复合还原剂硼氢化钠/三氯化铁对亚砜的还原

硼氢化钠是一种温和、高选择性的亲核还原剂。一般它只能还原醛、酮和酰氯,而对其它功能团不起作用。因而其应用范围有一定的限制。据文献报道,某些金属卤化物能有效地提高硼氢化钠的还原性能^[1]。复合还原剂硼氢化钠/三氯化铁已应用于将β-二烷基氨基共轭烯酮还原为相应的饱和γ-氨基醇^[2]。本文研究了硼氢化钠/三氯化铁对亚砜的还原反应。     

Synthesis and Characterization of Methylzinc Tri(tert‐butyl)silylphosphanide as well as Related Sodium and Potassium Phosphanylzincates

The reaction of dimethylzinc and tri(tert‐butyl)silylphosphane in toluene yielded dimeric methylzinc tri(tert‐butyl)silylphosphanide ( 1 ) which crystallized tetrameric. Compound 1 was deprotonated with sodium in DME and the solvent‐separated dimeric ion pair [(dme)₃Na]⁺ [(dme)Na(MeZn)₂(μ‐PSitBu₃)₂]^? ( 2 ) was isolated. The reaction of 1 in THF with two equivalents of potassium and one equivalent of tri(tert‐butyl)silylphosphane gave dimeric [{tBu₃Si(H)P}{(thf)₂K}₂(MeZn)(PSitBu₃)]₂ ( 3 ). Both of these phosphanylzincates contain Zn₂P₂ cycles with Zn‐P bond lengths of approximately 237 pm, whereas in 1 larger Zn‐P bond lengths of 248.5 pm were found due to the larger coordination numbers of the phosphorus and zinc atoms.     

Simultaneous speciation of mercury and butyltin compounds in natural waters and snow by propylation and species-specific isotope dilution mass spectrometry analysis

A robust method has been developed for simultaneous determination of mercury and butyltin compounds in aqueous samples. This method is capable of providing accurate results for analyte concentrations in the picogram per liter to nanogram per liter range. The simultaneous determination of the mercury and tin compounds is achieved by species-specific isotope dilution, derivatization, and gas chromatography–inductively coupled plasma mass spectrometer (GC–ICP–MS). In derivatization by ethylation and propylation, reaction conditions such as pH and the effect of chloride were carefully studied. Ethylation was found to be more sensitive to matrix effects, especially for mercury compounds. Propylation was thus the preferred derivatization method for simultaneous determination of organomercury and organotin compounds in environmental samples. The analytical method is highly accurate and precise, with RSD values of 1 and 3% for analyte concentrations in the picogram per liter to nanogram per liter range. By use of cleaning procedures and SIDMS blank measurements, detection limits in the range 10–60 pg L^–1 were achieved; these are suitable for determination of background levels of these contaminants in environmental samples. This was demonstrated by using the method for analysis of real snow and seawater samples. This work illustrates the great advantage of species-specific isotope dilution for the validation of an analytical speciation method—the possibility of overcoming species transformations and non-quantitative recovery. Analysis time is saved by use of the simultaneous method, because of the use of a single sample-preparation procedure and one analysis.     

Microchip electrophoretic protein separation using electroosmotic flow induced by dynamic sodium dodecyl sulfate-coating of uncoated plastic chips

Separation of sodium dodecyl sulfate (SDS)-protein complexes is difficult on plastic microchips due to protein adsorption onto the wall. In this paper, we elucidated the reasons for the difficulties in separating SDS-protein complexes on plastic microchips, and we then demonstrated an effective method for separating proteins using polymethyl methacrylate (PMMA) microchips. Separation difficulties were found to be dependent on adsorption of SDS onto the hydrophobic surface of the channel, by which cathodic electroosmotic flow (EOF; reversed flow) was generated. Our developed method effectively utilized the reversed flow from this cathodic EOF as a driving force for sample proteins using permanently uncoated but dynamic SDS-coated PMMA microchips. High-speed (6 s) separation of proteins and peptides up to 116 kDa was successfully achieved using this system.     

Influnence of Sodium Polyacrylate on Crystallization and Aggregation of Butterfly-like Calcium Carbonate

Butterfly-like calcium carbonate(CaCO₃) particles were successfully prepared via a facile precipitation reaction of Na₂CO₃ with CaCl₂ in the presence of sodium polyacrylate(PAAS). The as-prepared samples were characterized with field emission scanning electron microscopy(FESEM), X-ray diffraction(XRD) and Fourier transform infrared spectroscopy(FTIR). Butterfly-like CaCO₃ particles composed of three segment rods were obtained. Rod aggregates would act as the template for butterfly-like CaCO₃ crystals consisted of regular shaped crystallites with 150―200 nm in diameter. The influences of reaction temperature, the amount of PAAS and reaction time on the nucleation and growth of CaCO₃ crystals were investigated. The possible growth mechanism of CaCO₃ crystals was discussed. This research can not only make us further understand the general principles of the reaction, but also open up a new avenue of industrial production of CaCO₃ particles with exquisite and unique morphologies.     

Sodium Alginate and Poly(ethylene glycol) Blends: Thermal and Morphological Behaviors

Sodium alginate (SA) was blended with varying amounts of poly(ethylene glycol) (PEG) viz., 10, 20, 30, 40 and 50 wt % by using water as a solvent. The obtained SA/PEG blends have been characterized for thermal behavior by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) and surface morphology by scanning electron microscopic (SEM) methods. DSC analysis indicates the increase in glass transition temperature (T_g) of the blends with an increase in PEG content in the blend, which is due to chain entanglement. TGA results reveal the enhancement of thermal stability of SA/PEG blends in terms of the onset of degradation and percentage of weight loss. SEM photomicrographs shows the two phase morphology. This result indicates the immiscible nature of the SA/PEG blends.     

Micellar Effects on the Oxidation of d‐Glucose by Chromic Acid in Perchloric Acidic Medium

Kinetics of the reaction between d‐glucose and Cr(VI) in the absence and presence of surfactant micelles have been studied by a spectrophotometric method in aqueous‐acidic solutions of perchloric acid. It was observed that the reaction has a nonautocatalytic followed by an autocatalytic pathway. The rate of the initial stage increases with increase in [glucose], [HClO₄] and temperature. Due to precipitation, the effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) could not be studied whereas the oxidation is catalyzed by anionic micelles of sodium dodecyl sulfate (SDS) and nonionic micelles of Triton X‐100 (TX‐100). The results are discussed in terms of the pseudo‐phase kinetic model. Activation parameters are evaluated and a mechanism consistent with the results is proposed. A rate law for the reaction has also been derived. The redox reaction occurs through a Cr(VI)→Cr(IV) path.     

NiCo_2S_4六角片作为钠离子电池负极材料的电化学性能及储钠动力学

通过共沉淀以及后续的气相硫化成功制备了横向边长约为2μm,纵向厚度约为30 nm的NiCo_2S_4六角片,并研究了其作为钠离子电池负极材料的电化学性能。电化学性能测试结果显示在1000 mA·g~(-1)的电流密度下,NiCo_2S_4电极循环60次后仍然可保持约387mAh·g~(-1)的可逆比容量。此外,NiCo_2S_4电极还具有良好的倍率性能,在200、400、800、1000和2000mA·g~(-1)的电流密度下,容量分别为542、398、347、300和217mAh·g~(-1)。通过进一步动力学机制分析发现,NiCo_2S_4电极的良好的倍率性能得益于其二维片层状结构诱导产生的赝电容。上述结果表明,NiCo_2S_4纳米六角片是一种极具潜力的钠离子电池负极材料。     

Sensitive Determination of 2‐Methoxyestradiol in Pharmaceutical Preparations and Biological Fluids by KMnO4‐Na2SO3 Chemiluminescence System

A simple and novel flow‐injection chemiluminescence (FI‐CL) method was established for the determination of 2‐Methoxyestradiol (2‐ME) in pharmaceutical preparations and biological fluids. The method was based on the significant enhancement of the CL from the KMnO₄‐Na₂SO₃ reaction by 2‐ME in acidic medium. Under optimized conditions, the CL intensity was correlated linearly with concentration of 2‐ME in the range of 5.0 × 10^?8‐5.0 × 10^?6 M (r = 0.9995). The detection limit (3σ) of 2‐ME was 7.5 × 10^?9 M and the relative standard deviation was 0.8% at 5.0 × 10^?7 M 2‐ME (n = 8). The proposed method was successfully applied for the flow‐injection CL determination of 2‐ME in pharmaceutical preparations and biological fluids with the recoveries from 92.4 to 106.8%. The possible CL reaction mechanism was also discussed briefly.     

NaBH4/DOWEX(R)50WX4: A Convenient Reducing System for Fast and Efficient Reduction of Carbonyl Compounds to Their Corresponding Alcohols

The reduction of a variety of carbonyl compounds was efficiently carried out with NaBH₄/DOWEX(R)50WX4 system. The reactions were performed to give the corresponding alcohols derivatives in perfect yields in THF at room temperature. Reduction of acyloins and a‐diketones by this reducing system produced efficiently the corresponding vicinal diols. Also, the reduction of aldehydes over ketones has been accomplished successfully by this system. Regioselectivity of this system was also investigated with exclusive 1,2‐reduction of conjugated carbonyl compounds to their corresponding allylic alcohols in high to excellent yields.