Isomerization of perfluorinated cyclic amines under the action of antimony pentafluoride

Conclusions When perfluorinated tertiary cyclic amines containing a substituent at the nitrogen atom are heated with antimony pentafluoride, they isomerize to the corresponding azomethines.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 646–649, March, 1989.     

Regularities of the photodestruction of acridine dyes in aqueous media

Acridine dyes were found to exhibit a low light fastness in oxygen-containing aqueous solutions because of photooxidation with the participation of molecular oxygen. The values of the quantum yield for the photooxidation of Acridine Yellow, Acridine Orange, and proflavin acetate at their initial concentration 2 × 10^?5 mol/l were determined to be 1.8 × 10^?3, 1.5 × 10^?3, and 0.8 × 10^?3, respectively. It was concluded that the photooxidation of these acridine dyes in dilute solutions results in the formation of primary photoproducts of peroxide nature. For proflav in acetate, as an example, it was demonstrated that the increase of the substrate concentration to 6 × 10^?4 mol/l results in a fourfold increase in the quantum yield, a behavior indicative of a change in the photodecomposition mechanism. The rate of the interaction between exited and unexcited proflavin molecules, the process responsible for the photodecomposition of this compound, was found to be ～4 × 10⁷ l/(mol s). The quantum yield for the photooxidation of the proflavin base was estimated to exceed that for the photooxidation of the proflavin monocation by more than an order of magnitude.     

Estimations of subgraph positions in molecular graphs and their common subgraph peculiarities

Some questions emerged from electronic data processing of molecular structures (graphs) and its fragments have been considered in this work. Quantitative estimations of subgraph positions in molecular graphs are presented and some properties of their maximal common subgraphs are described.     

4-(<Emphasis Type="Italic">N,N</Emphasis>-Dialkylthiocarbamoylthio)-5-nitropyrimidines as new potential nitric oxide donors

On heating at pH 6.86, 4-(N,N-dialkylthiocarbamoylthio)-5-nitropyrimidines are transformed into dithiolopyrimidines, which are either oxidized to bis(4-dialkylthiocarbamoylpyrimidin-5-yl) disulfides or converted into 4,6-diamino-5-nitropyrimidine derivatives with carbon disulfide elimination. The direction of the reaction is determined by the nature of a substituent in position 2 of pyrimidine and the bulk of the thiocarbamate substituent. Mechanistic schemes for these processes were proposed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2777–2783, December, 2005.     

Multiphoton Dissociation of Sulfur Hexafluoride in a Vibrationally Cooled Compression Shock

Multiphoton IR dissociation of SF₆ (in a mixture with CH₄) under nonequilibrium conditions of a compression shock formed by an intense, gas dynamically cooled, pulsed molecular beam impacting a solid surface was studied using the HF* luminescence detection ( 2.5 m) technique. The dependences of the HF* luminescence intensity on the distance x between the region in which molecules were excited and the surface and on the laser radiation frequency at different values of x were obtained. It was shown that, as the distance x decreased from 4 to 1.5 mm, the HF* luminescence intensity increased by more than an order of magnitude as compared to the case of excitation of molecules in an undisturbed flow, whereas the frequency dependences of luminescence intensity (SF₆ dissociation yield) were broadened only insignificantly.     

Topography of the free-energy landscape probed via mechanical unfolding of proteins

Single-molecule experiments in which proteins are unfolded by applying mechanical stretching forces generally force unfolding to proceed along a reaction coordinate that is different from that in chemical or thermal denaturation. Here we simulate the mechanical unfolding and refolding of a minimalist off-lattice model of the protein ubiquitin to explore in detail the slice of the multidimensional free-energy landscape that is accessible via mechanical pulling experiments. We find that while the free-energy profile along typical "chemical" reaction coordinates may exhibit two minima, corresponding to the native and denatured states, the free energy G(z) is typically a monotonic function of the mechanical coordinate z equal to the protein extension. Application of a stretching force along z tilts the free-energy landscape resulting in a bistable (or multistable) free energy G(z)-fz probed in mechanical unfolding experiments. We construct a two-dimensional free-energy surface as a function of both chemical and mechanical reaction coordinates and examine the coupling between the two. We further study the refolding trajectories after the protein has been prestretched by a large force, as well as the mechanical unfolding trajectories in the presence of a large stretching force. We demonstrate that the stretching forces required to destabilize the native state thermodynamically are larger than those expected on the basis of previous experimental estimates of G(z). This finding is consistent with the recent experimental studies, indicating that proteins may refold even in the presence of a substantial stretching force. Finally, we show that for certain temperatures the free energy of a polyprotein chain consisting of multiple domains is a linear function of the chain extension. We propose that the recently observed "slow phase" in the refolding of proteins under mechanical tension may be viewed as downhill diffusion in such a linear potential.     

1,2-Diisophthalimidoethane. X-ray diffraction evidence for the structure of the product of acylation of 1,2-diaminoethane with phthaloyl chloride

It was demonstrated by x-ray diffraction investigation of the product of the reaction of 1,2-diaminoethane with phthalic acid dichloride that the resulting compound has the 1,2-diisophthalimidoethane structure. An improved method for its synthesis is proposed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1320–1323, October, 1987.     

High pressure [4+2] and [2+2+2] reactions between cycloheptatriene and methyl propiolate

Under high pressure conditions, cycloheptatriene reacts with methyl propiolate to afford mono-, bis- and trisadducts all retaining, the norcaradiene structure. The four new compounds are formed via [4+21] and [2+2+2] cycloadditions. The latter are examples for the high pressure extension of the scope of homo-Diels-Alder reactions.     

Gas phase photoreaction of SO2 with n-pentane in the presence of NO

The spectrum of an intermediate, ascribed to nitrosopentane, has been detected in the photolysis of SO₂-pentane-NO mixtures. This may be explained by a radical photolysis mechanism involving an initial H-atom abstraction from the pentane molecule by SO₂.

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SO₂--NO , . , H .

     

Nature of the activity and the kinetics of cyclohexene hydrogenation by the catalytic system (C5H5)2 TiCl2?LiC4H9

The reaction of tributylphosphine with the catalytic system (C₅H₅)₂ TiCl₂–LiC₄H₉ prepared in an atmosphere of H₂ has been investigated in toluene solution. By using the ESR technique, a hydride complex Cp₂Ti(H) (PBu₃) has been detected. The proportionality between the rate of cyclohexene hydrogenation and the complex concentration has been established. The kinetics of cyclohexene hydrogenation has been investigated and a reaction mechanism is proposed.

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Cp₂TiCl₂–LiC₄H₉ (Cp–C₅H₅), H₂, Cp₂Ti(H) (PBu₃). Ti (III). .