Fabrication of solid‐state nanopores and its perspectives

Nanofluidics is becoming an extensively developing technique in the field of bioanalytical chemistry. Nanoscale hole embed in an insulating membrane is employed in a vast variety of sensing platforms and applications. Although, biological nanopores have several attractive characteristics, in this paper, we focused on the solid‐state nanopores due to their advantages as high stability, possibility of diameter control, and ease of surface functionalizing. A detection method, based on the translocation of analyzed molecules through nanochannels under applied voltage bias and resistive pulse sensing, is well established. Nevertheless, it seems that the new detection methods like measuring of transverse electron tunneling using nanogap electrodes or optical detection can offer significant additional advantages. The aim of this review is not to cite all related articles, but highlight the steps, which in our opinion, meant important progresses in solid‐state nanopore analysis.     

载体表面酸碱性质对无碱水溶液中Au催化的甘油氧化反应产物选择性的调控作用

甘油(GL)是一种重要的生物平台分子,通过催化选择氧化反应将其转化为具有高附加值化学品是可持续发展化学化工的重要课题之一.以Au为催化剂的GL水相选择氧化反应可以生成甘油酸(GLA)、二羟基丙酮(DHA)、羟基丙二酸(TTA)、羟基乙酸(GCA)和乳酸(LA)等多种产物.通常,该反应需要碱(NaOH)存在时才能进行,产物往往以GLA为主(选择性40%-70%),副产物主要有GCA, TTA和草酸(OA).一般认为,可溶性碱(OH-)是通过夺取GL分子中羟基上的质子而诱发反应的.尽管在Au催化的反应体系中从未检测到有甘油醛(GLD)生成, GLD和/或DHA被认为是该反应的中间物种.本课题组前期工作表明,氧化物(TiO2, Al2O3, ZrO2, CuO等)负载的纳米Au催化剂能够在无碱(无外加OH-)水溶液中选择性催化GL氧化生成DHA(而不是GLA).因此, OH-的存在与否很可能会改变水溶液中Au催化剂上GL氧化反应的途径.本文试图回答当GL的水溶液中不存在NaOH时, Au催化剂载体的表面酸碱性质是否也会对GL氧化反应的选择性产生调控作用.我们选用Mg/Al比(x)不同的MgO-Al2O3样品为Au催化剂的载体,以尿素为沉淀剂,采用沉积沉淀法制备了相应的Au/MgO-Al2O3(x)催化剂样品.采用X射线衍射、电感耦合等离子体-原子发射光谱仪、透射电镜以及N2吸附-脱附等温线等对MgO-Al2O3(x)和/或Au/MgO-Al2O3样品的物相、元素组成、Au颗粒大小以及比表面积等进行了表征分析;采用NH3和CO2程序升温脱附(TPD)分别对MgO-Al2O3(x)载体表面的酸、碱性进行了测定. NH3-TPD和CO2-TPD结果表明,随着Mg/Al比x从0增加至4.8, MgO-Al2O3(x)的表面酸量从0.94降到0.20μmol/m2,而其表面碱量却从0.05剧增至0.80μmol/m2.因此,载体中MgO含量越多或Mg/Al比越大,其酸性越弱而碱性越强.在无碱水溶液中的催化反应结果表明, Au/MgO-Al2O3(x)上GL氧化反应的主要产物为DHA, GLA以及GCA等.随着x值(催化剂表面碱性)不断增大,产物DHA的选择性从约80%下降到10%左右,而GLA的选择性却从约4%增加至约50%.当载体为酸性最强的Al2O3(x =0)时,产物DHA的选择性为最高(80%).由此可见,载体表面的酸碱性质决定了无碱水溶液中Au催化剂上的GL氧化产物的分布. 此外,当保持Au粒子的尺寸基本不变(如3.1或6.6 nm左右),而改变载体的酸碱性质时, Au/MgO-Al2O3催化GL氧化反应的活性(TOF)可相差8-9倍.本文还通过改变Au/MgO-Al2O3样品焙烧温度,制备了表面酸碱性质相同而颗粒大小不同的三个Au/MgO-Al2O3(0.2)催化剂,考察了Au粒径对GL氧化反应选择性的影响.在这三个催化剂上, Au颗粒的平均尺寸分别为2.8,3.2和6.6 nm, GL氧化反应的产物选择性近乎相同(DHA和GLA的选择性分别为65%和15%左右),但平均尺寸为6.6 nm Au粒子的催化活性(TOF)是3.2 nm Au粒子的1.6倍,2.8 nm Au粒子的2.7倍.因此,本文建立了载体表面酸碱性质与无碱水溶液中GL氧化产物选择性之间的关系,通过改变载体表面酸碱性质实现了对无碱水溶液中Au催化剂上GL氧化反应选择性的调控.尽管载体酸碱性质和Au粒子尺寸都对Au/MgO-Al2O3催化剂的本征活性有重要影响,但载体酸碱性质的影响更显著.     

Impact of the flexibility of pillar linkers on the structure and CO_2 adsorption property of ‘‘pillar-layered' MOFs

A new metal–organic framework {[Zn_2(bpta)(bpy-ee)(H_2O)_2]·x solve}_n(1)(H_4bpta = biphenyl-2,20,6,60-tetracarboxylic acid and bpy-ee = 1,2-bis(4-pyridyl)ethylene) has been obtained under hydrothermal condition, and structurally characterized by single-crystal X-ray diffraction. Complex 1 reveals a threedimensional(3D) ‘‘pillar-layered' framework with non-flexible linker, in which some different structure characters can be found compared to that of some related other ‘‘pillar-layered' MOFs based on flexible pillar linkers. It demonstrates the impact of the flexibility of pillar linker on the final structure in this system. In addition, the selective CO_2 adsorption performance of 1 was also investigated.     

Highly sensitive and selective sensing platform based on π–π interaction between tricyclic aromatic hydrocarbons with thionine–graphene composite

We are just beginning to exploit the fascinating potential of thionine, called electrochemical probe that can selectively recognize specific polycyclic aromatic hydrocarbons (PAHs), as tools for the detection of tricyclic aromatic hydrocarbons phenanthrene (PHE) and anthracene (ANT). A novel electrochemical sensing platform by modification of electroactive thionine functionalized graphene onto glass carbon electrode (Th/GRs/GCE) surface was constructed. The immobilized thionine showed a remarkable stability, which may benefit from the π–π stacking force with graphene. Under optimum conditions, the proposed electrochemical sensor exhibited high sensitivity and low detection limit for detecting PHE and ANT. The total amount of PHE and ANT could be quantified in a wide range of 10 pM–0.1 μM with a good linearity (R² = 0.9979) and a low detection limit of 0.1 pM (S/N = 3). Compounds which possess one or two benzene rings or PAHs with more than three rings, such as benzene, naphthalene (NAP), benzo[a]pyrene (BaP) and pyrene (PYR) show little interference on the detection. Consequently, a simple and sensitive electrochemical method was proposed for the determination of PHE and ANT, which was used to determine PHE and ANT in waste water samples. The electrochemical method provides a general tool that complements the commonly used spectroscopic methods and immune method for the detection of PAHs.     

Synthesis of new dendrimers—trimesic acid derivatives

The efficient synthesis of new dendrimeric polyesters up to generation 3 that consist of 1,3,5-benzenetricarboxylic acid building blocks with potential applications in drug delivery is described. The dendrimers possess hydroxy or allyl functional groups on the surface and were prepared through a divergent approach using readily available 2-(hydroxymethyl)-2-ethylpropan-1,3-diol and 1,3,5-benzenetrimethanol as central cores, with 3,5-bis[(allyloxy)methyl]benzoic acid being an essential unit of the dendrimer. The latter compound was synthesized, in high yield, from 1,3,5-benzenetricarboxylic acid, applying selective hydrolysis of the corresponding triester as the key step.     

Study of the surface ionization detector for gas chromatography

The structure of the surface ionization detector (SID) and the operation parameters of GC-SID were investigated to reduce peak tailing and to enhance sensitivity. The performances of the GC-SID, including its repeatability, linearity, sensitivity, selectivity, and tolerance towards water vapor, were evaluated systematically. Compared with nitrogen-phosphorus detector (NPD), the SID was able to detect fg level triethylamine, and selectively respond to alkylamines, some anilines, and some nitrogen heterocyclic compounds. Among alkylamines, the SID sensitivity to diisobutylamine was rather small. Even so, it was also still 10 times higher than that on NPD. The SID selectivity, defined as the sensitivity ratio between triethylamine and various tested non-nitrogen compounds, was higher than 10(6). It was found that the SID is highly tolerant towards water vapor, allowing direct injection of water sample. Finally, the GC-SID was applied to directly measure trace amines in headspace gases of rotted meat and trace simazine in tap water. The SID sensitivity to simazine was proven to be 5 times higher than that on flame ionization detector (FID). This study suggests that the SID is a promising GC detector.     

A highly selective and easy-to-synthesize Zn(Ⅱ) fluorescent probe based on 6-methoxyquinolin

A novel fluorescent Zn²⁺ probe based on 6-methoxyquinolin was synthesized in four steps from inexpensive starting materials.It exhibits very strong fluorescence responses and has a remarkably high selectivity to Zn²⁺ than other physiological relevant metal ions.This new compound could be used as low-priced yet high-quality Zn²⁺ probe.     

Effects of first dimension eluent composition in two-dimensional liquid chromatography

Comprehensive two-dimensional liquid chromatography (LC×LC) has received a great deal of attention during the past few years because of its extraordinary resolving power. The biggest advantage of this technique is that very high peak capacities can be generated in a relatively short time. Numerous approaches to maximize the peak capacity in LC×LC have been employed. In this work we investigate the impact of the first dimension mobile phase on selectivity. LC×LC has several potential advantages over one-dimensional LC (1DLC) in that unconventional solvents, at least in reversed-phase LC, can be used. For example, solvents which strongly adsorb in the UV in the first dimension are not problematic in LC×LC. This so because the UV detector is placed after the second dimensional column, as pulses of the first dimension eluent arrive at the second dimensional column, they elute well before the solutes of interest and therefore do not interfere at all with detection of solute peaks. So far, the most widely used solvents in reversed-phase 1DLC are methanol and acetonitrile. However, the "UV advantage" of 2DLC allows us to employ UV active solvents, such as acetone. We compare their differential selectivities to that of acetonitrile for the separation of 23 indole acetic acids of interest in plant biology. We also apply them to the separation of a maize seed extract, a very complex sample. In both sample sets, mobile phase composition can be an important parameter to increase the orthogonality of the two dimensions and thus, to increase the effective peak capacity of LC×LC.     

The statistical overlap theory of chromatography using power law (fractal) statistics

The chromatographic dimensionality was recently proposed as a measure of retention time spacing based on a power law (fractal) distribution. Using this model, a statistical overlap theory (SOT) for chromatographic peaks is developed that estimates the number of peak maxima as a function of the chromatographic dimension, saturation and scale. Power law models exhibit a threshold region whereby below a critical saturation value no loss of peak maxima due to peak fusion occurs as saturation increases. At moderate saturation, behavior is similar to the random (Poisson) peak model. At still higher saturation, the power law model shows loss of peaks nearly independent of the scale and dimension of the model. The physicochemical meaning of the power law scale parameter is discussed and shown to be equal to the Boltzmann-weighted free energy of transfer over the scale limits. The scale is discussed. Small scale range (small β) is shown to generate more uniform chromatograms. Large scale range chromatograms (large β) are shown to give occasional large excursions of retention times; this is a property of power laws where "wild" behavior is noted to occasionally occur. Both cases are shown to be useful depending on the chromatographic saturation. A scale-invariant model of the SOT shows very simple relationships between the fraction of peak maxima and the saturation, peak width and number of theoretical plates. These equations provide much insight into separations which follow power law statistics.