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Medientyp:
E-Artikel
Titel:
Untersuchungen an Hämoprotein‐Modellen : Zur Wechselwirkung zwischen Poly‐(N‐Vinylimidazol), Hämin und Cyanid‐Ionen
:
Zur Wechselwirkung zwischen Poly‐(<i>N</i>‐Vinylimidazol), Hämin und Cyanid‐Ionen
Beteiligte:
Scheler, W.;
Mohr, P.;
Pommerening, K.;
Behlke, J.
Beschreibung:
<jats:p>
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<jats:list-item><jats:p>In aqueous alkaline solution poly‐(<jats:italic>N</jats:italic>‐vinylimidazole) interacts with haemin to form two types of complexes. The molecular weight of the PVIm was about 12000 and the number of binding sites for haemin monomer varied between 8 to 17 per PVIm molecule in dependence on the pH. At pH < 11.0 a red haemin‐PVIm complex is formed showing absorption maxima at 532 and 411 mμ and at pH > 11.5 a green complex with maxima at 595, 578 and 391 mμ.</jats:p></jats:list-item>
<jats:list-item><jats:p>At pH < 9 the equilibrium between haemin and PVIm is nearly independent of pH but clearly dependent on the haemin concentration. This dependence as well as the asymmetry of the haemin‐PVIm association curves prove a dissociation of the haemin dimers into monomers in combining to PVIm.</jats:p></jats:list-item>
<jats:list-item><jats:p>The spectral type of the red complex and the characteristics of the complex formation at pH < 11 suggest a co‐ordinative interaction of one imidazole group of PVIm with the haemin iron. In the green compound above pH 11.5 there is no co‐ordinative linkage between PVIm imidazole residues and haemin iron or at most a very weak one.</jats:p></jats:list-item>
<jats:list-item><jats:p>Complex formation between <jats:italic>N</jats:italic>‐ethylimidazole or <jats:italic>N</jats:italic>‐methylimidazole with haemin is mainly due to enthalpy changes whilst the combination of PVIm with haemin is mainly related to entropy effects. The free enthalpies of the formation of the co‐ordinative red haemin‐PVIm complex and the non‐co‐ordinative green complex do not differ significantly. The stability of the haemin‐PVIm complexes can therefore be attributed mainly to non‐co‐ordinative interactions between both partners, probably to hydrophobic bonding.</jats:p></jats:list-item>
<jats:list-item><jats:p>The red haemin‐PVIm complex can bind one cyanide anion per haemin with high affinity. The spectrum of the resulting haemin‐PVIm‐cyanide complex shows absorption maxima at 542 and 419 mμ. Formation of the complex is independent of the pH, proving that the co‐ordinatively bound imidazole group is displaced from the iron by CN<jats:sup>−</jats:sup>. However, the haemin remains attached to the PVIm‐matrix.</jats:p></jats:list-item>
<jats:list-item><jats:p>The differences in complex formation of haemin with monomeric imidazole derivatives and with PVIm are essentially due to the existence of multiple non‐co‐ordinative interactions between PVIm and haemin. There are some analogies between this binding and the multiple non‐co‐ordinative bonds between haemin and apolar amino acid residues in hemoglobins.</jats:p></jats:list-item>
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