Mechanism.

Distribution by Scientific Domains


Selected Abstracts


Epitaxial Sn1-xPbxS nanorods on iso-compositional thin films

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2010
K. Bente
Abstract Based on SnS (Herzenbergite) , SnPbS2 (Teallite) mixed crystals with orthorhombic layer structures, thin films and lawns of Sn1-xPbxS nanorods were produced using hot wall vacuum deposition method (HWVD). The lawn was formed onto the surface of an underlying thin Sn1-xPbxS film which is build by differently oriented blocks. The density of rods arranged like a lawn depends on the metal ratio and substrate temperature. X-ray and TEM analysis of the epitaxial material showed preferential (001) orientation perpendicular to the surface of the glass substrate. The roughness of the films measured by atomic force microscopy was in the range of Rq = 49.5,86.3 nm depending on lead concentration The rods were about 500 nm high and 300 nm in diameter. As revealed by TEM-EDX experiments the droplet at the tip of rods consists of tin. Therefore it is assumed the rods grew via a self-consuming vapor,liquid,solid (VLS) mechanism. ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Nucleation kinetics and growth of nonlinear optical bis (dimethyl sulfoxide) manganese mercury thiocyanate single crystals

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2008
C. M. Raghavan
Abstract Nonlinear optical (NLO) material of bis (dimethyl sulfoxide) manganese mercury thiocyanate (MMTD) was synthesized by two step reaction method. The solubility and metastable zonewidth were experimentally determined in order to optimize the growth parameters. Bulk crystals of MMTD were grown by slow cooling and slow evaporation methods. The structure of the grown crystal was confirmed by X-ray diffraction analysis. Presence of functional groups and the coordination of Lewis base ligand of dimethyl sulfoxide (DMSO) were confirmed by FT-IR analysis. Optical transparency of the grown crystals was studied by UV-Vis spectroscopy. Nonlinear optical property of the grown crystal was confirmed by Kurtz powder method. Etching studies reveal the formation of triangular hillock etch patterns, indicative of 2D nucleation mechanism. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Growth and properties of ferroelectric potassium ferrocyanide trihydrate single crystals

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2006
R. Kanagadurai
Abstract Single crystals of potassium ferrocyanide trihydrate, K4[Fe(CN)63H2O (KFCT), a ferroelectric material with Curie temperature 251K were grown in silica gel at room temperature for the first time by the solubility reduction method. Resorcinol and ethyl alcohol were used for the purpose of gel setting and supernatant liquid respectively. Optical and mechanical properties were studied for the grown crystal. The structure of the grown crystal was confirmed by X-ray diffraction analysis. Fourier Transform Infrared (FTIR) and FT Raman spectral analysis of the crystalline samples reveal that the crystalline sample consist consists of all functional groups. Thermal analysis of the crystalline sample was performed by TGA and DTA methods. The Vicker's micro hardness value was measured for KFCT crystals. The square etch pits with a hopper-like structure is an indicative of 2D nucleation mechanism. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Impact of magnetic field on the nucleation and morphology of calcium carbonate crystals

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2005
K. V. Saban
Abstract The influence of static magnetic field of strength 0.75 T on the nucleation of calcium carbonate crystals has been investigated. Particle size analysis shows that magnetic field can cause marked difference in distribution. One of the major impacts of magnetic exposure is the increase in number of the critical nuclei formed. Also, magnetic field promotes the formation of parallelepipedic calcite crystals and the dissolution of the smaller crystals by Ostwald ripening mechanism. ( 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Testosterone and dihydrotestosterone, but not estradiol, enhance survival of new hippocampal neurons in adult male rats

DEVELOPMENTAL NEUROBIOLOGY, Issue 10 2007
Mark D. Spritzer
Abstract Past research suggested that androgens may play a role in the regulation of adult neurogenesis within the dentate gyrus. We tested this hypothesis by manipulating androgen levels in male rats. Castrated or sham castrated male rats were injected with 5-Bromo-2,deoxyuridine (BrdU). BrdU-labeled cells in the dentate gryus were visualized and phenotyped (neural or glial) using immunohistochemistry. Castrated males showed a significant decrease in 30-day cell survival within the dentate gyrus but there was no significant change in cell proliferation relative to control males, indicating that androgens positively affect cell survival, but not cell proliferation. To examine the role of testosterone on hippocampal cell survival, males were injected with testosterone s.c. for 30 days starting the day after BrdU injection. Higher doses (0.5 and 1.0 mg/kg) but not a lower dose (0.25 mg/kg) of testosterone resulted in a significant increase in neurogenesis relative to controls. We next tested the role of testosterone's two major metabolites, dihydrotestosterone (DHT), and estradiol, upon neurogenesis. Thirty days of injections of DHT (0.25 and 0.50 mg/kg) but not estradiol (0.010 and 0.020 mg/kg) resulted in a significant increase in hippocampal neurogenesis. These results suggest that testosterone enhances hippocampal neurogenesis via increased cell survival in the dentate gyrus through an androgen-dependent mechanism. 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2007. [source]


Neural precursor cells from a fatal human motoneuron disease differentiate despite aberrant gene expression

DEVELOPMENTAL NEUROBIOLOGY, Issue 3 2007
Niklas Pakkasjrvi
Abstract Precursor cells of the human central nervous system can be cultured in vitro to reveal pathogenesis of diseases or developmental disorders. Here, we have studied the biology of neural precursor cells (NPCs) from patients of lethal congenital contracture syndrome (LCCS), a severe motoneuron disease leading to prenatal death before the 32nd gestational week. LCCS fetuses are immobile because of a motoneuron defect, seen as degeneration of the anterior horn and descending tracts of the developing spinal cord. The genetic defect for the syndrome is unknown. We show that NPCs isolated postmortem from LCCS fetuses grow and are maintained in culture, but display increased cell cycle activity. Global transcript analysis of undifferentiated LCCS precursor cells present with changes in EGF-related signaling when compared with healthy age-matched human controls. Further, we show that LCCS-derived NPCs differentiate into cells of neuronal and glial lineage and that the initial differentiation is not accompanied by overt apoptosis. Cells expressing markers Islet-1 and Hb9 are also generated from the LCCS NPCs, suggesting that the pathogenic mechanism of LCCS does not directly affect the differentiation capacity or survival of the cells, but the absence of motoneurons in LCCS may be caused by a noncell autonomous mechanism. 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2007 [source]


Protection of seismic structures using semi-active friction TMD

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 6 2010
Chi-Chang Lin
Abstract Although the design and applications of linear tuned mass damper (TMD) systems are well developed, nonlinear TMD systems are still in the developing stage. Energy dissipation via friction mechanisms is an effective means for mitigating the vibration of seismic structures. A friction-type TMD, i.e. a nonlinear TMD, has the advantages of energy dissipation via a friction mechanism without requiring additional damping devices. However, a passive-friction TMD (PF-TMD) has such disadvantages as a fixed and pre-determined slip load and may lose its tuning and energy dissipation abilities when it is in the stick state. A novel semi-active-friction TMD (SAF-TMD) is used to overcome these disadvantages. The proposed SAF-TMD has the following features. (1) The frictional force of the SAF-TMD can be regulated in accordance with system responses. (2) The frictional force can be amplified via a braking mechanism. (3) A large TMD stroke can be utilized to enhance control performance. A non-sticking friction control law, which can keep the SAF-TMD activated throughout an earthquake with an arbitrary intensity, was applied. The performance of the PF-TMD and SAF-TMD systems in protecting seismic structures was investigated numerically. The results demonstrate that the SAF-TMD performs better than the PF-TMD and can prevent a residual stroke that may occur in a PF-TMD system. Copyright 2009 John Wiley & Sons, Ltd. [source]


An Approach to the Synthesis of Silicon Carbide Nanowires by Simple Thermal Evaporation of Ferrocene onto Silicon Wafers

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 25 2007
Jun-Jie Niu
Abstract Scales of silicon carbide nanowires (SiC-NWs) with high quality were synthesized by direct thermal evaporation of ferrocene onto silicon wafers at high temperature. Ferrocene decomposed into iron and carbon, which was subsequently treated with silicon to form SiC-NWs at high temperature. The SiC-NWs possess small diameters of , 20 nm and lengths of several ,ms. Furthermore, the samples show a uniform morphology, crystalline structure, and a very thin oxide layer. The main crystal direction of [111] was confirmed by high-resolution field-emission-transmission electron microscopy (HR-FETEM). The Raman scattering spectra showed two peaks at , 796 (TO) and , 980 cm,1 (LO) with varying intensity ratios at different positions. The band line fluctuation was contributed to the Raman selection rules. With reference to the experimental results, we suggested a tentative growth model according to the vapor,liquid,solid (VLS) mechanism. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]


Ferromagnetism in [Mn(Cp*)2]+ -Derived Complexes: the "Miraculous" Stacking in [Mn(Cp*)2][Ni(dmit)2]

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2003
Christophe Faulmann
Abstract The synthesis and characterisation (X-ray structure and magnetism) of metal complexes (Ni, Au) with the [Mn(Cp*)2]+ cation and the dmit2, and dmid2, ligands are reported. [Mn(Cp*)2][Ni(dmit)2] (1) and [Mn(Cp*)2][Au(dmit)2] (2) exhibit the same structural arrangement, built on stacks of [Ni(dmit)2], pairs separated by two [Mn(Cp*)2]+ cations, showing a D+D+A,A,D+D+A,A, motif. On the contrary, the dmid2, derivative [Mn(Cp*)2][Ni(dmid)2]CH3CN (3) exhibits a totally different structure, built on mixed layers composed of one [Ni(dmid)2], unit separated by two [Mn(Cp*)2]+ cations, showing a D+D+A,D+D+A,motif. The layers are separated from each other by perpendicular [Ni(dmid)2], units and solvent molecules. Compound 2 exhibits antiferromagnetic interactions, whereas 1 and 3 exhibit ferromagnetic interactions at low temperature. Moreover, as confirmed by AC and DC magnetic susceptibility measurements, 1 is a ferrimagnet, the first ever derived from a 1,2-bis-dithiolene ligand. The ferromagnetic interactions in 1 and 3 are explained using the McConnell I mechanism. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]


Cyclization of Trichloroacetimidates by Olefin Aminopalladation ,-Heteroatom Elimination

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 36 2009
Ansis Maleckis
Abstract The cyclization of ,-acetoxy- O -allyl- and ,-acetoxy- O -homoallyl-trichloroacetimidates to 4-vinyloxazolines and a 4-vinyldihydrooxazine has been efficiently achieved by olefin aminopalladation,,-heteroatom elimination. (Z)-Allylic imidates bearing a secondary ,-acetoxy group underwent PdII -catalysed cyclization to give the E isomers of 4-vinyloxazolines selectively and gave no Overman rearrangement products. Using a chiral substrate, it has been demonstrated that cyclization to 4-vinyloxazolines occurs with high chirality transfer. Stereoselective E isomer formation and chirality transfer provided a basis from which to discuss the possible reaction mechanism. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]


Cyclic 2:1 and 1:2 Aldehyde-to-Acetone Byproduct Adducts in Aldol Reactions Promoted by Supported Proline-Incorporated Catalysts

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2009
Lital Tuchman-Shukron
Abstract Significant amounts of cyclic byproducts of aldol addition with stoichiometry deviating from a regular 1:1 addition pattern were formed when the reaction of acetone with aromatic aldehydes was promoted by polymer-supported proline-incorporated catalysts. These adducts, unprecedented in the context of the aldol reaction, are most probably formed via a multistep domino mechanism.( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]


Alternative Mechanistic Paths in the Hetero-Diels,Alder Reaction of ,-Oxothiones: A Theoretical Study

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2007
Laura Legnani
Abstract DFT calculations at the B3LYP/6-311+G(d,p) level for the C, H, and O atoms and at the 6-311+G(2df,p) level for the S atom were used to study the hetero-Diels,Alder reactions between several ,-oxothiones and ethylene or methyl vinyl ether (MVE). All the transition states and the intermediates along the reaction pathways, as well as the reaction products, were located. The reactions with ethylene are all concerted though asynchronous whereas in the reactions with MVE the electron-releasing character of the methoxy substituent lowers the energy barriers and enhances the asynchronicity and the charge transfer process to such an extent that the reaction may become unconcerted and exhibit a two-step mechanism with a zwitterionic intermediate derived from nucleophilic attack of electron-rich MVE to the sulfur atom of the strongly electrophilically activated ,-oxothiones. The reactions are also favored by the conjugation of the newly formed C=C bond. Moreover, the geometric features of the diene exert a nonnegligible role, as dienes that are planar or almost planar in their ground state show a lower energy barrier. Thus, both geometric and electronic features of the dienes as well as of the dienophiles play a significant role in the easiness of the reactions and in their mechanism. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]


Novel Chiral (Salen)MnIII Complexes Containing a Calix[4]arene Unit as Catalysts for Enantioselective Epoxidation Reactions of (Z)-Aryl Alkenes

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 16 2005
Maria E. Amato
Abstract New asymmetric (salen)MnIII and UO2 complexes containing a calix[4]arene unit in the ligand framework were synthesized. The UO2 complexes were characterized by 1H-, 13C-, 2D TOCSY and T-ROESY NMR spectroscopy. Furthermore, the structure of one UO2 complex was determined by single-crystal X-ray analysis. The data showed that UO2 complexes, which can be considered in first approximation models of the Mn=O oxidant active species, possess a chiral pocket and adopt relevant conformations for the selectivity of the oxygen transfer process. Epoxidation data of model alkenes with the MnIII complexes showed moderate ee values and were not conclusive in indicating that the calix[4]arene unit might be able to influence the selectivity by a molecular recognition mechanism. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]


Novel Model Sulfur Compounds as Mechanistic Probes for Enzymatic and Biomimetic Oxidations

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2005
Alicia B. Peory
Abstract To test for the intermediacy of sulfide radical cations in biomimetic and enzymatic oxidations, the sulfides PhSCH3 (1a), PhSCH2Ph (1b), PhSCHPh2 (1c), PhSCPh3 (1d), CH3SCHPh2 (2), PhSCH2CH=CH2 (3), PhSCH2CH=CHPh (4) and CH3SCH2CH=CHPh (5) were studied, and their results were compared to those obtained for the corresponding chemical electron transfer (CET) and photoinduced electron transfer (PET) oxidations. The radical cations generated from 3,5 by CET in the presence of cerium(IV) ammonium nitrate (CAN) yielded only fragmentation products from the alkyl cations and the thiyl radicals (RS), whereas 2+ afforded both fragmentation and mainly ,-deprotonation products. Photochemical treatment of the sulfides 1a and 1b with C(NO2)4 gave only the corresponding sulfoxides, while fragmentation was the main pathway for the photoreactions of 1c, 2 and 5, and for 1d only this latter process was observed. These results support our selection of the sulfides RSCHPh2, RSCH2CH=CHPh (R = Me, Ph) and PhSCPh3 as models for the biomimetic and enzymatic studies. As evidenced by the sulfoxides and sulfones detected as unique products both in protic and in aprotic solvents, it is proposed that the mechanism of the biomimetic sulfoxidations of sulfides 1c and 2,5 by TPPFeIIICl is direct oxygen transfer. Three enzymes , Coprinus cinereus peroxidase (CiP), horseradish peroxidase (HRP) and chloroperoxidase (CPO) , were studied in the oxidation of sulfides 1a, 2, 4 and 5. The use of a racemic alkyl hydroperoxide in the CiP enzymatic oxidation of sulfides 5 and 2 yielded the corresponding sulfoxides (23 and 29%) and the aldehyde or benzophenone (5%), respectively. These results suggest the involvement of an ET process for the CiP-catalysed oxidation. Fragmentation products were observed in the enzymatic oxidation of sulfide 4 with HRP, which confirms the previously proposed ET mechanism. On the other hand, the CPO-enzymatic oxidation of sulfide 5 yielded only the corresponding sulfoxide, as would be expected for a direct oxygen-transfer or oxene mechanism. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]


Epithelial-to-mesenchymal transition of murine liver tumor cells promotes invasion,,

HEPATOLOGY, Issue 3 2010
Wei Ding
Epithelial-to-mesenchymal transition (EMT) is predicted to play a critical role in metastatic disease in hepatocellular carcinoma. In this study, we used a novel murine model of EMT to elucidate a mechanism of tumor progression and metastasis. A total of 2 106 liver cells isolated from Ptenloxp/loxp/Alb-Cre+ mice, expanded from a single CD133+CD45, cell clone, passage 0 (P0), were sequentially transplanted to obtain two passages of tumor cells, P1 and P2. Cells were analyzed for gene expression using microarray and real-time polymerase chain reaction. Functional analysis included cell proliferation, migration, and invasion in vitro and orthotopic tumor metastasis assays in vivo. Although P0, P1, and P2 each formed tumors consistent with mixed liver epithelium, within the P2 cells, two distinct cell types were clearly visible: cells with epithelial morphology similar to P0 cells and cells with fibroblastoid morphology. These P2 mesenchymal cells demonstrated increased locomotion on wound healing; increased cell invasion on Matrigel basement membrane; increased EMT-associated gene expression of Snail1, Zeb1, and Zeb2; and down-regulated E-cadherin. P2 mesenchymal cells demonstrated significantly faster tumor growth in vivo compared with P2 epithelial counterparts, with invasion of intestine, pancreas, spleen, and lymph nodes. Furthermore, P2 mesenchymal cells secreted high levels of hepatocyte growth factor (HGF), which we propose acts in a paracrine fashion to drive epithelial cells to undergo EMT. In addition, a second murine liver cancer stem cell line with methionine adenosyltransferase 1a deficiency acquired EMT after sequential transplantations, indicating that EMT was not restricted to Pten-deleted tumors. Conclusion: EMT is associated with a high rate of liver tumor proliferation, invasion, and metastasis in vivo, which is driven by HGF secreted from mesenchymal tumor cells in a feed-forward mechanism. (HEPATOLOGY 2010) [source]


Specific role for acyl CoA:Diacylglycerol acyltransferase 1 (Dgat1) in hepatic steatosis due to exogenous fatty acids,

HEPATOLOGY, Issue 2 2009
Claudio J. Villanueva
Nonalcoholic fatty liver disease, characterized by the accumulation of triacylglycerols (TGs) and other lipids in the liver, often accompanies obesity and is a risk factor for nonalcoholic steatohepatitis and fibrosis. To treat or prevent fatty liver, a thorough understanding of hepatic fatty acid and TG metabolism is crucial. To investigate the role of acyl CoA:diacylglycerol acyltransferase 1 (DGAT1), a key enzyme of TG synthesis, in fatty liver development, we studied mice with global and liver-specific knockout of Dgat1. DGAT1 was required for hepatic steatosis induced by a high-fat diet and prolonged fasting, which are both characterized by delivery of exogenous fatty acids to the liver. Studies in primary hepatocytes showed that DGAT1 deficiency protected against hepatic steatosis by reducing synthesis and increasing the oxidation of fatty acids. In contrast, lipodystrophy (aP2-SREBP-1c436) and liver X receptor activation (T0901317), which increase de novo fatty acid synthesis in liver, caused steatosis independently of DGAT1. Pharmacologic inhibition of Dgat1 with antisense oligonucleotides protected against fatty liver induced by a high-fat diet. Conclusion: Our findings identify a specific role for hepatic DGAT1 in esterification of exogenous fatty acids and indicate that DGAT1 contributes to hepatic steatosis induced by this mechanism. (HEPATOLOGY 2009.) [source]


A sequential equilibrium for the army's targeted selective reenlistment bonus program

HUMAN RESOURCE MANAGEMENT, Issue 1 2007
Scott E. Carrell
Wecompute a sequential equilibrium for the U.S.Army'sTargeted Selective Reenlistment Bonus Program in whichtheArmy offers a bonus, soldiers with a low cost of serving in an undesirable location accept the bonus and are sent to an undesirable location, and soldiers with a high cost of serving in an undesirable location reenlist but decline the bonus.Wefind that this program benefits both theArmy and soldiers, increases retention, increases the number of soldierswho serve in an undesirable location, and better matches soldiers to assignments. We discuss implications of our model on human resource management practices for theArmy in its administration of the bonus program and its application to other large organizations that set wages through a rules-based mechanism. 2007 Wiley Periodicals, Inc. [source]


Dietary prevention of malignant glioma aggressiveness, implications in oxidant stress and apoptosis

INTERNATIONAL JOURNAL OF CANCER, Issue 2 2008
Daniel Pouliquen
Abstract Our study explored the influence of diet on gliomagenesis and associated systemic effects (SE) in rats. The experimental diet contained various ingredients supposed to interfere with carcinogenesis, mainly phytochemicals (PtcD for phytochemical diet) and its effects were compared to those of the same diet without the phytochemicals (BD for basal diet). Glioma was induced by ethylnitrosourea to pregnant females fed the diets from the start of gestation until the moment of sacrifice of the offpsrings. In male rats fed the PtcD or the BD the incidence of gliomas was markedly reduced compared to rats fed a standard diet (StD). In females this effect was weaker and was limited to the PtcD. A significant proportion of rats with brain tumors and fed the StD exhibited SE evidenced by weight loss, a shorter survival, reduction in liver weight and an increased proportion of liver mitochondria, effects that were not observed in their counterpart fed PtcD. Comparison of the expression of genes involved in the balance proliferation/apoptosis and in the response to oxidative stress in male brain tumors showed that the prevention of SE was associated with an increase in bcl-2 and catalase and a decrease in ki-67, sod-1 and sod- 2 transcripts. These results show that the degree of agressiveness of gliomas can be modulated by dietary interventions and suggest that some phytochemicals with antioxidant properties could participate to the mechanism. 2008 Wiley-Liss, Inc. [source]


Multiple criticality and staged ignition of methane in the counterflow

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2009
Wei Liu
The counterflow ignition of methane was investigated, with particular interest in the role of radical versus thermal runaway. Simulation with different kinetic mechanisms showed that the ignition response is qualitatively sensitive to the kinetic mechanism adopted, either exhibiting or not exhibiting two ignition turning points in the S-curve response. For the former situation, ignition could take place in a staged manner with either increasing temperature or decreasing strain rate of the counterflow, characterized by the first ignition event being radical induced with negligible thermal effect and the second ignition event requiring thermal feedback. Sensitivity analysis and a recently developed chemical explosive mode analysis were performed to identify the dominant reactions in the radical runaway stage, revealing the importance of branching pathways involving the HO2 radical. Counterflow experiments were also conducted, yielding useful information on the ignition response. The study identifies items of further research to sharpen the comprehensiveness and accuracy of the methane oxidation mechanism. 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 764,776, 2009 [source]


Synthesis of polyetherols with isocyanuric ring.

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2009
Kinetics, mechanisms of reactions, part 2: Consecutive reaction of ethylene carbonate with isocyanuric acid
The kinetics and mechanism of the reaction between isocyanuric acid and ethylene carbonate was studied. The multistep reaction in the presence of potassium carbonate as catalyst leads to polyetherols. The imide and hydroxyl groups of intermediates react with ethylene carbonate by slightly different mechanism and kinetics. The rate constants for these elementary processes were established, and based on these experimental data the mechanism of reaction was proposed. Using the isocyanuric acid and 1,3,5-tris(2-hydroxyethyl)isocyanurate, it has been found that the reaction of ethylene carbonate with intermediates occurs via a mixed mechanism. 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 523,531, 2009 [source]


Kinetics and mechanism of adducts formation of tetraaza cobalt(II) complexes with some organic bases in DMF solvent

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2007
Mozaffar Asadi
The kinetics and mechanism of the adduct formation of two Co(II) tetraaza complexes, [Co(ampen)] {[(N,N,-ethylenebis-(o -amino-,-phenylbenzylideneiminato)cobalt(II)]} and [Co(campen)] {[(N,N,-ethylenebis-(5-chloro- o -amino-,-phenylbenzylideneiminato)cobalt(II)]}, with four organic bases, 4-nitro imidazole (4-NO2Imid), 4-methyl imidazole (4-MeImid), imidazole (Imid), and 1-methyl imidazole (1-MeImid), in DMF were studied spectrophotometrically. The kinetic parameters and the second-order k2 rate constants show the following nucleophilicity trend of the bases toward the given substrate: 4-NO2Imid > 4-MeImid > Imid > 1-MeImid. The linear plots of kobs vs. the molar concentration of the base, the high span of k2 values, and the large negative values of ,S, suggest an associative (A) mechanism. 2007 Wiley Periodicals, Inc. 39: 137,144, 2007 [source]


The unimolecular elimination kinetics of benzaldoxime in the gas phase

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2007
Libia L. Julio
The kinetics of the gas-phase elimination of benzaldoxime was determined in a static reaction system over the temperature and pressure range 350C,400C and 56,140 Torr, respectively. The products obtained were benzonitrile and water. The reaction was found to be homogeneous, unimolecular, and tend to obey a first-order rate law. The observed rate coefficient is represented by the following Arrhenius equation: According to kinetic and thermodynamic parameters, the reaction proceeds through a concerted, semi-polar, four-membered cyclic transition state type of mechanism. 2007 Wiley Periodicals, Inc. 39: 145,147, 2007 [source]


Kinetics of Fe(II) reduction of cis -halogeno(dodecylamine) bis(ethylenediamine)- cobalt(III) complex ion in aqueous solutions

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2006
K. Santhakumar
Kinetics of reduction of the surfactant complex ions, cis -chloro/bromo (dodecylamine)bis(ethylenediamine)cobalt(III) by iron(II) in aqueous solution was studied at 303, 308, and 313 K by spectrophotometry method under pseudo-first-order conditions, using an excess of the reductant. The second-order rate constant remains constant below critical micelle concentration (cmc), but increases with cobalt(III) concentration above cmc, and the presence of aggregation of the complex itself alters the reaction rate. The rate of reaction was not affected by the added [H+]. Variation of ionic strength (,) influences the reaction rate. Activation and thermodynamic parameters have been computed. It is suggested that the reaction of Fe2+ (aq) with cobalt(III) complex proceeds by the inner-sphere mechanism. 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 98,105, 2006 [source]


The elimination kinetics and mechanisms of ethyl piperidine-3-carboxylate, ethyl 1-methylpiperidine-3-carboxylate, and ethyl 3-(piperidin-1-yl)propionate in the gas phase

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2006
Angiebelk Monsalve
The gas-phase elimination kinetics of the above-mentioned compounds were determined in a static reaction system over the temperature range of 369,450.3C and pressure range of 29,103.5 Torr. The reactions are homogeneous, unimolecular, and obey a first-order rate law. The rate coefficients are given by the following Arrhenius expressions: ethyl 3-(piperidin-1-yl) propionate, log k1(s,1) = (12.79 0.16) , (199.7 2.0) kJ mol,1 (2.303 RT),1; ethyl 1-methylpiperidine-3-carboxylate, log k1(s,1) = (13.07 0.12),(212.8 1.6) kJ mol,1 (2.303 RT),1; ethyl piperidine-3-carboxylate, log k1(s,1) = (13.12 0.13) , (210.4 1.7) kJ mol,1 (2.303 RT),1; and 3-piperidine carboxylic acid, log k1(s,1) = (14.24 0.17) , (234.4 2.2) kJ mol,1 (2.303 RT),1. The first step of decomposition of these esters is the formation of the corresponding carboxylic acids and ethylene through a concerted six-membered cyclic transition state type of mechanism. The intermediate ,-amino acids decarboxylate as the ,-amino acids but in terms of a semipolar six-membered cyclic transition state mechanism. 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 106,114, 2006 [source]


Inorganic reactions of iodine(+1) in acidic solutions

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2004
Guy Schmitz
We present a thorough analysis of the former works concerning the hydrolysis of iodine and its mechanism in acidic or neutral solutions and recommend values of equilibrium and kinetic constants. Since the literature value for the reaction H2OI+ , HOI + H+ appeared questionable, we have measured it by titration of acidic iodine solutions with AgNO3. Our new value, K(H2OI+ , HOI + H+) , 2 M at 25C, is much larger than accepted before. It decreases slowly with the temperature. We have also measured the rate of the reaction 3HOI , IO3, + 2I, + 3H+ in perchloric acid solutions from 5 10,2 M to 0.5 M. It is a second order reaction with a rate constant nearly independent on the acidity. Its value is 25 M,1 s,1 at 25C and decreases slightly when the temperature increases, indicating that the disproportionation mechanism is more complicated than believed before. An analysis of the studies of this disproportionation in acidic and slightly basic solutions strongly supports the importance of a dimeric intermediate 2HOI , I2OH2O in the mechanism. 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:480,493, 2004 [source]


Kinetics and mechanism of oxidation of a ternary complex involving dipicolinatochromium(III) and DL -aspartic acid by N -bromosuccinimide

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2004
Hassan A. Ewais
The kinetics of oxidation of [CrIII(Dpc)(Asp)(H2O)2] (Dpc = dipicolinic acid and Asp = DL -aspartic acid) by N -bromosuccinimide (NBS) in aqueous solution have been found to obey the equation: where k2 is the rate constant for the electron transfer process, K1 is the equilibrium constant for deprotonation of [CrIII(Dpc)(Asp)(H2O)2], K2 and K3 are the pre-equilibrium formation constants of precursor complexes [CrIII(Dpc)(Asp)(H2O)(NBS)] and [CrIII(Dpc)(Asp)(H2O)(OH)(NBS)],. Values of k2 = 4.85 10,2 s,1, K1 = 1.85 10,7 mol dm,3, and K2 = 78.2 mol,1 dm3 have been obtained at 30C and I = 0.1 mol dm,3. The experimental rate law is consistent with a mechanism in which the deprotonated [CrIII(Dpc)(Asp)(H2O)(OH)], is considered to be the most reactive species compared to its conjugate acid. It is assumed that electron transfer takes place via an inner-sphere mechanism. 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 394,400, 2004 [source]


Kinetics and mechanism of oxidation of antimony(III) by keggin-type 12-tungstocobaltate(III) in aqueous hydrochloric acid medium

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2003
B. D. Bhosale
The reaction between Sb(III) and [CoIIIW12O40]5, proceeds with two, one-electron steps; formation of unstable Sb(IV) is the slow first step followed by its reaction with another oxidant in a fast step. The reaction rate is unaffected by the [H+] as there are no protonation equlibria involved with both the reactants, whereas the accelerating effect of chloride ion is due to the formation of an active chlorocomplex of the reductant, SbCl63,. Increase in the ionic strength and decrease in the relative permittivity of the medium increases the rate of the reaction, which is attributed to the formation of an outer-sphere complex between the reactants. The activation parameters were also determined and these values support the proposed mechanism. 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 9,14, 2003 [source]


Kinetics and mechanism of the reaction of para -chlorophenyl aryl chlorophosphates with anilines in acetonitrile

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2002
Hai Whang Lee
The kinetics and mechanism of the nucleophilic substitution reactions of p -chlorophenyl aryl chlorophosphates (2) with anilines are investigated in acetonitrile at 55C. Relatively large magnitudes of ,X and ,X values are indicative of a large degree of bond making in the TS. Smaller magnitudes of ,X (0.20 for X = H) and ,XY (,0.30) than those for the corresponding reactions with phenyl aryl chlorophosphates (1) (,X = 0.54 for X = H and ,XY = ,1.31) are interpreted to indicate partial electron loss, or shunt, towards the electron acceptor equatorial ligand (p -ClC6H4O-) in the bipyramidal pentacoordinated transition state. The inverse secondary kinetic isotope effects (kH/kD = 0.64,0.87) involving deuterated aniline (ND2C6H4X) nucleophiles, and small ,H, and large negative ,S, are obtained. These results are consistent with a concerted nucleophilic substitution mechanism. 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 632,637, 2002 [source]


Kinetics and mechanism of oxidation of aurate(I) by peroxydisulphate in aqueous hydrochloric acid

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2002
R. M. Babshet
The reaction between Au(I), generated by reaction of thallium(I) with Au(III), and peroxydisulphate was studied in 5 mol dm,3 hydrochloric acid. The reaction proceeds with the formation of an ion-pair between peroxydisulphate and chloride ion as the Michealis,Menten plot was linear with intercept. The ion-pair thus formed oxidizes AuCl2, in a slow two-electron transfer step without any formation of free radicals. The ion-pair formation constant and the rate constant for the slow step were determined as 113 20 dm,3 mol,1 and 5.0 1.0 10,2 dm3 mol,1 s,1, respectively. The reaction was retarded by hydrogen ion, and formation of unreactive protonated form of the reductant, HAuCl2, causes the rate inhibition. From the hydrogen ion dependence of the reaction rate, the protonation constant was calculated to be as 0.6 0.1 dm3 mol,1. The activation parameters were determined and the values support the proposed mechanism. 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 589,594, 2002 [source]


Approximate knowledge modeling and classification in a frame-based language: The system CAIN

INTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 6 2001
Colette Faucher
In this article, we present an extension of the frame-based language Objlog+, called CAIN, which allows the homogeneous representation of approximate knowledge (fuzzy, uncertain, and default knowledge) by means of new facets. We developed elements to manage approximate knowledge: fuzzy operators, extension of the inheritance mechanisms, and weighting of structural links. Contrary to other works in the domain, our system is strongly based on a theoretical approach inspired from Zadeh's and Dubois' works. We also defined an original instance classification mechanism, which has the ability to take into account the notions of typicality and similarity as they are presented in the psychological literature. Our model proposes consideration of a particular semantics of default values to estimate the typicality between a class and the instance to classify (ITC). In that way, the possibilities of the typicality representation proposed by frame-based languages are exploited. To find the most appropriate solution we do not systematically choose the most specific class that matches the ITC but we retain the most typical solution. Approximate knowledge is used to make the matching used during the classification process more flexible. Taking into account additional knowledge concerning heuristics and elements of cognitive psychology leads to the enrichment of the classification mechanism. 2001 John Wiley & Sons, Inc. [source]