Charge-dependent hierarchical self-assembling of fluorinated gold nanoclusters.

Au(SR) nanoclusters decorated with semifluorinated thiolate ligands (SFLs) self-assemble hierarchically depending on the charge state of the nanocluster component; the use of the anionic cluster ([Au]) resulted in the generation of nanofibers, whereas the neutral counterpart ([Au]) gave micron-sized filaments as a result of the bundling/twisting of the nanofibers.

Controlled nanocrystallization of gold nanoclusters within surfactant envelopes: enhancing aggregation-induced emission in solution.

The nanocrystallization of functional molecules has been a subject of recent interest in the current development of nanotechnology. Herein, we report the unprecedented synthesis of single nanocrystals of a molecular gold nanocluster in a homogeneous solution by using surfactant-based nano-envelopes. The co-assembling of a Au nanocluster carrying lipophilic phosphine ligands with sodium dodecyl sulfate (SDS) in an aqueous solution results in the formation of sphere-shaped amorphous nano-aggregates coated with the surfactant.

Collective Effects of Multiple Fluorine Atoms Causing π-philic Characteristic within a Caged Polyoxometalate Framework.

Perfluorination brings about distinctive properties arising from the unusual nature of the F element, which have been extensively developed in materials science and chemistry. Herein we report that the construction of F-rich inner space within a hollowed Mo O cage ([Mo O (OCOR) (H O) ] ) leads to the emergence of unique guest binding activities in encapsulation. Prominently, the trifluoroacetate-modified cage (R=CF , 2) having as many as 90 F groups inside favors trapping cyclopentadiene (Cp), which is hardly trapped by the non-fluorinated counterpart (R=CH , 1).

In situ Microinflammation Detection Using Gold Nanoclusters and a Tissue-clearing Method.

Microinflammation enhances the permeability of specific blood vessel sites through an elevation of local inflammatory mediators, such as interleukin (IL)-6 and tumor necrosis factor (TNF)-α. By a two-dimensional immunohistochemistry analysis of tissue sections from mice with experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis (MS), we previously showed that pathogenic immune cells, including CD4 T cells, specifically accumulate and cause microinflammation at the dorsal vessels of the fifth lumbar cord (L5), resulting in the onset of disease. However, usual pathological analyses by using immunohistochemistry on sections are not effective at identifying the microinflammation sites in organs.

Anion-π interaction inside the polyanionic MoO cage with hydrophobic inner space.

In this paper, we provide experimental evidence to indicate that the polyanionic MoO cage with a hydrophobic inner nanospace has a unique capability to participate in anion-π interactions by showing a preference for electron-deficient mono-substituted benzenes over non-electron-deficient guests in inclusion.

Aggregation-induced chirality amplification of optically active fluorescent polyurethane and a cyclic dimer in the ground and excited states.

Optically active linear polyurethane and a cyclic dimer were synthesized from 2,7-diisocyanatofluorene and 2,2'-dihydroxy-1,1'-binaphthyl. The circular dichroism (CD) spectral intensity of the polymer was amplified at a higher concentration through aggregate formation, while circularly polarized light (CPL) emission was not enhanced. The cyclic dimer's CPL emission was largely amplified ( 1.

Diarsine- vs diphosphine-protected Au clusters: Effect of subtle geometric differences on optical property and electronic structure.

In the design of ligand-protected metal clusters, the choice of protecting ligands is a critical factor because they can profoundly affect the nuclearity, geometry, and electronic structures to afford a diverse range of cluster compounds. Here, we report the synthesis of two novel diarsine-protected Au clusters ([AuLCl], L = diarsine) and compare these clusters with diphosphine analogs in terms of the core geometry and optical properties. In the crystal structure, the cluster bearing C3-bridged diarsines {[Au(dpap)Cl], 3} had an apparently identical icosahedral Au core to [Au(dppe)Cl] (1) with C2-bridged diphosphines, but slight structural differences associated with the bridging unit of the ligands were found.

Self-promoted solid-state covalent networking of Au(SR) through reversible disulfide bonds. A critical effect of the nanocluster in oxidation processes.

Covalent crosslinking of ligand-protected gold nanoclusters offers interesting platforms to investigate the properties associated with the synergetic effects of multiple nanoclusters. In this paper, we report the synthesis of covalent networks of [Au(SR)] nanoclusters using reversible disulfide linkages, which was facilitated by the unique capabilities of the nanocluster to mediate oxidation processes. The conventional Au synthesis using 1,6-hexanedithiol afforded a soluble oligodisulfide-appended [Au(SR)] monomer possessing uncoordinated anionic thiolate sites at the terminal ends.

Chiroptical activity of Au clusters: experimental and theoretical understanding of the origin of helical charge movements.

Ligand-protected gold clusters with an asymmetric nature have emerged as a novel class of chiral compounds, but the origins of their chiroptical activities associated with helical charge movements in electronic transitions remain unexplored. Herein, we perform experimental and theoretical studies on the structures and chiroptical properties of Au clusters protected by mono- and di-phosphine ligands. Based on the experimental reevaluation of diphosphine-ligated Au clusters, we show that these surface ligands slightly twist the Au cores from a true icosahedron to generate intrinsic chirality in the gold frameworks.

Terahertz Raman Spectroscopy of Ligand-Protected Au Clusters.

For ligand-protected gold clusters, geometrical differences of gold cores and/or the presence of secondary gold core-ligand interactions influence their unique optical and electronic properties and can, in principle, be detected by spectral changes of gold core vibrations (phonon modes) in ultralow-frequency Raman spectroscopy. We report experimental and theoretical Raman spectra of Au clusters protected by phosphine ligands particularly in the "gold cluster fingerprint" region from 50 to 150 cm Raman shift (1.5 to 4.

Unusual Attractive Au-π Interactions in Small Diacetylene-Modified Gold Clusters.

It is well known that alkynes act as π-acids in the formation of complexes with metals. We found unprecedented attractive Au-π interactions in diacetylene-modified [core+exo]-type [Au ] clusters. The 4-phenyl-1,3-butadiynyl-modified cluster has unusually short Au-C distances in the crystal structure, revealing the presence of attractive interactions between the coordinating C≡C moieties and the neighboring bitetrahedral Au core, which is further supported by IR and NMR spectra.

Phosphine-Ligated Gold Clusters with Core+ exo Geometries: Unique Properties and Interactions at the Ligand-Cluster Interface.

Over recent years, research on the structures and properties of ligand-protected gold cluster molecules has gained significant interest. The crystal structure information accumulated to date has revealed the structural preference to adopt closed polyhedral geometries, but the use of multidentate ligands sometimes leads to the formation of exceptional structures. This Account describes results of our studies on diphosphine-coordinated [core+ exo]-type gold clusters featuring extra gold atoms outside the polyhedral cores, highlighting (1) their distinct optical properties due to the unique electronic structures generated by the exo gold atoms and (2) electronic/attractive ligand-cluster interactions that cause definite perturbation effects on the cluster properties.

Preparation of Carbodiimides with One-Handed Axial Chirality.

The axial chirality of carbodiimide was proposed in 1932, but the synthesis of carbodiimide with one-handed axial chirality has not been achieved because of the low barrier of racemization. This work presents a strategy to use a conformationally restrained cyclic structure for creating carbodiimides whose biases of the axial chirality (labeled as S/ R) are higher than 100:1, as determined by vibrational circular dichroism spectroscopy and density functional theory calculations.

An Inherently Chiral Au Framework with Double-Helical Hexagold Strands.

2,3-bis(diphenylphosphino)butane enantiomers (chiraphos, L) used as chiral auxiliaries results in the preferential formation of an unprecedented Au framework with inherent chirality. The crystal structure of [Au L Cl ] (1) has a square antiprism-like octagold core twinned by two helicene-like hexagold motifs, where the inherent chirality is associated with the helical arrangement. The clusters carrying (R,R)- and (S,S)- diphosphines had right- and left-handed strands, respectively.

Aggregation-Induced Fluorescence-to-Phosphorescence Switching of Molecular Gold Clusters.

Aggregation-induced optical responses are ubiquitous among a wide range of organic and inorganic compounds. Here, we demonstrate an unprecedented effect of aggregation on the photoluminescence (PL) profiles of [core + exo]-type [Au] clusters, which displayed a change in the dominant PL emission mode from fluorescence to phosphorescence-type upon aggregation. In solvents in which cluster molecules are highly soluble and exist as monomers, they displayed single PL bands at ∼600 nm at ambient temperatures.

Hydrogen bonds to Au atoms in coordinated gold clusters.

It is well known that various transition elements can form M···H hydrogen bonds. However, for gold, there has been limited decisive experimental evidence of such attractive interactions. Herein we demonstrate an example of spectroscopically identified hydrogen bonding interaction of C-H units to Au atoms in divalent hexagold clusters ([Au]) decorated by diphosphine ligands.

Hexanuclear Platinum(II) Thiolate Macrocyclic Host: Charge-Transfer-Driven Inclusion of a Ag(I) Ion Guest.

The inclusion of a Ag(I) ion by a hexanuclear platinum(II) thiolate macrocycle in solution was demonstrated, and the inclusion structure was determined by X-ray crystallography. Unique host-guest intermetallic interactions driven by charge transfer were elucidated by optical absorption spectroscopy and theoretical calculations.

Facile Diastereoseparation of Glycosyl Sulfoxides by Chiral Stationary Phase.

Separation of the diastereomers of glycosyl sulfoxides differing in the sulfur chirality has been difficult. This article presents a fast and scalable method for their diastereoseparation using a chiral stationary phase. The usefulness of this method was demonstrated in a 500-mg scale separation within 20 min, and in the separation of trisaccharyl sulfoxide diastereomers.

Unexpected electronic perturbation effects of simple PEG environments on the optical properties of small cadmium chalcogenide clusters.

Poly(ethylene glycol) (PEG) has been widely used for the surface protection of inorganic nanoobjects because of its virtually 'inert' nature, but little attention has been paid to its inherent electronic impacts on inorganic cores. Herein, we definitively show, through studies on optical properties of a series of PEG-modified Cd(10)Se(4)(SR)(10) clusters, that the surrounding PEG environments can electronically affect the properties of the inorganic core. For the clusters with PEG units directly attached to an inorganic core (R = (CH(2)CH(2)O)nOCH(3), 1-PEGn, n = 3, ∼7, ∼17, ∼46), the absorption bands, associated with the low-energy transitions, continuously blue-shifted with the increasing PEG chain length.

Chiral Polyurethane Synthesis Leading to π-Stacked 2/1-Helical Polymer and Cyclic Compounds.

()-1,1'-Bi(2-naphthol) was reacted with 1,4-phenylene diisocyanate leading to a mixture of linear polyurethane and cyclic compounds including a cyclic dimer and a cyclic trimer. The structure of the cyclic dimer was elucidated by X-ray crystal structure analysis. The polymer was proposed to possess a rather stiff, π-stacked, 2/1-helical conformation on the basis of NMR, CD, and UV spectra and molecular dynamics simulations.

Cluster-π electronic interaction in a superatomic Au13 cluster bearing σ-bonded acetylide ligands.

An organometallic Au13 cluster having two σ-bonded acetylide ligands was synthesized and its structure was determined by X-ray crystallography. Absorption spectral studies indicated the presence of electronic coupling between the superatomic Au13 core and the acetylide π-orbitals, which was supported by theoretical considerations.

[Au7](3+): a missing link in the four-electron gold cluster family.

Ligand-stabilized ultrasmall gold clusters offer a library of diverse geometrical and electronic structures. Among them, clusters with four valence electrons form an exceptional but interesting family because of their unique geometrical structures and optical properties. Here, we report a novel diphosphine-ligated four-electron Au7 cluster (2).