Tailoring the interaction between a gold nanocluster and a fluorescent dye by cluster size: creating a toolbox of range-adjustable pH sensors.

We present a novel strategy for tailoring the fluorescent azadioxatriangulenium (KU) dye-based pH sensor to the target pH range by regulating the p value of the gold nanoclusters. Based on the correlation between the p and surface curvature of ligand-protected nanoparticles, the p value of the gold nanoclusters was controlled by size. In particular, three different-sized -mercaptobenzoic acid (-MBA) protected gold nanoclusters, Au(-MBA), Au(-MBA), and Au(-MBA) were used as the regulator for the pH range of the KU response.

Covalent and non-covalent coupling of a Au nanocluster with a fluorophore: energy transfer, quenching and intracellular pH sensing.

Interactions between an atomically precise gold nanocluster Au(-MBA) (-MBA = mercaptobenzoic acid) and a fluorescent organic dye molecule (KU, azadioxatriangulenium) are studied. In solution, the constituents form spontaneously a weakly bound complex leading to quenching of fluorescence of the KU dye energy transfer. The KU can be separated from the complex by lowering pH, leading to recovery of fluorescence, which forms a basis for an optical reversible pH sensor.

Systematic study of SYBR green chromophore reveals major improvement with one heteroatom difference.

Five nucleic acid binding cyanine dyes were synthesized and their photophysical properties were evaluated. Changing a single heteroatom in the chromophore causes major differences both in brightness and photostability between the dyes. With such alteration, the brightness of the chromophore increased two-fold compared to the one found in SYBR Green I.

Chemically Selective Imaging of Individual Bonds through Scanning Electron Energy-Loss Spectroscopy: Disulfide Bridges Linking Gold Nanoclusters.

As proof-of-principle of chemically selective, spatially resolved imaging of individual bonds, we carry out electron energy-loss spectroscopy in a scanning transmission electron microscopy instrument on atomically precise, thiolate-coated gold nanoclusters linked with 5,5'-bis(mercaptomethyl)-2,2'-bipyridine dithiol ligands. The images allow the identification of bridging disulfide bonds (R-S-S-R) between clusters, and X-ray photoelectron spectra support the finding.

Dithiol-Induced Oligomerization of Thiol-Protected Gold Nanoclusters.

Controlled synthesis of nanostructure oligomers requires detailed understanding of their wet chemistry and the forces driving the polymerization process. In this paper, we report the main factors affecting the reaction yields of a dithiol-induced synthesis of covalently bound nanocluster dimers and oligomers and present a detailed analysis of possible reaction mechanisms. We synthesize the nanocluster oligomers using monodisperse -mercaptobenzoic acid (-MBA)-protected gold nanoclusters with a nominal composition of Au(-MBA) to minimize ensemble effects on size, shape, and surface structure.

Atomically Precise Nanocluster Assemblies Encapsulating Plasmonic Gold Nanorods.

The self-assembled structures of atomically precise, ligand-protected noble metal nanoclusters leading to encapsulation of plasmonic gold nanorods (GNRs) is presented. Unlike highly sophisticated DNA nanotechnology, this strategically simple hydrogen bonding-directed self-assembly of nanoclusters leads to octahedral nanocrystals encapsulating GNRs. Specifically, the p-mercaptobenzoic acid (pMBA)-protected atomically precise silver nanocluster, Na [Ag (pMBA) ], and pMBA-functionalized GNRs were used.

Exploring the atomic structure of 1.8nm monolayer-protected gold clusters with aberration-corrected STEM.

Monolayer-protected (MP) Au clusters present attractive quantum systems with a range of potential applications e.g. in catalysis.

Template-Free Supracolloidal Self-Assembly of Atomically Precise Gold Nanoclusters: From 2D Colloidal Crystals to Spherical Capsids.

We report supracolloidal self-assembly of atomically precise and strictly monodisperse gold nanoclusters involving p-mercaptobenzoic acid ligands (Au -pMBA ) under aqueous conditions into hexagonally packed monolayer-thick two-dimensional facetted colloidal crystals (thickness 2.7 nm) and their bending to closed shells leading to spherical capsids (d ca. 200 nm), as controlled by solvent conditions.

Covalently linked multimers of gold nanoclusters Au(p-MBA) and Au(p-MBA).

We present the synthesis, separation, and characterization of covalently-bound multimers of para-mercaptobenzoic acid (p-MBA) protected gold nanoclusters. The multimers were synthesized by performing a ligand-exchange reaction of a pre-characterized Au(p-MBA) nanocluster with biphenyl-4,4'-dithiol (BPDT). The reaction products were separated using gel electrophoresis yielding several distinct bands.

Hydrophobic pocket targeting probes for enteroviruses.

Visualization and tracking of viruses without compromising their functionality is crucial in order to understand virus targeting to cells and tissues, and to understand the subsequent subcellular steps leading to virus uncoating and replication. Enteroviruses are important human pathogens causing a vast number of acute infections, and are also suggested to contribute to the development of chronic diseases like type I diabetes. Here, we demonstrate a novel method to target site-specifically the hydrophobic pocket of enteroviruses.

Molecule-like photodynamics of Au102(pMBA)44 nanocluster.

Photophysical properties of a water-soluble cluster Au102(pMBA)44 (pMBA = para-mercaptobenzoic acid) are studied by ultrafast time-resolved mid-IR spectroscopy and density functional theory calculations in order to distinguish between molecular and metallic behavior. In the mid-IR transient absorption studies, visible or near-infrared light is used to electronically excite the sample, and the subsequent relaxation is monitored by studying the transient absorption of a vibrational mode in the ligands. Based on these studies, a complete picture of energy relaxation dynamics is obtained: (1) 0.

Solvation chemistry of water-soluble thiol-protected gold nanocluster Au₁₀₂ from DOSY NMR spectroscopy and DFT calculations.

The hydrodynamic diameter of Aum(pMBA)n [(m, n) = (102, 44) and (144, 60)] clusters in aqueous media was determined via DOSY NMR spectroscopy. The apparent size of the same (n, m) cluster depends on the counter ion of the deprotonated pMBA(-) ligand as explained by the competing ion-pair strength and hydrogen bonding interactions studied in DFT calculations. The choice of the counter ion affects the surface chemistry and molecular structure at the organic/water interface, which is relevant for biological applications.

4,4-Di-fluoro-2,3;5,6-bis-(tetra-methylene)-4-bora-3a,4a-di-aza-s-indacene (LD540).

The title compound, C18H21BF2N2, is a lipophilic dye based on a BODIPY fluoro-phore backbone, which was developed for microscopic imaging of lipid droplets; the mol-ecule has a planar BODIPY core [dihedral angle between the pyrrole rings = 2.3 (3)°] and two tetra-methyl-ene substituents at the 2,3- and 5,6-positions in a half-chair conformation. One of the tetra-methyl-ene substituents is disordered over two two sets of sites with site occupancies of 0.

Site-specific targeting of enterovirus capsid by functionalized monodisperse gold nanoclusters.

Development of precise protocols for accurate site-specific conjugation of monodisperse inorganic nanoparticles to biological material is one of the challenges in contemporary bionanoscience and nanomedicine. We report here a successful site-specific covalent conjugation of functionalized atomically monodisperse gold clusters with 1.5-nm metal cores to viral surfaces.

Vibrational Perturbations and Ligand-Layer Coupling in a Single Crystal of Au144(SC2H4Ph)60 Nanocluster.

We have determined vibrational signatures and optical gap of the Au144(PET)60 (PET: phenylethylthiol, SC2H4Ph) nanocluster solvated in deuterated dichloromethane (DCM-D2, CD2Cl2) and in a single crystal. For crystals, solid-state (13)C NMR and X-ray diffraction were also measured. A revised value of 2200 cm(-1) (0.

Nondestructive size determination of thiol-stabilized gold nanoclusters in solution by diffusion ordered NMR spectroscopy.

Diffusion ordered NMR spectroscopy (DOSY) was used as an analytical tool to estimate the size of thiol-stabilized gold nanoclusters in solution, namely, phenylethanethiol (PET) stabilized Au25(PET)18, Au38(PET)24, and Au144(PET)60. This was achieved by determining the diffusion coefficient and hydrodynamic radius from solution samples that were confirmed to be monodispersed by electrospray ionization mass spectrometry. The average cluster diameters obtained by this technique were estimated to be 1.

An overview of the methods used in the characterisation of natural organic matter (NOM) in relation to drinking water treatment.

Natural organic matter (NOM) is found in all surface, ground and soil waters. During recent decades, reports worldwide show a continuing increase in the color and NOM of the surface water, which has an adverse affect on drinking water purification. For several practical and hygienic reasons, the presence of NOM is undesirable in drinking water.

N-Benzyl-2,3,4,5,6-penta-fluoro-benz-amide.

In the title compound, C(14)H(8)F(5)NO, the dihedral angle between the planes of the penta-fluoro-phenyl and phenyl rings is 18.34 (5)°. An inter-molecular N-H⋯O hydrogen bond between the amide groups connects these mol-ecules to form an infinite chain through the crystal structure.

(E)-7-(Pyren-1-yl)hept-6-enoic acid.

The title compound, C(23)H(20)O(2), is a precursor of a pyrene-based supra-molecular element for non-covalent attachment to a carbon nanotube. The asymmetric unit contains three independent mol-ecules. The carb-oxy-lic acid group in each of these mol-ecules serves as an inter-molecular hydrogen-bond donor and acceptor, generating the commonly observed double O-H⋯O hydrogen-bond motif in an eight-membered ring.