Singlet and Triplet State Spectra and Dynamics of Structurally Modified Peridinins

Abstract

The peridinin-chlorophyll a-protein (PCP) is a light-harvesting pigment-protein complex found in many species of marine algae. It contains the highly substituted carotenoid peridinin and chlorophyll a, which together facilitate the transfer of absorbed solar energy to the photosynthetic reaction center. Photoexcited peridinin exhibits unorthodox spectroscopic and kinetic behavior for a carotenoid, including a strong dependence of the S(1) excited singlet state lifetime on solvent environment. This effect has been attributed to the presence of an intramolecular charge transfer (ICT) state in the molecule. The present work explores the effect of changing the extent of π-electron conjugation and attached functional groups on the nature of the ICT state of peridinin and how these factors affect the excited singlet and triplet state spectra and kinetics of the carotenoid. In this investigation three peridinin analogues denoted C-1-R-peridinin, C-1-peridinin, and D-1-peridinin were synthesized and studied using steady-state absorption and fluorescence techniques and ultrafast time-resolved transient absorption spectroscopy. The study explores the effect on the singlet and triplet state spectra and dynamics of removing the allene group from the peridinin structure and either replacing it with a rigid furanoid ring, replacing it with an epoxide group, or extending the polyene chain into the β-ionylidine ring.

Study of carotenoids in cyanobacteria by Raman spectroscopy

“…These strains can be found generally in severe stress environments and under highest radiation levels [29], which contributes to the range of colors observed for these species, from green to orange hues [17,[30][31][32][33][34][35]. In these photosynthetic organisms, an universal pigment is the carotenoids class; carotenoids have important functions for maintenance of the cellular matrix integrity, an important supporting for light harvesting and other, for example in the prevention/repair of the photo-oxidative damage [18,36].…”

“…Generally, for algae and cyanobacteria, the main pigments identified in their matrix are peridinin [32,44,45], β-carotene, nostoxanthin, xanthophyll, caloxanthin, echinenone, myxoxanthophyll, echinenone, canthaxanthin, oscillaxanthin, zeaxanthin and scytonemin [17,22,[30][31][32][46][47][48]. Carotenoids are non-water soluble dyes and, jointly with chlorophylls compounds, are present in lipophilic environments inside of sturdy membranes [49].…”

“…Numerous biological systems have been investigated by Raman spectroscopy aiming to fill this gap, these studies cover of fruits until corals which contain carotenoids in their matrices but, generally, at low concentrations [39,42,59,60]. These studies have provide new information about the pigment localization into the matrix and possible spectra interferences; added to this, the Raman-active modes have assisted in the interpretation of the molecular assignments and enabled conclusions about the correlation of the spectra bands positions, regardless of the dye concentration present in the sample [17,31,32,43,48,61].…”

Triplet excitation dynamics of β -carotene studied in three solvents by ns flash photolysis spectroscopy

“…And the photophysical and photochem-331 ical mechanism depends not only on sensitizer [40][41][42], but also 332 the solvents [18,20,42,43]. 333 In this study in the hydrophobic solvent n-hexane, upon 334…”

“…38 The study of the effects of solvents on the formation mechanism 39 of triplets and radicals of carotenoids is relatively limited: In 40 chloroform, no matter whether by directly excitation or triplet 41 sensitizing, both lycopene and b-carotene (b-Car) generate radical 42 cations [18,20], while in n-hexane, under anthracene-sensitizing 43 [20], only the triplet carotenoid is produced; in chloroform, the 44 anthracene-sensitizing formation of fucoxanthin radical cation is 45 mainly from its S 2 state, but conversely from the T 1 state in 46 methanol [39]. A similar study on peridinin and its structural 47 analogs upon chlorophyll anthracene-sensitized triplet excitation 48 in acetonitrile did not generate any carotenoid cation species 49 [40,41]; in THF, anthracene-sensitized triplet excitation of a polar 50 carotenoid derivative, RetInd, the production of a dication was 51 observed [42]. Most recently, we proposed that the polar solvent, 52 methanol, could assist two natural carbonyl carotenoids producing 53 the cation dehydrodimers # [Car] 2 + upon anthracene-sensitized 54 triplet excitation [43].…”