1 research outputs found
pH-Dependent Synthesis of Anisotropic Gold Nanostructures by Bioinspired Cysteine-Containing Peptides
In
the present study, alkaline peptides AAAXCX (X = lysine or arginine
residues) were designed based on the conserved motif of the enzyme
thioredoxin and used for the synthesis of gold nanoparticles (GNPs)
in the pH range of 2–11. These peptides were compared with
free cysteine, the counterpart acidic peptides AAAECE and γ-ECG
(glutathione), and the neutral peptide AAAACA. The objective was to
investigate the effect of the amino acids neighboring a cysteine residue
on the pH-dependent synthesis of gold nanocrystals. Kohn–Sham
density functional theory (KS-DFT) calculations indicated an increase
in the reducing capacity of AAAKCK favored by the successive deprotonation
of their ionizable groups at increasing pH values. Experimentally,
it was observed that gold speciation and the peptide structure also
have a strong influence on the synthesis and stabilization of GNPs.
AAAKCK produced GNPs at room temperature, in the whole investigated
pH range. By contrast, alkaline pH was the best condition for the
synthesis of GNP assisted by the AAARCR peptide. The acidic peptides
produced GNPs only in the presence of polyethylene glycol, and the
synthesis using AAAECE and γ-ECG also required heating. The
ionization state of AAAKCK had a strong influence on the preferential
growth of the GNPs. Therefore, pH had a remarkable effect on the synthesis,
kinetics, size, shape, and polydispersity of GNPs produced using AAAKCK.
The AAAKCK peptide produced anisotropic decahedral and platelike nanocrystals
at acidic pH values and spherical GNPs at alkaline pH values. Both
alkaline peptides were also efficient capping agents for GNPs, but
they produced a significant difference in the zeta potential, probably
because of different orientations on the gold surface