Triplet state spectra and dynamics of geometric isomers of carotenoids

Pendon, Zeus; Hoef, Ineke der; Lugtenburg, J.; Frank, Harry A.

doi:10.1007/s11120-005-9026-8

Cited by 10 publications

(12 citation statements)

References 68 publications

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“…In order to obtain actual triplet lifetimes for the Cars in solvent a more sophisticated kinetic model must be applied. For that analysis the kinetic scheme developed previously (Bruckner et al 2003;Kaligotla et al 2010;Pendon et al 2006) has been adopted: where k ET is a triplet energy transfer rate from BChl to Car, k Car and k BChl are the rate constants for triplet state decays of Car and BChl. Based on the scheme the differential equations for decay of population of triplets of BChl and Car may be expressed as follows:…”

Section: Carotenoidmentioning

confidence: 99%

Triplet excited state spectra and dynamics of carotenoids from the thermophilic purple photosynthetic bacterium Thermochromatium tepidum

2011

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Light-harvesting complex 2 from the anoxygenic phototrophic purple bacterium Thermochromatium tepidum was purified and studied by steady-state absorption, fluorescence and flash photolysis spectroscopy. Steady-state absorption and fluorescence measurements show that carotenoids play a negligible role as supportive energy donors and transfer excitation to bacteriochlorophyll-a with low energy transfer efficiency of ~30%. HPLC analysis determined that the dominant carotenoids in the complex are rhodopin and spirilloxanthin. Carotenoid excited triplet state formation upon direct (carotenoid) or indirect (bacteriochlorophyll-a Q(x) band) excitation shows that carotenoid triplets are mostly localized on spirilloxanthin. In addition, no triplet excitation transfer between carotenoids was observed. Such specific carotenoid composition and spectroscopic results strongly suggest that this organism optimized carotenoid composition in the light-harvesting complex 2 in order to maximize photoprotective capabilities of carotenoids but subsequently drastically suppressed their supporting role in light-harvesting process.

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Section: Carotenoidmentioning

confidence: 99%

Triplet excited state spectra and dynamics of carotenoids from the thermophilic purple photosynthetic bacterium Thermochromatium tepidum

2011

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“…Hence, an analytical method which is capable of identifying the different isomers of AST is warranted. Isomers of AST have been widely isolated by high performance liquid chromatography (HPLC) techniques and identified by UV–Vis spectroscopy . Other studies such as NMR have also been used to identify the isomers .…”

Section: Introductionmentioning

confidence: 99%

Investigations on the geometrical isomers of astaxanthin: Raman spectroscopy of conjugated polyene chain with electronic and mechanical confinement

Subramanian

Tchoukanova²,

Djaoued

et al. 2014

J Raman Spectroscopy

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Recent research interests in geometrical isomers of astaxanthin (AST) are motivated by their metabolic activities in aquatic animals and human. It has been established that cis‐isomers of AST are selectively absorbed in human plasma during the metabolic process; however, exact absorption mechanism is still unclear. Hence, a detailed investigation of the structural and optical properties of geometrical isomers of AST is required. Among the techniques available for the study of AST and other carotenoids, Raman spectroscopy has been much acclaimed. Raman spectra have been shown to be influenced by the electronic and mechanical confinement effects arising from the conjugated polyene chain of carotenoids. In this work, we present Raman studies of geometrical isomers of AST, along with their optical absorption characteristics. Geometrical isomers of AST were prepared by heating all trans‐AST in solution form, and the isomers were separated using high performance liquid chromatography. Optical absorption spectra of cis‐isomers of AST showed hypsochromic shifts in the main absorption band and formation of new bands at lower wavelengths. A detailed Raman spectral analysis performed on the cis‐isomers of AST showed new modes which have not been observed and accounted for so far. In addition, we demonstrate that the electronic and mechanical confinement effects in the polyene chain of AST play an important role in the Raman spectra of geometrical isomers of AST. It is anticipated that this work will demonstrate that Raman spectroscopy is an important diagnostic tool in distinguishing and identifying the geometrical isomers of AST. Copyright © 2014 John Wiley & Sons, Ltd.

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“…Triplet states of bacteriochlorophyll (and chlorophyll) are known to sensitize the formation of singlet oxygen, a powerful oxidizing agent, which must be deactivated to protect the photosynthetic apparatus [19,21,22]. Work by other researchers have questioned whether specific geometric isomers and geometric isomerization are controlling factors in the mechanism of photoprotection [23,24]. However, more systematic investigations of the photophysics and photochemistry of well-defined, purified geometric isomers of carotenoids are needed to understand if a relationship between stereochemistry and biological function exists.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast time-resolved absorption spectroscopy of geometric isomers of carotenoids

et al. 2009

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The structures of a number of stereoisomers of carotenoids have been revealed in three-dimensional X-ray crystallographic investigations of pigment-protein complexes from photosynthetic organisms. Despite these structural elucidations, the reason for the presence of stereoisomers in these systems is not well understood. An important unresolved issue is whether the natural selection of geometric isomers of carotenoids in photosynthetic pigment-protein complexes is determined by the structure of the protein binding site or by the need for the organism to accomplish a specific physiological task. The association of cis isomers of a carotenoid with reaction centers and trans isomers of the same carotenoid with light-harvesting pigment-protein complexes has led to the hypothesis that the stereoisomers play distinctly different physiological roles. A systematic investigation of the photophysics and photochemistry of purified, stable geometric isomers of carotenoids is needed to understand if a relationship between stereochemistry and biological function exists. In this work we present a comparative study of the spectroscopy and excited state dynamics of cis and trans isomers of three different open-chain carotenoids in solution. The molecules are neurosporene (n=9), spheroidene (n=10), and spirilloxanthin (n=13), where n is the number of conjugated π-electron double bonds. The spectroscopic experiments were carried out on geometric isomers of the carotenoids purified by high performance liquid chromatography (HPLC) and then frozen to 77 K to inhibit isomerization. The spectral data taken at 77 K provide a high resolution view of the spectroscopic differences between geometric isomers. The kinetic data reveal that the lifetime of the lowest excited singlet state of a cis-isomer is consistently shorter than that of its corresponding all-trans counterpart despite the fact that the excited state energy of the cis molecule is typically higher than that of the trans molecule. Quantum theoretical calculations on an n=9 linear polyene were carried out to examine this process. The calculations indicate that the electronic coupling terms are significantly higher for the cis isomer, and when combined with the Franck-Condon factors, predict internal conversion rates roughly double those of the all-trans species. The electronic effects more than offset the decrease in coupling efficiencies associated with the higher system origin energies and explain the observed shorter cis isomer lifetimes.

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Triplet state spectra and dynamics of geometric isomers of carotenoids

Cited by 10 publications

References 68 publications

Triplet excited state spectra and dynamics of carotenoids from the thermophilic purple photosynthetic bacterium Thermochromatium tepidum

Triplet excited state spectra and dynamics of carotenoids from the thermophilic purple photosynthetic bacterium Thermochromatium tepidum

Investigations on the geometrical isomers of astaxanthin: Raman spectroscopy of conjugated polyene chain with electronic and mechanical confinement

Ultrafast time-resolved absorption spectroscopy of geometric isomers of carotenoids

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