Crystal structure of ferrioxamine B: a comparative analysis and implications for molecular recognition

Abstract.

Ferrioxamine B was successfully co-crystallized with ethanolpentaaquomagnesium(II) and perchlorate ions as counter ions, C₂₇H₆₂Cl₃FeMgN₆O₂₆, and the crystal structure has been determined by single-crystal X-ray diffraction. The crystals are monoclinic, space group P2₁/n, four molecules per unit cell with dimensions a=21.1945(7) Å, b=10.0034(3) Å, c=106.560(1) Å, and β=106.560(1)°. The crystal structure contains a racemic mixture of Λ-N-cis,cis and Δ-N-cis,cis coordination isomers. The structural parameters and the conformational features of ferrioxamine B compare very well with those of ferrioxamines D₁ and E, with an exception of the orientation of the pendant protonated amine, which is pointing away from the connecting amide chains and towards the carbonyl face of the inner coordination shell distorted octahedron. This pendant protonated amine, in conjunction with the carbonyl face of the Fe(III) coordination shell, is proposed to play an important role in the recognition and membrane transport processes.