Electrochemical Oxidation of Galenite in Carbonate Solutions

Linear voltammetry, X-ray phase and differential thermal analyses, diffuse reflection IR Fourier spectroscopy, Raman spectroscopy, and scanning electron microscopy (SEM) were used to study the electrochemical oxidation of galenite in carbonate electrolytes.     

Efficient synthesis of serically constrained smmetrically alpha,alpha-disubstituted alpha-amino acids under operationally convenient conditions

Homologation of the nucleophilic glycine equivalent Ni-Gly-PABP [Ni(II) complex of glycine Schiff base with 2-[N-(alpha-picolyl)amino]benzophenone (PABP)] 2 via alkyl halide alkylations and Michael addition reactions was systematically studied as a general method for preparing symmetrically alpha,alpha-disubstituted alpha-amino acids (sym-alpha,alpha-AA). The dialkylation reactions are conducted under operationally convenient conditions without recourse to inert atmosphere, dried solvents, and low temperatures, thus enjoying key advantages of the experimental simplicity and attractive cost structure. The method has been shown to be particularly successful for the dialkylation of complex 2 with activated and nonactivated alkyl halides, including propargyl derivatives, affording a generalized and practical access to the corresponding sym-alpha,alpha-AA. This study has also shown some limitation of the method, as it cannot be extended to alpha- or beta-branched alkyl halides or Michael acceptors to be used for the dialkylation of glycine equivalent 2. High chemical yields of the dialkylated products, combined with the simplicity of the experimental procedure, render this method worth immediate use for multigram scale preparation of the sym-alpha,alpha-AA.     

Synthesis and structures of molecular complexes of the cis-anti-cis diastereomer of dicyclohexano-18-crown-6 with o-nitroanilines

In the reaction of the cis-syn-cis and cis-anti-cis diastereomers of dicyclohexano-18-crown-6 with 2-nitro and 2,4-dinitroaniline crystalline complexes with a 1:2 stoichiometric composition were obtained only when the cis-anti-cis diastereomer was used. The three-dimensional structure of the complex of the cis-anti-cis diastereomer of dicyclohexano-18-crown-6 with 2,4-dinitroaniline was determined by an x-ray diffraction study. The complexing of o-nitroanilines with the cis-anti-cis diastereomer is explained by the topological conformity of the interacting compounds. The isolation of the individual cis diastereomers from the mixture of them formed as a result of the catalytic hydrogenation of dibenzo-18-crown-6 was accomplished by means of the selective formation of the crystalline complex of the cis-anti-cis diastereomer with 2-nitroaniline.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1190–1195, September, 1988.     

Fluorine addition to polychlorinated and polybrominated ethenes and arenes using vanadium pentafluoride

Reaction of vanadium pentafluoride with trichloroethene, tetrabromoethene, hexachlorobenzene, and octachloronaphthalene at −20 to 50 °C gave products from fluorine addition, CFCl₂CFClH, C₂Br₄F₂, C₆Cl₆F₆, and C₁₀Cl₈F₈, respectively. The fluorine addition to pentachloropyridine and hexabromobenzene was accompanied by the partial replacement of halogen atoms by fluorine and led to products C₅Cl₄F₅N and C₆Br₄F₈, respectively.     

Application of inorganic anionites as catalysts for oxyalkylation of alcohols

The low thermal stability of anion exchange resins, which prevents them from being used as catalysts for oxyalkylation of alcohols, can be solved by the application of the inorganic anionite — mercarbide, a promising catalyst.

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Reactions of ferrocene with phthalonitrile on the surface of oxide powders

The reaction of ferrocene with phthalonitrile at 200°C in a vacuum in the absence of solvents forms crystals of the monoclinic phthalocyanine β phase and ferrocene polymerization products. The use of oxide powders (SiO₂, V₂O₅) as a surface for the reaction of ferrocene with phthalonitrile makes it possible to obtain iron phthalocyanines. The samples of pure compounds and deposited phthalocyanine complexes were analyzed by electronic absorption and IR spectroscopy, and X-ray diffraction.     

1,2,5]Thiadiazolo[3,4-c][1,2,5]thiadiazolidyl: a long-lived radical anion and its stable salts

[1,2,5]Thiadiazolo[3,4-c][1,2,5]thiadiazole (1) is synthesized in 62% yield by fluoride ion-induced condensation of 3,4-difluoro-1,2,5-thiadiazole with (Me(3)SiN=)(2)S. The reversible electrochemical reduction of 1 leads to the long-lived [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazolidyl radical anion (2) and further to the dianion (3). The radical anion 2 is also obtained by the chemical reduction of the precursor 1 with t-BuOK in MeCN. The radical anion 2 is characterized by ESR spectroscopy in solution and in the crystalline state. The stable salts [K(18-crown-6)][2] and [K(18-crown-6)][2].MeCN (8 and 9, respectively) are isolated from the spontaneous decomposition of the [K(18-crown-6)][PhXNSN] (6, X = S; 7, X = Se) salts in MeCN solution followed by XRD characterization. The radical anion 2 acts as a bridging ligand in 8 and as chelating ligand in 9. The structural changes observed by XRD in going from 1 to 2 are explained by means of DFT/(U)B3LYP/6-311+G calculations.     

SDS-induced multi-stage unfolding of a small globular protein through different denatured states revealed by single-molecule fluorescence

Ionic surfactants such as sodium dodecyl sulfate (SDS) unfold proteins in a much more diverse yet effective way than chemical denaturants such as guanidium chloride (GdmCl). But how these unfolding processes compare on a molecular level is poorly understood. Here, we address this question by scrutinising the unfolding pathway of the globular protein S6 in SDS and GdmCl with single-molecule Förster resonance energy transfer (smFRET) spectroscopy. We show that the unfolding mechanism in SDS is strikingly different and convoluted in comparison to denaturation in GdmCl. In contrast to the reversible two-state unfolding behaviour in GdmCl characterised by kinetics on the timescale of seconds, SDS demonstrated not one, but four distinct regimes of interactions with S6, dependent on the surfactant concentration. At ≤1 mM SDS, S6 and surfactant molecules form quasi-micelles on a minute timescale; at millimolar [SDS], the protein denatures through an unfolded/denatured ensemble of highly heterogeneous states on a multi-second timescale; at tens of millimolar of SDS, the protein unfolds into a micelle-packed conformation on the second timescale; and >50 mM SDS, the protein unfolds with millisecond timescale dynamics. We propose a detailed model for multi-stage unfolding of S6 in SDS, which involves at least three different types of denatured states with different level of compactness and dynamics and a continually changing landscape of interactions between protein and surfactant. Our results highlight the great potential of single-molecule fluorescence as a direct probe of nanoscale protein structure and dynamics in chemically complex surfactant environments.

Multi-stage unfolding of S6 in SDS involving various types of denatured states with different levels of compactness and dynamics.     

Systematic control of nonlinear optical processes using optimally shaped femtosecond pulses.

This article reviews experimental efforts to control multiphoton transitions using shaped femtosecond laser pulses, and it lays out the systematic study being followed by us for elucidating the effect of phase on nonlinear optical laser-molecule interactions. Starting with a brief review of nonlinear optics and how nonlinear optical processes depend on the electric field inducing them, a number of conclusions can be drawn directly from analytical solutions of the equations. From a Taylor expansion of the phase in the frequency domain, we learn that nonlinear optical processes are affected only by the second- and higher-order terms. This simple result has significant implications on how pulse-shaping experiments are to be designed. If the phase is allowed to vary arbitrarily as a continuous function, then an infinite redundancy that arises from the addition of a linear phase function across the spectrum with arbitrary offset and slope could prevent us from carrying out a closed-loop optimization experiment. The early results illustrate how the outcome of a nonlinear optical transition depends on the cooperative action of all frequencies in the bandwidth of a laser pulse. Maximum constructive or destructive interference can be achieved by programming the phase using only two phase values, 0 and pi. This assertion has been confirmed experimentally, where binary phase shaping (BPS) was shown to outperform other alternative functions, sometimes by at least on order of magnitude, in controlling multiphoton processes. Here we discuss the solution of a number of nonlinear problems that range from narrowing the second harmonic spectrum of a laser pulse to optimizing the competition between two- and three-photon transitions. This Review explores some present and future applications of pulse shaping and coherent control.     

Isoxazolium enolates derived from α,β-unsaturated and 1,3-dicarbonyl compounds. The through-space effect of the enolate moiety on the chemical shift of α-protons

The reaction of 4-phenyl-3,5-dihydroxyisoxazole with α,β-unsaturated cyclic ketones and 1,3-cyclic diketones was studied. β-Substituted α,β-unsaturated ketones give pairs of isomeric isoxazolium enolates. The remarkable influence of the heterocyclic betaine on the proton chemical shifts is discussed. 1,3-Cyclic diketones reacted spontaneously with 4-phenyl-3,5-dihydroxyisoxazole yielding isoxazolium enolate enols and enol ethers.