Transverse momentum distribution of the Z produced at the Large Hadron Collider and related phenomena

From the recent theoretical result on the production of the Higgs boson at the Large Hadron Collider, it follows that other particles will also be produced with small transverse momentum, of the order of 1 GeV/c$1\text{GeV}/c$. The leptonic decay mode of the Z is especially suited for a first observation of this phenomenon. Other related effects, such as paired jets, are also discussed.     

Role of ions in the colloidal synthesis of gold nanowires

Gold nanocrystals of different shapes have been made by a wet chemical approach based on a two-step, seed-mediated synthesis. In this paper, we demonstrate a one-step synthetic method for achieving simple and systematic control over the shape of gold nanoparticles. Gold nanowires, which have been prepared by multi-step approaches, are produced in very high yield in this single-step technique. The width of the rods can be varied over a broader range compared to previously reported methods. Rectangle-, cube- or tetrapod-like gold nanocrystals can also be prepared in aqueous solution at room temperature. The formation of various shapes, in the presence of silver nitrate, requires bromide ion and alkylammonium surfactant ion of appropriate hydrocarbon tail length. The shape, dimension and yield of the nanocrystals depend on the nature and concentrations of the stabilizing cationic surfactants and other additives, such as salts, in addition to the reactants.     

Stabilizer-free nanosized gold sols

The paper describes a convenient, rapid, and reproducible method for the synthesis of stable dispersions of uniform gold nanoparticles at ambient temperatures by mixing aqueous solutions of tetrachloroauric acid and iso-ascorbic acid. The influence of the experimental conditions on the size of the gold particles and the stability of the final sols was monitored by dynamic light scattering and UV-vis spectrophotometry. It was found that the size of the resulting nanoparticles is affected by the concentration and the pH of gold solution, while the stability of the electrostatically stabilized final sols is strongly dependent on the excess of reductant in the system, the ionic strength, and the temperature of the precipitation. Since the preparation process does not require the addition of a dispersing agent, the surface of the resulting gold nanoparticles can be easily functionalized to make them suitable for applications in medicine, biology, and catalysis.     

Four new isoflavonoids from the stem bark of Erythrina variegata

Bioassay-directed fractionation of the stem bark extract of Erythrina variegata L. has resulted in the isolation of three new isoflavones: 5,4'-dihydroxy-8-(3,3-dimethylallyl)-2'-methoxyisopropylfurano[4,5:6,7]isoflavone (1), 5,7,4'-trihydroxy-6-(3,3-dimethylallyloxiranylmethyl)isoflavone (2), 5,4'-dihydroxy-8-(3,3-dimethylallyl)-2'-hydroxymethyl-2'-methylpyrano[5,6:6,7]isoflavone (3) and a new isoflavanone, 5,4'-dihydroxy-2'-methoxy-8-(3,3-dimethylallyl)-2',2'-dimethylpyrano[5,6:6,7]isoflavanone (4) together with seven known compounds, euchrenone b10 (5), isoerysenegalensein E (6), wighteone (7), laburnetin (8), lupiwighteone (9), erythrodiol (10), and oleanolic acid (11). The structures were determined on the basis of spectroscopic analyses and chemical evidence. The effect of these compounds on the proliferation of rat osteogenic sarcoma (UMR106) is also reported.     

Real-time characterization of cytotoxicity using single-cell impedance monitoring

Cellular impedance sensors have attracted great attention as a powerful characterization tool for real-time, label-free detection of cytotoxic agents. However, impedance measurements with conventional cell-based sensors that host multiple cells on a single electrode neither provide optimal cell signal sensitivity nor are capable of recording individual cell responses. Here we use a single-cell based platform to monitor cellular impedance on planar microelectrodes to characterize cellular death. In this study, individual cells were selectively patterned on microelectrodes with each hosting one live cell through ligand-mediated natural cell adhesion. Changes in cellular morphology and cell-electrode adherence were monitored after the patterned cells were treated with varying concentrations of hydrogen peroxide, sodium arsenite, and disodium hydrogen arsenate, three potent toxicants related to neurotoxicity and oxidative stress. At low toxicant concentrations, impedance waveforms acquired from individual cells showed variable responses. A time- and concentration-dependent response was seen in the averaged single-cell impedance waveform for all three toxicants. The apoptosis and necrosis characterizations were performed to validate cell impedance results. Furthermore, time constants of apoptosis and necrosis in response to toxicant exposure were analytically established using an equivalent circuit model that characterized the mechanisms of cell death.     

Plasmonic properties of single multispiked gold nanostars: correlating modeling with experiments

Gold nanostars, possessing multiple sharp spikes, have emerged as promising plasmonic particles in the field of ultrasensitive sensing. We have developed a water-based method for high-yield synthesis of size-tunable anisotropic gold nanoparticles with a varying number of spiky surface protrusions, and performed systematic experimental and theoretical analyses of the optical properties of the single gold nanostars by characterizing them simultaneously with scanning electron microscopy and dark-field scattering spectroscopy. The morphologies and corresponding scattering spectra of the individual gold nanostars have been compared with electromagnetic simulations of the plasmonic resonances utilizing the finite-difference time-domain (FDTD) method. The study provides a correlation between the experimental and calculated scattering spectra and charge distributions of the different plasmon modes in the individual gold nanostars with varying numbers and relative orientations of surface protrusions. Our results provide guidelines for choosing gold nanostars with a proper number of spikes and appropriate dimensions of the core and arms for particular plasmonic applications as well as for further developing preparation methods of multispiked metal nanoparticles.     

Abnormal N-heterocyclic carbene palladium complex: living catalyst for activation of aryl chlorides in Suzuki-Miyaura cross coupling

Palladium complexes bearing abnormal N-heterocyclic carbene were used as catalysts in Suzuki-Miyaura cross coupling of aryl chlorides at 25 °C. The catalyst remained active for 10 successive catalytic runs and can activate 4-chlorotoluene at 25 °C with 0.01 mol% catalyst loading resulting in a TON of 9500 within 6 h.     

Photoswitchable architectural polymer: Toward azo‐based polyamidoamine side‐chain dendritic polyester

A versatile approach to the synthesis of novel polyamidoamine (PAMAM) side‐chain dendritic polyester (SCDPE) possessing azobenzene motifs in the polymeric core is described and displayed reversible cis–trans (E/Z) isomerization upon exposure to UV light. A polymerization reaction was conducted in solution using ester‐terminated PAMAM dendritic diol ( 1a , G 3.5) and azobenzene dicarboxylic acid chloride in the presence of triethylamine. PAMAM dendritic diol 1a as well as SCDPE ( 1 ) were thoroughly characterized by means of IR and NMR (¹H and ¹³C) spectroscopies. The intrinsic viscosity of 1 at 36 °C in CHCl₃ was found to be 0.38 dl/g. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4182–4188, 2001     

Carbonylative Suzuki coupling reactions catalyzed by ONO pincer–type Pd(II) complexes using chloroform as a carbon monoxide surrogate

Benzoylhydrazone Schiff base–ligated three new ONO pincer–type palladium(II) complexes, [(PdL¹(PPh₃)] ( 1 ), [(PdL²(PPh₃)] ( 2 ), and [(PdL³(PPh₃)] ( 3 ), were synthesized by the reaction of the respective ligand, N-(2-hydroxybenzylidene)benzohydrazide (HL¹), N-(2-hydroxy-3-methoxybenzylidene)benzohydrazide (HL²), or N-(5-bromo-2-hydroxybenzylidene) benzohydrazide (HL³), with Pd(OAc)₂ and PPh₃ in methanol and isolated as air-stable reddish-orange crystalline solids in high yields (78%–83%). All three complexes were fully characterized by elemental analysis, Fourier-transform infrared spectroscopy, UV–Visible, ¹H nuclear magnetic resonance (NMR), ¹³C{¹H} NMR, and ³¹P{¹H} NMR spectroscopic studies. The molecular structure of all three complexes was established unambiguously by single-crystal X-ray diffraction studies which revealed a distorted square planar geometry of all three complexes. The ONO pincer–type ligands occupied three coordination sites at the palladium, while the fourth site is occupied by the monodentate triphenylphosphine ligand. The catalytic potential of all three complexes was explored in the carbonylative Suzuki coupling of aryl bromides and iodides with arylboronic acids to yield biaryl ketones, using CHCl₃ as the source of carbonyl. The reported protocol is convenient and safe as it obviates the use of carbon monoxide (CO) balloons or pressured CO reactors which are otherwise needed for the carbonylation reactions. The methodology has been successfully applied to the synthesis of two antineoplastic drugs, namely, phenstatin and naphthylphenstatin, in good yields (81% and 85%, respectively). Under the optimized reaction conditions, complex 2 exhibited the best catalytic activity in the carbonylative Suzuki couplings. The reported catalysts have wide reaction scope with good functional group tolerance. All catalysts could be retrieved from the reaction after completion and recycled up to three times with insignificant loss in the catalytic activity.