Reactions of ethoxyethynylphosphines with phenyl azide and nucleophiles. 1,5-Alkylotropic migration in phosphorus(IV)-substituted ketene acetals

Ethoxyethynyl-di-tert-butylphosphine reacts with phenyl azide in the presence of amines, alcohols, phenol, or water by addition of the nucleophile to the triple bond of the unstable ethoxyethynyldi-tert-butyl-N-phenyliminophosphorane. It has been found that iminophosphorylated ketene acetals are usually unstable, undergoing 1,5-alkylotropic migration to give alkoxycarbonylmethyl-ene(alkylphenylamino)phosphoranes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2850–2855, December, 1991.     

Polarization effects in photosynthetic membranes

This paper investigates the polarization effects associated with functional processes in photosynthetic membranes.     

Electric-field effects in dry films of D85N and D85,96N mutant bacteriorhodopsin

In the D85N mutant of the protein bacteriorhodopsin (BR), the Schiff base, by which the retinal chromophore is bound to the protein, exhibits an abnormally low proton affinity (pKa approximately 8.9). Recent experiments on thin films of this protein have shown that this causes the protonation state of the Schiff base, and thus the visible absorption spectrum, to be sensitive to external electric fields. In this paper, we explore the dependence of this effect on parameters such as pH, humidity, and film thickness. The results of these experiments point to the importance of water molecules bound in the acceptor part of the proton channel as sources and donors in field-induced proton-transfer reactions. We describe additional results obtained with the D85,96N mutant, which also exhibits a low Schiff-base pK. The similar behavior of the two mutants under applied electric fields at high pH implies that the residue Asp-96 plays no role in field-induced Schiff-base protonation.     

Isolobal analogy between trivalent boron and divalent silicon

Singlet organosilylenes with a lone pair and an emptyp orbital are isolobal to trivalent borane if a B-H is equated to the lone pair on Si. Using this analogy, a particular isomer of CSi₂H₂ (24) is predicted to be a stable structure. MNDO calculations on24 and many of its possible isomers suggest that24 is at global minimum on the potential energy surface of CSi₂H₂.Ab initio calculations using a, minimal STO-3G basis set, on some selected structures also support these results.     

Effect of Mechanical Activation on the Reaction of Magnesium Hydride with Water

The effect of the parameters of mechanochemical activation of magnesium hydride and MgH₂-graphite binary compositions on the parameters of materials and their hydrolytic activity has been studied. It is concluded that mechanochemical treatment increases the reactivity of magnesium hydride in its reaction with water. Graphite provides an additional activating effect during the mechanochemical treatment of MgH₂. A deformation dose of 20 kJ/g was determined to be the optimum one for achieving the highest reactivity in the hydrolysis reaction with the formation of MgH₂-graphite composites. As a result of the hydrolysis of such materials, up to 970–1280 mL hydrogen per composite gram is evolved in 40 min of the reaction with water without an additional change in the solution acidity.     

Electric-Field Effects in 13-Demethyl-11,14-Epoxyretinal-Bacteriorhodopsin Films

Abstract— We report the results of experiments on the application of electric fields across thin, dry Alms of a bacteriorho-dopsin (BR) analog pigment in which the retinal chro-mophore has been replaced with 13-demethyl-11,14-epoxyretinal. As previously observed in other BR variants with low Schiff-base pK values, this pigment exhibits protonation and deprotonation of the Schiff base under an applied electric field, depending on the initial Schiff-base protonation state or effective pH. At low effective pH, a fast (<200 μs) deprotonation reaction dominates. At high pH, an apparently different mechanism leads to Schiff-base protonation on the time scale of seconds. Comparison of our results with a simple model suggests that the external field causes a shift in the pK of the Schiff base by1–2 pH units.     

Cascade Transformations of [1,2,3]Triazolo[1,5-a]pyridines as Convenient Precursors of Diazo Compounds and Metal Carbenes

Russian Journal of Organic Chemistry - The review is devoted to the use of [1,2,3]triazolo[1,5-a]pyridines as precursors of tautomeric 2-(diazomethyl)pyridines. This methodology represents a...     

Conversion of carbonyl steroid derivatives to 1,1-dibromoalkenes by the catalytic olefination reaction and synthesis of functionally substituted steroids on their basis

Russian Chemical Bulletin - Catalytic olefination of carbonyl steroid derivatives were used to obtain the corresponding 1,1-dibromoalkenes. For this, N-unsubstituted steroid hydrazones were...