Biodirected Synthesis and Nanostructural Characterization of Anisotropic Gold Nanoparticles

Gold nanoparticles with anisotropic structures have tunable absorption properties and diverse bioapplications as image contrast agents, plasmonics, and therapeutic–diagnostic materials. Amino acids with electrostatically charged side chains possess inner affinity for metal ions. Lysine (Lys) efficiently controlled the growing into star-shape nanoparticles with controlled narrow sizes (30–100 nm) and produced in high yields (85–95%). Anisotropic nanostructures showed tunable absorbance from UV to NIR range, with extraordinary colloidal stability (−26 to −42 mV) and surface-enhanced Raman scattering properties. Advanced electron microscopy characterization through ultra-high-resolution SEM, STEM, and HR-TEM confirmed the size, nanostructure, crystalline structure, and chemical composition. Molecular dynamics simulations revealed that Lys interacted preferentially with Au­(I) through the −COOH group instead of their positive side chains with a binding free energy (BFE) of 3.4 kcal mol^–1. These highly monodisperse and colloidal stable anisotropic particles prepared with biocompatible compounds may be employed in biomedical applications

Biodirected Synthesis and Nanostructural Characterization of Anisotropic Gold Nanoparticles

Gold nanoparticles with anisotropic structures have tunable absorption properties and diverse bioapplications as image contrast agents, plasmonics, and therapeutic–diagnostic materials. Amino acids with electrostatically charged side chains possess inner affinity for metal ions. Lysine (Lys) efficiently controlled the growing into star-shape nanoparticles with controlled narrow sizes (30–100 nm) and produced in high yields (85–95%). Anisotropic nanostructures showed tunable absorbance from UV to NIR range, with extraordinary colloidal stability (−26 to −42 mV) and surface-enhanced Raman scattering properties. Advanced electron microscopy characterization through ultra-high-resolution SEM, STEM, and HR-TEM confirmed the size, nanostructure, crystalline structure, and chemical composition. Molecular dynamics simulations revealed that Lys interacted preferentially with Au­(I) through the −COOH group instead of their positive side chains with a binding free energy (BFE) of 3.4 kcal mol^–1. These highly monodisperse and colloidal stable anisotropic particles prepared with biocompatible compounds may be employed in biomedical applications

Thermodynamics of Amyloid‑β Fibril Elongation: Atomistic Details of the Transition State

Amyloid-β (Aβ) fibrils and plaques are one of the hallmarks of Alzheimer’s disease. While the kinetics of fibrillar growth of Aβ have been extensively studied, several vital questions remain. In particular, the atomistic origins of the Arrhenius barrier observed in experiments have not been elucidated. Employing the familiar thermodynamic integration method, we have directly simulated the dissociation of an Aβ_(15–40) (D23N mutant) peptide from the surface of a filament along its most probable path (MPP) using all-atom molecular dynamics. This allows for a direct calculation of the free energy profile along the MPP, revealing a multipeak energetic barrier between the free peptide state and the aggregated state. By definition of the MPP, this simulated unbinding process represents the reverse of the physical elongation pathway, allowing us to draw biophysically relevant conclusions from the simulation data. Analyzing the detailed atomistic interactions along the MPP, we identify the atomistic origins of these peaks as resulting from the dock-lock mechanism of filament elongation. Careful analysis of the dynamics of filament elongation could prove key to the development of novel therapeutic strategies for amyloid-related diseases

Thermodynamics of Amyloid‑β Fibril Elongation: Atomistic Details of the Transition State

Amyloid-β (Aβ) fibrils and plaques are one of the hallmarks of Alzheimer’s disease. While the kinetics of fibrillar growth of Aβ have been extensively studied, several vital questions remain. In particular, the atomistic origins of the Arrhenius barrier observed in experiments have not been elucidated. Employing the familiar thermodynamic integration method, we have directly simulated the dissociation of an Aβ_(15–40) (D23N mutant) peptide from the surface of a filament along its most probable path (MPP) using all-atom molecular dynamics. This allows for a direct calculation of the free energy profile along the MPP, revealing a multipeak energetic barrier between the free peptide state and the aggregated state. By definition of the MPP, this simulated unbinding process represents the reverse of the physical elongation pathway, allowing us to draw biophysically relevant conclusions from the simulation data. Analyzing the detailed atomistic interactions along the MPP, we identify the atomistic origins of these peaks as resulting from the dock-lock mechanism of filament elongation. Careful analysis of the dynamics of filament elongation could prove key to the development of novel therapeutic strategies for amyloid-related diseases

Modulating the Physicochemical and Structural Properties of Gold-Functionalized Protein Nanotubes through Thiol Surface Modification

Biomolecules are advantageous scaffolds for the synthesis and ordering of metallic nanoparticles. Rotavirus VP6 nanotubes possess intrinsic affinity to metal ions, a property that has been exploited to synthesize gold nanoparticles over them. The resulting nanobiomaterials have unique properties useful for novel applications. However, the formed nanobiomaterials lack of colloidal stability and flocculate, limiting their functionality. Here we demonstrate that it is possible to synthesize thiol-protected gold nanoparticles over VP6 nanotubes, which resulted in soluble nanobiomaterials. With this strategy, it was possible to modulate the size, colloidal stability, and surface plasmon resonance of the synthesized nanoparticles by controlling the content of the thiolated ligands. Two types of water-soluble ligands were tested, a small linear ligand, sodium 3-mercapto-1-propanesulfonate (MPS), and a bulky ligand, 5-mercaptopentyl β-d-glucopyranoside (GlcC₅SH). The synthesized nanobiomaterials had a higher stability in suspension, as determined by Z-potential measurements. To the extent of our knowledge, this is the first time that a rational strategy is developed to modulate the particular properties of metal nanoparticles in situ synthesized over a protein bioscaffold through thiol coating, achieving a high spatial and structural organization of nanoparticles in a single integrative hybrid structure

Analytical Characterization of Size-Dependent Properties of Larger Aqueous Gold Nanoclusters

Gold nanoclusters (AuNCs) with well-defined structure and arrangement possess particular physical and functional properties. AuNCs that differ only by less than 1 nm in diameter corresponding to one atomic layer show different structural, optical, and physicochemical properties in a size-dependent mode, making their analytical characterization a challenge. Herein we describe an integrative approach to characterization of larger aqueous AuNC (Au₁₀₂-pMBA₄₄, Au₁₄₄pMBA₆₀ and higher) selected by gel electrophoresis (PAGE). We employ UV–vis, dynamic light scattering, and zeta-potential in combination with high-performance analytical techniques such as multiwavelength analytical ultracentrifugation and electrospray ionization mass spectrometry were used to separate aqueous AuNCs and to determine their specific hydrodynamic diameter, partial abundance, molecular weight, and mass/charge ratios when present in a complex mixture of AuNCs containing Au₁₀₂ (1.6 nm), Au₁₄₄ (2 nm), and Au_288–328 (2.5 nm). Advanced analytical electron microscopy imaging (spherical aberration corrected BF/HAADF-STEM at low voltages dose) also revealed the structures of discrete arrangements of gold nanocluster populations

Analytical Characterization of Size-Dependent Properties of Larger Aqueous Gold Nanoclusters

Gold nanoclusters (AuNCs) with well-defined structure and arrangement possess particular physical and functional properties. AuNCs that differ only by less than 1 nm in diameter corresponding to one atomic layer show different structural, optical, and physicochemical properties in a size-dependent mode, making their analytical characterization a challenge. Herein we describe an integrative approach to characterization of larger aqueous AuNC (Au₁₀₂-pMBA₄₄, Au₁₄₄pMBA₆₀ and higher) selected by gel electrophoresis (PAGE). We employ UV–vis, dynamic light scattering, and zeta-potential in combination with high-performance analytical techniques such as multiwavelength analytical ultracentrifugation and electrospray ionization mass spectrometry were used to separate aqueous AuNCs and to determine their specific hydrodynamic diameter, partial abundance, molecular weight, and mass/charge ratios when present in a complex mixture of AuNCs containing Au₁₀₂ (1.6 nm), Au₁₄₄ (2 nm), and Au_288–328 (2.5 nm). Advanced analytical electron microscopy imaging (spherical aberration corrected BF/HAADF-STEM at low voltages dose) also revealed the structures of discrete arrangements of gold nanocluster populations

Triethylamine Solution for the Intractability of Aqueous Gold–Thiolate Cluster Anions: How Ion Pairing Enhances ESI-MS and HPLC of <i>aq</i>-Au_<i>n</i>(pMBA)_<i>p</i>

Herein we disclose methods that greatly improve the solution- and gas-phase handling properties of larger aqueous-phase gold–thiolate clusters, which previously presented extreme technical obstacles to molecular analysis and size control, even as they have enjoyed ever-wider applications in materials science and biomedicine. The methods are based upon an analogy between the polyacidic surface structure of the pMBA-protected clusters (pMBA = <i>p</i>-mercaptobenzoic acid) and that of oligonucleotides. A volatile ion-pairing reagent, TEA = triethylamine, greatly improves solution-phase stability near neutral pH and thus facilitates both electrospray generation of the gas-phase ions and the in-line reversed-phase ion-pairing HPLC-ESI-MS approach to analyzing complex mixtures of Au-pMBA oligomers and clusters. Previously anticipated but never established compounds, including Au₃₆(pMBA)₂₄, are thereby demonstrated. These results are in accord with recent theoretical simulations of ion pairing of model Au₁₄₄(pMBA)₆₀ clusters in aqueous solutions. This advance complements our recent work on their <i>nonaqueous</i> (hydrophobic) counterparts, in which redox electrochemistry is sufficient to support the efficient LC-ESI processes, enabling various precise measurements on the intact molecular ions. Here, we report (i) novel conditions for enhanced ESI generation of polyanions of the aqueous clusters and by extension (ii) a notably improved method by which mixtures of these clusters may be successfully separated and detected by ion-pair reversed-phase HPLC-MS

Hidden Components in Aqueous “Gold-144” Fractionated by PAGE: High-Resolution Orbitrap ESI-MS Identifies the Gold-102 and Higher All-Aromatic Au‑<i>p</i>MBA Cluster Compounds

Experimental and theoretical evidence reveals the resilience and stability of the larger aqueous gold clusters protected with <i>p</i>-mercaptobenzoic acid ligands (<i>p</i>MBA) of composition Au_<i>n</i>(<i>p</i>MBA)_p or (<i>n</i>, <i>p</i>). The Au₁₄₄(<i>p</i>MBA)₆₀, (144, 60), or gold-144 aqueous gold cluster is considered special because of its high symmetry, abundance, and icosahedral structure as well as its many potential uses in material and biological sciences. Yet, to this date, direct confirmation of its precise composition and total structure remains elusive. Results presented here from characterization via high-resolution electrospray ionization mass spectrometry on an Orbitrap instrument confirm Au₁₀₂(<i>p</i>MBA)₄₄ at isotopic resolution. Further, what usually appears as a single band for (144, 60) in electrophoresis (PAGE) is shown to also contain the (130, 50), recently determined to have a truncated-decahedral structure, and a (137, 56) component in addition to the dominant (144, 60) compound of chiral-icosahedral structure. This finding is significant in that it reveals the existence of structures never before observed in all-aromatic water-soluble species while pointing out the path toward elucidation of the thermodynamic control of protected gold nanocrystal formation

Helical Growth of Ultrathin Gold–Copper Nanowires

In this work, we report the synthesis and detailed structural characterization of novel helical gold–copper nanowires. The nanowires possess the Boerdijk–Coxeter–Bernal structure, based on the pile up of octahedral, icosahedral, and/or decahedral seeds. They are self-assembled into a coiled manner as individual wires or into a parallel-ordering way as groups of wires. The helical nanowires are ultrathin with a diameter of less than 10 nm and variable length of several micrometers, presenting a high density of twin boundaries and stacking faults. To the best of our knowledge, such gold–copper nanowires have never been reported previously