Absorption and fluorescence spectra of hybrid silicon-organic materials in solutions and films

The spectroscopic characteristics of hybrid organic-inorganic films and solutions of ethoxysilicon-containing amidophosphate ligands in acetonitrile have been investigated. Inhomogeneous broadening of the absorption and fluorescence spectra which is characterized by the spectral dependence of the fluorescence and fluorescence excitation bands on the excitation and registration wavelength, respectively, is associated with the presence of a set of -(Si-O)_n- siloxane structures with various terminal fragments in both the films and solutions. The established general spectral rules are discussed with allowance for the characteristic features of the electronic structure of silicon-organic compounds containing an oxygen atom the unshared electron pair of which ensures the delocalization of the electron density over the siloxane chain.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, pp. 788–792, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Palladium(II) extraction by sulfur-containing calix[4,6]arenes from hydrochloric acid solutions

The comparison of the extraction properties of calixarenes, thiacalixarenes, and calix[4,6]arene thioethers showed that methyl(thiamethyl)calix[4,6]arenes 3a and 4a have the highest extraction abilities. These extractants rapidly and completely extract palladium from hydrochloric acid solutions; regarding distribution factors achieved in the kinetic mode, they three to four orders of magnitude exceed their monodentate analogue, octylbenzyl sulfide (OBnS). Approaches are considered to enhance palladium extraction via generating mixed palladium species in low-acidity solutions and via intramolecular catalysis by the protonated oxygen atoms of alkoxy groups in the lower rim. For 1 M HCl, the kinetic order of diluent effects on palladium extraction was established. The substitution of sulfur atoms for bridging CH₂ groups was discovered to enhance palladium extraction by calix[4]arene thioether 3c.     

Effect of colored noise on chains of chaotic oscillators

Equations that describe a ring system consisting of a closed circuit of n (n = 2, 3, 4, ...) unidirectionally coupled self-oscillation systems that exhibit chaotic dynamics are analyzed in the presence of external colored noise. For simplicity, detailed results of numerical calculations are presented for three oscillators. It is demonstrated that the external colored noise that is exerted upon partial oscillators of the ring system may facilitate the development of synchronous oscillations and reduce transient processes related to stabilization of chaotic synchronization. The effect is qualitatively interpreted. For comparison, numerical methods are employed to analyze the effect of external colored noise on an open circuit consisting of three oscillators.     

Ion-selective electrodes in titrations involving azo-coupling reactions

An organic cation-selective indicator electrode based on a PVC membrane plasticized with 2-nitrophenyl 2-ethylhexyl ether can be used in potentiometric titrations of aromatic hydroxy compounds, amines, and compounds containing active methylene groups, with 4-methyl-, 4-bromo-, or 4-nitro-benzenediazonium chloride solutions as titrants. Useful results were obtained in determinations of 16 passive components, including 2-naphthol, some 2-naphthol sulfonic acids, 8-quinolinol and its 5-sulfonic acid, ammo-1-naphthol-3-sulfonic acids, 1-naphthylamine sulfonic acids, resorcinol, 2,4-toluylenediamine, two acetanilide derivatives, and two substituted sulfophenyl pyrazolone derivatives. 4-Bromobenzenediazonium chloride proved to be the best titrant of the diazonium salts tested.     

Adaptation of the molecular imprinted polymers towards polar environment

A new simple method for the post-polymerisation treatment of molecularly imprinted polymers was proposed. A layer of mineral oil was deposited onto the surface of the polymer in order to create a hydrophobic environment in the binding sites and to improve the recognition properties of the polymer in polar solvents. The testing of polymers performed in acetonitrile showed that the modified polymers possessed significantly increased selectivity as compared with non-treated ones. The three-fold improvement of recognition of the template (cocaine) was achieved; the same time, for non-specific molecule (morphine) the improvement was only 1.3 times. The investigation of the stability of mineral oil coating on the polymer surface suggested that the effect produced is stable over a long period of time. This approach could be used to broaden the range of experimental conditions where molecularly imprinted polymers can perform successfully.     

On equilibria with participation of gold(I) complexes in sulfite-thiocarbamide media

The constants of protonation and sulfite ligand substitution by thiocarbamide for Au(SO₃) ₂ ^3? complex were determined. Mixed forms Autu(SO₃)^? and probably binuclear complex [Au₂tu₂SO₃] were shown to occur in noticeable concentrations in sulfite-thiocarbamide media in addition to Autu ₂ ⁺ and Au(SO₃) ₂ ^3? complex forms.     

Epitaxial assembly of graphene on face (0001) of silicon carbide: Modeling by semiempirical methods

The epitaxial growth of graphene on silicon face (0001) of silicon carbide is simulated using the semiempirical methods of quantum chemistry. The experimental conditions for the epitaxial growth of graphene on SiC, at which the probability of seams and similar defects appearing is reduced to a minimum, are formulated. Possible ways of the emergence of reconstructions of the singular carbon and silicon SiC faces during the synthesis of graphenes are investigated as a test of the approach’s efficiency. It is noted that simulation reproduces the reconstruction periods experimentally determined for both faces, and yields the most likely atomic arrangements in cases where the experimental formula of the superstructure allows different versions of such arrangements.     

Bio‐inspired Nonheme Iron Oxidation Catalysis: Involvement of Oxoiron(V) Oxidants in Cleaving Strong C−H Bonds

Nonheme iron enzymes generate powerful and versatile oxidants that perform a wide range of oxidation reactions, including the functionalization of inert C?H bonds, which is a major challenge for chemists. The oxidative abilities of these enzymes have inspired bioinorganic chemists to design synthetic models to mimic their ability to perform some of the most difficult oxidation reactions and study the mechanisms of such transformations. Iron‐oxygen intermediates like iron(III)‐hydroperoxo and high‐valent iron‐oxo species have been trapped and identified in investigations of these bio‐inspired catalytic systems, with the latter proposed to be the active oxidant for most of these systems. In this Review, we highlight the recent spectroscopic and mechanistic advances that have shed light on the various pathways that can be accessed by bio‐inspired nonheme iron systems to form the high‐valent iron‐oxo intermediates.     

Rhodium-Catalyzed Enantioselective Synthesis of Highly Fluorescent and CPL-Active Dispiroindeno[2,1-c]fluorenes

The enantioselective synthesis of chiral [7]-helical dispirodihydro[2,1-c]indenofluorenes (DSF-IFs) was achieved for the first time in good yields with high er values (er up to 99 : 1). The crucial step of the whole reaction sequence was the enantioselective intramolecular [2+2+2] cycloaddition of tethered triynediols to indenofluorenediols, which was catalyzed by a Rh/SEGPHOS® complex. Further transformations led to the corresponding DSF-IFs. The prepared helically chiral DSF-IFs combine circularly polarized luminescence (CPL) activity (g_lum=∼10⁻³) with exceptionally high fluorescence quantum yields (up to Φ_lum=0.97).     

Approximation of (ψ, β)-differentiable functions by Weierstrass integrals

We obtain asymptotic equalities for upper bounds of approximations of functions from the classes C _ψ ^{β, ∞} and L _ψ ^{β, 1} by Weierstrass integrals. __________ Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 59, No. 7, pp. 953–978, July, 2007.