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Equilibrium Constant (equilibrium + constant)
Terms modified by Equilibrium Constant Selected AbstractsActivated Carbon Adsorbent for the Aqueous Phase Adsorption of Amoxicillin in a Fixed BedCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 4 2010N. J. R. Ornelas Abstract Equilibrium constant and mass transfer parameters are needed for the study of amoxicillin separation in any process involving adsorption in fixed beds. In this work, the adsorption of amoxicillin and 6-aminopenillanic acid in aqueous solution on activated carbon were studied using static adsorption tests. The adsorption capacity was found to be strongly dependent on the pH of the aqueous phase. The adsorption constants, overall mass transfer coefficients, and axial dispersion coefficients for amoxicillin and 6-aminopenillanic acid were determined, by moment analysis, from a series of step tests in a fixed bed packed with activated carbon. The total bed voidage and axial dispersion coefficient were estimated from blue dextran pulse test data at different flow rates. The results show that adsorption intensity increased with increasing temperature. Furthermore, the increasing trend of HETP with velocity suggests that axial dispersion and mass transfer resistance control the column efficiency. [source] Kinetic and Equilibrium Studies of Reactions of N-Heterocycles with Dimeric and Monomeric Oxorhenium(V) ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2003James 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] Reactions of 1,2,5-thiadiazole 1,1-dioxide derivatives with nitrogenated nucleophiles.JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 4 20031-dioxide, 4-diphenyl-, 5-thiadiazole , Addition of amines, Part , amides to Abstract The addition reactions of some amides and aromatic amines to a CN double bond of 3,4-diphenyl-1,2,5-thiadiazole 1,1-dioxide (1) were studied in aprotic solvent solutions [N,N -dimethylformamide (DMF) and acetonitrile (MeCN)]. Equilibrium constants for the reactions of 1 with acetamide, 2-fluoroacetamide, butyramide, benzamide, aniline and 3-aminopyridine were measured using a previously reported cyclic voltammetric (CV) method. Aliphatic amines gave unstable solutions, probably owing to reactions of anionic species derived from 1. Other N nucleophiles tested (formamide, succinimide, thioacetamide and cyanamide) yielded different products that have not yet been characterized. DMF, N,N -dimethylacetamide (DMA) and N -methylacetamide did not react. The addition thiadiazoline produced in the reaction of acetamide with 1 was characterized by IR and 1H and 13C RMN NMR spectroscopy as a prototype compound. For this system, the equilibrium constant could also be measured by a standard UV,VIS method and was found to be in agreement with the value obtained by CV. The reaction of 1 with urea produced a bicyclic product, identified as 3a,6a-diphenyltetrahydroimidazo[4,5- c]-1,2,5-thiadiazol-5-one 2,2-dioxide. Copyright © 2003 John Wiley & Sons, Ltd. [source] Monitoring the non-specific interactions of catechin through diffusion measurements based on pulsed-field gradientsMAGNETIC RESONANCE IN CHEMISTRY, Issue 13 2002C. Monteiro Abstract The self-association of aqueous catechin as a function of concentration was monitored through variations in 1H chemical shifts, proton T1 and T2 data and translational diffusion coefficients obtained with the pulsed-field gradient spin-echo method. The latter approach is very efficient and it is not restricted to aromatic compounds. Equilibrium constants were estimated for various models of self-association and the apparent enthalpy of dissociation was measured with isothermal titration calorimetry. Comparison of the latter parameter with thermodynamic data reported for various types of non-specific interactions suggests that such phenomena could be studied using this approach. Copyright © 2002 John Wiley & Sons, Ltd. [source] Vapor species over cerium and samarium trichlorides, enthalpies of formation of (LnCl3)n molecules and Cl,(LnCl3)n ionsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2001A. M. Pogrebnoi A Knudsen effusion cell mass spectrometric technique was used to study vapor species over CeCl3 and SmCl3. Monomer, dimer, and trimer (Sm3Cl9) molecules, and LnCl4,, Ln2Cl7,, Ln3Cl10, (Ln,=,Ce, Sm) negative ions, were observed in saturated vapor in the temperature range 958,1227,K. Partial vapor pressures of neutral constituents were determined and the enthalpies of sublimation (,sH, 298,K, kJ·mol,1) to monomers and associated molecules obtained: 328,±,6 (CeCl3), 306,±,6 (SmCl3), 453,±,16 (Ce2Cl6), 408,±,12 (Sm2Cl6), and 468,±,40 (Sm3Cl9). Equilibrium constants for various chemical reactions were measured and the enthalpies of reactions obtained using the second and third laws of thermodynamics. The enthalpies of formation (,fH, 298,K, kJ·mol,1) of molecules and ions have been calculated as follows: ,730,±,6 (CeCl3), ,722,±,6 (SmCl3), ,1663,±,16 (Ce2Cl6), ,1649,±,13 (Sm2Cl6), ,2617,±,40 (Sm3Cl9), ,1250,±,15 (CeCl4,), ,1252,±,15 (SmCl4,), ,2184,±,35 (Ce2Cl7,), ,2172,±,26 (Sm2Cl7,), ,3183,±,43 (Ce3Cl10,), and ,3147,±,43 (Sm3Cl10,). Copyright © 2001 John Wiley & Sons, Ltd. [source] Spectroelectrochemical and Voltammetric Studies of L -DOPAELECTROANALYSIS, Issue 2 2003Xiaoqiang Liu Abstract The electrooxidation of L -dopa at GC electrode was studied by in situ UV-vis spectroelectrochemistry (SEC) and cyclic voltammetry. The mechanism of electrooxidation and some reaction parameters were obtained. The results showed that the whole electrooxidation reaction of L -dopa at glassy carbon (GC) electrode was an irreversible electrochemical process followed by a chemical reaction in neutral solution (EC mechanism). The spectroelectrochemical data were treated by the double logarithm method together with nonlinear regression, from which the formal potential E0=228,mV, the apparent electron-transfer number of the electrooxidation reaction ,n=0.376 (R=0.99, SD=0.26), the standard electrochemical rate constant k0=(3.93±0.12)×10,4,cm s,1 (SD=1.02×10,2), and the formation equilibrium constant of the following chemical reaction kc=(5.38±0.34)×10,1,s,1 (SD=1.02×10,2) were also obtained. [source] Kinetics of Bis(p -nitrophenyl)phosphate (BNPP) Hydrolysis Reactions with Trivalent Lanthanide Complexes of N -Hydroxyethyl(ethylenediamine)- N,N,,N, -triacetate (HEDTA),EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2009C. Allen Chang Abstract Kinetic studies of hydrolysis reactions of BNPP [sodium bis(p -nitrophenyl)phosphate] with trivalent lanthanide (Ln3+) complexes of HEDTA [HEDTA = N -hydroxyethyl(ethylenediamine)- N,N,,N, -triacetate] were performed at pH 6.96,11.34 and 25 °C by a spectrophotometric method and by HPLC analysis. The reaction rates increase with increasing atomic number of lanthanide and solution pH from PrHEDTA to EuHEDTA and then decrease for heavier LnHEDTA complexes. Plots of pseudo-first-order rate constants (kobs) vs. pH could be fitted to the equation kobs = kLnL(OH)[LnL]T/{1,+,exp[,2.303(pH,,,pKh)]}, where kLnL(OH) is the rate constant for the reaction of LnHEDTA(OH), with BNPP, Kh is the hydrolysis constant of LnHEDTA, and [LnL]T is the total concentration of LnHEDTA. The pKh values obtained by the kinetic method are in the range 8.2,10.3 and are similar to those measured by potentiometric methods. At [LnL]T = 10,70 mM and pH 10.5, most of the observed pseudo-first-order rate constants could be fitted to a simple saturation kinetic model, kobs = k1K[LnHEDTA(OH),]/{1 + K[LnHEDTA(OH),]}, where K is the equilibrium constant for the formation for LnHEDTA(OH),BNPP and is in the range 2,147 M,1. The k1 values are in the range 1.12,×,10,5,2.71,×,10,3 s,1. The kobs data for TbHEDTA and HoHEDTA were fitted to a quadratic equation. It was observed that the dinuclear species are more reactive. ESI mass spectrometry confirmed that the reaction between BNPP and EuHEDTA is a simple hydrolysis but not a transesterification, presumably because the three inner-sphere coordinated water molecules are far away from the coordinated hydroxyethyl group. Hydrolysis is likely to occur by proton transfer from one inner-sphere coordinated water molecule to the deprotonated ethyl oxide group followed by nucleophilic attack of the resulting hydroxide ion on the bonded BNPP anion.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Effect of the Leaving Group on the Rate and Mechanism of the Palladium-Catalyzed Isomerization of Cyclic Allylic Benzoates in Allylic SubstitutionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2006Christian Amatore Abstract In chloroform, the reaction of cis -5-phenylcyclohex-2-enyl 4-Z-benzoate (cis - 1Z, Z = NO2, Cl, H, Me, MeO) with Pd0 complexes ligated to PPh3 is reversible and proceeds with isomerization at the allylic position. The rate of isomerization of cis - 1Z to trans - 1Z depends on the catalytic precursor: Pd0(PPh3)4 > {Pd0(dba)2 + 2PPh3} in agreement with an SN2 mechanism in the rate-determining isomerization of the cationic (,3 -allyl)palladium complexes formed in the oxidative addition. For a given precursor, the rate of isomerization of cis - 1Z to trans - 1Z also depends on the substituent Z, i.e., on the leaving group. The isomerization rate follows the same order as the leaving group properties: 4-NO2,C6H4 -CO2,> 4-Cl,C6H4 -CO2, > C6H5 -CO2, > 4-Me,C6H4 -CO2, > 4-MeO,C6H4 -CO2,. The same tendency is found for the equilibrium constant between the neutral cis - 1Z and the cationic (,3 -allyl)palladium complex in DMF. The higher the concentration of the cationic (,3 -allyl)palladium complex, the faster the isomerization of cis - 1Z to trans - 1Z is. The isomerization of cis - 1Z to trans - 1Z and that of the cationic (,3 -allyl)palladium complexes are at the origin of the lack of stereospecificity observed in catalytic nucleophilic allylic substitutions. These isomerizations are affected by both the leaving groups and the Pd0 precursors, which therefore are not "innocent" but may play an important role in palladium-catalyzed nucleophilic substitutions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Partitioning of metals (Cd, Co, Cu, Ni, Pb, Zn) in soils: concepts, methodologies, prediction and applications , a reviewEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2009F. Degryse Summary Prediction of the fate of metals in soil requires knowledge of their solid,liquid partitioning. This paper reviews analytical methods and models for measuring or predicting the solid,liquid partitioning of metals in aerobic soils, and collates experimental data. The partitioning is often expressed with an empirical distribution coefficient or Kd, which gives the ratio of the concentration in the solid phase to that in the solution phase. The Kd value of a metal reflects the net effect of various reactions in the solid and liquid phases and varies by orders of magnitude among soils. The Kd value can be derived from the solid,liquid distribution of added metal or that of the soil-borne metal. Only part of the solid-phase metal is rapidly exchangeable with the solution phase. Various methods have been developed to quantify this ,labile' phase, and Kd values based on this phase often correlate better with soil properties than Kd values based on total concentration, and are more appropriate to express metal ion buffering in solute transport models. The in situ soil solution is the preferred solution phase for Kd determinations. Alternatively, water or dilute-salt extracts can be used, but these may underestimate in situ concentrations of dissolved metals because of dilution of metal-complexing ligands such as dissolved organic matter. Multi-surface models and empirical models have been proposed to predict metal partitioning from soil properties. Though soil pH is the most important soil property determining the retention of the free metal ion, Kd values based on total dissolved metal in solution may show little pH dependence for metal ions that have strong affinity for dissolved organic matter. The Kd coefficient is used as an equilibrium constant in risk assessment models. However, slow dissociation of metal complexes in solution and slow exchange of metals between labile and non-labile pools in the solid phase may invalidate this equilibrium assumption. [source] Allosteric modulation of anti-HIV drug and ferric heme binding to human serum albuminFEBS JOURNAL, Issue 24 2005Alessio Bocedi Human serum albumin (HSA), the most prominent protein in plasma, is best known for its exceptional capacity to bind ligands (e.g. heme and drugs). Here, binding of the anti-HIV drugs abacavir, atazanavir, didanosine, efavirenz, emtricitabine, lamivudine, nelfinavir, nevirapine, ritonavir, saquinavir, stavudine, and zidovudine to HSA and ferric heme,HSA is reported. Ferric heme binding to HSA in the absence and presence of anti-HIV drugs was also investigated. The association equilibrium constant and second-order rate constant for the binding of anti-HIV drugs to Sudlow's site I of ferric heme,HSA are lower by one order of magnitude than those for the binding of anti-HIV drugs to HSA. Accordingly, the association equilibrium constant and the second-order rate constant for heme binding to HSA are decreased by one order of magnitude in the presence of anti-HIV drugs. In contrast, the first-order rate constant for ligand dissociation from HSA is insensitive to anti-HIV drugs and ferric heme. These findings represent clear-cut evidence for the allosteric inhibition of anti-HIV drug binding to HSA by the heme. In turn, anti-HIV drugs allosterically impair heme binding to HSA. Therefore, Sudlow's site I and the heme cleft must be functionally linked. [source] The helix nucleation site and propensity of the synthetic mitochondrial presequence of ornithine carbamoyltransferaseFEBS JOURNAL, Issue 18 2000Harmen H. J. De Jongh This study describes the helix nucleation site and helix propagation of the amphiphilic helical structure of the mitochondrial presequence of rat ornithine carbamoyltransferase. We investigated this property of the 32-residue synthetic presequence using CD and 2D-HR NMR techniques by determining the structure as a function of the concentration of trifluoroethanol. It was found that the hydrophobic cluster Ile7-Leu8-Leu9 forms the helix nucleation site, expanding to include residues Asn4 to Lys16 when the concentration of trifluoroethanol is increased from 10 to 30%. At higher trifluoroethanol concentrations an increased ,stiffening' of the polypeptide backbone (to Arg26) is observed. In addition, by recording CD spectra at different trifluoroethanol concentrations as a function of temperature, it was found that the equilibrium constant between helix and random coil formation for this peptide exhibits a strong temperature dependence with maximum values between 20 and 30 °C. Comparison of these equilibrium constants with those of homopolymers stressed the unique character of the mitochondrial presequence. The findings are discussed in relation to the molecular recognition events at different stages of the transport process of this protein into mitochondria. [source] Kinetics of the simultaneous oxidation of nickel(II) and sulfur(IV) by oxygen in alkaline medium in Ni(II),sulfur(IV),O2 systemINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2010Anil Kumar Sharma In the Ni(II),S(IV),O2 system in the region of pH > 8.4, both Ni(II) and S(IV) are simultaneously autoxidized, and when sulfur is consumed fully NiOOH precipitates. At pH > 8.4, ethanol has no effect on the rate, whereas ammonia strongly inhibits the reaction when pH > 7.0. The kinetics of the reaction, in both the presence and the absence of ethanol, is defined by the rate law where k is the rate constant, KO is the equilibrium constant for the adsorption of O2 on Ni(OH)2 particle surface. In ammonia buffer, the factor F is defined by where K, KOH, K1, K2, K3, and K4 are the stability constants of NiSO3, NiOH+, Ni(NH3)2+, Ni(NH3), Ni(NH3), and Ni(NH3), respectively. In unbuffered medium, the factor F reduces to The values of k and Ksp were found to be (1.3 ± 0.08) × 10,1 s,1 and (4.2 ± 3.5) × 10,16, respectively, at 30°C. A nonradical mechanism that assumes the adsorption of both SO32, and O2 on the Ni(OH)2 particle surface has been proposed. At pH , 8.2, Ni(II) displays no catalytic activity for sulfur(IV)-autoxidation and it is also not oxidized to NiOOH. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 464,478, 2010 [source] Kinetics and mechanism of oxidation of a ternary complex involving dipicolinatochromium(III) and DL -aspartic acid by N -bromosuccinimideINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2004Hassan 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 30°C 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] MP2, DFT-D, and PCM study of the HMB,TCNE complex: Thermodynamics, electric properties, and solvent effects,INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 9 2008Ondrej Kysel Abstract Geometry, thermodynamic, and electric properties of the ,-EDA complex between hexamethylbenzene (HMB) and tetracyanoethylene (TCNE) are investigated at the MP2/6-31G* and, partly, DFT-D/6-31G* levels. Solvent effects on the properties are evaluated using the PCM model. Fully optimized HMB,TCNE geometry in gas phase is a stacking complex with an interplanar distance 2.87 × 10,10 m and the corresponding BSSE corrected interaction energy is ,51.3 kJ mol,1. As expected, the interplanar distance is much shorter in comparison with HF and DFT results. However the crystal structures of both (HMB)2,TCNE and HMB,TCNE complexes have interplanar distances somewhat larger (3.18 and 3.28 × 10,10 m, respectively) than our MP2 gas phase value. Our estimate of the distance in CCl4 on the basis of PCM solvent effect study is also larger (3.06,3.16 × 10,10 m). The calculated enthalpy, entropy, Gibbs energy, and equilibrium constant of HMB,TCNE complex formation in gas phase are: ,H0 = ,61.59 kJ mol,1, ,S = ,143 J mol,1 K,1, ,G0 = ,18.97 kJ mol,1, and K = 2,100 dm3 mol,1. Experimental data, however, measured in CCl4 are significantly lower: ,H0 = ,34 kJ mol,1, ,S = ,70.4 J mol,1 K,1, ,G0 = ,13.01 kJ mol,1, and K = 190 dm3 mol,1. The differences are caused by solvation effects which stabilize more the isolated components than the complex. The total solvent destabilization of Gibbs energy of the complex relatively to that of components is equal to 5.9 kJ mol,1 which is very close to our PCM value 6.5 kJ mol,1. MP2/6-31G* dipole moment and polarizabilities are in reasonable agreement with experiment (3.56 D versus 2.8 D for dipole moment). The difference here is due to solvent effect which enlarges interplanar distance and thus decreases dipole moment value. The MP2/6-31G* study supplemented by DFT-D parameterization for enthalpy calculation, and by the PCM approach to include solvent effect seems to be proper tools to elucidate the properties of ,-EDA complexes. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] The Planck,Benzinger thermal work function in the condensation of water vaporINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2006Paul W. Chun Abstract Based on the Planck,Benzinger thermal work function using Chun's method, the innate temperature-invariant enthalpy at 0 K, ,H0(T0), for the condensation of water vapor as well as the dimer, trimer, tetramer, and pentamer form in the vapor phase, was determined to be 0.447 kcal mol,1 for vapor, 1.127 for the dimer, 0.555 for the trimer, 0.236 for the tetramer, and 0.079 kcal mol,1 for the pentamer using ,G(T) data reported by Kell et al. in 1968 and Kell and McLaurin in 1969. These results suggest that the predominant dimeric form is the most stable of these n -mers. Using Nemethy and Scheraga's 1962 data for the Helmholtz free energy of liquid water, the value of ,H0(T0) was determined to be 1.21 kcal mol,1. This is very close to the value for the energy of the hydrogen bond EH of 1.32 kcal mol,1 reported by Nemethy and Scheraga, using statistical thermodynamics. It seems clear that very little energy is required for interconversion between the hypothetical supercooled water vapor and glassy water at 0 K. A hypothetical supercooled water vapor at 0 K is apparently almost as highly associated as glassy water at that temperature, suggesting a dynamic equilibrium between vapor and liquid. This water vapor condensation is highly similar in its thermodynamic behavior to that of sequence-specific pairwise (dipeptide) hydrophobic interaction, except that the negative Gibbs free energy change minimum at ,Ts,, the thermal setpoint for vapor condensation, where T,S = 0, occurs at a considerably lower temperature, 270 K (below 0°C) compared with ,350 K. The temperature of condensation ,Tcond, at which ,G(T) = 0, where water vapor begins to condense, was found to be 383 K. In the case of a sequence-specific pairwise hydrophobic interaction, the melting temperature, ,Tm,, where ,G(Tm) = 0 was found to be 460 K. Only between two temperature limits, ,Th, = 99 K and ,Tcond, = 383 K, where ,G(Tcond) = 0, is the net chemical driving force favorable for polymorphism of glassy water and hypothetical supercooled water vapor. Analysis of the water vapor condensation process based on the Planck,Benzinger thermal work function confirms that a thermodynamic molecular switch occurs at 10 K, wherein a change of sign in [,Cp(T)]cond leads to a true negative minimum in the Gibbs free energy of vapor condensation, and hence a maximum in the related equilibrium constant, Kcond. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] The totally miscible in ternary hydrogen-bonded polymer blend of poly(vinyl phenol)/phenoxy/phenolicJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2009Shiao-Wei KuoArticle first published online: 28 MAY 200 Abstract The individual binary polymer blends of phenolic/phenoxy, phenolic/poly(vinyl phenol) (PVPh), and phenoxy/PVPh have specific interaction through intermolecular hydrogen bonding of hydroxyl,hydroxyl group to form homogeneous miscible phase. In addition, the miscibility and hydrogen bonding behaviors of ternary hydrogen bond blends of phenolic/phenoxy/PVPh were investigated by using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy, and optical microscopy. According to the DSC analysis, every composition of the ternary blend shows single glass transition temperature (Tg), indicating that this ternary hydrogen-bonded blend is totally miscible. The interassociation equilibrium constant between each binary blend was calculated from the appropriate model compounds. The interassociation equilibrium constant (KA) of each individually binary blend is higher than any self-association equilibrium constant (KB), resulting in the hydroxyl group tending to form interassociation hydrogen bond. Photographs of optical microscopy show this ternary blend possess lower critical solution temperature (LCST) phase diagram. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Solvent extraction studies of Sm(III) from nitrate medium and separation factors of rare earth elements with mixtures of sec -octylphenoxyacetic acid and 1,10-phenthrolineJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2010Shujuan Fan Abstract BACKGROUND: Liquid,liquid extraction is widely used for the separation of rare earths, among which synergistic extraction has attracted more and more attention. Numerous types of synergistic extraction systems have been applied to rare earths with high extraction efficiency and selectivities. In the present study, mixtures of sec -octylphenoxyacetic acid (CA12, H2A2) and 1,10-phenanthroline (phen, B) have been used for the extraction of rare earths from nitrate medium. The stoichiometry of samarium(III) extraction has been studied using the methods of slope analysis and constant molar ratio. The possibility of using synergistic extraction effects to separate rare earths has also been studied. RESULTS: Mixtures of CA12 and phen display synergistic effects in the extraction of rare earth elements giving maximum enhancement coefficients of 5.5 (La); 13.7 (Nd); 15.9 (Sm); 24.5 (Tb); 45.4 (Yb) and 12.3 (Y). Samarium(III) is extracted as SmHA4B3 with mixtures of CA12 and phen instead of SmHA4 when extracted with CA12 alone. The calculated logarithm of the equilibrium constant is 6.0 and the thermodynamic functions, ,H, ,G, and ,S, have been calculated as 4.3 kJ mol,1, , 33.7 kJ mol,1 and 129.7 J mol,1 K,1, respectively. CONCLUSION: Mixtures of CA12 and phen exhibit synergistic effects on rare earth elements. Graphical and numerical methods have been successfully used to determine their stoichiometries. The different synergistic effects may provide the possibility of separating yttrium from heavy lanthanoids at an appropriate ratio of CA12 and phen. Copyright © 2010 Society of Chemical Industry [source] Alkaline hydrolysis of cinnamaldehyde to benzaldehyde in the presence of ,-cyclodextrinAICHE JOURNAL, Issue 2 2010Hongyan Chen Abstract A facile, novel, and cost-effective alkaline hydrolysis process of cinnamaldehyde to benzaldehyde under rather mild conditions has been investigated systematically in the presence of ,-cyclodextrin (,-CD), with water as the only solvent. ,-CD could form inclusion complex with cinnamaldehyde in water, with molar ratio of 1:1, so as to promote the reaction selectivity. The complex has been investigated experimentally and with computational methods. 1H-NMR, ROESY, UV,Vis, and FTIR have been utilized to analyze the inclusion complex. It shows that the equilibrium constant for inclusion (Ka) is 363 M,1, and the standard Gibbs function for the reaction, ,,G (298 K), is ,14.6 kJ mol,1. In addition, the structures of the proposed inclusion compounds were optimized with hybrid ONIOM theory. Benzaldehyde could be obtained at an yield of 42% under optimum conditions [50°C, 18 h, 2% NaOH (w/v), cinnamaldehyde:,-CD (molar ratio) = 1:1]. To explain the experimental data, NMR, FTIR, and elemental analysis results were used to determine the main reaction by-product 1-naphthalenemethanol. A feasible reaction mechanism including the retro-Aldol condensation of cinnamaldehyde and the Aldol condensation of acetaldehyde and cinnamaldehyde in basic aqueous ,-CD solution has been proposed. The calculated activation energy for the reaction was 45.27 kJ mol,1 by initial concentrations method. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Monitoring of unfolding of metallo-proteins by electrospray ionization mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 5 2003Vincenzo Cunsolo Abstract An electrospray ionisation (ESI) mass spectrometric method for the determination of the equilibrium constant and free energy (,G) of protein unfolding was used to monitor the denaturation process at different pH of three metallo-proteins, i.e. wild-type copper azurin, zinc azurin and wild-type amicyanin. The time course of the unfolding process was followed by dissolving the proteins under denaturing conditions (methanol,water (1 : 1, v/v)) at different pH (2.5, 3.0, 3.5) and recording ESI spectra at time intervals. The spectra showed two series of peaks, corresponding to the native holo-protein and the unfolded apo-protein. From the intensity ratio of these two series of peaks at increasing time and at equilibrium, the equilibrium constants for the unfolding process for the three proteins could be determined. From these equilibrium constants a ,G° derivation was attempted. The ,G° values obtained decrease with decrease in pH, in agreement with the expected reduction of conformational stability of proteins at lower pH. The results obtained confirm that ESI-MS can be used for monitoring of unfolding process and to derive quantitative thermodynamic data. Copyright © 2003 John Wiley & Sons, Ltd. [source] Lattice-fluid equation of state with hydrogen-bond cooperativityAICHE JOURNAL, Issue 2 2002Poongunran Muthukumaran Hydrogen bonding plays an important role in thermodynamic properties of polar fluids. Existing equations of state that include h-bonding cannot accurately predict the phase behavior for polar fluids. In the theories for h-bond-chain forming molecules, h-bonding strength is considered a constant at a given temperature and pressure. Infrared spectroscopy and ab initio calculations show that the h-bonding strength depends on whether or not the molecule was previously h-bonded at other sites. When an h-bond is formed between an already hydrogen-bonded species and a free species, the second h-bond has different energetic characteristics from the primary h-bond. In the case of l-alkanol self-h-bonding, the equilibrium constant for the second h-bond is ten times that for the primary h-bond. This phenomenon called h-bond cooperativity was incorporated in a lattice-fluid-hydrogen-bonding equation of state. Calculations for pure l-alkanols, show that the theory can be improved significantly by the incorporation of h-bond cooperativity. Agreement with the phase behavior and spectroscopic h-bonding data improves using cooperativity, without any additional adjustable parameters. Heat of mixing calculations agree well with the experimental data. [source] Kinetic study on the prooxidative effect of vitamin C on the autoxidation of glycerol trioleate in micellesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 2 2006Zai-Qun Liu Abstract Vitamin C (L -ascorbic acid) protects human health by scavenging toxic free radicals and other reactive oxygen species formed in cell metabolism. The surplus supplementation of vitamin C, however, may be harmful to health because the level of 8-oxoguanine and 8-oxoadenine in lymphocyte DNA varies remarkably. In the process of the kinetic investigation on the 2,2,-azobis(2-amidinopropane dihydrochloride) (AAPH)-induced autoxidation of glycerol trioleate (GtH) in the micelles of cetyl trimethyl ammonium bromide (CTAB), sodium dodecyl sulfate (SDS) and Triton X-100, the addition of vitamin C accelerates the autoxidation of GtH even in the absence of the free radical initiator, AAPH. The initiating rate, Ri, of vitamin C (VC)-induced autoxidation of GtH is related to the micelle charge, i.e. Ri,=,14.4,×,10,6 [VC] s,1 in SDS (anionic micelle), Ri,=,1961,×,10,6 [VC] s,1 in Triton X-100 (neutral micelle) and Ri is a maximum in CTAB (cationic micelle) when the vitamin C concentration is ,300,µM. Thus, vitamin C can initiate autoxidation of GtH in micelles, especially in the neutral one. Moreover, the attempt to explore whether ,-tocopherol (TocH) could rectify vitamin C-induced autoxidation of GtH leads us to find that the rate constant of TocH reacting with the anionic radical of vitamin C (VC.,), k,inh, is ,103M,1,s,1, which is less than that of the ,-tocopherol radical (Toc.) with vitamin C (kinh,=,,105,M,1,s,1). Thus, the equilibrium constant of the reaction Toc.+VC,,TocH+VC., is prone strongly to the regeneration of Toc. by vitamin C rather than the reverse reaction. Copyright © 2006 John Wiley & Sons, Ltd. [source] Reactions of 1,2,5-thiadiazole 1,1-dioxide derivatives with nitrogenated nucleophiles.JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 4 20031-dioxide, 4-diphenyl-, 5-thiadiazole , Addition of amines, Part , amides to Abstract The addition reactions of some amides and aromatic amines to a CN double bond of 3,4-diphenyl-1,2,5-thiadiazole 1,1-dioxide (1) were studied in aprotic solvent solutions [N,N -dimethylformamide (DMF) and acetonitrile (MeCN)]. Equilibrium constants for the reactions of 1 with acetamide, 2-fluoroacetamide, butyramide, benzamide, aniline and 3-aminopyridine were measured using a previously reported cyclic voltammetric (CV) method. Aliphatic amines gave unstable solutions, probably owing to reactions of anionic species derived from 1. Other N nucleophiles tested (formamide, succinimide, thioacetamide and cyanamide) yielded different products that have not yet been characterized. DMF, N,N -dimethylacetamide (DMA) and N -methylacetamide did not react. The addition thiadiazoline produced in the reaction of acetamide with 1 was characterized by IR and 1H and 13C RMN NMR spectroscopy as a prototype compound. For this system, the equilibrium constant could also be measured by a standard UV,VIS method and was found to be in agreement with the value obtained by CV. The reaction of 1 with urea produced a bicyclic product, identified as 3a,6a-diphenyltetrahydroimidazo[4,5- c]-1,2,5-thiadiazol-5-one 2,2-dioxide. Copyright © 2003 John Wiley & Sons, Ltd. [source] Identification of dopamine transporter in bovine pineal gland using [3H]GBR 12935JOURNAL OF PINEAL RESEARCH, Issue 1 2003P. Govitrapong Abstract: The mammalian pineal gland contains several neurotransmitters and receptors for amino acids, biogenic amines, and peptides. Some of these, such as D1 and D2 dopamine receptors, have been previously identified and characterized in the bovine pineal gland by our group. As a matter of fact, the density of D1 dopamine receptors in the pineal gland is higher than that of corpus striatum, suggesting that this organ must possess a high affinity dopamine transporter, which has been identified in this study by using [3H]GBR 12935 as a radiological ligand and nomifensine to determine non-specific binding. The association rate of [3H]GBR 12935 binding to the pineal membrane was examined as a function of time. The binding reached equilibrium within 45 min of incubation at 25°C. The specific binding was reversible and saturable. The dissociation time course of the specific [3H]GBR 12935 binding from the bovine pineal membrane was also studied. A half-life (t1/2) of 14-min was obtained. The saturation analysis of the [3H]GBR 12935 binding revealed a dissociation equilibrium constant (Kd) of 6.0 ± 0.9 nm and a receptor density (Bmax) of 6.9 ± 0.3 pmol/mg protein, which were comparable with those values obtained from bovine striatum and frontal cortex. In competitive experiments, the concentrations of drugs required to inhibit 50% of the binding (IC50) were in descending order GBR 12909 > GBR 12935 > trans -flupenthixol > nomifensine > cis -flupenthixol > amitriptyline > imipramine > desipramine > dopamine > fluoxetine > fuvoxamine > d -amphetamine. However, nisoxetine, SCH 23390, norepinephrine, and serotonin were unable to displace [3H]GBR binding. These results show that drugs capable of blocking dopamine transporters were effective in displacing [3H]GBR binding; whereas specific norepinephrine and serotonin transporter inhibitors were less effective or ineffective. In addition, the dopamine transporter is ion-dependent as sodium increased [3H]GBR binding in a concentration related manner. These results indicate that a high affinity dopamine transporter exists in the bovine pineal, which may exhibit circadian periodicity, and whose physiological functions need to be delineated and characterized in future investigations. [source] Determination of the equilibrium constant for the reaction between bisphenol A and diphenyl carbonateJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2002Stephen M. Gross Abstract Despite the industrial significance of poly(bisphenol A carbonate), there is a scarcity of open literature on the equilibrium of the melt-phase process. In fact, the equilibrium constant (Keq) for this reaction has never been measured directly. This article describes a process on the basis of NMR for the measurement of Keq for the reaction between bisphenol A and diphenyl carbonate in the presence and absence of a catalyst. The apparent enthalpy and entropy were calculated using a van't Hoff plot. Decomposition of bisphenol A is a common side reaction in the melt-phase reaction performed at high temperatures in the presence of catalyst. The effect of these side reactions on the Keq in the presence of catalyst is determined. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 171,178, 2002 [source] Quantitative Raman spectroscopy: speciation of cesium silicate glassesJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2009Wim J. Malfait Abstract The silicate speciation forms an important aspect of the structure of silicate melts, a subject of interest to both the earth- and materials science communities. In this study, the Qn speciation of binary cesium silicate glasses was studied by Raman spectroscopy. A method to extract the equilibrium constant from a set of Raman spectra is presented, and the least-squares optimization algorithm is given (in Supporting Information). Log(K), the equilibrium constant of the speciation reaction, 2Q3 = Q4 + Q2, equals ,2.72 ± 0.11 at the glass transition. This extends the previously established correlation between log(K) and the inverse of the ionic radius of the network modifier to cesium. Copyright © 2009 John Wiley & Sons, Ltd. [source] Investigation of the mechanism of lubrication in starch,oil composite dry film lubricants,LUBRICATION SCIENCE, Issue 1 2007G. Biresaw Abstract The boundary coefficient of friction (COF) of starch,oil composite dry film lubricants was investigated as a function of starch type (waxy vs. normal purified food grade corn starch), oil chemistry (hexadecane vs. oleic acid and various vegetable oils), and starch-to-oil ratio. Based on the results, a mechanism of starch,oil interaction in these composites was proposed. According to the proposed mechanism: (a) the oil in the composite is distributed between the bulk and the surface of the starch; and (b) the fraction of the oil trapped in the bulk and that adsorbed on the surface are related to each other by an equilibrium constant, and are functions of the total oil concentration in the composite. In line with the proposed mechanism, an adsorption model was used to quantify the free energy of adsorption (,Gads) of the polar oils onto the starch surface. The analysis gave ,Gads values that were higher than those reported for the adsorption of the same polar oils onto steel surfaces. This result is consistent with the effect of the relative surface energies of steel and starch on the adsorption of polar oils. The adsorption property of the non-polar hexadecane relative to the polar oils was estimated by comparing their interfacial tensions with starch. The result showed a higher interfacial tension for hexadecane,starch than that for the polar oil,starch composites. This result predicts a relatively poorer compatibility with, and, hence, poorer adsorption of hexadecane onto starch leading to higher COF, as was observed in the friction measurements. Published in 2006 by John Wiley & Sons, Ltd. [source] Polycondensation Kinetics of Lactic AcidMACROMOLECULAR REACTION ENGINEERING, Issue 6 2007Yogesh M. Harshe Abstract The direct polycondensation of D,L -lactic acid in the absence and presence of different catalysts at various temperatures has been studied experimentally. Two types of reactions were carried out, one under closed conditions to estimate the equilibrium constant and the other under flow of nitrogen to estimate the polymerization rate constant. A mathematical model was developed based on a suitable kinetic scheme for polycondensation reaction accounting for the rate of water removal. The effects of different operating conditions (temperature and pressure) on the average molecular weight of the polymer have been explored through experiments and model simulations. [source] Simulation of Styrene Polymerization by Monomolecular and Bimolecular Nitroxide-Mediated Radical Processes over a Range of Reaction ConditionsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2007Juliana Belincanta-Ximenes Abstract Simulations of polymerization rate, molecular weight development and evolution of the concentrations of species participating in the reaction mechanism over a range of operating conditions, and a parameter sensitivity analysis showing the effects of temperature, activation/deactivation equilibrium constant and initial concentrations of controller and initiator (if present) on these variables are presented for the nitroxide-mediated radical polymerization of styrene. The simulations were performed with a computer program based on a detailed reaction mechanism. The simulated profiles of conversion, number average molecular weight (), and polydispersity agree well with experimental data. Previously unknown activation energies for reactions involved in the mechanism are estimated. The temperature dependence of the kinetic rate constants obtained in this study will be useful for future modeling and optimization studies. [source] Is the Addition-Fragmentation Step of the RAFT Polymerisation Process Chain Length Dependent?,MACROMOLECULAR THEORY AND SIMULATIONS, Issue 5 2006Ekaterina I. Izgorodina Abstract Summary: The chain length dependence of the addition-fragmentation equilibrium constant (K) for cumyl dithiobenzoate (CDB) mediated polymerisation of styrene has been studied via high level ab initio molecular orbital calculations. The results indicate that chain length and penultimate unit effects are extremely important during the early stages of the polymerisation process. In the case of the attacking radical (i.e., R, in: R,,+,SC(Z)SR,,,,RSC,(Z)SR,), the equilibrium constant varies by over three orders of magnitude on extending R, from the styryl unimer to the trimer species and actually increases with chain length, further confirming that K is high in this system. When the reactions of the cumyl leaving group and cyanoisopropyl initiating species, which are also present in CDB-mediated polymerisation of styrene in the presence of the initiator 2,2,-azoisobutyronitrile, are also included, the variation in K extends over five orders of magnitude. Although less significant, the influence of the R, group should also be taken into account in a complete kinetic model of the RAFT process. However, for most practical purposes, its chain length effects beyond the unimer stage may be ignored. These results indicate that current simplified models of the RAFT process, which typically ignore all chain length effects in the R and R, positions, and all substituent effects in the R, position, may be inadequate, particularly in modelling the initial stages of the process. [source] On the Nitroxide Quasi-Equilibrium in the Alkoxyamine-Mediated Radical Polymerization of StyreneMACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2006Enrique Saldívar-Guerra Abstract Summary: The range of validity of two popular versions of the nitroxide quasi-equilibrium (NQE) approximation used in the theory of kinetics of alkoxyamine mediated styrene polymerization, are systematically tested by simulation comparing the approximate and exact solutions of the equations describing the system. The validity of the different versions of the NQE approximation is analyzed in terms of the relative magnitude of (dN/dt)/(dP/dt). The approximation with a rigorous NQE, kc[P][N],=,kd[PN], where P, N and PN are living, nitroxide radicals and dormant species respectively, with kinetic constants kc and kd, is found valid only for small values of the equilibrium constant K (10,11,10,12 mol,·,L,1) and its validity is found to depend strongly of the value of K. On the other hand, the relaxed NQE approximation of Fischer and Fukuda, kc[P][N],=,kd[PN]0 was found to be remarkably good up to values of K around 10,8 mol,·,L,1. This upper bound is numerically found to be 2,3 orders of magnitude smaller than the theoretical one given by Fischer. The relaxed NQE is a better one due to the fact that it never completely neglects dN/dt. It is found that the difference between these approximations lies essentially in the number of significant figures taken for the approximation; still this subtle difference results in dramatic changes in the predicted course of the reaction. Some results confirm previous findings, but a deeper understanding of the physico-chemical phenomena and their mathematical representation and another viewpoint of the theory is offered. Additionally, experiments and simulations indicate that polymerization rate data alone are not reliable to estimate the value of K, as recently suggested. Validity of the rigorous nitroxide quasi-equilibrium assumption as a function of the nitroxide equilibrium constant. [source] | ||||||||||||||||||||||||||||||||||||||||