Thiol-functionalized undecagold clusters by ligand exchange: synthesis, mechanism, and properties

Modifying carbon dots with L-phenylalanine for rapid discrimination of tryptophan enantiomers

New chiral carbon dots (CDs), L-PCDs, for discriminating tryptophan (Trp) enantiomers were prepared in this work. Firstly, original CDs were synthesized through a hydrothermal method using pyridine-2,6-dicarboxylic acid and o-phenylenediamine as raw materials. Then, the surface of original CDs was modified with L-phenylalanine to create chiral fluorescent carbon L-PCDs. In the presence of D-Trp, the fluorescence intensity of L-PCDs decreased significantly while it remained unchanged in the presence of L-Trp. The chiral sensing system used in this study has a rapid response time of 3 minutes and can identify enantiomers with an enantioselectivity (ID/IL) of up to 3.3. For D-Trp, a good linear relationship can be obtained in the range of 0.3-4.2 mM with a limit of detection of 0.06 mM. This sensor allows for both quantitative detection of D-Trp and determination of enantiomeric percentage in the racemate. The chiral recognition mechanism is attributed to the different interaction between D-/L-Trp and L-PCDs.

In Situ Incorporation of Atomically Precise Au Nanoclusters within Zeolites for Ambient Temperature CO Oxidation

Preserving ultrasmall sizes of metal particles is a key challenge in the study of heterogeneous metal-based catalysis. Confining the ultrasmall metal clusters in a well-defined crystalline porous zeolite has emerged as a promising approach to stabilize these metal species. Successful encapsulation can be achieved by the addition of ligated metal complexes to zeolite synthesis gel before hydrothermal synthesis. However, controlling the metal particle size during post-reduction treatment remains a major challenge in this approach. Herein, an in situ incorporation strategy of pre-made atomically precise gold clusters within Na-LTA zeolite was established for the first time. With the assistance of mercaptosilane ligands, the gold clusters were successfully incorporated within the Na-LTA without premature precipitation and metal aggregation during the synthesis. We have demonstrated that the confinement of gold clusters within the zeolite framework offers high stability against sintering, leading to superior CO oxidation catalytic performance (up to 12 h at 30 °C, with a space velocity of 3000 mL g-1 h-1).

Effects of protecting groups on luminescent metal nanoclusters: spectroscopic signatures and applications

Luminescent metal nanoclusters (NCs) have been established as next-generation fluorophores. Their biocompatible and non-toxic nature, along with excellent chemical- and photo-stability, enables them to find applications in multi-disciplinary areas. However, preparing NCs which are stable is always challenging, primarily owing to their small size and propensity to self-aggregate. In this review, we highlight a holistic approach as to how ligands and templates can monitor the stability of NCs, tune their spectroscopic signatures, and alter their applications. The role of small molecules of a large ligand in the preparation of NCs and their associated limitations are also discussed. We have summarized how these NCs can be utilized in sensing several metal ions, pH, viscosity and temperature of many systems which have biological relevance. Additionally, these luminescent metal NCs find usage in cell-imaging, discriminating between cancerous and non-cancerous cell lines and also targeting specific organelles within the cellular environment.

Ligand engineering of immobilized nanoclusters on surfaces: ligand exchange reactions with supported Au11(PPh3)7Br3

The properties of gold nanoclusters, apart from being size-dependent, are strongly related to the nature of the protecting ligand. Ligand exchange on Au nanoclusters has been proven to be a powerful tool for tuning their properties, but has so far been limited to dissolved clusters in solution. By supporting the clusters previously functionalized in solution, it is uncertain that the functionality is still accessible once the cluster is on the surface. This may be overcome by introducing the desired functionality by ligand exchange after the cluster deposition on the support material. We herein report the first successful ligand exchange on supported (immobilized) Au11 nanoclusters. Dropcast films of Au11(PPh3)7Br3 on planar oxide surfaces were shown to react with thiol ligands, resulting in clusters with a mixed ligand shell, with both phosphines and thiolates being present. Laser ablation inductively coupled plasma mass spectrometry and infrared spectroscopy confirmed that the exchange just takes place on the cluster dropcast. Contrary to systems in solution, the size of the clusters did not increase during ligand exchange. Different structures/compounds were formed depending on the nature of the incoming ligand. The feasibility to extend ligand engineering to supported nanoclusters is proven and it may allow controlled nanocluster functionalization.

Switching the subcellular organelle targeting of atomically precise gold nanoclusters by modifying the capping ligand

Here, we have achieved the target switching fluorescence imaging and photodynamic activity of hydrosoluble AuNCs from lysosomes to mitochondria through ligand exchange.

Small Gold Nanoparticles Interfaced to Electrodes through Molecular Linkers: A Platform to Enhance Electron Transfer and Increase Electrochemically Active Surface Area

For the smallest nanostructures (<5 nm), small changes in structure can lead to significant changes in properties and reactivity. In the case of nanoparticle (NP)-functionalized electrodes, NP structure and composition, and the nature of the NP-electrode interface have a strong influence upon electrochemical properties that are critical in applications such as amperometric sensing, photocatalysis and electrocatalysis. Existing methods to fabricate NP-functionalized electrodes do not allow for precise control over all these variables, especially the NP-electrode interface, making it difficult to understand and predict how structural changes influence NP activity. We investigated the electrochemical properties of small (d_core < 2.5 nm) gold nanoparticles (AuNPs) on boron doped diamond electrodes using three different electrode fabrication techniques with varying degrees of nanoparticle-electrode interface definition. Two methods to attach AuNPs to the electrode through a covalently bound molecular linker were developed and compared to NP-functionalized electrodes fabricated using solution deposition methods (drop-casting and physiadsorption of a monolayer). In each case, a ferrocene redox probe was tethered to the AuNP surface to evaluate electron transfer through the AuNPs. The AuNPs that were molecularly interfaced with the electrode exhibited nearly ideal, reproducible electrochemical behavior with narrow redox peaks and small peak separations, whereas the solution deposited NPs had broader redox peaks with large peak separations. These data suggest that the molecular tether facilitates AuNP-mediated electron transfer. Interestingly, the molecularly tethered NPs also had significantly more electrochemically active surface area than the solution deposited NPs. The enhanced electrochemical behavior of the molecularly interfaced NPs demonstrates the significant influence of the interface on NP-mediated electron transfer and suggests that similar modified electrodes can serve as versatile platforms for studies and applications of nanoparticles.

Subnanometer Control of Mean Core Size during Mesofluidic Synthesis of Small (D(core) < 10 nm) Water-Soluble, Ligand-Stabilized Gold Nanoparticles

A convenient, single-step synthesis is reported that produces ligand-stabilized, water-soluble gold nanoparticles (AuNPs) with subnanometer-level precision of the mean core diameter over a range of 2-9 nm for a series of desired surface chemistries. The synthesis involves the reduction of a Au(III) species with sodium borohydride in the presence of a functionalized alkyl thiosulfate (Bunte salt) to yield thiolate-protected AuNPs. A key advantage of this synthesis is that simply adjusting the pH of the gold salt solution leads to control over the AuNP core size. The speciation of Au(III), and therefore the kinetics for its reduction and the core size produced, depends upon pH. The use of pH as the sole variable to control core size is a more reliable and convenient method than traditional approaches that rely on adjusting the concentrations and ratios of ligand, metal salt, and reducing agent. The average core size increased as the pH was raised for each ligand studied. Because the influence of pH was different for each of the ligands, working curves were plotted for each ligand to identify conditions to synthesize particles with specific, targeted core diameters. Using this approach, reaction conditions can be rapidly optimized using a combination of a mesofluidic reactor and small-angle X-ray scattering (SAXS) size analysis. The use of the mesofluidic reactor was needed to ensure fast mixing given the rapid kinetics for core formation. Using the reactor, it is possible to obtain reproducible sizes across multiple syntheses (<1-2% core size variation) and subnanometer control of the mean core dimensions. The synthetic method demonstrated here provides an attractive alternative to two-step syntheses involving ligand exchange because it is more efficient and eliminates the possibility of nanoparticle core size changes during exchange steps. This approach enables the development of "size ladders" of particles with the same surface chemistry for investigations of structure-function relationships.

Aggregation kinetics and colloidal stability of functionalized nanoparticles

The functionalization of nanoparticles has primarily been used as a means to impart stability in nanoparticle suspensions. In most cases even the most advanced nanomaterials lose their function should suspensions aggregate and settle, but with the capping agents designed for specific solution chemistries, functionalized nanomaterials generally remain monodisperse in order to maintain their function. The importance of this cannot be underestimated in light of the growing use of functionalized nanomaterials for wide range of applications. Advanced functionalization schemes seek to exert fine control over suspension stability with small adjustments to a single, controllable variable. This review is specific to functionalized nanoparticles and highlights the synthesis and attachment of novel functionalization schemes whose design is meant to affect controllable aggregation. Some examples of these materials include stimulus responsive polymers for functionalization which rely on a bulk solution physicochemical threshold (temperature or pH) to transition from a stable (monodisperse) to aggregated state. Also discussed herein are the primary methods for measuring the kinetics of particle aggregation and theoretical descriptions of conventional and novel models which have demonstrated the most promise for the appropriate reduction of experimental data. Also highlighted are the additional factors that control nanoparticle stability such as the core composition, surface chemistry and solution condition. For completeness, a case study of gold nanoparticles functionalized using homologous block copolymers is discussed to demonstrate fine control over the aggregation state of this type of material.

Cooperative Gold Nanoparticle Stabilization by Acetylenic Phosphaalkenes

Acetylenic phosphaalkenes (APAs) are used as a novel type of ligands for the stabilization of gold nanoparticles (AuNP). As demonstrated by a variety of experimental and analytical methods, both structural features of the APA, that is, the P=C as well as the C≡C units are essential for NP stabilization. The presence of intact APAs on the AuNP is demonstrated by surface-enhanced Raman spectroscopy (SERS), and first principle calculations indicate that bonding occurs most likely at defect sites on the Au surface. AuNP-bound APAs are in chemical equilibrium with free APAs in solution, leading to a dynamic behavior that can be explored for facile place-exchange reactions with other types of anchor groups such as thiols or more weakly binding phosphine ligands.

Ligand-induced change of the crystal structure and enhanced stability of the Au11 nanocluster

Compared with the Au₁₁(PPh₃)₇Cl₃ and [Au₁₁(PPh₃)₈Cl₂]Cl, [Au₁₁(PPh₂(CH₂)₅Ph₂P)₄(SePh)₂]⁺ exhibits some structural differences and shows significantly enhanced stability in storage and thiol etching.

Designing nanomaterials to maximize performance and minimize undesirable implications guided by the Principles of Green Chemistry

A sustainable material design framework is proposed that emphasizes the importance of establishing structure–property–function (SPF) and structure–property–hazard (SPH) relationships to guide the rational design of ENMs.

Structurally similar triphenylphosphine-stabilized undecagolds, Au11(PPh3)7Cl3 and [Au11(PPh3)8Cl2]Cl, exhibit distinct ligand exchange pathways with glutathione

Ligand exchange is frequently used to introduce new functional groups on the surface of inorganic nanoparticles or clusters while preserving the core size. For one of the smallest clusters, triphenylphosphine (TPP)-stabilized undecagold, there are conflicting reports in the literature regarding whether core size is retained or significant growth occurs during exchange with thiol ligands. During an investigation of these differences in reactivity, two distinct forms of undecagold were isolated. The X-ray structures of the two forms, Au₁₁(PPh₃)₇Cl₃ and [Au₁₁(PPh₃)₈Cl₂]Cl, differ only in the number of TPP ligands bound to the core. Syntheses were developed to produce each of the two forms, and their spectroscopic features correlated with the structures. Ligand exchange on [Au₁₁(PPh₃)₈Cl₂]Cl yields only small clusters, whereas exchange on Au₁₁(PPh₃)₇Cl₃ (or mixtures of the two forms) yields the larger Au₂₅ cluster. The distinctive features in the optical spectra of the two forms made it possible to evaluate which of the cluster forms were used in the previously published papers and clarify the origin of the differences in reactivity that had been reported. The results confirm that reactions of clusters and nanoparticles may be influenced by small variations in the arrangement of ligands and suggest that the role of the ligand shell in stabilizing intermediates during ligand exchange may be essential to preventing particle growth or coalescence.

Blue emitting undecaplatinum clusters

A blue luminescent 11-atom platinum cluster showing step-like optical features and the absence of plasmon absorption was synthesized. The cluster was purified using high performance liquid chromatography (HPLC). Electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) mass spectrometry (MS) suggest a composition, Pt11(BBS)8, which was confirmed by a range of other experimental tools. The cluster is highly stable and compatible with many organic solvents.

Identification of gold nanoparticle-resistant mutants of Saccharomyces cerevisiae suggests a role for respiratory metabolism in mediating toxicity

Positively charged gold nanoparticles (0.8-nm core diameter) reduced yeast survival, but not growth, at a concentration of 10 to 100 μg/ml. Among 17 resistant deletion mutants isolated in a genome-wide screen, highly significant enrichment was observed for respiration-deficient mutants lacking genes encoding proteins associated with the mitochondrion.

Size control in the synthesis of 1-6 nm gold nanoparticles via solvent-controlled nucleation

We report a facile synthetic route for size-controlled preparation of gold nanoparticles. Nearly monodisperse gold nanoparticles with core diameters of 1-6 nm were obtained by reducing AuP(Phenyl)(3)Cl with tert-butylamine borane in the presence of dodecanethiol in the solvent mixture of benzene and CHCl(3). Mechanism studies have shown that the size control is achieved by the solvent-controlled nucleation in which the nuclei concentration increases with increasing the fraction of CHCl(3), leading to smaller particles. It was also found that, following the solvent-controlled nucleation, particle growth occurs via ligand replacement of PPh(3) on the nuclei by Au(I)thiolate generated by the digestive etching of small particles. This synthetic strategy was successfully demonstrated with other alkanethiols of different chain length with which size-controlled, monodisperse gold nanoparticles were prepared in remarkable yield without requiring any postsynthesis treatments.

Crystal structures of Au2 complex and Au25 nanocluster and mechanistic insight into the conversion of polydisperse nanoparticles into monodisperse Au25 nanoclusters

We previously reported a size-focusing conversion of polydisperse gold nanoparticles capped by phosphine into monodisperse [Au(25)(PPh(3))(10)(SC(2)H(4)Ph)(5)Cl(2)](2+) nanoclusters in the presence of phenylethylthiol. Herein, we have determined the crystal structure of [Au(25)(PPh(3))(10)(SC(2)H(4)Ph)(5)Cl(2)](2+) nanoclusters and also identified an important side-product-a Au(I) complex formed in the size focusing process. The [Au(25)(PPh(3))(10)(SC(2)H(4)Ph)(5)Cl(2)](2+) cluster features a vertex-sharing bi-icosahedral core, resembling a rod. The formula of the Au(I) complex is determined to be [Au(2)(PPh(3))(2)(SC(2)H(4)Ph)](+) by electrospray ionization (ESI) mass spectrometry, and its crystal structure (with SbF(6)(-) counterion) reveals Au-Au bridged by -SC(2)H(4)Ph and with terminal bonds to two PPh(3) ligands. Unlike previously reported [Au(2)(PR(3))(2)(SC(2)H(4)Ph)](+) complexes in the solid state, which exist as tetranuclear complexes (i.e., dimers of [Au(2)(PR(3))(2)(SC(2)H(4)Ph)](+) units) through a Au···Au aurophilic interaction, in our case we found that the [Au(2)(PPh(3))(2)(SC(2)H(4)Ph)](+) complex exists as a single entity, rather than being dimerized to form a tetranuclear complex. The observation of this Au(I) complex allows us to gain insight into the intriguing conversion process from polydisperse Au nanoparticles to monodisperse Au(25) nanoclusters.

Reaction mechanism governing formation of 1,3-bis(diphenylphosphino)propane-protected gold nanoclusters

This report outlines the determination of a reaction mechanism that can be manipulated to develop directed syntheses of gold monolayer-protected clusters (MPCs) prepared by reduction of solutions containing 1,3-bis(diphenylphosphino)propane (L(3)) ligand and Au(PPh(3))Cl. Nanocluster synthesis was initiated by reduction of two-coordinate phosphine-ligated [Au(I)LL'](+) complexes (L, L' = PPh(3), L(3)), resulting in free radical complexes. The [Au(0)LL'](•) free radicals nucleated, forming a broad size distribution of ligated clusters. Timed UV-vis spectroscopy and electrospray ionization mass spectrometry monitored the ligated Au(x), 6 ≤ x ≤ 13, clusters, which comprise reaction intermediates and final products. By employing different solvents and reducing agents, reaction conditions were varied to highlight the largest portion of the reaction mechanism. We identified several solution-phase reaction classes, including dissolution of the gold precursor, reduction, continuous nucleation/core growth, ligand exchange, ion-molecule reactions, and etching of colloids and larger clusters. Simple theories can account for the reaction intermediates and final products. The initial distribution of the nucleation products contains mainly neutral clusters. However, the rate of reduction controls the amount of reaction overlap occurring in the system, allowing a clear distinction between reduction/nucleation and subsequent solution-phase processing. During solution-phase processing, the complexes undergo core etching and core growth reactions, including reactions that convert neutral clusters to cations, in a cyclic process that promotes formation of stable clusters of specific metal nuclearity. These processes comprise "size-selective" processing that can narrow a broad distribution into specific nuclearities, enabling development of tunable syntheses.

Systematic evaluation of nanomaterial toxicity: utility of standardized materials and rapid assays

The challenge of optimizing both performance and safety in nanomaterials hinges on our ability to resolve which structural features lead to desired properties. It has been difficult to draw meaningful conclusions about biological impacts from many studies of nanomaterials due to the lack of nanomaterial characterization, unknown purity, and/or alteration of the nanomaterials by the biological environment. To investigate the relative influence of core size, surface chemistry, and charge on nanomaterial toxicity, we tested the biological response of whole animals exposed to a matrix of nine structurally diverse, precision-engineered gold nanoparticles (AuNPs) of high purity and known composition. Members of the matrix include three core sizes and four unique surface coatings that include positively and negatively charged headgroups. Mortality, malformations, uptake, and elimination of AuNPs were all dependent on these parameters, showing the need for tightly controlled experimental design and nanomaterial characterization. Results presented herein illustrate the value of an integrated approach to identify design rules that minimize potential hazard.

Quantum-sized gold nanoclusters: bridging the gap between organometallics and nanocrystals

This Concept article provides an elementary discussion of a special class of large-sized gold compounds, so-called Au nanoclusters, which lies in between traditional organogold compounds (e.g., few-atom complexes, <1 nm) and face-centered cubic (fcc) crystalline Au nanoparticles (typically >2 nm). The discussion is focused on the relationship between them, including the evolution from the Au⋅⋅⋅Au aurophilic interaction in Au(I) complexes to the direct Au-Au bond in clusters, and the structural transformation from the fcc structure in nanocrystals to non-fcc structures in nanoclusters. Thiolate-protected Au(n)(SR)(m) nanoclusters are used as a paradigm system. Research on such nanoclusters has achieved considerable advances in recent years and is expected to flourish in the near future, which will bring about exciting progress in both fundamental scientific research and technological applications of nanoclusters of gold and other metals.

Antibody-mediated self-limiting self-assembly for quantitative analysis of nanoparticle surfaces by atomic force microscopy

Quantification of very low density molecular coatings on large (60 nm) gold nanoparticles (AuNPs) is demonstrated via the use of antibody-mediated self-limiting self-assembly of small and large AuNPs into raspberry-like structures subsequently imaged by atomic force microscopy (AFM). AFM imaging is proposed as an automated, lower-cost, higher-throughput alternative to immunostaining and imaging by transmission electron microscopy. Synthesis of large AuNPs, containing one of three ligand molecules in one of three stoichiometries (1, 2, or 10 ligands per AuNP), and small probe AuNPs with one of three antibody molecules in a one antibody per AuNP ratio, enabled a range of predicted self-limiting self-assembled structures. A model predicting the probability of observing a given small to large AuNP ratio based on a topography measurement such as AFM is described, in which random orientational deposition is assumed and which accounts for the stochastic synthesis method of the library AuNPs with varied ligand ratios. Experimental data were found to agree very well with the predictive models when using an established AFM sample preparation method that avoids drying-induced aggregation.

Electron microscopic visualization of the filament binding mode of actin-binding proteins

A large number of actin-binding proteins (ABPs) regulate various kinds of cellular events in which the superstructure of the actin cytoskeleton is dynamically changed. Thus, to understand the actin dynamics in the cell, the mechanisms of actin regulation by ABPs must be elucidated. Moreover, it is particularly important to identify the side, barbed-end or pointed-end ABP binding sites on the actin filament. However, a simple, reliable method to determine the ABP binding sites on the actin filament is missing. Here, a novel electron microscopic method for determining the ABP binding sites is presented. This approach uses a gold nanoparticle that recognizes a histidine tag on an ABP and an image analysis procedure that can determine the polarity of the actin filament. This method will facilitate future study of ABPs.

High-rate synthesis of phosphine-stabilized undecagold nanoclusters using a multilayered micromixer

Growth in the potential applications of nanomaterials has led to a focus on the development of new manufacturing approaches for these materials. In particular, an increased demand due to the unique properties of nanomaterials requires a substantial yield of high-performance materials and a simultaneous reduction in the environmental impact of these processes. In this paper, a high-rate production of phosphine-stabilized undecagold nanoclusters was achieved using a layer-up strategy which involves the use of microlamination architectures; the patterning and bonding of thin layers of material (laminae) to create a multilayered micromixer in the range of 25-250 µm thick was used to step up the production of phosphine-stabilized undecagold nanoclusters. The continuous production of highly monodispersed phosphine-stabilized undecagold nanoclusters at a rate of about 11.8 (mg s(-1)) was achieved using a microreactor with a size of 1.687 cm(3). This result is about 500 times over conventional batch syntheses based on the production rate per reactor volume.

Direct synthesis of polymerizable surfactant-stabilized nanoparticles: the macromolecular monomers for fabricating nanoparticle-polymer composites

Incorporation of inorganic nanoparticles (NPs) into polymers is the current means for enhancing the performance of polymer materials, the key to which is the increase of compatibility between NPs and polymer media. In this paper, the polymerizable surfactant octadecyl-p-vinylbenzyldimethylammonium chloride (OVDAC) is synthesized and used as a capping agent for direct synthesis of various metal NPs, for instance Au, Ag, Pd, and Pt, and semiconductor NPs, for instance ZnS, CdS, and PbS. The preformed OVDAC-stabilized NPs are lipophilic and act as macromolecular monomers in the copolymerization with lipophilic monomers.

On the ligand's role in the fluorescence of gold nanoclusters

The fluorescence of metal nanoparticles (such as gold and silver) has long been an intriguing topic and has drawn considerable research interest. However, the origin of fluorescence still remains unclear. In this work, on the basis of atomically monodisperse, 25-atom gold nanoclusters we present some interesting results on the fluorescence from [Au(25)(SR)(18)](q) (where q is the charge state of the particle), which has shed some light on this issue. Our work explicitly shows that the surface ligands (-SR) play a major role in enhancing the fluorescence of gold nanoparticles. Specifically, the surface ligands can influence the fluorescence in two different ways: (i) charge transfer from the ligands to the metal nanoparticle core (i.e., LMNCT) through the Au-S bonds, and (ii) direct donation of delocalized electrons of electron-rich atoms or groups of the ligands to the metal core. Following these two mechanisms, we have demonstrated strategies to enhance the fluorescence of thiolate ligand-protected gold nanoparticles. This work is hoped to stimulate more experimental and theoretical research on the atomic level design of luminescent metal nanoparticles for promising optoelectronic and other applications.

Direct synthesis of large water-soluble functionalized gold nanoparticles using Bunte salts as ligand precursors

The widespread use of functionalized gold nanoparticles (AuNPs) in a rapidly increasing number of sensing and biomedical applications has made the development of synthetic methods that combine precise surface chemistry control (functionality) with effective core size control over the range of 1-20 nm crucial. Although a variety of effective methods exist for controlling the core size and functionality during gold nanoparticle synthesis, there is a lack of synthetic methods that permit the direct synthesis of thiol-protected gold nanoparticles with core diameters greater than 5.0 nm. Inspired by previous reports on the use of alkyl thiosulfates (Bunte salts) as ligand precursors, we anticipated that the slow passivation kinetics of these masked thiols would provide a method to synthesize large functionalized AuNPs directly. We found that Bunte salts produce larger AuNPs under the same synthesis conditions than do thiols. We investigated the effect of the ligand/gold ratio, temperature, and reducing agent concentration on the particle diameter and dispersity to understand better how to control particle size. The AuNP core size can be systematically controlled by varying the ratio of ligand precursor/gold (L/Au) and the temperature of the reaction. The synthesis produces functionalized AuNPs ranging from 1.5 to 20.0 nm in diameter. The use of Bunte salts provides a convenient synthetic platform for the synthesis of AuNPs across this size range that possess a variety of surface functionalities, including positive, negative, and neutral functional groups.

On the size evolution of gold-monolayer-protected clusters by ligand place-exchange reactions: the effect of headgroup-gold interactions

To functionalize Au MPCs (monolayer-protected gold clusters), ligand place-exchange reactions provide a convenient route in which the initial capping ligands are displaced by mixing the MPCs with an excess amount of incoming ones. However, literature reports show that the diameters of the modified products do not always stay unchanged. Because of the diversity of experimental conditions carried out in the documented studies, there is still a lack of comprehensive understanding concerning the size evolution. Herein, carefully controlled and examined parameters include the initial size of MPCs [Au(101)(PPh(3))(21)Cl(5)], the reaction time, the concentration of incoming ligands, a homologous series of incoming ligands, and the anchoring headgroups. The results show that the final particle size is determined by the strength of headgroup-gold adsorption which is correlated with the curvature of the final product in a thermodynamic model derived from Gibbs-Thomson equation.

Quantum sized, thiolate-protected gold nanoclusters

The scientific study of gold nanoparticles (typically 1-100 nm) has spanned more than 150 years since Faraday's time and will apparently last longer. This review will focus on a special type of ultrasmall (<2 nm) yet robust gold nanoparticles that are protected by thiolates, so-called gold thiolate nanoclusters, denoted as Au(n)(SR)(m) (where, n and m represent the number of gold atoms and thiolate ligands, respectively). Despite the past fifteen years' intense work on Au(n)(SR)(m) nanoclusters, there is still a tremendous amount of science that is not yet understood, which is mainly hampered by the unavailability of atomically precise Au(n)(SR)(m) clusters and by their unknown structures. Nonetheless, recent research advances have opened an avenue to achieving the precise control of Au(n)(SR)(m) nanoclusters at the ultimate atomic level. The successful structural determination of Au(102)(SPhCOOH)(44) and [Au(25)(SCH(2)CH(2)Ph)(18)](q) (q = -1, 0) by X-ray crystallography has shed some light on the unique atomic packing structure adopted in these gold thiolate nanoclusters, and has also permitted a precise correlation of their structure with properties, including electronic, optical and magnetic properties. Some exciting research is anticipated to take place in the next few years and may stimulate a long-lasting and wider scientific and technological interest in this special type of Au nanoparticles.

3-(2-aminophenyl)-4-methyl-1,3-thiazole-2(3H)-thione as an ecofriendly sulphur transfer agent to prepare alkanethiols in high yield and high purity

A new process is described for preparing very pure linear alkanethiols and linear α,ω-alkanedithiols using a sequential alkylation of the title compound, followed by a ring closure to quantitatively give the corresponding 3-methyl[1,3]thiazolo[3,2-a]-[3,1]benzimidazol-9-ium salt and the alkanethiol derivative under mild conditions. The alkanethiol and the heteroaromatic salt are easily separated by a simple extraction process. The intermediate thiazolium quaternary salts resulting from the first reaction step can be isolated in quantitative yields, affording an odourless protected form of the thiols.

Chiral gold nanoparticles

Monolayer-protected gold nanoparticles have many appealing physical and chemical properties such as quantum size effects, surface plasmon resonance, and catalytic activity. These hybrid organic-inorganic nanomaterials have promising potential applications as building blocks for nanotechnology, as catalysts, and as sensors. Recently, the chirality of these materials has attracted attention, and application to chiral technologies is an interesting perspective. This minireview deals with the preparation of chiral gold nanoparticles and their chiroptical properties. On the basis of the latter, together with predictions from quantum chemical calculations, we discuss different models that were put forward in the past to rationalize the observed optical activity in metal-based electronic transitions. We furthermore critically discuss these models in view of recent results on the structure determination of some gold clusters as well as ligand-exchange experiments examined by circular dichroism spectroscopy. It is also demonstrated that vibrational circular dichroism can be used to determine the structure of a chiral adsorbate and the way it interacts with the metal. Finally, possible applications of these new chiral materials are discussed.

Polymer-encapsulated gold-nanoparticle dimers: facile preparation and catalytical application in guided growth of dimeric ZnO-nanowires

Rational assembly of nanoparticles is of vital importance for exploring fundamental electronic and optical properties and for constructing novel nanoscale devices. Through controlling aggregation kinetics, dimers and trimers of gold nanoparticles were generated and encapsulated with polymer by using a one-pot synthesis that involved simple heating and cooling. Dimers of gold nanoparticles were enriched from the resulting solution by centrifugation. The polymer shells maintain the stability of the nanoparticle organization, preventing aggregation and disintegration during subsequent purification, enrichment, and application. A typical enriched sample showed that the dimer population reached 61% among 989 nanoparticles surveyed. In a proof-of-concept application, the gold nanoparticle dimers were used as catalyst to guide the growth of dimeric zinc oxide nanowires. Nanowire dimers with unprecedented narrow spacing (20 to 60 nm) were achieved using a vapor transport growth method; dimeric nanowire population reached approximately 25%.