Preparation of 103Pd seeds Part II. “Molecular Plating” of 103Pd onto copper rod

A method for ¹⁰³Pd molecular plating onto the surface of the copper rod is reported. The optimal composition of the plating bath was: palladium chloride 2 g/l, ammonium hydroxide (28%) 150 ml/l, sodium hypophosphite 12 g/l, and ammonium chloride 37 g/l. The whole procedure of ¹⁰³Pd molecular plating will last 50 minutes at 40 °C. This article provides valuable experience for the preparation of ¹⁰³Pd seeds.     

Analysis of nuclear quantum effects on hydrogen bonding

The impact of nuclear quantum effects on hydrogen bonding is investigated for a series of hydrogen fluoride (HF)n clusters and a partially solvated fluoride anion, F-(H2O). The nuclear quantum effects are included using the path integral formalism in conjunction with the Car-Parrinello molecular dynamics (PICPMD) method and using the second-order vibrational perturbation theory (VPT2) approach. For the HF clusters, a directional change in the impact of nuclear quantum effects on the hydrogen-bonding strength is observed as the clusters evolve toward the condensed phase. Specifically, the inclusion of nuclear quantum effects increases the F-F distances for the (HF)n=2-4 clusters and decreases the F-F distances for the (HF)n>4 clusters. This directional change occurs because the enhanced electrostatic interactions between the HF monomers become more dominant than the zero point energy effects of librational modes as the size of the HF clusters increases. For the F-(H2O) system, the inclusion of nuclear quantum effects decreases the F-O distance and strengthens the hydrogen bonding interaction between the fluoride anion and the water molecule because of enhanced electrostatic interactions. The vibrationally averaged 19F shielding constant for F-(H2O) is significantly lower than the value for the equilibrium geometry, indicating that the electronic density on the fluorine decreases as a result of the quantum delocalization of the shared hydrogen. Deuteration of this system leads to an increase in the vibrationally averaged F-O distance and nuclear magnetic shielding constant because of the smaller degree of quantum delocalization for deuterium.     

Neighboring group participation of phosphine oxide functionality in the highly regio- and stereoselective iodohydroxylation of 1,2-allenylic diphenyl phosphine oxides

Two sets of reaction conditions were established to enable the highly regio- and stereoselective iodohydroxylation of 1,2-allenylic diphenyl phosphine oxides, yielding (E)-2-iodo-3-hydroxy-1-alkenyl diphenyl phosphine oxides with very high stereoselectivity. The scope of this reaction was examined extensively. Notably, studies on the reactivity of optically active substrates indicated that the axial chirality in the starting allenes may be efficiently transferred to the center chirality of the products with no discernible loss of enantiopurity. Due to the importance of phosphine-containing compounds, both as reagents and ligands, this reaction shows potentials in organic synthesis. Investigations using ESI-MS technology on the (18)O-labeled product, which was prepared using (18)O-water as the solvent, indicated that the (18)O atom was bound to phosphorus in the final product and the oxygen atom of the hydroxyl comes from the phosphinyl functionality of the allene reactant. These results provided solid evidence for the formation of a five-membered cyclic intermediate from the neighboring group participation of the diphenylphosphinyl group. To the best of our knowledge, this is the first time that the neighboring group participation of this type of group was observed.     

γ-Oxygenation of α,β-unsaturated esters by vinylogous O-nitroso Mukaiyama aldol reaction

A practical procedure has been developed for γ-oxygenation of α,β-unsaturated esters by a vinylogous O-nitroso Mukaiyama aldol reaction followed by a one-pot N-O bond heterolysis of the in situ generated γ-aminoxy-α,β-unsaturated esters.     

Using a TEMPO-based fluorescent probe for monitoring oxidative stress in living cells

Generation of too many reactive oxygen species (ROS) in relation to available antioxidants in living cells can cause oxidative stress, which is involved in the development and progression of several serious diseases. 2',7'-Dichlorodihydrofluorescein (DCFH) and its diacetate form, DCFH-DA, are widely used probes for monitoring general oxidative stress in cells, but DCFH oxidation is not always related to ROS. We report here a new method for quantifying cellular oxidative stress using a 2,2,6,6-tetramethyl- piperidine-1-oxyl (TEMPO)-based probe. We tested and verified the probe both in cell-free solutions and in living cells under conditions of increased or reduced oxidative stress. The probe revealed the oxidative stress status in living cells and may be a useful complement to DCFH fluorescent probes.     

锰（Ⅱ）—邻菲口罗啉配合物极谱吸附波及其应用

在ｐＨ９．５ＮＨ３ＮＨ４Ｃｌ缓冲溶液中，Ｍｎ（Ⅱ）与邻菲口罗啉形成的配合物在－１．３６Ｖ（ｖｓ．ＳＣＥ）处产生一灵敏的吸附波，一阶导数峰电流与Ｍｎ（Ⅱ）浓度在５×１０－８５×１０－６ｍｏｌ／Ｌ范围内呈线性关系，检出限为２×１０－８ｍｏｌ／Ｌ对极谱性质及反应机理进行了研究，用该法测定了大豆和茶叶中的微量锰，结果满意     

A light-driven rotaxane molecular shuttle with dual fluorescence addresses

[reaction: see text] A molecular shuttle containing an alpha-CD macrocycle, an azobenzene unit, and two different fluorescent naphthalimide units was synthesized. The cis-trans photoisomerization of the azobenzene unit resulted in the motion of the CD macrocycle on the track. Because of the easy regulation and full reversibility of the fluorescence change of the two stopper units, the molecular shuttle could be used as a molecular storage medium or switch with all-optical inputs and outputs.     

Direct Ab Initio Dynamics Study for the Hydrogen Abstraction Reaction: CH _{2} ({^{3}}B_{1}) + H2CO \rightarrow CH3 + CHO

We present a direct ab initio dynamics study of thermal rate constants of the hydrogen abstraction reaction of CH $_{2}(^{3}B_{1})$ + H₂CO $\rightarrow $ CH₃ + CHO. The MP2/cc-pVDZ method is employed to optimize the geometries of stationary points as well as the points on the minimum energy path. The energies of all the points were further refined at the CCSD(T)/cc-pVTZ level of theory based on the Moller– Plesset perturbation theory (MP2) optimized geometries. The rate constants were evaluated using the conventional transition state theory, the canonical variational TST, and the improved canonical variational TST, also both including small-curvature tunneling correction in the temperature range of 300–2,500 K. The calculated results show that the rate constants have positive temperature dependence in the calculated temperature range. The calculated results show that the tunneling effect is important at low temperature region.     

Calix[4] open-chain crown ether-modified, vinyl-functionalized hybrid silica monolith for capillary electrochromatography

A novel calix[4] open-chain crown ether (p-tert-butylcalix[4]arene-1,3-bis(allyloxyethy) ether)-modified, organic-inorganic hybrid silica-based monolithic column possessing vinyl ligands for CEC is described. The monolithic silica matrix containing a vinyl functionality was synthesized by in situ cocondensation of tetramethoxysilane (TMOS) and vinyltrimethoxysilane (VTMS) via sol-gel process and chemically modified with calix[4] open-chain crown ether by free radical polymerization procedure using alpha, alpha'-azobisisobutyronitrile (AIBN) as an initiator. Morphology of the monolithic column was examined by SEM and the successful incorporation of calix[4] open-chain crown ether to the vinyl-hybrid monolith was characterized by infrared (IR) spectra. Compared with an unmodified vinyl-hybrid monolithic column, slightly stronger EOF at pH >7.5 was observed for this monolithic column due to the ionization of phenolic hydroxyls on the lower rim of calix[4]arene. VTMS/TMOS ratios in the reaction mixture were varied and 1:4 was found to be optimum to obtain homogeneous monolith with good permeability. The performance of the column was evaluated by nucleotides, beta-blockers, neurotransmitters, and PAHs as test solutes and compared with that of unmodified vinyl-hybrid monolithic column. Greatly improved column performance was obtained due to the host-guest interaction and intermolecular hydrogen bonding provided by the calix[4] open-chain crown ether moiety. The column efficiencies for neurotransmitters and nucleotides are up to 120 000 and 110 000 plates/m, respectively. Migration time and theoretical plate number reproducibilities were reasonable with RSDs less than 1.0 and 1.8% each for within column runs and not more than 7.2 and 8.6% each for column-to-column measurements, using four nucleotides as test solutes.     

Mg-catalyzed autoclave synthesis of aligned silicon carbide nanostructures

In this article, a novel magnesium-catalyzed co-reduction route was developed for the large-scale synthesis of aligned beta-SiC one-dimensional (1D) nanostructures at relative lower temperature (600 degrees C). By carefully controlling the reagent concentrations, we could synthesize beta-SiC rodlike and needlelike nanostructures. The possible growth mechanism of the as-synthesized beta-SiC 1D nanostructures has been investigated. The structure and morphology of the as-synthesized beta-SiC nanostructures are characterized using X-ray diffraction, Fourier transform infrared absorption, and scanning and transmission electron microscopes. Raman and photoluminescence properties are also investigated at room temperature. The as-synthesized beta-SiC nanostructures exhibit strong shape-dependent field emission properties. Corresponding to their shapes, the as-synthesized nanorods and nanoneedles display the turn-on fields of 12, 8.4, and 1.8 V/microm, respectively.