Studies of the interaction of potassium(I), calcium(II), magnesium(II), and copper(II) with cyclosporin A.
Metal ion binding properties of the immunosuppressant drug cyclosporin A have been investigated.  Complexation studies in acetonitrile solution using 1H NMR and CD spectroscopy yielded 1:1 metal-peptide binding constants (log(10)K) for potassium(I), <1, magnesium(II), 4.8+/-0.2, and calcium(II), 5.0+/-1.0.  The interaction of copper(II) with cyclosporin A in methanol was investigated with UV/visible and electron paramagnetic resonance (EPR) spectroscopy.  No complexation of copper(II) was observed in neutral solution.  In the presence of base, monomeric copper(II) complexes were detected.  These results support the possibility that cyclosporin A has ionophoric properties for biologically important essential metal ions.