Water – A key parameter in the stability of anion exchange membrane fuel cells

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The synthesis of key intermediates in cembranolides

Two key intermediates of cembranolides- (2E,6E,10E)-3,7,11,15-tetramethyl-9-phenylsulfonyl-2,6,10,14-tetraen-1-hexadecanol (1) and (2E,6E,10E,14E)-2,6,10,14-tetramethyl-8-phenylsulfonyl-2,6,10,14-tetraen-1,16-hexadecanediol (2) were synthesized starting from geraniol and linalool and some improved synthetic methods were used.     

Systematic study for the stereochemistry of the Atherton–Todd reaction

Under the Atherton–Todd reaction conditions, the stereochemistry on the reaction of H-phosphinates with different nucleophiles (e.g., amines, alcohols, phenols) was investigated. All reactions took place stereospecifically with inversion of configurations at the phosphorus centers. The reaction might proceed via a phosphoryl chloride intermediate with retention of configuration at phosphorus, followed by the attack of nucleophiles from the backside of Cl to give the substitution products with inversion of configuration at the phosphorus center. A plausible mechanism was proposed for these reactions.     

Liquid‐crystalline glycolipids: towards understanding the roles of liquid crystals in biological and life processes

A Commentary on the paper ”Liquid‐crystalline behaviour in the n‐alkyl gluconamides and other related carbohydrates?, by B. Pfannemüller, W. Welte, E. Chin and J.W. Goodby. First published in Liquid Crystals, 1, 357‐370 (1986).     

831 — The human amniotic membrane: One membrane or several membranes?

The measured dilution potentials, when the maternal and the fetal salt concentrations on both sides and when the intracellular ion concentrations of the amnion are modified, are consistent with the prediction of a single membrane. Thus, the human amnion must be considered as a single membrane with the cell membrane on the maternal side dominating the cell membrane on the fetal side.     

Total synthesis of violaceimides A–E and consideration of the reported stereochemistry

Here we report the first total synthesis of violaceimides A–E, a family of sulfur-containing metabolites from Aspergillus violaceus, a sponge-associated fungus. A concise, convergent and enantioselective synthesis was developed for all five family members, from a common advanced intermediate. However, while the NMR spectral data matched that of the reported natural products, the optical rotations were of opposite sign. This result prompted the enantioselective synthesis of all four diastereomeric pairs of violaceimide E, and suggests that the stereochemistry might have been misassigned.     

The design of membrane vapor–gas separation systems

Membrane vapor–gas separation systems are beginning to be applied to a number of gas separation problems in the petrochemical and refinery areas. In this paper, some of the factors that affect the design of these systems are described using, as an application example, the separation of propylene from nitrogen in polyolefin resin degassing vents.     

The Pharmacophore Hypothesis of Novel Inhibitors for Aurora A Kinase

A three-dimensional pharmacophore model was developed from a series of inhibitors of Aurora A kinase to discover new potent anti-cancer agents using the HypoGen module in the Catalyst software. The pharmacophore model was developed based on the structure of 20 currently available inhibitors, which were carefully selected from the literature. The best hypothesis （Hypo 1） was defined by four features： one hydrogen-bond donor and three hy- drophobic points, with the best correlation coefficient of 0.909, the lowest rms deviation of 1.563, and the highest cost difference of 99.075. The Hypo 1 was then validated by a test set consisting of 24 compounds and by a cross-validation of 95% confidence level through randomizing the data using the CatScramble program, which suggested that a predictive pharmacophore model had been successfully obtained.     

Binding of α-hydroxy-β-amino acid inhibitors to methionine aminopeptidase. The performance of two types of scoring functions

The binding mode of a recently described set of -hydroxy--amino acid inhibitors of methionine aminopeptidase type 2 is suggested in the present work. The binding mode is supported by analysis of published structures of transition state analogues co-crystallised with E. coli methionine aminopeptidase and by a comparison of molecular interaction fields calculated using GRID for E. coli and human methionine aminopeptidase. Based on the suggested binding mode two types of scoring functions have been evaluated and compared. These are the commercially available consensus score, CScore, and scoring of the ligands employing energies calculated using the Merck Molecular Force Field (MMFF). Enriched subsets of ligands were obtained when using CScore, but these scores could not be used to assess the relative affinities of individual compounds. Although still not sufficiently accurate for reliable predictive purposes, an improved correlation was obtained between structure and affinity using a combined force field energy including contributions from solvation and conformational energy penalty for binding.     

Catalytic phosphorylation of polyfluoroalkanols. 17. Synthesis and the stereochemistry of tris(α-trifluoromethylbenzyl) phosphates

Catalytic phosphorylation of -trifluoromethylbenzyl alcohols with POCl₃ taken in a ratio of 3 : 1 under particular temperature conditions afforded predominantly symmetrical tris(-trifluoromethylbenzyl) phosphates. The latter were obtained as mixtures of two diastereomers with a statistical ratio of the components.     

Predicting the tautomeric equilibrium of acetylacetone in solution. I. The right answer for the wrong reason?

This study investigates how the various components (method, basis set, and treatment of solvent effects) of a theoretical approach influence the relative energies between keto and enol forms of acetylacetone, which is an important model system to study the solvent effects on chemical equilibria from experiment and theory. The computations show that the most popular density functional theory (DFT) approaches, such as B3LYP overestimate the stability of the enol form with respect to the keto form by ～10 kJ mol^?1, whereas the very promising SCS‐MP2 approach is underestimating it. MP2 calculations indicate that in particular the basis set size is crucial. The Dunning Huzinaga double ζ basis (D95z(d,p)) used in previous studies overestimates the stability of the keto form considerably as does the popular split‐valence plus polarization (SVP) basis. Bulk properties of the solvent included by continuum approaches strongly stabilize the keto form, but they are not sufficient to reproduce the reversal in stabilities measured by low‐temperature nuclear magnetic resonance experiments in freonic solvents. Enthalpic and entropic effects further stabilize the keto form, however, the reversal is only obtained if also molecular effects are taken into account. Such molecular effects seem to influence only the energy difference between the keto and the enol forms. Trends arising due to variation in the dielectric constant of the solvent result from bulk properties of the solvent, i.e., are already nicely described by continuum approaches. As such this study delivers a deep insight into the abilities of various approaches to describe solvent effects on chemical equilibria. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Allosteric effects in norbadione A. A clue for the accumulation process of 137Cs in mushrooms?

A fruitful combination of potentiometry, absorption spectrophotometry, ESMS and 1H NMR enabled the characterisation of two caesium complexes with norbadione A and the determination of the respective stability constants of a mononuclear and a dinuclear caesium complex at pH approximately 6; a preliminary study allowed the assignment of five protonation sites of this pigment; a positively cooperative binding of the second Cs+ cation was observed.     

The key elements of traceability in chemical measurement: agreed or still under debate?

Talking about "traceability" means talking about a "property of the result of a measurement", about "the value of a standard", about "stated references" and about an "unbroken chain of comparisons". It describes by which comparison, and to which other value, the result of a measurement has been obtained, i.e. is "traceable to". It is about the underlying structure of the measurement process of the result of a measurement and therefore about the authority of the result. Since values carried by (certified) reference materials have also been obtained by measurement, the definition of traceability equally applies. Traceability in the context of reference materials is also about the authority of the values carried by the (certified) reference materials and is, therefore, of key importance for the authority of the reference materials themselves. Hence, values of results of measurements constitute part of the traceability chain and their uncertainties are an intrinsic accompanying phenomenon. Uncertainties need a traceability chain against which they can be evaluated, and a traceability chain is an a priori requirement for evaluating the uncertainty budget of a measurement result. An attempt has been made to exemplify "traceability" chains in some types of chemical measurement and to identify the degree of international agreement on the key elements of "traceability". It is concluded that there is less than universal agreement on this issue. The debate should continue in order to arrive at the international understanding and agreement needed, as "traceability" is now being incorporated in the International Organization for Standardization (ISO), the International Laboratory Accreditation Co-operation (ILAC) and in other "guiding" or regulatory documents. It is also the reason why the Institute for Reference Materials and Measurements (IRMM) has taken up the study of the concept in its core programme on Metrology in Chemistry, and why it sponsored the Workshop in Bratislava.     

The key elements of traceability in chemical measurement: agreed or still under debate?

 Talking about "traceability" means talking about a "property of the result of a measurement", about "the value of a standard", about "stated references" and about an "unbroken chain of comparisons". It describes by which comparison, and to which other value, the result of a measurement has been obtained, i.e. is "traceable to". It is about the underlying structure of the measurement process of the result of a measurement and therefore about the authority of the result. Since values carried by (certified) reference materials have also been obtained by measurement, the definition of traceability equally applies. Traceability in the context of reference materials is also about the authority of the values carried by the (certified) reference materials and is, therefore, of key importance for the authority of the reference materials themselves. Hence, values of results of measurements constitute part of the traceability chain and their uncertainties are an intrinsic accompanying phenomenon. Uncertainties need a traceability chain against which they can be evaluated, and a traceability chain is an a priori requirement for evaluating the uncertainty budget of a measurement result. An attempt has been made to exemplify "traceability" chains in some types of chemical measurement and to identify the degree of international agreement on the key elements of "traceability". It is concluded that there is less than universal agreement on this issue. The debate should continue in order to arrive at the international understanding and agreement needed, as "traceability" is now being incorporated in the International Organization for Standardization (ISO), the International Laboratory Accreditation Co-operation (ILAC) and in other "guiding" or regulatory documents. It is also the reason why the Institute for Reference Materials and Measurements (IRMM) has taken up the study of the concept in its core programme on Metrology in Chemistry, and why it sponsored the Workshop in Bratislava.

     

The key role of 3-glycidoxypropyltrimethoxysilane sol–gel precursor in the development of wearable sensors for health monitoring

Textiles represent an attractive class of materials for realizing wearable biosensors. Electronic textiles, or smart textiles, describe the convergence of electronics and textiles into fabrics, which are able to sense, compute, communicate, and actuate. As many different electronic systems can be connected to any clothing, a wearable system becomes more versatile, and the user can change its look depending on environmental changes and individual preference. In this review, we want to explain how it is possible to develop the sensing component of a wearable sensor by sol–gel method based on the use of opportune organofunctional trialkoxysilane precursors, such as 3-glycidoxypropyltrimethoxysilane. Results show that the halochromic dyestuffs are completely entrapped in the sol–gel coatings, both through chemical and physical interactions with the textile fabric. Moreover, a certain washing fastness was observed. Sensor films show excellent reproducibility, reversibility, and short response times, with dynamic ranges from pH 4.4–6.0 (Methyl Red), pH 6.0–7.0 (Nitrazine Yellow), and pH 4.5–8.3 (Litmus), respectively.

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The scientific work of John G. Verkade—A retrospect

The scientific work of John G. Verkade—A retrospect

All authors

Dietrich Gudat

https://doi.org/10.1080/10426507.2017.1273643

Published online:

25 January 2017

Dr. John G. Verkade

Photo courtesy of Iowa State University     

18.

The potential of proton exchange membrane–based electrolysis technology     

Katherine Ayers 《Current Opinion in Electrochemistry》2019

Hydrogen is an important chemical feedstock for many industrial applications, and today, more than 95% of this feedstock is generated from fossil fuel sources such as reforming of natural gas. In addition, the production of hydrogen from fossil fuels represents most carbon dioxide emissions from large chemical processes such as ammonia generation. Renewable sources of hydrogen such as hydrogen from water electrolysis need to be driven to similar production costs as methane reforming to address global greenhouse gas emission concerns. Water electrolysis has begun to show scalability to relevant capacities to address this need, but materials and manufacturing advancements need to be made to meet the cost targets. This article describes specific needs for one pathway based on proton exchange membrane electrolysis technology.     

19.

A comparative study of electrochemical performances of carbon nanomaterial-modified electrodes for DNA detection. Nanotubes or graphene?     

Báez  Daniela F.  Bollo  Soledad 《Journal of Solid State Electrochemistry》2016,20(4):1059-1064

Journal of Solid State Electrochemistry - A comparative study about the electrochemical response of glassy carbon electrode modified with four different carbon nanomaterial (CNM) against dsDNA is...     

20.

The reaction of perfluoroalkanesulfonyl halides Ⅷ. A mild method for introducing BrCF_2 group to organic molecules     

《中国化学》1992,(3)

BrCF_2SO_2Br, prepared from sulfinatodehalogenation of CF_2Br_2 followed by bromination ofthe intermediate BrCF_2SO_2Na, was shown to be a mild and efficient bromodifluoromethylating agent.     

The potential of proton exchange membrane–based electrolysis technology

Hydrogen is an important chemical feedstock for many industrial applications, and today, more than 95% of this feedstock is generated from fossil fuel sources such as reforming of natural gas. In addition, the production of hydrogen from fossil fuels represents most carbon dioxide emissions from large chemical processes such as ammonia generation. Renewable sources of hydrogen such as hydrogen from water electrolysis need to be driven to similar production costs as methane reforming to address global greenhouse gas emission concerns. Water electrolysis has begun to show scalability to relevant capacities to address this need, but materials and manufacturing advancements need to be made to meet the cost targets. This article describes specific needs for one pathway based on proton exchange membrane electrolysis technology.     

A comparative study of electrochemical performances of carbon nanomaterial-modified electrodes for DNA detection. Nanotubes or graphene?

Journal of Solid State Electrochemistry - A comparative study about the electrochemical response of glassy carbon electrode modified with four different carbon nanomaterial (CNM) against dsDNA is...     

The reaction of perfluoroalkanesulfonyl halides Ⅷ. A mild method for introducing BrCF_2 group to organic molecules

BrCF_2SO_2Br, prepared from sulfinatodehalogenation of CF_2Br_2 followed by bromination ofthe intermediate BrCF_2SO_2Na, was shown to be a mild and efficient bromodifluoromethylating agent.