UV/vis spectroscopy and direct-infusion ESI-QTOF-MS demonstrate reduction of Fe(III) by coumarins and the formation of Fe(II)-coumarin complexes <i>in vitro</i>.

<p>(A) Optical spectra of solutions (CH₃CN) of ligands esculetin (<b>1</b>), fraxetin (<b>2</b>) and scopoletin (<b>3</b>), of iron salts, of mixtures of ligands and 2 equiv of NEt₃, and of mixtures containing 3 equiv of ligand, 6 equiv of NEt₃, and 1 equiv of FeCl₂ or FeCl₃. Left: <b>1</b> (blue); <b>1</b>+ NEt₃ (orange); <b>1</b>+ NEt₃+ FeCl₂ (green); <b>1</b>+ NEt₃+ FeCl₃ (red); FeCl₃ (black); FeCl₂ (magenta). Center: <b>2</b> (blue); <b>2</b>+ NEt₃ (orange); <b>2</b>+ NEt₃+ FeCl₂ (green); <b>2</b>+ NEt₃+ FeCl₃ (red). Right: <b>3</b> (blue); <b>3</b>+ NEt₃ (orange); <b>3</b>+ NEt₃+ FeCl₂ (green); <b>3</b>+ NEt₃+ FeCl₃ (red). (B) Interpretation of the UV/vis spectra depicted in (A). (C) Results of direct-infusion ESI-QTOF-MS of a mixture of Fe(II) with synthesized and purified scopoletin. (D) MS-MS spectrum of the main signal at <i>m/z</i> 316.02.