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'Stereochemistry' in keywords Facet   Publication Year 1981  [X]
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1Author    PaavoH. Hynninen, Gunnel SieversRequires cookie*
 Title    Conformations of Chlorophylls a and a' and their Magnesium-Free Derivatives as Revealed by Circular Dichroism and Proton Magnetic Resonance  
 Abstract    The electronic absorption (UV/VIS), circular dichroism (CD) and proton magnetic resonance (*H NMR) spectra have been recorded for C-l0 epimeric chlorophylls a and a', pheophytins a and a' as well as pheophorbides a and a'. Although the epimers in each pair showed virtually identical UV/VIS spectra, their CD spectra were profoundly different and exhibited opposite signs at most wavelengths in the UV region. The differences were interpreted as arising, in part, from different C-10 configurations, and, in part, from conformational alterations induced by the steric strain in the crowded periphery of the macrocycle. The conformational alterations were also clearly indicated by the X H NMR zJö-values observed for the a,ß and <5 methine protons, the C-10 protons and most methyl group protons of the epimers in each pair. This was considered to imply changes in the geometry of the whole macrocycle. The A 6-values were larger for the Mg-free epimers than for the chlorophyll epimers, which shows that the central Mg-atom makes the macrocycle more rigid. Correlations between the signs of the CD bands and configurations are discussed. 
  Reference    Z. Naturforsch. 36b, 1000—1009 (1981); received May 19 1981 
  Published    1981 
  Keywords    Stereochemistry, Conformational Analysis, Chlorophyll and Pheophytin Epimers, X H NMR Spectra, Circular Dichroism 
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 TEI-XML for    default:Reihe_B/36/ZNB-1981-36b-1000.pdf 
 Identifier    ZNB-1981-36b-1000 
 Volume    36