An extremely stable Ni(II) complex derived from the hydrolytic cleavage of the C-terminal tail of histone H2A

The C-terminal blocked tetrapeptides SHHK– and SAHK–, which represent the fragments produced from the hydrolysis of the hexapeptides’ –TASHHK–, –TESHHK–, and –TESAHK– complexes with Ni(II), were synthesized and their interactions with Ni(II) ions were studied potentiometrically and spectroscopically. Both tetrapeptides interact strongly with Ni(II) ions leading to square-planar complexes with 4N {NH 2,2N −,N im} coordination. The stability of the Ni–SHHK– complex is about 2 orders of magnitude higher than the Ni–SAHK– complex. Spectroscopic evidence and theoretical predictions suggest the positioning of the free imidazole ring, in the Ni–SHHK– complex, above the coordination plane, explaining the extra stability of the complex.