Electrodes of strongly nitrogenated nanocrystalline diamond

Electrochemical behavior of nanocrystalline diamond films grown in microwave plasma initiated in Ar-CH₄-H₂-N₂ mixtures containing 30 to 90 vol % N₂ is studied. Thin-film nanocrystalline-diamond electrodes grown at this high (30 to 90 vol %) N₂ content in reactor behave as nearly metal-like: reaction in the [Fe(CN)₆]^3−/4− redox couple proceeds in a reversible manner. Generally, with the increasing of the N₂ content in the reactor the electrochemical behavior of a “poor conductor” gives place to the metal-like one; in a sense, the material’s electrochemical activity saturates and does not change beyond some critical value of the N₂ content (∼30 vol %). This conclusion is substantiated by the study of Raman spectra of the nanocrystalline diamond films: at this N₂ content the diamond-graphite structure of the material is stabilized.     

Electrochemical behavior of nitrogenated nanocrystalline diamond electrodes

Nitrogenated nanocrystalline diamond films with controlled conductivity are deposited from microwave plasma in CH₄-Ar-H₂-N₂ gas mixtures. They are characterized using atomic force microscopy, Raman spectroscopy, and electrophysical measurements. Their electrochemical properties are studied by cyclic voltammetry and electrochemical impedance spectroscopy. Kinetic parameters of reactions in [Fe(CN)₆]^3-/4- redox system are determined. The character of electrode behavior is controlled by the degree on nitrogenation. With the increasing of the nitrogen content in the reaction gas mixture (from 0 to 25%), the potential window somewhat narrows, the background current increases, the reversibility of reactions in the [Fe(CN)₆]^3-/4- redox system increases. By and large, the transition occurs from the electrochemical behavior of a “poor conductor” to that of a metal-like electrode.     

New nitrogenated siloxy butadienes from 1,3-dichloroacetone

New 1-formamido-2-siloxy-1,3-butadienes have been generated from 1,3-dichloroacetone by means of phosphorane formation, formamido substitution, Wittig olefination and silylation. The procedure demonstrates the utility and versatility of this methodology for the formation of polysubstituted dienes, designed as useful building blocks for the synthesis of polycyclic alkaloids and related analogues.     

Expeditious synthesis of nitrogenated spongianes: 4-methyldecarboxyspongolactams

Herein, the synthesis of 4-methyldecarboxyhaumanamide (9) and 4-methyldecarboxyspongolactams A (11) and C (13) is presented. (−)-Sclareol is the starting material and the chloroderivative 7 is the common intermediate. Moreover, this synthesis represents a new strategy for the preparation of pyrrolinones.     

PECVD of amorphous hydrogenated oxygenated nitrogenated carbon films

An actinometric optical emission spectroscopy (AOES) study of the trends in the concentrations of the plasma species H, CH, CO, OH, and CN in film-producing glow discharges of mixtures of isopropanol and nitrogen was undertaken. Conventional AOES was used to obtain the trends in the plasma concentrations of these species as a function of the proportion of nitrogen in the feed, R_n. A dynamic variant of actinometry in which trends in the concentrations of plasma species are measured as a function of time following the cutting of one of the principal gas flows was also employed to investigate the relative importance of gas phase and plasma/polymer–surface interactions in the production of the species of interest. Each of the above-mentioned species is produced, to some degree, by plasma/polymer–surface reactions. As revealed by transmission infrared spectroscopy, the films deposited contain C H, CO, and O H groups. For R_n > 0, the films become nitrogenated, with both N H and CN groups being present. As revealed by transmission ultraviolet-visible spectroscopy, both the optical gap and the refractive index of the deposited films decrease as R_n is increased. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1881–1888, 1998     

Mobile gamma-irradiation robot

The source container with 98 TBq of ¹³⁷Cs and shielding made from depleted uranium has the total weight of 264 kg, height of 0.370 and diameter 0.272 m. The container is joined to accessories allowing movment of the radiation beam. The dose rate at a distance of 0.4 m in the beam axis is 50 Gy/h. Various technical means are available for manipulation and transport. The irradiation process proceeds according to a precalculated program.The safety measures have been taken to secure the possible application in historical buildings and similar objects. The licence from health physics authorities has been obtained. The first irradiation process performed is described.     

Features of Behavior of Isotactic Polypropylene Films upon Pervaporation

The most important aspects of the large-tonnage synthesis of isotactic polypropylene represent a commercial secret. After polypropylene synthesis is completed, catalysts and other substances involved in the formation of the final product pass into the category of worthless and unknown impurities. This circumstance determines the peculiarities and difficulties of studying the behavior of impurities in polypropylene films. In this paper, the interaction of hydrophobic and hydrophilic probe liquids with polypropylene films (membranes) containing such impurities has been studied using pervaporation at different temperatures. The supramolecular structure of the polypropylene films has been successively modified by one- and two-sided hexane sorption. This procedure has decreased the apparent activation energy of permeability during pervaporation of water and acetone. It has been shown that, in the long run, the transmembrane convective pervaporation stream of acetone displaces hydrophobic and hydrophilic impurities from the polypropylene films.     

New approaches to the synthesis of organofluorine nitrogenated derivatives

Fluorinated carboxylic acids are valuable building blocks for several types of organofluorine nitrogenated derivatives. In this review paper, several strategies that use these compounds as starting materials are described. First, fluorinated seven-membered cyclic β-amino esters can be diastereoselectively synthesized from these compounds with a ring-closing metathesis (RCM) reaction as the key step. The use of the RCM reaction in a different approach enables the preparation of fluorinated cyclic α-amino acid derivatives. Fluorinated carboxylic acids also constitute the starting material for the asymmetric synthesis of fluorinated allylic amines. Finally, a solution and solid-phase synthesis of fluorinated uracils and thiouracils is described.     

Three different tyrosyl radicals identified in L-tyrosine HCl crystals upon gamma-irradiation: magnetic characterization and temporal evolution

High-frequency electron paramagnetic resonance (EPR) and X-band electron-nuclear double resonance (ENDOR) spectroscopies were used to investigate the effect of gamma-irradiation on single crystals of L-tyrosine hydrochloride at room temperature. The oxidation product is the tyrosyl radical formed by hydrogen abstraction from the phenolic group; interestingly, on freshly irradiated crystals, two tyrosyl radicals were identified, characterized by slightly different magnetic parameters. In particular, one of the two radicals, with a gxx value of 2.00621, has its phenoxyl oxygen strongly hydrogen-bonded to one or more donors; to our knowledge, this is the lower gxx value reported for tyrosyl radicals. These two oxidation radicals are found to evolve very slowly to a third, single more stable radical conformation. To interpret the experimental data, a possible molecular scenario is presented, where the process of radical formation can be seen as a hydrogen atom transfer or a proton-coupled electron transfer. These processes seem to be controlled by the specific network of hydrogen-bond interactions present in the crystal. The results are discussed in relation to their relevance for the interpretation of EPR spectra of tyrosyl radicals in biological systems.     

Synthesis of a new nitrogenated drimane derivative with antifungal activity

Drimane sesquiterpenes are highly valuable due to their strong biological activity. In this work, we report the enhanced antifungal activity of 11-guanidinodrimene, a new compound derived from drimenol. The binding of the guanidine group at the C-11 carbon increased the antifungal activity when tested against Candida albicans, one of the most commonly found human pathogens.     

Ethylenebisdithiocarbamate fungicides

DTA curves were run for the ethylenebisdithiocarbamate fungicides maneb, mancozeb and zineb in a nitrogen atmosphere. Zineb produces a curve quite different from the others, with weak endothermic peaks at 166°C, 252°C and 293°C. Maneb and mancozeb have a relatively strong endothermic peak at 185–190°C corresponding to carbon disulphide evolution and a weaker endothemic peak at 290°C corresponding to hydrogen sulphide evolution. Maneb samples and some mancozeb samples also had a minor endothermic peak at 235°C, but this peak was lost after solvent extraction, which proved that it was due to an impurity or impurities. Elemental sulphur was found in the extract and on mixing sulphur with mancozeb, the peak at 235°C made its appearance. There is no distinguishing feature between the DTA curves for maneb and mancozeb. The shapes of the curves are, within experimental limits, indistinguishable, which means that the temperatures and energies of decomposition are the same. The chemist is left with the question whether differences in structure between maneb and mancozeb should lead to different DTA curves.     

Pork fat peroxidation by gamma-irradiation

In this paper, pork fat peroxidation by γ-irradiation and the possible effects of oxygen, UV-irradiation and storage after the γ-irradiation have been investigated. It has been found that the level of peroxides in irradiated pork increases linearly with the increasing absorbed dose. The chemical yield of peroxides formed in the irradiated fat is about 4.2 and independent on the sample temperature or absorbed dose rate, but dependent on storage time of sample before γ-irradiation. The irradiated pork exhibits some unusual features as following: 1) the peroxide content in irradiated pork is higher than that in unirradiated one; 2) the peroxide content in irradiated pork increases gradually on storage and is essentially constant in unirradiated one, which is very useful for the detection of irradiated pork; 3) the further peroxidation in irradiated pork is much more susceptible to UV radiation than that in unirradiated pork.     

Autophobic dewetting of Z-tetraol perfluoropolyether lubricant films on the amorphous nitrogenated carbon surface

The thermodynamic stability of thin films of the perfluoropolyether (PFPE) Z-Tetraol, as a function of molecular weight, on amorphous nitrogenated carbon, CNx, is investigated. An optical surface analyzer is used to image the autophobic dewetting of the Z-Tetraol films. Film dewetting results when the PFPE film thickness applied to the CNx surface exceeds a critical value. This critical dewetting thickness is identified as the monolayer thickness of the adsorbed PFPE film via measurements of the changes in the surface energy as a function of lubricant film thickness. The observed dewetting coincides with the film thickness at which the disjoining pressure goes to zero. The critical dewetting thickness is dependent on the PFPE molecular weight.     

Synthesis and convenient functionalisation of pyridazinofurocoumarins: nitrogenated isosters of potent DNA inhibitors

Pyridazino[3,4-h]psoralens and pyridazino[3,4-j]angelicins are prepared in good yield from resorcinols through a direct, easy and generally applicable synthetic route. The key step in this route is the inverse electron-demand Diels-Alder reaction between linear or angular furocoumarins and 3,6-bis(methoxycarbonyl)-1,2,4,5-tetrazine to give the dicarboxymethylated tetracycles. The ester group in the peri position with respect to the oxygen in the furan ring can be regioselectively transformed to give primary or secondary amides. Similarly, the two ester groups in the tetracycle can be transformed in a high-efficiency process to give bis-amides that can be either symmetrical (from the same amine) or unsymmetrical (from two different amines).     

The stability of ultra-thin perfluoropolyether mixture films on the amorphous nitrogenated carbon surface

The thermodynamic stability of boundary lubricant films based upon mixtures of liquid perfluoropolyethers (PFPEs) is reported. Mixtures of A20H-2000 with Zdols 2000, 2500, and 4000 and Zdol-TX 2200 on amorphous carbon nitride films are investigated. An optical surface analyzer is used to image the autophobic dewetting of the mixture PFPE films. The critical dewetting thickness coincides with the monolayer thickness of the adsorbed mixture PFPE films as determined by the changes in the surface energy as a function of lubricant film thickness. The critical dewetting thickness varies linearly with mixture concentration.     

表面张力对PEO稀溶液粘度行为的影响

测定了不同分子量聚氧化乙烯(PEO)在水和苯溶剂中的粘度,发现在低浓度区PEO水溶液的比浓粘度出现负偏离, PEO苯溶液比浓粘度与浓度之间依旧满足线性关系.表面张力测定结果表明, PEO分子显著降低了水的表面张力,而苯的表面张力则不受影响.PEO水溶液和纯溶剂水表面张力的不同干扰了高分子溶液和溶剂在粘度计中流过时间的测量,导致低浓度区PEO水溶液比浓粘度出现负偏离.利用PEO水溶液和水表面张力测定结果,结合乌式粘度计的几何尺寸,定量分析了PEO水溶液和纯溶剂水表面张力的差异对粘度测量结果的影响,计算结果与实验结果基本相符.如果用PEO水溶液流过时间对浓度作图的外推值t0*计算相对粘度,可以完全消除PEO水溶液和水表面张力差异对粘度测量的影响.     

Optical Detection of Nonequilibrium Swelling Behavior of a Polymer Gel upon Solvent Substitution

We report a novel transient swelling and shrinking behavior of a thin poly(acrylamide)-based gel film upon solvent substitution between water and ethylene glycol. These size changes could be optically detected through a change in the Bragg diffraction wavelength for the colloidal crystal of charged polystyrene latex particles that was fixed in the gel. The transient size change that was observed in this study could not be explained on the basis of the equilibrium characteristics, but it was attributable to the transient variation of osmotic pressure in the gel.     

Behavior of CSTR upon fast external effects: Possibility of increasing average conversion

The objective of the work was to study the influence of external factors (changes in composition, load and temperature) on the regimes of heterogeneous catalytic reactors. As shown, a rather fast change in external parameters causes an internal reorganization of the CSTR thus leading to an increase in average conversion.

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Chiral separation of agricultural fungicides

Fungicides are very important and diverse environmental and agricultural concern species. Their determination in commercial formulations or environmental matrices, requires highly efficient, selective and sensitive methods. A significant number of these chemicals are chiral with the activity residing usually in one of the enantiomers. The different toxicological and degradation behavior observed in many cases for fungicide enantiomers, results in the need to investigate them separately. For this purpose, separation techniques such as GC, HPLC, supercritical fluid chromatography (SFC) and CE have widely been employed although, at present, HPLC still dominates chromatographic chiral analysis of fungicides. This review covers the literature concerning the enantiomeric separation of fungicides usually employed in agriculture grouping the chiral separation methodologies developed for their analysis in environmental, biological, and food samples.