Synthesis of a Pair of Derivatives of N-Methylpyrrole Polyamide

A pair of derivatives of tetrameric N-methylpyrrole polyamide were synthesized in order to develop a new method for the study of interaction of the polyamide derivatives with DNA. Indole acetic acid and nicotinic acid were introduced to the polyamide in the synthesized compound, which showed an expected red shift in the UV spectrum. These compounds may function as a potential tool in the detection of the polyamide binding to DNA.     

Study of Self-Ignition of PVC

The self-ignition of rigid PVC has been studied under static and dynamic conditions. Only a high-temperature boundary has been found, and the self-ignition temperature in air at atmospheric pressure lies between 555 and 560°C. The effect of preliminary HC1 evolution has been investigated, and it is shown that the more the HC1 evolution, the higher the self-ignition limit. It has been impossible to make polyacetylene ignite spontaneously in the presence of HC1 in oxygen up to 900° C. This is attributed to a special role of HC1 in combustion of PVC. The rate of HC1 release was measured by a potentiometric method, and the overall activation energy of the process was found to be 9.4 kcal/mole. This low value seems to be due to the presence of oxygen. Chromatographic analysis showed CH4 and CO to be the major gaseous products of oxidation of PVC in this parametric zone.     

Precision of Flash Pyrolysis-GC-MS Analysis: Experimental Evaluation of the Sources of Variability

The present study was carried out to evaluate the precision and to identify significant sources of variability in flash pyrolysis-GC-MS experiments. The analysis of variance has been applied to the example of polyethylene pyrolysis to estimate the impact of several controlled factors: sample handling, flash pyrolysis filament ageing and calibration. It was demonstrated that to get the best precision in experimental results, it is recommended to set the operator to reduce the impact of sample handling procedure and the filament to avoid variability due to changes in filament characteristics. In comparison, filament ageing and filament calibration are shown to influence in a limited extent the experimental results.     

Elucidation of the mechanism of redox grafting of diazotated anthraquinone

Redox grafting of aryldiazonium salts containing redox units may be used to form exceptionally thick covalently attached conducting films, even in the micrometers range, in a controlled manner on glassy carbon and gold substrates. With the objective to investigate the mechanism of this process in detail, 1-anthraquinone (AQ) redox units were immobilized on these substrates by electroreduction of 9,10-dioxo-9,10-dihydroanthracene-1-diazonium tetrafluoroborate. Electrochemical quartz crystal microbalance was employed to follow the grafting process during a cyclic voltammetric sweep by recording the frequency change. The redox grafting is shown to have two mass gain regions/phases: an irreversible one due to the addition of AQ units to the substrate/film and a reversible one due to the association of cations from the supporting electrolyte with the AQ radical anions formed during the sweeping process. Scanning electrochemical microscopy was used to study the relationship between the conductivity of the film and the charging level of the AQ redox units in the grafted film. For that purpose, approach curves were recorded at a platinum ultramicroelectrode for AQ-containing films on gold and glassy carbon surfaces using the ferro/ferricyanide redox system as redox probe. It is concluded that the film growth has its origin in electron transfer processes occurring through the layer mediated by the redox moieties embedded in the organic film.     

Effect of microwave pretreatment of coal for improvement of rheological characteristics of coal-water slurries

Indian high-ash coal contains alpha-silica components of the mineral matter. When coal is transported in the form of a slurry, alpha-silica adds to the settling properties of coal and enhances erosion of pipelines. As such any technique that will contribute to changing the characteristics of mineral matter by selective demineralization is bound to supplement the knowledge of coal slurries in the science of rheology. One such method is the use of a novel microwave technology, which changes the alpha-silica to less harmful beta-silica. Thus microwave-treated coal slurry facilitates enhanced flow characteristics and abates the erosion problem in pipeline transport as well as in coal-slurry injection furnaces. This paper reports on the rheological study of closely sized coal particles of medium-volatile, low-ash, low-moisture cleans and high-ash rejects with and without microwave treatment. Viscosity of suspensions of microwave-treated coal was found to be less than that of untreated coal, in the case of both cleans and rejects. Microwave pretreatment thus reduces the viscosity and the pumping cost and opens a new outlook for pipeline transport. An attempt has been made to quantify the improvement of rheological characteristics due to microwave pretreatment.     

Structural investigations of a series of petrified woods of different origin

Since the investigations on petrified wood performed so far have not proved the assumption that the ring structure is coupled to the changes in the crystalline form of silica, attention was paid to other possible reasons. Using small angle X-ray scattering methods we determined the Porod curves and pore size distributions for five different samples of petrified wood, of different origin. We observed clear porosity differences in different samples. In addition, the normal X-ray diffractometric measurements were carried out, which gave a totally uniform image of the crystallographic structure of all the samples. All of them were made of pure α-quartz. The differentiation of rings in dark and bright zones should be put down to the changes in porosity rather than to other factors. The pores seem to be much more concentrated in those ring locations, which correspond to the original dark wood positions in living wood.     

Formation of ring-shaped deposits as a result of evaporating droplets of dispersions of silver nanoparticles and study of their fine structure

Scanning electron microscopy is employed to study ring-shaped deposits formed at different time moments of evaporating droplets of silver colloidal solutions on a glass substrate. It is shown that, in addition to an external fringe, several rings are formed at intermediate stages of evaporation; these rings are, in the course of time, transformed into one dense fringe and a transition zone adjacent to its internal side. The time dependences of the height and width of the fringe are determined. It is established that an increase in the width and height of the fringe is due to the transfer of silver nanoparticles to this region, which play a key role in imparting specific structural organization to the fringe. It is noted that the height of the formed fringe may be qualitatively determined by energy dispersive X-ray microanalysis.     

Application of boundary element method to calculation of the complex permittivity of suspensions of cells in shape of Dinfinityh symmetry

A numerical method using the boundary element method was developed to calculate the complex permittivity of suspensions of particles in the shape of Dinfinityh symmetry covered with a shell phase. It was an extension of the analytical methods based on Maxwell-Wagner-Sillars' effects in suspensions of shelled ellipsoids. This method was applied to particles, which were relevant to budding yeast cells and erythrocytes, to examine the effects of the shape on frequency-dependence of the permittivity and conductivity of their suspensions. Results of the calculations showed that the permittivity and conductivity at high frequencies were insensitive to the change in the shape. The change in shape affected the permittivity and conductivity at low frequencies and their frequency-dependence in the intermediate frequency region. This behavior could not be imitated by the calculation using analytical methods with shelled spheroid models.     

Efficient quantification of the importance of contacts for the dynamical stability of proteins

Understanding the stability of the native state and the dynamics of a protein is of great importance for all areas of biomolecular design. The efficient estimation of the influence of individual contacts between amino acids in a protein structure is a first step in the reengineering of a particular protein for technological or pharmacological purposes. At the same time, the functional annotation of molecular evolution can be facilitated by such insight. Here, we use a recently suggested, information theoretical measure in biomolecular design - the Kullback-Leibler-divergence - to quantify and therefore rank residue-residue contacts within proteins according to their overall contribution to the molecular mechanics. We implement this protocol on the basis of a reduced molecular model, which allows us to use a well-known lemma of linear algebra to speed up the computation. The increase in computational performance is around 10(1)- to 10(4)-fold. We applied the method to two proteins to illustrate the protocol and its results. We found that our method can reliably identify key residues in the molecular mechanics and the protein fold in comparison to well-known properties in the serine protease inhibitor. We found significant correlations to experimental results, e.g., dissociation constants and Φ values.     

Mechanism of radiothermoluminescence of crystalline tetracosane

Radiothermoluminescence (RTL) of tetracosane irradiated in liquid nitrogen with γ-rays is due to trapped charges. At doses below 2 kGy, all processes leading to RTL are localized in tetracosane intracrystalline areas in traps with a depth of 0.1–2.0 eV that were present in tetracosane before irradiation. With increasing the dose, radiation-induced traps with a depth of 3 eV or higher appear in addition. At the same time, part of the charges reach the surface and become available for interaction with an electron acceptor. The presence of shallow traps (less than 0.15 eV) leads to a decrease in the RTL intensity over the entire temperature range from 100 to 300 K during storage of irradiated samples in liquid nitrogen.     

紫外拉曼光谱研究焙烧气氛对氧化锆相变的影响

 以紫外拉曼光谱技术研究了在不同焙烧气氛中氧化锆样品的表面晶相结构及其转变过程．结果表明，在有氧气氛中焙烧的氧化锆样品易转变为单斜相，而在惰性气氛中焙烧可以有效地稳定样品体相和表面的四方相结构．在缺氧气氛中焙烧的样品暴露于空气中后，表面极易转变为单斜相，而其体相仍为四方相结构，这表明四方相氧化锆在样品表面是极不稳定的．     

Characterization of the barrier properties of composites of HDPE and purified cellulose fibers

The present work presents and discusses the interrelation between composition, morphology, thermal history, mechanical and barrier properties to oxygen and limonene of composites of HDPE/MA-PE/cellulose fibers of significant interest in, among others, food packaging applications. From the overall results, it was observed that increasing the loading of purified alpha-cellulose fibers in the polyethylene matrix beyond 10 wt.% led to a decrease in the permeability coefficient of d-limonene, effect which was found to be primarily related to a decrease in the overall solubility of this strongly plasticizing aroma component. On the other hand, the oxygen permeability was found to decrease to a significant extend with increasing fiber content beyond 5 wt.%, but this effect was more strongly ascribed to a significant decrease in the diffusion coefficient. Therefore, the fibers are thought to generate a more tortuous path for the non-interacting gas molecules to travel across the composites thickness, even when tested at high relative humidity conditions. Optimum fiber loading levels in terms of overall property balance were found to be around 20 wt.%.     

聚丙烯酰胺胶状杂质的形成因为

在聚丙烯酰胺(PAM)配制现场发现过滤器滤袋内存在大量黑色和黄色且有刺鼻腐臭气味的胶状条形物;这类杂质造成过滤装置严重堵塞和设备腐蚀.鉴于此,从细菌和无机离子含量两方面着手分析了聚丙烯酰胺胶状条形杂质的形成因为.结果表明:由于细菌和金属离子Fe3+含量的增加,PAM的侧酰胺基降解成羧基;而含大量金属离子的PAM溶液经缠...     

The effect of structural characteristics of porous hydrophobized electrodes on selectivity of electrolysis of organic substances

A theoretical study of the effect of the electrode structure on the electrosynthesis in hydrophobized electrodes (HPE) for a case of further electrochemical conversion of the target product is performed by the example of nitromethane electroreduction to methyl hydroxylamine followed by its reduction to methylamine. The effect of the electrode structure on the selectivity of electrosynthesis in HPE was shown to be related to the effective diffusivity and conductivity.     

Effects of micelle properties on the conformation of oligocholates and importance of rigidity of foldamers

The conformation of a cholate hexamer with a clicked tether in between two tricholate units and pyrene groups at the chain ends was studied by fluorescence spectroscopy. In contrast to the parent cholate hexamer that folded in all micelles investigated, the folding of the clicked hexamer was highly dependent on the type of surfactant used to solubilize the compound. The clicked oligocholate folded in the Brij 35 micelle, possibly due to the latter's small size and strong internal hydrophobicity. The oligocholate formed intermolecular aggregates in SDS solutions below the CMC of the surfactant. The aggregates were dissociated by the SDS micelles but the individual oligocholate stayed unfolded. In Triton X-100 and sodium cholate solutions, the aggregated, unfolded, and folded oligocholates coexisted and gradual unfolding occurred with an increasing concentration of the surfactant. The conformation of the clicked oligocholate was sensitive to the nonideal mixing of ionic/nonionic micelles and to the unconventional aggregation of sodium cholate.     

Quantum-chemical investigation of the effect of solvent polarity on the direction of sulfonation of pyrrole

The relative stability of the isomeric σ-complexes formed in the sulfonation of pyrrole at the α-or β-position (the α-isomer is energetically more favorable) does not agree with the experimentally established positional selectivity of substitution (the formation of β-pyrrolesulfonic acid). However, quantum-chemical calculations of the energy parameters for the reaction of pyrrole and SO₃ with due regard to the solvation effect in the model solvent methylene chloride (ε = 8.93) lead to the conclusion that the calculated activation energy of the rearrangement to the more favorable β-pyrrolesulfonic acid for the less favorable β-isomer of the σ-complex is lower than on the path to the formation of the α-pyrrolesulfonic acid. It was shown that the significant increase in the polarity of the model medium in the transition to DMSO (ε = 46.7) does not lead to substantial change in the energy parameters of the reaction. The explanation for the positional selectivity during the sulfonation of pyrrole using Py·SO₃, according to previous data, involves the participation of the pyridine in the transformation of the σ-complexes into the products. The calculations were made by the B3LYP/6-31G(d) and HF/3-21+G methods using the model of overlapping spheres to take account of solvation. Dedicated to E. J. Lukevics on his 70th birthday __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 34–40, January, 2007.     

CARS-spectra of excited states of metalloporphyrins

It is shown that resonance coherent anti-Stokes Raman scattering (RCARS) spectra of Cu- and Ni-octaethylporphyrins contain lines corresponding to molecule vibrations both in the ground and excited electronic states. Mechanisms are given which lead to the appearance of vibrations in the excited state in RCARS spectra. The RCARS methods are shown to be promising for comparing molecule vibrations in different electronic states.     

Review of Mesoscopic Modeling of Liquids in Materials Science

Mesoscopic theories can be used in the field of materials science to derive local average properties of relevance to the engineer such as flux, pressure, average density or composition. In the following density functional theory will be described and applied to different systems of interest and in particular, to materials formed from complex liquids as characterized by atomic structure and the type of interaction between the individual particles. The calculation of the solid to liquid transition will be explained in detail as a prototype for other order disorder transitions. The theory of polymers in solution will be revisited and used to calculate phase separation in mixtures. An extension of the theory to include the orientation of rodlike, long molecules will be applied to liquid crystals. In the presence of an interface, the system properties depend strongly on position in space and can be predicted from parameters obtained in the bulk in a square gradient approximation for sufficiently smooth and small deviations from the uniform distribution. A phase transition is often used to prepare heterogeneous materials by nucleation and growth. It will be shown how the equilibrium theory can be extended to study the dynamics of nonequilibrium phenomena.