Wydział Chemii

Łukasz Szyrwiel

Dávid Lukács

Dávid Srankó

Zsolt Kerner

Aleksandra Kotynia

Justyna Brasuń

Bartosz Setner

Zbigniew Szewczuk

Katarzyna Malec

József Sándor Pap

2017

RSC Advances

7

24657-24666

10.1039/c7ra03814c

Naukowa

Angielski

Artykuł

The imidazole ring of histidine (His) and the methylcarboxylate function of aspartic acid (Asp) are crucial for
Cu coordination in enzymes, artificial proteins and other bioinspired systems. In order to elucidate the effect
of Asp at the C-terminus, a new branched peptide, H-Gly-Dap(H-Gly)-Asp-NH2 (2GD, Dap ¼ 2,3-
diaminopropionic acid) has been synthesized to ligate CuII. While at pH < 8, 2GD favours dimeric
complexes at 1 : 1 metal-to-ligand ratio, at increasingly alkaline pH the Asp at the C-terminus creates
a {NH2,N,N,O}eq set and the dominance of mononuclear CuLH2 and CuLH3 species, according
to potentiometry, molecular spectroscopy (UV-visible, circular dichroism and X-band electron
paramagnetic resonance) and ESI-MS analysis. The changes in speciation with pH are accompanied by
shifts in the CuIII/II redox current peaks that were analyzed by square wave voltammetry (SWV) and
allowed the calculation of the pKa values for the CuII and CuIII forms. The 2GD complex exhibits
electrocatalytic activity in water oxidation in phosphate buffer. However, when Asp residues are present
at all three termini to produce 3D (H-Asp-Dap(H-Asp)-Asp-NH2), the electrocatalysis of water oxidation
decreases and, if present only at the N-termini in 2DG (H-Asp-Dap(H-Asp)-Gly-NH2), it ceases. As for
CuII ligated by 2GD, a TOF of 16 s1 was calculated at pH ¼ 11 in 0.2 M phosphate electrolyte, which is
crucial for catalysis, but also acts as inhibitor anion according to cyclic voltammetry observations. The
system is highly tolerant to the presence of chloride, which is a feature of practical importance in

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http://dx.doi.org/10.1039/c7ra03814c

https://www.rsc.org/