Tomás Polívka

University of South Bohemia in České Budějovice · Department of Physics

This work examines the influence of applied external voltage in bulk electrolysis on the excited‐state properties of 8′‐apo‐β‐carotenal in acetonitrile by steady‐state and ultrafast time‐resolved absorption spectroscopy. The data collected under bulk electrolysis were compared with those taken without applied voltage. The steady‐state measurements...

The excited states of carotenoids have been a subject of numerous studies. While a majority of these reports target the excited state dynamics initiated by the excitation of the S2 state, the upper excited state(s) absorbing in the UV spectral region (denoted as SUV) has been only scarcely studied. Moreover, the relation between the SUV and Sn, the...

The invention of the laser in 1960 gave us the ruby laser, which generally produced chaotic pulses of light. Six years later, in 1966, a concept called passive mode-locking applied to neodymium-glass lasers produced reasonably well-behaving picosecond pulses. This triggered an intense activity, with respect to developing improved laser pulse source...

The functions of both (bacterio) chlorophylls and carotenoids in light-harvesting complexes have been extensively studied during the past decade, yet, the involvement of BChl a high-energy Soret band in the cascade of light-harvesting processes still remains a relatively unexplored topic. Here, we present transient absorption data recorded after ex...

Phycobilisome (PBS) structures are elaborate antennae in cyanobacteria and red algae1,2. These large protein complexes capture incident sunlight and transfer the energy through a network of embedded pigment molecules called bilins to the photosynthetic reaction centres. However, light harvesting must also be balanced against the risks of photodamag...

Carotenoids are an integral part of natural photosynthetic complexes, with tasks ranging from light harvesting to photoprotection. Their underlying energy deactivation network of optically dark and bright excited states is extremely efficient: after excitation of light with up to 2.5 eV of photon energy, the system relaxes back to ground state on a...

Phototrophic Gemmatimonadetes evolved the ability to use solar energy following horizontal transfer of photosynthesis-related genes from an ancient phototrophic proteobacterium. The electron cryo-microscopy structure of the Gemmatimonas phototrophica photosystem at 2.4 Å reveals a unique, double-ring complex. Two unique membrane-extrinsic polypepti...

Higher plants defend themselves from bursts of intense light via the mechanism of Non-Photochemical Quenching (NPQ). It involves the Photosystem II (PSII) antenna protein (LHCII) adopting a conformation that favors excitation quenching. In recent years several structural models have suggested that quenching proceeds via energy transfer to the optic...

The Cover Feature shows the carotenoid canthaxanthin (top) that is bound to orange carotenoid protein (OCP) and helical carotenoid protein (HCP) complexes depicted in the background of the orange (OCP) and purple (HCP) graphs. The transient absorption spectra obtained after visible‐light (green) or UV‐light (black) excitations demonstrate the diffe...

Life on Earth depends on photosynthesis, the conversion of light energy into chemical energy. Plants collect photons by light harvesting complexes (LHC)—abundant membrane proteins containing chlorophyll and xanthophyll molecules. LHC-like proteins are similar in their amino acid sequence to true LHC antennae, however, they rather serve a photoprote...

Photoprotection is an essential mechanism in photosynthetic organisms to balance the harvesting of light energy against the risks of photodamage. In cyanobacteria, photoprotective non-photochemical quenching relies on the interaction between a photoreceptor, the Orange Carotenoid Protein (OCP), and the antenna, the phycobilisome (PBS). Here we repo...

The phycobilisome is an elaborate antenna that is responsible for light-harvesting in cyanobacteria and red-algae. This large macromolecular complex captures incident sunlight and transfers the energy via a network of pigment molecules called bilins to the photosynthetic reaction centers. The phycobilisome of the model organism Synechocystis PCC 68...

Higher plants defend themselves from bursts of intense light via the mechanism of Non-Photochemical Quenching (NPQ). It involves the Photosystem II (PSII) antenna protein (LHCII) adopting a conformation that favours excitation quenching. In recent years several structural models have suggested that quenching proceeds via energy transfer to the opti...

Over the last decade the orange carotenoid protein (OCP) gained attention due to its role in photoprotection in cyanobacteria. Recently, other carotenoid binding proteins such as helical carotenoid proteins (HCPs) have been identified and characterized, although the function of the HCPs is not yet clarified. Here we have examined OCP1 and two HCPs,...

Here, we propose a possible photoactivation mechanism of a 35-kDa blue light-triggered photoreceptor, the Orange Carotenoid Protein (OCP), suggesting that the reaction involves the transient formation of a protonated ketocarotenoid (oxocarbenium cation) state. Taking advantage of engineering an OCP variant carrying the Y201W mutation, which shows s...

Femtosecond transient absorption spectroscopy following two-photon excitation (2PE) is used to determine the contributions of carotenoids and chlorophylls to the 2PE signals in the main plant light-harvesting complex (LHCII). For 2PE, excitation at 1210 and 1300 nm was used, being within the known 2PE profile of LHCII. At both excitation wavelength...

Carotenoids are molecules with rich photophysics that are in many biological systems involved in photoprotection. Yet, their response to excess energy excitation is only scarcely studied. Here we have explored excited state properties of three keto‐carotenoids, echinenone, canthaxanthin and rhodoxanthin after excess energy excitation to a singlet s...

We present the first examples of alkylated derivatives of the macropolyhedral boron hydride, anti-B18H22, which is the gain medium in the first borane laser. This new series of ten highly stable and colorless organic-inorganic hybrid clusters are capable of the conversion of UVA irradiation to blue light with fluorescence quantum yields of unity. T...

Xanthophylls in light harvesting complexes perform a number of functions ranging from structural support to light-harvesting and photoprotection. In the major light harvesting complex of photosystem II in plants (LHCII), the innermost xanthophyll binding pockets are occupied by lutein molecules. The conservation of these sites within the LHC protei...

The major light-harvesting complex of photosystem II (LHCII) is the main contributor to sunlight energy harvesting in plants. The flexible design of LHCII underlies a photoprotective mechanism whereby this complex switches to a dissipative state in response to high light stress, allowing the rapid dissipation of excess excitation energy (NPQ). In t...

Steady-state and transient absorption spectra with <50 fs time resolution were obtained for two conjugated polymers, both with >200 conjugated double bonds (N), constrained in planar, stable, polyene frameworks. Solutions of the polymers exhibit the same S2 → S1 → S* → S0 decay pathway observed for the N = 11-19 polyene oligomers and for zeaxanthin...

Photosynthetic organisms had to evolve diverse mechanisms of light-harvesting to supply photosynthetic apparatus with enough energy. Cryptophytes represent one of the groups of photosynthetic organisms combining external and internal antenna systems. They contain one type of immobile phycobiliprotein located at the lumenal side of the thylakoid mem...

Recently a new family of carotenoproteins, homologs of the N-terminal domain of the orange carotenoid protein (NTD-OCP) have been identified in cyanobacteria. These homologs are called helical carotenoid proteins (HCPs) as they are all predicted to maintain the all-helical structure of the NTD-OCP and to bind carotenoid. Here, HCP2 and HCP3 isolate...

We used ultrafast transient absorption spectroscopy to study excited-state dynamics of two keto-carotenoids, siphonaxanthin and siphonein. These two carotenoids differ in the presence of dodecanoyl-oxy group in siphonein, which is attached to the C19 carbon on the same side of the molecule as the conjugated keto group. We show that this dodecanoyl-...

The keto-carotenoid deinoxanthin, which occurs in UV-resistant bacterium Deinococcus radiodurans, has been investigated by ultrafast time-resolved spectroscopic techniques. We have explored excited-state properties of deinoxanthin in solution and bound to the S-layer Deinoxanthin Binding Complex (SDBC), a protein complex important for UV resistance...

The orange carotenoid protein (OCP) is a structurally and functionally modular photoactive protein involved in cyanobacterial photoprotection. Recently, based on bioinformatic analysis and phylogenetic relationships, new families of OCP have been described, OCP2 and OCPx. The first characterization of the OCP2 showed both faster photoconversion and...

Chlorophyll triplet excited states are by-products of photosynthetic processes that can indirectly harm biological membranes by forming highly reactive oxygen species. A crucial photoprotective mechanism evolved by plants to counter this threat involves the triplet energy transfer from chlorophylls to carotenoid molecules, which triplet states are...

Carotenoids in photosynthetic light-harvesting proteins carry out the dual function of harvesting light and defending against high light by quenching excess energy. The latter involves the low-lying, dark, excited electronic state labelled S1. Here "dark" means optically-forbidden, a property that is often (in the photosynthetic field at least) vag...

In some molecular systems, such as nucleobases, polyenes or the active ingredients of sunscreens, substantial amounts of photo-excitation energy are dissipated on a sub-picosecond time scale, raising questions such as: where does this energy go or among which degrees of freedom it is being distributed at such early times? Here we use transient abso...

We have developed an experimental set-up allowing to measure transient absorption spectra of carotenoids after two-photon excitation (2PE), thereby exciting the lowest excited state S 1 directly. We have compared 2PE and 1PE data of three carotenoids, lycopene, β-carotene, and neurosporene. Compared to ‘standard’ 1PE, the transient absorption spect...

The Helical Carotenoid Proteins (HCPs) are a large group of newly identified carotenoid-binding proteins found in ecophysiologically diverse cyanobacteria. They likely evolved before becoming the effector (quenching) domain of the modular Orange Carotenoid Protein (OCP). The number of discrete HCP families—at least nine—suggests they are involved i...

Fucoxanthin-chlorophyll a protein from Emiliania huxleyi (E-FCP) is a member of the LHC family of light-harvesting proteins. It has rather unusual pigment composition as its binds more Chl-c than Chl-a, and 19’-hexanoyloxyfucoxanthin (hFx) as the main carotenoid instead of fucoxanthin (Fx) typically found in various FCP complexes. The presence of h...

Photosynthetic eukaryotes whose cells harbor plastids originating from secondary endosymbiosis of a red alga include species of major ecological and economic importance. Since utilization of solar energy relies on the efficient light-harvesting, one of the critical factors for the success of the red lineage in a range of environments is to be found...

Mimicking light‐harvesting and photoprotective processes of natural photosynthesis by artificial supramolecular systems is of considerable interest for artificial photosynthesis. The authors of the highlighted paper report on synthesis and spectroscopic characterization of a novel Pd‐phthalocyanine‐carotenoid dyads that allow to directly follow the...

To demonstrate the value of the multi-pulse method in revealing the nature of coupling between excited states and explore the environmental dependencies of S1 and ICT state equilibration, we performed ultrafast transient absorption pump-dump-probe and pump-repump-probe spectroscopies on fucoxanthin in various solvent conditions. The effects of pola...

Photoprotection is fundamental in photosynthesis to avoid oxidative photodamage upon excess light exposure. Excited chlorophylls (Chl) are quenched by carotenoids but the precise molecular origin remains controversial. The cyanobacterial HliC protein belongs to the Hlip family ancestral to plant light-harvesting complexes, and binds Chl a and β-car...

RC-LH1-PufX complexes from a genetically modified strain of Rhodobacter sphaeroides that accumulates carotenoids with very long conjugation were studied by ultrafast transient absorption spectroscopy. The complexes predominantly bind the carotenoid diketospirilloxanthin, constituting about 75% of the total carotenoids, which has 13 conjugated C=C b...

We used ultrafast transient absorption spectroscopy to study excited-state dynamics of the keto-carotenoid fucoxanthin (Fx) and its two derivatives: 19’-butanoyloxyfucoxanthin (bFx) and 19’-hexanoyloxyfucoxanthin (hFx). These derivatives occur in some light-harvesting systems of photosynthetic microorganisms and their presence is typically related...

We have applied femtosecond transient absorption spectroscopy in pump-probe and pump-dump-probe regimes to study energy transfer between fucoxanthin and Chl a in fucoxanthin-Chl a complex from the pennate diatom Phaeodactylum tricornutum. Experiments were carried out at room temperature and 77 K to reveal temperature dependence of energy transfer....

The majority of life on Earth depends directly or indirectly on the sun as a source of energy. The initial step of photosynthesis is facilitated by light-harvesting complexes, which capture and transfer light energy into the reaction centers (RCs). Here, we analyzed the organization of photosynthetic (PS) complexes in the bacterium G. phototrophica...

Detailed discussion of the BChl a stoichiometry in PS complex. BChl, bacteriochlorophyll; PS, photosynthetic. (DOC)

Flash-induced absorbance spectra of purified photosynthetic complexes of G. phototrophica. As expected for the type 2 RC, the signal is dominated by signatures of the oxidized primary donor (P870+): bleaching around 865 nm, electrochomic shift of the accessory BChl a around 800 nm and bleaching of the Qx band of the primary donor at 600 nm. BChl, b...

Parameters used for computation of the steady-state optical spectra of G. phototrophica PS complex. PS, photosynthetic. (PDF)

Absorption spectra of PS membranes from G. phototrophica (red) and R. rubrum (grey). PS, photosynthetic. (TIF)

Upper panel: size exclusion chromatography of the partially purified PS complexes from G. phototrophica. The blue line recorded at 820 nm shows the fraction with the purified complex, and the red trace at 490 nm represent the carotenoids. Lower panel: the absorption spectrum of the obtained complex (blue) and the spectrum of the “free” carotenoids...

Example of a raw TEM image of G. phototrophica complexes. TEM, transmission electron microscopy. (TIF)

PS complex of G. phototrophica analyzed by native and SDS polyacrylamide gel electrophoresis. (A) Clear-native gel electrophoresis of G. phototrophica membrane complexes in comparison with membrane complexes of R. rubrum and Synechocystis sp. PCC 6803; the membranes were solubilized using 2% dodecyl-β-maltoside and loaded on 4%–14% clear-native gel...

BChl a fluorescence induction and relaxation recorded using the kinetic fluorometer FL-3000 (Photon Systems Instruments Ltd., Brno, Czech Republic). The BChl fluorescence induction transient was elicited by a 140 μs-long square-wave pulse of light with an intensity of approximately 0.1 mol photon m−2s−1 provided by an array of blue-green 505 nm Lux...

Estimated angular distance between neighboring subunits of the PS complex. The angle was measured as shown in the insert. The data were derived from 23 measurements from 4 individual complex images. PS, photosynthetic. (TIF)

The spectro-temporal datasets obtained from the measurements were analyzed globally by fitting package DAFit (Pascher Instruments). To visualize the excited state dynamics, we assumed that the excited states evolved according to a sequential, irreversible scheme A → B, B → C, C → D. The arrows represent increasingly slower processes and the time co...

Comparison of B816 and B868 absorption bands. Red line: absorption spectrum of G. phototrophica PS complex. Grey area: absorption spectrum of R. rubrum complex scaled and blue-shifted to match the B868 band. Blue area: the difference between the red and grey spectra, corresponds to the pure spectrum of the B816 absorption band. The ratio of B816 an...

Ultrafast transient absorption spectroscopy and single-wavelength anisotropy measurements were used to study the effect of isomerization on the excited-state properties of fucoxanthin in polar and non-polar solvents. The excitation wavelengths were 477 nm for the all-trans fucoxanthin and 333 nm and 477 nm, respectively, for the cis-fucoxanthin. Al...

Properties of the S1 state of neurosporene, spheroidene and lycopene were studied after excess energy excitation in the S2 state. Excitation of carotenoids into higher vibronic levels of the S2 state generates excess vibrational energy in the S1 state. The vibrationally hot S1 state relaxes faster when carotenoid is excited into the S2 state with e...

Cyanobacteria possess a family of one-helix high-light-inducible proteins (Hlips) that are homologous to light-harvesting antenna of plants and algae. An Hlip protein, high light inducible protein D (HliD) purified as a small complex with the Ycf39 protein is evaluated using resonance Raman spectroscopy. We show that the HliD binds two different β-...

A quenching mechanism mediated by the orange carotenoid protein (OCP) is one of the ways cyanobacteria protect themselves against photooxidative stress. Here, we present a femtosecond spectroscopic study comparing OCP and RCP (red carotenoid protein) samples binding different carotenoids. We confirmed significant changes in carotenoid configuration...

Plants harvest photons for photosynthesis using light-harvesting complexes (LHCs)-an array of chlorophyll proteins that can reversibly switch from harvesting to energy-dissipation mode to prevent over-excitation and damage of the photosynthetic apparatus. In unicellular algae and lower plants this process requires the LHCSR proteins which senses ov...

In π-conjugated chain molecules such as carotenoids, coupling between electronic and vibrational degrees of freedom is of central importance. It governs both dynamic and static properties, such as the timescales of excited state relaxation as well as absorption spectra. In this work, we treat vibronic dynamics in carotenoids on four electronic stat...

A new method for recording femtosecond stimulated Raman spectra was developed that dramatically improves and automatizes baseline problems. Instead of using a narrowband Raman source, the experiment is performed using shaping of a broadband source. This allows locking the signal into carefully crafted watermarks that can be recovered from measured...

Chl synthase (ChlG) is an important enzyme of the Chl biosynthetic pathway catalyzing attachment of phytol/geranylgeraniol tail to the chlorophyllide molecule. Here we have investigated the Flag-tagged ChlG (f.ChlG) in a complex with two different high-light inducible proteins (Hlips) HliD and HliC. The f.ChlG-Hlips complex binds a Chl a and three...

Octadecaoctaenal is a psittacofulvin pigment associated with the bright red coloration of parrots. It consists of a linear polyene chain terminated by an aldehyde group and therefore provides an opportunity to examine the fundamental factors controlling the excited state ordering and dynamics of polyenals. Steady-state and ultrafast time-resolved s...

Room temperature transient absorption spectroscopy with nanosecond resolution was used to study quenching of the chlorophyll triplet states by carotenoids in two light-harvesting complexes of the dinoflagellate Amphidinium carterae: the water soluble peridinin-chlorophyll protein complex and intrinsic, membrane chlorophyll a - chlorophyll c2 – peri...