Compositions and conformations of several transition metal complexes with a nonapeptide hormone oxytocin

摘要

Similar co-oridation characteristics of oxytocin (OT) towards Cu~(II), Ni~(II) Mn~(II) and Zn~(II) at different pH avlues have been demonstrated by electrospray mass spectrometry (ESMS) and rationalized by molecular mechanics simulation. At ca. pH 2 oxytocin does not interact with the metal ions; at pH 5 species with metal bound oxytocin were detected including [OT + H~+]~+, [M + OT]~(2+), [M + OT - H~+]~+, [M + OT + ClO_4~- + H~+]~(2+) and [M + OT + ClO_4~-]~+ and only stable 4N complexes were found at pH (approx =) 9. Molecular modelling studies using the Universal force field (UFF) showed that the four N-donor centers of oxytocin prefer the square planar geometry in complexes of Ni~(II) and Mn~(II). For Pd~(II), the S_r(1) co-ordinated conformer was found to be more stable than the S_r(6) co-ordinated one. Dramatic conformational changes occur upon oxytocin co-ordinating to Ni~(II), Mn~(II) or Pd~(II).