Synthesis and Comparison of Extraction Properties of p‐tert‐Butylcalix[n]arene Nitrile Derivatives for Selected Metals and Dichromate Anions

The article describes the syntheses and extraction properties of two p‐tert‐butylcalix[6]arene nitrile derivatives (3 and 4). The trinitrile derivative 3 has been synthesized from 5,11,17,23,29,35‐hexa‐tert‐butyl‐37,38,39,40,41,42‐hexahydroxycalix[6]arene 1. The compound 1 was directly converted to its hexanitrile derivative 4. In these syntheses, it was thought to explore the role of nitrile sites in the extraction of various metal cations and HCr₂O₇ ^?/Cr₂O₇ ^2? anions. The liquid‐liquid extraction properties of 3 and 4 towards selected alkali/transition metal cations and HCr₂O₇ ^?/Cr₂O₇ ^2? anions are reported. It has been observed that receptor 3 does not extract alkali/transition metal cations effectively, but shows affinity towards HCr₂O₇ ^?/Cr₂O₇ ^2? anions at low pH. The compound 4 is an effective form for transferring Ni²⁺ selectively, while it shows poor transferring ability for HCr₂O₇ ^?/Cr₂O₇ ^2? anions from an aqueous into a dichloromethane layer. It was observed that the cavity size of the calix[n]arenes and the cooperativity of the functionalities play important roles in two phase extraction systems.     

Oxidation of Benzylic Alcohols to Carbonyl Compounds with Potassium Permanganate in Ionic Liquids

Abstract

The selective oxidation of primary and secondary benzylic alcohols with potassium permanganate in ionic liquids to give corresponding aldehydes and ketones in 83–97% yields has been described.     

Adjusting the selectivity of inorganic anion separation by capillary electrophoresis

The separation of the principal inorganic anions (bromide, carbonate, chlorate, chloride, fluoride, nitrate, nitrite, sulfate, phosphate) has been achieved using a capillary electrophoresis system with indirect UV detection at 260 nm. Several types of cationic surfactants (quaternary ammonium, phosphonium or methonium) were tested as electroosmotic flow modifiers and added to a chromatebased buffer prepared from potassium dichromate. The influence of many physicochemical parameters such as nature and concentration of cationic surfactant, buffer pH, dichromate concentration buffer, voltage and temperature upon the migration time of an analyte anion, peak efficiency, asymmetry factor, and finally resolution has been investigated. A linear relationship between the corrected area and the anion concentration in the 2.5–50 ppm range was obtained, thus allowing the quantitative analysis of anions in mineral water. Finally, by increasing the hydrodynamic injection time, the separation of inorganic anions at a low concentration level of 50 ng/ml was achieved without any loss of resolution.     

氯化钾水溶液微观结构的分子动力学模拟研究

氯化钾水溶液不同于氯化钠的,其在低温下只能形成无水盐和冰.现有研究表明在氯化钠水溶液中不仅存在着水分子连续分布的区域与离子团簇,而且这二者的物质组成也与该溶液所形成晶体的分别对应.为了探寻其他溶液中是否存在此类对应关系,并考察溶液的微观结构,本文采用分子动力学方法对氯化钾水溶液进行了研究,表明了该溶液的一些性质.氯化钾水溶液中K⁺-K⁺和Cl^--Cl^-径向分布函数的特征具有一致性,峰的最大值所对应的位置都分别相同,明显不同于氯化钠水溶液的.系列时刻下瞬态图像内O到其最近离子距离中最大值的统计结果表明氯化钾水溶液中存在着一定大小的水分子连续分布的区域,其平均尺寸至少为2.26 nm;瞬态图像中K⁺与其最近邻Cl^-之间的距离主要分布在0.28 nm～0.38 nm之间,占比约为97.4%;溶液中存在着较大和较小两类离子团簇,较大团簇的平均尺寸为1.73nm,平均离子数是25.0,其内部的离子与周围离子之间具有与氯化钾晶体类似的结构;这些结果表明氯化钾水溶液中也...     

流动注射化学发光法测定山奈酚

采用流动注射技术,研究了高锰酸钾-山奈酚-过氧化氢体系的化学发光行为,对影响化学发光强度的因素进行了试验,建立了流动注射化学发光法测定山奈酚的新方法.方法检出限为1×10-10g·mL-1,线性范围为1.0×10-7-1.0×10-4g·mL-1.对1.0×10-6g·mL-1的山奈酚平行测定11次,其RSD为2.1%...     

Preparation of modified MFI (ZSM-5 and silicalite-1) zeolites for potassium extraction from seawater

Modified nanosized MFI (ZSM-5 and silicalite-1) zeolites were successfully synthesized by a hydrothermal method using aluminum isopropoxide and tetraethylorthosilicate as the raw materials. The synthetic zeolites were characterized by X-ray diffraction, energy dispersion spectroscopy, and scanning electron microscopy. The ZSM-5 and silicalite-1 zeolites exhibited ellipse-like and cubic columns, respectively. The K⁺ ion-exchange equilibrium and ion-exchange capacity of the synthetic zeolites in seawater were investigated. The K⁺ ion-exchange of synthetic zeolites was rapid and reached an ion-exchange balance in approximately 20 min. The K⁺ ion-exchange capacity of ZSM-5 and silicalite-1 in seawater was 56.7 and 48.7 mg/g, respectively. The synthetic zeolites have high selectivity toward K⁺, and therefore, they can be used to selectively extract potassium from seawater.     

Syntheses and Crystal Structures of Potassium–Lanthanoid(III) Complexes with the 1,2‐Benzenedisulfonate Ligand

The complexes [K(H₂O)₂LnL₂] (Ln = La or Nd; L = 1,2‐benzenedisulfonate) and [K(H₂O)Yb(H₂O)₄L₂] were initially isolated fortuitously from attempts to prepare the corresponding Ln₂L₃ complexes from Ln₂O₃ and H₂L in water. Indeed the bulk products from these reactions have the composition Ln₂L₃. Subsequently, deliberate syntheses by reacting equimolar amounts of Ln₂L₃ with K₂L in water gave the complexes in good yield. X‐ray crystal structures of [K(H₂O)₂LnL₂] (Ln = La or Nd) showed the complexes to be isostructural with a two dimensional polymeric network structure in which LnL₂ units are linked into chains crosslinked by potassium ions. Each Ln is nine coordinate with solely sulfonate oxygen donor atoms. Between adjacent lanthanoid ions there are three different types of sulfonate bridges and two examples of each. Most noteworthy is highly unsymmetrical bridging through μ‐η²‐sulfonate oxygen atoms. Consequently, one Ln–O bond is ca. 0.5 Å longer than the other eight. Potassium is nine‐coordinate with seven sulfonate oxygen atoms and two aqua ligands, and surprisingly <K–O(sulfonate)> is much longer than <K–O(H₂O)>. Pairs of potassium ions are linked by two μ‐η²‐sulfonate oxygen atoms, which are unsymmetrically bridging. The structure of [K(H₂O)Yb(H₂O)₄L₂] comprises discrete tetranuclear units containing two independent ytterbium ions, each coordinated by four water molecules and two chelating (via seven membered rings) disulfonate ligands, and two potassium ions, each coordinated by six sulfonate oxygen atoms and a water molecule. For each potassium, four of the coordinated sulfonate oxygen atoms are from sulfonate ligands bonded to one ytterbium atom and two from sulfonate ligands attached to the other ytterbium atom. In contrast to the Nd and La complexes, <K–O(sulfonate)> is shorter than <K–O(H₂O)>.     

Synthetic K+ Channels Constructed by Rebuilding the Core Modules of Natural K+ Channels in an Artificial System

Different types of natural K⁺ channels share similar core modules and cation permeability characteristics. In this study, we have developed novel artificial K⁺ channels by rebuilding the core modules of natural K⁺ channels in artificial systems. All the channels displayed high selectivity for K⁺ over Na⁺ and exhibited a selectivity sequence of K⁺≈Rb⁺ during the transport process, which is highly consistent with the cation permeability characteristics of natural K⁺ channels. More importantly, these artificial channels could be efficiently inserted into cell membranes and mediate the transmembrane transport of K⁺, disrupting the cellular K⁺ homeostasis and eventually triggering the apoptosis of cells. These findings demonstrate that, by rebuilding the core modules of natural K⁺ channels in artificial systems, the structures, transport behaviors, and physiological functions of natural K⁺ channels can be mimicked in synthetic channels.     

A Novel Spectrophotometric Method for the Determination of Levodopa with the Detection System of Potassium Ferricyanide‐Fe(III)

In this paper, a novel method has been established to determine levodopa with the detection system of potassium ferricyanide‐Fe(III). In the presence of potassium ferricyanide, it has been demonstrated that Fe(III) is reduced to Fe(II) by levodopa at pH 4.0. In addition, the in situ formed Fe(II) reacts with potassium ferricyanide to form soluble prussian blue (KFe^III[Fe^II(CN)₆]). Beer's law is obeyed in the range of levodopa concentrations of 0.01–4.00 μg mL^?1 at the maximal absorption wavelength of 735 nm. The linear regression equation is A = 0.0082 + 0.61365 C (μg mL^?1) with a correlation coefficient of 0.9996. The detection limit (3σ/k) is 9 ng mL^?1, and R.S.D. is 0.73% (n = 11). Moreover, the apparent molar absorption coefficient of indirect determination of levodopa is 1.2 × 10⁵ Lmol^?1cm^?1. The parameters with regard to determination are optimized, and the reaction mechanism is discussed. This method has been successfully applied to determine levodopa in pharmaceutical, serum and urine samples. Analytical results obtained with this novel assay are satisfactory.     

Silica supported potassium oxide catalyst for dehydration of 2-picolinamide to form 2-cyanopyridine

The dehydration of 2-picolinamide to produce 2-cyanopyridine was investigated thoroughly using silica supported potassium oxide as a heterogeneous catalyst. Both large specific surface area and pore size of SiO_2 (B) contributed to the favorable catalytic performance for the synthesis of 2-CP. In addition, the yield of 2-CP showed the linear relationship with the amounts of medium basicity of the catalysts,demonstrating that medium basic sites were the active sites of silica supported potassium oxide catalysts. The catalysts were further characterized by XRD and FT-IR to clarify the active species. The results indicated the Si—O—K group produced by the reaction of K_2CO_3 with Si—OH was the active species, which was further evidenced by the adjustment of the amount of Si—OH by silylation and hydroxylation procedure.