinguish its different components in order to clarify the EET mechanisms within LHC-II.

13 Acknlowdegments Research Team Joseba Alberdi-Rodríguez (EHU/UPV) Bruce F. Milne (Univ. Coimbra) Angel Rubio (EHU/UPV, MPI) Collaborators Micael J.T. Oliveira (Belgium) Fernando Nogueira (Portugal) Xavier Andrade (USA) Miguel A.L. Marques (Germany) James J.P. Stewart (USA) nano-bio spectroscopy group Computational Resources Financial Support Beatriu de Pinós Fellowship (2010 BP-A )

14 PCCP Thank you Full article in Open Access Insights into colour-tuning of chlorophyll optical response in green plants Physical Chemistry Chemical Physics, 2015, DOI: /C5CP03392F