Coordination abilities of the 1–16 and 1–28 fragments of β-amyloid peptide towards copper(II) ions: a combined potentiometric and spectroscopic study

Abstract

Stoichiometry, stability constants and solution structures of the copper(II) complexes of the (1–16 H), (1–28 H), (1–16 M), (1–28 M), (Ac-1–16 H) and (Ac-1–16 M) fragments of human ( H) and mouse ( M) β-amyloid peptide were determined in aqueous solution in the pH range 2.5–10.5. The potentiometric and spectroscopic data (UV–Vis, CD, EPR) show that acetylation of the amino terminal group induces significant changes in the coordination properties of the (Ac-1–16 H) and (Ac-1–16 M) peptides compared to the (1–16 H) and (1–16 M) fragments, respectively. The (Ac-1–16 H) peptide forms the 3N {N Im 6, N Im 13, N Im 14} complex in a wide pH range (5–8), while for the (Ac-1–16 M) fragment the 2N {N Im 6, N Im 14} complex in the pH range 5–7 is suggested. At higher pH values sequential amide nitrogens are deprotonated and coordinated to copper(II) ions. The N-terminal amino group of the (1–16) and (1–28) fragments of human and mouse β-amyloid peptide takes part in the coordination of the metal ion, although, at pH above 9 the complexes with the 4N {N Im, 3N −} coordination mode are formed. The phenolate –OH group of the Tyr 10 residue of the human fragments does not coordinate to the metal ion.