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Possible Reactions (possible + reaction)
Terms modified by Possible Reactions Selected AbstractsKinetics of Urea Decomposition in the Presence of Transition Metal Ions: Ni2+JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2006Bora Mavis The literature on kinetics of the urea decomposition reaction was reviewed for the 333,373 K range of temperature. Possible reactions in the pH range of 5,9 were identified. Kinetic simulations indicated significant accumulation of the cyanate intermediate in the pH-time,temperature range that was studied. The effects of Ni2+ hydrolysis and complexation with the urea decomposition products were incorporated into the simulations. The kinetic simulation of the rate of Ni2+ removal from the solutions was compared against the experimental data. The experimental results indicated an agglomerative growth mechanism for the precipitation process. Chemical analyses showed that the composition of the precipitate varies with digestion time, in agreement with the predictions of the kinetic simulation. [source] Effect of the type of nylon chain-end on the compatibilization of PP/PP-GMA/nylon 6 blendsPOLYMER INTERNATIONAL, Issue 2 2002Adriana Tedesco Abstract Polyamide and polypropylene (PP) are two important classes of commercial polymers; however, their direct mixing leads to incompatible blends with poor properties. Polypropylene functionalized with glycidyl methacrylate (PP-GMA) was used as a compatibilizer in blends of PP and nylon 6, because of the possible reaction of NH2 and COOH groups with the epoxide group of GMA. Two types of nylon 6 with different ratios between NH2 and COOH groups were used. The one with higher concentration of COOH groups was less compatible with PP in a binary blend. When PP-GMA was used as a compatibilizer, a better dispersion of nylon in the PP matrix was obtained together with better mechanical properties for both nylons used in this work. © 2001 Society of Chemical Industry [source] Quantum chemical study of penicillin: Reactions after acylationINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 10 2007Rui Li Abstract The density functional theory methods were used on the model molecules of penicillin to determine the possible reactions after their acylation on ,-lactamase, and the results were compared with sulbactam we have studied. The results show that, the acylated-enzyme tetrahedral intermediate can evolves with opening of ,-lactam ring as well as the thiazole ring; the thiazole ring-open products may be formed via ,-lactam ring-open product or from tetrahedral intermediate directly. Those products, in imine or enamine form, can tautomerize via hydrogen migration. In virtue of the water-assisted, their energy barriers are obviously reduced. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Theoretical study of the · H reaction with cytosineINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2007Hongyu Zhang Abstract We studied three possible reactions of H atom attacking the cytosine, using density functional theory (DFT) calculations. The results indicate that the H atom addition to the N3 site of cytosine is energetically more favorable than to the C5 or C6 site. The reaction of addition to the C6 site has an energy barrier of ,2.77 kcal/mol, which is ,2 kcal/mol higher than addition to C5. The energy of C5 H-adduct radical is also lower than that of C6 H-adduct radical. From the point of view of both energetics and reaction kinetics, the addition of the H atom to the C5 site is preferred to the addition to the C6 site. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Theoretical study of ribonucleotide reductase mechanism-based inhibition by 2,-azido-2,-deoxyribonucleoside 5,-diphosphatesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2004Susana Pereira Abstract 2,-Azido-2,-deoxyribonucleoside 5,-diphosphates are mechanism-based inhibitors of Ribonucleotide Reductase. Considerable effort has been made to elucidate their mechanism of inhibition, which is still controversial and not fully understood. Previous studies have detected the formation of a radical intermediate when the inhibitors interact with the enzyme, and several authors have proposed possible structures for this radical. We have conducted a theoretical study of the possible reactions involved, which allowed us to identify the structure of the new radical among the several proposals. A new reactional path is also proposed that is the most kinetically favored to yield this radical and ultimately inactivate the enzyme. The energetic involved in this mechanism, both for radical formation and radical decay, as well as the calculated Hyperfine Coupling Constants for the radical intermediate, are in agreement with the correspondent experimental values. This mechanistic alternative is fully coherent with remaining experimental data. © 2003 Wiley Periodicals, Inc. J Comput Chem 25: 227,237, 2004 [source] Volume of distribution at steady state for a linear pharmacokinetic system with peripheral eliminationJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2004Leonid M. Berezhkovskiy Abstract The problem of finding the steady-state volume of distribution Vss for a linear pharmacokinetic system with peripheral drug elimination is considered. A commonly used equation Vss,=,(D/AUC)*MRT is applicable only for the systems with central (plasma) drug elimination. The following equation, Vss,=,(D/AUC)*MRTint, was obtained, where AUC is the commonly calculated area under the time curve of the total drug concentration in plasma after intravenous (iv) administration of bolus drug dose, D, and MRTint is the intrinsic mean residence time, which is the average time the drug spends in the body (system) after entering the systemic circulation (plasma). The value of MRTint cannot be found from a drug plasma concentration profile after an iv bolus drug input if a peripheral drug exit occurs. The obtained equation does not contain the assumption of an immediate equilibrium of protein and tissue binding in plasma and organs, and thus incorporates the rates of all possible reactions. If drug exits the system only through central compartment (plasma) and there is an instant equilibrium between bound and unbound drug fractions in plasma, then MRTint becomes equal to MRT,=,AUMC/AUC, which is calculated using the time course of the total drug concentration in plasma after an iv bolus injection. Thus, the obtained equation coincides with the traditional one, Vss,=,(D/AUC)*MRT, if the assumptions for validity of this equation are met. Experimental methods for determining the steady-state volume of distribution and MRTint, as well as the problem of determining whether peripheral drug elimination occurs, are considered. The equation for calculation of the tissue,plasma partition coefficient with the account of peripheral elimination is obtained. The difference between traditionally calculated Vss,=,(D/AUC)*MRT and the true value given by (D/AUC)*MRTint is discussed. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:1628,1640, 2004 [source] Computational study of the mechanism of thermal decomposition of xanthates in the gas phase (the Chugaev reaction),JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2008Ederley Vélez Abstract A theoretical study on the mechanism of the thermal decomposition of a series of xanthates, O-alkyl S-methyl and S-alkyl O - methyl dithiocarbonates, has been carried out, and the alkyl groups being ethyl, isopropyl, and tert -butyl. Kinetically, these xanthates can be classified in two groups: those where the oxygen atom is involved in the bonding changes of the transition state (properly the Chugaev reaction), and those where it is not, O-alkyl S-methyl and S-alkyl O - methyl dithiocarbonates, respectively. We have studied not only the thermal elimination reactions but also the other possible reactions such as the thione-to-thiol rearrangement and the nucleophilic substitution to give ethers or thioethers. Two possible mechanisms for the thermal elimination reactions, in one and in two steps, respectively, have been studied. Calculations were made at the MP2/6-31G(d) level of theory, and the progress of the reactions has been followed by means of the Wiberg bond indices. Copyright © 2008 John Wiley & Sons, Ltd. [source] Pulsed Laser Polymerization of Alkyl Acrylates: Potential Effects of the Oxygen Presence and High Laser Power,MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 1 2006Patrice Castignolles Abstract Summary: Unexpected difficulties are encountered in the determination of propagation rate coefficients (kp) in free radical polymerization of alkyl acrylates by pulsed laser polymerization (PLP), mainly due to intramolecular transfer to polymer.1 This article is focused on the role played by the high laser power in these difficulties and the possible reactions of mid-chain radical with residual oxygen. Removing the oxygen by simple bubbling of nitrogen is sufficient to avoid alteration of the polymerization kinetics of acrylates by residual oxygen under PLP conditions. Moreover, no degradation of polymer (or solvent) has been detected after irradiation with the high laser power typically used in PLP experiments. However, it has been shown that this high laser power completely prevents from having a temporally and spatially homogeneous radical concentration in the PLP cell. A model is proposed here to simulate the pulsed laser polymerization taking initiator consumption and laser energy absorption into account. According to our simulation results, this non-negligible initiator consumption and laser power absorption can indeed have a positive influence, i.e., it favors the obtainment of a bimodal molar mass distribution fulfilling the IUPAC consistency criteria. This observation may contradict the idea that PLP-SEC is not suitable to determine accurate kp values for acrylates above 20,30,°C. Instantaneous MMDs formed after N pulses. Simulation taking initiator consumption and laser absorption into account. [source] Biases affecting the proportional reporting ratio (PRR) in spontaneous reports pharmacovigilance databases: the example of sertindolePHARMACOEPIDEMIOLOGY AND DRUG SAFETY, Issue 4 2003Nicholas Moore Abstract Background Automated measures of reporting disproportionality in databases of spontaneous reports of adverse drug reactions are an emerging tool to identify drug-related alerts. Sertindole, a new atypical neuroleptic known to prolong the QT interval, was suspended in November 1998 because the proportion of reports of fatal reactions suggesting arrhythmia among all reports with sertindole was almost ten times higher than that for other atypical neuroleptics in the UK. This excess risk was not predicted in preclinical data and had not been found in premarketing trials. Method Reporting patterns over time were analysed. Prescription Event Monitoring (PEM) studies and a large retrospective cohort allowed for the comparison of actual death rates with atypical neuroleptics, and to assess which proportion of the deaths that occurred were reported. Results There were indications of possible skewing of reporting related to notoriety, surveillance and market size effects. Death rates in PEM studies were essentially similar between sertindole and other neuroleptics. Cardiac deaths had been two to three times more often reported than other causes of death. Conclusion Proportional reporting ratios indicate differential reporting of possible reactions, not necessarily differential occurrence. There was no indication of an actual increase of risk of all causes or cardiac deaths during sertindole treatment, but only an increased risk of its being reported. The suspension of sertindole was rescinded by Committee on Proprietary Medicinal Products (CPMP) in October 2001. Copyright © 2003 John Wiley & Sons, Ltd. 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