Multiple spectroscopic and magnetic techniques show that chloroquine induces formation of the μ-oxo dimer of ferriprotoporphyrin IX.

Multiple spectroscopic and magnetic techniques show that chloroquine induces formation of the μ-oxo dimer of ferriprotoporphyrin IX.
J Inorg Biochem. 2014 Jan 16;133C:40-49
Authors: Kuter D, Benjamin SJ, Egan TJ
Abstract
Interaction of the antimalarial chloroquine (CQ) with ferriprotoporphyrin IX, Fe(III)PPIX, was investigated in aqueous solution (pH7.4) and as a precipitate from aqueous medium at pH5.0. In solution, spectrophotometric titrations indicated strong association (logKobs 13.3±0.2) and a Job plot gave a stoichiometry of 1:2 CQ:Fe(III)PPIX. UV-visible absorbance and magnetic circular dichroism spectra of the complex were compared to various Fe(III)PPIX species. Close similarity to the spectra of the μ-oxo dimer, μ-[Fe(III)PPIX]2O, was revealed. The induction of this species by CQ was confirmed by magnetic susceptibility measurements using the Evans NMR method. The observed low-magnetic moment (2.25±0.02μB) could only be attributed to antiferromagnetically coupled Fe(III) centers. The value was comparable to that of μ-[Fe(III)PPIX]2O (2.0±0.1μB). In the solid-state, mass spectrometry confirmed the presence of CQ in the complex. Dissolution of this solid in aqueous solution (pH7.4) resulted in a solution with a UV-visible spectrum consistent with the same 1:2 stoichiometry observed in the Job plot. Magnetic susceptibility measurements made on the solid using an Evans balance produced a magnetic moment (2.3±0.1μB) consistent...

Source: Journal of Inorganic Biochemistry - January 16, 2014 Category: Biochemistry Authors: Kuter D, Benjamin SJ, Egan TJ Tags: J Inorg Biochem Source Type: research