The effect of pressure on the dissociation constant of hydrofluoric acid and the association constant of the NaF ion pair at 25°C

The effect of pressure on the dissociation constant of hydrofluoric acid was determined by using the indicator technique at 25°C at an ionic strength of 0.1m over a pressure range of 1 to 2000 atm. A value of 3.14 for pK _a ^* at I =0 was obtained by extrapolation to zero ionic strength at 1 atm. The pressure dependence yielded a partial molar volume change of –9.6 cm³-mol^–1 and a compressibility change of — 35×10^–3 cm³-mol^–1 –atm^–1 for the dissociation. The dependence of ionic strength on the association constant K _A ^* of NaF was studied at 25°C and 1 atm. Extrapolation to I=0 yielded a pK _A ^* of –0.78. The pressure dependence of K _A ^* gave a change of volume of 3.26 cm³-mol^–1 and a change in compressibility of 6×10^–3 cm³-mol^–1-atm^–1 for the formation of the ion pair.     

Solubilization of methane,ethane, propane andn-butane in aqueous solutions of sodium dodecylsulfate

The solubilities of methane, ethane, propane, and n-butane were measured in aqueous solutions of sodium dodecylsulfate (NaDS) (0–0.1M) from 15 to 27°C. From these measurements the standard Gibbs energies, entropies, and enthalpies for the process of transferring the solute molecules from the gaseous phase into the solutions were calculated. An approximate relationship was found relating the volume fraction of the micelles to NaDS concentration.     

Die Kristallstrukturen der Vanadium-Weberite Na2MIIVIIIF7 (MII  Mn,Ni, Cu) und von NaVF4

The Crystal Structures of the Vanadium Weberites Na₂M^IIV^IIIF₇ (M^II ? Mn, Ni, Cu) and of NaVF₄ At single crystals of the vanadium(III) compounds NaVF₄ (a = 790.1, b = 531.7, c = 754.0 pm, β = 101.7°; P2₁/c, Z = 4), Na₂NiVF₇ (a = 726.0, b = 1031.9, c = 744.6 pm; Imma, Z = 4) and Na₂CuVF₇ (a = 717.6, b = 1043.5, c = 754.6 pm; Pmnb, Z = 4) X-ray structure determinations were performed, at Na₂MnVF₇ (a = 746.7, c = 1821.6 pm; P3₂21, Z = 6) a new refinement. NaVF₄ crystallizes in the layer structure type of NaNbO₂F₂. The fluorides Na₂M^IIVF₇ represent new orthorhombic (M^II ? Ni; Cu) resp. trigonal (M^II ? Mn) weberites. The average distances within the [VF₆] octahedra of the four compounds are in good agreement with each other and with data of related fluorides (V? F: 193.3 pm). The differences between mean bond lengths of terminal and bridging F ligands are 5% in NaVF₄, but less than 1% in the weberites. Details and data for comparison are discussed.     

Synthesis and Crystal Structure of Complex of Sodium Perrhenate with Tetraethyl p-tert-Butylcalix[4]arene Tetraacetate

Recently,theconformationofthecalixarenehasbeenshowntobeimportantincontrollingtheseIectivityofthereceptor.Forexample,sodiumioncouldbeboundverystronglybyesterderivativesofcalix[4]areneintheconeconformationl.Wehavefoundthatinthepresenceofcertainamountofsodiumion,microamountofReO4-canbequantitativelyextractedintol,2-dichloroethanebytheligandtetraethylp-tert-butylcalix[4]arenetetraacetate(L).ItshowsthatthepresenceofNa inaqueoussolutioncanpromotetheformationofhydrophobiccomplex[NaL] .ReO'-whichc…     

A novel method for determination of magnesium in urine and water samples with mercury film-plated carbon paste electrode

A square wave adsorptive stripping voltammetric (SWAdSV) method for the indirect determination of trace amounts of magnesium with thiopentone sodium (TPS) as an electroactive ligand, at carbon paste mercury film electrode (CP-MFE) is proposed. It is observed that the increase of the square wave voltammetric cathodic peak current of TPS, under alkaline conditions, is linear with the increase of Mg concentration. Under optimum experimental conditions viz.; pH 10.75, 3×10⁻⁵ M TPS and 0.05 M phosphate buffer (Na₂HPO₄-NaH₂PO₄), a linear relation in the range 6×10⁻⁹ to 9×10⁻⁸ M Mg²⁺ (0.14-2.16 ppb), at 60 s deposition time, is obtained. The detection limit of Mg²⁺ is 0.14 ppb for 60 s deposition time with the relative standard deviation is 0.5% (n=5). The proposed method was successfully applied to the determination of magnesium in urine and tap water samples with satisfactory results. The data obtained are compared with the standard flame atomic absorption spectrophotometric method (FAAS).     

水／AOT／正庚烷微乳体系中磺酸根水化作用的FT—IR研究

运用傅立叶变换红外光谱（FT－IR）对水／琥珀酸（乙基已基）磺酸钠（AOT）／正庚烷微乳体系中磺酸根的水化作用进行了研究．由于微乳体系中水分子与表面活性剂分子的相互作用，S＝O对称伸缩振动的红外吸收峰向低频方向移动．体系中的加水量W0（水与AOT的摩尔比）由0.5增大至25时，磺酸根对称伸缩振动的红外吸收峰由1051．39cm－1向低频移动至1046．15cm－1．同时，由于Na 的不对称作用，AOT分子中磺酸根反对称伸缩振动分裂成两个吸收峰，分别位于正215cm-1及1245cm－1附近，两个劈裂峰的距离及各自的峰面积均随体系中加水量的变化而变化，应用二阶导数、傅立叶退卷积及曲线拟会等分辨率增强技术可更清楚地反映出这个二重峰的变化情况．固体AOT分子中碳酸根反对称伸缩振动分裂的两个峰之间频率的差值约为42cm－1，形成微乳液以后，这两个峰的差值变小，W0为20时，这两个峰频率的差值逐渐减小到29cm-1，这些变化与磺酸根的水化程度直接相关     

The microstructure and optical transmittance thermal analysis of sodium borosilicate bio-glasses

The conditions to fabricate the bulk porous specimens have been studied on account of sodium borosilicate (NBS) glasses. Glass composition, heat treatment at phase separation and TiO₂ addition have been considered in this study. Original glass samples of composition in mol%: sample A: 9.19 Na₂O - 23.58 B₂O₃ - 67.23 SiO₂, sample B: 9.29 Na₂O - 3.17 TiO₂ - 23.82 B₂O₃ - 63.72 SiO₂ were prepared by melting reagent grade chemicals (Na₂CO₃, HBO₃, SiO₂ and AgNO₃) in platinum crucibles at 1480°C for 1 h in air. The melts were poured onto stainless steel plates and were annealed at 500°C for 0.5 h after cooling. Thus, obtained samples were phase separated at 700°C for 2, 15, 25 and 50 h to study their microstructure by scanning electron microscope (SEM). Besides the direct study of the microstructure by SEM, information on glass structural changes of samples are provided by measuring in situ changes by the optical transmittance thermal analysis. The isothermal measurements were carried out at 700, 720 and 740°C. The temperature of phase separation, the leaching and nucleator addition (TiO₂), significantly influence the microstructure of the resulting leached product. TiO₂ additive seems to suppress crystallization of cristobalite: especially at the extended above heat treatment phase separation runs. The phase-separated domains of glasses containing above 80 moles of SiO₂ are so small that it is very hard to observe them by SEM. The glass composition in our case was selected in a way to have relatively large phase separated areas easily observed by SEM at magnification 20 000·. The influence of TiO₂ is not too pronounced. It seems to suppress the cristobalite crystallization, especially of longer heating runs. The image analysis of leached glasses shows the prevailing content of the skeletal phase in a comparison to pores. The TiO₂ content diminishes the content of the skeletal phase. This revised version was published online in July 2006 with corrections to the Cover Date.     

An Efficient and Practical Process for Pd/Cu Cocatalyzed Homocoupling Reaction of Terminal Alkynes Using Sodium Percarbonate as a Dual Reagent in Aqueous Media

A new process for the Pd/Cu co-catalyzed homocoupling reaction of terminal alkynes was developed. The reaction was carried out in aqueous media with sodium percarbonate as both a clean oxidant and a base. Meanwhile, a palladium complex immobilized on a synthetic PS-PEG400-PPh2 resin was used as the catalyst, which may be recovered by simple filtration and reused for several times with high activity.     

A study for quality evaluation of Taxilli Herba from different hosts based on fingerprint-activity relationship modeling and multivariate statistical analysis

In this study, a fingerprint-activity relationship modeling between chemical fingerprints and antirheumatic activity was established, and multivariate statistical analysis was used to evaluate the quality of Taxilli Herba (TH) from different hosts. Characteristic fingerprints of 20 batches of TH samples were generated by high-performance liquid chromatography coupled with triple quadrupole-time of flight tandem mass spectrometry (HPLC-Triple TOF-MS/MS), and the similarity analysis was calculated based on thirteen common characteristic peaks by hierarchical clustering analysis (HCA). Subsequently, nine efficacy markers were discovered by combining fingerprints and antirheumatic activity through grey correlation analysis (GCA) and bivariate correlation analysis (BCA). Meanwhile, the content of 5 constituents in 9 markers was determined by high-performance liquid chromatography coupled with triple quadrupole-linear ion trap tandem mass spectrometry (HPLC-QTRAP-MS/MS). The comprehensive quality of TH was assessed using multivariate statistical analysis, including principal components analysis (PCA) and technique for order preference by similarity to ideal solution (TOPSIS). The results showed that a high dose of TH extract could markedly ameliorate arthritis damage compared to other doses, with flavonoids playing an important role in the antirheumatic activity. The comprehensive quality of samples from Morus alba L. (SS) was superior to those from Liquidambar formosana Hance (FXS). The present study will demonstrate the markers associated with efficacy, and provide an applicable strategy for more comprehensive quality control and evaluation of TH.     

荧光光度法直接测定环境水中苯酚和十二烷基苯磺酸钠的含量

本文研究了用荧光分光光度法直接测定环境水中苯酚和十二烷基苯磺酸钠（ＳＤＢＳ）二种水中污染物。在ｐＨ〉１１直接测定ＳＤＢＳ含量，波长为λｅｘ／λｅｍ＝２３０／２９５ｎｍ，检出限４．４ｎｇ／ｍＬ，线性范围０￣２．２μｇ／ｍｌ。在ｐＨ＝６，波长为λｅｘ／λｅｍ＝２３０／２９５ｎｍ，测得二者合量，从合量中减去ＳＤＢＳ含量即得苯酚含量，检出限４．０ｎｇ／ｍｌ，线性范围０￣０．８５μｇ／ｍＬ，回收率达９９％￣