On problems of the laminar–turbulent transition

The initial stage of the laminar–turbulent transition is reconstructed. Its mechanism is based on spinodal decomposition (diffusion separation).     

Pincer Receptors for Anions Based on Triazolyl Bile Acids

Copper-catalyzed 1,3-dipolar cycloaddition of azides to acetylenes successfully afforded pincer bistriazolium receptor containing two lithocholic acid fragments and phenylphosphonic diamide bridge. The obtained receptor showed high complexing power toward fluoride ions and organic acid anions, which decreased in the series fluoride > succinate ≥ malonate > oxalate ≥ lithocholate > benzoate > acetate > hydrogen sulfate > bromide.     

Copper(i) complexes with polymeric 2,2′-biquinoline-containing ligands as electrocatalysts for selective oxidation of the secondary hydroxy group in 3,24-dihydroxy-5β-cholane with oxygen

Indirect electrocatalytic selective oxidation of the secondary hydroxy group in 3,24-dihydroxy-5β-cholane was performed using atmospheric oxygen in the presence of copper(I) complex with a polymeric 2,2′-biquinoline-containing ligand as catalyst. The reaction was characterized by a high yield (85%), 100% selectivity, and mild conditions, the Cu^II/Cu^I redox potential being ?0.55 V relative to Ag/AgCl/KCl.     

Phosphirenes and Azaphosphetines: IX. 1-Aza-2-phospha-1,3-dienes, 1,2-Azaphosphetines,and 1-Aza-2-phosphacyclohexa-2,4-dienes in Reactions with P-Bromoimino-N-(tri-tert-butylphenyl)phosphine with 1-Dialkylamino-1-alkynes

The reaction of P-bromoimino-N-(tri-tert-butylphenyl)phosphine with 1-dialkylamino-1-alkynes primarily forms 1-aza-2-phosphabitadienes. The latter are unstable and can further rearrange into 1,2-azaphos-phetines or take up one more aminoacetylene molecule to give 1-aza-2-phospha-2,4-cyclohexadienes.     

Phosphirenes and Azaphosphetines: X. 1-Aza-2-phosphabutadienes in Electrophilic Addition of P-Haloiminophosphines to 1-Alkoxyacetylenes: Synthesis and Chemical Properties

Reaction of P-chloro-, P-bromo-, and P-iodoiminophosphines with 1-alkoxyacetylenes proceeds as an electrophilic regioselective addition across the triple bond with conservation of biscoordinate phosphorus providing 1-aza-2-phosphabutadienes. The stereochemistry of the resulting product depends on the character of the alkyl and alkoxy substituents in the alkyne, on the halogen in the iminophosphine, on the polarity of the solvent and the concentration of reagents. The azaphosphabutadienes easily enter into [2+1]-cycloaddition with the second equiv of alkyne to furnish P-alkenyl-substituted phosphirenes. They also add hydrogen halides to the P = N bond forming acyl halides of alkenylphosphonous acids amides. The possibility of Z/E-isomerization of the alkenyl moiety in all the compounds synthesized was investigated.     

Novel lithocholaphanes: Syntheses, NMR, MS, and molecular modeling studies

Novel head-to-head lithocholaphanes 6 and 11 have been synthesized via precursors 1–5 and 7–10 with overall good yields, and characterized by ¹H, ¹³C, and ¹⁵N NMR spectroscopy, ESI-TOF mass spectrometry, thermal analysis, and molecular modeling. In addition, the binding abilities of 6 and 11 towards alkali metal cations have been investigated via competitive complexation studies using equimolar mixtures of Li⁺, Na⁺, K⁺, and Rb⁺-cations, and cholaphanes 6 and 11. The formation of cation–cholaphane adducts was detected by ESI-TOF mass spectrometry. The trends in these comparative binding studies are nicely reproduced theoretically with PM3 energetically optimized structures of 6 and 11 and their interaction energies with alkali metal cations calculated by molecular mechanics. Cholaphane 11 possessing a peptoid type structural fragment, –(CH₂CONHCH₂CH₂)₂O–, as a coordination sphere, shows binding tendency towards lithium and sodium cations, whereas 6 possessing an ester type, –(CH₂OCOCH₂)₂O–, moiety and a bigger cavity size than 11, shows merely a tendency towards bigger alkali metal cations, potassium and rubidium.     

Catalytic alkynylation of 6-bromosteroids

An efficient method for synthesis of 6-alkynyl-substituted androstane derivatives was developed via the Pd-catalyzed Sonogashira—Hagihara coupling reaction. The use of AgCl as the cocatalyst (instead of traditionally used CuI) was shown to increase the activity of the catalytic system in several cases. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 486–490, March, 2007.     

Measurement of the ground state 2n pickup probability for 28Si+68Zn and its role in sub-barrier fusion enhancement

The ground state and excited state transfer yields for the 2-neutron pickup channel in the ²⁸Si+⁶⁸Zn system have been measured explicitly. The recoil mass separator at the nuclear Science Centre, New Delhi was used for the measurement. A NaI(T1) detector was used for detecting the deexcitation γ’s from the transfer products. The kinematic coincidence technique was employed for the transfer measurement. Simplified coupled channels calculations show that out of all transfer channels the major contribution to the sub-barrier enhancement comes from the ground state 2 neutron pickup channel with a ground state Q-value of+1.83 MeV.