The role of induced current density in Steroelectronic effects: Perlin effect

The normal and reverse Perlin effect is usually explained by the redistribution of electron density produced by hyperconjugative mechanisms, which increases the electron population within axial or equatorial proton in normal or reverse effect, respectively. Here an alternative explanation for the Perlin effect is presented on the basis of the topology of the induced current density, which directly determines the nuclear magnetic shielding. Current densities around the C? H bond critical point and intra‐atomic and interatomic contributions to the magnetic shielding explain the observed Perlin effect. The balance between intra‐atomic and interatomic contributions determines the difference in the total atomic shielding. Normal Perlin effect is dominated by intra‐atomic part, whereas reverse effect is dominated by interatomic contribution. © 2015 Wiley Periodicals, Inc.     

纳米腔限制环境下2-(2-羟苯基)苯并噻唑的质子转移

采用稳态和瞬态荧光法对2-(2-羟苯基)苯并噻唑(HBT)与七元瓜环(CB7)的超分子作用及CB7分子纳米腔限制作用对HBT激发态质子转移(ESIPT)过程进行了研究,并采用Benesi-Hildebrand方程对荧光数据进行处理,以确定超分子复合物的组成比.结果表明,在N,N-二甲基甲酰胺(DMF)和二氯甲烷溶液中,CB7与HBT的作用均形成化学计量比为1∶1的主客体复合物,HBT的质子转移对溶剂很敏感,CB7的加入,使HBT的荧光寿命降低,量子产率增大.在DMF溶液中,CB7的加入促进了酚氧负离子的形成,而在二氯甲烷溶液中,CB7的加入限制了HBT的激发态质子转移.结构优化计算表明,CB7与HBT能形成化学计量比为1∶1的复合物.     

生物质热解制备木醋液及其性质研究

对杉木屑、棉杆、竹屑三种生物质热解制得的木醋液产率、基本理化性质及其有机成分进行了分析研究。结果表明,三种生物质原料在350℃下热解制得的粗木醋液、精制木醋液产率相差不大,相同条件下氯化钾浸渍处理后的杉木屑热解所得的粗木醋液、精制木醋液的产率有所降低。三种原料制得的精制木醋液的理化性质不同,杉木屑木醋液的pH值最小,密度最大,竹屑和棉杆木醋液的有机酸含量相对较高。采用GC-MS对精制木醋液中的有机成分进行了分析,结果表明,杉木屑木醋液中的主要组分为酸类、酚类和酮类化合物,棉杆和竹屑木醋液中的主要组分除这三类有机物质外,还含有相对含量较高的醇类化合物。酸类和酚类化合物在三种木醋液中的相对含量依次是竹屑 >棉杆 >木屑;酮类的相对含量依次是木屑 >棉杆 >竹屑。氯化钾处理后的木屑热解所得的木醋液中主要组分酚类和酮类化合物的相对含量有所降低,酸类化合物的相对含量增加,主要表现为乙酸相对含量的增加。与杉木屑木醋液相比,KCl处理后的杉木屑木醋液中的醇类化合物相对含量增加了1倍左右。     

Interactions of DNA with graphene and sensing applications of graphene field-effect transistor devices: A review

Graphene field-effect transistors (GFET) have emerged as powerful detection platforms enabled by the advent of chemical vapor deposition (CVD) production of the unique atomically thin 2D material on a large scale. DNA aptamers, short target-specific oligonucleotides, are excellent sensor moieties for GFETs due to their strong affinity to graphene, relatively short chain-length, selectivity, and a high degree of analyte variability. However, the interaction between DNA and graphene is not fully understood, leading to questions about the structure of surface-bound DNA, including the morphology of DNA nanostructures and the nature of the electronic response seen from analyte binding. This review critically evaluates recent insights into the nature of the DNA graphene interaction and its affect on sensor viability for DNA, small molecules, and proteins with respect to previously established sensing methods. We first discuss the sorption of DNA to graphene to introduce the interactions and forces acting in DNA based GFET devices and how these forces can potentially affect the performance of increasingly popular DNA aptamers and even future DNA nanostructures as sensor substrates. Next, we discuss the novel use of GFETs to detect DNA and the underlying electronic phenomena that are typically used as benchmarks for characterizing the analyte response of these devices. Finally, we address the use of DNA aptamers to increase the selectivity of GFET sensors for small molecules and proteins and compare them with other, state of the art, detection methods.     

Tutorial review on validation of liquid chromatography–mass spectrometry methods: Part I

This is the part I of a tutorial review intending to give an overview of the state of the art of method validation in liquid chromatography mass spectrometry (LC–MS) and discuss specific issues that arise with MS (and MS/MS) detection in LC (as opposed to the “conventional” detectors). The Part I briefly introduces the principles of operation of LC–MS (emphasizing the aspects important from the validation point of view, in particular the ionization process and ionization suppression/enhancement); reviews the main validation guideline documents and discusses in detail the following performance parameters: selectivity/specificity/identity, ruggedness/robustness, limit of detection, limit of quantification, decision limit and detection capability. With every method performance characteristic its essence and terminology are addressed, the current status of treating it is reviewed and recommendations are given, how to determine it, specifically in the case of LC–MS methods.     

Comparing Cyclophellitol N‐Alkyl and N‐Acyl Cyclophellitol Aziridines as Activity‐Based Glycosidase Probes

The synthesis and evaluation as activity‐based probes (ABPs) of three configurationally distinct, fluorescent N‐alkyl cyclophellitol aziridine isosteres for profiling GH1 β‐glucosidase (GBA), GH27 α‐galactosidase (GLA) and GH29 α‐fucosidase (FUCA) is described. In comparison with the corresponding acyl aziridine ABPs reported previously, the alkyl aziridine ABPs are synthesized easily and are more stable in mild acidic and basic media, and are thus easier to handle. The β‐glucose‐configured alkyl aziridine ABP proves equally effective in labeling GBA as its N‐acyl counterpart, whereas the N‐acyl aziridines targeting GLA and FUCA outperform their N‐alkyl counterparts. Alkyl aziridines can therefore be an attractive alternative in retaining glycosidase ABP design, but in targeting a new retaining glycosidase both N‐alkyl and N‐acyl aziridines are best considered at the onset of a new study.     

Graphene Quantum Dots Assembled with Metalloporphyrins for “Turn on” Sensing of Hydrogen Peroxide and Glucose

Noncovalent and multifunctional hybrids have been generated via π–π stacking and electrostatic interactions by combining the nanometer‐scale graphene structure of graphene quantum dots (GQDs) with Fe^III 5,10,15,20‐tetrakis(1‐methyl‐4‐pyridyl)porphine (FeTMPyP). The inner filter effect (IFE) of FeTMPyP on the GQDs results in substantial PL quenching of the GQDs. The quenched PL of GQDs by the FeTMPyP can be switched back “on” in response to the reaction between FeTMPyP and H₂O₂, which causes rupture of the cyclic tetrapyrrolic nucleus with consequential loss of iron from FeTMPyP, and then proceeds further to produce colorless dipyrroles and monopyrroles. This “turn on” system can be applied for simple and convenient H₂O₂ sensing and can be further extended to the detection of glucose in combination with the specific catalytic effect of glucose oxidase (GOx) through the oxidation of glucose and formation of H₂O₂. Because of the inherent synthetic control available for the design of metalloporphyrins, the GQDs‐based optical sensing approach described here has the potential to be highly versatile for other target analytes.     

Dioxygen Binding in the Active Site of Histone Demethylase JMJD2A and the Role of the Protein Environment

JMJD2A catalyses the demethylation of di‐ and trimethylated lysine residues in histone tails and is a target for the development of new anticancer medicines. Mechanistic details of demethylation are yet to be elucidated and are important for the understanding of epigenetic processes. We have evaluated the initial step of histone demethylation by JMJD2A and demonstrate the dramatic effect of the protein environment upon oxygen binding using quantum mechanics/molecular mechanics (QM/MM) calculations. The changes in electronic structure have been studied for possible spin states and different conformations of O₂, using a combination of quantum and classical simulations. O₂ binding to this histone demethylase is computed to occur preferentially as an end‐on superoxo radical bound to a high‐spin ferric centre, yielding an overall quintet ground state. The favourability of binding is strongly influenced by the surrounding protein: we have quantified this effect using an energy decomposition scheme into electrostatic and dispersion contributions. His182 and the methylated lysine assist while Glu184 and the oxoglutarate cofactor are deleterious for O₂ binding. Charge separation in the superoxo‐intermediate benefits from the electrostatic stabilization provided by the surrounding residues, stabilizing the binding process significantly. This work demonstrates the importance of the extended protein environment in oxygen binding, and the role of energy decomposition in understanding the physical origin of binding/recognition.     

钛表面钠氢氧钛纳米线的结构、生物活性和MC3T3-E1细胞响应

采用化学方法处理微弧氧化(MAO)制备的含Si、Ca元素的Ti O2涂层(SC),获得钛氢氧钠(Na0.8H1.2Ti3O7)生物活性纳米线结构。化学处理过程中,SC涂料表面出现了Ca、Na元素溶解,Si元素沉积的现象。化学处理后的SC涂层比SC涂料具有更好的吸水性和诱导磷灰石形成能力。这与处理后涂层(SHTO)特殊的纳米结构有关,在模拟体液浸泡过程中更容易形成Ti-OH。同时,钠氢氧钛纳米线的表面形貌、相组成、OH基团以及良好的湿润能力使其更加适合于MC3T3-E1细胞的粘附和增值。     

甲氧基多溴联苯醚色谱相对保留时间的QSRR研究

基于有机化合物定量结构与色谱相对保留时间的关系,对26个甲氧基多溴联苯醚化合物进行了B3LYP/6-31G*水平上的结构优化,并在优化结构基础上进行了分子连接性指数和量子化学结构参数的提取。应用SPSS统计软件对甲氧基多溴联苯醚化合物的色谱相对保留时间与分子连接性指数进行了多元线性回归(MLR)。结果表明,三阶类分子连接性指数可以很好地表达甲氧基多溴联苯醚化合物色谱相对保留时间与结构描述符之间的定量关系。用外部测试集的方法对模型预测能力进行了验证,结果表明:所建立的QSRR模型具有较强的稳健性和预测能力。