Colloidal nanoparticles are being intensely pursued in current nanoscience research. Nanochemists are often frustrated by the well-known fact that no two nanoparticles are the same, which precludes the deep understanding of many fundamental properties of colloidal nanoparticles in which the total structures (core plus surface) must be known. Therefore, controlling nanoparticles with atomic precision and solving their total structures have long been major dreams for nanochemists. Recently, these goals are partially fulfilled in the case of gold nanoparticles, at least in the ultrasmall size regime (1–3 nm in diameter, often called nanoclusters). This review summarizes the major progress in the field, including the principles that permit atomically precise synthesis, new types of atomic structures, and unique physical and chemical properties of atomically precise nanoparticles, as well as exciting opportunities for nanochemists to understand very fundamental science of colloidal nanoparticles (such as the s...

Atomically Precise Colloidal Metal Nanoclusters and Nanoparticles: Fundamentals and Opportunities

Atomically precise pieces of matter of nanometer dimensions composed of noble metals are new categories of materials with many unusual properties. Over 100 molecules of this kind with formulas such as Au25(SR)18, Au38(SR)24, and Au102(SR)44 as well as Ag25(SR)18, Ag29(S2R)12, and Ag44(SR)30 (often with a few counterions to compensate charges) are known now. They can be made reproducibly with robust synthetic protocols, resulting in colored solutions, yielding powders or diffractable crystals. They are distinctly different from nanoparticles in their spectroscopic properties such as optical absorption and emission, showing well-defined features, just like molecules. They show isotopically resolved molecular ion peaks in mass spectra and provide diverse information when examined through multiple instrumental methods. Most important of these properties is luminescence, often in the visible–near-infrared window, useful in biological applications. Luminescence in the visible region, especially by clusters prot...

Atomically Precise Clusters of Noble Metals: Emerging Link between Atoms and Nanoparticles

Due to their atomically precise structures and intriguing chemical/physical properties, metal nanoclusters are an emerging class of modular nanomaterials. Photo-luminescence (PL) is one of their most fascinating properties, due to the plethora of promising PL-based applications, such as chemical sensing, bio-imaging, cell labeling, phototherapy, drug delivery, and so on. However, the PL of most current nanoclusters is still unsatisfactory-the PL quantum yield (QY) is relatively low (generally lower than 20%), the emission lifetimes are generally in the nanosecond range, and the emitted color is always red (emission wavelengths of above 630 nm). To address these shortcomings, several strategies have been adopted, and are reviewed herein: capped-ligand engineering, metallic kernel alloying, aggregation-induced emission, self-assembly of nanocluster building blocks into cluster-based networks, and adjustments on external environment factors. We further review promising applications of these fluorescent nanoclusters, with particular focus on their potential to impact the fields of chemical sensing, bio-imaging, and bio-labeling. Finally, scope for improvements and future perspectives of these novel nanomaterials are highlighted as well. Our intended audience is the broader scientific community interested in the fluorescence of metal nanoclusters, and our review hopefully opens up new horizons for these scientists to manipulate PL properties of nanoclusters. This review is based on publications available up to December 2018.

Tailoring the photoluminescence of atomically precise nanoclusters.

ConspectusA comprehensive understanding of chemical bonding and reactions at the surface of nanomaterials is of great importance in the rational design of their functional properties and applicatio...

Surface Chemistry of Atomically Precise Coinage-Metal Nanoclusters: From Structural Control to Surface Reactivity and Catalysis.

Atomic clusters, consisting of a few to a few thousand atoms, have emerged over the past 40 years as the ultimate nanoparticles, whose structure and properties can be controlled one atom at a time. One of the early motivations in studying clusters was to understand how the properties of matter evolve as a function of size, shape, and composition. Over the past few decades, more than 200 000 papers have been published in this field. These studies have not only led to a considerable understanding of this evolution from clusters to crystals, but also have revealed many unusual size-specific properties that make cluster science an interdisciplinary field on its own, bridging physics, chemistry, materials science, biology, and medicine. More importantly, the possibility of creating a new class of materials, composed of clusters instead of atoms as building blocks, has fueled the hope that one can synthesize materials from the bottom-up with unique and tailored properties. This Review focuses on the properties ...

Super Atomic Clusters: Design Rules and Potential for Building Blocks of Materials

Quantum Mechanical Studies of Large Metal, Metal Oxide, and Metal Chalcogenide Nanoparticles and Clusters.

CRISPR-Cas9 is a genome editing technology with major impact in life sciences. In this system, the endonuclease Cas9 generates double strand breaks in DNA upon RNA-guided recognition of a complementary DNA sequence, which strictly requires the presence of a protospacer adjacent motif (PAM) next to the target site. Although PAM recognition is essential for cleavage, it is unknown whether and how PAM binding activates Cas9 for DNA cleavage at spatially distant sites. Here, we find evidence of a PAM-induced allosteric mechanism revealed by microsecond molecular dynamics simulations. PAM acts as an allosteric effector and triggers the interdependent conformational dynamics of the Cas9 catalytic domains (HNH and RuvC), responsible for concerted cleavage of the two DNA strands. Targeting such an allosteric mechanism should enable control of CRISPR-Cas9 functionality.

http://pubs.acs.org/doi/pdf/10.1021/jacs.7b05313

Protospacer Adjacent Motif-Induced Allostery Activates CRISPR-Cas9.

Ligand exchange reactions are important to functionalize and modify the optical and electronic properties of thiolate-protected gold nanoparticles. A theoretical investigation of the kinetics of the ligand exchange process was performed for the Au25(SH)18– nanocluster with CH3SH as the incoming thiol ligand. Three possible ligand exchange sites were investigated: between the core gold atom and the terminal −SH unit, between the staple gold atom and the terminal −SH unit, and between a staple gold atom and the central −SH unit. We found that the most favorable ligand exchange takes place between terminal −SH units and staple gold atoms.

Ligand Exchange Mechanism on Thiolate Monolayer Protected Au25(SR)18 Nanoclusters

Hybrid density functional theory calculations have been employed to investigate the water oxidation reaction on model cobalt oxide dimer and cubane complexes. Electronic structure and energetics of these model compounds were thoroughly investigated. The thermodynamically lowest energy pathway on the dimer catalyst proceeds through a nucleophilic attack of a solvent water molecule to Co(V)-O radical moiety. The lowest energy pathway on the cubane catalyst involves a geminal coupling of Co(V)-O radical oxo group with bridging oxo sites. Model systems were found to be very sensitive to the positions of ligands and to the hydrogen-bonding environment leading to different isomer energies.

Reaction Pathways for Water Oxidation to Molecular Oxygen Mediated by Model Cobalt Oxide Dimer and Cubane Catalysts

Manganese is selected by nature for the water oxidation process. In this study, we use an in silico approach to study a manganese cubane complex Mn4O4(H2O)x(OH)y x = 4–8, y = 8–4 with water-derived ligands. We investigate oxidation state configurations ranging from all Mn(IV) to all Mn(III) states. Understanding these simplest architectures for water splitting is essential for the bottom up design of commercially viable electrocatalysts. Both μ3-oxo and μ3-hydroxo versions of the catalysts were examined; μ3-hydroxo versions are generally higher in energy in all the oxidation state configurations except for the Mn4(III III III III) state (this rearranges to a Mn4(II III III IV) state) and the Mn4(III III III IV) state (this rearranges to a Mn4(II III IV IV) state). Out of all the oxidation state configurations we studied, we observed that Mn4(IV IV IV IV), Mn4(III IV IV IV), and Mn4(III III IV V) configurations are thermodynamically viable for water oxidation. All three reaction pathways proceed via nucleo...

Amendra Fernando

Papers

Quantum Mechanical Studies of Large Metal, Metal Oxide, and Metal Chalcogenide Nanoparticles and Clusters.

Protospacer Adjacent Motif-Induced Allostery Activates CRISPR-Cas9.

Ligand Exchange Mechanism on Thiolate Monolayer Protected Au25(SR)18 Nanoclusters

Reaction Pathways for Water Oxidation to Molecular Oxygen Mediated by Model Cobalt Oxide Dimer and Cubane Catalysts

Theoretical Investigation of Water Oxidation Catalysis by a Model Manganese Cubane Complex