Controlling the outcome of overacylation of N-protected aminooxyacetic acid during the synthesis of an aminooxy-peptide for chemical ligation

An aminooxy-containing peptide, the nucleophile partner for oxime ligations, is usually grafted on a NH₂-peptide resin by activating a protected aminooxyacetic acid as an active ester. Here, we have shown that its subsequent coupling to NH₂-peptide resin competes with the overacylation of the -NH-O- nitrogen and that the overacylation level increases with the basicity of the reaction mixture. Moreover, we found that overacylation is prevented when the COOH of the Aoa-derivatives is engaged in an amide bond.     

Reference Electrode for Ionic Liquids

Reference electrodes for room temperature ionic liquid (RTIL) applications were constructed that have a known and reproducible potential versus the ferrocene/ferrocenium couple. They are based on reference electrodes of the first kind, Ag/Ag⁺ couple type, or of the second kind, based on Ag/AgCl in M⁺Cl^?. The former uses AgNO₃ salt and the latter tetrabutylammonium chloride, Bu₄NCl, dissolved in acetonitrile which are then introduced to the ionic liquid of choice for a final concentration of 0.1 M. The reference electrodes can be easily and reproducibly constructed. An ionic contact of these reference systems with the test electrolyte was made using an asbestos fiber liquid junction. The internal compartment of the reference system was filled with the same ionic liquid as used for the electrochemical experiment. The performance of these reference electrodes was tested in selected ionic liquids using the ferrocene/ferrocenium redox couple. The stability, reproducibility, and temperature behavior of the two reference systems have been characterized in the following ionic liquids: 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMIBF₄), 1‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide (BMI(CF₃SO₂)₂N), and 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIPF₆). It has been found that the formal potentials of the examined reference systems are stable over several days. There is a linear relationship for the temperature studied in the range from 25 to 60 °C.     

Electrochemistry and Voltammetric Determination of Adenosine with N‐Hexylpyridinium Hexafluorophosphate Modified Electrode

An ionic liquid N‐hexylpyridinium hexafluorophosphate (HPPF₆) modified carbon paste electrode was fabricated for the sensitive voltammetric determination of adenosine in this paper. Carbon ionic liquid electrode (CILE) was prepared by mixing graphite powder and HPPF₆ together and the CILE was characterized by scanning electron microscopy (SEM) and electrochemical methods. The electrochemical behaviors of adenosine on the CILE were studied carefully. Compared with the traditional carbon paste electrode (CPE), a small negative shift of the oxidation peak potential appeared with greatly increase of the oxidation peak current, which indicated the presence of ionic liquid in the carbon paste not only as the binder but also as the modifier and promoter. Under the optimal conditions the oxidation peak current increased with the adenosine concentration in the range from 1.0×10^?6 mol/L to 1.4×10^?4 mol/L with the detection limit of 9.1×10^?7 mol/L (S/N=3) by differential pulse voltammetry. The proposed method was applied to the human urine samples detection with satisfactory results.     

DFT Study on the Structure of Ionic Liquid 1-Ethyl-3-methylimidazolium Hexafluorophosphate

1 INTRODUCTION Ionic compounds generally have high melting points and always exist in solid state since they are main- tained by electrovalent bonds. Ionic Liquids (ILs), which are liquids at or near ambient temperature, have been a class of ionic compounds extensively studied experimentally and theoretically in recent years[1, 2]. ILs consist exclusively of anions and ca- tions and do not contain any neutral molecule. They have many attractive properties, such as low vapor pressure, no…     

含膦酸酯官能团离子液体对钢/铝摩擦副的润滑作用研究

合成了3种新型1-(O,O-二乙基膦酰丙基)-3-烷基咪唑六氟磷酸盐离子液体,采用SRV型摩擦磨损试验机评价了所制备的离子液体作为润滑剂对钢／铝摩擦副摩擦学性能的影响,并探讨了其润滑机理．结果表明,所合成的离子液体作为润滑剂对钢／铝摩擦副具有优良的润滑作用,摩擦系数低,抗磨性能优良．表面分析结果表明含膦酸酯官能团的离子液体在摩擦副接触表面形成化学吸附边界润滑膜,从而有效地起到抗磨和提高承载能力的作用．     

Kinetic studies on the hydrosilylation of phenylacetylene with R3SiH (R3 = PhMe2, Ph2Me,Ph3, Et3) using bis(1,2‐diphenylphosphinoethane)norbornadiene rhodium(I) hexafluorophosphate as catalyst

Product distribution and kinetic studies on the hydrosilylation of phenylacetylene by Ph₃SiH, Ph₂MeSiH, PhMe₂SiH and Et₃SiH were performed using bis‐[1,2‐diphenylphosphinoethane]norbornadienerhodium(I) hexafluorophosphate, 1, as catalyst. Pre‐equilibration of the catalyst with the acetylene produced hydrosilylations, pre‐equilibration with the silane did not. The catalyst showed a pronounced selectivity for cis‐addition to form β‐products, t‐PhCH­CHSiR₃, unlike most hydrosilylation catalysts. The kinetic studies showed a hydrosilylation reaction that is zero order with respect to both acetylene and the silane, with a dependency upon catalyst concentration. The k_obs value is directly influenced by the substituents on the silane: k(PhMe₂SiH) > k (Et₃SiH > k (Ph₂MeSiH) > k (Ph₃SiH). Intercalation of the catalyst in hectorite was not useful, since either no reaction occurred in non‐polar solvents, or extraction of the catalyst occurred in polar solvents to produce the same product distributions. Copyright © 2000 John Wiley & Sons, Ltd.     

Kinetics of Thermal Decomposition of Lithium Hexafluorophosphate

With on-line coupled thermo-gravimetric analyzer-Fourier transform infrared spectrometer technique, the thermal decomposition of lithium hexafluorophosphate (LiPF₆) and its gas evolution at inert environment (H₂O<10 ppm) were studied under both non-isothermal and isothermal conditions. The results showed that the LiPF₆ decomposition is a single-stage reaction with LiF as final residue and PF₅ as gas product. In addition, its decomposi-tion kinetics was determined as 2D phase boundary movement (cylindrical symmetry) under both non-isothermal and isothermal conditions. Furthermore, the activation energy of LiPF₆ decomposition was calculated as 104 and 92 kJ/mol for non-isothermal and isothermal con-ditions, respectively.     

A new room temperature ionic liquid 1-butyl-3-trimethylsilylimidazolium hexafluorophosphate as a solvent for extraction and preconcentration of mercury with determination by cold vapor atomic absorption spectrometry

A new room temperature ionic liquid 1-butyl-3-trimethylsilylimidazolium hexafluorophosphate abbreviated as [C₄tmsim][PF₆] was synthesized and developed as a novel medium for liquid/liquid extraction of inorganic mercury in this work. Under optimal condition, o-carboxyphenyldiazoamino-p-azobenzene abbreviated as CDAA reacted with inorganic mercury to form a neutral Hg-CDAA complex, the complex was rapidly extracted into ionic liquid phase. After back-extracting into aqueous phase with sulfide sodium solution, the mercury concentration was detected by cold vapor atomic absorption spectrometry. The extraction and back-extraction efficiencies were 99.9 and 100.1% for 5.0 μg L⁻¹ standard mercury in 1000 mL of water solution, respectively. The detection limit, calculated using three times the standard error of estimate of the calibration graph, is 0.01 ng of mercury per milliliter water sample. The proposed method has been used to the determination of trace inorganic mercury in natural water with satisfactory results. Moreover, Zeta potential and surface tension of [C₄tmsim][PF₆] solution were measured and applied to explain the extraction mechanism of [C₄tmsim][PF₆] system.     

Sensitive determination of verticine and verticinone in Bulbus Fritillariae by ionic liquid assisted capillary electrophoresis-electrochemiluminescence system

CE/Ru(bpy)₃²⁺ electrochemiluminescence (ECL) system with the assistance of ionic liquids (ILs) was successfully established for sensitive determination of verticine and verticinone in Bulbus Fritillariae for the first time. Migration behavior of alkaloid largely relies on the hydrogen bonding interactions between alkyl imidazolium cations in ILs and the alkaloids. Running buffer containing 40 mmol/L 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF₄) IL-8 mmol/L phosphate resulted in significant changes in separation selectivity for alkaloids with similar structures. The highest sensitivity of the detection was obtained by maintaining the detection potential at 1.2 V. Under the optimized conditions, relative standard derivations of the ECL intensity and the migration time were 3.27 and 2.84% for verticine and 4.42 and 1.69% for verticinone, respectively. The standard curves were linear between 1 × 10⁻⁸ and 1 × 10⁻⁶ mol/L for verticine and between 5 × 10⁻⁸ and 1 × 10⁻⁶ mol/L for verticinone, respectively. Detection limits of 1.25 × 10⁻¹⁰ mol/L for verticine and 1 × 10⁻¹⁰ mol/L for verticinone were obtained (S/N = 3). Developed method was successfully applied to determine the amounts of alkaloids in Bulbus Fritillariae.     

Direct Electrochemistry of Myoglobin in a Nafion‐Ionic Liquid Composite Film Modified Carbon Ionic Liquid Electrode

In this paper two kinds of ionic liquids (ILs) were used for the construction of a myoglobin (Mb) electrochemical biosensor. Firstly a hydrophilic ionic liquid of 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIMBF₄) was used as binder to prepare a carbon ionic liquid electrode (CILE), then a Nafion and hydrophobic ionic liquid of 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆) composite film was applied on the surface of the CILE. The direct electrochemistry of Mb in the Nafion‐BMIMPF₆/CILE was achieved with the cathodic and anodic peak potentials located at ?0.345 V and ?0.213 V (vs. SCE). The formal potential (E°′) was located at ?0.279 V, which was the characteristic of Mb Fe^III/Fe^II redox couples. The electrochemical behaviors of Mb in the Nafion‐ionic liquid composite film modified CILE were carefully investigated. The Mb modified electrode showed good electrocatalytic behaviors to the reduction of trichloroacetic acid (TCA) and NaNO₂. Based on the Nafion‐BMIMPF₆/Mb/CILE, a new third generation reagentless biosensor was constructed.