CONFIGURATIONS OF NEUROSPORENE ISOMERS ISOLATED FROM THE REACTION CENTER AND THE LIGHT‐HARVESTING COMPLEX OF Rhodobacter spheroides G1C. A RESONANCE RAMAN, ELECTRONIC ABSORPTION, AND ₁H‐NMR STUDY

Abstract

Abstract— HPLC analysis of neurosporene extracted from the chromatophore membranes of Rhodobacter spheroides G1C showed two isomeric components 1 and 2. Extract from the light‐harvesting complex (LH) gave only component 2, while extract from the reaction center (RC) mainly gave component 1. Both components were isolated, and their configurations were determined by means of (1) resonance Raman, (2) electronic absorption, and (3) 1H‐HMR spectroscopy. The configuration of component 2 originating from LH was determined to be all‐trans and that of component 1 from RC was determined to be 15‐cis. Thus, our previous configurational prediction of this particular carotenoid bound to RC, by means of resonance Raman spectroscopy, to be 15‐cis [Y. Koyama, T. Takii, K. Saiki and K. Tsukida, Photobiochem. Photobiophys.5 (1983)139–150] is confirmed.

Effect of Isomerization on Excited-State Dynamics of Carotenoid Fucoxanthin

“…Besides the S 0 –S 2 transition that dominates the absorption spectrum of all samples, cis -fucoxanthin contains an additional absorption band known as cis -peak. ,,,, The cis -peak appears in the 300–360 nm spectral region and also exhibits a clear vibronic structure, which is more pronounced in n -hexane, mirroring the behavior of the S 0 –S 2 transition. The lowest energy band of the cis -peak has the largest amplitude and has maximum at 332 (methanol) or 330 nm ( n -hexane).…”

DFT-based Raman spectral study of astaxanthin geometrical isomers

“…2 and Table 1 , the most significant difference from all- trans isomers is that 9- cis has a moderate intensity band at 1135 cm −1 . The Raman spectral difference between cis - trans isomers can also be found in many carotenoids in previous reports, like β-carotene ( Koyama et al, 1982 ), neurosporene ( Koyama et al, 1988 ), β-Apo-8′- carotenal ( Hashimoto et al, 1993 ), spheroidene ( Jiang et al, 1996 ). Based on this 1135 cm −1 Raman band in Fig.…”

“…And the 13,15-di- cis isomer does not have an observable band at about 1135 to 1140 cm −1 . This characteristic Raman difference around 1130 cm −1 bands in the ν 2 region has also been found and used to distinguish cis - trans isomers of many carotenoids, for instance, in β-carotene ( Koyama et al, 1982 ), neurosporene ( Koyama et al, 1988 ), β-Apo-8′- carotenal ( Hashimoto et al, 1993 ), spheroidene ( Jiang et al, 1996 ), and etc. The assignment of this important band is specially listed in Table 3 .…”

“…It is known that isomers of other carotenoids also exhibit different biological properties. For example, it is reported that the mono- cis configuration (15- cis ) of neurosporene is bound to the reaction center, while the all- trans -neurosporene is bound to the light-harvesting complex ( Koyama et al, 1988 , Koyama et al, 1982 ).…”

Carotenoids in Vegetables

“…In the pigment-protein complexes of photosyn thetic organisms, the all-trans configurations of carotenoids are the major component of the light-harvesting complexes, while the pho tosynthetic reaction centers contain 15-cis carot enoid configurations [24][25][26]. The all-trans carotenoids in the light-harvesting complexes provide efficient singlet-energy transfer to chlorophyll molecules, and thus participate mainly in light-harvesting.…”