Reconformation of polyvinylamine adsorbed on glass fibers

Surface area exclusion chromatography was used to investigate the reconformation of fully hydrolyzed polyvinylamine. The polymer is adsorbed on stacked glass fiber filters constituting the stationary phase while the polymer solution is injected at the inlet of the chromatography column. From numerical simulation and experimental chromatograms of nonreconforming polyelectrolytes, the amount of polymer adsorbed per filter represented as a function of the filter position along the column (the histogram) was determined to be continuously decreasing and not to depend on the rate of elution. For polyvinylamine, the histograms are peaked and the height of the peak was determined to depend greatly on the rate of polymer supply to the column that was controlled by monitoring the polymer concentration and/or the rate of elution (mass-transfer-controlled adsorption). Modifications in the adsorption on the successive filters were converted into changes in the interfacial area of adsorbed molecules taking into account model histograms as well as experimental adsorption histograms of non reconforming systems. Macromolecule concentration in the mobile phase and contact time between solute and adsorbed molecules were determined to be the two parameters controlling the extent of polymer desorption. The unusual shape of the histogram thus was attributed to reconformation of the adsorbed polymer, which was stimulated by interfacial exchange between segments belonging to trains of adsorbed macromolecules and chain segments of solute ones.     

Investigation of the asymmetric ionic Diels-Alder reaction for the synthesis of cis-decalins

The ionic Diels-Alder reaction, whereby an alpha,beta-unsaturated acetal in combination with a Lewis or Bronsted acid forms an equilibrium concentration of an activated dienophile, has been developed to provide an enantioselective synthesis of cis-decalins. Cyclohex-2-enone type chiral acetals of (2R,3R)-butane-2,3-diol have been screened against Lewis and Br?nsted acids with a variety of dienes and are efficient for the synthesis of a limited subset of cis-decalin structures. Diastereoselectivities of 73% and 82% have been found for the asymmetric ionic Diels-Alder reaction between the chiral acetal derivatives of cyclohex-2-enone (6) and 2-methylcyclohex-2-enone (18) with 2,3-dimethyl-1,3-butadiene (7). Terminal substituents on the diene partner in general render the system unreactive. However a synthetically useful cis-decalin 31, derived from the reaction of 2-methylcyclohex-2-enone and Z-3-t-butyldimethyl-silyloxypenta-1,3-diene has been prepared in enantiomerically pure form in 74% isolated yield using this asymmetric ionic Diels-Alder protocol.     

Synthesis and structure of [(Sn(mu-PCy))3(Na x PMDETA)2], containing an electron-deficient [(Sn(mu-PCy))3]2- dianion

The reaction of CyPHNa with Sn(NMe2)2 in the presence of PMDETA (= (Me2NCH2CH2)2NMe) gives the title compound [(Sn(mu-PCy))3(Na x PMDETA)2] (1), containing an electron-deficient [(Sn(mu-PCy))]3(2-) dianion with a novel two-electron, three centre (2e-3c) bonding arrangement.     

New dicationic porphyrin ligands suited for intercalation into B-form DNA

This paper describes the synthesis and characterization of a new series of sterically nondemanding, dicationic porphyrins that exhibit novel DNA-binding interactions. Cationic porphyrins continue to be the focus of a great deal of effort because of the promise they have for use in photodynamic, antiviral, and anticancer therapies. The systems explored here include 5,15-di(N-methylpyridinium-4-yl)porphyrin (H2D4), 5,15-di(N-methylpyridinium-3-yl)porphyrin (H2D3), and 5,15-di(N-methylpyridinium-2-yl)porphyrin (H2D2), as well as Zn(D4) and Zn(D3), the zinc(II)-containing derivatives of H2D4 and H2D3, respectively. Viscometry studies, in conjunction with various spectroscopic techniques, reveal the nature of the adducts formed with DNA. Irrespective of the base composition, H2D4 and H2D3 bind to DNA by intercalation. The zinc derivatives Zn(D4) and Zn(D3) are also intercalators; however, the binding constants are smaller because uptake requires the loss of an axial ligand. The decisive roles that steric factors and structural rigidity play in shaping the adducts with DNA become clear. Sequences that contain mainly adenine-thymine base pairs easily depart from the canonical B-form DNA structure and generally accommodate bulky porphyrins in external binding sites. However, with the H2D3 and H2D4 systems, the steric requirements are so minimal that intercalation becomes the preferred mode of binding, even in [poly(dA-dT)]2. The intercalated form of the H2D2 isomer is less stable, probably because of frontal strain associated with the (N-methyl)pyridinium-2-yl groups. A qualitative energy-level diagram is useful for assessing the forces that influence binding and could guide the design of new porphyrin ligands.     

Electron ionization mass spectra and their reproducibility for trialkylsilylated derivatives of organic acids, sugars and alcohols

Mass spectra of trialkylsilyl derivatives of fatty acids, dicarboxylic acids, hydroxyacids, oxoacids, sugars, amino acids and alcohols were obtained. Amino acids were analyzed as tert-butyldimethylsilyl derivatives; all other model compounds were analyzed as trimethylsilyl derivatives. Reproducibility of the electron ionization (EI) mass spectra for the derivatives obtained was discussed. It was shown that, for many investigated derivatives, composition of the respective mass spectra depended greatly on ion source contamination. The trimethylsilylated alpha-tocopherol mass spectrum composition was most significantly influenced by ion source contamination. This compound can be used to test ion source contamination.     

Synthesis of a new polyfluorinated vinylogue of tetrathiafulvalene through 1,3-dipolar cycloaddition of ethyl beta-bromoperfluorodithiocrotonate with dimethyl acetylenedicarboxylate

The ethyl ester of beta-bromoperfluorodithiocrotonic acid reacts with dimethyl acetylenedicarboxylate to give 1,4-difluoro-2,3-bis(trifluoromethyl)-but-2-ene-1,4-diylidene-2,2'-bis(4',5'-dicarbomethoxy-1',3'-dithiole) (4), a new type of vinylogue of tetrathiafulvalene. The thermal transformations of this compound lead, depending on the temperature, to the formation of the cyclization products: 11,14-difluoro-2,3,8,9-tetra(carbomethoxy)-12,13-bis(trifluoromethyl)-1,4,7,10-tetrathiadispiro[4.0.4.4]tetradeca-2,8,11,13-tetraene (8) or 5,8-difluoro-6,7-bis(trifluoromethyl)-2,3-bis(carboxymethyl)-1,4-benzodithiine (11).     

Basicity and mechanism of transmission of electronic effects of substituents in the series of 2-amino-5-aryl-1,3,4-thiadiazoles

The basicity of 2-amino-5-aryl-1,3,4-thiadiazoles was studied. A correlation was obtained between the pK_BH+ values of the compounds and the constants of the substituents. It was shown that the electronic effects of the substituents in the phenyl ring are transmitted both on account of conjugation and by an induction mechanism.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 267–270, February, 1987.     

Intramolecular Cyclizations of Allenic Acylureas and -Amides

Allenic acids are found to add to dicyclohexylcarbodiimide affording, in the presence of Et₂NH, the 4H-1,3-oxazin-4-ones 5 via 4 . Under neutral conditions, they add to diaryl- or pyridyl(cyclohexyl)carbodiimides and triphenylketene imine to give the corresponding tricyclo[5.2.2.0^1,5]undeca-4,8,10-trien-3-ones 7 , 8 , 9 , and 12 . The allenic phenyl ester 13a dimerises, on heating in a [2+2] head-to-head fashion, to 14 but fails to undergo intramolecular Diels-Alder cyclization, to 15 .     

Combining Deep Eutectic Solvents with TEMPO-based Polymer Electrodes: Influence of Molar Ratio on Electrode Performance**

For sustainable energy storage, all-organic batteries based on redox-active polymers promise to become an alternative to lithium ion batteries. Yet, polymers contribute to the goal of an all-organic cell as electrodes or as solid electrolytes. Here, we replace the electrolyte with a deep eutectic solvent (DES) composed of sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) and N-methylacetamide (NMA), while using poly(2,2,6,6-tetramethylpiperidin-1-yl-oxyl methacrylate) (PTMA) as cathode. The successful combination of a DES with a polymer electrode is reported here for the first time. The electrochemical stability of PTMA electrodes in the DES at the eutectic molar ratio of 1 : 6 is comparable to conventional battery electrolytes. More viscous electrolytes with higher salt concentration can hinder cycling at high rates. Lower salt concentration leads to decreasing capacities and faster decomposition. The eutectic mixture of 1 : 6 is best suited uniting high stability and moderate viscosity.     

Spectral Photoluminescent Parameters of Barley Seeds (Hordéum vulgáre) Infected with Fusarium ssp

We needed effective and sustainable technologies for better microbiological control of crops, including Fusarium. However, photoluminescent UV–Vis methods are potential for diagnosing plant diseases with Fusarium. It has not been sufficiently studied despite the application of these methods for other biological researches. The excitation spectrum of the seeds during infection shifts to the shorter wavelength and a new maximum appears in the region λ ≈ 232 nm. The photoluminescence of infected seeds increases with excitation by radiation of wavelengths λ_e,1 = 232 nm, λ_e,2 = 362 nm and λ_e,3 = 424 nm by 1.33–3.14 times, and λ_e,3 = 424 nm—decreases by 1.1 times. Statistical moments μ₃ and μ₄, asymmetry and kurtosis change only with short-wave excitation. When analyzing the decomposition of the frequency spectrum into Gaussian curves, the most informative ratio is the ratio of right-handed and left-handed Gaussians under excitation λ_e,2 = 362 nm and λ_e,3 = 424 nm. The ratios of their maxima change during infection by 1.36–3.2 times, and for excitation by radiation λ_e,2, the frequency boundaries of Gaussians change. The results of measurements and calculations provide a basis for the development of a method and device for photoluminescence diagnostics of fusarium seeds in UV–Vis ranges.