Decarboxylative Coupling Reaction in ESI(−)-MS/MS of 4-Nitrobenzyl 4-Hydroxybenzoates: Triplet Ion–Neutral Complex-Mediated 4-Nitrobenzyl Transfer

In negative electrospray ionization mass spectrometry of 4-nitrobenzyl 4-hydroxybenzoates, a decarboxylation reaction, which was significantly promoted by the presence of a nitro group on the benzyl group, competed with radical elimination reactions. Density functional theory calculations indicated that decarboxylation of deprotonated 4-nitrobenzyl vanillate occurred via a radical route involving homolytic cleavage of the C_benzyl–O bond to give a triplet ion–neutral complex, followed by decarboxylative coupling.

Open image in new window

Graphical Abstract ?

     

A Double Atomic-Tuned RuBi SAA/Bi@OG Nanostructure with Optimum Charge Redistribution for Efficient Hydrogen Evolution

Charge redistribution on surface of Ru nanoparticle can significantly affect electrocatalytic HER activity. Herein, a double atomic-tuned RuBi SAA/Bi@OG nanostructure that features RuBi single-atom alloy nanoparticle supported by Bi−O single-site-doped graphene was successfully developed by one-step pyrolysis method. The alloyed Bi single atom and adjacent Bi−O single site in RuBi SAA/Bi@OG can synergistically manipulate electron transfer on Ru surface leading to optimum charge redistribution. Thus, the resulting RuBi SAA/Bi@OG exhibits superior alkaline HER activity. Its mass activity is up to 65000 mA mg⁻¹ at an overpotential of 150 mV, which is 72.2 times as much as that of commercial Pt/C. DFT calculations reveal that the RuBi SAA/Bi@OG possesses the optimum charge redistribution, which is most beneficial to strengthen adsorption of water and weaken hydrogen-adsorption free energy in HER process. This double atomic-tuned strategy on surface charge redistribution of Ru nanoparticle opens a new way to develop highly efficient electrocatalysts.     

New platinum compounds containing the diphosphine ligand 2-(ferrocenylidene)-4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (fbpcd): Synthesis, redox behavior, and X-ray diffraction structures of PtCl2(fbpcd) and Pt(mnt)(fbpcd)

The reaction of the redox-active diphosphine ligand 2-(ferrocenylidene)-4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (fbpcd) with PtCl₂(1,5-cod) furnishes the platinum(II) compound PtCl₂(fbpcd) (2). Treatment of 2 with disodium maleonitriledithiolate (Na₂mnt) yields the chelating thiolate compound Pt(mnt)(fbpcd) (3). Both 2 and 3 have been fully characterized in solution by IR, UV–Vis, and NMR spectroscopies, and their molecular structures established by X-ray crystallography. The redox properties of the fbpcd ligand and compounds 2 and 3 have been investigated by cyclic voltammetry, and the composition of the HOMO and LUMO levels in these systems have been determined by extended Hückel MO calculations, the results of which are discussed with respect to electrochemical data.     

Complexation of L-lactate with boronic acids: a solution and holographic analysis

Boronic acids have been used as receptors for the detection of diols and alpha-hydroxy acids. The incorporation of 3-acrylamide phenyl boronic acid (3-APB) into a hydrogel generates a suitably responsive and fully reversible holographic sensor for L-lactate. However, it was also found that the use of 3-APB resulted in the sensor being responsive towards a number of other compounds containing two hydroxy groups. This report details the further investigation into the reaction between L-lactate and three boronic acid-based receptors, both in the holograms and in solution, in order to establish the mechanism of binding. A novel boronate receptor is proposed based on this understanding.     

Development of a method for the determination of 9 currently used cotton pesticides by gas chromatography with electron capture detection

A reliable, sensitive, and reproducible method was developed for quantitative determination of nine new generation pesticides currently used in cotton agriculture. Injector temperature significantly affected analyte response as indicated by electron capture detector (ECD) chromatograms. A majority of the analytes had an enhanced response at injector temperatures between 240 and 260 degrees C, especially analytes such as acephate that overall had a poor response on the ECD. The method detection limits (MDLs) were 0.13, 0.05, 0.29, 0.35, 0.08, 0.10, 0.32, 0.05, and 0.59 ng/mL for acephate, trifuralin, malathion, thiamethozam, pendimethalin, DEF6, acetamiprid, brifenthrin, and lambda-cyhalothrin. This study provides a precision (0.17-13.1%), accuracy (recoveries=88-107%) and good reproducible method for the analytes of interest. At relatively high concentrations, only lambda-cyhalothrin was unstable at room temperature (20-25 degrees C) and 4 degrees C over 10 days. At relatively low concentrations, acephate and acetamiprid were also unstable regardless of temperature. After 10 days storage at room temperature, 30-40% degradation of lambda-cyhalothrin was observed. It is recommended that acephate, acetamiprid, and lambda-cyhalothrin be stored at -20 degrees C or analyzed immediately after extraction.     

CE Determination of Creatinine and Uric Acid in Saliva and Urine During Exercise

A simple and reliable method based on capillary electrophoresis with electrochemical detection (CE–ED) was applied to study the effect of aerobic exercises on creatinine and uric acid concertration in saliva and urine. The pH value, the running buffer concentration, the SDS concentration, separation voltage, injection time and the potential applied to the working electrode were investigated to find the optimum conditions. The detection limits (S/N = 3) for creatinine and uric acid were 3.6 μmol L^?1 and 0.86 μmol L^?1, respectively. This method was successfully used in the rapid analysis of creatinine and uric acid in saliva samples. After aerobic exercises, creatinine concentration decreased, and uric acid concentration increased in saliva. In urine, the concentrations of creatinine and uric acid both increased after exercise.     

Improved Synthesis of Phytosphingosine and Dihydrosphingosine from 3,4,6‐Tri‐O‐benzyl‐D‐galactal

An efficient and facile synthesis of phytosphingosine and dihydrosphingosine derivatives is described with less steps and in improved overall yield (66–72%) starting from commercially available tri‐O‐benzyl‐D ‐galactal. The key steps include Wittig reaction, Mitsunobu transformation, reduction, and deprotection.     

A Kind of Topology Aggregation Algorithm in Hierarchical Wavelength-Routed Optical Networks

In large scale networks composed of several hierarchical subnetworks, topology aggregation is implemented for both scalability and security consideration. However, due to the special characteristic of optical wavelength-routed networks, existing topology aggregation algorithms cannot be applied directly for topology compression. In this paper, we propose a kind of topology aggregation algorithm suitable for hierarchical wavelength-routed optical networks, thereby considering information of residual wavelengths on network links. Basically, our topology aggregation algorithm is based on a transition matrix technique for constructing a full mesh topology and asymmetric star approach for a more compact topology. Simulations with randomly-generated networks show that topology information compression can be achieved with a little loss of its accuracy: the ratio of border node pairs with representation deviation being well below 10%. Results also indicate that the advantage of our algorithm is also behaved on reducing the amount of link-state-advertisement messages and making networks less vulnerable to propagation delay of these messages over communication links. This work is supported by National 863 Program 2003AA122220.     

Performance Analysis of Distributed Protocols for Bidirectional Wavelength Reservations in Dynamic WDM Networks

In this paper, we present an analytical model to investigate the blocking performance of distributed wavelength reservation protocols in dynamic WDM networks. This model extends the approach of [S. Arakawa et al., Proceedings of ITC-CSCC, (Sado, Japan, July 1999), pp. 828--831] in two aspects: firstly we take into account the contention between the two end nodes of bidirectional links in bidirectional wavelength reservations. Secondly, we make a distinction between the effects of different kinds of network delays, which include signaling transmission delay, signaling processing delay, and optical cross-connects (OXC) operation delay. As an application, we use our method to analyze the performance of two different signaling processing schemes, namely forward after cross-connect (FAXC) and forward before cross-connect (FBXC) [M. Goyal et al., Technical Digest of OFC2002 (Anaheim, CA, Mar. 2002) pp. 489--490]. The accuracy of our analytical model is validated by discrete-event simulations. Numerical results show that the FBXC scheme can give a lower network blocking probability than FAXC, and the efficiency of FBXC becomes more significant as the OXC operation delay increases.     

The electrochemical properties of nano-LiFeBO<Subscript>3</Subscript>/C as cathode materials for Li-ion batteries

Carbon-coated LiFeBO₃ is prepared by sol-gel method, and polyethylene glycol 6000 (PEG-6000) is chosen as carbon source. Compared with conventional solid-state method, the LiFeBO₃/C nano-particles were obtained at a relatively lower temperature (500 °C). It was demonstrated that the prepared LiFeBO₃ is a highly pure monoclinic structure with space group of C2/c, the primary particle size of the carbon-coated LiFeBO₃ is about 20–50 nm, and the thickness of carbon coating is about 6.2 nm. In comparison with the LiFeBO₃/C with lower carbon content, the LiFeBO₃/C with higher carbon content exhibits better electrochemical properties. The specific capacities of LiFeBO₃/C are 206.9, 181.3, and 166.1 mAh g^?1 after 50 cycles in the range of 5, 40, and 100 mA g^?1 current density, respectively. Particularly, the LiFeBO₃/C with higher carbon content is demonstrated to own great structural stability, which can maintain its original crystal structure and Li storage properties even after 6 months of air exposure at room temperature.