Carotenoid Molecules Research Articles

Singlet-triplet fission of carotenoid excitation in the purple phototrophic bacteria Thermochromatium tepidum

Confirmation of intermolecular mechanism of excitation fission involving two carotenoid molecules in the purple phototrophic bacteria Thermochromatium tepidum is obtained.

Singlet-triplet Fission of Carotenoid Excitation in the Purple Phototrophic Bacteria Thermochromatium tepidum.

Singlet fission of carotenoid excitation is studied in purple phototrophic bacterium Thermochromatium tepidum. Using time-resolved EPR and magnetic field-induced modulation of fluorescence yield it is shown that the concept of intramolecular excitation fission developed in a number of publications is not supported by the experimental results. The obtained data favor intermolecular fission mechanism involving two carotenoid molecules.

Carotenoids in Photosynthesis: The Revenge of the “Accessory” Pigments

The subtle details of energy transport in light-harvesting complexes remain still mostly unknown, especially in the ultrafast regime. In this issue of Chem, Schlau-Cohen and co-workers employ 2D spectroscopy to unveil the unforeseen role of a carotenoid molecule in the optimization of the energy flow among pigments.

LHC-like proteins involved in stress responses and biogenesis/repair of the photosynthetic apparatus.

LHC (light-harvesting complex) proteins of plants and algae are known to be involved both in collecting light energy for driving the primary photochemical reactions of photosynthesis and in photoprotection when the absorbed light energy exceeds the capacity of the photosynthetic apparatus. These proteins usually contain three transmembrane (TM) helices which span the thylakoid membranes and bind several chlorophyll, carotenoid and lipid molecules. In addition, the LHC protein family includes LHC-like proteins containing one, two, three or even four TM domains. One-helix proteins are not only present in eukaryotic photosynthetic organisms but also in cyanobacteria where they have been named high light-inducible proteins. These small proteins are probably the ancestors of the members of the extant LHC protein family which arouse through gene duplications, deletions and fusions. During evolution, some of these proteins have diverged and acquired novel functions. In most cases, LHC-like proteins are induced in response to various stress conditions including high light, high salinity, elevated temperature and nutrient limitation. Many of these proteins play key roles in photoprotection, notably in non-photochemical quenching of absorbed light energy. Moreover, some of these proteins appear to be involved in the regulation of chlorophyll synthesis and in the assembly and repair of Photosystem II and also of Photosystem I possibly by mediating the insertion of newly synthesized pigments into the photosynthetic reaction centers.

Nonlinear correlations between ν1 Raman band and global scalar properties for different length carotenoids

The Raman ν1 band corresponding to the polarization of various length carotenoid (Car) and polyene molecules was theoretically analysed using the density functional theory (DFT) approach. The polarization and other properties of Car and polyene monomers were estimated by using global scalar properties. The results demonstrate a linear dependence between the frequency of the so-called ν1 Raman band corresponding to the C=C stretching modes, and the global hardness (and global softness) for all molecules of different conjugation lengths. Linear correlations between all global scalar properties and the conjugation length were for polyene structures only. From these calculations an additional relationship was also identified: upon s-cis-isomerisation the effective conjugation length and global softness increased for polyenes, while the effective conjugation length and global softness decreased for carotenoids containing β-rings at their ends. According to the electrophilicity index study, charge transfer processes (CT) should be favourable in longer carotenoid and polyene structures. A linear dependence of electronegativity was found for polyene and particular Cars subgroups. The electrophilicity index was very sensitive to special groups bonded to the polyene chain of Cars. Finally, the conjugation length of the Cars did not have a linear dependence on the electronegativity, chemical potential and electrophilicity index, but almost a linear dependence was seen on the global hardness while the polyene models had a linear dependence in all cases.

Retinal-Salinixanthin Interactions in a Thermophilic Rhodopsin.

In microbial rhodopsins (also called retinal proteins), the retinal chromophore is used for harvesting light. A carotenoid molecule has been reported to complement the retinal as light harvesting antenna in bacterial retinal proteins, although examples are scarce. In this paper, we present the formation of a novel antenna complex between thermophilic rhodopsin (TR) and the carotenoid salinixanthin (Sal). The complex formation and its structure were studied using UV-visible absorption as well as circular dichroism (CD) spectroscopies. Our studies indicate that the complex is formed in both the trimeric and monomeric forms of TR. CD spectroscopy suggests that excitonic coupling takes place between retinal and Sal. The binding of Sal with artificial TR pigments derived from synthetic retinal analogues further supports the contribution of the retinal chromophore to the CD spectrum. These studies further support the possibility of interaction between the 4-keto ring of the Sal and the retinal in TR-Sal complexes. Temperature-dependent CD spectra indicate that the positive band (ca. 482 nm) of the bisignate CD spectra of the studied complexes originates from the contribution of excitonic coupling and induced chirality of Sal in the protein binding site. The presence of a relatively smaller glycine residue in the vicinity of the retinal chromophore in TR is proposed to be crucial for binding with Sal. The results are expected to shed light on the mechanism of retinal-carotenoid interactions in other biological systems.

The Influence of the Number of Conjugated Double Bonds in Carotenoid Molecules on the Energy Transfer Efficiency to Bacteriochlorophyll in Light-Harvesting Complexes LH2 from Allochromatium vinosum Strain MSU.

Seven different carotenoids with the number of conjugated double bonds (N) from 5 to 11 were incorporated in vitro into carotenoidless complexes LH2 of the sulfur bacterium Allochromatium vinosum strain MSU. The efficiency of their incorporation varied from 4 to 99%. The influence of N in the carotenoid molecules on the energy transfer efficiency from these pigments to bacteriochlorophyll (BChl) in the modified LH2 complexes was studied for the first time. The highest level of energy transfer was recorded for rhodopin (N = 11) and neurosporene (N = 7) (37 and 51%, respectively). In the other carotenoids, this parameter ranged from 11 to 33%. In the LH2 complexes studied, we found no direct correlation between the decrease in N in carotenoids and increase in the energy transfer efficiency from these pigments to BChl.

The Effect of the Number of Conjugated Double Bonds in Carotenoid Molecules on the Efficiency of Energy Transfer to Bacteriochlorophyll in LH2 Light-Harvesting Complexes from Allochromatium Vinosum, MSU Strain

The Effect of the Number of Conjugated Double Bonds in Carotenoid Molecules on the Efficiency of Energy Transfer to Bacteriochlorophyll in LH2 Light-Harvesting Complexes from Allochromatium Vinosum, MSU Strain

Raman investigation of the pigment families in recent and fossil brachiopod shells.

Shells of the three subphyla of extant and extinct representatives of the phylum Brachiopoda display coloured patterns with diverse shapes and at different degrees. These colourations are readily visible in natural light but are best revealed under UV light for the fossils concerned. To identify these pigments, Raman spectroscopy has been used for the first time on brachiopod shells. The widespread identified pigments belong to the carotenoid family, best represented in all the animal kingdom, the second one concerns the melanin/melanin-like pigments and, surprisingly, additional molecules of the cytochrome family are revealed for the first time in one of the brachiopod shells studied. The putative functions of shell pigmentation, still under debate, are discussed.

15N photo-CIDNP MAS NMR on both photosystems and magnetic field-dependent 13C photo-CIDNP MAS NMR in photosystem II of the diatom Phaeodactylum tricornutum.

Diatoms contribute about 20-25% to the global marine productivity and are successful autotrophic players in all aquatic ecosystems, which raises the question whether this performance is caused by differences in their photosynthetic apparatus. Photo-CIDNP MAS NMR presents a unique tool to obtain insights into the reaction centres of photosystems (PS), by selective enhancement of NMR signals from both, the electron donor and the primary electron acceptor molecules. Here, we present the first observation of the solid-state photo-CIDNP effect in the pennate diatoms. In comparison to plant PSs, similar spectral patterns have been observed for PS I at 9.4T and PS II at 4.7T in the PSs of Phaeodactylum tricornutum. Studies at different magnetic fields reveal a surprising sign change of the 13C photo-CIDNP MAS NMR signals indicating an alternative arrangement of cofactors which allows to quench the Chl a donor triplet state in contrast to the situation in plant PS II. This unusual quenching mechanism is related to a carotenoid molecule in close vicinity to the Chl a donor. In addition to the photo-CIDNP MAS NMR signals arising from the donor and the primary electron acceptor cofactors, a complete set of signals of the imidazole ring ligating to the magnesium of Chl a can be observed.

Chlorophyll-Carotenoid Excitation Energy Transfer in High-Light-Exposed Thylakoid Membranes Investigated by Snapshot Transient Absorption Spectroscopy.

Nonphotochemical quenching (NPQ) provides an essential photoprotection in plants, assuring safe dissipation of excess energy as heat under high light. Although excitation energy transfer (EET) between chlorophyll (Chl) and carotenoid (Car) molecules plays an important role in NPQ, detailed information on the EET quenching mechanism under in vivo conditions, including the triggering mechanism and activation dynamics, is very limited. Here, we observed EET between the Chl Q y state and the Car S1 state in high-light-exposed spinach thylakoid membranes. The kinetic and spectral analyses using transient absorption (TA) spectroscopy revealed that the Car S1 excited state absorption (ESA) signal after Chl excitation has a maximum absorption peak around 540 nm and a lifetime of ∼8 ps. Snapshot TA spectroscopy at multiple time delays allowed us to track the Car S1 ESA signal as the thylakoid membranes were exposed to various light conditions. The obtained snapshots indicate that maximum Car S1 ESA signal quickly rose and slightly dropped during the initial high-light exposure (<3 min) and then gradually increased with a time constant of ∼5 min after prolonged light exposure. This suggests the involvement of both rapidly activated and slowly activated mechanisms for EET quenching. 1,4-Dithiothreitol (DTT) and 3,3'-dithiobis(sulfosuccinimidyl propionate) (DTSSP) chemical treatments further support that the Car S1 ESA signal (or the EET quenching mechanism) is primarily dependent on the accumulation of zeaxanthin and partially dependent on the reorganization of membrane proteins, perhaps due to the pH-sensing protein photosystem II subunit S.

Hybrid complexes of photosynthetic reaction centers and quantum dots in various matrices: resistance to UV irradiation and heating.

The effects of ultraviolet (UV) irradiation (up to 0.6J/cm2) and heating (65°C, 20min) on the absorption spectra and electron transfer in dehydrated film samples of photosynthetic reaction centers (RCs) from purple bacterium Rhodobacter (Rb.) sphaeroides, as well as in hybrid structures consisting of RCs and quantum dots (QDs), have been studied. The samples were placed in organic matrices containing the stabilizers of protein structure-polyvinyl alcohol (PVA) and trehalose. UV irradiation led to partially irreversible oxidation of some RCs, as well as to transformation of some fraction of the bacteriochlorophyll (BChl) molecules into bacteriopheophytin (BPheo) molecules. In addition, UV irradiation causes degradation of some BChl molecules that is accompanied by formation of 3-acetyl-chlorophyll a molecules. Finally, UV irradiation destroys the RCs carotenoid molecules. The incorporation of RCs into organic matrices reduced pheophytinization. Trehalose was especially efficient in reducing the damage to the carotenoid and BChl molecules caused by UV irradiation. Hybrid films containing RC + QD were more stable to pheophytinization upon UV irradiation. However, the presence of QDs in films did not affect the processes of carotenoid destruction. The efficiency of the electronic excitation energy transfer from QD to P865 also did not change under UV irradiation. Heating led to dramatic destruction of the RCs structure and bacteriochlorins acquired the properties of unbound molecules. Trehalose provided strong protection against destruction of the RCs and hybrid (RC + QD) complexes.

Unified analysis of optical absorption spectra of carotenoids based on a stochastic model

The chemical structures of the carotenoid molecules are very simple and one might think that their electronic features are easily predicted. However, there is still has so much unknown information excepting the correlation between the electronic energy state and the length of effective conjugation chain of carotenoids. To investigate the electronic feature of the carotenoids, the most essential method is measuring the optical absorption spectra, but simulations based on the resonance Raman spectra are also an effective approach. For this reason, we studied the optical absorption spectra as well as resonance Raman spectra of 15 different carotenoid molecules each possessing a cyclic end-group, recorded in tetrahydrofuran (THF) solutions at room temperature. The whole band shapes of the absorption spectra of all these carotenoid molecules were successfully simulated using a stochastic model and Brownian oscillators. The parameters obtained from the simulation make it possible to discuss the intermolecular interaction between carotenoids and solvent THF molecules quantitatively.

A DFT study of a set of natural dyes for organic electronics.

We systematically investigate, at density functional theory level, the electronic properties of a set of ten carotenoid molecules with different conjugation length. Ground state geometries were fully optimized using both B3LYP and its long-range corrected version, i.e., the CAM-B3LYP functional. The time-dependent DFT approach (TD-DFT) was also performed for the calculation of the excited states of the optimized geometries and the results were compared to the experimental ones, when available. Our findings indicate a dependence of the transition vertical energies, oscillator strengths, and transition dipole moments on the extension of conjugation, as expected. We also investigate the impact of the intra-molecular vibrations on the absorption spectrum by means of the Franck-Condon (FC) and nuclear ensemble (NE) approach to spectra simulation. Our simulations suggest that the Franck-Condon approximation may not be suitable to appropriately characterize the vibronic progression of these molecules, whereas the NE approach provides a contribution that vary from negligible to meaningful depending on which molecule and energy region is under analysis.

Probing structure–function relationships in early events in photosynthesis using a chimeric photocomplex

The native core light-harvesting complex (LH1) from the thermophilic purple phototrophic bacterium Thermochromatium tepidum requires Ca2+ for its thermal stability and characteristic absorption maximum at 915 nm. To explore the role of specific amino acid residues of the LH1 polypeptides in Ca-binding behavior, we constructed a genetic system for heterologously expressing the Tch. tepidum LH1 complex in an engineered Rhodobacter sphaeroides mutant strain. This system contained a chimeric pufBALM gene cluster (pufBA from Tch. tepidum and pufLM from Rba. sphaeroides) and was subsequently deployed for introducing site-directed mutations on the LH1 polypeptides. All mutant strains were capable of phototrophic (anoxic/light) growth. The heterologously expressed Tch. tepidum wild-type LH1 complex was isolated in a reaction center (RC)-associated form and displayed the characteristic absorption properties of this thermophilic phototroph. Spheroidene (the major carotenoid in Rba. sphaeroides) was incorporated into the Tch. tepidum LH1 complex in place of its native spirilloxanthins with one carotenoid molecule present per αβ-subunit. The hybrid LH1-RC complexes expressed in Rba. sphaeroides were characterized using absorption, fluorescence excitation, and resonance Raman spectroscopy. Site-specific mutagenesis combined with spectroscopic measurements revealed that α-D49, β-L46, and a deletion at position 43 of the α-polypeptide play critical roles in Ca binding in the Tch. tepidum LH1 complex; in contrast, α-N50 does not participate in Ca2+ coordination. These findings build on recent structural data obtained from a high-resolution crystallographic structure of the membrane integrated Tch. tepidum LH1-RC complex and have unambiguously identified the location of Ca2+ within this key antenna complex.

Paralogs of the C-Terminal Domain of the Cyanobacterial Orange Carotenoid Protein Are Carotenoid Donors to Helical Carotenoid Proteins.

The photoactive Orange Carotenoid Protein (OCP) photoprotects cyanobacteria cells by quenching singlet oxygen and excess excitation energy. Its N-terminal domain is the active part of the protein, and the C-terminal domain regulates the activity. Recently, the characteristics of a family of soluble carotenoid-binding proteins (Helical Carotenoid Proteins [HCPs]), paralogs of the N-terminal domain of OCP, were described. Bioinformatics studies also revealed the existence of genes coding for homologs of CTD. Here, we show that the latter genes encode carotenoid proteins (CTDHs). This family of proteins contains two subgroups with distinct characteristics. One CTDH of each clade was further characterized, and they proved to be very good singlet oxygen quenchers. When synthesized in Escherichia coli or Synechocystis PCC 6803, CTDHs formed dimers that share a carotenoid molecule and are able to transfer their carotenoid to apo-HCPs and apo-OCP. The CTDHs from clade 2 have a cysteine in position 103. A disulfide bond is easily formed between the monomers of the dimer preventing carotenoid transfer. This suggests that the transfer of the carotenoid could be redox regulated in clade 2 CTDH. We also demonstrate here that apo-OCPs and apo-CTDHs are able to take the carotenoid directly from membranes, while HCPs are unable to do so. HCPs need the presence of CTDH to become holo-proteins. We propose that, in cyanobacteria, the CTDHs are carotenoid donors to HCPs.

Optimization of β-Carotene Production from Rhodotorula glutinis ATCC 4054 Growing on Agro-industrial Substrate Using Plackett–Burman Design

Beta-carotene, one of most widely known carotenoid molecules, is commercially used as food and feed additive, cosmetic and pharmaceutical products. The current study was aimed to evaluate the utilization of some agro-industrial wastes for β-carotene production by Rhodotorula glutinis yeast and optimization of the production process using Plackett–Burman design. Rice bran, sugarcane molasses and sugarcane bagasse were used in the production medium. Rice bran was the best low-cost substrate for biomass and β-carotene production of R. glutinis. Physical and nutritional parameters such as glucose, sucrose, yeast extract, NH4Cl, NaCl, MgSO4, KH2PO4, pH, inoculum size and agitation rate were screened using Plackett–Burman design to identify critical factors. Results of Plackett–Burman design suggest that sucrose, NaCl, KH2PO4 and pH were the most significant factors for β-carotene accumulation on rice bran. A quadratic model was constructed by response surface methodology—central composite design to study the impact of interaction and quadratic effect of these critical factors on β-carotene production. From predicted values obtained using quadratic equations, it was seen that the optimization to achieve maximum production of β-carotene was; sucrose 18.6 g/l, initial pH at 5.4, KH2PO4 1.01 g/l, NaCl 0.66 g/l to achieve a β-carotene content from 1.23 mg/kg rice bran to 3.20 mg/kg. As far as HPLC analysis is concerned, it clearly proved the presence of β-carotene which had 68.2% purity as compared with standard.

The Effects of ultraviolet irradiation on hybrid films of photosynthetic reaction centers and quantum dots in various organic matrices

The effects of ultraviolet radiation (up to 0.6 J/cm2) on the absorption spectra and electron transfer in dehydrated films of photosynthetic reaction centers from purple bacteria Rb. sphaeroides and hybrid structures that included reaction centers, quantum dots, and protein structure stabilizers (trehalose, polyvinyl alcohol, and methylcellulose) have been studied. Ultraviolet irradiation led to partial destruction of bacteriochlorophyll molecules (pheophytinization) and the reaction center carotenoid. In this case, ultraviolet irradiation did not exert a significant effect on electron transfer between the photoactive bacteriochlorophyll and quinone electron acceptors. The incorporation of reaction centers into organic matrices reduced pheophytinization. Trehalose was the most efficient in reducing the damage evoked by ultraviolet irradiation of the carotenoid molecule. Hybrid films that contained quantum dots were resistant to pheophytinization upon ultraviolet irradiation, but the presence of quantum dots did not affect the processes of carotenoid destruction upon exposure to ultraviolet radiation. Ultraviolet radiation had an insignificant effect on the characteristics of quantum dots (the fluorescence lifetime).

Excitation of photosystem I by 760 nm femtosecond laser pulses: transient absorption spectra and intermediates

Excitation of photosystem I (PS I) by a femtosecond 760 nm pump leads to one- and two-photon absorption. The one-photon excitation produces intermediates with transient absorption spectra similar to the spectra of the primary and secondary ion-radical pairs in the PS I reaction center. The two-photon absorption generates the upper level excited states of chlorophyll (Chl) and carotenoid molecules in the antenna. These excited states are converted into the long-lived intermediates and can be tentatively attributed to the excited and charge–transfer ion-radical states of Chl molecules and to the excited states of carotenoids in the antenna. The transient spectra of intermediates generated by two-photon excitation differ from the transient one-photon spectra of the primary and secondary ion-radical pairs.

Different molecular organization of two carotenoids, lutein and zeaxanthin, in human colon epithelial cells and colon adenocarcinoma cells

Two cell lines, human normal colon epithelial cells (CCD 841 CoTr) and human colon adenocarcinoma cells (HT-29) were cultured in the presence of exogenous carotenoids, either zeaxanthin or lutein. Both carotenoids demonstrated cytotoxicity with respect to cancer cells but not to normal cells. Cells from both the cell lines were analyzed with application of fluorescence lifetime imaging microscopy and Raman scattering microscopy. Both imaging techniques show effective incorporation of carotenoid molecules into growing cells. Comparison of the Raman scattering and fluorescence lifetime characteristics reveals different molecular organization of carotenoids in the carcinoma and normal cells. The main difference consists in a carotenoid aggregation level which is substantially lower in the carcinoma cells as compared to the normal cells. Different molecular organization of carotenoids was interpreted in terms of a different metabolism of normal and carcinoma cells and has been concluded to provide a possibility of cancer diagnosis based on spectroscopic analyses.