Kai F. Schwedhelm, Martin Horstmann, Johan H. Faber, Yana Reichert, Michael Büchner, Gerhard Bringmann, Cornelius Faber
(CF) Department of
Experimental Physics 5, Am Hubland, University of Würzburg, Germany;
E-mail: firstname.lastname@example.org and (GB) Institute of Organic
Chemistry, Am Hubland, University of Würzburg, Germany.
Complex formation between the antimalarial drug chloroquine and its presumed target ferriprotoporphyrin IX
in three different solutions (pH 6.5, pH 9, and in a water methanol mixture) is characterized by nuclear magnetic
resonance, UV spectroscopy, and mass spectrometry. NMR paramagnetic relaxation measurements are used to derive
intermolecular distances between the molecules and model structures of the complexes are calculated by molecular
dynamics simulations. Observation of an unusual spin state in NMR measurements leads to the postulation of a novel 4:2
stoichiometry of the complex, which is supported by mass spectrometry and UV spectroscopy.