Peptide synthesis of gold nanoparticles: the early steps of gold reduction investigated by density functional theory

Exploring Bimetallic Nanoparticles in Alzheimer's Therapy: A Novel Bio-Assisted Synthesis with Multitarget Potential

Unlocking the potential of metal nanoparticles (NPs) in biomedical applications represents a leading endeavor in contemporary research. Among these, gold NPs (AuNPs) and silver NPs (AgNPs) have shown promising strides in combatting complex neurodegenerative ailments like Alzheimer's disease. Yet, the unexplored realm of bimetallic Au/Ag-NP harbors immense potential, concealing undiscovered opportunities for enhanced therapeutic effectiveness through the synergistic interaction of metal ions. Nonetheless, the limitations of traditional synthesis methods have restricted the preparation, biocompatibility, and versatility of these NPs, prompting an urgent requirement for innovative approaches. Biobased synthetic methodologies have emerged as a noteworthy solution to address these challenges. Our study ventures into uncharted terrain, harnessing collagen-mimicking peptide nanofibers as a bioactive template for the synthesis of bimetallic NPs. These green NPs exhibit remarkable activity in inhibiting amyloid β (Aβ) protein aggregation with almost 74% inhibition, surpassing the individual impacts of Au and Ag NPs, which show inhibition percentages of 66 and 43, respectively. The bimetallic Au/Ag-NPs not only demonstrate powerful inhibition of Aβ, but they also demonstrate inhibitory activity against esterase (∼50%) and against reactive oxygen species (ROS) (∼75%), metamorphosing into multifaceted therapeutic agents for Alzheimer's disease. Au/Ag-NPs have proven highly beneficial in surpassing cellular barriers, as evidenced by studies on tissue penetration, 3D uptake, and endosomal escape, and these attributes also hold promise for the future treatment modalities. The findings indicate that the intrinsic traits of Au/Ag-NPs provide numerous mechanistic benefits, such as inhibiting Aβ and acetylcholinesterase (AChE), and reducing stress related to ROS, in addition to their advantageous internalization properties. This research represents a notable advancement in the development of multitargeted treatments for neurodegenerative disorders using bimetallic NPs, diverging from the prevalent emphasis on AuNPs in the current literature.

Mechanism of Producing Metallic Nanoparticles, with an Emphasis on Silver and Gold Nanoparticles, Using Bottom-Up Methods

Bottom-up nanoparticle (NP) formation is assumed to begin with the reduction of the precursor metallic ions to form zero-valent atoms. Studies in which this assumption was made are reviewed. The standard reduction potential for the formation of aqueous metallic atoms-E0(Mn+aq/M0aq)-is significantly lower than the usual standard reduction potential for reducing metallic ions Mn+ in aqueous solution to a metal in solid state. E0(Mn+aq/M0solid). E0(Mn+aq/M0aq) values are negative for many typical metals, including Ag and Au, for which E0(Mn+aq/M0solid) is positive. Therefore, many common moderate reduction agents that do not have significantly high negative reduction standard potentials (e.g., hydrogen, carbon monoxide, citrate, hydroxylamine, formaldehyde, ascorbate, squartic acid, and BH4-), and cannot reduce the metallic cations to zero-valent atoms, indicating that the mechanism of NP production should be reconsidered. Both AgNP and AuNP formations were found to be multi-step processes that begin with the formation of clusters constructed from a skeleton of M+-M+ (M = Ag or Au) bonds that is followed by the reduction of a cation M+ in the cluster to M0, to form Mn0 via the formation of NPs. The plausibility of M+-M+ formation is reviewed. Studies that suggest a revised mechanism for the formation of AgNPs and AuNPs are also reviewed.

Binding of chloroaurate to polytyrosine-PEG micelles leads to an anti-Turkevich pattern of reduction

Here we report formation of gold nanoparticles (GNPs) in micelles of polytyrosine-PEG copolymers that combine the properties of a reducer and a stabilizer. The size and properties of the GNPs were tailored by the excess chloroaurate over the copolymer. The latter quickly formed non-covalent complexes with HAuCl4 and then slowly reduced it to form GNPs. 3 Tyr residues are consumed by reduction of one mole of chloroaurate. The size of the GNPs was controlled by the [Tyr]/[Au(iii)] molar ratio. Small GNPs with D ≅ 8 nm were formed at [Tyr]/[Au(iii)] = 0.5-1.5. 90% of these small GNPs remained bound to the copolymer and could be stored in a lyophilized state. Such polypeptide-gold hybrid materials produced at [Tyr]/[Au(iii)] = 0.5 demonstrated high activity in the catalytic reduction of 4-nitrophenol by sodium borohydride. [Tyr]/[Au(iii)] = 5 led to the formation of large nanoplates (D ≅ 30-60 nm). Thus, in the polymer-based system the GNP size grew in line with the excess of the reducing agent in contrast to Turkevich synthesis of GNPs with citric acid, which also combines the functions of a stabilizer and a reducer. The difference results from the reduction of HAuCl4 in solution according to the Turkevich method and in the micelles of the amphiphilic polymer where the seed growth is limited by the amount of neighboring reducer.

Synthesis of Well-Defined Gold Nanoparticles Using Pluronic: The Role of Radicals and Surfactants in Nanoparticles Formation

Synthesis of gold nanoparticles (GNP) by reacting chloroauric acid (HAuCl₄) and Pluronic F127 was thoroughly investigated. The rate of reduction of HAuCl₄ and the yield and morphology of GNP strongly depended on the concentration of the reactants and sodium chloride, as well as pH and temperature. Upon completion of the reaction heterogeneous mixtures of small GNP of defined shape and Pluronic aggregates were formed. GNP were separated from the excess of Pluronic by centrifugal filtration. Under optimized conditions the GNP were small (ca. 80 nm), uniform (PDI ~0.09), strongly negatively charged (ζ-potential −30 mV) and nearly spherical. They were stable in distilled water and phosphate-buffered saline. Purified GNP contained ~13% by weight of an organic component, yet presence of polypropylene oxide was not detected suggesting that Pluronic was not adsorbed on their surface. Analysis of the soluble products suggested that the copolymer undergoes partial degradation accompanied by cleavage of the C–O bonds and appearance of new primary hydroxyl groups. The reaction involves formation of free radicals and hydroperoxides depends on the oxygen concentration. GNP did not form at 4 °C when the micellization of Pluronic was abolished reinforcing the role of the copolymer self-assembly. In conclusion, this work provides insight into the mechanism of HAuCl₄ reduction and GNP formation in the presence of Pluronic block copolymers. It is useful for improving the methods of manufacturing uniform and pure GNP that are needed as nanoscale building blocks in nanomedicine applications.

Direct Synthesis of a Covalently Self-Assembled Peptide Nanogel from a Tyrosine-Rich Peptide Monomer and Its Biomineralized Hybrids

There has been significant progress in the self-assembly of biological materials, but the one-step covalent peptide self-assembly for well-defined nanostructures is still in its infancy. Inspired by the biological functions of tyrosine, a covalently assembled fluorescent peptide nanogel is developed by a ruthenium-mediated, one-step photo-crosslinking of tyrosine-rich short peptides under the visible light within 6 minutes. The covalently assembled peptide nanogel is stable in various organic solvents and different pH levels, unlike those made from vulnerable non-covalent assemblies. The semipermeable peptide nanogel with a high density of redox-active tyrosine acts as a novel nano-bioreactor, allowing the formation of uniform metal-peptide hybrids by selective biomineralization under UV irradiation. As such, this peptide nanogel could be useful in the design of novel nanohybrids and peptidosomes possessing functional nanomaterials.

On the formation of gold nanoparticles from [AuIIICl4]− and a non-classical reduced polyoxomolybdate as an electron source: a quantum mechanical modelling and experimental study

DFT calculations and experimental data prove that the [Na{(MoV2O₄)₃(μ₂-O)₃(μ₂-SO₃)₃(μ₆-SO₃)}₂]¹⁵⁻ POM is capable of completely reducing Au(iii) to Au(0).

A facile synthesis-fabrication strategy for integration of catalytically active viral-palladium nanostructures into polymeric hydrogel microparticles via replica molding

The synthesis of small, uniform, well-dispersed and active Pd nanocatalysts under mild conditions in a predictable and controlled manner is an unmet challenge. Viral nanomaterials are attractive biotemplates for the controlled synthesis of nanoparticles due to their well-defined and monodisperse structure along with abundant surface functionalities. Here, we demonstrate spontaneous formation of small (1-2 nm), uniform and highly crystalline palladium (Pd) nanoparticles along genetically modified tobacco mosaic virus (TMV1cys) biotemplates without external reducing agents. The ratio between TMV and Pd precursor plays an important role in the exclusive formation of well-dispersed Pd nanoparticles along TMV biotemplates. The as-prepared Pd-TMV complexes are then integrated into the poly(ethylene glycol) (PEG)-based microparticles via replica molding (RM) technique in a simple, robust and highly reproducible manner. High catalytic activity, recyclability and stability of the hybrid Pd-TMV-PEG microparticles are further demonstrated through dichromate reduction as a model reaction. Taken together, these findings demonstrate a significant step toward simple, robust, and scalable synthesis and fabrication of efficient biotemplate-supported Pd nanocatalysts in readily deployable polymeric scaffolds with high capacity in a controlled manner.

Preparation of gold nanoparticles by surfactant-promoted reductive reaction without extra reducing agent

Cetyltrimethyl ammonium bromide (CTAB) has been extensively applied in the solution-phase synthesis of many types of colloidal nanoparticles. However, the uses of CTAB were mainly considered as template or capping agents to form controllable shape and protect the product from agglomeration. Here it was discovered that CATB could serve as a very mild reductant to reduce gold salt precursors preparing gold nanoparticles (GNPs) at base environment. CTAB acted as the reducing agent suffering a partial degradation and forming CTA macro radicals. FTIR proved the formation of CCl and/or CBr bond after CTAB degraded. The characterization of synthesized GNPs was examined by UV-Vis spectra, TEM and XRD. Several factors affecting the process of reaction, such as the amount of NaOH, the molar ratio of CTAB and HAuCl(4), the reaction temperature, the effect of light and oxygen, and stirring were discussed.

In situ synthesis of gold nanoparticles in exponentially-growing layer-by-layer films

In situ synthesis of inorganic nanoparticles (NPs) in polyelectrolytes multilayers (PEMs) has recently gained much attention. Due to the versatility of their composition, PEMs offer a unique opportunity to synthesize a variety of NPs. So far, mostly cationic precursors have been used and only few studies have investigated the possibility of using amine groups to bind anionic precursors. Here, we use exponentially growing poly(L-lysine)/hyaluronan (PLL/HA) films as a nanoreservoir to bind and sequester aurochlorate (AuCl(4)(-)) anions thanks to the large number of free amine groups. The polypeptide-polysaccharide reactive template enabled the formation in a spatially-confined environment of gold NP at a very high yield. The synthesized gold NPs were homogenous and well-dispersed in the nanocomposite. Importantly, there was no particular effect of the film-ending layer (either PLL or HA). The largest particles of ~9 nm and the largest amount of gold were obtained at acidic pH of 3. When the pH was increased, smaller and more numerous NPs were synthesized but the total amount of gold was lower. Based on UV-visible spectrometry, FTIR and TEM data, we finally propose a scheme for the mechanism of gold NPs formation, in which several groups of PLL and HA contribute to the binding of gold ions, the nucleation and growth of NPs, and their stabilization in the "bulk" of the film.

Docking of ubiquitin to gold nanoparticles

Protein-nanoparticle associations have important applications in nanoscience and nanotechnology such as targeted drug delivery and theranostics. However, the mechanisms by which proteins recognize nanoparticles and the determinants of specificity are still poorly understood at the microscopic level. Gold is a promising material in nanoparticles for nanobiotechnology applications because of the ease of its functionalization and its tunable optical properties. Ubiquitin is a small, cysteine-free protein (ubiquitous in eukaryotes) whose binding to gold nanoparticles has been characterized recently by nuclear magnetic resonance (NMR). To reveal the molecular basis of these protein-nanoparticle interactions, we performed simulations at multiple levels (ab initio quantum mechanics, classical molecular dynamics and Brownian dynamics) and compared the results with experimental data (circular dichroism and NMR). The results provide a model of the ensemble of structures constituting the ubiquitin-gold surface complex, and insights into the driving forces for the binding of ubiquitin to gold nanoparticles, the role of nanoparticle surfactants (citrate) in the association process, and the origin of the perturbations in the NMR chemical shifts.

The influence of amino acid sequence and functionality on the binding process of peptides onto gold surfaces

We present a molecular dynamics study of the binding process of peptide A3 (AYSSGAPPMPPF) and other similar peptides onto gold surfaces, and identify the functions of many amino acids. Our results provide a clear picture of the separate regimes present in the binding process: diffusion, anchoring, crawling and binding. Moreover, we explored the roles of individual residues. We found that tyrosine, methionine, and phenylalanine are strong binding residues; serine serves as an effective anchoring residue; proline acts as a dynamic anchoring point, while glycine and alanine give flexibility to the peptide backbone. We then show that our findings apply to unrelated phage-derived sequences that have been reported recently to facilitate AuNP synthesis. This new knowledge may aid in the design of new peptides for the synthesis of gold nanostructures with novel morphologies.