pH-Dependent Synthesis of Anisotropic Gold Nanostructures by Bioinspired Cysteine-Containing Peptides

Abstract

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.

Comparative study of gold and silver interactions with amino acids and nucleobases

“…Generally, the interaction of gold atoms with protonated and deprotonated amino acid residues do not differ greatly, which is in agreement with the experimental evidences that gold cluster synthesis occurs in a wide range of pH. 24,67 The fact that deprotonated cysteine has the highest binding energy with both Au 2 and Au + among all the amino acids explains the ne synthesis of gold nanoclusters on thiolates. 68,69 Our results suggest that binding energy between neutral silver clusters and DNA is rather weak (DG is equal to À1 to À9 kcal mol À1 ) as compared to charged particles (À55 to À63 kcal mol À1 ).…”

Proteins and Peptides at the Interfaces of Nanostructures

“…In the crystalline growth process of metallic nanoparticles, functional groups of proteins and peptides have specific affinity for certain metallic facets. Thus, proteins and peptides direct the crystalline growth of the nanostructures to a diversity of size and shape (Tofanello et al 2016). Proteins, and peptides are also largely used for the stabilization and functionalization of a diversity of nanostructured materials providing properties such as biocompatibility, plasmonenhanced catalysis, sensing, fabrication of micro/ nanomotors and others.…”

“…The mechanism characterizes the existence of competition among Pd ions and FAD for the reduction in such a way that formic acid was necessary as a co-adjuvant reducing agent for the PdNP growing. In another study, Tofanello et al demonstrated that not only the presence of cysteine residues in a peptide structure is the warranty of an adequate reducing capacity for the synthesis of gold nanoparticles (GNPs) (Tofanello et al 2016).…”

“…For that study, alkaline peptides AAAXCX (X = lysine or arginine residues) were designed having as inspiration the conserved motif of the enzyme thioredoxin (Tofanello et al 2016). The alkaline peptides were compared with free cysteine, the counterpart acidic peptides γ-ECG (glutathione) and AAAeCe, as well as the neutral peptide AAAACA.…”

Increased Stability of Oligopeptidases Immobilized on Gold Nanoparticles

“…Surface functionalization of gold nanoparticles has opened new frontiers for the delivery of drugs such as anticancer and antimicrobial drugs as well as functional studies of biomolecules such as enzymes and antibodies [3][4][5][6]. GNPs can also be synthesized by one-pot, rapid processes, including the in-situ synthesis using the organic functionalizing agent as the reducing compound to convert gold ions (Au 3+ ) to the metallic form [7][8][9]. A diversity of biomolecules and their mimetics has been used for in-situ synthesis of GNPs, but the use of proteins is particularly attractive because these biomolecules act as a template and reducing agents for GNP fabrication [10][11][12][13].…”