Kinetic

Distribution by Scientific Domains
Distribution within Chemistry

Terms modified by Kinetic

  • kinetic analysis
  • kinetic approach
  • kinetic aspect
  • kinetic asymmetric transformation
  • kinetic barrier
  • kinetic behavior
  • kinetic behaviour
  • kinetic characteristic
  • kinetic characterization
  • kinetic coefficient
  • kinetic constant
  • kinetic control
  • kinetic curve
  • kinetic data
  • kinetic data show
  • kinetic description
  • kinetic diameter
  • kinetic difference
  • kinetic effect
  • kinetic effects
  • kinetic energy
  • kinetic equation
  • kinetic evaluation
  • kinetic evidence
  • kinetic experiment
  • kinetic expression
  • kinetic factor
  • kinetic feature
  • kinetic interpretation
  • kinetic investigation
  • kinetic isotope effect
  • kinetic isotope effects
  • kinetic law
  • kinetic limitation
  • kinetic measurement
  • kinetic mechanism
  • kinetic method
  • kinetic methods
  • kinetic model
  • kinetic modeling
  • kinetic modelling
  • kinetic models
  • kinetic parameter
  • kinetic parameter estimation
  • kinetic perimetry
  • kinetic process
  • kinetic profile
  • kinetic property
  • kinetic rate
  • kinetic rate constant
  • kinetic reaction
  • kinetic regime
  • kinetic resolution
  • kinetic result
  • kinetic scheme
  • kinetic simulation
  • kinetic stability
  • kinetic step
  • kinetic studies
  • kinetic study
  • kinetic theory
  • kinetic value

  • Selected Abstracts


    Quantitative Studies of Metal Ion Adsorption on a Chemically Modified Carbon Surface: Adsorption of Cd(II) and Hg(II) on Glutathione Modified Carbon

    ELECTROANALYSIS, Issue 8 2009
    Poobalasingam Abiman
    Abstract The adsorption behavior of model toxic metal cations namely Cd(II) and Hg(II) on carbon surfaces chemically modified by glutathione was investigated as a function of the concentration of Cd2+ and Hg2+ ions, time and the amount of modified carbon used. Square wave and linear sweep anodic stripping voltammetry was used to monitor the uptake of Cd(II) and Hg(II) ions respectively. Kinetic and adsorption isotherm studies reveal that both Cd(II) and Hg(II) ions undergo similar large adsorption with the modified glutathione carbon material (Glu-carbon). [source]


    Ni2+ removal from aqueous solutions using conditioned clinoptilolites: Kinetic and isotherm studies

    ENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 1 2009
    Semra Çoruh
    Abstract The aim of this study is to investigate the effects of conditioning with NaCl and HCl solutions on removal of Ni2+ ions from aqueous solutions using natural clinoptilolite. Batch studies were performed to evaluate the effects of various parameters such as chemically conditioning, adsorbent amount, contact time, initial pH of the solution, mixing temperature, and initial metal ions. The results clearly showed that the conditioning improved both the exchange capacity and the removal efficiency. Langmuir, Freundlich, Temkin, and Dubinin-Kaganer-Radushkevich (DKR) isotherm models were adopted to describe the adsorption isotherms. Adsorption isotherms of Ni2+ ions could be best modeled by Langmuir equation. Three simplified models including pseudo-second-order, intraparticle diffusion and Elovich were used to test the adsorption kinetics. These results indicate a significant potential for the natural and conditioned clinoptilolites as an adsorbent/ion-exchange material for heavy metal removal. © 2008 American Institute of Chemical Engineers Environ Prog, 2009 [source]


    Synthesis, Protonation and CuII Complexes of Two Novel Isomeric Pentaazacyclophane Ligands: Potentiometric, DFT, Kinetic and AMP Recognition Studies

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2009
    Andrés G. Algarra
    Abstract The synthesis and coordination chemistry of two novel ligands, 2,6,9,12,16-pentaaza[17]metacyclophane (L1) and 2,6,9,12,16-pentaaza[17]paracyclophane (L2), is described. Potentiometric studies indicate that L1 and L2 form a variety of mononuclear complexes the stability constants of which reveal a change in the denticity of the ligand when moving from L1 to L2, a behaviour that can be qualitatively explained by the inability of the paracyclophanes to simultaneously use both benzylic nitrogen atoms for coordination to a single metal centre. In contrast, the formation of dinuclear hydroxylated complexes is more favoured for the paraL2 ligand. DFT calculations have been carried out to compare the geometries and relative energies of isomeric forms of the [CuL]2+ complexes of L1 and L2 in which the cyclophane acts either as tri- or tetradentate. The results indicate that the energy cost associated with a change in the coordination mode of the cyclophane from tri- to tetradentate is moderate for both ligands so that the actual coordination mode can be determined not only by the characteristics of the first coordination sphere but also by the specific interactions with additional nearby water molecules. The kinetics of the acid promoted decomposition of the mono- and dinuclear CuII complexes of both cyclophanes have also been studied. For both ligands, dinuclear complexes convert rapidly to mononuclear species upon addition of excess acid, the release of the first metal ion occurring within the mixing time of the stopped-flow instrument. Decomposition of the mononuclear [CuL2]2+ and [CuHL2]3+ species occurs with the same kinetics, thus showing that protonation of [CuL2]2+ occurs at an uncoordinated amine group. In contrast, the [CuL1]2+ and [CuHL1]3+ species show different decomposition kinetics indicating the existence of significant structural reorganisation upon protonation of the [CuL1]2+ species. The interaction of AMP with the protonated forms of the cyclophanes and the formation of mixed complexes in the systems Cu,L1 -AMP, Cu,L2 -AMP, and Cu,L3 -AMP, where L3 is the related pyridinophane containing the same polyamine chain and 2,6-dimethylpyridine as a spacer, is also reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]


    Kinetic and Thermodynamic Studies of the Disproportionation of Hydrogen Peroxide by Dimanganese(ii,ii) and -(ii,iii) Complexes of a Bridging Phenolate Ligand

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2005
    Lionel Dubois
    Abstract The dimanganese(ii,ii) complexes [Mn2(L)(OAc)2(CH3OH)]-(ClO4) (1a) and [Mn2(L)(OBz)2(H2O)](ClO4) (1b) as well as the dimanganese(ii,iii) complex [Mn2(L)(OAc)2(CH3OH)]-(ClO4)2 (2a), where HL is the asymmetric phenol ligand2-[bis(2-pyridylmethyl)aminomethyl]-6-{[(benzyl)(2-pyridyl-methyl)amino]methyl}-4-methylphenol, react with hydrogen peroxide in acetonitrile solution. The initial reaction rates and their temperature and acid/base dependencies were investigated by monitoring the dioxygen evolution. These studies revealed a first-order dependence on both the catalyst and H2O2 and a strong influence of the carboxylate. Electrospray ionisation mass spectrometry as well as EPR and UV/Vis spectroscopy were used to monitor the reaction catalysed by 2a. The same bis(,-oxo)dimanganese(III,IV) and (,-oxo)dimanganese(ii,iii) active species as found for 1a were detected in the catalytic medium. The EPR spectra recorded during the catalase-like reaction revealed the accumulation of the magnetically uncoupled dimanganese(ii,iii) precursor of the active bis(,-oxo)dimanganese(III,IV) species which dominates the spectra in the case of 1a. This difference can be attributed to the different pH conditions generated by the reaction and reflects differences in the initiation phases for the two catalysts. Overall, the kinetic and thermodynamic studies of H2O2 disproportionation by these dimanganese complexes are fully consistent with the mechanism deduced from our previous extensive spectroscopic studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]


    Kinetic and Equilibrium Studies of Reactions of N-Heterocycles with Dimeric and Monomeric Oxorhenium(V) Complexes

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2003
    James H. Espenson
    Abstract Equilibrium constants have been evaluated for the reaction {MeReO(edt)}2 + 2 L , 2 MeReO(edt)L, where edt is 1,2-ethanedithiolate and L is any of 13 N-donor heterocyclic ligands. The values of K range from 1.37(27)×10,2 for pyrimidine to 1.95(6)×106 for imidazole at 25 °C in chloroform. A successful correlation of logK with log (Ka) of HL+ was realized except in the case of the 2-substituted ligands 2-picoline and quinoline, where steric effects make K smaller than expected from the proton basicity of L. The kinetics of the same reactions were studied; the rate law for the reaction in the forward direction is given by ,d[{MeReO(edt)}2]/dt = {ka + kb[L]}[L] × [{MeReO(edt)}2]. Except for 2-picoline and quinoline, the major pathway is provided by the term that shows the quadratic dependence on [L]. Values of log (kb) also correlate with log K, and therefore necessarily with log (Ka). [source]


    Activation Mechanism and Infiltration Kinetic for Pressureless Melt Infiltration of Ti Activated Al2O3 Preforms by High Melting Alloy,

    ADVANCED ENGINEERING MATERIALS, Issue 8 2009
    Srdan Vasi
    The infiltration mechanism of X3CrNi13-4 in titanium activated porous alumina preforms has been studied. Investigations revealed isolated steel-covered titanium particles beyond the infiltration front. The only transport path possible for the steel to form such wetted islands is through the gas phase. Supersaturation due to the mixing of the steel gas phase with the titanium rich gas phase over the activator particle surfaces is proposed as condensation mechanism. Progressive condensation leads to the formation of a melt network, which serves as pathway for the original steel melt to infiltrate the preforms and to fill the remaining pore space in the non-wetting X3CrNi13-4/Ti-Al2O3 sytem. [source]


    Kinetic and biochemical analyses on the reaction mechanism of a bacterial ATP-citrate lyase

    FEBS JOURNAL, Issue 14 2002
    Tadayoshi Kanao
    The prokaryotic ATP-citrate lyase is considered to be a key enzyme of the carbon dioxide-fixing reductive tricarboxylic acid (RTCA) cycle. Kinetic examination of the ATP-citrate lyase from the green sulfur bacterium Chlorobium limicola (Cl -ACL), an ,4,4 heteromeric enzyme, revealed that the enzyme displayed typical Michaelis-Menten kinetics toward ATP with an apparent Km value of 0.21 ± 0.04 mm. However, strong negative cooperativity was observed with respect to citrate binding, with a Hill coefficient (nH) of 0.45. Although the dissociation constant of the first citrate molecule was 0.057 ± 0.008 mm, binding of the first citrate molecule to the enzyme drastically decreased the affinity of the enzyme for the second molecule by a factor of 23. ADP was a competitive inhibitor of ATP with a Ki value of 0.037 ± 0.006 mm. Together with previous findings that the enzyme catalyzed the reaction only in the direction of citrate cleavage, these kinetic features indicated that Cl -ACL can regulate both the direction and carbon flux of the RTCA cycle in C. limicola. Furthermore, in order to gain insight on the reaction mechanism, we performed biochemical analyses of Cl -ACL. His273 of the , subunit was indicated to be the phosphorylated residue in the catalytic center, as both catalytic activity and phosphorylation of the enzyme by ATP were abolished in an H273A mutant enzyme. We found that phosphorylation of the subunit was reversible. Nucleotide preference for activity was in good accordance with the preference for phosphorylation of the enzyme. Although residues interacting with nucleotides in the succinyl-CoA synthetase from Escherichia coli were conserved in AclB, AclA alone could be phoshorylated with the same nucleotide specificity observed in the holoenzyme. However, AclB was necessary for enzyme activity and contributed to enhance phosphorylation and stabilization of AclA. [source]


    Kinetic and crystallographic analysis of complexes formed between elastase and peptides from ,-casein

    FEBS JOURNAL, Issue 10 2001
    Penny A. Wright
    Human ,-casomorphin-7 (NH2 -Tyr-Pro-Phe-Val-Glu-Pro-Ile-CO2H) is a naturally occurring peptide inhibitor of elastase that has been shown to form an acyl-enzyme complex stable enough for X-ray crystallographic analysis at pH 5. To investigate the importance of the N-terminal residues of the ,-casomorphin-7 peptide for the inhibition of elastase, kinetic and crystallographic analyses were undertaken to identify the minimum number of residues required for effective formation of a stable complex between truncated ,-casomorphin-7 peptides and porcine pancreatic elastase (PPE). The results clearly demonstrate that significant inhibition of PPE can be effected by simple tri-, tetra-and pentapeptides terminating in a carboxylic acid. These results also suggest that in vivo regulation of protease activity could be mediated via short peptides as well as by proteins. Crystallographic analysis of the complex formed between N -acetyl-Val-Glu-Pro-Ile-CO2H and PPE at pH 5 (to 1.67 Å resolution) revealed an active site water molecule in an analogous position to that observed in the PPE/,-casomorphin-7 structure supportive of its assignment as the ,hydrolytic water' in the deacylation step of serine protease catalysis. [source]


    How closely do acute lethal concentration estimates predict effects of toxicants on populations?

    INTEGRATED ENVIRONMENTAL ASSESSMENT AND MANAGEMENT, Issue 2 2005
    John D. Stark
    Abstract Acute lethal dose/concentration estimates are the most widely used measure of toxicity and these data often are used in ecological risk assessment. However, the value of the lethal concentration (LC50) as a toxicological endpoint for use in ecological risk assessment recently has been criticized. A question that has been asked frequently is how accurate is the LC50 for prediction of longer-term effects of toxicants on populations of organisms? To answer this question, Daphnia pulex populations were exposed to nominal concentrations equal to the 48-h acute LC50 of 6 insecticides, Actara, Aphistar diazinon, pymetrozine, Neemix, and Spinosad; and 8 agricultural adjuvants, Bond, Kinetic, Plyac, R-11, Silwet, Sylgard 309, Water Maxx, and X-77; for 10 d. None of the D. pulex populations exposed to the acute LC50 of these insecticides were 50% lower than the control populations at the end of the study; exposure to diazinon resulted in populations that were higher than expected (91% of the control). Exposure to Actara and Aphistar resulted in populations that were <1 and 29% of the control, respectively. Exposure to Fulfill, Neemix, and Spinosad resulted in extinction. Extinction occurred after exposure to all of the adjuvants, except Silwet L-77 where the population was 31% of the control. These results corroborate other studies that indicate that the LC50 is not a good predictor of effects on population growth. Although lethal concentration estimates have their place in toxicology, namely to compare intrinsic toxicity of chemicals among species or susceptibility of a species to different chemicals over short time periods, population growth and growth-rate studies are necessary to predict toxicant effects on populations. [source]


    Metal-complex formation and DNA interaction of 5, 10,15,20-tetrakis(1-methyl-4-pyridiyl)-porphine: Study of the mechanistic aspects

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2010
    Sabriye Aydinoglu
    The macrocyclic porphyrin 5,10,15,20-tetrakis(1-methyl-4-pyridiyl)-porphine is studied in its ability to coordinate Cu(II) even at very low pH values and to interact, as a copper complex, with calf-thymus (CT-DNA). The kinetics and equilibria for metal-ligand complexes formation are spectrophotometrically studied, particularly focussing on the mechanistic information provided by the kinetic approach. The rate constants of complex formation is much lower than that of water exchange at Cu(II); this behavior is ascribed to an equilibrium between two porphyrin populations, only one of them being reactive. Concerning the interaction of the copper,porphyrin complex (D) with CT-DNA, it has been found that the complex binds to G,C base pairs by intercalation while forms external complex with the A,T base pairs. The kinetic results agree with a reaction mechanism that takes into account the slow shuffling from an AT-bound form (DAT) to a GC-bound form (DGC) of the copper complex (D), finally leading to a more stable DGC* intercalated form. Kinetic and equilibrium parameters for the copper complex binding to the nucleic acid are obtained, and the binding mechanism is discussed. A mechanism is proposed where D reacts simultaneously with (G,C) and (A,T) base pairs. The resulting bound forms interconvert according to a "shuffling" process, which involves formation of an intermediate (DGC) form. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 79,89, 2010 [source]


    Kinetic and mechanistic investigation into the influence of chelate substituents on the substitution reactions of platinum(II) terpyridine complexes

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2008
    Deogratius Jaganyi
    The substitution kinetics of the complexes [Pt{4,-(o -CH3 -Ph)-terpy} Cl]SbF6 (CH3PhPtCl(Sb)), [Pt{4,-(o -CH3 -Ph)-terpy}Cl]CF3SO3 (CH3PhPtCl(CF)), [Pt(4,-Ph-terpy)Cl]SbF6 (PhPtCl), [Pt(terpy)Cl]Cl·2H2O (PtCl), [Pt{4,-(o -Cl-Ph)-terpy}Cl]SbF6 (ClPhPtCl), and [Pt{4,-(o -CF3 -Ph)-terpy}Cl]SbF6 (CF3PhPtCl), where terpy is 2,2,:6,,2,-terpyridine, with the nucleophiles thiourea (TU), N,N,-dimethylthiourea (DMTU), and N,N,N,,N,-tetramethylthiourea (TMTU) were investigated in methanol as a solvent. The substitution reactions of the chloride displacement from the metal complexes by the nucleophiles were investigated as a function of nucleophile concentration and temperature under pseudo-first-order conditions using the stopped-flow technique. The reactions followed the simple rate law kobs = k2[Nu]. The results indicate that the introduction of substituents in the ortho position of the phenyl group on the ancillary ring of the terpy unit does influence the extent of ,-backbonding in the terpy ring. This controls the electrophilicity of the platinum center, which in turn controls the lability of the chloro-leaving group. The strength of the electron-donating or -withdrawing ability of the substituents correlates with the reactivity of the complexes. Electron-donating substituents decrease the rate of substitution, whereas electron-withdrawing substituents increase the rate of substitution. This was supported by DFT calculations at the B3LYP/LACVP+** level of theory, which showed that most of the electron density of the HOMO is concentrated on the phenyl ligand rather than on the metal center in the case of the strongest electron-withdrawing substituent in CF3PhPtCl. The opposite was found to be true with the strongest electron-donating substituent in CH3PhPtCl. Thiourea was found to be the best nucleophile with N,N,N,,N,-tetramethylthiourea being the weakest due to steric effects. The temperature dependence studies support an associative mode of activation. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 808,818, 2008 [source]


    Dediazoniation of 1-naphthalenediazonium tetrafluoroborate in aqueous acid and in micellar solutions

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2008
    Carlos Bravo-Diaz
    We have measured the rates and product yields of dediazoniation of 1-naphthalenediazonium (1ND) tetrafluoroborate in the presence and absence of sodium dodecyl sulfate (SDS) micellar aggregates by employing a combination of UV,vis spectroscopy and high-performance liquid chromatography (HPLC) measurements. Kinetic data were obtained by a derivatization procedure with product yields were determined by HPLC. HPLC chromatograms show that in aqueous acid and in micellar solutions only one dediazoniation product is formed in significant quantities, 1-naphthol (NOH), and the observed rate constants (kobs) are the same when 1ND loss is monitored spectrometrically and when NOH formation is monitored by HPLC. Activation parameters were obtained both in the presence and absence of SDS micellar aggregates. In both the systems, the enthalpies of activation are high and the entropies of activation are positive. The enthalpy of activation in the absence of SDS is very similar to that in the presence of SDS micelles, but the entropy of activation is lower by a factor of 4. As a consequence, SDS micelles speed up the thermal decomposition of 1ND and increase kobs by a factor of 1.5 when [SDS] = 0.02 M. In contrast, results obtained in the presence of complexing systems such as crown ethers and polyethers show significant stabilization of the parent arenediazonium ions. Kinetic and HPLC data are consistent with the heterolytic DN + AN mechanism that involves the rate-determining fragmentation of the arenediazonium ion into a very reactive phenyl cation that reacts competitively with available nucleophiles. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 301,309, 2008 [source]


    Kinetic and product study of the gas-phase reaction of sabinaketone with OH radical

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2007
    Nathalie Carrasco
    Sabinaketone is one major photooxidation product of sabinene, an important biogenic volatile organic compound. This article provides the first product study and the second rate constant determination of its reaction with OH radicals. Experiments were investigated under controlled conditions for pressure and temperature in the LISA indoor simulation chamber using FTIR spectrometry. Kinetic study was carried out at 295 ± 2 K and atmospheric pressure using the relative rate technique with isoprene as the reference compound. The rate constant was found to be ksabinaketone + OH = (7.1 ± 1.0) × 10,12 molecule,1 cm3 s,1. Acetone and formaldehyde were detected as products of the reaction with the respective yields of Racetone = 0.9 ± 0.2 and RHCHO = 1.2 ± 0.3. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 415,421, 2007 [source]


    Comparative studies on the pyrolysis of N -arylideneaminoamides: Kinetic and mechanistic studies

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2007
    Nouria A. Al-Awadi
    Rates of thermal decomposition of title compounds have been measured using a static reaction system. They undergo a unimolecular first-order elimination to give arylnitrile and the corresponding substituted amides. The decomposition parallels that of N -arylidenamino cyclic amide. The relative elimination rates at 600 K were calculated. The kinetic data reveal that the electronic effects of substituents, such as methyl, phenyl, benzyl, and allyl groups, are associated with the opposing directions in which the lone pair of electrons on the nitrogen atom of the arylidene moiety is being delocalized. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 59,66, 2007 [source]


    Kinetic and mechanistic study on the thermal reactivity of stabilized phosphorus ylides, part 3: [(Acetyl)(arylcarbamoyl)methylene]triphenylphosphoranes and [(alkoxycarbonyl)(arylcarbamoyl)methylene]triphenylphosphoranes and their thiocarbamoyl analogues

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2007
    R. Alan Aitken
    A series of five [(acetyl)(arylcarbabmoyl)methylene]triphenyl-phosphoranes 1a,e and their thiocarbamoyl analogues 2a,e, [(alkoxycarbonyl)(arylcarbamoyl)methylene]triphenylphosphoranes 3a,e and their thiocarbamoyl analogues 4a,e were prepared and fully characterized. All ylides are found under conditions of flash vacuum pyrolysis to fragment giving arylisocyanate or isothiocyanate and acetyl ylides or alkoxy ylides which undergo thermal extrusion of Ph3PO. A kinetic study shows that these reactions are unimolecular and are of first-order nature with no significant substituent effect. The thiocarbamoyl ylides 2 react from 4.6 to 42 times faster than their carbamoyl ylides 1, while the thiocarbamoyl ylides 4 react from 6.6 to 20.9 times faster than their carbamoyl ylides 3. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 6,16, 2007 [source]


    Kinetic and thermodynamic study of thiolato and sulfenato Co(III) complexes in water,acetonitrile mixtures

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2004
    Monika Aranyosiová
    Rate constants are reported for peroxodisulfate as well as periodate oxidation of[Co(en)2{SCH2CH(COO)NH2}]+, [Co(en)2(SCH2CH2NH2)]2+, and [Co(en)2(SOCH2CH2NH2)]2+ in water,acetonitrile mixtures. The dependence of rate constants on the acetonitrile concentration is established and discussed. Ancillary information relevant to solvation of reactants has been obtained from solvatochromism and from Gibbs transfer functions. The solvent effect is discussed from the viewpoint of change in solvation of initial and transition state on going from water to water,acetonitrile mixtures. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 34,40, 2004 [source]


    Kinetic and mechanistic study of the reaction of O(1D) with CF2HBr

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2001
    R. S. Strekowski
    A laser flash photolysis,resonance fluorescence technique has been employed to investigate the kinetics and mechanism of the reaction of electronically excited oxygen atoms, O(1D), with CF2HBr. Absolute rate coefficients (k1) for the deactivation of O(1D) by CF2HBr have been measured as a function of temperature over the range 211,425 K. The results are well described by the Arrhenius expression k1(T) = 1.72 × 10,10 exp(+72/T) cm3molecule,1 s,1; the accuracy of each reported rate coefficient is estimated to be ±15% (2,). The branching ratio for nonreactive quenching of O(1D) to the ground state, O(3P), is found to be 0.39 ± 0.06 independent of temperature, while the branching ratio for production of hydrogen atoms at 298 K is found to be 0.02,0.02+0.01. The above results are considered in conjunction with other published information to examine reactivity trends in O(1D) + CF2XY reactions (X,Y = H, F, Cl, Br). © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 262,270, 2001 [source]


    Synthesis, characterization, and kinetic of thermal degradation of oligo-2-[(4-bromophenylimino)methyl]phenol and oligomer-metal complexes

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2009
    smet Kaya
    Abstract Oligo-2-[(4-bromophenylimino)methyl]phenol (OBPIMP) was synthesized from the oxidative polycondensation reaction of 2-[(4-bromophenylimino)methyl]phenol (BPIMP) with air and NaOCl oxidants in an aqueous alkaline medium between 50 and 90°C. The yield of OBPIMP was found to be 67 and 88% for air and NaOCl oxidants, respectively. Their structures were confirmed by elemental and spectral such as IR, ultraviolet,visible spectrophotometer (UV,vis), 1H-NMR, and 13C-NMR analyses. The characterization was made by TG-DTA, size exclusion chromatography, and solubility tests. The resulting complexes were characterized by electronic and IR spectral measurements, elemental analysis, AAS, and thermal studies. According to TG analyses, the weight losses of OBPIMP, and oligomer-metal complexes with Co+2, Ni+2, and Cu+2 ions were found to be 93.04%, 59.80%, 74.23%, and 59.30%, respectively, at 1000°C. Kinetic and thermodynamic parameters of these compounds investigated by Coats-Redfern, MacCallum-Tanner, and van Krevelen methods. The values of the apparent activation energies of thermal decomposition (Ea), the reaction order (n), preexponential factor (A), the entropy change (,S*), enthalpy change (,H*), and free energy change (,G*) obtained by earlier-mentioned methods were all good in agreement with each other. It was found that the thermal stabilities of the complexes follow the order Cu(II) > Co(II) > Ni(II). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]


    Kinetic and heat transfer modeling of rubber blends' sulfur vulcanization with N - t -butylbenzothiazole-sulfenamide and N,N -di- t -butylbenzothiazole-sulfenamide

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007
    Likozar
    Abstract Vulcanization kinetics and heat transfer for various blends of natural (NR) and polybutadiene (BR) rubber were studied simultaneously using a mechanistic approach when developing vulcanization model kinetics. Rubber process analyzer (RPA), dynamic scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR) methods were used for the study. The model reaction scheme was based on one of the best possible proposed individual reaction mechanisms. Molecular modeling was applied to distinguish between the reactivity of chemically similar species. The kinetics of N - t -butylbenzothiazole-sulfenamide (TBBS) and N,N -di- t -butylbenzothiazole-sulfenamide (TBSI) were treated separately using FTIR experiment data, and then incorporated in a model suitable for two-accelerator vulcanization. The proposed model quite well describes the thermal equilibration during the induction period despite a few simplifications. During cure and over-cure periods the course of vulcanization was described using a rigorous kinetic model. Physical and chemical model parameters were calculated from experimental data. Average heat transfer coefficient minimum during induction period was found to be at a weight ratio of BR and NR 1 : 1. The activation energy of significant reactions between rubber and other species was found to vary linearly with vulcanization compound composition. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 293,307, 2007 [source]


    Alterations in the expression of intestinal enzymes in rats exposed to nickel

    JOURNAL OF APPLIED TOXICOLOGY, Issue 5 2006
    Amika Singla
    Abstract The effect of feeding nickel (50 mg kg,1 body weight) daily for 7 days was studied on the development of various brush border enzymes across the crypt,villus axis. The activities of brush border maltase (P < 0.05), lactase (P < 0.05), alkaline phosphatase (P < 0.05) and leucine amino peptidase (P < 0.05) were augmented in purified brush borders, whereas sucrase, trehlase (P < 0.01) and glutamyl transpeptidase (P < 0.05) were reduced in nickel fed animals compared with controls. Kinetic and heat inactivation studies with brush border sucrase and alkaline phosphatase confirmed these findings. Western blot analysis of alkaline phosphatase showed a strong signal for the enzyme protein but a reduced level of sucrase antigen in nickel fed rat intestine compared with the controls. These findings suggest that the expression of various brush border enzymes along the crypt,villus axis is modulated in rat intestine exposed to nickel, which may disrupt the digestive functions of the intestinal tissue. Copyright © 2006 John Wiley & Sons, Ltd. [source]


    Effect of Heat Treatment on Bovine Lactoperoxidase Activity in Skim Milk: Kinetic and Thermodynamic Analysis

    JOURNAL OF FOOD SCIENCE, Issue 1 2003
    E. Marín
    ABSTRACT: The effect of heat on lactoperoxidase activity in bovine milk was studied over a range of 68 to 76 °C. Values of residual enzymatic activity after different treatments were studied by kinetic analysis, obtaining D-values and the Z-value (3.1 °C). Denaturation of lactoperoxidase, measured by loss in activity, can be described as a 1st-order reaction. Rate constants were calculated, as was the energy of activation, which was 737.69 kJ/mol. Thermodynamic parameters were also calculated. The high value obtained for the variation in enthalpy of activation indicates that a high amount of energy is required to initiate denaturation, probably due to the molecular conformation of lactoperoxidase. [source]


    Kinetic and dynamic study of liquid,liquid extraction of copper in a HFMC: Experimentation, modeling, and simulation

    AICHE JOURNAL, Issue 6 2010
    M. Younas
    Abstract In this work, we present the dispersion-free liquid,liquid extraction of copper from aqueous streams in a hollow fiber membrane contactor (HFMC). Copper has been transferred from aqueous solutions to heptane using LIX 84-I (2-hydroxy-5-nonylacetephenone oxime) as extracting agent. In a first step, batch experiments have been performed to identify the extraction kinetics and to measure the partition coefficient of copper aqueous-organic phase system. Then, the continuous recycled-base extraction process has been performed in a HFMC Liqui-Cel® module. The module has been modeled from resistance in series concept to gain the exit concentrations, which are used to develop a dynamic model to calculate the exit concentration of copper from the output of storage tanks. The model has been validated with experimental data at various operating conditions. The integrated process model algorithm was scripted in MATLAB® 7.4 R (a). Simulations have been made for a range of different operating parameters to determine the optimum criterion conditions. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]


    Kinetic and thermodynamic characterization of HIV-1 protease inhibitors

    JOURNAL OF MOLECULAR RECOGNITION, Issue 2 2004
    Cynthia F. Shuman
    Abstract Interaction kinetic and thermodynamic analyses provide information beyond that obtained in general inhibition studies, and may contribute to the design of improved inhibitors and increased understanding of molecular interactions. Thus, a biosensor-based method was used to characterize the interactions between HIV-1 protease and seven inhibitors, revealing distinguishing kinetic and thermodynamic characteristics for the inhibitors. Lopinavir had fast association and the highest affinity of the tested compounds, and the interaction kinetics were less temperature-dependent as compared with the other inhibitors. Amprenavir, indinavir and ritonavir showed non-linear temperature dependencies of the kinetics. The free energy, enthalpy and entropy (,G, ,H, ,S) were determined, and the energetics of complex association (,Gon, ,Hon, ,Son) and dissociation (,Goff, ,Hoff, ,Soff) were resolved. In general, the energetics for the studied inhibitors was in the same range, with the negative free energy change (,G,<,0) due primarily to increased entropy (,S,>,0). Thus, the driving force of the interaction was increased degrees of freedom in the system (entropy) rather than the formation of bonds between the enzyme and inhibitor (enthalpy). Although the ,Gon and ,Goff were in the same range for all inhibitors, the enthalpy and entropy terms contributed differently to association and dissociation, distinguishing these phases energetically. Dissociation was accompanied by positive enthalpy (,Hoff,>,0) and negative entropy (,Soff,<,0) changes, whereas association for all inhibitors except lopinavir had positive entropy changes (,Son,>,0), demonstrating unique energetic characteristics for lopinavir. This study indicates that this type of data will be useful for the characterization of target,ligand interactions and the development of new inhibitors of HIV-1 protease. Copyright © 2004 John Wiley & Sons, Ltd. [source]


    Kinetic and mechanistic studies on the inhibition of free radical-initiated polymerization of styrene by ,-carotene and ,-tocopherol

    JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 6 2002
    Zhaolong Li
    Abstract The inhibition of free radical-initiated polymerization of styrene by ,-carotene (,C) and ,-tocopherol (TOH) was studied by dilatometry. The polymerization was initiated by 2,2,-azobis(isobutyronitrile) at 50,°C in chlorobenzene and inhibited by ,C and/or TOH. It was found that ,C and TOH could efficiently inhibit the polymerization, either used individually or in combination, and a significant synergistic effect was observed when they were used in combination. It is proposed that retinal, which is the principal oxidation product of ,C, may be involved in the synergistic inhibition reaction of ,C and TOH. Copyright © 2002 John Wiley & Sons, Ltd. [source]


    Photoinitiated polymerization of methacrylic monomers in a polybutadiene matrix (PB): Kinetic, mechanistic, and structural aspects

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2001
    J. L. Mateo
    Abstract The kinetics and mechanism of the photoinitiated polymerization of tetrafunctional and difunctional methacrylic monomers [1,6-hexanediol dimethacylate (HDDMA) and 2-ethylhexyl methacrylate (EHMA)] in a polybutadiene matrix (PB) have been studied. The maximum double-bond conversion, the maximum polymerization rate, the intrinsic reactivity, and the kinetic constants for propagation and termination have been calculated. Unlike the behavior followed by the SBS-HDDMA and PS-HDDMA systems, where a reaction-diffusion mechanism occurs from the start of the polymerization at low monomer concentrations (<30,40%), in the PB-HDDMA system the reaction diffusion controls the termination process only after approximately 10% conversion is reached, as for the bulk polymerization of polyfunctional methacrylic monomers. Before reaching 10% conversion the behavior observed can be better explained by a combination of segmental diffusion-controlled (autoaccelerated) and reaction-diffusion mechanisms. This is probably a consequence of the lower force of attraction between the monomer and the matrix and between the growing macroradical and the matrix than those corresponding to the other systems mentioned. For the PB-EHMA system, the termination mechanism is principally diffusion-controlled from the beginning of the polymerization for monomer concentrations below 30,40%, and for higher monomer concentrations, a standard termination mechanism takes place (kt , 106) at low double-bond conversions, which is diffusion-controlled for high conversions (>40%). For PB-HDDMA and PB-EHMA systems, crosslinked polymerized products are obtained as a result of the participation of the double bonds of the matrix in the polymerization process. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2444,2453, 2001 [source]


    Photoinitiated polymerization of methacrylic monomers in a polystyrene matrix: Kinetic, mechanistic, and structural aspects

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2001
    J. L. Mateo
    Abstract The kinetics and mechanism of the photoinitiated polymerization of tetrafunctional and difunctional methacrylic monomers [1,6-hexanediol dimethacrylate (HDDMA) and 2-ethylhexyl methacrylate (EHMA)] in a polystyrene (PS) matrix were studied. The aggregation state, vitreous or rubbery, of the monomer/matrix system and the intermolecular strength of attraction in the monomer/matrix and growing macroradical/matrix systems are the principal factors influencing the kinetics and mechanism. For the PS/HDDMA system, where a relatively high intermolecular force of attraction between monomer and matrix and between growing macroradical and matrix occurs, a reaction-diffusion mechanism takes place at low monomer concentrations (<30,40%) from the beginning of the polymerization. For the PS/EHMA system, which presents low intermolecular attraction between monomer and matrix and between growing macroradical and matrix, the reaction-diffusion termination is not clear, and a combination of reaction-diffusion and diffusion-controlled mechanisms explains better the polymerization for monomer concentrations below 30,40%. For both systems, for which a change from a vitreous state to a rubbery state occurs when the monomer concentration changes from 10 to 20%, the intrinsic reactivity and kp/kt1/2 ratio (where kp is the propagation kinetic constant and kt is the termination kinetic constant) increase as a result of a greater mobility of the monomer in the matrix (a greater kp value). The PS matrix participates in the polymerization process through the formation of benzylic radical, which is bonded to some extent by radical,radical coupling with the growing methacrylic radica, producing grafting on the PS matrix. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2049,2057, 2001 [source]


    Kinetic and strain-driven growth phenomena on Si(001)

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2004
    C. Schelling
    Abstract Self-organization phenomena in semiconductors are usually based on strain-driven island growth during hetero epitaxial layer deposition. However, kinetic phenomena can become important and even dominating at the low growth temperatures usually employed during molecular beam epitaxy. We report on kinetic step bunching on Si(001), and identify the driving mechanism on the atomic scale via kinetic Monte Carlo simulations. Another phenomena discussed is facet formation during annealing of SiO2 -covered Si(001) nanostructures at the relatively low temperatures usually employed for oxide desorption. Both phenomena are combined to facilitate perfect ordering of self-assembled Ge dots on facetted Si(001) nanostructure templates. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Facile synthesis and characterization of star-shaped polystyrene: self-condensing atom transfer radical copolymerization of N -[4-(,-bromoisobutyryloxy)phenyl]maleimide and styrene

    POLYMER INTERNATIONAL, Issue 10 2008
    Yun Cao
    Abstract BACKGROUND: Generation of stars around in situ formed cores provides a facile approach to star-shaped polymers. Therefore the self-condensing atom transfer radical copolymerization (SCATRCP) of N -[4-(,-bromoisobutyryloxy)phenyl]maleimide (BiBPM) and a large excess of styrene (St) was investigated. RESULTS: BiBPM and St formed a charge transfer complex (CTC), which underwent the SCATRCP, leading to the branched core initiating the atom transfer radical polymerization of St, finally giving star-shaped polystyrene (PS). Kinetic and structural study showed that a higher dosage of BiBPM resulted in an enhanced polymerization rate, a higher degree of branching and a larger number of short PS arms. Differential scanning calorimetry suggested that the glass transition temperature of the star-shaped PS decreased with molecular weight. Melt rheometry showed that even a slightly branched architecture of the PS led to a significantly lower viscosity; both the melt flow index and the activation energy increased with the degree of branching. CONCLUSION: Due to the preferential consumption of BiBPM and formation of a CTC, even a very low dosage of BiBPM could lead to star-shaped PS, which, in comparison with linear analogues, could possess much better melt fluidity. Copyright © 2008 Society of Chemical Industry [source]


    Kinetic and thermodynamic study of methanolysis of poly(ethylene terephthalate) waste powder

    POLYMER INTERNATIONAL, Issue 3 2003
    S Mishra
    Abstract Depolymerization of poly(ethylene terephthalate) waste (PETW) was carried out by methanolysis using zinc acetate in the presence of lead acetate as the catalyst at 120,140,°C in a closed batch reactor. The particle size ranging from 50 to 512.5,µm and the reaction time 60 to 150,min required for methanolysis of PETW were optimized. Optimal percentage conversion of PETW into dimethyl terephthalate (DMT) and ethylene glycol (EG) was 97.8% (at 120,°C) and 100% (at 130 and 140,°C) for the optimal reaction time of 120,min. Yields of DMT and EG were almost equal to PET conversion. EG and DMT were analyzed qualitatively and quantitatively. To avoid oxidation/carbonization during the reaction, methanolysis reactions were carried out below 150,°C. A kinetic model is developed and the experimental data show good agreement with the kinetic model. Rate constants, equilibrium constant, Gibbs free energy, enthalpy and entropy of reaction are also evaluated at 120, 130 and 140,°C. The methanolysis rate constant of the reaction at 140,°C (10.3 atm) was 1.4,×,10,3,g PET mol,1 min,1. The activation energy and the frequency factor for methanolysis of PETW were 95.31,kJ,mol,1 and 107.1,g PET mol,1 min,1, respectively. © 2003 Society of Chemical Industry [source]


    Systematic interpretation of cyclic nucleotide binding studies using KinetXBase

    PROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 6 2008
    Sonja Schweinsberg
    Abstract Functional proteomics aims to describe cellular protein networks in depth based on the quantification of molecular interactions. In order to study the interaction of adenosine-3,,5,-cyclic monophosphate (cAMP), a general second messenger involved in several intracellular signalling networks, with one of its respective target proteins, the regulatory (R) subunit of cAMP dependent protein kinase (PKA), a number of different methods was employed. These include fluorescence polarisation (FP), isothermal titration calorimetry (ITC), surface plasmon resonance (SPR), amplified luminescence proximity homogeneous assay (ALPHA-screen), radioligand binding or activity-based assays. Kinetic, thermodynamic and equilibrium binding data of a variety of cAMP derivatives to several cAMP binding domains were integrated in a single database system, we called KinetXBase, allowing for very distinct data formats. KinetXBase is a practical data handling system for molecular interaction data of any kind, providing a synopsis of data derived from different technologies. This supports ongoing efforts in the bioinformatics community to devise formal concepts for a unified representation of interaction data, in order to enable their exchange and easy comparison. KinetXBase was applied here to analyse complex cAMP binding data and highly site-specific cAMP analogues could be identified. The software package is free for download by academic users. [source]