Összes szerző

Parveen Akhtar

az alábbi absztraktok szerzői között szerepel:

Lambrev Petar
Exciton–radical-pair equilibration in Photosystem II observed by two-dimensional electronic spectroscopy

Aug 28 - szerda

11:10 – 11:30

Bioenergetika és fotobiofizika

E30

Exciton–radical-pair equilibration in Photosystem II observed by two-dimensional electronic spectroscopy

Petar Lambrev1, Parveen Akhtar1,2, Pawel Nowakowski3, Gábor Sipka1, Guangye Han4, Jian-Ren5 Shen, Győző Garab1, Howe-Siang Tan3

1 Biological Research Centre HAS, Plant Biology Institute

2 ELI-ALPS, ELI Nonprofit Ltd.

3 Nanyang Technological University, School of Physical and Mathematical Sciences, Singapore

4 Photosynthesis Research Center, Chinese Academy of Sciences, Beijing, China

5 Photosynthesis Research Center, Okayama University, Okayama, Japan

The kinetics of energy transfer and charge separation in isolated Photosystem II (PSII) core complexes was studied by time-resolved fluorescence, femtosecond transient absorption and two-dimensional electronic spectroscopy (2DES). Time-resolved fluorescence showed that the main excited-state deactivation time constant in PSII with open reaction centres is around 40 ps, in accordance with literature results. Global analysis of the transient absorption data revealed lifetimes of 200 fs and 3–4 ps (assigned mainly to energy equilibration among antenna chlorophylls), 35–40 ps (the main photochemical trapping), 200–250 ps (electron transfer from pheophytin to QA) and a nanosecond component (re-reduction of P680+). The transient spectra of the reduced pheophytin and oxidized P680 are well defined. These data are in excellent agreement with previous results. 2DES, performed under identical excitation conditions, further resolved uphill and downhill pathways of energy transfer in the antenna as well as equilibration between the primary radical pair and the antenna occurring on a sub-picosecond timescale. The results bring new evidence supporting the exciton–radical-pair equilibrium model of PSII kinetics.

Acknowledgements

The work was supported by grants from the Hungarian Ministry of Finance (GINOP-2.3.2-15-2016-00001), the National Research, Development and Innovation Office (NKFIH NN 124904; 2018-1.2.1-NKP-2018-00009), and the Singapore Ministry of Education Academic Research Fund (Tier 2 MOE2015-T2-039).

Parveen Akhtar
Temperature-dependent energy transfer in LHCII probed by 2D electronic spectroscopy

Aug 28 - szerda

13:30 – 15:30

II. Poszterszekció

P36

Temperature-dependent energy transfer in LHCII probed by 2D electronic spectroscopy

Parveen Akhtar1,2, Thanh Nhut Do3, Adriana Huerta-Viga3, Pawel Nowakowski3, Howe-Siang Tan3, Petar H. Lambrev1

1 Biological Research Centre HAS, Plant Biology Institute

2 ELI-ALPS, ELI Nonprofit Ltd.

3 Nanyang Technological University, School of Physical and Mathematical Sciences, Singapore

The efficiency of photosynthetic light energy conversion depends on the ability of the photosynthetic apparatus to harvest the solar energy and transfer to the photochemical reaction centres without losses. Excitonic interactions between chlorophylls in LHCII, the main light-harvesting antenna of Photosystem II, provide a way for fast and efficient directional excitation energy transfer (EET) in a less than 100 femtoseconds to picoseconds. Despite the wealth of data about the kinetics of EET, the presently existing models report different kinetics of EET in LHCII. Two-dimensional electronic spectroscopy (2DES) is a powerful technique for mapping EET pathways. We studied EET in LHCII by 2DES at various temperatures from 77 K to 293 K under conditions free from singlet-singlet annihilation. Global lifetime analysis revealed that spectral equilibration occurs over distinct timescales – from < 200 fs to 5 ps at 293 K, as previously published [1]. However, slower timescales are observed at lower temperatures – up to tens of picoseconds at 77 K. A clear temperature dependence of uphill energy transfer processes is also discerned, which follows the detailed-balance condition. We applied phenomenological model fitting to resolve exciton states and microscopic rates of energy transfer. The experimental and modeling results at 77 K are generally in good agreement with existing exciton models of LHCII, but specific differences especially in the slow picosecond relaxation kinetics suggest the need for model refinement. Protein motions substantially improve the efficiency of light harvesting at physiological temperature.

Acknowledgements

The work was supported by grants from the Singapore Ministry of Education Academic Research Fund (Tier 2 MOE2015-T2-039), the Hungarian Ministry of Finance (GINOP-2.3.2-15-2016-00001), and the National Research, Development and Innovation Office (NKFIH NN 124904; 2018-1.2.1-NKP-2018-00009). The ELI-ALPS project (GINOP-2.3.6-15-2015-00001) is supported by the European Union and co-financed by the European Regional Development Fund.

References

[1] Akhtar P, Zhang C, et al (2017) J Phys Chem Lett 8: 257–263