Oxidation of α,β-un saturated aldehydes

A variety of methods for the conversion of α,β-unsaturated aldehydes to the corresponding acids have been explored. The best approach uses sodium chlorite and gives the desired transformation even in systems where steric hindrance and/or sensitive functionality are present.     

Three-step analytic model for high-energy heavy-ion collisions

We discuss within the framework of an analytical model central collisions between large nuclei at an intermediate energy. The model assumes three stages: the ignition stage in which thermalized nucleons are created within the reaction volume; the expansion phase in which the hot nuclear matter expands and cools; and finally, the evaporation stage in which the system disintegrates through a surface evaporation. The model provides a qualitative insight into the connections between the main physical processes throughout the collision event.     

Polarography of thiodiglycolic acid and thiodipropionic acid at the dropping mercury electrode

The polarographic behaviour of thiodiglycolic acid (R?S?R) and thiodipropionic acid (R?CH₂?S?CH₂R) at the DME, has been investigated in presence of 0.1 M KCl and 0.01% thymol with respect to the effects of changes in pH, concentration, drop time, and temperature on the wave characteristics. Well-defined irreversible cathodic waves were obtained in the pH range 2.40 to 4.76 for R?S?R and 2.3 to 4.98 for R?CH₂?S?CH₂R. At lower (<2.0) and higher (>5) pH values, ill-defined waves were obtained. The mechanism of the electrode process in aqueous solutions has also been elucidated.     

Far-IR lattice absorption spectra in ZnS:Be system

Calculated far-IR lattice absorption due to a small concentration of beryllium impurities in cubic zinc sulphide has been reported for the first time. The method of calculation follows the Green's function technique. The evaluation of the involved Green's function for zinc sulphide is made by incorporating the real phonons obtained from a second-neighbor-ionic (SNI) model. A defect model that considers the change of mass at the impurity site as well as the changes in the nearest-neighbor (central and angular interactions) is employed in calculating the absorption and the impurity modes. The experimentally observed IR absorption below 100 cm^?1 can be understood only if one takes into account the changes in the angular force constants around the impurity. The calculated absorption is compared and discussed with the existing experimental data.     

Algorithm for solving the equation of radiative transfer in the frequency domain

We present an algorithm that provides a frequency-domain solution of the equation of radiative transfer (ERT) for heterogeneous media of arbitrary shape. Although an ERT is more accurate than a diffusion equation, no ERT code for the widely employed frequency-domain case has been developed to date. In this work the ERT is discretized by a combination of discrete-ordinate and finite-volume methods. Two numerical simulations are presented.     

Changes in the order of elution of some organic compounds in high-resolution gas chromatography on polar columns depending on the injection method and water content in the sample

During the GC analysis of apple aroma essence using a capillary column with polar stationary phases, i.e., bonded/crosslinked polyethylene glycol (HP-Innowax) and acid-modified polyethylene glycol (FFAP) the phenomenon of changing the elution order of some compounds was observed ("cross-over phenomenon"). The elution order within two pairs of closely eluting compounds: 2-methylbutyl acetate/pentan-3-ol (internal standard) and trans-2-hexen-1-al/2-methylbutan-1-ol differed between samples introduced onto the column with direct injection and with static headspace method. Experiments carried out on standard solutions of investigated compounds in water-acetone mixtures of gradually reduced water ratio (99:1 to 0:100) proved that changes of elution times leading first to co-elution and subsequently to reversion of elution order of compounds within both pairs depended on the amount of water in the injected sample. The same effect was observed while the amount of water was diminished by reducing the sample volume introduced into the column.     

The Potential of Micellar Media in the Synthesis of DNA-Encoded Libraries

DNA-encoded library (DEL) technology has become widely used in drug discovery research. The construction of DELs requires robust organic transformations that proceed in aqueous media under mild conditions. Unfortunately, the application of water as reaction medium for organic synthesis is not evident due to the generally limited solubility of organic reagents. However, the use of surfactants can offer a solution to this issue. Oil-in-water microemulsions formed by surfactant micelles are able to localize hydrophobic reagents inside them, resulting in high local concentrations of the organic substances in an otherwise poorly solvated environment. This review provides a conceptual and critical summary of micellar synthesis possibilities that are well suited to DEL synthesis. Existing examples of micellar DEL approaches, together with a selection of micellar organic transformations fundamentally suitable for DEL are discussed.     

Halogenation of the Hexaphosphabenzene Complex [(Cp*Mo)2(μ,η6:η6-P6)]: Snapshots on the Reaction Progress

The oxidation of [(Cp*Mo)₂(μ,η⁶:η⁶-P₆)] ( 1 ) with halogens or halogen sources was investigated. The iodination afforded the ionic complexes [(Cp*Mo)₂(μ,η³:η³-P₃)(μ,η¹:η¹:η¹:η¹-P₃I₃)][X] (X=I₃⁻, I⁻) ( 2 ) and [(Cp*Mo)₂(μ,η⁴:η⁴-P₄)(μ-PI₂)][I₃] ( 3 ), while the reaction with PBr₅ led to the complexes [(Cp*Mo)₂(μ,η³:η³-P₃)(μ-Br)₂][Cp*MoBr₄] ( 4 ) [(Cp*MoBr)₂(μ,η³:η³-P₃)(μ,η¹-P₂Br₃)] ( 5 ) and [(Cp*Mo)₂(μ-PBr₂)(μ-PHBr)(μ-Br)₂] ( 6 ). The reaction of 1 with the far stronger oxidizing agent PCl₅ was followed via time- and temperature-dependent ³¹P{¹H} NMR spectroscopy. One of the first intermediates detected at 193 K was [(Cp*Mo)₂(μ,η³:η³-P₃)(μ-PCl₂)₂][PCl₆] ( 8 ) which rearranges upon warming to [(Cp*Mo)₂(μ-PCl₂)₂(μ-Cl)₂] ( 9 ), [(Cp*MoCl)₂(μ,η³:η³-P₃)(μ-PCl₂)] ( 10 ) and [(Cp*Mo)₂(μ,η⁴:η⁴-P₄)(μ-PCl₂)][Cp*MoCl₄] ( 11 ), which could be isolated at room temperature. All complexes were characterized by single-crystal X-ray diffraction, NMR spectroscopy and their electronic structures were elucidated by DFT calculations.     

Halogenation and Nucleophilic Quenching: Two Routes to E−X Bond Formation in Cobalt Triple-Decker Complexes (E=As,P; X=F,Cl, Br,I)

The oxidation of [(Cp’’’Co)₂(μ,η² : η²-E₂)₂] (E=As ( 1 ), P ( 2 ); Cp’’’=1,2,4-tri(tert-butyl)cyclopentadienyl) with halogens or halogen sources (I₂, PBr₅, PCl₅) was investigated. For the arsenic derivative, the ionic compounds [(Cp’’’Co)₂(μ,η⁴ : η⁴−As₄X)][Y] (X=I, Y=[As₆I₈]_0.5 ( 3 a ), Y=[Co₂Cl_6-nI_n]_0.5 (n=0, 2, 4; 3 b ); X=Br, Y=[Co₂Br₆]_0.5 ( 4 ); X=Cl, Y=[Co₂Cl₆]_0.5 ( 5 )) were isolated. The oxidation of the phosphorus analogue 2 with bromine and chlorine sources yielded the ionic complexes [(Cp’’’Co)₂(μ-PBr₂)₂(μ-Br)][Co₂Br₆]_0.5 ( 6 a ), [(Cp’’’Co)₂(μ-PCl₂)₂(μ-Cl)][Co₂Cl₆]_0.5 ( 6 b ) and the neutral species [(Cp’’’Co)₂(μ-PCl₂)(μ-PCl)(μ,η¹ : η¹-P₂Cl₃] ( 7 ), respectively. As an alternative approach, quenching of the dications [(Cp’’’Co)₂(μ,η⁴ : η⁴-E₄)][TEF]₂ (TEF=[Al{OC(CF₃)₃}₄]⁻, E=As ( 8 ), P ( 9 )) with KI yielded [(Cp’’’Co)₂(μ,η⁴ : η⁴-As₄I)][I] ( 10 ), representing the homologue of 3 , and the neutral complex [(Cp’’’Co)(Cp’’’CoI₂)(μ,η⁴ : η¹-P₄)] ( 11 ), respectively. The use of [(CH₃)₄N]F instead of KI leads to the formation of [(Cp’’’Co)₂(μ-PF₂)(μ,η² : η¹ : η¹-P₃F₂)] ( 12 ) and 2 , thereby revealing synthetic access to polyphosphorus compounds bearing P−F groups and avoiding the use of very strong fluorinating reagents, such as XeF₂, that are difficult to control.