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  • carotenoid  (2)
  • 13C MAS NMR  (1)
  • Aldolase  (1)
  • Amino acids  (1)
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  • 1
    ISSN: 1573-5079
    Keywords: carotenoid ; electron spin resonance ; energy transfer ; geometric isomerization ; optical spectroscopy ; photoprotection ; triplet state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The spectroscopic and photochemical properties of the synthetic carotenoid, locked-15,15′-cis-spheroidene, were studied by absorption, fluorescence, circular dichroism, fast transient absorption and electron spin resonance spectroscopies in solution and after incorporation into the reaction center of Rhodobacter (Rb.) sphaeroides R-26.1. HPLC purification of the synthetic molecule reveals the presence of several di-cis geometric isomers in addition to the mono-cis isomer of locked-15,15′-cis-spheroidene. In solution, the absorption spectrum of the purified mono-cis sample was red-shifted and showed a large cis-peak at 351 nm compared to unlocked all-trans spheroidene. Molecular modeling and semi-empirical calculations reveal how geometric isomerization and structural factors affect the room temperature spectra. The spectroscopic studies of the purified locked-15,15′-mono-cis molecule in solution reveal a more stable manifold of excited states compared to the unlocked spheroidene. Reaction centers of Rb. sphaeroides R-26.1 in which the locked-15,15′-cis-spheroidene was incorporated show no difference in either the spectroscopic properties or photochemistry compared to reaction centers in which unlocked spheroidene was incorporated or to Rb. sphaeroides wild type strain 2.4.1 reaction centers which naturally contain spheroidene. The data suggest that the natural selection of a cis-isomer of spheroidene for incorporation into native reaction centers of Rb. sphaeroides wild type strain 2.4.1 is more determined by the structure or assembly of the reaction center protein than by any special quality of the cis-isomer of the carotenoid that would affect its ability to participate in triplet energy transfer or carry out photoprotection.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5079
    Keywords: 13C MAS NMR ; EPR ; FTIR ; spheroidene ; stable isotope labelling ; ubiquinone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In this minireview the information at the atomic level that has been obtained by studying photosynthetic reaction centers with site-directed isotope labelling is discussed. The required isotopically labelled RCs are prepared using isotopically labelled amino acids and cofactors that have been prepared via organic total synthetic chemistry. In some cases the results of isotopically labelled RCs that are prepared via other methods are also discussed.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-5079
    Keywords: bacteriochlorophyll ; carotenoid ; flash absorbance spectroscopy ; light-harvesting complex ; Rhodobacter sphaeroides ; triplet state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The build-up and decay of bacteriochlorophyll (BChl) and carotenoid triplet states were studied by flash absorption spectroscopy in (a) the B800-850 antenna complex ofRhodobacter (Rb.)sphaeroides wild type strain 2.4.1, (b) theRb. sphaeroides R-26.1 B850 light-harvesting complex incorporated with spheroidene, (c) the B850 complex incorporated with 3,4-dihydrospheroidene, (d) the B850 complex incorporated with 3,4,5,6-tetrahydrospheroidene and (e) theRb. sphaeroides R-26.1 B850 complex lacking carotenoids. Steady state absorption and circular dichroism spectroscopy were used to evaluate the structural integrity of the complexes. The transient data were fit according to either single or double exponential rate expressions. The triplet lifetimes of the carotenoids were observed to be 7.0±0.1 μs for the B800-850 complex, 14±2 μs for the B850 complex incorporated with spheroidene, and 19±2 μs for the B850 complex incorporated with 3,4-dihydrospheroidene. The BChl triplet lifetime in the B850 complex was 80±5 μs. No quenching of BChl triplet states was seen in the B850 complex incorporated with 3,4,5,6-tetrahydrospheroidene. For the B850 complex incorporated with spheroidene and with 3,4-dihydrospheroidene, the percentage of BChl quenched by carotenoids was found to be related to the percentage of carotenoid incorporation. The triplet energy transfer efficiencies are compared to the values for singlet energy transfer measured previously (Frank et al. (1993) Photochem. Photobiol. 57: 49–55) on the same samples. These studies provide a systematic approach to exploring the effects of state energies and lifetimes on energy transfer between BChls and carotenoids in vivo.
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  • 4
    ISSN: 1434-193X
    Keywords: Amino acids ; Isotopic labelling ; Ethyl benzoate ; Benzonitrile ; Sodium phenylpyruvate ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A synthetic route to stable-isotope-substituted L-phenylalanine is presented, which allows the introduction of 13C, 15N, and deuterium labels at any position or combination of positions. For labelling of the aromatic ring, a synthetic route to ethyl benzoate (or benzonitrile) has been developed, based on the electrocyclic ring-closure of a 1,6-disubstituted hexatriene system, with in situ aromatization by elimination of one (amino) substituent. Several important (highly isotopically enriched) synthons have been prepared, namely benzonitrile, benzaldehyde, ethyl benzoate, and ethyl diphenyloxyacetate. Labelled L-phenylalanines have been synthesized from both aromatic precursors by initial conversion into sodium phenylpyruvate and subsequent transformation of this intermediate into the L-α-amino acid by an enzymatic reductive amination reaction. In this manner, highly enriched phenylalanines are obtained on the 10-gram scale and with high enantiomeric purities (≥ 99% ee). The method has been validated by the synthesis of [1′-13C]-L-Phe and [2-D]-L-Phe. In addition, two methods are described for the introduction of isotopes into L-tyrosine starting from the isotopically enriched precursors benzonitrile and ethyl benzoate.
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  • 5
    ISSN: 1434-193X
    Keywords: DNA ; Dihydroxyacetone monophosphate ; Aldolase ; Carbon-13 ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A synthesis of [3′,4′-13C2]thymidine (1) is described in which [13C2]acetic acid (2) is converted into the nucleoside in twelve steps with 9% overall yield. D-2-Deoxyribose-5-phosphate aldolase (DERA, EC 4.1.2.4) and triosephosphate isomerase (TPI, EC 5.3.1.1) are used for the stereocontrolled formation of D-[3,4-13C2]-2-deoxyribose-5-phosphate (8) from [2,3-13C2]dihydroxyacetone monophosphate (DHAP, 7) and acetaldehyde in 80% yield. The route permits the introduction of isotopically enriched carbon atoms at any position or combination of positions in the furanose ring and the product can be coupled with any of the four naturally occurring base moieties.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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