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1Author    PaavoH. Hynninen, Riikka RäisänenRequires cookie*
 Title    Stepwise pH-Gradient Elution for the Preparative Separation of Natural Anthraquinones by Multiple Liquid-Liquid Partition  
 Abstract    Preparative-scale separation of substituted anthraquinones by multiple liquid-liquid parti­ tion was studied using isopropylmethyl ketone (IM K)/aqueous phosphate buffer (aq .) as the solvent system and the H ietala apparatus with 100 partition units as the partition equipment. The lower (aq.) phase was chosen as mobile, while the upper (IM K) phase remained station­ ary. H ence, the principle of stepwise pH-gradient elution could be utilized to separate the components in two com plex mixtures of hydroxyanthraquinones and hydroxyanthraquinone carboxylic acids, isolated from the fungus Dermocybe sanguinea. In spite of the nonlinearity of the partition isotherm s for these anthraquinones, implying deviations from the Nernst partition law, rem arkable separations were achieved for the components in each mixture. E very anthraquinone carboxylic acid showed markedly irregular partition behavior, appear­ ing in the effluent as two m ore or less resolved concentration zones. Such splitting was attributed to the form ation of relatively stable sandwich-dimers, which were in a slow equilib­ rium with the m onom ers in the m ore nonpolar organic phase. A t lower pH-values, only the polar monomers were distributed into the mobile aqueous phase and moved forward, whereas the nonpolar sandwich-dimers remained almost entirely in the stationary organic phase and lagged behind. When the pH of the mobile aqueous phase was raised high enough, the firmly linked dimers were monomerized and emerged from the apparatus as a second concentration profile. Interm olecular hydrogen bonding and jt-jt interaction between the n-systems of two anthraquinone molecules in a parallel orientation were considered responsible for the nonlinear and markedly irregular partition behavior of the natural anthraquinones studied. The nonlinearity of the partition behavior of the hydroxyanthraquinones lacking the carboxyl group, appeared merely as excessive broadening of the experimental concentration profile, which impaired the resolution between the components only insignificantly. Thus, e.g. the main components, dermocybin and emodin, could both be obtained from Separation 1 in a purity of at least 99% . 
  Reference    Z. Naturforsch. 56c, 719 (2001); received March 12/April 9 2001 
  Published    2001 
  Keywords    Liquid-Liquid Distribution, pH-Gradient, Anthraquinone 
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 TEI-XML for    default:Reihe_C/56/ZNC-2001-56c-0719.pdf 
 Identifier    ZNC-2001-56c-0719 
 Volume    56