Cobalt-catalyzed aziridination with diphenylphosphoryl azide (DPPA): direct synthesis of N-phosphorus-substituted aziridines from alkenes

A new catalytic aziridination system that consists of cobalt(II) tetraphenylporphyrin [Co(TPP)] as the catalyst and diphenylphosphoryl azide (DPPA) as the nitrene source has been developed. The cobalt-based catalytic system allows direct synthesis of N-phosphorus-substituted aziridines from alkenes with dinitrogen as the byproduct. Cobalt ion seems essential to the catalytic aziridination with DPPA as no or only trace amounts of the desired products were observed with other metal complexes of tetraphenylporphyrin.     

The temperature-dependent electrical transport properties of liquid Sn using pseudopotential theory

We present the calculations of electrical resistivity, thermo-electric power and thermal conductivity based on the self-consistent approximation. The pseudopotential due to Hasegawa et al. [J. Non-Cryst. Solids 117/118, 300 (1990) M. Hasegawa, K. Hoshino, M. Watabe, and H. Young, J. Non-Cryst. Solids 117/118, 300 (1990).[Crossref], [Web of Science ®] , [Google Scholar]] for full electron–ion interaction, which is valid for all electrons and contains the repulsive delta function to achieve the necessary s-pseudisation, was used in the calculation. Temperature dependence of structure factor is achieved through temperature-dependent potential parameter in the pair-potential. The outcome of the present study is discussed in the light of other such results and with predictions of Wiedemann and Franz law up to moderately high temperature. Specially, high-temperature resistivity data necessitates the careful investigation of electron energy dispersion close to the Fermi level and possible metal to non-metal transition while going from dense-fluid to low density-fluid state. In the absence of experimental data at high temperature, these findings may serve as future guideline.     

Calix Receptor Edifice; Scrupulous Turn Off Fluorescent Sensor for Fe(III), Co(II) and Cu(II)

Novel Supramolecular fluorescence receptor derived from calix-system i.e. calix[4]resorcinarene bearing dansylchloride as fluorophore was designed and synthesized. The compound was purified by column chromatography and characterized by elemental analysis, NMR and Mass spectroscopy. Tetradansylated calix[4] resorcinarene (TDCR) shows a boat conformation with C₂v symmetry. The complexation behaviour of metal cations [Ag(I), Cd(II), Co(II), Fe(III), Hg(II), Cu(II), Pb(II), Zn(II), U(VI) (1?×?10^-4?M)] with tetra dansylated calix[4]resorcinarene (1?×?10^-6?M) was studied by spectophotometry and spectrofluorometry. Red shift in the absorption spectra led us to conclude that there is strong complexation Fe(III), Co(II) and Cu(II) with TDCR. These metal cations also produce quenching with red shifts in the emission spectra. The maximum quenching in emission intensity was observed in the case of Fe(III) and its binding constant was also found to be significantly higher than that of Co(II) and Cu(II). Quantum yield of metal complexes of Fe(III) was found to be lower in comparison with Co(II) and Cu(II) complexes. Stern Volmer analysis indicates that the mechanism of fluorescence quenching is either purely dynamic, or purely static.     

Dislocation etch pits in anhydrous diglycine sulfate

New dislocation etchants for anhydrous diglycine sulfate single crystals have been developed and the etching results are reported. Dichloroacetic acid, glacitel acetic acid and their mixtures work as dislocation etchants on the cleavage plane of the crystal. Morphology of the etch pits was found to vary with the etchant composition.     

Causally discontinuous space-times

Along with certain properties of the region where distinguishingness is violated, it is proved that the violation of distinguishingness and reflectingness cannot occur individually.     

Magnetogravitational Instability of a Thermally Conducting Rotating Plasma through a Porous Medium

Magnetogravitational instability of an infinite homogeneous, viscous, thermally conducting, rotating plasma flowing through a porous medium has been studied with the help of relevant linearized perturbation equations, using the method of normal mode analysis. Rotation is taken parallel and perpendicular to the magnetic field for both, the longitudinal and the transverse modes of propagation. The joint influence of the various parameters do not, essentially, change the Jeans' criterion but modifies the same. The adiabatic velocity of sound is being replaced by the isothermal one due to the thermal conductivity. Porosity reduces the effects of both, the magnetic field and the rotation, in the transverse mode of propagation, whereas the rotation is effective only along the magnetic field for an inviscid plasma. The viscosity removes the effect of rotation in the transverse mode of propagation.     

Isothermal compressibility and sound velocity of binary liquid systems: Application of hard sphere models

Sound velocity and density were measured in six binary liquid mixtures namely,n-heptane+toluene (I);n-heptane+n-hexane (II); toluene+n-hexane (III); cyclohexane+n-heptane (IV); cyclohexane+n-hexane (V), andn-decane+n-hexane (VI) at 298.15 K. The experimental isothermal compressibility has been evaluated from measured values of density and sound velocity. The isothermal compressibility of these mixtures has been calculated theoretically using different models for the hard sphere equation of state and also using Flory’s statistical theory. The computed values of isothermal compressibility were also compared with the experimentally evaluated values. A satisfactory agreement has been observed.     

Control of electron demand in the cycloadditions of 2(H)-1,4-oxazin-2-ones

3-Methoxy-5-chloro-6-methyl-2(H)-1,4-oxazin-2-one 4, 3-methoxy-5-chloro-6-phenyl-2(H)-1,4-oxazin-2-one 5, 3-phenylsulfenyl-5-chloro-6-methyl-2(H)-1,4-oxazin-2-one 6, and 3-phenylsulfenyl-5-chloro-6-phenyl-2(H)-1,4-oxazin-2-one 7, are ambident dienes and undergo Diels-Alder cycloadditions with electron neutral, rich and deficient dienophiles.     

Synthesis of 7beta-sulfur analogues of paclitaxel utilizing a novel epimerization of the 7alpha-thiol group

Paclitaxel analogues with a sulfur group at the 7beta position were required for SAR studies. Attempts to generate these compounds by displacing a 7alpha leaving group with sulfur nucleophiles were unsuccessful. Instead, these compounds were successfully prepared from a 7beta-thiol intermediate that was obtained by a base-catalyzed epimerization of the 7alpha-thiol derivative. The epimerization presumably proceeds through a thioaldehyde intermediate and exhibits the opposite stereochemical preference of its oxygen counterpart.     

Resurrection and Reactivation of Acetylcholinesterase and Butyrylcholinesterase

Organophosphorus (OP) nerve agents and pesticides present significant threats to civilian and military populations. OP compounds include the nefarious G and V chemical nerve agents, but more commonly, civilians are exposed to less toxic OP pesticides, resulting in the same negative toxicological effects and thousands of deaths on an annual basis. After decades of research, no new therapeutics have been realized since the mid-1900s. Upon phosphylation of the catalytic serine residue, a process known as inhibition, there is an accumulation of acetylcholine (ACh) in the brain synapses and neuromuscular junctions, leading to a cholinergic crisis and eventually death. Oxime nucleophiles can reactivate select OP-inhibited acetylcholinesterase (AChE). Yet, the fields of reactivation of AChE and butyrylcholinesterase encounter additional challenges as broad-spectrum reactivation of either enzyme is difficult. Additional problems include the ability to cross the blood brain barrier (BBB) and to provide therapy in the central nervous system. Yet another complication arises in a competitive reaction, known as aging, whereby OP-inhibited AChE is converted to an inactive form, which until very recently, had been impossible to reverse to an active, functional form. Evaluations of uncharged oximes and other neutral nucleophiles have been made. Non-oxime reactivators, such as aromatic general bases and Mannich bases, have been developed. The issue of aging, which generates an anionic phosphylated serine residue, has been historically recalcitrant to recovery by any therapeutic approach—that is, until earlier this year. Mannich bases not only serve as reactivators of OP-inhibited AChE, but this class of compounds can also recover activity from the aged form of AChE, a process referred to as resurrection. This review covers the modern efforts to address all of these issues and notes the complexities of therapeutic development along these different lines of research.