Cyclodextrin Molecular Reactors

The ability of cyclodextrins to form inclusion complexes with hydrophobic species in aqueous solution makes them well-suited to the development of molecular reactors, to be used as miniature reaction vessels in order to control the outcomes of chemical transformations at the molecular level. In this manner, reaction rates can be increased and products may be obtained that are different to those normally accessible from reactions in free solution. Examples used to illustrate these effects include: the application of cyclodextrins to control the regioselectivity of bromination of aromatic substrates with pyridinium dichlorobromate: the use of a metallocyclodextrin to increase the rate of hydrolysis of a phosphate triester by almost five orders of magnitude; the development of modified cyclodextrins to increase the rates and reverse the regioselectivity of nitrile oxide cycloadditions ; and the use of a cyclodextrin dimer to change the ratio of formation of indigoid dyes by a factor of more than 3500.     

Controlling electrophoretic trapping of circular DNA by addition of starch preparations to agarose gels

Starch preparations were added to agarose gels to enhance the electrophoretic trapping of circular plasmid DNA. The critical voltages required to trap the open circular (OC) and the supercoiled (SC) forms of a 13.1-kbp plasmid were measured in gels composed of agarose and added starch preparations. Modified starch preparations reduced the critical voltage required to trap the OC form of the plasmid to approximately one-third of the control value (in 1% agarose gels). Amylose (a fraction of starch with a low amount of branching) also reduced the critical voltage to trap the OC form in a similar manner. The critical voltage to trap the SC form of the plasmid was not significantly reduced by the starch preparations. The capacity to trap OC DNA was increased by the addition of higher amounts of the starch preparations added to the gels. Field inversion gel electrophoresis was used to characterize the length of the traps in the gels. The starch preparations and amylose increased the trap lengths approximately twofold. The increased trap length correlated with the decreased critical voltage required to trap the OC form of the 13.1-kbp plasmid. Certain commercial equipment, instruments, or materials are identified in this article to specify adequately the experimental procedures. Such identification does not imply recommendation by National Institute of Standards and Technology, nor does it imply that the materials or equipment are necessarily the best available for the purpose.     

Thermal degradation of vinylidene chloride/4-vinylpyridine copolymers

Vinylidene chloride polymers are prominent in the barrier plastics packaging industry. They display good barrier to the transport of oxygen (to prevent spoilage of food items) and flavor and aroma constituents (to prevent 'scalping' on the supermarket shelf). However, these polymers undergo thermal dehydrochlorination during processing. This can lead to a variety of problems including the evolution of hydrogen chloride which must be scavenged to prevent its interaction with the metallic walls of process equipment. Such interaction leads to the formation of metal halides which act as Lewis acids to facilitate the degradation. A potentially effective means to capture hydrogen chloride generated might be to incorporate into the polymer a mild organic base. Accordingly, copolymers of vinylidene chloride and 4-vinylpyridine have been prepared and subjected to thermal aging. Results suggest that the pyridine moiety is sufficiently basic to actively promote dehydrochlorination in the vinylidene chloride segments of the polymer.     

What is and what should never be: artifacts,improbable phytochemicals,contaminants and natural products

Abstract

The scope of this review is to sensitize the natural product chemists to the underestimated problem related to artifact, comprising contaminants and improbable natural compounds. This review wants to give an overview about the various facets of this problem and to provide some hints to avoid incurring these situations. It does not pretend to report exhaustively about all the cases available in literature. The issue of artifacts has always existed and is quite impossible to completely eliminate because the results of phytochemical analysis are known only at the end of the work and in many cases there is not the possibility to compare the results. Therefore, it is important to take the necessary precautions during the workout in order to minimize the possibility that an unexpected event may occur. In second instance, anyone involved in these studies should increase the level of self-criticism with respect to the obtained experimental results.     

Gel formation in free radical polymerization via chain transfer and terminal branching

Gel formation in free-radical polymerization via chain transfer to polymer, recombination termination, and terminal branching due to either chain transfer to monomer or disproportionation termination is investigated using the method of moments. It is found that no gel can possibly form in the systems consisting of initiation, propagation, and one of the above reactions. However, systems with the following combination of reactions are found to be capable of gelling. They are: chain transfer to polymer + recombination termination; chain transfer to polymer + terminal branching due to disproportionation termination; and terminal branching due to transfer to monomer + recombination termination. Systems with the following combination of reactions are incapable of gelling; transfer to polymer + terminal branching due to transfer to monomer; and terminal branching due to disproportionation termination + recombination termination. An examination of the gelation mechanisms reveals that the formation of multivinyl macromonomers during the course of polymerization is the reason that systems involving terminal branching gel. Sol/gel diagrams are generated to give critical kinetic parameters required for gelation. It is found that terminal branching does not always promote gelation due to the adverse effect on chain length through chain transfer to monomer and termination by disproportionation, reactions which generate terminal double bonds. © 1994 John Wiley & Sons, Inc.     

NMR spectroscopic study of the Murex trunculus dyeing process

It is widely accepted that indigo dyes derived from Murex trunculus were used to produce the biblical dyes tekhelet and argaman. We describe a method of following the debromination of natural leucoindigos and their binding to wool using NMR spectroscopy. Debromination is observed prior to reaction with the wool and prior to oxidation. Binding to the wool is shown to occur prior to oxidation. NMR allows the dyeing process to be followed. This, in principle, could be used to correct problems during dyeing that would increase the reliability of the process.     

Emerging analytical methods to determine gluten markers in processed foods—method development in support of standard setting

The availability of analytical methods to detect and determine levels of markers of priority allergens in foods is of the utmost importance to support standard setting initiatives, the development of compliance and enforcement activities, as well as to provide guidance to industry on implementation of quality control practices, ensuring the effectiveness of allergen-related sanitation techniques. This paper describes the development and implementation of a mass-spectrometry-based technique to determine markers for individual sources of gluten in beer products. This methodology was shown to answer the requirements of Health Canada’s proposed labeling standard for individual gluten source declaration, in order to achieve its policy objectives (i.e., protection of sensitive consumers, while promoting choice). Minimal sample work-up was required and the results obtained by ELISA were further complemented using the LC-MS/MS method. This paper aims to demonstrate the feasibility of alternative techniques to ELISA-based methodologies to determine allergen and gluten markers in food.     

CaO杂质对铝型材厂工业污泥合成堇青石材料晶相结构及其含量影响

探讨原料组成对铝型材厂工业污泥合成堇青石材料的影响是非常重要的。研究目的有助于确定不同杂质在原料中允许的存在量,为选择其他原料提供可靠的依据。采用XRD法和SEM法分析各试样的晶相结构:用半定量分析方法确定各晶相的含量:用philipsX抪ertplus软件确定试样中各晶相结构参数。实验结果表明:CaO杂质含量从1.2~2.5%对合成堇青石有利:从2.5~2.8%堇青石含量开始下降:确定2.5%为CaO杂质最佳存在量,其对应的堇青石含量为91%。经plus软件确定结果:CaO杂质含量为1.2%时,其结构与单晶相同,晶胞参数变化很小:CaO含量从1.2~2.8%,其晶系由六方转变为四方结构,晶胞参数发生较大变化。镁铝尖晶石结构与晶胞参数变化较大,由单晶的立方结构转变为四方结构。     

The electrochemistry of electrode edges and its relevance to partially blocked voltammetric electrodes

Analytical mathematics and digital simulation are used to predict the response, to a potential jump, of the junction between insulating and conducting regions of an electrode. The simulation is carried out differentially and employs other novel features. Concentrations in the vicinity of edges of positive and negative curvatures, as well as straight edges, are analyzed by the model and thereby the faradaic current densities and currents are predicted. It is shown that, in addition to the well-understood cottrellian current arising from the surface of the conducting electrode, currents are generated that are proportional to the length of the edge and to its curvature. These results are then applied to inlaid disks and to partially blocked electrodes. The possibility is explored of using the response to a potential step to gain information on the geometry of a partially blocked electrode.     

Rheological properties of crystallizing polylactide: Detection of induction time and modeling the evolving structure and properties

Linear viscoelastic properties of polymer melts are highly sensitive to any structural changes, including molecular weight changes and the formation and growth of crystallites. Here, we make use of this sensitivity to study the homogeneous crystallization of polylactide. As this polymer is rather quickly susceptible to thermal degradation even at moderate temperatures, it is essentially impossible to study homogeneous crystallization in the absence of degradation. Thus, the evolution of complex viscosity of a polylactide due to thermal degradation in the absence of crystallization was studied. A simple empirical model is used to characterize the variation of complex viscosity due to thermal degradation and to determine the induction time of homogeneous crystallization at wide range of degrees of supercooling. Next, the evolution of complex viscosity due to crystallization was measured at several temperatures. Based on the results, a phenomenological model describing the viscosity evolution during homogeneous crystallization is proposed and validated. Finally, the linear viscoselastic data in the early stages of crystallization are shown to be consistent with gelation due to the formation of a network of tie molecules between spherulites. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 812–822, 2010     

Orthogonal signal correction applied to the classification of wine and molasses vinegar samples by near-infrared spectroscopy. Feasibility study for the detection and quantification of adulterated vinegar samples

The most common fraudulent practice in the vinegar industry is the addition of alcohol of different origins to the base wine used to produce wine vinegar with the objective of reducing manufacturing costs. The mixture is then sold commercially as genuine wine vinegar, thus constituting a fraud to consumers and an unfair practice with respect to the rest of the vinegar sector. A method based on near-infrared spectroscopy has been developed to discriminate between white wine vinegar and alcohol or molasses vinegar. Orthogonal signal correction (OSC) was applied to a set of 96 vinegar NIR spectra from both original and artificial blends made in the laboratory, to remove information unrelated to a specific response. The specific response used to correct the spectra was the extent of adulteration of the vinegar samples. Both raw and corrected NIR spectra were used to develop separate classification models using the potential functions method as a class-modeling technique. The previous models were compared to evaluate the suitability of near-infrared spectroscopy as a rapid method for discrimination between vinegar origin. The transformation of vinegar NIR spectra by means of an orthogonal signal-correction method resulted in notable improvement of the specificity of the constructed classification models. The same orthogonal correction approach was also used to perform a calibration model able to detect and quantify the amount of exogenous alcohol added to the commercial product. This regression model can be used to quantify the extent of adulteration of new vinegar samples.     

CFD modelling of a spray deposition process of paint

The paint deposition process by spraying has been studied by means of Computational Fluid Dynamics in order to predict the final thickness of the coating and to determine theoretically the overspraying phenomenon. The VOF model has been used to describe the impact phenomena onto the wall and the Euler-Lagrange approach to simulate droplet trajectories on their way to the surface. Particular attention has been devoted to the prediction of the maximum diameter reached by an impinging droplet at the end of the spreading phase. This diameter is very important in the study of the paint processes because the high viscosity and the small surface tension of paints reduce the impingement practically only to the spreading phase. Two different configurations of atomizers have been considered. The air flux provides a finer atomisation of the liquid, gives to the droplets the necessary velocity to reach the wall, but is also the main cause of overspray since the small droplets tend to follow its deviation near the wall.     

Formation of Neutral Peptide Aggregates as Studied by Mass‐Selective IR Action Spectroscopy

The spontaneous aggregation of proteins and peptides is widely studied owing to its relation to neurodegenerative diseases. To understand the underlying principles of peptide aggregation, elucidation of structure and structural changes upon their formation is key. This level of detail can be obtained by studying the peptide self‐assembly in the gas phase. Structural characterization of aggregates is mainly done on charged species, as adding charges is an intrinsic part of the technique to bring molecules into the gas phase. Studying neutral peptide aggregates will complement the existing picture. These studies are restricted to dimers due to experimental limitations. Herein, we present advances in laser desorption molecular beam spectroscopy to form neutral peptide aggregates consisting of up to 14 monomeric peptides in the gas phase. The combination of this technique with IR–UV spectroscopy allowed us to select each aggregate by size and subsequently characterize its structure.     

Measurement of <Emphasis Type="Italic">T</Emphasis><Subscript>g</Subscript> in lyophilized protein and protein excipient mixtures by dynamic mechanical analysis

The glass transition of lyophilized materials is normally measured by conventional or temperature modulated differential scanning calorimetry (TMDSC). However, because of the weakness of these transitions when protein concentrations are high, these techniques are often unable to detect the glass transition (T _g). High ramp rate DSC, where heating rates of 100 K per min and higher are used, has been shown to be able to detect weak transitions in a wide range of materials and has been applied to these materials in previous work. Dynamic mechanical analysis (DMA) is also known to be much more sensitive to the presence of relaxations in materials than other commonly used thermal techniques. The development of a method to handle powders in the DMA makes it now possible to apply this technique to protein and protein-excipient mixtures. HRR DSC, TMA and DMA were used to characterize the glass transition of lyophilized materials and the results correlated. DMA is shown to be a viable alternative to HRR DSC and TMA for lyophilized materials.     

Concise Synthesis of Dimethyl (2-Oxopropyl)phosphonate and Homologation of Aldehydes to Alkynes in a Tandem Process

The synthesis of dimethyl (diazomethyl)phosphonate, a useful reagent for the homologation of aldehydes to alkynes, is described as a one-pot process and comprises the generation of the azide transfer agent, diazotransfer to dimethyl (2-oxopropyl)phosphonate, and methanolysis, followed by a simple extraction protocol. Previously described syntheses for this bulk product are much more elaborate. The homologation of aldehydes to alkynes can also be extended to a single-step process by adding the aldehyde directly to the reaction mixture prior to isolation of the reagent. The homologation process using dimethyl (diazomethyl)phosphonate was shown to proceed also in nonprotic solvents with mild bases, emphasizing the importance of a facile access to the reagent. The oxidation of alcohols to the required aldehydes was performed by a TEMPO-mediated process using chloramine-T as electron acceptor.     

Interpretation of analysis of variance models using principal component analysis to assess the effect of a maternal anticancer treatment on the mineralization of rat bones

The aim of this paper is to show how it is possible to extract analytical information from images acquired with a flatbed scanner and make use of this information for real time control of a nickel plating process. Digital images of plated steel sheets in a nickel bath are used to follow the process under degradation of specific additives. Dedicated software has been developed for making the obtained results accessible to process operators. This includes obtaining the RGB image, to select the red channel data exclusively, to calculate the histogram of the red channel data and to calculate the mean colour value (MCV) and the standard deviation of the red channel data. MCV is then used by the software to determine the concentration of the additives Supreme Plus Brightner (SPB) and SA-1 (for confidentiality reasons, the chemical contents cannot be further detailed) present in the bath (these two additives degrade and their concentration changes during the process). Finally, the software informs the operator when the bath is generating unsuitable quality plating and suggests the amount of SPB and SA-1 to be added in order to recover the original plating quality.     

高校无机化学实验室资源合理配置的探索与实践

高校实验室是“立德树人”的重要阵地,实验技术队伍是实现“三全育人”的重要保障。高校快速发展过程中,对实验技术队伍赋予了建设和管理的多重任务,而自身缺乏明确的发展方向和目标,实验技术队伍职业化研究成为高校发展的现实需求。构建适应高等学校发展的实验技术队伍专业化管理体系,明确实验队伍职业化发展路径选择的具体措施,促进实验技术队伍稳定性,强化实验技术队伍在高等学校治理结构和提升内涵建设的有效作用,为提升高校实验室育人功能奠定基础,为高等学校快速发展提供有力支撑。     

烷基膦酸键合的纳米氧化物上甲苯选择氧化制苯甲醛的类酶机理

在传统催化反应中,分子氧催化氧化烷烃生成目标产物的选择性最低,常产生副产物以及大量的COx和水,因需要复杂的分离过程而导致流程的投资成本高.因此,在过去几十年里,针对此类反应的研究以提高选择性为首要目标,但克服这一挑战的任务依然艰巨.在此类反应中,甲苯经O2选择性催化氧化是制备苯甲醛的最佳途径,但从未实现工业化,其中的主要难点在于苯甲醛在临氧条件下的继续氧化反应速率比甲苯氧化高4个数量级以上.因此,在高甲苯转化率下高选择性获得苯甲醛是绿色化学研究中一个极具挑战性的课题.本文发现一种甲苯/水的类皮克林乳液催化体系对甲苯转化为苯甲醛有很高的活性和选择性,其中两性纳米颗粒(十六烷基膦酸,简写为HDPA,键合的纳米铁基氧化物)作为催化剂并处在乳液相界面处.在温和条件下通过O2氧化,苯甲醛的时空产率大于2 g·g-1·h-1,整个过程没有使用H2O2、卤素或其它自由基引发剂.实验发现,用于甲苯氧化反应的相关催化剂HDPA-FeMOx/γ-Al2O3(M:V和Mo等)的作用机制类似甲烷单加氧酶.在传统固定床反应器中和温和的条件下(70～160°C,常压),催化剂能将甲苯单一氧化为苯甲醛.催化剂的活性中心与HDPA以单齿态与氧化物表面键合有关,并且它的另一个磷羟基与氧化物表面在非键合态和键合态之间循环变化,分别对应甲苯反应中催化剂的氧化态和还原态,即HDPA与氧化物表面通过单齿和双齿键合循环变化,极大地提升了该铁基复合氧化物晶格氧的移动性而使得催化剂反应活性得到明显提升.透射电子显微镜、X射线衍射和氮吸附测量结果表明,铁基复合金属氧化物在γ-Al2O3纳米棒上具有良好的分散性和较大的比表面积.X射线光电子能谱、吡啶吸附FT-IR和31P NMR结果表明,与表面键合的HDPA保留了有机膦酸属性,没有与FeMOx/γ-Al2O3生成体相磷酸盐,其中,以单齿状态与表面键合HDPA分子只占总数的2％左右.H2-TPR和CO-TPR结果表明,HDPA的键合强烈影响了晶格氧的流动性或金属氧化物的活性.反应条件下原位FT-IR结果表明,HDPA-FeVOx/γ-Al2O3在70°C下即能催化甲苯氧化成苯甲醛,且不会过度氧化,该催化剂的晶格氧物种可参与甲苯转化为苯甲醛.此外,发现HDPA-Fe2O3/γ-Al2O3对甲苯的吸附具有特殊的分子识别作用,以苯甲醇氧化作为对照反应的研究结果也表明HDPA-Fe2O3/γ-Al2O3对甲苯氧化为苯甲醛的反应存特异催化作用.宏观反应动力学测试结果表明,催化剂上苯甲醛生成的表观活化能仅为～44.5 kJ/mol.在低H2O浓度下,甲苯氧化速率对甲苯浓度为一级反应,对O2浓度为零级反应,基元反应步骤推导出来的动力学方程与实验结果良好吻合,说明了该催化剂上类酶反应基元步骤假设的合理性.     

Developing front‐end devices for improved sample preparation in MS‐based proteome analysis

Chemical analysis has long relied on instrumentation, from the simplest (eg, burets) to the more sophisticated (eg, mass spectrometers) to facilitate precision measurements. Regardless of their complexity, the development of a new instrumental device can be a valued approach to address problems in science. In this perspective, we outline the process of novel device design, from early phase conception to the manufacturing and testing of the tool or gadget. Focus is placed on the development of improved front‐end devices to facilitate protein sample manipulations ahead of mass spectrometry, which therefore augment the proteomics workflow. Highlighted are some of the many training secrets, choices, and challenges that are inherent to the often iterative process of device design. In hopes of inspiring others to pursue instrument design to address relevant research questions, we present a summary list of points to consider prior to innovating their own devices.