Unraveling the Intrinsic Color of Chlorophyll

Milne, Bruce F.; Toker, Yoni; Rubio, Ángel; Nielsen, Steen Brøndsted

doi:10.1002/anie.201410899

Cited by 56 publications

(59 citation statements)

References 30 publications

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“…The electronic excitation spectral characteristics of isolated chlorophyll pigments exert peaks between 1.9–2.0 eV for the Q-band in a recent TD-DFT computational study 29 , while the experimental values in LHCII appear at 1.86 eV for the Q-band 57 . Higher energies are expected for in vacuo simulated spectra, as in vacuo experiments demonstrate a shift of the Q-band to 1.93 eV (chl-a) and 1.98 eV (chl-b) 58, 59 . In our study, following the ground-state geometry optimizations of the Chl 613/614 pairs at different conformations, their electronic excitation spectra ( Qy ) were derived (Table 2).…”

Section: Resultsmentioning

confidence: 84%

A pathway for protective quenching in antenna proteins of Photosystem II

Papadatos

Charalambous

Daskalakis

2017

Sci Rep

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Photosynthesis is common in nature, converting sunlight energy into proton motive force and reducing power. The increased spectral range absorption of light exerted by pigments (i.e. chlorophylls, Chls) within Light Harvesting Complexes (LHCs) proves an important advantage under low light conditions. However, in the exposure to excess light, oxidative damages and ultimately cell death can occur. A down-regulatory mechanism, thus, has been evolved (non-photochemical quenching, NPQ). The mechanistic details of its major component (qE) are missing at the atomic scale. The research herein, initiates on solid evidence from the current NPQ state of the art, and reveals a detailed atomistic view by large scale Molecular Dynamics, Metadynamics and ab initio Simulations. The results demonstrate a complete picture of an elaborate common molecular design. All probed antenna proteins (major LHCII from spinach-pea, CP29 from spinach) show striking plasticity in helix-D, under NPQ conditions. This induces changes in Qy bands in excitation and absorption spectra of the near-by pigment pair (Chl613-614) that could emerge as a new quenching site. Zeaxanthin enhances this plasticity (and possibly the quenching) even at milder NPQ conditions.

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Section: Resultsmentioning

confidence: 84%

A pathway for protective quenching in antenna proteins of Photosystem II

Papadatos

Charalambous

Daskalakis

2017

Sci Rep

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“…Thedifference in the first excitation energies of chlorophyll (for both the aand bforms) using the charge tags 1 + and 3 + was previously found to be less than 0.03 eV,a nd it was for this reason that in the present work only the simpler 1 + was employed in the theoretical calculations. [14] TheT D-DFT excitation energies together with the experimental band maxima are given in Table 1. Va lues for both dimer configurations are given because the energy difference between them was only 0.018 eVat the DFT/CAM-B3LYP/Def2-SVP level of theory,a nd so both can be expected to be significantly populated at 298 K. Thedistances between the two magnesium centers are 5.05 ( stacked configuration) and 19.04 ( linear configuration).…”

Section: Zuschriftenmentioning

confidence: 99%

“…[14,15] In this case,the absorption was obtained from the dissociation of the complex, and ac alibrated value was determined for the neutral molecule based on the deviation between theory and experiment. Using this same technique,Q-band maxima were obtained for Chl b, [14] and the Soret band was measured for both Chl aa nd Chl b. [15] Importantly,t he large difference in the absorption spectra of Chl aand Chl bwas concluded to be an intrinsic effect and not due to local hydrogen-bond interactions with the formyl group of Chl b, for example, clearly demonstrating the advantage of looking at isolated molecules.Compared to literature values for Chl in avariety of natural protein complexes,a bsorption in vacuo was found to be blue-shifted by 50 nm.…”

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confidence: 99%

“…[14,15] Thee xperimental setup has been described in detail elsewhere. [21,22] Chl a( provided by Sigma-Aldrich) was dissolved in methanol, and salts of either tetramethylammonium (1 + )o ra cetylcholine (3 + )w ere added (see Figure 1).…”

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confidence: 99%

“…Numbering of the cationic tags chosen to be consistent with our previous related work on Chl spectra. [14,15] …”

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confidence: 99%

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On the Exciton Coupling between Two Chlorophyll Pigments in the Absence of a Protein Environment: Intrinsic Effects Revealed by Theory and Experiment

et al. 2016

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Exciton coupling between two or more chlorophyll (Chl) pigments is ak ey mechanism associated with the color tuning of photosynthetic proteins but it is difficult to disentangle this effect from shifts that are due to the protein microenvironment. Herein, we report the formation of the simplest coupled system, the Chl adimer,tagged with aquaternary ammonium ion by electrospray ionization. Based on action spectroscopic studies in vacuo,t he dimer complexes were found to absorb 50-70 meV to the red of the monomers under the same conditions.First-principles calculations predict shifts that somewhat depend on the relative orientation of the two Chl units,namely 50 and 30 meV for structures where the Chl rings are stacked and unstacked, respectively.O ur work demonstrates that Chl association alone can produce al arge portion of the color shift observed in photosynthetic macromolecular assemblies.The absorption wavelengths of chlorophyll (Chl) molecules are modulated by the microenvironment surrounding each pigment molecule.I nt his way,n ature has evolved am ethod by which the coverage of the optical spectrum and the subsequent transfer of the absorbed energy is optimized, [1,2] leading to photon energy conversion efficiencies of 95 %i n photosynthetic systems.[3] Theh arvesting of light energy in photosynthesis is therefore far more efficient than anything thus far developed by our most cutting-edge scientific and technological efforts.Furthermore,small modifications to the basic Chl structure,for example,the replacement of amethyl group in Chl awith aformyl group in Chl b, also lead to some fine-tuning of the absorption spectra. [4] Ford ecades ag reat deal of research activity has been directed at understanding precisely how natural systems modulate the absorption energies of Chl species.T he highly complex nature of the macromolecular systems involved has, however, always served to complicate such attempts.Inrecent years,experimental approaches have been joined by theoretical/computational methods,and this has permitted studies at levels of detail that were previously unattainable. [5][6][7][8][9][10][11][12] Experimental methods have also continued to develop, and recently it has become possible to study absorption processes in Chl molecules free of solvent and other microenvironmental effects.Inpioneering experiments,Shafizadeh et al.[13] utilized two-color pump-probe spectroscopy to measure the lowest energy absorption band of neutral Chl a evaporated from spinach leaves.T hey found the origin band of the Q y transition to be at 647 nm. Recent action spectroscopy experiments on Chl at agged with quaternary ammonium cations,i nc ombination with theory,p rovided an absorption band maximum of similar value (642 nm). [14,15] In this case,the absorption was obtained from the dissociation of the complex, and ac alibrated value was determined for the neutral molecule based on the deviation between theory and experiment. Using this same technique,Q-band maxima were obtained for Chl b, [14] and the Soret ban...

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Intrinsic Photoprotective Mechanisms in Chlorophylls

2017

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Photosynthetic energy conversion competes with the formation of chlorophyll triplet states and the generation of reactive oxygen species.These may,especially under high light stress,d amage the photosynthetic apparatus.M any sophisticated photoprotective mechanisms have evolved to secure aharmless flow of excitation energy through the photosynthetic complexes.Time-resolved laser-induced optoacoustic spectroscopyw as used to compare the properties of the T 1 states of pheophytin aa nd its metallocomplexes.T he lowest quantum yield of the T 1 state is always observed in the Mg complex, which also shows the least efficient energy transfer to O 2 .Axial coordination to the central Mg further lowers the yield of both T 1 and singlet oxygen. These results reveal the existence of intrinsic photoprotective mechanisms in chlorophylls,e mbedded in their molecular design, which substantially suppress the formation of triplet states and the efficiency of energy transfer to O 2 ,e achb y2 0-25 %. Such intrinsic photoprotective effects must have created al arge evolutionary advantage for the Mg complexes during their evolution as the principal photoactive cofactors of photosynthetic proteins.

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Unraveling the Intrinsic Color of Chlorophyll

Cited by 56 publications

References 30 publications

A pathway for protective quenching in antenna proteins of Photosystem II

A pathway for protective quenching in antenna proteins of Photosystem II

On the Exciton Coupling between Two Chlorophyll Pigments in the Absence of a Protein Environment: Intrinsic Effects Revealed by Theory and Experiment

Intrinsic Photoprotective Mechanisms in Chlorophylls

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