Accelerating Electrochemical Reactions in a Voltage-Controlled Interfacial Microreactor

Microdroplet chemistry is attracting increasing attention for accelerated reactions at the solution–air interface. We report herein a voltage-controlled interfacial microreactor that enables acceleration of electrochemical reactions which are not observed in bulk or conventional electrochemical cells. The microreactor is formed at the interface of the Taylor cone in an electrospray emitter with a large orifice, thus allowing continuous contact of the electrode and the reactants at/near the interface. As a proof-of-concept, electrooxidative C−H/N−H coupling and electrooxidation of benzyl alcohol were shown to be accelerated by more than an order of magnitude as compared to the corresponding bulk reactions. The new electrochemical microreactor has unique features that allow i) voltage-controlled acceleration of electrochemical reactions by voltage-dependent formation of the interfacial microreactor; ii) “reversible” electrochemical derivatization; and iii) in situ mechanistic study and capture of key radical intermediates when coupled with mass spectrometry.     

Metal-Free Twofold Electrochemical C−H Amination of Activated Arenes: Application to Medicinally Relevant Precursor Synthesis

The efficient production of many medicinally or synthetically important starting materials suffers from wasteful or toxic precursors for the synthesis. In particular, the aromatic non-protected primary amine function represents a versatile synthetic precursor, but its synthesis typically requires toxic oxidizing agents and transition metal catalysts. The twofold electrochemical amination of activated benzene derivatives via Zincke intermediates provides an alternative sustainable strategy for the formation of new C−N bonds of high synthetic value. As a proof of concept, we use our approach to generate a benzoxazinone scaffold that gained attention as a starting structure against castrate-resistant prostate cancer. Further improvement of the structure led to significantly increased cancer cell line toxicity. Thus, exploiting environmentally benign electrooxidation, we present a new versatile and powerful method based on direct C−H activation that is applicable for example the production of medicinally relevant compounds.     

Role of SrMoO4 in Sr2MgMoO6 synthesis

Here we investigate the elemental and phase compositions during the solid-state synthesis of the promising SOFC-anode material, Sr₂MgMoO₆, and demonstrate that molybdenum does not notably evaporate under the normal synthesis conditions with temperatures up to 1200 °C due to the formation of SrMoO₄ as an intermediate product at low temperatures, below 600 °C. However, partial decomposition of the Sr₂MgMoO₆ phase becomes evident at the higher temperatures (∼1500 °C). The effect of SrMoO₄ on the electrical conductivity of Sr₂MgMoO₆ is evaluated by preparing a series of Sr₂MgMoO₆ samples with different amounts of additional SrMoO₄. Under the reducing operation conditions of an SOFC anode the insulating SrMoO₄ phase is apparently reduced to the highly conductive SrMoO₃ phase. Percolation takes place with 20-30 wt% of SrMoO₄ in a Sr₂MgMoO₆ matrix, with a notable increase in electrical conductivity after reduction. Conductivity values of 14, 60 and 160 S/cm are determined at 800 °C in 5% H₂/Ar for the Sr₂MgMoO₆ samples with 30, 40 and 50 wt% of added SrMoO₄, respectively.     

Silver and gold icosahedra: one-pot water-based synthesis and their superior performance in the electrocatalysis for oxygen reduction reactions in alkaline media

Much effort has gone into generating polyhedral noble metal nanostructures because of their superior electrocatalytic activities for fuel cells. Herein, we report uniform, high-yield icosahedral silver and gold nanoparticles by using a facile one-pot, seedless, water-based approach that incorporates polyvinyl pyrrolidone and ammonia. Electrocatalysis of the oxygen-reduction reaction was carried out in alkaline media to evaluate the performance of the icosahedral nanoparticles. They showed excellent stability and much higher electrocatalytic activity than the spherelike nanoparticles; they display a positive shift in reduction peak potential for O(2) of 0.14 and 0.05 V, while the reduction peak currents of the silver and gold icosahedra are 1.5- and 1.6-fold, respectively, better than the spherelike nanoparticles. More importantly, the icosahedral nanoparticles display electrocatalytic activities comparable with commercial Pt/C electrocatalysts. The facile preparation of icosahedral silver and gold nanoparticles and their superior performance in the oxygen reduction reaction render them attractive replacements for Pt as cathode electrocatalysts in alkaline fuel cells.     

Storage Stability of LiFePO4/C in Humid‐hot Air

Storage stabilities of LiFePO₄/C composite at different conditions are investigated in terms of structural and electrochemical evolutions. The results from different aging tests indicate that moisture and temperature are the key factors that have the most profound effects on the structure homogeneity which in turn influences the electrochemical performance of LiFePO₄/C. Although the storage in a humid‐hot environment, such as saturated humidity air at 50°C, does not greatly influence the discharging capacity of LiFePO₄/C, it does reduce the initial charging capacity, thus the amount of reversible Li⁺ ions in a practical LiFePO₄/graphite cell decreases. This impact is explained by the lithium extraction during the storage, forming olivine FePO₄ and associated Li₃PO₄. Elevated storage temperature also favors the delithiation process. The degree of delithiation increases from about 6% at 50°C to 18% at 80°C. It is also found that re‐calcination at 650°C effectively resolves the problem of the structural heterogeneity of the stored LiFePO₄/C. Therefore both the initial charging capacity and coulombic efficiency of the stored sample in the first cycle revert to the original value of the fresh one.     

Cu-Doped ZnO Nanoparticles for Non-Enzymatic Glucose Sensing

Copper-doped zinc oxide nanoparticles (NPs) Cu_xZn_1−xO (x = 0, 0.01, 0.02, 0.03, and 0.04) were synthesized via a sol-gel process and used as an active electrode material to fabricate a non-enzymatic electrochemical sensor for the detection of glucose. Their structure, composition, and chemical properties were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) and Raman spectroscopies, and zeta potential measurements. The electrochemical characterization of the sensors was studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). Cu doping was shown to improve the electrocatalytic activity for the oxidation of glucose, which resulted from the accelerated electron transfer and greatly improved electrochemical conductivity. The experimental conditions for the detection of glucose were optimized: a linear dependence between the glucose concentration and current intensity was established in the range from 1 nM to 100 μM with a limit of detection of 0.7 nM. The proposed sensor exhibited high selectivity for glucose in the presence of various interfering species. The developed sensor was also successfully tested for the detection of glucose in human serum samples.     

Electrochemical Quantification of Mercury in Solutions Using Boron-doped Diamond Electrodes: Electrode Regeneration and Role of Gold and Impurities

Abstract

For determining Hg in solutions in the ppb to ppt range using boron-doped diamond (BDD) electrochemistry, the role of an added gold solution for enhanced sensitivity is investigated. Using differential pulse anodic stripping voltammetry (DPASV), peaks due to Cu and Ag as impurities from gold are identified. With the proper choice of the potential for deposition, effects of the impurities are minimized and an electrode regeneration procedure is devised and tested, resulting in reproducible slopes of the calibration curves in successive runs. The location and shift of the DPASV peak potentials with concentration are explained with the use of the Nernst equation.     

Decorating nickel phthalocyanine periphery by aryl-1,3,4-oxadiazole pendants: synthesis,characterization, and conductivity studies

We have decorated nickel phthalocyanine (NiPc) periphery by four different aryl-[1,3,4]-oxadiazole pendants. Introduction of aryl-[1,3,4]-oxadiazole pendants into the NiPc core results in improved thermal stability, fine-tuning of the position of the Q-band with decrease in band gap, indicating effective electronic communication between the two different ring systems with NiPc core. The magnitude of DC electrical conductivity for aryl-[1,3,4]-oxadiazole-substituted NiPcs 3a–3d is found to be ～10⁵ times higher than the parent NiPc (1). The temperature-dependent DC conductivity studies reveal semiconducting nature of the newly synthesized NiPc compounds with significant decrease in thermal activation energy (ΔE) compared to parent NiPc.     

Synthesis,spectroscopic studies,and preliminary antibacterial assays of a palladium(II) complex with 2-mercaptothiazoline

In this article, synthesis of a palladium(II) complex with 2-mercaptothiazoline in aqueous solution is presented. Composition of the complex was defined as 1?:?2 (metal?:?ligand). Infrared and solid-state nuclear magnetic resonance indicate ligand coordination to Pd(II) through nitrogen of thiazole ring and sulfur of thiol. ESI–QTOF–mass spectrometric analysis shows primarily the dimeric form in solution. An antibiogram assay of the complex was performed by the disc diffusion method. The compound did not show antibacterial activity against the considered bacterial cells in the tested concentrations.     

Solid-State 17O NMR studies of organic and biological molecules: Recent advances and future directions

This Trends article highlights the recent advances published between 2012 and 2015 in solid-state ¹⁷O NMR for organic and biological molecules. New developments in the following areas are described: (1) new oxygen-containing functional groups, (2) metal organic frameworks, (3) pharmaceuticals, (4) probing molecular motion in organic solids, (5) dynamic nuclear polarization, and (6) paramagnetic coordination compounds. For each of these areas, the author offers his personal views on important problems to be solved and possible future directions.