Time-dependent selectivity of glass membrane electrodes

Time-dependent selectivities of both sodium- and hydrogen-selective glass membrane electrodes are investigated. Results indicate that these electrodes display little selectivity shortly after an increase or decrease in the activityof another cation at the electrode surface. Selectivity appears to increase as the potential approaches a steady-state value. A physical model is considered which accounts for the time-dependent selectivity with the generation of a chemical potential difference across the interface between the bulk solution and the hydrated glass layer.     

手印显现选择性的量化研究

本研究旨在提出手印显现选择性的量化方法,并讨论手印显现选择性的影响因素。首先利用Image J软件得到手印图像的灰度曲线,再利用Origin软件对灰度曲线进行分析,最终得到手印显现选择性的定量计算方法,即灰度曲线的波峰（对应乳突纹线）与波谷（对应小犁沟）积分的比值。本研究通过502熏染显现法、氨基黑10B显现法对量化方法进行了验证,结果表明该量化方法可行,此外,从显现试剂与客体性质两方面分析了影响手印显现选择性的主要因素。通过该研究,为手印显现效果的量化特别是选择性的定量评估提供了有益的参考。     

Separation selectivity patterns in the capillary electrophoretic separation of anionic enantiomers by octakis-6-sulfato-gamma-cyclodextrin

The capillary electrophoretic separation of anionic enantiomers with multiply-charged, single-isomer, anionic resolving agents was reexamined with the help of the charged resolving agent migration model. Three general model parameters were identified that influence the shape of the separation selectivity and enantiomer mobility difference curves: parameter b, the binding selectivity (K(RCD)/K(SCD)), parameter s, the size selectivity (micro0RCD/micro0SCD), and parameter a, the complexation-induced alteration of the analyte's mobility (micro0SCD/micro0). Function analysis of the model indicates that there are six unique separation selectivity vs. resolving agent concentration patterns: in two of the patterns, separation selectivity asymptotically increases to the limiting value set by parameter b; in two other patterns, separation selectivity passes a local maximum and asymptotically decreases to the limiting value set by parameter b; and in the last two patterns, separation selectivity passes a local maximum, decreases to unity, then, after reversal of the intrinsic migration order, asymptotically increases to the limiting value set by parameter b. Though the patterns with asymptotically increasing selectivities were observed in earlier work, this paper reports the first experimental verification of the existence of the local selectivity maximum during the capillary electrophoretic separation of the enantiomers of several weak acids in high pH background electrolytes with octakis-6-sulfato-gamma-cyclodextrin as the resolving agent.     

Likely Mechanism of the Hydrophobic Sensitizer Accumulation in Tumor Cells: Mathematical Models

Abstract— Two mathematical models describing the accumulation kinetics of hydrophobic sensitizers in the cell membrane and cytoplasm and the influence of intra- and extracellular pH values on intracellular accumulation are suggested. Numerical calculations were done for hematopor-phyrin (Hp) as an example. When compared with the experimental data, both models gave satisfactory results describing the accumulation time and level. A biphasic character of the sensitizer accumulation process was obtained as a result of the difference in the accumulation times characteristic for the plasma membrane and cytoplasm. The ratio of characteristic times was determined by the ratio of membrane and cytoplasm volumes and a "water-lipid" partition coefficient reflecting the height of the membrane barrier for the sensitizer penetration through the plasma membrane lipid bilayer. Generally, the enhanced uptake of Hp molecules by cells was obtained when both extracellular and intracellular pH (pH,.,) values were lower than the physiological ones. A "selectivity" of accumulation was achieved in "tumor" cells for reasonable pH_in values (about 6.0). But when compared with the experimental data, the value of selectivity was not high enough, indicating that, though the pH value is an important factor in Hp intracellular accumulation, it might be less important as a factor for selectivity of Hp accumulation in tumors.     

Visible-Light-Promoted Switchable Selective Oxidations of Styrene Over Covalent Triazine Frameworks in Water

Using photocatalytic oxidation to convert basic chemicals into high value compounds in environmentally benign reaction media is a current focus in catalytic research. The challenge lies in gaining controllability over product formation selectivity. We design covalent triazine frameworks as heterogeneous, metal-free, and recyclable photocatalysts for visible-light-driven switchable selective oxidation of styrene in pure water. Selectivity in product formation was achieved by activation or deactivation of the specific photogenerated oxygen species. Using the same photocatalyst, by deactivation of photogenerated H₂O₂, benzaldehyde was obtained with over 99 % conversion and over 99 % selectivity as a single product. The highly challenging and sensitive epoxidation of styrene was carried out by creating peroxymonocarbonate as an initial epoxidation agent in the presence of bicarbonate, which led to formation of styrene oxide with a selectivity up to 76 % with near quantitative conversion. This study demonstrates a preliminary yet interesting example for simple control over switchable product formation selectivity for challenging oxidation reactions of organic compounds in pure water.     

Studies on the matched potential method for determining the selectivity coefficients of ion-selective electrodes based on neutral ionophores: experimental and theoretical verification.

A theory is presented that describes the matched potential method (MPM) for the determination of the potentiometric selectivity coefficients (KA,Bpot) of ion-selective electrodes for two ions with any charge. This MPM theory is based on electrical diffuse layers on both the membrane and the aqueous side of the interface, and is therefore independent of the Nicolsky-Eisenman equation. Instead, the Poisson equation is used and a Boltzmann distribution is assumed with respect to all charged species, including primary, interfering and background electrolyte ions located at the diffuse double layers. In this model, the MPM-selectivity coefficients of ions with equal charge (ZA = ZB) are expressed as the ratio of the concentrations of the primary and interfering ions in aqueous solutions at which the same amounts of the primary and interfering ions permselectively extracted into the membrane surface. For ions with unequal charge (ZA not equal to ZB), the selectivity coefficients are expressed as a function not only of the amounts of the primary and interfering ions permeated into the membrane surface, but also of the primary ion concentration in the initial reference solution and the delta EMF value. Using the measured complexation stability constants and single ion distribution coefficients for the relevant systems, the corresponding MPM selectivity coefficients can be calculated from the developed MPM theory. It was found that this MPM theory is capable of accurately and precisely predicting the MPM selectivity coefficients for a series of ion-selective electrodes (ISEs) with representative ionophore systems, which are generally in complete agreement with independently determined MPM selectivity values from the potentiometric measurements. These results also conclude that the assumption for the Boltzmann distribution was in fact valid in the theory. The recent critical papers on MPM have pointed out that because the MPM selectivity coefficients are highly concentration dependent, the determined selectivity should be used not as "coefficient", but as "factor". Contrary to such a criticism, it was shown theoretically and experimentally that the values of the MPM selectivity coefficient for ions with equal charge (ZA = ZB) never vary with the primary and interfering ion concentrations in the sample solutions even when non-Nernstian responses are observed. This paper is the first comprehensive demonstration of an electrostatics-based theory for the MPM and should be of great value theoretically and experimentally for the audience of the fundamental and applied ISE researchers.     

Automated screening of reversed‐phase stationary phases for small‐molecule separations using liquid chromatography with mass spectrometry

There are various reversed‐phase stationary phases that offer significant differences in selectivity and retention. To investigate different reversed‐phase stationary phases (aqueous stable C₁₈, biphenyl, pentafluorophenyl propyl, and polar‐embedded alkyl) in an automated fashion, commercial software and associated hardware for mobile phase and column selection were used in conjunction with liquid chromatography and a triple quadrupole mass spectrometer detector. A model analyte mixture was prepared using a combination of standards from varying classes of analytes (including drugs, drugs of abuse, amino acids, nicotine, and nicotine‐like compounds). Chromatographic results revealed diverse variations in selectivity and peak shape. Differences in the elution order of analytes on the polar‐embedded alkyl phase for several analytes showed distinct selectivity differences compared to the aqueous C₁₈ phase. The electron‐rich pentafluorophenyl propyl phase showed unique selectivity toward protonated amines. The biphenyl phase provided further changes in selectivity relative to C₁₈ with a methanolic phase, but it behaved very similarly to a C₁₈ when an acetonitrile‐based mobile phase was evaluated. This study shows the value of rapid column screening as an alternative to excessive mobile phase variation to obtain suitable chromatographic settings for analyte separation.     

Potentiometric titrations with ion-exchanging membrane electrodes : Part II. A theoretical treatment of the effect of membrane selectivity

The possible influence of the selectivity of the membrane used in an indicating electrode with potentiometric titrations was investigated by introducing some simple modifications in the calculations performed earlier. The influence of the selectivity is visible only before the equivalence point when the counter-ion is precipitated initially from the titrated solution. When the co-ion is precipitated initially, the shape of the titration curve is altered only after the equivalence point. The reliability of the determination of the equivalence point can be either advantageously or disadvantageously influenced by the selectivity, depending on the value of the selectivity coeffcient and the ratio of the diffusion coefficients.     

Effect of antiplasticization on selectivity and productivity of gas separation membranes

Addition of certain low molecular diluents cause glassy polymers to become stiffer owing to reduced rates of segmental motions. This antiplasticization response is accompanied by a decrease in permeability to gases and may be accompanied by either an increase or a decrease in the selectivity of transport for any two gases. When compared to the trade-off between selectivity and productivity of gas separation membranes made from a variety of polymer structures, antiplasticization does not offer any advantageous combination of these traits for either polysulfone or poly(phenylene oxide). However, this approach may have value when increased selectivity at the expense of productivity is justified but developing membranes from another polymer is not desirable.     

ZnZrOx-HZSM-5双功能催化剂催化甲苯与合成气烷基化制对二甲苯

作为重要的有机化工原料,近些年来随着聚酯行业的高速发展,对二甲苯(PX)需求量逐年增高.目前,PX主要通过传统的石油路线生产,例如石脑油催化重整、甲苯歧化和C₈芳烃异构化,这些路线的后续精馏能耗较高.甲醇作为碳源与甲苯烷基化制备PX有效提高了目标产物的选择性,且已实现工业化.然而,由于甲醇生成甲氧基烷基化物种的能垒较高,使反应温度较高,促进了甲醇制烯烃(MTO)副反应的进行,降低了甲醇利用率;且由于积炭的形成,催化剂容易失活.合成气是非石油基资源如煤炭、天然气和生物质等利用的重要平台,在转化为醇类、烯烃以及芳烃路径中将经过甲氧基中间体,因此,本文研发以合成气代替甲醇与甲苯烷基化制备PX的催化剂和催化过程.基于本课题组关于CO₂加氢耦合甲苯烷基化制PX的研究基础,本文将ZnZrO_x(ZZO)与ZSM-5(Z5)混合制得双功能催化剂,用于合成气转化耦合甲苯烷基化制PX.研究结果表明,通过优化催化剂的组成和烷基化反应条件,调控CO加氢反应和甲苯烷基化反应的匹配性,在甲苯转化率为10.3%时,可获得64.8%的二甲苯选择性(不计水煤气变换反应),其中PX占81.8%,气态烃副产物的选择性为10.9%;在相同条件下采用甲醇为烷基化试剂时,二甲苯选择性仅38.5%,其中PX占38.8%,此时气态烃副产物的选择性达26.2%.同位素效应实验结果表明,二甲苯中新增甲基来自于合成气,而非甲苯的歧化反应.催化剂构效研究结果表明,PX的选择性与分子筛孔径、酸性强度以及Br?nsted酸性位点有关;原位红外结果也证实了该反应呈现逆同位素效应(k_H2/k_D2=0.92),表明反应中甲酸盐物种(HCOO*)加氢可能是反应的决速步骤.与传统的甲醇甲苯烷基化路径相比,采用来源广泛和成本较低的合成气与甲苯进行烷基化反应的温度(340℃)更低,有效避免了MTO副反应的发生,同时,该催化剂可在100 h内保持良好稳定性.综上,本工作结果为高效制备高值芳烃PX提供了新思路.     

ZnZrOx-HZSM-5双功能催化剂催化甲苯与合成气烷基化制对二甲苯

作为重要的有机化工原料,近些年来随着聚酯行业的高速发展,对二甲苯(PX)需求量逐年增高.目前,PX主要通过传统的石油路线生产,例如石脑油催化重整、甲苯歧化和C₈芳烃异构化,这些路线的后续精馏能耗较高.甲醇作为碳源与甲苯烷基化制备PX有效提高了目标产物的选择性,且已实现工业化.然而,由于甲醇生成甲氧基烷基化物种的能垒较高,使反应温度较高,促进了甲醇制烯烃(MTO)副反应的进行,降低了甲醇利用率;且由于积炭的形成,催化剂容易失活.合成气是非石油基资源如煤炭、天然气和生物质等利用的重要平台,在转化为醇类、烯烃以及芳烃路径中将经过甲氧基中间体,因此,本文研发以合成气代替甲醇与甲苯烷基化制备PX的催化剂和催化过程.基于本课题组关于CO₂加氢耦合甲苯烷基化制PX的研究基础,本文将ZnZrO_x(ZZO)与ZSM-5(Z5)混合制得双功能催化剂,用于合成气转化耦合甲苯烷基化制PX.研究结果表明,通过优化催化剂的组成和烷基化反应条件,调控CO加氢反应和甲苯烷基化反应的匹配性,在甲苯转化率为10.3%时,可获得64.8%的二甲苯选择性(不计水煤气变换反应),其中PX占81.8%,气态烃副产物的选择性为10.9%;在相同条件下采用甲醇为烷基化试剂时,二甲苯选择性仅38.5%,其中PX占38.8%,此时气态烃副产物的选择性达26.2%.同位素效应实验结果表明,二甲苯中新增甲基来自于合成气,而非甲苯的歧化反应.催化剂构效研究结果表明,PX的选择性与分子筛孔径、酸性强度以及Br?nsted酸性位点有关;原位红外结果也证实了该反应呈现逆同位素效应(k_H2/k_D2=0.92),表明反应中甲酸盐物种(HCOO*)加氢可能是反应的决速步骤.与传统的甲醇甲苯烷基化路径相比,采用来源广泛和成本较低的合成气与甲苯进行烷基化反应的温度(340℃)更低,有效避免了MTO副反应的发生,同时,该催化剂可在100 h内保持良好稳定性.综上,本工作结果为高效制备高值芳烃PX提供了新思路.     

NiSO4／HY催化剂上丙烯齐聚反应研究

本文考察了ＮｉＳＯ_４／ＨＹ催化剂用于丙烯齐聚反应的催化性能，研究了镍含量、镍盐、焙烧温度以及反应条件对催化活性和选择性的影响，随镍含量增加，反应活性及二聚选择性都升高，镍含量为９一２０ｗｔ％时活性达最好，液体收率达９５ｗｔ％，随焙烧温度升高，二聚选择性不断升高。催化活性则在８２３Ｋ时有最大值。用吸附指示剂法测定了样品的酸分布，ＣＯ－ＴＰＤ法测定了暴露的Ｎｉ中心量，ＸＲＤ法测定了ＮｉＳＯ_４在ＨＹ上的分散阈值，讨论了它们与丙烯齐聚活性的关联。     

H-ZSM-5分子筛硅铝比对其催化的甲醇转化丙烯选择性的影响

本研究合成了一系列硅铝比不同（SiO₂/Al₂O₃=50-4000），但晶粒粒径相近的ZSM-5分子筛，并考察了硅铝比对甲醇转化反应丙烯选择性的影响。采用XRD、N₂吸附-脱附、NH₃-TPD和Py-FTIR方法对合成的HZSM-5分子筛进行物化性质表征。实验结果表明，随着硅铝比的增大，初始甲醇转化率降低，其中，硅铝比为50-1600的样品可以实现甲醇的完全转化。在甲醇完全转化的条件下，随着硅铝比的增大，丙烯选择性单调增加，从机理角度出发，揭示了甲醇转化制丙烯反应中，甲基化/裂化循环相较于甲基化/脱烷基化循环进行程度更大。此外，本研究提出了在甲醇完全转化条件下，保证最大丙烯选择性所需要的临界酸密度值（[AS]_S），当甲醇进料量为0.162g/min时，该临界值为0.175μmol/m²。     

Selective Electrochemical Reduction of Carbon Dioxide to Ethanol on a Boron‐ and Nitrogen‐Co‐doped Nanodiamond

Electrochemical reduction of CO₂ to ethanol, a clean and renewable liquid fuel with high heating value, is an attractive strategy for global warming mitigation and resource utilization. However, converting CO₂ to ethanol remains great challenge due to the low activity, poor product selectivity and stability of electrocatalysts. Here, the B‐ and N‐co‐doped nanodiamond (BND) was reported as an efficient and stable electrode for selective reduction of CO₂ to ethanol. Good ethanol selectivity was achieved on the BND with high Faradaic efficiency of 93.2 % (−1.0 V vs. RHE), which overcame the limitation of low selectivity for multicarbon or high heating value fuels. Its superior performance was mainly originated from the synergistic effect of B and N co‐doping, high N content and overpotential for hydrogen evolution. The possible pathway for CO₂ reduction revealed by DFT computation was CO₂→*COOH→*CO→*COCO→*COCH₂OH→*CH₂OCH₂OH→CH₃CH₂OH.     

助剂促进的Rh-Fe/Al_2O_3催化剂上CO加氢制乙醇反应性能

考察了Fe,Rh载量以及助剂对Rh-Fe/Al2O3催化剂上合成气制乙醇反应性能的影响.结果表明,随着Fe载量的增加,甲醇选择性持续上升伴随着甲烷选择性的持续下降,而乙醇选择性有最优值.助剂的添加或多或少促进了甲醇耦合、CO插入和解离的活性,或抑制了催化剂加氢能力,使得乙醇选择性有所上升,甲醇选择性有所下降,而烃类选择性变化不大.随着CO加氢反应的进行,Rh-Fe/Al2O3催化剂上烃类选择性逐渐下降,但甲醇的生成活性逐渐上升,而乙醇选择性和生成活性逐渐下降;然而,助剂的添加并未提高催化剂的稳定性.这可能是由于在反应过程中Fe物种逐渐被合成气还原使得乙醇生成活性位数量逐渐减少所致.     

渗透汽化法分离二氧六环－水混合物

研究了二氧六环一水混合物在ＰＶＡ（聚乙烯酸）－ＰＡＮ（聚丙烯腈）复合膜中的渗透汽化分离性能。结果表明透过速率Ｑ和分离系数α均随料液温度的提高而增大。α随料液中二氧六环浓度的提高而增大，Ｑ的变化趋势相反．有代表性的数据是在９０℃对９５％的二氧六环水溶液，α可达１９８１，Ｑ＝７３．８ｇ／ｍ２·ｈ．在低浓度二氧六环溶液时扩散过程对选择性起主要作用。而高浓度时溶解选择性是主要的，随着分离温度的提高，扩散或溶解均提高了选择性。     

L-N-(3,5-Dimethoxybenzoyl)isoleucine chiral stationary phase for separation of enantiomers by HPLC

Summary L-N-(3,5-dimethoxyoxybenzoyl)isoleucine, ionically bonded to γ-aminopropyl silica, has been tested as a chiral stationary phase for the separation of racemates by HPLC. The phase shows good selectivity towards different types of racemates and in particular for those having an electron-poor aromatic group in their molecule. The separation of benzoin racemate can be achieved on the developed chiral phase with an α value of 1.10.     

丙烯环氧化反应中TS-1催化剂失活研究

采用丙烯气相进料,在预混段中先与双氧水的甲醇溶液混合后进入固定床反应器,考察了进料液中pH值、丙二醇单甲醚、乙硫醇以及铁锈等对丙烯环氧化连续反应中TS-1分子筛催化剂性能的影响。结果表明,进料液体pH值对催化剂的催化性能有影响,适宜的进料液体pH值在7左右;副产物丙二醇单甲醚含量的增加不会对催化剂性能产生影响;乙硫醇量的增加使环氧丙烷选择性下降,但不会引起催化剂的失活;而进料液体中铁锈的引入会导致催化剂中部分孔堵塞,使催化剂部分失活。当进料液中的pH值用0.1mol/L的氨水调节为7左右,在反应温度55℃,反应压力0.7MPa,TS-1催化剂具有较好的稳定性,经130h的连续试验考察,双氧水的转化率和环氧丙烷的选择性约为90%。     

In situ preparation of powder and the sorption behaviors of molecularly imprinted polymers through the complexation between polymer ion of methyl methacrylate/acrylic acid and Ca ion

Molecularly imprinted polymer (MIP) powders were prepared using a simple complexation strategy between the polymer carboxylate groups and template molecule followed by metal cation cross-linking of residual polymer carboxylates. Polymer powders were formed in situ by templating carboxylic acid containing polymers with 4-ethylaniline (4-EA), followed by addition of an aqueous CaCl₂ solution. The solution remained homogeneous. The powders were prepared by precipitation by slowly adding a non-solvent, H₂O, to the mixture. The resulting particles were very porous with uptake capacity that approached the theoretical value. We suggest two types of complexes are formed between the template, 4-EA, and polymer. The isolated entry type forms well defined cavities for the template with high specific selectivity, while the adjacent entry type forms wider binding sites without specific sorption for isomeric molecules. To evaluate conditions for forming materials with high affinity and selectivity, three MIPs were prepared containing 0.5, 1.0, and 1.5 equivalents of template to the base polymer. The MIP containing 0.5 eq showed higher specific selectivity to 4-EA, but the MIP containing 1.5 eq had noticeably lower selectivity. The lower selectivity is attributed to poorly formed binding sites with little selective sorption to any isomer when the higher ratio of template was used. However at the lower ratio of template the isolated entry is preferably formed to produce well defined binding cavities with higher selectivity to template.     

Synthesis and evaluation of a maltose‐bonded silica gel stationary phase for hydrophilic interaction chromatography and its application in Ginkgo Biloba extract separation in two‐dimensional systems

Maltose covalently bonded to silica was prepared by using carbonyl diimidazole as a cross‐linker and employed as a stationary phase for hydrophilic interaction liquid chromatography. The column efficiency and the effect of water content, buffer concentration, and pH value influenced on retention were investigated. The separation or enrichment selectivity was also studied with nucleosides, saccharides, amino acids, peptides, and glycopeptides. The results indicated that the stationary phase processed good separation efficiency and separation selectivity in hydrophilic interaction liquid chromatography mode. Moreover, a two‐dimensional hydrophilic interaction liquid chromatography× reversed‐phase liquid chromatography method with high orthogonality was developed to analyze the Ginkgo Biloba extract fractions. The development of this two‐dimensional chromatographic system would be an effective tool for the separation of complex samples of different polarities and contents.