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Chemical Methods (chemical + methods)
Kinds of Chemical Methods Selected AbstractsDownsizing of Enzymes by Chemical Methods: Arginine Mimics with Low pKa,Values Increase the Rates of Hydrolysis of RNA Model CompoundsANGEWANDTE CHEMIE, Issue 36 2009Johan Ein talentierter Imitator: Sehr viel schneller werden katalytische Reaktionen von RNA-Modellen, wenn zwei Argininreste und zwei Histidinreste in einem gefalteten Polypeptidkatalysator durch Reste mit einer Guanidiniocarbonylpyrrol(Gcp)-Seitenkette (siehe Struktur) ersetzt werden. Gcp übernimmt nicht nur die Funktionen von Arg und His, sondern übertrifft diese sogar leistungsmäßig. [source] One-Dimensional Conducting Polymer Nanostructures: Bulk Synthesis and ApplicationsADVANCED MATERIALS, Issue 14-15 2009Henry D. Tran Abstract This Progress Report provides a brief overview of current research activities in the field of one-dimensional (1D) conducting polymer nanostructures. The synthesis, properties, and applications of these materials are outlined with a strong emphasis on recent literature examples. Chemical methods that can produce 1D nanostructures in bulk quantities are discussed in the context of two different strategies: 1) procedures that rely on a nanoscale template or additive not inherent to the polymer and 2) those that do not. The different sub-classifications of these two strategies are delineated and the virtues and vices of each area are discussed. Following this discussion is an outline of the properties and applications of 1D conducting polymer nanostructures. This section focuses on applications in which nanostructured conducting polymers are clearly advantageous over their conventional counterparts. We conclude with our perspective on the main challenges and future research directions for this new class of nanomaterials. This Progress Report is not intended as a comprehensive review of the field, but rather a summary of select contributions that we feel will provide the reader with a strong basis for further investigation into this fast emerging field. [source] Use of various processes for pilot plant treatment of wastewater from a wood-processing factoryJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2001Nikolaos S Athanasopoulos Abstract The wastewater from a wood-processing factory is characterized by a high COD, chlorides and nitrogen content. Various treatment processes were applied to treat this wastewater in pilot-scale units. By applying one-stage denitrification,activated sludge biological treatment it was not possible to remove nitrogen. Nitrification was inhibited by wastewater compounds. By applying a second stage of a nitrification biofilter it was possible to have a high degree of nitrification. The denitrification was complete. With biological methods the reduction of COD, and -N and -N concentrations to acceptable values was not achievable. Physical,Chemical methods as H2O2/UV, electrolysis and ozonation were used as post-treatment of effluents from the biological system. Radical degradation, initiated by the powerful hydroxyl radicals which are generated from H2O2 by UV activation, is used for wastewater post-treatment. The combination of H2O2/UV was not suitable for post-treatment of this wastewater. With electrolysis, -N and COD removal can be complete. The total amount of ammonia and organic nitrogen converted to nitrate nitrogen for current density of 1.15,Adm,2 and energy consumption of 71.6,kWhm,3 was 0.35,gdm,3. Further biological denitrification is required for -N removal to permitted values. Energy consumption for the elimination of 1,kg COD was 40.4,kWh and 35.8,kWh for current densities of 0.7,Adm,2 and 1.15,Adm,2 respectively. The energy required to reach the limit value of COD equal to 150,mgdm,3 for current density of 1.15,Adm,2 was 71.6,kWhm,3. With ozonation, the COD removal can be complete. Further biological nitrification,denitrification is required to remove -N and -N to permitted values. At pH 7.0, in order to reach the limit value of COD equal to 150,mgdm,3, specific ozone dose was 6.0,g per g of COD removed and the total amount of ammonia and organic nitrogen converted to nitrate nitrogen was 0.25,gdm,3. The total equivalent energy required is estimated to be 75.0,kWhm,3. © 2001 Society of Chemical Industry [source] Lactulose as a food ingredientJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 12 2009Agustín Olano Abstract Lactulose is a synthetic ketose disaccharide that can be obtained from lactose by different methods of synthesis. Chemical methods are based on the isomerization of lactose in the presence of basic catalysts and enzymatic methods using lactose as a galactose donor and fructose as an acceptor. The prebiotic properties of lactulose have been known for more than 50 years and numerous studies have confirmed several health benefits of lactulose as a food ingredient, including selective stimulation of intestinal flora, laxative effect and improvement of calcium absorption. Its use in fermented milk manufacture may reduce the incubation period and favour the growth of bifidobacteria. The synthesis of lactulose-derived oligosaccharides may provide a new group of prebiotics with properties complementary to those of native lactulose. Copyright © 2009 Society of Chemical Industry [source] Inorganic Analogues of GrapheneEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 27 2010C. N. R. Rao Abstract The discovery of graphene has aroused great interest in the properties and phenomena exhibited by two-dimensional inorganic materials, especially when they comprise only a single, two or a few layers. Graphene-like MoS2 and WS2 have been prepared by chemical methods, and the materials have been characterized by electron microscopy, atomic force microscopy (AFM) and other methods. Boron nitride analogues of graphene have been obtained by a simple chemical procedure starting with boric acid and urea and have been characterized by various techniques that include surface area measurements. A new layered material with the composition BCN possessing a few layers and a large surface area discovered recently exhibits a large uptake of CO2. [source] Azide,Tetrazole Ring-Chain Isomerism in Polyazido-1,3,5-triazines, Triazido- s -heptazine, and DiazidotetrazinesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2006Anton Hammerl Abstract The azide,tetrazole isomerism in several polyazido-1,3,5-triazines, triazido- sym -heptazine, and some diazido-1,2,4,5-tetrazines was investigated by ab initio quantum chemical methods in order to determine whether the polyazides are suitable starting materials for the synthesis of the isomeric tetrazoles. The effects of solvation in CCl4, DMSO and water on this isomerism were included using the self consistent reaction field (SCRF) method. The effect of amino- and nitrosubstituents on the azide,tetrazole isomerism was also examined. In the gas phase all investigated polyazidoheterocycles do not cyclize to form tetrazoles. An electron-donating amino group favors the ring closure to tetrazoles, whereas an electron-withdrawing nitro group favors the azides. Solvation in polar solvents favors the formation of a tetrazole ring system due to higher charge separation in the tetrazole ring system, but for all polyazido-1,3,5-triazines, including triazido- s -heptazine, the effects of solvation are not strong enough to shift the equilibrium to the tetrazole side, which explains why several attempts to detect these compounds have failed. The monotetetrazoles of diazidotetrazine and bis(azido)azo-1,2,4,5-tetrazine and the ditetrazole of bis(azido)hydrazo-1,2,4,5-tetrazine are the minimum energy species in DMSO and water. Thus we predict that the diazidoazo- and hydrazotetrazines will readily cyclize to the tetrazoles in polar solvents. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Structures of two cell wall-associated polysaccharides of a Streptococcus mitis biovar 1 strainFEBS JOURNAL, Issue 24 2000A unique teichoic acid-like polysaccharide, the group O antigen which is a C-polysaccharide in common with pneumococci The cell wall of Streptococcus mitis biovar 1 strain SK137 contains the C-polysaccharide known as the common antigen of a closely related species Streptococcus pneumoniae, and a teichoic acid-like polysaccharide with a unique structure. The two polysaccharides are different entities and could be partially separated by gel chromatography. The structures of the two polysaccharides were determined by chemical methods and by NMR spectroscopy. The teichoic acid-like polymer has a heptasaccharide phosphate repeating unit with the following structure: The structure neither contains ribitol nor glycerol phosphate as classical teichoic acids do, thus we have used the expression teichoic acid-like for this polysaccharide. The following structure of the C-polysaccharide repeating unit was established: where AAT is 2-acetamido-4-amino-2,4,6-trideoxy- d -galactose. It has a carbohydrate backbone identical to that of one of the two structures of C-polysaccharide previously identified in S. pneumoniae. C-polysaccharide of S. mitis is characterized by the presence, in each repeating unit, of two residues of phosphocholine and both galactosamine residues in the N-acetylated form. Immunochemical analysis showed that C-polysaccharide constitutes the Lancefield group O antigen. Studies using mAbs directed against the backbone and against the phosphocholine moiety of the C-polysaccharide revealed several different patterns of these epitopes among 95 S. mitis and Streptococcus oralis strains tested and the exclusive presence of the group O antigen in the majority of S. mitis biovar 1 strains. [source] Controlled Synthesis of CdSe Nanowires by Solution,Liquid,Solid MethodADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Zhen Li Abstract Semiconductor nanowires prepared by wet chemical methods are a relatively new field of 1D electronic systems, where the dimensions can be controlled by changing the reaction parameters using solution chemistry. Here, the solution,liquid,solid approach where the nanowire growth is governed by low-melting-point catalyst particles, such as Bi nanocrystals, is presented. In particular, the focus is on the preparation and characterization of CdSe nanowires, a material which serves a prototype structure for many kinds of low dimensional semiconductor systems. To investigate the influence of different reaction parameters on the structural and optical properties of the nanowires, a comprehensive synthetic study is presented, and the results are compared with those reported in literature. How the interplay between different reaction parameters affects the diameter, length, crystal structure, and the optical properties of the resultant nanowires are demonstrated. The structural properties are mainly determined by competing reaction pathways, such as the growth of Bi nanocatalysts, the formation and catalytic growth of nanowires, and the formation and uncatalytic growth of quantum dots. Systematic variation of the reaction parameters (e.g., molecular precursors, concentration and concentration ratios, organic ligands, or reaction time, and temperature) enables control of the nanowire diameter from 6 to 33,nm, while their length can be adjusted between several tens of nanometers and tens of micrometers. The obtained CdSe nanowires exhibit an admixture of wurtzite (W) and zinc blende (ZB) structure, which is investigated by X-ray diffraction. The diameter-dependent band gaps of these nanowires can be varied between 650 and 700,nm while their fluorescence intensities are mainly governed by the Cd/Se precursor ratio and the ligands used. [source] N,N -Dimethylformamide as a Reaction Medium for Metal Nanoparticle SynthesisADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Isabel Pastoriza-Santos Abstract The versatility of wet chemical methods has rendered them extremely popular for the preparation of metal nanoparticles with tailored size and shape. This Feature Article reviews the use of N,N -dimethylformamide (DMF) for the reduction of metal salts, mainly Au and Ag, while also acting as a solvent. Apart from describing the ability of DMF to reduce metal salts, the effect of different parameters, such as the concentration of capping agent and metal precursors, the presence of preformed seeds acting as catalysts or their crystalline structure, on particle morphology are analyzed. Published reports on the use of different capping agents are summarized, with particular emphasis on the role of poly(vinylpyrrolidone) to determine the morphology of the particles. Finally, a brief overview is provided on the modulation of the optical response in DMF-based metal nanoparticle colloids with tunable size and shape. [source] Two New Kaempferol Glycosides from Androsace umbellataHELVETICA CHIMICA ACTA, Issue 7 2009Jun Lei Abstract Two new kaempferol glycosides, 5-hydroxy-2-(4-hydroxyphenyl)-4-oxo-7-(, - L -rhamnopyranosyloxy)-4H -chromen-3-yl 2- O -acetyl-3- O - , - D -glucopyranosyl- , - L -rhamnopyranoside (1) and 5-hydroxy-2-(4-hydroxyphenyl)-4-oxo-7-(, - L -rhamnopyranosyloxy)-4H -chromen-3-yl , - D -glucopyranosyl-(1,2)-6- O -[(2E)-3-(4-hydroxyphenyl)prop-2-enoyl]- , - D -glucopyranosyl-(1,2)- , - D -glucopyranoside (2), along with ten known compounds, were isolated from the 95% EtOH extract of the whole plant of Androsace umbellata. The structures of the new glycosides were determined on the basis of detailed spectroscopic analyses, including 1D- and 2D-NMR, MS, and chemical methods. [source] Four New 9,19-Cyclolanostane Derivatives from the Rhizomes of Cimicifuga yunnanensisHsiaoHELVETICA CHIMICA ACTA, Issue 1 2009Yin Nian Abstract Four new 9,19-cyclolanostane-type triterpenes, 24- O -acetyl-25-anhydroshengmanol-3- O - , - D -xylopyranoside (1), 25- O- butylcimigenol-3- O - , - D -xylopyranoside (2), 12- ,- hydrocimigenol-3-one (3), and 12- ,- hydrocimigenol-1-en-3-one (4), together with 15 known analogues were isolated from the rhizome of Cimicifuga yunnanensisHsiao. Their structures were determined by spectroscopic and chemical methods. [source] Two New Cholestane Bisdesmosides from Reineckia carneaHELVETICA CHIMICA ACTA, Issue 3 2007Zhong-Quan Zhang Abstract Three cholestane bisdesmosides, together with the corresponding aglycone, were isolated from the whole plant of Reineckia carnea. By detailed analysis of the 1D- and 2D-NMR spectra, chemical methods, and comparison with spectral data of known compounds, the structures were determined to be (1,,3,,16,,22S)-cholest-5-ene-1,3,16,22-tetrol (1), (1,,3,,16,,22S)-cholest-5-ene-1,3,16,22-tetrol 1,16-di(, - D -glucopyranoside) (2), (1,,3,,16,,22S)-cholest-5-ene-1,3,16,22-tetrol 1-[O - , - L -rhamnopyranosyl-(1,2)- , - D -glucopyranoside] 16-(, - D -glucopyranoside) (3), (1,,3,,16,,22S)-cholest-5-ene-1,3,16,22-tetrol 1-(, - D -glucopyranoside) 16-(3- O -acetyl- , - D -glucopyranoside) (4). Compounds 3 and 4 appeared to be new compounds, while compound 1 was isolated for the first from a natural source. Compound 2 was isolated from the genus Reineckia for the first time. [source] Paxillamide: a Novel Phytosphingosine Derivative from the Fruiting Bodies of Paxillus panuoidesHELVETICA CHIMICA ACTA, Issue 6 2004Jin-Ming Gao The new phytosphingosine-type ceramide 1, named paxillamide (=2,3-dihydroxy- N -[(1S,2S,3R)-2,3-dihydroxy-1-(hydroxymethyl)heptadecyl]tetracosanamide), was isolated from the CHCl3/MeOH extract of the fruiting bodies of the Basidiomycete Paxillus panuoides, and its structure was elucidated by spectroscopic and chemical methods. [source] Two Novel Triterpenes from the Leaves of Ficus microcarpaHELVETICA CHIMICA ACTA, Issue 5 2004Yueh-Hsiung Kuo Two novel triterpenes, 29(20,19)abeolupane-3,20-dione (4) and 19,20-secoursane-3,19,20-trione (5), besides (3,)-3-hydroxy-29(20,19)abeolupan-20-one (2), lupenone, and , -amyrone (6), were isolated from the leaves of Ficus microcarpa and were characterized by spectroscopic means, including 2D-NMR techniques and chemical methods. Compound 4 is the second derivative having the 29(20,19)abeolupane skeleton, and 5 is a novel skeleton. A biosynthetic pathway to 5 is proposed (Scheme). [source] Synthesis of Inorganic NanotubesADVANCED MATERIALS, Issue 42 2009C. N. R. Rao Abstract Nanotubes constitute an exciting class of one-dimensional nanomaterials of which carbon nanotubes are recognized widely as materials of importance. The possibility of having inorganic nanotubes was recognized early in the 1990s, accompanied by the report of nanotubes of MoS2 and WS2. Since then, nanotubes of several inorganic materials have been prepared and characterized. While nanotubes of metal chalcogenides and oxides form a high proportion of the inorganic nanotubes investigated hither to, nanotubes of many other materials have also been prepared and characterized. Several synthetic strategies including both physical and chemical methods have been employed, of which the use of templates, precursors, and hydro- or solvothermal methods are prominent. In this article, we shall present a brief account of the present status of the synthesis of nanotubes of elemental materials as well as binary and complex metal oxides, chalcogenides, pnictides and carbides. [source] A miniaturized assay for influenza neuraminidase-inhibiting antibodies utilizing reverse genetics-derived antigensINFLUENZA AND OTHER RESPIRATORY VIRUSES, Issue 5 2009Matthew R. Sandbulte Background, Antibodies to neuraminidase (NA) contribute to protection during influenza virus infection, but NA inhibition (NI) titers are not routinely analyzed in vaccine trials. One reason is the cumbersome nature of the conventional thiobarbituric acid (TBA) NI assay, which uses chemical methods to quantify free sialic acid following incubation of NA with substrate in the presence of serum. In addition, the assay is complicated by the need to use virus of a hemagglutinin (HA) subtype novel to the host to detect NA-specific antibodies only. Objectives, Our primary objectives were to miniaturize the colorimetric NI assay to a format suitable for quantitative analysis of large numbers of samples, and validate the specificity and sensitivity of the miniaturized format with ferret and human sera. An additional aim was to use reverse genetics to construct HA-mismatched viral reagents bearing NA of recent influenza A vaccine strains and H6 HA. Results, Analysis of ferret antisera by the miniaturized assay demonstrated sensitivity and specificity comparable with the conventional assay. Similar increases in the NI titers in sera from vaccinated human volunteers were measured in miniaturized and conventional assays. Inactivated and live-attenuated vaccines increased NI titers against a given subtype at approximately the same rate. Conclusions, The reagents and miniaturized format of the TBA method described here provide a platform for practical serological monitoring of functional antibodies against NA. [source] The chemiionization reactions Ce + O and Ce + O2: Assignment of the observed chemielectron bandsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 10 2009Tanya K. Todorova Abstract Multiconfigurational quantum chemical methods (CASSCF/CASPT2) have been used to study the chemiionization reactions Ce + O , CeO+ + e, and Ce + O2 , CeO + e,. Selected spectroscopic constants for CeOn and CeO (n = 1, 2), as well as reaction enthalpies of the chemiionization reactions of interest, have been computed and compared with experimental values. In contrast to the lanthanum case, for both Ce + O2(X3,) and Ce + O2( a1,g), the Ce + O2 , CeO + e, reaction is shown to be exothermic, and thus, contributes to the experimental chemielectron spectra. The apparent discrepancy between the computed reaction enthalpies and the high kinetic energy offset values measured in the chemielectron spectra is rationalized by arguing that chemielectrons are produced mainly via two sequential reactions (Ce + O2 , CeO + O, followed by Ce + O , CeO+ + e,) as in the case of lanthanum. For Ce + O2 (a1,g), a chemielectron band with higher kinetic energy than that recorded for Ce + O2( X3,) is obtained. This is attributed to production of O( 1D) from the reaction Ce + O2( a1,g) , CeO + O( 1D), followed by chemiionization via the reaction Ce + O( 1D) , CeO+ + e,. Accurate potential energy curves for the ground and a number of excited states of CeO and CeO+ have been computed, and a mechanism for the chemiionization reactions investigated experimentally was proposed. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] From quantum chemistry and the classical theory of polar liquids to continuum approximations in molecular mechanics calculations,INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005Sergio A. Hassan Abstract Biological macromolecules and other polymers belong to the class of mesoscopic systems, with characteristic length scale of the order of a nanometer. Although microscopic models would be the preferred choice in theoretical calculations, their use in computer simulations becomes prohibitive for large systems or long simulation times. On the other hand, the use of purely macroscopic models in the mesoscopic domain may introduce artifacts, with effects that are difficult to assess and that may compromise the reliability of the calculations. Here is proposed an approach with the aim of minimizing the empirical nature of continuum approximations of solvent effects within the scope of molecular mechanics (MM) approximations in mesoscopic systems. Using quantum chemical methods, the potential generated by the molecular electron density is first decomposed in a multicenter-multipole expansion around predetermined centers. The monopole and dipole terms of the expansion at each site create electric fields that polarize the surrounding aqueous medium whose dielectric properties can be described by the classical theory of polar liquids. Debye's theory allows a derivation of the dielectric profiles created around isolated point charges and dipoles that can incorporate Onsager reaction field corrections. A superposition of screened Coulomb potentials obtained from this theory makes possible a simple derivation of a formal expression for the total electrostatic energy and the polar component of the solvation energy of the system. A discussion is presented on the physical meaning of the model parameters, their transferability, and their convergence to calculable quantities in the limit of simple systems. The performance of this continuum approximation in computer calculations of amino acids in the context of an atomistic force field is discussed. Applications of a continuum model based on screened Coulomb potentials in multinanosecond simulations of peptides and proteins are briefly reviewed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Enantioselective Reduction of Diaryl Ketones Catalyzed by a Carbonyl Reductase from Sporobolomyces salmonicolor and its Mutant EnzymesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2009Hongmei Li Abstract The carbonyl reductase from red yeast Sporobolomyces salmonicolor AKU4429 (SSCR) and its mutant enzymes effectively catalyzed the enantioselective reduction of diaryl ketones to give the corresponding chiral alcohols. Both conversion and enantioselectivity were dependent on the co-solvent in the reaction medium. Diaryl ketones with a para -substituent on one of the phenyl groups were reduced with high enantioselectivity (up to 99% ee), which is difficult to achieve using chemical methods such as chiral borane reduction, asymmetric hydrogenation or hydrosilylation. Mutation of SSCR at Q245 resulted in a higher amount of (S)-enantiomer in the products, and in the case of mutant Q245P with para -substituted diaryl ketones as substrate, this effect was so remarkable that the reduction enantiopreference was switched from (R) to (S). The present study provides valuable information about the catalytic properties of the carbonyl reductase SSCR toward the reduction of diaryl ketones, serving as basis for further engineering of this enzyme to develop efficient biocatalysts for highly enantiospecific reduction of diaryl ketones without high electronic dissymmetry or an ortho -substituent on one of the aryl groups. [source] Concrete canal lining cracking in low to medium plastic soils,IRRIGATION AND DRAINAGE, Issue 2 2002H. Rahimi sol plastique; gonflement; revêtement bétonique; Iran Abstract Failure of concrete irrigation canal linings in the form of cracking, rupture, uplifting and opening of joints, causes loss of water and money in many countries. Following the appearance of extensive cracking of concrete linings in one of the Shoeybieh sugar cane industry farms in the Khoozestan province of Iran, extensive research work was conducted to identify the main causes. In this paper, the final results of the research are presented. The testing program consisted of laboratory as well as field tests, including identification, chemical and mechanical tests of soil samples taken from the borrow pits and canal embankments. Dispersivity tests were performed using pin-hole and chemical methods. Swelling tests were conducted using the ASTM standard and ISSMFE method. The field test includes measurement of deformations of the concrete lining and embankment of an actual lined canal resulting from the filling of the canal with water. The canal was 60 m in length. The deformations were recorded by surveying the elevations of steel bars driven to different depths under the canal lining and at different points in the canal and its embankment sections. The results of laboratory tests showed the soil to have low to medium plasticity with a classification of CL-ML, having less than 1% soluble content, and being nondispersive. Swelling tests conducted by the ASTM and ISSMFE methods showed completely different results. The ISSMFE method resulted in a high free swell potential, while the ASTM method indicated a low to medium potential. The results of full-scale field tests were all in favor of the ISSMFE method. The greatest difference between the results of the two methods was found to be due to the different compaction methods used during construction of the canal, as well as the moisture content of the soil sample being prepared for the swell tests. The flocculent structure and lower compaction water content of soil samples in the ISSMFE method resulted in much higher free swell. The similarity between compaction methods used in the field and the static effort used in the ISSMFE method, as well as very low soil water content of the canal embankments during lining operations, were found to be the main reasons for swelling of the soil and the eventual cracking of the concrete linings. Copyright © 2002 John Wiley & Sons, Ltd. RÉSUMÉ L'écroulement du revêtement bétonique des canaux d'irrigation en forme de fissure, de la rupture, de la sous-pression et de l'ouverture des joints, est la cause de la perte d' eau et par conséquence des fonds publics de plusieurs pays dans le monde entier. Après avoir observé ce phénomène dans des canaux d'irrigation d'un grand projet de canne à sucre à Shoeybieh dans la région de Khozestan, située au sud de l'Iran, une équipe de recherche a été engagée pour trouver les causes principales de cetécroulement. Cet article présente les résultats finaux de cette recherche. Le programme consiste de deux types d'essai, en laboratoire et sur le terrain. Les échantillons du sol pour l'essai mécanique et chimique ont été pris dans des emprunts de terre et la digue du canal. Les essais de dispersivité ont été faits par les méthodes de pin-hole et de chimique. La méthode del ISSMFE et la standard del ASTM ont été utilisés pour les essais de gonflement du sol. Le mesurage de la déformation d'un canal revêté en béton et aussi de digue du canal a été fait par rempliz le canal avee de l'eau. Le canal avait une longueur de 60 m. La déformation a été observée en examinant les élévations à plusieurs points sur la profondeur du canal en dessous de la partie revêtée et aussi la digue du canal par un instrument spécifique. Les résultats des essais de laboratoire montrent que les sols qui ont une plasticité entre petite et moyenne situés dans la classification de CL-ML ayant moins d'un pour cent de contenude soluble sont non-dispersifes. Les essais de gonflement par les méthodes de l'ASTM et l'ISSME montrent des résultats tout à fait différents. La méthode ISSMFE montre un potentiel de gonflement assez élevé, tandis que la méthode ASTM montre un potentiel entre petit et moyen. Les résultats des essais en champs d'étude confirme la méthode ISSMFE. La plus grande différence entre le résultat de deux méthodes est à cause d'usage de plusieurs méthodes de compaction dans la période de la construction du canal. La structure floculée du sol ayant une humidité moins compactée dans la méthode ISSMFE montre un gonflement plus élevée du sol. Les méthodes similaires de compaction utilisées dans le champs d'étude et énergie statique utilisée par la méthode ISSFE, et aussi une petite humidité de digue du canal en période de revêtement sont les causes principales de gonflement et éventuellement de fissure. Copyright © 2002 John Wiley & Sons, Ltd. [source] Hydrodenitrification with PdCu Catalysts: Catalyst Optimization by Experimental and Quantum Chemical ApproachesISRAEL JOURNAL OF CHEMISTRY, Issue 1 2006Irena Efremenko A continuous process for nitrate and nitrite abatement from drinking water by catalytic hydrogenation has been developed in our lab. We describe the experimental process development procedure, and support it with semiempirical quantum chemical methods. Comparisons of activated carbon (ACC) and silica glass fiber (GFC) cloths as supports for mono- and bimetallic Pd-Cu catalysts show the former to be 45-fold and 15-fold more active for nitrite and nitrate hydrogenation, respectively, than the latter. Catalysts prepared by selective deposition of Cu on Pd/ACC led to better activity for nitrate hydrogenation than catalysts prepared by co-impregnation or ion exchange methods. The optimal Cu:Pd atomic ratio was found to be 1:2. The computational results show the following: (i) The dispersion of Pd catalysts supported on ACC is much higher than that on GFC due to the larger surface area and higher density of adsorption sites, and that accounts for the higher activity of PdCu/ACC; (ii) Nanosized Pd particles supported on ACC have a semispherical shape and possess preferentially close-packed triangular surfaces, while Pd/GFC particles are extended in the direction parallel to the support surface and show both fcc (100) and (111) planes; (iii) The interaction of Cu atoms with both supports is stronger than that of Pd; adsorbed Cu atoms show a greater ability to form monometallic than bimetallic bonds and that should result in poor mixing of the metal upon co-impregnation, as was observed experimentally; (iv) Cu atoms in bimetallic PdCu particles admit a significant positive charge; the experimentally measured solubility of metal atoms correlates with their calculated charges. The best catalyst (2 wt%Pd-0.6 wt%Cu/ACC) was employed in a novel continuous flow reactor for nitrate hydrogenation in distilled and tap water. The advantages of the reactor investigated over a conventional packed bed reactor are discussed, suggesting a potential for further process intensification. [source] Polystyrene nanocomposite materials by in situ polymerization into montmorillonite,vinyl monomer interlayersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007Ahmed Akelah Abstract A different series of new polystyrene,clay nanocomposites have been prepared by grafting polymerization of styrene with vinyl-montmorillonite (MMT) clay. The synthesis was achieved through two steps. The first step is the modification of clay with the vinyl monomers, such as N,N -dimethyl- n -octadecyl-4-vinylbenzyl-ammonium chloride, n -octadecyl-4-vinylbenzyl-ammonium chloride, triphenyl-4-vinylbenzyl-phosphonium chloride, and tri- n -butyl-4-vinylbenzyl-phosphonium chloride. The second step is the polymerization of styrene with different ratios of vinyl-MMT clay. The materials produced were characterized by different physical and chemical methods: (1) IR spectra, confirming the intercalation of the vinyl-cation within the clay interlayers; (2) thermogravimetric analysis (TGA), showing higher thermal stability for PS,nanocomposites than polystyrene (PS) and higher thermal stability of nanocomposites with of phosphonium moieties than nanocomposites with ammonium moieties; (3) swelling measurements in different organic solvents, showing that the swelling degree in hydrophobic solvents increases as the clay ratio decreases; (4) X-ray diffraction (XRD), illustrating that the nanocomposites were exfoliated at up to a 25 wt % of organoclay content; and (5) scanning electron microscopy (SEM), showing a complete dispersion of PS into clay galleries. Also, transmission electron microscopy (TEM) showed nanosize spherical particles of , 150,400 nm appearing in the images. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3739,3750, 2007 [source] Microbial transformation of androst-4-ene-3, 17-dione by Bordetella sp.JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 5 2009B4 CGMCC 222 Abstract BACKGROUND: Microbial transformation of steroids has attracted widespread attention, especially the transformation of those steroids synthesized with difficulty by chemical methods. In this study, microbial transformation of androst-4-ene-3, 17-dione (AD) by Bordetella sp. B4 was investigated, and the effect of temperature on transformation was studied. RESULTS: Three metabolites were purified by preparative TLC and HPLC, and identified as androsta-1,4-diene-3,17-dione (ADD), 9,-hydroxyandrost-4-ene-3, 17-dione (9,-OH-AD), and 3-hydroxy-9, 10-secoandrost-1, 3, 5-triene-9, 17-dione (3-OH-SATD) by nuclear magnetic resonance imaging (NMR), Fourier transform infrared spectroscopy (FTIR) and mass spectroscopy (MS). It was first reported that the genus of Bordetella has the capability of AD degradation. Microbial transformation of AD was performed at 30 °C, 37 °C, 40 °C and 45 °C. The 9,-OH-AD yield reached a maximum within 16 h when the strain was cultivated in media with AD as sole carbon at 37 °C. Surprisingly, ADD was produced by the strain cultivated at 40 °C but not at 37 °C, which was different from previous reports. It was deduced that the alcohol dehydrogenase that catalyzed the transformation of AD to ADD may be temperature sensitive. CONCLUSION: Androst-4-ene-3,17-dione was converted into 9,-hydroxyandrost-4-ene-3, 17-dione and other metabolites rapidly by Bordetella sp. B4. It is anticipated that the strain Bordetella sp. B4 CGMCC 2229 can be used in the steroids industry. Copyright © 2009 Society of Chemical Industry [source] Substituent electronic descriptors for fast QSAR/QSPRJOURNAL OF CHEMOMETRICS, Issue 3-4 2007Bahram Hemmateenejad Abstract Substituent electronic descriptors (SED), calculated by ab initio quantum chemical methods for radical substituents, were proposed as an efficient and simple to use descriptors for use in Quantitative structure-activity/property relationships (QSPR/QSAR) studies. Twenty five SED parameters were calculated for a set of simple substituents using orbital energies, local charges, and dipole moments. Calculation of these parameters for a substituent takes much lower time comparing with that for parent molecule. Different chemical and biological data were analyzed by the SED parameters and it was found that in addition to the simplicity and speed of calculations, models obtained by SED parameters have better or comparable efficiency in relative to existing models. Copyright © 2007 John Wiley & Sons, Ltd. [source] Deproteinization of serum: Another best approach to eliminate all forms of bilirubin interference on serum creatinine by the kinetic Jaffe reactionJOURNAL OF CLINICAL LABORATORY ANALYSIS, Issue 3 2001Porntip H. Lolekha Abstract The negative interference of conjugated, unconjugated, and delta bilirubin on patient serum creatinine determined by the kinetic Jaffe reaction is the unresolved problem. We compared bilirubin interference on thirty patients' serum creatinine obtained from four analyzers, with and without deprotenization before the Jaffe reaction, to the Vitros dry enzymatic method. We found significant negative interference from bilirubin on serum creatinine in all samples directly applied to four wet chemical methods, except the one incorporated with serum blank rate. The negative interferences linearly related to bilirubin concentration. However, bilirubin did not interfere on serum creatinine obtained from all wet chemical methods incorporated with deproteinization process before the reaction. We conclude that deproteinized serum before the reaction is the best approach to eliminate all forms of bilirubin interference on serum creatinine determined by the kinetic Jaffe reaction. J. Clin. Lab. Anal. 15:116,121, 2001. © 2001 Wiley-Liss, Inc. [source] Electronic structure and reactivity of guanylthiourea: A quantum chemical studyJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2010Ahmed Mehdi Abstract Electronic structure analysis of guanylthiourea (GTU) and its isomers has been carried out using quantum chemical methods. Two major tautomeric classes (thione and thiol) have been identified on the potential energy (PE) surface. In both the cases conjugation of pi-electrons and intramolecular H-bonds have been found to play a stabilizing role. Various isomers of GTU on its PE surface have been analyzed in two different groups (thione and thiol). The interconversion from the most stable thione conformer (GTU-1) to the most stable thiol conformer (GTU-t1) was found to take place via bimolecular process which involves protonation at sulfur atom of GTU-1 followed by subsequent CN bond rotation and deprotonation. The detailed analysis of the protonation has been carried out in gas phase and aqueous phase (using CPMC model). Sulfur atom (S1) was found to be the preferred protonation site (over N4) in GTU-1 in gas phase whereas N4 was found to be the preferred site of protonation in aqueous medium. The mechanism of S-alkylation reaction in GTU has also been studied. The formation of alkylated analogs of thiol isomers (alkylated guanylthiourea) is believed to take place via bimolecular process which involves alkyl cation attack at S atom followed by CN bond rotation and deprotonation. The reactive intermediate RS(NH2)CNC(NH2)2+ belongs to the newly identified ,N(,L)2 class of species and provides the necessary dynamism for easy conversion of thione to thiol. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] MOLCAS 7: The Next GenerationJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2010Francesco Aquilante Abstract Some of the new unique features of the MOLCAS quantum chemistry package version 7 are presented in this report. In particular, the Cholesky decomposition method applied to some quantum chemical methods is described. This approach is used both in the context of a straight forward approximation of the two-electron integrals and in the generation of so-called auxiliary basis sets. The article describes how the method is implemented for most known wave functions models: self-consistent field, density functional theory, 2nd order perturbation theory, complete-active space self-consistent field multiconfigurational reference 2nd order perturbation theory, and coupled-cluster methods. The report further elaborates on the implementation of a restricted-active space self-consistent field reference function in conjunction with 2nd order perturbation theory. The average atomic natural orbital basis for relativistic calculations, covering the whole periodic table, are described and associated unique properties are demonstrated. Furthermore, the use of the arbitrary order Douglas-Kroll-Hess transformation for one-component relativistic calculations and its implementation are discussed. This section especially focuses on the implementation of the so-called picture-change-free atomic orbital property integrals. Moreover, the ElectroStatic Potential Fitted scheme, a version of a quantum mechanics/molecular mechanics hybrid method implemented in MOLCAS, is described and discussed. Finally, the report discusses the use of the MOLCAS package for advanced studies of photo chemical phenomena and the usefulness of the algorithms for constrained geometry optimization in MOLCAS in association with such studies. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010 [source] Ab initio computational study of positron emission tomography ligands interacting with lipid molecule for the prediction of nonspecific bindingJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 14 2008Lula Rosso Abstract Nonspecific binding is a poorly understood biological phenomenon of relevance in the study of small molecules interactions in vivo and in drug development. Nonspecific binding is thought to be correlated in part to a molecule's lipophilicity, typically estimated by measuring (or calculating) octanol,water partition coefficient. This is, however, a gross simplification of a complex phenomenon. In this article, we present a computational method whose aim is to help identify positron emission tomography (PET) ligands with low nonspecific binding characteristics by investigating the molecular basis of ligand,membrane interaction. We considered a set consisting of 10 well-studied central nervous system PET radiotracers acting on a variety of molecular targets. Quantum mechanical calculations were used to estimate the strength of the interaction between each drug molecule and one phospholipid molecule commonly present in mammalian membranes. The results indicate a correlation between the computed drug,lipid interaction energy and the in vivo nonspecific distribution volume relative to the free tracer plasma concentration, calculated using standard compartmental modeling for the analysis of PET data. Significantly, the drugs whose interaction with the lipid molecule more favorably possessed, in general, a higher nonspecific binding value, whereas for the drugs taken in consideration in this study, the water-octanol partition coefficient, log P, did not show good predictive power of the nonspecific binding. This study also illustrates how ab initio chemical methods may offer meaningful and unbiased insights for the understanding of the underlying chemical mechanisms in biological systems. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Systematic quantum chemical study of DNA-base tautomersJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2004M. Piacenza Abstract The relative energies of the energetically low-lying tautomers of pyridone, cytosine, uracil, thymine, guanine, and iso-cytosine are studied by a variety of different quantum chemical methods. In particular, we employ density functional theory (DFT) using the six functionals HCTH407, PBE, BP86, B-LYP, B3-LYP, and BH-LYP, and the ab initio methods Hartree-Fock (HF), standard second-order Møller-Plesset perturbation theory (MP2), an improved version of it (SCS-MP2), and quadratic configuration interaction including single and double excitations (QCISD) and perturbative triple corrections [QCISD(T)]. A detailed basis set study is performed for the formamide/formamidic acid tautomeric pair. In general, large AO basis sets of at least valence triple-, quality including f-functions (TZV) are employed, which are found to be necessary for an accurate energetic description of the various structures. The performance of the more approximate methods is evaluated with QCISD(T)/TZV(2df,2dp) data taken as reference. In general it is found that DFT is not an appropriate method for the problem. For the tautomers of pyridone and cytosine, most density functionals, including the popular B3-LYP hybrid, predict a wrong energetic order, and only for guanine, the correct sequence of tautomers is obtained with all functionals. Out of the density functionals tested, BH-LYP, which includes a rather large fraction of HF exchange, performs best. A consistent description of the nonaromatic versus aromatic tautomers seems to be a general problem especially for pure, nonhybrid functionals. Tentatively, this could be assigned to the exchange potentials used while the functional itself, including the correlation part, seems to be appropriate. Out of the ab initio methods tested, the new SCS-MP2 approach seems to perform best because it effectively reduces some outliers obtained with standard MP2. It outperforms the much more costly QCISD method and seems to be a very good compromise between computational effort and accuracy. © 2003 Wiley Periodicals, Inc. J Comput Chem 1: 83,98, 2004 [source] Triterpenoid Saponins from Pulsatilla cernua (Thunb.) Bercht. et Opiz.JOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 2 2007Tun-Hai Xu Abstract To investigate saponins from the roots of Pulsatilla cernua (Thunb.) Bercht. et Opiz., two new compounds together with five known triterpenoid saponins were isolated. The structures of the two new triterpenoid saponins, named cernuasides A and B, were elucidated as 3-O-[p-,- D -xylopyranosyl(1,2)]-[,- L -rhamnopyranosyl(1,4)]-,- L -arabinopyranosyl hederagenin 28-O-,- D -glucopyranosyl ester (compound 1) and 3-O-[,- L -arabinopyranosyl(1,3)]-[,- L -rhamnopyranosyl (1,2)]-,- L -arabinopyranosyl hederagenin 28-O-,- D -glucopyranosyl ester (compound 2) by 1D, 2D-NMR techniques, ESIMS analysis, as well as chemical methods. [source] | |||||||||||||||||||||||||||||||||||||