Abstract
The stoichiometry, stability constants and solution structure of the complexes formed in the reaction of copper(II) with hexapeptide NPTNLH, i.e. the Neobelliera Bullata Trypsin Modulating Oostatic Factor ( Neb-TMOF), and its analogues DPTNLH, Ac-NPTNLH and Ac-DPTNLH have been determined by potentiometric, UV–visible, CD and EPR spectroscopic methods. Upon raising pH for Ac-NPTNLH and Ac-DPTNLH peptides, copper(II) coordination starts from the imidazole nitrogen of the His 6; afterwards three deprotonated amide nitrogens are progressively involved in metal ions coordination. In a wide pH range of 4.5–8.5 for the NPTNLH and DPTNLH ligands the CuL complex dominates with the imidazole nitrogen of His 6 coordinated to form a macrochelate. The N-terminal amino group of the NPTNLH and DPTNLH peptides takes part in the coordination of the metal ion in the CuL, CuH −1L and CuH −2L complexes. However, at pH above 9 the CuH −3L complex with the {N Im, 3N −} coordination mode is formed. For the CuH −2L complex the spectroscopic data clearly indicate the 4N {NH 2, CO or COO −, 2N −, N Im} bonding mode with the axial coordination of the N-terminal amine group to the metal ion.
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