Modified carotenoids: spectroscopy and conformation of capsorubin and related end group isomers

Martin, Hans‐Dieter; Werner, T.

doi:10.1016/0022-2860(92)80053-k

Cited by 7 publications

(5 citation statements)

References 10 publications

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“…At higher pH zeaxanthin is not able to create hydrogen bonds, which clearly favors formation of J-zeaxanthin, indicating that the head-to-tail aggregates can be formed only in the absence of hydrogen bonding. On the other hand, the pH dependence supports the earlier hypothesis that the card-pack H-aggregates are held together via a hydrogen-bonding network. ,, It is worth mentioning that similar results were obtained by Simonyi et al, who showed that for the carotenoids lutein and capsanthol the presence of free hydroxyl groups produces solely H-aggregates, while acetylation of the hydroxyl groups favors formation of J-aggregates. These results are essentially the same as ours, except Simonyi et al achieved the inhibition of hydrogen bonding by modification of the molecules, while here we showed that a pH change can control the aggregation type of the same carotenoid.…”

Section: Discussionsupporting

confidence: 88%

Self-Assembled Aggregates of the Carotenoid Zeaxanthin: Time-Resolved Study of Excited States

2005

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In this study, we present a way of controlling the formation of the two types of zeaxanthin aggregates in hydrated ethanol: J-zeaxanthin (head-to-tail aggregate, characteristic absorption band at 530 nm) and H-zeaxanthin (card-pack aggregate, characteristic absorption band at 400 nm). To control whether J- or H- zeaxanthin is formed, three parameters are important: (1) pH, that is, the ability to form a hydrogen bond; (2) the initial concentration of zeaxanthin, that is, the distance between zeaxanthin molecules; and (3) the ratio of ethanol/water. To create H-aggregates, the ability to form hydrogen bonds is crucial, while J-aggregates are preferentially formed when hydrogen-bond formation is prevented. Further, the formation of J-aggregates requires a high initial zeaxanthin concentration and a high ethanol/water ratio, while H-aggregates are formed under the opposite conditions. Time-resolved experiments revealed that excitation of the 530-nm band of J-zeaxanthin produces a different relaxation pattern than excitation at 485 and 400 nm, showing that the 530-nm band is not a vibrational band of the S2 state but a separate excited state formed by J-type aggregation. The excited-state dynamics of zeaxanthin aggregates are affected by annihilation that occurs in both J- and H-aggregates. In H-aggregates, the dominant annihilation component is on the subpicosecond time scale, while the main annihilation component for the J-aggregate is 5 ps. The S(1) lifetimes of aggregates are longer than in solution, yielding 20 and 30 ps for H- and J-zeaxanthin, respectively. In addition, H-type aggregation promotes a new relaxation channel that forms the zeaxanthin triplet state.

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Section: Discussionsupporting

confidence: 88%

Self-Assembled Aggregates of the Carotenoid Zeaxanthin: Time-Resolved Study of Excited States

2005

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“…This clearly favours formation of J-zeaxanthin, indicating that the head-to-tail aggregates can be formed only in the absence of hydrogen bonding. On the other hand, the pH dependence supports the earlier hypothesis that the card-pack H-aggregates are held together via a hydrogen-bonding network [10,31,32,38]. The inhibition of hydrogen bonding by modification of the molecules (be it by a pH change that can control the H-bonding via deprotonation or protonation, a derivatization of OH-groups, or the wrong stereochemistry) will determine the aggregation type of a particular carotenoid.…”

Section: J-aggregate Monomer H-aggregatesupporting

confidence: 73%

“…Four isomers of capsorubin, namely the epimers capsorubin (413) and epicapsorubin (3), and the 2-hydroxy analogues isocapsorubin (4) and epiisocapsorubin (5) (Scheme 1), show different spectroscopic behaviour, depending on the stereochemistry of the OH group. A strong hydrogen bond between the OH proton and the carbonyl lone pair determines the conformation of the (3,6-cis) isomers epicapsorubin (3) and epiisocapsorubin (5) [32].…”

Section: D) Chirality Of Aggregatesmentioning

confidence: 99%

Aggregation and Interface Behaviour of Carotenoids

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“…45 This difference was connected with the observation of intramolecular hydrogen bonding in epicapsorubin which contains the carbonyl and OH groups in cis-configuration. 46 Supposing that intramolecular hydrogen bonding competes with intermolecular ones, the stability of epicapsorubin aggregates was suggested to be weaker than that of capsorubin. 45 However, the capsantholon epimers, 2 and 3, are not in that relation: the carbonyl group is on the k-ring and the aggregate spectra are basically different (no trace of a …”

Section: Carotenoid Aggregatesmentioning

confidence: 99%

“…An attractive proposal put forward by Martin and colleagues 45,46 emphasized the role of hydrogen bonds. They have found the aggregate of capsorubin (22) to be of H-type with a small J-type contribution, while the aggregate of epicapsorubin (24) to be mixed with an increased share of head-to-tail structures.…”

Section: Carotenoid Aggregatesmentioning

confidence: 99%

Supramolecular exciton chirality of carotenoid aggregates

et al. 2003

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The conventional organic chemistry concept of chirality relates to single molecules. This article deals with cases in which exciton chirality is generated by the interaction of associated carotenoids. The handed property responsible for exciton signals in these systems is due to the alignment of neighboring molecules held together by secondary chemical forces. Their mutual positions are characterized by the overlay angle. Experimental manifestation is obtained by spectroscopic studies on carotenoid aggregates. Compared to molecular spectra, both UV/visible and circular dichroism spectroscopic observations reveal modified absorption bands and induced Cotton effects of opposite sign (exciton couplets), respectively. A new term, "supramolecular exciton chirality," is suggested for these phenomena, allowing the detection of weak chemical interactions not readily accessible for experimental studies, although highly important in the mechanism of biological processes.

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Modified carotenoids: spectroscopy and conformation of capsorubin and related end group isomers

Cited by 7 publications

References 10 publications

Self-Assembled Aggregates of the Carotenoid Zeaxanthin: Time-Resolved Study of Excited States

Self-Assembled Aggregates of the Carotenoid Zeaxanthin: Time-Resolved Study of Excited States

Aggregation and Interface Behaviour of Carotenoids

Supramolecular exciton chirality of carotenoid aggregates

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