Reznikov A.N.,Samara State Technical University |
Sibiryakova A.E.,Samara State Technical University |
Rybakov V.B.,Moscow State UniversityMoscow |
Klimochkin Y.N.,Samara State Technical University
Tetrahedron Asymmetry | Year: 2015
Transition metal catalyzed asymmetric Michael additions of dimethyl (2-oxo-2-phenylethyl)phosphonate to a variety of aromatic nitroalkenes have been developed. The effects of ligand structure, metal ions, and solvent on the reaction are described. Ni(II)-bis[(1R,2R)-N,N′-dibenzylcyclohexane-1,2-diamine]Br2 was found to be an effective catalyst for this reaction. The corresponding adducts were obtained in the presence of this complex in good yields and with excellent enantioselectivity (up to 99% ee). The absolute configurations of the reaction products were determined by X-ray diffraction. © 2015 Elsevier Ltd.
Korchagina E.V.,University of Montreal |
Philippova O.E.,Moscow State UniversityMoscow
Macromolecules | Year: 2015
The effect of two monovalent salts differing in the anions (sodium acetate and sodium chloride) on intermolecular aggregation of fully protonated hydrophobically modified (HM) chitosan in dilute aqueous solutions was studied by light scattering. It was demonstrated that both salts promote the aggregation of similarly charged macromolecules. At the same time, strong ion specificity is observed: acetate ions induce the growth of the aggregates, whereas chloride ions increase the fraction of aggregated chains. The behavior observed was attributed to different mechanisms of interactions of these ions with HM chitosan. Acetate ions possessing higher affinity to chitosan involving electrostatic and hydrophobic interactions as well as hydrogen bonding screen more effectively the electrostatic repulsion between polycationic chains, which allows accommodating more macromolecules within one aggregate. On the other hand, more compact chloride ions seem to promote the formation of crystalline zones within the aggregates, thereby increasing the association energy in the system. This provides a higher fraction of associated chains, whereas keeping a small aggregation number, because large amount of macromolecules in one aggregate can hinder sterically a proper mutual arrangement of the chains necessary for the formation of crystallites. © 2015 American Chemical Society.
Abramovich A.I.,Moscow State UniversityMoscow |
Lanshina L.V.,Moscow State UniversityMoscow
Russian Journal of Physical Chemistry A | Year: 2015
Abstract The curve of the concentration dependence of the total molecular light scattering coefficient of xC3H7OH-(1 - x)H2O solutions showed two sharp maxima (at x = 0.04 and 0.09) and a minimum at x = 0.06 mole fractions, suggesting a considerable rearrangement of the structure of the solutions near these concentrations. The concentration dependences of excess molar volume, adiabatic compressibility, and molar refraction showed negative deviations from the ideal with a minimum in the range x = 0.18-0.3. The structure of water was assumed to undergo a rearrangement at x = 0.04 accompanied by structural fluctuations, which dispersed at 0.04 < x < 0.06. At x = 0.06, associates of isopropanol molecules started to form, whose number and size increased linearly up to x = 0.13. In the 0.13 < x < 0.35 concentration range, some kind of an aqueous alcohol emulsion containing pure alcohol "nanodrops" formed and the solutions became microheterogeneous. © 2015 Pleiades Publishing, Ltd.
Cabaret J.,University of Maine, France |
Bequin P.,University of Maine, France |
Theocharis G.,University of Maine, France |
Andreev V.,Moscow State UniversityMoscow |
And 2 more authors.
Physical Review Letters | Year: 2015
We theoretically study and experimentally report the propagation of nonlinear hysteretic torsional pulses in a vertical granular chain made of cm-scale, self-hanged magnetic beads. As predicted by contact mechanics, the torsional coupling between two beads is found to be nonlinear hysteretic. This results in a nonlinear pulse distortion essentially different from the distortion predicted by classical nonlinearities and in a complex dynamic response depending on the history of the wave particle angular velocity. Both are consistent with the predictions of purely hysteretic nonlinear elasticity and the Preisach-Mayergoyz hysteresis model, providing the opportunity to study the phenomenon of nonlinear dynamic hysteresis in the absence of other types of material nonlinearities. The proposed configuration reveals a plethora of interesting phenomena including giant amplitude-dependent attenuation, short-term memory, as well as dispersive properties. Thus, it could find interesting applications in nonlinear wave control devices such as strong amplitude-dependent filters. © 2015 American Physical Society.
Rybakov A.A.,Moscow State UniversityMoscow |
Larin A.V.,Moscow State UniversityMoscow
Molecular Physics | Year: 2016
Microstructure factor (MF) is one of the most important properties of hydrogenated silicon (HS) used in industry. It is expressed via vibrational intensities of low stretching modes (LSM) of Si–H and high stretching modes (HSM) of SiH2/SiH3 bonds, i.e. MF = IHSM/(ILSM + IHSM). Mixed character of HSM due to Si–H contributions (together with SiH2/SiH3 ones) is confirmed by vibrational analysis of Si–H valence bonds in a 120Si:18H model of amorphous HS at the Perdew-Burke-Ernzerhof (PBE)/projector augmented wave (PAW)level. Comparison with precedent solutions for di- and poly-vacancies in microcrystalline HS shows that the redistribution of its Si–H modes between HSM and LSM bands depends on the extent of perturbation of the vacancies. This relation between the HSM/LSM repartition and HS distortion explains possible MF dependence from short or medium range ordering and its link with crystallisation kinetics. © 2016 Informa UK Limited, trading as Taylor & Francis Group.