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Chlorophylls & Carotenoids: Colourful Molecules for Solar Energy Conversion, Photoprotection and Health

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Photochemistry".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 31635

Special Issue Editor

Prof. Dr. Leszek Fiedor

E-Mail Website
Guest Editor
Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Kraków, Poland
Interests: chlorophylls; carotenoids; chemical modifications; structure-function relationships; photophysics & photochemistry; primary photosynthetic reactions; photosensitization; photoprotection; photodynamic therapy

Special Issue Information

Dear Colleagues,

It is a great pleasure for me to have the privilege of writing the opening words for this Special Issue of Molecules with a focus on Chlorophylls and Carotenoids: Colorful Molecules for Solar Energy Conversion, Photoprotection, and Health. I would like to take this opportunity to cordially invite you to contribute to this publication. Chlorophylls and carotenoids, as the major photosynthetic pigments, are still fascinating, in spite, or better, thanks to over a century of very challenging and invigorating investigations. Generations of researchers have contributed piece by piece to show that these relatively simple natural compounds, chlorophylls–macrocyclic tetrapyrroles, and carotenoids–polyunsaturated isoprenoids, are very sophisticated and versatile biological photodevices, perfectly suited to carry out their native functions in photosynthesis and other biological processes. Further, they inspire and find many applications in a variety of fields, from solar energy conversion, through photoprotection and protection against reactive oxygen species, to photodynamic therapy.

These colorful molecules are full of surprises. For instance, we have recently learnt that chlorophylls can no longer be regarded as coordination complexes of Mg2+ and that this centrally bound cation activates intrinsic photoprotective mechanisms in them. By contrast, the molecular symmetry plays no role in the photophysics of Crts, but the mechanisms responsible for the complete inactivity of their S1 state remain to be elucidated, both experimentally and theoretically. In this  Special Issue all aspects of molecular mechanisms which determine the (photo)chemical, photophysical and biochemical features of chlorophylls and carotenoids, and the intra- and intermolecular factors that control their functioning in natural and artificial systems can be represented. Previously unpublished manuscripts that report new results on the molecular mechanisms of pigments’ photochemistry, their functioning, and the structure–function/ structure–activity relationships are mostly welcome for this Special Issue.

Prof. Dr. Leszek Fiedor
Guest Editor

Manuscript Submission Information

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Keywords

  • Molecular mechanisms of natural and artificial solar energy conversion
  • (Photo)chemistry and biochemistry of chlorophylls and carotenoids
  • Health-related applications of chlorophylls and carotenoids

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Published Papers (7 papers)

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Research

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15 pages, 26289 KiB  
Article
Carotenoids Do Not Protect Bacteriochlorophylls in Isolated Light-Harvesting LH2 Complexes of Photosynthetic Bacteria from Destructive Interactions with Singlet Oxygen
by Zoya K. Makhneva, Maksim A. Bolshakov and Andrey A. Moskalenko
Molecules 2021, 26(17), 5120; https://doi.org/10.3390/molecules26175120 - 24 Aug 2021
Cited by 12 | Viewed by 2854
Abstract
The effect of singlet oxygen on light-harvesting (LH) complexes has been studied for a number of sulfur (S+) and nonsulfur (S−) photosynthetic bacteria. The visible/near-IR absorption spectra of the standard LH2 complexes (B800-850) of Allochromatium (Alc.) vinosum [...] Read more.
The effect of singlet oxygen on light-harvesting (LH) complexes has been studied for a number of sulfur (S+) and nonsulfur (S−) photosynthetic bacteria. The visible/near-IR absorption spectra of the standard LH2 complexes (B800-850) of Allochromatium (Alc.) vinosum (S+), Rhodobacter (Rba.) sphaeroides (S−), Rhodoblastus (Rbl.) acidophilus (S−), and Rhodopseudomonas (Rps.) palustris (S−), two types LH2/LH3 (B800-850 and B800-830) of Thiorhodospira (T.) sibirica (S+), and an unusual LH2 complex (B800-827) of Marichromatium (Mch.) purpuratum (S+) or the LH1 complex from Rhodospirillum (Rsp.) rubrum (S−) were measured in aqueous buffer suspensions in the presence of singlet oxygen generated by the illumination of the dye Rose Bengal (RB). The content of carotenoids in the samples was determined using HPLC analysis. The LH2 complex of Alc. vinosum and T. sibirica with a reduced content of carotenoids was obtained from cells grown in the presence of diphenylamine (DPA), and LH complexes were obtained from the carotenoidless mutant of Rba. sphaeroides R26.1 and Rps. rubrum G9. We found that LH2 complexes containing a complete set of carotenoids were quite resistant to the destructive action of singlet oxygen in the case of Rba. sphaeroides and Mch. purpuratum. Complexes of other bacteria were much less stable, which can be judged by a strong irreversible decrease in the bacteriochlorophyll (BChl) absorption bands (at 850 or 830 nm, respectively) for sulfur bacteria and absorption bands (at 850 and 800 nm) for nonsulfur bacteria. Simultaneously, we observe the appearance of the oxidized product 3-acetyl-chlorophyll (AcChl) absorbing near 700 nm. Moreover, a decrease in the amount of carotenoids enhanced the spectral stability to the action of singlet oxygen of the LH2 and LH3 complexes from sulfur bacteria and kept it at the same level as in the control samples for carotenoidless mutants of nonsulfur bacteria. These results are discussed in terms of the current hypothesis on the protective functions of carotenoids in bacterial photosynthesis. We suggest that the ability of carotenoids to quench singlet oxygen (well-established in vitro) is not well realized in photosynthetic bacteria. We compared the oxidation of BChl850 in LH2 complexes of sulfur bacteria under the action of singlet oxygen (in the presence of 50 μM RB) or blue light absorbed by carotenoids. These processes are very similar: {[BChl + (RB or carotenoid) + light] + O2} → AcChl. We speculate that carotenoids are capable of generating singlet oxygen when illuminated. The mechanism of this process is not yet clear. Full article
(This article belongs to the Special Issue Chlorophylls & Carotenoids: Colourful Molecules for Solar Energy Conversion, Photoprotection and Health)
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16 pages, 3412 KiB  
Article
Limitations of Linear Dichroism Spectroscopy for Elucidating Structural Issues of Light-Harvesting Aggregates in Chlorosomes
by Lisa M. Günther, Jasper Knoester and Jürgen Köhler
Molecules 2021, 26(4), 899; https://doi.org/10.3390/molecules26040899 - 9 Feb 2021
Cited by 7 | Viewed by 2862
Abstract
Linear dichroism (LD) spectroscopy is a widely used technique for studying the mutual orientation of the transition-dipole moments of the electronically excited states of molecular aggregates. Often the method is applied to aggregates where detailed information about the geometrical arrangement of the monomers [...] Read more.
Linear dichroism (LD) spectroscopy is a widely used technique for studying the mutual orientation of the transition-dipole moments of the electronically excited states of molecular aggregates. Often the method is applied to aggregates where detailed information about the geometrical arrangement of the monomers is lacking. However, for complex molecular assemblies where the monomers are assembled hierarchically in tiers of supramolecular structural elements, the method cannot extract well-founded information about the monomer arrangement. Here we discuss this difficulty on the example of chlorosomes, which are the light-harvesting aggregates of photosynthetic green-(non) sulfur bacteria. Chlorosomes consist of hundreds of thousands of bacteriochlorophyll molecules that self-assemble into secondary structural elements of curved lamellar or cylindrical morphology. We exploit data from polarization-resolved fluorescence-excitation spectroscopy performed on single chlorosomes for reconstructing the corresponding LD spectra. This reveals that LD spectroscopy is not suited for benchmarking structural models in particular for complex hierarchically organized molecular supramolecular assemblies. Full article
(This article belongs to the Special Issue Chlorophylls & Carotenoids: Colourful Molecules for Solar Energy Conversion, Photoprotection and Health)
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13 pages, 1640 KiB  
Article
Stability of Chlorophyll a Monomer Incorporated into Cremophor EL Nano-Micelles under Dark and Moderate Light Conditions
by Ewa Janik-Zabrotowicz, Marta Arczewska, Patrycja Prochniewicz, Izabela Świetlicka and Konrad Terpiłowski
Molecules 2020, 25(21), 5059; https://doi.org/10.3390/molecules25215059 - 30 Oct 2020
Cited by 9 | Viewed by 2456
Abstract
In this paper, stability of chlorophyll a monomers encapsulated into the Cremophor EL nano-micelles was studied under dark and moderate light conditions, typical of a room with natural or artificial lighting, in the presence of oxygen. The pigment stability against visible light was [...] Read more.
In this paper, stability of chlorophyll a monomers encapsulated into the Cremophor EL nano-micelles was studied under dark and moderate light conditions, typical of a room with natural or artificial lighting, in the presence of oxygen. The pigment stability against visible light was determined using the dynamic light scattering and molecular spectroscopy (UV-Vis absorption and stationary fluorescence) methods. Chlorophyll a, at the molar concentration of 10−5 M, was dissolved in the 5 wt% Cremophor emulsion for comparison in the ethanolic solution. The stability of such a self-assembly pigment–detergent nano-system is important in the light of its application on the commercial-scale. The presented results indicate the high stability of the pigment monomeric molecular organization in the nano-emulsion. During the storage in the dark, the half-lifetime was calculated as about 7 months. Additionally, based on the shape of absorption and fluorescence emission spectra, chlorophyll aggregation in the Cremophor EL aqueous solution along with the time was excluded. Moreover, the average size of detergent micelles as chlorophyll carriers was not affected after 70 days of the nano-system storage. Pigment stability against the moderate white light (0.1 mW) did not differ significantly from storage conditions in the dark. The photooxidation products, detected by occurrence of new absorption and fluorescence emission bands, was estimated on the negligible level. The stability of such a self-assembly pigment–detergent nano-system would potentially broaden the field of chlorophyll a (chl a) application in the food industry, medicine or artificial photosynthesis models. Full article
(This article belongs to the Special Issue Chlorophylls & Carotenoids: Colourful Molecules for Solar Energy Conversion, Photoprotection and Health)
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13 pages, 2344 KiB  
Article
Establishment of the Qy Absorption Spectrum of Chlorophyll a Extending to Near-Infrared
by Kristjan Leiger, Juha Matti Linnanto and Arvi Freiberg
Molecules 2020, 25(17), 3796; https://doi.org/10.3390/molecules25173796 - 20 Aug 2020
Cited by 6 | Viewed by 3377
Abstract
A weak absorption tail related to the Qy singlet electronic transition of solvated chlorophyll a is discovered using sensitive anti-Stokes fluorescence excitation spectroscopy. The quasi-exponentially decreasing tail was, at ambient temperature, readily observable as far as −2400 cm−1 from the absorption [...] Read more.
A weak absorption tail related to the Qy singlet electronic transition of solvated chlorophyll a is discovered using sensitive anti-Stokes fluorescence excitation spectroscopy. The quasi-exponentially decreasing tail was, at ambient temperature, readily observable as far as −2400 cm−1 from the absorption peak and at relative intensity of 10−7. The tail also weakened rapidly upon cooling the sample, implying its basic thermally activated nature. The shape of the spectrum as well as its temperature dependence were qualitatively well reproduced by quantum chemical calculations involving the pigment intramolecular vibrational modes, their overtones, and pairwise combination modes, but no intermolecular/solvent modes. A similar tail was observed earlier in the case of bacteriochlorophyll a, suggesting generality of this phenomenon. Long vibronic red tails are, thus, expected to exist in all pigments of light-harvesting relevance at physiological temperatures. Full article
(This article belongs to the Special Issue Chlorophylls & Carotenoids: Colourful Molecules for Solar Energy Conversion, Photoprotection and Health)
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Review

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24 pages, 6219 KiB  
Review
Photosynthetic Light-Harvesting (Antenna) Complexes—Structures and Functions
by Heiko Lokstein, Gernot Renger and Jan P. Götze
Molecules 2021, 26(11), 3378; https://doi.org/10.3390/molecules26113378 - 3 Jun 2021
Cited by 64 | Viewed by 7661
Abstract
Chlorophylls and bacteriochlorophylls, together with carotenoids, serve, noncovalently bound to specific apoproteins, as principal light-harvesting and energy-transforming pigments in photosynthetic organisms. In recent years, enormous progress has been achieved in the elucidation of structures and functions of light-harvesting (antenna) complexes, photosynthetic reaction centers [...] Read more.
Chlorophylls and bacteriochlorophylls, together with carotenoids, serve, noncovalently bound to specific apoproteins, as principal light-harvesting and energy-transforming pigments in photosynthetic organisms. In recent years, enormous progress has been achieved in the elucidation of structures and functions of light-harvesting (antenna) complexes, photosynthetic reaction centers and even entire photosystems. It is becoming increasingly clear that light-harvesting complexes not only serve to enlarge the absorption cross sections of the respective reaction centers but are vitally important in short- and long-term adaptation of the photosynthetic apparatus and regulation of the energy-transforming processes in response to external and internal conditions. Thus, the wide variety of structural diversity in photosynthetic antenna “designs” becomes conceivable. It is, however, common for LHCs to form trimeric (or multiples thereof) structures. We propose a simple, tentative explanation of the trimer issue, based on the 2D world created by photosynthetic membrane systems. Full article
(This article belongs to the Special Issue Chlorophylls & Carotenoids: Colourful Molecules for Solar Energy Conversion, Photoprotection and Health)
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26 pages, 9386 KiB  
Review
Zeaxanthin, a Molecule for Photoprotection in Many Different Environments
by Barbara Demmig-Adams, Jared J. Stewart, Marina López-Pozo, Stephanie K. Polutchko and William W. Adams III
Molecules 2020, 25(24), 5825; https://doi.org/10.3390/molecules25245825 - 10 Dec 2020
Cited by 62 | Viewed by 7565
Abstract
Conversion of sunlight into photochemistry depends on photoprotective processes that allow safe use of sunlight over a broad range of environmental conditions. This review focuses on the ubiquity of photoprotection associated with a group of interconvertible leaf carotenoids, the xanthophyll cycle. We survey [...] Read more.
Conversion of sunlight into photochemistry depends on photoprotective processes that allow safe use of sunlight over a broad range of environmental conditions. This review focuses on the ubiquity of photoprotection associated with a group of interconvertible leaf carotenoids, the xanthophyll cycle. We survey the striking plasticity of this process observed in nature with respect to (1) xanthophyll cycle pool size, (2) degree and speed of interconversion of its components, and (3) flexibility in the association between xanthophyll cycle conversion state and photoprotective dissipation of excess excitation energy. It is concluded that the components of this system can be independently tuned with a high degree of flexibility to produce a fit for different environments with various combinations of light, temperature, and other factors. In addition, the role of genetic variation is apparent from variation in the response of different species growing side-by-side in the same environment. These findings illustrate how field studies can generate insight into the adjustable levers that allow xanthophyll cycle-associated photoprotection to support plant photosynthetic productivity and survival in environments with unique combinations of environmental factors. Full article
(This article belongs to the Special Issue Chlorophylls & Carotenoids: Colourful Molecules for Solar Energy Conversion, Photoprotection and Health)
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Other

Jump to: Research, Review

9 pages, 548 KiB  
Perspective
Chlorophylls: A Personal Snapshot
by Hugo Scheer
Molecules 2022, 27(3), 1093; https://doi.org/10.3390/molecules27031093 - 7 Feb 2022
Cited by 10 | Viewed by 3899
Abstract
Chlorophylls provide the basis for photosynthesis and thereby most life on Earth. Besides their involvement in primary charge separation in the reaction center, they serve as light-harvesting and light-sensing pigments, they also have additional functions, e.g., in inter-system electron transfer. Chlorophylls also have [...] Read more.
Chlorophylls provide the basis for photosynthesis and thereby most life on Earth. Besides their involvement in primary charge separation in the reaction center, they serve as light-harvesting and light-sensing pigments, they also have additional functions, e.g., in inter-system electron transfer. Chlorophylls also have a wealth of applications in basic science, medicine, as colorants and, possibly, in optoelectronics. Considering that there has been more than 200 years of chlorophyll research, one would think that all has been said on these pigments. However, the opposite is true: ongoing research evidenced in this Special Issue brings together current work on chlorophylls and on their carotenoid counterparts. These introductory notes give a very brief and in part personal account of the history of chlorophyll research and applications, before concluding with a snapshot of this year’s publications. Full article
(This article belongs to the Special Issue Chlorophylls & Carotenoids: Colourful Molecules for Solar Energy Conversion, Photoprotection and Health)
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