On one class of three-webs with partially symmetric curvature tensor

A classification of six-dimensional webs H _s by type of the associated Lie algebra is carried out. Two approaches to the investigation of geometry of nontrivial class of webs H _s are considered.     

Homological determinacy of modules with torsion

The problem is solved of the homologlcal determinacy of modules with torsion over rings with a power basis.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova, Vol. 86, pp. 180–184, 1979.     

Study of reverse micelles of di-isobutyl-phenoxy-ethoxy-ethyl-dimethyl-benzyl ammonium methacrylate in benzene by nuclear magnetic resonance spectroscopy

(1)H NMR spectroscopy was used to investigate the aggregation of the surfactant di-isobutyl-phenoxy-ethoxy-ethyl-dimethyl-benzyl ammonium methacrylate (Hyamine-M) in benzene. Adding water makes swollen reverse micelles (microemulsion droplets). The droplets also contain cadmium ions and the sodium salt of the methacrylic acid. The critical micelle concentration of Hyamine-M was determined by NMR to be 3.95 mM under the current conditions. Two-dimensional NMR NOESY spectra were used to study the conformation of the surfactant in the micelle and the spatial localization of water and counterions. We found that the surfactant molecules are folded with both phenyl fragments oriented toward the micelle exterior and the oxyethylene and NCH(3) groups in the micelle core. The water molecules and counterions are distributed around the surfactant polar groups in the micelle interior and penetrate up to both aromatic rings. The investigated system can be further utilized as a microemulsion matrix for the synthesis of cadmium-containing semiconductor nanocrystals, eventually capped with a polymer shell, or of polymer nanoparticles.     

A novel reaction producing the rhodium(I) complexes with π-coordinated tetraphenylborate anion, (π-PhBPh3). X-ray study of [Rh(PPh3)2(π-PhBPh3)]

Treating the complexes [Rh(TFA)(PPh₃)₂], [Rh(HFA)(PPh₃)₂], and [Rh(TFA)(Cod)] (TFA - trifluoroacetylacetonate, HFA - hexafluoroacetylacetonate, Cod - 1,5 cyclooctadiene) with an excess of NaBPh₄ in acetonitrile yields the rhodium(I) complexes with coordinated [BPh₄]⁻ anion, [Rh(PPh₃)₂(π-PhBPh₃)] · 2MeCN (I) and [Rh(Cod)(π-PhBPh₃)] (II). The reactions present a new example of β-diketonate ligand replacement. The ¹H, ³¹P, and ¹¹B NMR spectra of I and II are discussed. [Rh(PPh₃)₂(π-PhBPh₃)] has been characterized by single crystal X-ray analysis.     

Synthesis of Cytotoxic 4-Sulfonyl-, 4-Sulfonylthio-and 4-Sulfothioazetidinones-2

4-Sulfonylazetidinones-2 were synthesized by the reaction of DBU and organic halides on the esters of penicillin sulfones. 4-Sulfonylthio- and 4-sulfothioazetindinones-2 were synthesized by nucleophilic substitution of the 2-benzothiazolylthio groups in 4-(benzothiazolylthio)azetidinones-2 using sodium sulfinates or sodium hydrogen sulfite. A study of their cytotoxic activities revealed the anticancer effect of compounds containing methylsulfonylthio-, 4-tolylsulfonylthio-, and 4-methoxycarbonylamino-phenylsulfonylthio-substituents at position 4 of the -lactam ring relative to a wide range of monolayer cultures of cancer cells in vitro.     

Synthesis and Cytotoxicity of Silyl- and Carbonyl-substituted Isoxazoles

We have obtained various diphenylmethylsilyl- and carbonyl-substituted isoxazoles by [2+3]-dipolar cycloaddition of nitrile oxides to diphenylmethylsilyl-, hydroxymethyl-, methoxymethyl-, and ethoxycarbonylacetylenes. We have observed that the isoxazoles obtained exhibit moderate cytotoxicity relative to the HT-1080 and MG-22A cell lines. The highest activity level is displayed by 3-methyl-5-diphenylmethylsilylisoxazole.     

Trans-3,4-diacetoxypiperidine as a model for novel pH-triggered conformational switches

An acid-induced conformational flip of trans-3,4-diacetoxy-1-benzylpiperidine has been determined by ¹H NMR. It occurs while the apparent pH (pD) of the d₄-methanol solution decreases from 6 to 3. Due to an intramolecular hydrogen bond, the conformer with axial position of both acetoxy groups becomes strongly predominant. The separation of the acetoxy groups increases drastically. Thus, in similar structures an incorporated trans-3,4-disubstituted piperidine moiety can serve as a conformational pH-trigger when equipped with substituents designed to perform certain geometry-dependent functions, for example, as cation chelators or as lipid tails. The power of this trigger was estimated as ∼10 kJ/mol.     

Integrating 31P DOSY NMR Spectroscopy and Molecular Mechanics as a Powerful Tool for Unraveling the Chemical Structures of Polyoxomolybdate‐Based Amphiphilic Nanohybrids in Aqueous Solution

Novel organic–inorganic hybrids of various sizes were generated by reaction of 1,8‐octanediphosphonic acid (ODP) and (NH₄)₆Mo₇O₂₄ in aqueous solution. The formation of rodlike hybrids with variable numbers of covalently bound ODP and polyoxomolybdate (POM) units can be tuned as a function of increasing (NH₄)₆Mo₇O₂₄ concentration at fixed ODP concentration. The chemical structure of the ODP/POM hybrids was characterized by ¹H, ³¹P, and ⁹⁵Mo NMR spectroscopy. Heteronuclear ³¹P DOSY (diffusion‐ ordered NMR spectroscopy) and molecular mechanics (MM) calculations were applied to determine the size and shape of the nanosized hybrids generated at various ODP/POM ratios. For this purpose, the structures of ODP/POM hybrids with variable numbers of ODP and POM units were optimized by MM and then approximated as cylinder‐shaped objects by using a recently described mathematical algorithm. The thus‐obtained cylinder length and diameter were further used to calculate the expected diffusion coefficients of the ODP/POM hybrids. Comparison of the calculated and experimentally determined diffusion coefficients led to the most probable ODP/POM hybrid length for each sample composition. The ³¹P DOSY results show that the length of the hybrids increases with increasing POM concentration and reaches a maximum corresponding to an average of 8 ODP/7 POM units per chain at a sample composition of 20 mM ODP and 14 mM POM. With excess POM, above the latter concentration, the formation of shorter‐chain hybrids terminated by Mo₇ clusters at one or both ends was evidenced on further increasing the POM concentration. The results demonstrate that the combination of ³¹P DOSY and MM, although virtually unexplored in POM chemistry, is a powerful innovative strategy for the detailed characterization of nanosized organic–inorganic POM‐based hybrids in solution.