Behavior of heavy solutes on a precolumn in on-column gas chromatography

The behavior of heavy solutes present in a sample injected on the precolumn has not been clarified in on-column injection onto gas chromatograph having a capillary column coupled to an uncoated precolumn in an oven. To investigate this point, an on-column gas chromatograph has been developed which is constructed with a heatable precolumn outside the oven. Some experiments were carried out in order to evaluate the performance. As a result, it was found that heavy solutes reach the first part of the main capillary column after the solvent has gone, resulting in sharp peaks without solvent effects. The reason why sharp peaks appear for the heavy solutes is also discussed. The cold-trapping effect has been shown to play an important role in narrowing the band width of the heavy solutes. Some of the advantages of the gas chromatograph developed are also presented.     

Cross-coupling reactions of aryl pivalates with boronic acids

The first cross-coupling of acylated phenol derivatives has been achieved. In the presence of an air-stable Ni(II) complex, readily accessible aryl pivalates participate in the Suzuki-Miyaura coupling with arylboronic acids. The process is tolerant of considerable variation in each of the cross-coupling components. In addition, a one-pot acylation/cross-coupling sequence has been developed. The potential to utilize an aryl pivalate as a directing group has also been demonstrated, along with the ability to sequentially cross-couple an aryl bromide followed by an aryl pivalate, using palladium and nickel catalysis, respectively.     

基于钯催化C-H键活化的多米诺反应

近年来,多米诺反应作为一种合成复杂分子的高效手段已得到有机合成化学家的广泛关注。该反应过程中,不需改变反应条件和添加试剂,中间体也无需分离和提纯,实现了原子经济和环境友好。通过C-H键活化直接构建碳-碳键和碳-杂原子键,大大拓展了传统偶联反应的底物范围,同样具有高原子经济性,已经广泛地作为多米诺反应中的一个高效步骤。此外,钯催化剂运用广泛,能够与多种官能团兼容,是多米诺反应的理想金属催化剂。本文综述了基于钯催化C-H键活化的多米诺反应的最新研究进展,以反应中钯的价态变化进行分类,介绍有关反应的特点、优势及其在天然产物合成中的应用。     

Finite element simulation of Off-Gel trade mark buffering

The protonation of an aqueous solution of two ampholytes AH and BH next to a gel buffered by immobilized acid moieties IH has been studied by finite element simulation in an iterative scheme. A ten species model has been formulated, taking into account transient diffusion and equilibrium kinetics of the two amphoteric species AH and BH, of water and of the immobilized species IH. This model has been developed to illustrate the pH evolution between an ampholyte solution and an Immobiline gel, and to study the influence of the Immobiline concentration on protons and ampholyte distributions. It has been demonstrated that a minimum initial Immobiline concentration of 10(-2) M is necessary to maintain the pH in the gel in contact with a closed chamber, when the difference between the isoelectric points of AH and BH is 4 and when the initial concentration of the ampholytes in solution is in the micromolar range. This approach provides a first theoretical framework for the recently developed Off-Gel trade mark electrophoresis.     

Label-free monitoring of the thrombin–aptamer recognition reaction using an array of nanochannels coupled with electrochemical detection

A sensitive and label-free method of monitoring the thrombin–aptamer recognition reaction has been developed using an array of nanochannels coupled with an electrochemical detection technique. Due to the highly amplified ion current produced by an array of nanochannels compared to a single nanochannel/pore, a significant increase in detection sensitivity has been achieved.     

Structural evolution during evaporation of a 3-glycidoxypropyltrimethoxysilane film studied in situ by time resolved infrared spectroscopy

Time resolved infrared spectroscopy has been applied to study in situ the evaporation process of a 3-glycidoxypropyltrimethoxysilane hybrid sol by casting a droplet on a ZnSe substrate; the analysis has been performed in the middle-infrared range and in the near-infrared range. The experiment has allowed following the structural changes induced by water evaporation and the formation of ordered structures within the cast film; the CH(2) scissoring bands have been used as a fingerprint for the disorder to order transition of the hybrid. The experiment has been done using both a fresh sol and an aged sol which produce respectively an amorphous material and a crystalline hybrid material. The analysis has shown that the epoxy groups do not react during the evaporation while the silica structure shows only a slight condensation and an increase in open cage-like species. At the end of evaporation the hybrid has a "soft-like" state which allows structural rearrangements to self-order.     

Open access atmospheric pressure chemical ionization Mass spectrometry for routine sample analysis

We report the introduction and use of an atmospheric pressure chemical ionization liquid chromatography-mass spectrometry instrument that has been designed specifically for use by the synthetic chemist on an open access, walk-in basis. This instrument has been configured with an easy-to-use sample log-in terminal that requires the user to provide only a sample identification number and a user name. Sample analysis takes approximately 4 min and provides the synthetic and medicinal chemist with rapid and reliable mass spectrometry analysis. Since installation of the system, it has analyzed an average of about 80 samples per day and has the capacity to run over 100 samples per day without the intervention of a specialist operator. This capability has eliminated the need for an operator to analyze routine samples and allows the mass spectroscopist more time to deal with problem solving.     

A crystallographic perspective on sharing data and knowledge

The crystallographic community is in many ways an exemplar of the benefits and practices of sharing data. Since the inception of the technique, virtually every published crystal structure has been made available to others. This has been achieved through the establishment of several specialist data centres, including the Cambridge Crystallographic Data Centre, which produces the Cambridge Structural Database. Containing curated structures of small organic molecules, some containing a metal, the database has been produced for almost 50 years. This has required the development of complex informatics tools and an environment allowing expert human curation. As importantly, a financial model has evolved which has, to date, ensured the sustainability of the resource. However, the opportunities afforded by technological changes and changing attitudes to sharing data make it an opportune moment to review current practices.     

Study of polyphenols in grape berries by reversed-phase high-performance liquid chromatography

Several polyphenols have been tested in grape berries from Spain. The flavonoid content is important because of the pharmacological properties of these compounds, whereas resveratrol has been proved to be an antifungal, antiinflammatory and an anticarcinogenic compound. A reversed-phase HPLC method has been developed and applied to determine resveratrol, quercetine, quercitrine and rutine content in several grape berries samples in a single analysis. Covering the grapes with a preservative paper yields a healthier product, but one which has a lower polyphenol content than unprotected grapes.     

The Staudinger ligation-a gift to chemical biology

Although the reaction between an azide and a phosphane to form an aza-ylide was discovered by Hermann Staudinger more than 80 years ago and has found widespread application in organic synthesis, its potential as a highly chemoselective ligation method for the preparation of bioconjugates has been recognized only recently. As the two reaction partners are bioorthogonal to almost all functionalities that exist in biological systems and react at room temperature in an aqueous environment, the Staudinger ligation has even found application in the complex environment of living cells. Herein we describe the current state of knowledge on this reaction and its application both for the preparation of bioconjugates and as a ligation method in chemical biology.     

The preparation of analytically stable,immobilized stationary phase coatings on colums packing materials

Summary A coating of silicone SE-54 on Chromosorb W has been converted to an analytically stable, immobilized stationary phase layer by cross-linking with an organic peroxide. Up to 10% by weight has been applied in this manner. Excellent high temperature qualities are exhibited, such as low bleeding and good base line stability, during typical analyses.Poly (2,6-dimethyl-p-phenylene oxide) has also been crosslinked as a surface coating on Chromosorb W with an organic peroxide. From 3 to 4% by weight has been immobilized in this way. The resultant packing material, following high temperature conditioning, has been examined for use as an adsorbent of trace substances, similar to the applications to which such adsorbents as Tenax GC have commonly been applied, e.g. trace analysis of air. It appears to exhibit satisfactory properties for this analytical purpose.     

Colloidal stability of IgG- and IgY-coated latex microspheres

The stabilization of antibody-latex complexes at high salt concentration is an event that cannot be explained by the widespread DLVO theory. Adsorption of antibodies on polystyrene latex usually leads to a loss in colloidal stability. However, after the expected particle aggregation induced by an increase in ionic strength, an 'anomalous' restabilization occurs when the electrolyte concentration increases even more. This non-DLVO behaviour can be explained taking into account the hydration forces, which become significant in hydrophilic surfaces. This restabilization has already been observed in different protein latex complexes. In the present work, a study on the stability patterns of polystyrene particles covered independently by mammalian and chicken antibodies has been performed. This study reveals that avian antibodies present a more hydrophobic surface than that of mammalian antibodies. In addition, it has been possible to obtain some information about the molecular orientation of the adsorbed antibodies from the stability experiments. This information has been corroborated by an immunoreactivity study.     

Pyrolysis-capillary gas chromatography of fibre-epoxy composites

A pulse-mode pyrolysis technique has been coupled with capillary gas chromatography to characterize epoxy-based composites. The pyrolysis has been optimized with respect to the pyrolysis temperature and the sample mass in order to obtain reproducible quantitative results. Pyrolysis at 650° C for 10 s using a sample mass of less than 1 mg has been found to give a sufficient quantity of pyrolyzed material without producing too complex a mixture of pyrolysis products. Pyrolysis-capillary gas chromatography (Py-GC) has been used to determine the amount of hardener in an epoxy resin system by ratioing the aniline peak area against the phenol peak area. It has also been used to characterize different prepregs, and to evaluate the curing of an epoxy resin. Some pyrolysis products have been identified by coupling Py-GC with Fourier transform infrared spectroscopy. In this case, the use of an OV-101 capillary column with a film thickness of 5 μm allows the injection of a larger amount of pyrolyzed resin, thus improving the detection without loss of resolution.     

Cycloartenol to Buxus alkaloids

Cycloartenol, a pentacyclic triterpene alcohol, has emerged as an obligatory intermediate in the biosynthesis of sterols in higher plants and algae. Cycloartenol has also been implicated in the biosynthesis of steroidal alkaloids. TheBuxus alkaloids, which have a pregnane-type framework, are considered to arise from cycloartenol by catabolic processes with nitrogen incorporation at an appropriate stage, although no biosynthetic studies appear to have been carried out. Thus, cycloartenol is an important substrate in nature for elaborating a rather large group of secondary metabolites. In an effort to mimic some of these processes in the laboratory, we have carried out transformations of cycloartenol intoBuxus alkaloids. New routes for side-chain degradation of cycloartenol and cyclolaudenol have been developed. A novel method for functionalization at C-16 has been worked out and a new strategy for regioselective oxygenation of 4-methyl has been exploited. Synthesis of buxandonine, cycloprotobuxine-F, cycloprotobuxine-A, cyclobuxophyllinine-M and 31-norcyclolaudenone have been achieved.     

Preservation mechanisms of trehalose in food and biosystems

The stability or shelf-life of food and biomaterials has always been a critical issue in the food and pharmaceutical industry. Trehalose (alpha-D-glucopyranosyl-alpha-D-glucopyranoside), a non-reducing diglucose sugar found in nature, confers to certain plant and animal cells the ability to survive dehydration for decades and to restore activity soon after rehydration. The interaction between trehalose and cell membranes or proteins, however, remains a debated subject, and a significant amount of work has been done to elucidate the mechanisms resulting in this unique behavior of preservation. This study shows how an interfacial phenomena approach has led to the use of trehalose as an excipient during freeze drying of a variety of products in the pharmaceutical industry. It also suggests opportunities as an ingredient for dried and processed food, as well as a non-toxic cryoprotectant of vaccines and organs for surgical transplants.     

Microwave‐activated Synthesis of Pyrroles: A Short Review

In the current scenario for continuous requirement of better drugs, medicinal chemists must visage the challenging task of preparing novel patentable compounds, combining high activity and selectivity, good drug‐likeness, and pharmacokinetic properties. There is an acute need of new molecules in both lead identification and lead optimization. Chemists thoroughly scrutinize ways to simplify synthetic protocols using green chemistry approaches, for example, microwaves. Reduction in the reaction time by the use of microwaves has emerged as a promising method for bringing out new leads in organic synthesis. Among the azaheterocyclic systems, synthesis of pyrrole moiety has been a highly attractive and an inspiring proposition. It has been found to be an inbuilt pharmacophore of various momentous pharmacologically active compounds in medicinal chemistry. This article outlines the basic principles of microwave technology and its use in the synthesis of pyrrole derivatives wherein this technology has made a tremendous impact.     

An electrochemical adaptation of Ellman's test

The electrochemically initiated reaction of thiols with N,N-diethyl-p-phenylenediamine has been coupled with an existing colorimetric sensing reaction developed by Ellman as a means of providing an electrochemical adaptation of the latter whereby the total thiol species present in a sample can be determined. The detection methodology has been proven to be robust with a linear range for cysteine from 2-120 microM, a limit of detection of 1.17 microM and has shown selectivity against a wide range of potential interferences. The efficiency of the methodology has been examined in the determination and recovery of thiol species in three growth tissue media, which contain a number of common biological interferences.     

The role of the pressing-on in the adhesion of elastic particles

One has carried out an analysis of the influence of the preliminary pressing-on on components of the adhesion force of different natures for the case of the contact of elastic particles with a rigid substrate. Two pressing-on variants are considered; as, - those realized under the effect of a dynamic and a static load. It has been shown that an increase in the adhesion of elastic particles to the surface resulting from the preliminary pressing-on is attributable to an increase in the adhesion force component due to a double electric layer in contact.     

Tandem time-of-flight experiment for low energy collision studies

We present an experiment adapted to collisional studies of cluster ions based on a laser vaporization setup coupled to a supersonic expansion. The ions are selected in a first time-of-flight, slowed down to the desired energy, and collided in an octopolar guide. The parent and fragment ions are then reaccelerated in order to be mass analyzed in a reflectron time-of-flight. An original method for the extraction of the ion that uses a double voltage pulse, is proposed. The experiment has been applied to collisions of hydrated cobalt ions. An absolute cross section of 17 A2 for the loss of one water molecule by Co(H2O)2+ in collision with neon at a center-of-mass energy of 10 eV, has been determined, with an accuracy of 10%. The threshold for this reaction has been measured at 1.5 eV and is in good agreement with the existing literature (Dalleska et al. J. Am. Chem. Soc. 1994, 116, 3519). Ions that cannot be formed by conventional ligand exchange methods, can also be studied. As an example, the threshold for dehydration of the Co2(H2O)+ ion has been measured at 1.5 +/- 0.2 eV.     

Reaction of 2-acetyltetralone with some esters of benzoic acid

In order to investigate the pharmacological screening of a number of pyran-4-ones their synthesis by cyclization with sulphuric acid of the corresponding 1,3,5-triketones has been carried out with high yields. In the course of preparation of the latter the reaction of 2-acetyltetralone with some esters of benzoic acid derivatives has been studied and in particular, for a number of them, an interesting nucleophilic substitution of a chlorine atom with an alkoxy group on a benzenic nucleus has been evidenced.