A periodic array of nano‐scale parallel slats for high‐efficiency electroosmotic pumping

It is known that the eletroosmotic (EO) flow rate through a nano‐scale channel is extremely small. A channel made of a periodic array of slats is proposed to effectively promote the EO pumping, and thus greatly improve the EO flow rate. The geometrically simple array is complicated enough that four length scales are involved: the vertical period 2L, lateral period 2aL, width of the slat 2cL as well as the Debye length . The EO pumping rate is determined by the normalized lengths: a, c, or the perforation fraction of slats and the dimensionless electrokinetic width . In a nano‐scale channel, K is of order unity or less. EO pumping in both longitudinal and transverse directions (denoted as longitudinal EO pumping (LEOP) and transverse EO pumping (TEOP), respectively) is investigated by solving the Debye–Hückel approximation and viscous electro‐kinetic equation. The main findings include that (i) the EO pumping rates of LEOP for small K are remarkably improved (by one order of magnitude) when we have longer slats () and a large perforation fraction of slats (η > 0.7); (ii) the EO pumping rates of TEOP for small K can also be much improved but less significantly with longer slats and a large perforation fraction of slats. Nevertheless, it must be noted that in practice K cannot be made arbitrarily small as the criterion of for the reference potential at the channel center put lower bounds on K; in other words, there are geometrical limits for the use of the Poisson–Boltzmann equation.     

超高效液相色谱-四极杆串联飞行时间质谱分析黄酮类化合物及小毛茛茎叶的成分

为了探索液相色谱-质谱联用(LC-MS)技术在快速识别中药及天然产物成分中的应用,以黄酮对照品为研究前体,药用植物小毛茛为研究对象,采用超高效液相色谱/二极管阵列检测器-电喷雾四极杆串联飞行时间质谱(UPLC/DAD-ESI/Q-TOF MS)分析了黄酮类化合物同系物及同分异构体的色谱、质谱特性。结果显示:黄酮氧苷和黄酮碳苷的紫外吸收光谱及二级质谱具有显著性差异,糖苷化位置同保留时间、二级质谱碎片及相对丰度具有相关性。将该方法应用于小毛茛茎叶醇提液的分析,结合其酸水解液的分析,解析了22个黄酮醇糖苷和3个苷元。方法简便,具有可操作性。     

HPLC with quadrupole TOF‐MS and chemometrics analysis for the characterization of Folium Turpiniae from different regions

Folium Turpiniae has been used as a traditional Chinese medicine for the treatment of abscesses, fevers, gastric ulcers, and inflammations. This paper describes a strategy of combining HPLC with photodiode array detection and quadrupole TOF‐MS, as well as phytochemical and chemometrics analysis for the characterization, isolation, and simultaneous quantification of the chemical constituents of Folium Turpiniae. 19 constituents were identified, namely, 11 flavonoids, seven gallic acid derivates, and quinic acid. Among them, 15 compounds were identified in this herbal medicine for the first time; compound 10 appears to be novel and was isolated and confirmed as ellagic acid‐3‐O‐α‐l ‐rhamnopyranoside by NMR spectroscopy and MS. In addition, nine marker compounds, namely gallic acid ( 2 ), ellagic acid‐3‐O‐α‐l ‐rhamnopyranoside ( 10 ), apigenin‐7‐O‐(2′′‐rhamnosyl)gentiobioside ( 11 ), ellagic acid ( 12 ), luteolin‐7‐O‐β‐d ‐neohesperidoside ( 13 ), ligustroflavone ( 14 ), 4′‐O‐methylellagic acid‐3‐O‐α‐l ‐rhamnopyranoside ( 16 ), rhoifolin ( 17 ), and neobudofficide ( 18 ), were quantified simultaneously in ten batches of Folium Turpiniae collected from different regions. Moreover, hierarchical clustering analysis and principal component analysis indicated that both samples from Hubei ( S1 ) and Guangxi ( S3 ) provinces showed apparent differences from the others. Samples from Jiangxi province ( S2 , S4 , and S7–10 ) possessed similar properties and therefore belong to the same group.     

Tandem mass spectrometry study of p38α kinase inhibitors and related substances

The p38 mitogen‐activated protein kinase α (p38α) is an important drug target widely investigated for therapy of chronic inflammatory diseases. Its inhibitors are rather lipophilic and as such not very favourable lead compounds in drug discovery. Therefore, we explored various approaches to access new chemical space, create diversity, and generate lead libraries with improved solubility and reduced lipophilicity, based on known p38α inhibitors, e.g., BIRB796 and TAK‐715. Compound modification strategies include incubation with human liver microsomes and bacterial cytochrome P450 mutants from Bacillus megaterium and treatment by electrochemical oxidation, H₂O₂, and intense light irradiation. The MS/MS fragmentation pathways of p38α inhibitors and their conversion products have been studied in an ion‐trap–time‐of‐flight MSⁿ instrument. Interpretation of accurate mass MSⁿ data for four sets of related compounds revealed unexpected and peculiar fragmentation pathways that are discussed in detail. Emphasis is put on the usefulness of HRMSⁿ‐based structure elucidation in a screening setting and on peculiarities of the fragmentation with regard to the analytes and the MS instrument. In one example, an intramolecular rearrangement reaction accompanied by the loss of a bulky group is observed. For BIRB796, the double‐charge precursor ion is used in MS², providing a wider range of fragment ions in our instrument. For TAK‐715, a number of related compounds could be produced in a large‐scale incubation with a Bacillus megaterium mutant, thus enabling comparison of the structure elucidation by ¹H NMR and MSⁿ. A surprisingly large number of homolytic cleavages are observed. Competition between two fragmentation pathways involving either the loss of CH₃^? or OH^? radicals was observed for SB203580 and its conversion products. Copyright © 2013 John Wiley & Sons, Ltd.     

N‐alkylpyridinium quaternization for assisting electrospray ionization of sterols in oil by quadrupole‐time of flight mass spectrometry

Rationale: The illegal cooking oil has become a serious social problem and raised widespread alarm recently. However, an efficient and sensitive technique for identifying the potential illegal cooking oil is still unavailable, especially when mixed with the ordinary ones; there is an urgent need to develop an efficient method for identifying the illegal cooking oil. Sterols in the cooking oil could be used as an indicator to identify the source and quality of oil by detecting the kinds of phytosterols and zoosterols. However, those sterols are difficult to be ionized by electrospray ionization, which resulted in the low sensitivity in electrospray ionization (ESI)‐mass spectrometric (MS) analysis. Methods: N‐alkylpyridinium isotope quaternization was extended to charge label sterols in different cooking oil and attached N‐cationic pyridinium tag onto the sterols in the presence of trifluoromethanesulfonic anhydride (Tf₂O); the kinds of sterols were identified and quantified by comparing d₀/d₅ pairs and product scan from ESI‐quadrupole‐time of flight (Q‐TOF) MS analysis. Results: The derivatized sterols were attached with permanent charge, resulting in the significant enhancement of ionization in ESI‐Q‐TOF MS analysis. The detection limits of analytes were improved to 0.02–0.05 ng/mL; different kinds of phytosterol, zoosterol and oxides were identified and quantified by comparing d₀/d₅ pairs from full scan and product scan. The method was applied in the detection of zoosterol for identifying the potential recycled cooking oil, even when the illegal oil has been blended into the ordinary one. More zoosterol was detected in the recycled oil compared with other cooking oil. Conclusions: The use of N‐alkylpyridinium isotope quaternization method provided an alternative method for identifying the potential illegal cooking oil. Copyright © 2013 John Wiley & Sons, Ltd.     

具有列维飞行与布朗运动特征的循环竞争博弈及物种稳定共存条件

循环竞争博弈常被用来研究物种多样性.以前有关循环竞争博弈的研究工作所考虑的相互作用距离模式包括最近邻、取固定距离或一定距离以内的随机值,这与实际情况不相符.考虑到实际生物系统中物种个体做列维飞行与布朗运动的情况广泛存在,综合考虑了最近邻相互作用模式和列维飞行(布朗运动)长程相互作用模式,对循环竞争博弈及保持物种多样性的条件进行了研究.得到了最大飞行距离与选择概率的临界关系(包括Logistic式和指数式关系),进一步得到了幂指数与选择概率的临界关系,以及保持物种共存的条件.     

Bolt axial stress measurement based on a mode-converted ultrasound method using an electromagnetic acoustic transducer

A method is proposed to measure the stress on a tightened bolt using an electromagnetic acoustic transducer (EMAT). A shear wave is generated by the EMAT, and a longitudinal wave is obtained from the reflection of the shear wave due to the mode conversion. The ray paths of the longitudinal and the shear wave are analyzed, and the relationship between the bolt axial stress and the ratio of time of flight between two mode waves is then formulated. Based on the above outcomes, an EMAT is developed to measure the bolt axial stress without loosening the bolt, which is required in the conventional EMAT test method. The experimental results from the measurement of the bolt tension show that the shear and the mode-converted longitudinal waves can be received successfully, and the ratio of the times of flight of the shear and the mode-converted longitudinal waves is linearly proportional to the bolt axial tension. The non-contact characteristic of EMAT eliminates the effect of the couplant and also makes the measurement more convenient than the measurement performed using the piezoelectric transducer. This method provides a promising way to measure the stress on tightened bolts.     

Temperature controlled Lévy flights of minority carriers in photoexcited bulk n-InP

We study by photoluminescence the spatial distribution of minority carriers (holes) arising from their anomalous photon-assisted diffusion upon photo-excitation at an edge of n-InP slab for temperatures ranging from 300 K to 78 K. Giant enhancement in the spread of holes — over distances exceeding 1 cm from the excitation edge — is seen at lower temperatures. We show that the experiment provides a realization of the “Lévy flight” random walk of holes, in which the Lévy distribution index γ   is controlled by the temperature. The variation γ(T)$\gamma (T)$ is close to that predicted earlier, γ=1−Δ/kT$\gamma =1-\Delta /kT$, where Δ(T)$\Delta (T)$ is the Urbach tailing parameter of the absorption spectra. This theoretical prediction is based on the assumption of a quasi-equilibrium intrinsic emission spectrum in the form due to van Roosbroeck and Shockley.     

钒氧阴离子团簇与小分子碳氢化合物反应的实验和理论研究

为了在分子层次上揭示相关催化反应的机理, 人们对过渡金属氧化物团簇与碳氢化合物分子反应进行了大量研究. 相比于过渡金属氧化物团簇阳离子, 阴离子对一些碳氢化合物的活性弱得多, 因此研究还很少. 在本工作中, 我们通过激光溅射产生钒氧团簇阴离子VxOy, 产生的团簇在接近热碰撞条件下与烷烃(C2H6和C4H10)以及烯烃(C2H4和C3H6) 在一个快速流动反应管中进行反应, 飞行时间质谱用来检测反应前后的团簇分布. 在VxOy与烷烃的反应中, 生成了产物V2O6H-和V4O11H-; 在与烯烃的反应中, 产生了相应的吸附产物V4O11X-(X=C2H4或C3H6). 密度泛函理论计算表明: V2O-6和V4O-11可以活化烷烃(C2H6和C4H10)的C—H键, 也可以与烯烃(C2H4和C3H6)发生3+2环化加成反应形成一个五元环结构(-V-O-C-C-O-), C—H键活化与环加成反应都需经历可以克服的反应能垒. 理论计算与实验观测结果相符合. V2O-6和V4O-11团簇都具有氧原子自由基(O·或O-)的成键特征, 活性O-物种也经常出现在钒氧催化剂表面, 因而本研究在分子水平上, 揭示了表面活性氧物种与碳氢化合物反应的机理.     

Structural characterization of a procyanidin tetramer and pentamer from the apple by low-temperature NMR analysis

The structures of a procyanidin tetramer and pentamer from unripe apple (Malus pumila) were elucidated by low-temperature NMR analysis at −34 °C. These structures were [epicatechin-(4β→6)-epicatechin-(4β→8)-epicatechin-(4β→8)-epicatechin (1)] and [epicatechin-(4β→8)-epicatechin-(4β→8)-epicatechin-(4β→8)-epicatechin-(4β→8)-epicatechin (2)].