Efficient addition reaction of bromonitromethane to aldehydes catalyzed by NaI: a new route to 1-bromo-1-nitroalkan-2-ols under very mild conditions

[Structure: see text] A catalytic NaI-mediated novel synthesis of 1-bromo-1-nitroalkan-2-ols was carried out by reaction of bromonitromethane with a variety of aldehydes, under very mild conditions. When the reaction was performed with chiral N,N-dibenzyl alaninal, the corresponding enantiopure (1S,2S,3S)-3-dibenzylamino-1-bromo-1-nitrobutan-2-ol was obtained with good stereoselectivity. The structure of this enantiopure bromohydrin was established by X-ray analysis.     

Electrochemical DNA Sensing at Single‐walled Carbon Nanotubes Chemically Assembled on Gold Surfaces

An electrochemical DNA sensor was constructed using single‐walled carbon nanotubes (SWNTs) attached to a self‐assembled monolayer of 11‐amino‐1‐undecanethiol on a gold surface. The voltammetric peak of methylene blue (MB), which interacts with the DNA guanine bases specifically, was used to follow the DNA hybridization process. After DNA hybridization with its complementary DNA strand, the MB electrochemical signal response decreased and the change in MB signal response was used as the basis for the electrochemical sensing of DNA hybridization. The as described DNA sensor demonstrated to have good stability, selectivity, a linear response over the DNA concentration range from 100 to 1,000 nM and a limit of detection of 7.24 nM.     

High-sensitivity analysis of specific peptides in complex samples by selected MS/MS ion monitoring and linear ion trap mass spectrometry: application to biological studies

Mass spectrometry (MS) is a technique of paramount importance in Proteomics, and developments in this field have been possible owing to novel MS instrumentation, experimental strategies, and bioinformatics tools. Today it is possible to identify and determine relative expression levels of thousands of proteins in a biological system by MS analysis of peptides produced by proteolytic digestion. In some situations, however, the precise characterization of a particular peptide species in a very complex peptide mixture is needed. While single-fragment ion-based scanning modes such as selected ion reaction monitoring (SIRM) or consecutive reaction monitoring (CRM) may be highly sensitive, they do not produce MS/MS information and their actual specificity must be determined in advance, a prerequisite that is not usually met in a basic research context. In such cases, the MS detector may be programmed to perform continuous MS/MS spectra on the peptide ion of interest in order to obtain structural information. This selected MS/MS ion monitoring (SMIM) mode has a number of advantages that are fully exploited by MS detectors that, like the linear ion trap, are characterized by high scanning speeds. In this work, we show some applications of this technique in the context of biological studies. These results were obtained by selecting an appropriate combination of scans according to the purpose of each one of these research scenarios. They include highly specific identification of proteins present in low amounts, characterization and relative quantification of post-translational modifications such as phosphorylation and S-nitrosylation and species-specific peptide identification.     

Kinetic interpretation of the thermal decomposition of anilinium octamolybdate at different heating rate

It has been shown many times, how difficult it is to discriminate among different kinetic models for the non-isothermal decompositions of solids. In this work non-isothermal decomposition data for the complex decomposition of anilinium octamolybdate at different heating rates have been analyzed taking into account temperature values at the same solid conversion in order to divide the temperature influence from the conversion influence in the kinetic model.Results for the apparent activation energy factor and kinetic conversion function are given. Nevertheless it has been not possible to assign a simple kinetic model to the decomposition.

---

Zusammenfassung Es ist oft gezeigt worden, da\ es schwierig ist, für nicht-isotherme Zersetzungen von Festkörpern unter verschiedenen kinetischen Modellen das entsprechende auszuwÄhlen. In der vorliegenden Arbeit wurden die für die komplexe nicht-isotherme, bei unterschiedlichen Aufheizgeschwindigkeiten ausgeführte Zersetzung von Anilinium-octamolybdat erhaltenen Daten analysiert, wobei die Temperaturwerte bei gleicher Konversion berücksichtigt wurden, um im kinetischen Modell den Einflu\ der Temperatur auf die Konversion auszuschalten. Die scheinbare Aktivierungsenergie und die kinetische Konversionsfunktion sind angeführt, jedoch war es nicht möglich, ein einfaches kinetisches Modell für die untersuchte Zersetzungsreaktion anzugeben.

---

. , . . .

     

Aldol reactions between L-erythrulose derivatives and chiral alpha-amino and alpha-fluoro aldehydes: competition between Felkin-Anh and Cornforth transition states

Both matched and mismatched diastereoselection have been observed in aldol reactions of a boron enolate of a protected L-erythrulose derivative with several chiral alpha-fluoro and alpha-amino aldehydes. Strict adherence to the Felkin-Anh model for the respective transition structures does not account satisfactorily for all the observed results, as previously observed in the case of alpha-oxygenated aldehydes. In some cases, only the Cornforth model provides a good explanation. The factors that influence this dichotomy are discussed and a general mechanistic model is proposed for aldol reactions with alpha-heteroatom-substituted aldehydes. Additional support for the model was obtained from density functional calculations.     

Solution to a conjecture on the norm of the Hardy operator minus the identity

We prove that for a decreasing weight w, the following inequality is sharp:

     

Solid-phase microextraction coupled to gas chromatography with flame ionization detection for monitoring of organic solvents in working areas

A solid-phase microextraction (SPME) method was developed for air monitoring of organic solvents frequently used in chemical laboratories (namely pentane, dimethyl ether, acetone, acetonitrile, dichloromethane, hexane, ethylacetate, tetrahydrofurane, cyclohexane, benzene, and toluene). SPME sampling conditions and chromatographic separation were optimised. Linearity of response for each component of the mixture was tested. Standard solutions containing all the compounds, at three different concentrations, were analysed in triplicate and the relative standard deviations (RSDs) were calculated. The method was applied to the monitoring of indoor air in a research chemical laboratory. An SPME fibre was used as a sampling device inside the laboratory. Moreover an SPME fibre was used as a portable sampling device in order to determine the effective human exposure. Comparison of the portable and fixed sampling device showed differences in the amount of solvents associated with activities performed nearby.     

Yttrium-succinates coordination polymers: Hydrothermal synthesis, crystal structure and thermal decomposition

New polymeric yttrium-succinates, Y₂(C₄H₄O₄)₃(H₂O)₄·6H₂O and Y₂(C₄H₄O₄)₃(H₂O)₂, have been synthesized, and their structures (solved by single crystal XRD) are compared with that of Y₂(C₄H₄O₄)₃(H₂O)₂·H₂O. Three compounds were obtained as single phases, and their thermal behaviour is described.     

Local ordering in liquids: solvent effects on the hyperfine couplings of the cyclohexadienyl radical

Ordering of solvent molecules in the vicinity of a dipolar free radical affects its hyperfine coupling constants (hfcs). Specifically, it is demonstrated how the variation of the experimental methylene proton and muon hfcs of the muoniated cyclohexadienyl radical in several solvents and solvent mixtures of varying polarity can be accounted for by a dipole-dipole reaction field model that is based on the model of Reddoch and Konishi (J. Chem. Phys. 1979, 70, 2121) which was developed to explain the solvent dependence of the 14N hfc in the di-tert-butyl-nitroxide radical. Ab initio calculations were carried out with the cyclohexadienyl radical in an electric field to model the electric field arising from the electric dipole moments of the surrounding solvent molecules. An extension of the model that includes the dipole-quadrupole interaction can account for the larger hfc in benzene compared with that in octadecane, and it is predicted that the hfc will be proportional to the concentration of quadrupole moments to the 4/3 power. The influence of hydrogen bonding between the radicals' pi electrons and the OH groups of the solvent on the hfcs is also discussed. Comparison with gas-phase data permits a separation of vibrational effects and reveals that approximately 28% of the temperature dependence in water is due to increasing solvent disorder.