Optical anisotropy of copper dipivaloylmethanate molecular films

The structures of films obtained from a coordination compound, copper dipivaloylmethanate, and by vacuum vapor deposition onto single crystal silicon substrates are studied. The size of crystals constituting films and intercrystal distances are microscopically estimated with the help of optical and scanning electron microscopes. The refractive index distribution along the film thickness and the optical anisotropy of films are determined by monochromatic zero ellipsometry. The optical anisotropy of films is shown to correlate with the surface morphology.     

A Sharp Condition for Scattering of the Radial 3D Cubic Nonlinear Schrödinger Equation

We consider the problem of identifying sharp criteria under which radial H ¹ (finite energy) solutions to the focusing 3d cubic nonlinear Schrödinger equation (NLS) i? _t u + Δu + |u|² u = 0 scatter, i.e., approach the solution to a linear Schrödinger equation as t → ±∞. The criteria is expressed in terms of the scale-invariant quantities ${\|u_0\|_{L^2}\|\nabla u_0\|_{L^2}}We consider the problem of identifying sharp criteria under which radial H ¹ (finite energy) solutions to the focusing 3d cubic nonlinear Schr?dinger equation (NLS) i∂ _t u + Δu + |u|² u = 0 scatter, i.e., approach the solution to a linear Schr?dinger equation as t → ±∞. The criteria is expressed in terms of the scale-invariant quantities and M[u]E[u], where u ₀ denotes the initial data, and M[u] and E[u] denote the (conserved in time) mass and energy of the corresponding solution u(t). The focusing NLS possesses a soliton solution e ^it Q(x), where Q is the ground-state solution to a nonlinear elliptic equation, and we prove that if M[u]E[u] < M[Q]E[Q] and , then the solution u(t) is globally well-posed and scatters. This condition is sharp in the sense that the soliton solution e ^it Q(x), for which equality in these conditions is obtained, is global but does not scatter. We further show that if M[u]E[u] < M[Q]E[Q] and , then the solution blows-up in finite time. The technique employed is parallel to that employed by Kenig-Merle [17] in their study of the energy-critical NLS.     

Synthesis of New Calix[4]arenes Functionalizated by Acetylhydrazide Groups

A series of new calix[4]phenols, calix[4]resorcinols and calix[4]pyrogallols with acetylhydrazide substitutes has been␣synthesized with high yields by hydrazinolysis of ester group containing calix[4]arenes. The synthesized calix[4]phenols adopt the cone conformation while the calix[4]resorcinol and calix[4]pyrogallol derivatives prefer the boat conformation. The amide fragment of the hydrazide groups predominantly exists in the trans-conformation. The binding ability of synthesized calix[4]arenes toward transition and alkali metals by solvent extraction has been investigated.     

Structure and magnetotransport properties of the new quasi-two-dimensional molecular metal β″-(BEDT-TTF)4H3O[Fe(C2O4)3] · C6H4Cl2

The β″-(BEDT-TTF)₄A^I[M^III(C₂O₄)₃] · G(A^I=NH ₄ ⁺ , H₃O⁺, K⁺, Rb⁺; M^III=Fe, Cr; G = “guest” solvent molecule) family of layered molecular conductors with magnetic metal oxalate anions exhibits a pronounced dependence of the conducting properties on the type of neutral solvent molecules introduced into the complex anion layer. A new organic dichlorobenzene (C₆H₄Cl₂)-containing conductor of this family, namely, β″-(BEDT-TTF)₄H₃O[Fe(C₂O₄)₃] · C₆H₄Cl₂, is synthesized. The structure of the synthesized single crystals studied by X-ray diffraction is characterized by the following parameters: a = 10.421(1) Å, b= 19.991(2) Å, c= 35.441(3) Å, β = 92.87(1)°, V= 7374(1) ų, space groupC2/c, and Z = 4. In the temperature range 0.5&;2-300 K, the conductivity of the crystals is metallic without changing into a superconducting state. The magnetotransport properties of the crystals are examined in magnetic fields up to 17 T at T = 0.5 K. In fields higher than 10 T, Shubnikov-de Haas oscillations are detected, and the Fourier spectrum of these oscillations contains two frequencies with maximum amplitudes of about 80 and 375 T. The experimental results are compared with the related data obtained for other phases of this family. The possible structural mechanisms of the effect of a guest solvent molecule on the transport properties of the β″-(BEDT-TTF)₄A^I[M^III(C₂O₄)₃] · G crystals are analyzed.     

Magnetic Field Effect in the Reaction of Recombination of Nitric Oxide and Superoxide Anion

Using a static magnetic field, we observed an important biological radical, nitric oxide, in solution by a spin-sensitive technique. Decomposition of 3-morpholinosydnonimine (SIN-1) in aqueous solution produces a radical pair consisting of nitric oxide and the superoxide anion which recombine to form peroxynitrite. The creation of this radical pair provides a favorable setting for the observation of magnetic field effects. Magnetic field effect of (1.8 ± 0.5)% on the yield of recombination was observed in a relatively high field of 4.7 T over the sampling of 96 samples. The effect is limited by extremely fast relaxation of nitric oxide in liquids due to unquenched orbital angular momentum, and develops in f-pairs via the Δg mechanism. Magnetic field effect due to a radical pair involving nitric oxide in a biological system would require either rather strong magnetic fields in the tesla range or an internal enhancer of magnetic field.     

Ideal‐Filter Capillary Electrophoresis (IFCE) Facilitates the One‐Step Selection of Aptamers

Selection of aptamers from oligonucleotide libraries currently requires multiple rounds of alternating steps of partitioning of binders from nonbinders and enzymatic amplification of all collected oligonucleotides. Herein, we report a highly practical solution for reliable one‐step selection of aptamers. We introduce partitioning by ideal‐filter capillary electrophoresis (IFCE) in which binders and nonbinders move in the opposite directions. The efficiency of IFCE‐based partitioning reaches 10⁹, which is ten million times higher than that of typical solid‐phase partitioning methods. One step of IFCE‐based partitioning is sufficient for the selection of a high‐affinity aptamer pool for a protein target. Partitioning by IFCE promises to become an indispensable tool for fast and robust selection of binders from different types of oligonucleotide libraries.     

Atomic H over plane: Effective potential and level reconstruction

The behavior of atomic H in a semi-bounded space z ≥ 0 with the condition of “not going through” the boundary (the surface z = 0) for the electronic wavefunction (WF) is considered. It is shown that in a wide range of “not going through” condition parameters the effective atomic potential, treated as a function of the distance h from H to the boundary plane, reveals a well pronounced minimum at certain finite but nonzero h, which describes the mode of “soaring” of the atom above the plane. In particular cases of Dirichlet and Neumann conditions, the analysis of the soaring effect is based on the exact analytical solutions of the problem in terms of generalized spheroidal Coulomb functions. For h varying between the regions h ≫ a_B and h ≪ a_B, both the deformation of the electronic WF and the atomic state are studied in detail. For a more general case of Robin (third type) condition, the variational estimates and direct numerical tools are used. By means of the latter it is also shown that in the case of a sufficiently large positive affinity of the atom to the boundary plane a significant reconstruction of the lowest levels takes place, including the change of both the asymptotics and the general dependence on h.     

Diastereoselective heterocyclization of geminal bromo-fluoro arylcyclopropanes by nitrosonium tetrafluoroborate: Access to 4-fluorinated isoxazolines and isoxazoles

A series of 5-aryl-4-bromo-4-fluoroisoxazolines was synthesized via nitrosation of 2-aryl-1-bromo-1-fluorocyclopropanes with NOBF₄. It was shown that the E-isomers of the cyclopropanes react highly regio- and diastereoselectively leading exclusively to the E-isomers of the isoxazolines. The obtained 5-aryl-4-bromo-4-fluoroisoxazolines were transformed selectively into the corresponding 5-aryl-4-fluoro- or 5-aryl-4-bromoisoxazoles in good yields in the reaction with Lewis acids.     

Synthesis of a novel family of water-soluble 2H,3H-[1,3]thia- and -selenazolo[3,2-a]pyridin-4-ium heterocycles by annulation reactions

Regioselective synthesis of a novel family of water-soluble 2H,3H-[1,3]chalcogenazolo[3,2-a]pyridin-4-ium derivatives was developed based on 2-pyridinesulfenyl and -selenenyl halides and unsaturated compounds. The annulation reactions with divinyl sulfide, selenide and N-vinylpyrrolidin-2-one led to addition of the chalcogen atom to the terminal carbon of the double bond whereas the reaction with tetravinylsilane proceeded with opposite regiochemistry. Tricyclic condensed heterocycles were obtained from 2,3-dihydrofuran and cycloalkenes. The products represent novel promising scaffolds for organic synthesis and possible drug discovery.     

Bifurcation in reflection spectra of holographic diffraction grating recorded on dicromated pullulan

Volume diffraction gratings were created holographically on a dichromated pullulan (polysaccharide doped with chromium). Specific and very rare multi-peak structure in the reflection spectra is observed. It was found that multiple peaks are consequence of non-ideal structure of volume diffraction grating. Theoretical analysis and numerical simulations confirm that the observed behavior arise from a slight randomness of grating parameters: refractive index, grating period, film thickness. The results of calculation are in agreement with experimental results.