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1.
The kinetics of the interactions between three sulfur‐containing ligands, thioglycolic acid, 2‐thiouracil, glutathione, and the title complex, have been studied spectrophotometrically in aqueous medium as a function of the concentrations of the ligands, temperature, and pH at constant ionic strength. The reactions follow a two‐step process in which the first step is ligand‐dependent and the second step is ligand‐independent chelation. Rate constants (k1 ~10?3 s?1 and k2 ~10?5 s?1) and activation parameters (for thioglycolic acid: ΔH1 = 22.4 ± 3.0 kJ mol?1, ΔS1 = ?220 ± 11 J K?1 mol?1, ΔH2 = 38.5 ± 1.3 kJ mol?1, ΔS2 = ?204 ± 4 J K?1 mol?1; for 2‐thiouracil: ΔH1 = 42.2 ± 2.0 kJ mol?1, ΔS1 = ?169 ± 6 J K?1 mol?1, ΔH2 = 66.1 ± 0.5 kJ mol?1, ΔS2 = ?124 ± 2 J K?1 mol?1; for glutathione: ΔH1 = 47.2 ± 1.7 kJ mol?1, ΔS1 = ?155 ± 5 J K?1mol?1, ΔH2 = 73.5 ± 1.1 kJ mol?1, ΔS2 = ?105 ± 3 J K?1 mol?1) were calculated. Based on the kinetic and activation parameters, an associative interchange mechanism is proposed for the interaction processes. The products of the reactions have been characterized from IR and ESI mass spectroscopic analysis. A rate law involving the outer sphere association complex formation has been established as   相似文献   

2.
The rates of an ene reaction between 4-phenyl-1,2,4-triazoline-3,5-dione and hex-1-ene were studied in a temperature range of 15–40 °C and in a pressure range of 1–2013 bar. The enthalpy of reaction in 1,2-dichloroethane (?158.2±1.0 kJ mol?1), the enthalpy (51.3±0.5 kJ mol?1), entropy (122±2 J mol?1 K?1), and volume of activation (?31.0±1.0 cm3 mol?1), and the volume of this reaction (?26.6±0.3 cm3 mol?1) were determined. The high exothermic effect of the reaction suggests its irreversibility.  相似文献   

3.
The kinetics of decomposition of an [Pect·MnVIO42?] intermediate complex have been investigated spectrophotometrically at various temperatures of 15–30°C and a constant ionic strength of 0.1 mol dm?3. The decomposition reaction was found to be first‐order in the intermediate concentration. The results showed that the rate of reaction was base‐catalyzed. The kinetic parameters have been evaluated and found to be ΔS = ? 190.06 ± 9.84 J mol?1 K?1, ΔH = 19.75 ± 0.57 kJ mol?1, and ΔG = 76.39 ± 3.50 kJ mol?1, respectively. A reaction mechanism consistent with the results is discussed. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 67–72, 2003  相似文献   

4.
Equilibrium vapor pressures were determined at temperatures between 294 K and 353 K for the NiCl2-CH3CN system.Compositions studied ranged from molar ratios of CH3CN to NiCl2 of 0.27 to 1.90. Three stoichiometric compounds were identified: NiCl2(CH3CN)2, NiCl2(CH3CN), NiCl2(CH3CN)0.88. Per mole of gaseous CH3CN the values of ΔHo and ΔSo were calculated to be 52.0 ±0.4 kJ mol?1 and 149.0±1.3 J mol?1 K?1 for the decomposition of NiCl2(CH3CN)2, and 25.9 ±0.8 kJ mol?1 and 58.6± 2.1 J mol?1 K?1 for the decomposition of NiCl2(CH3CN). Below a composition of NiCl2(CH3CN)0.88 the phase diagram is complex and could not be interpreted in terms of specific stoichiometric compounds.  相似文献   

5.
At room temperature and below, the proton NMR spectrum of N-(trideuteriomethyl)-2-cyanoaziridine consists of two superimposed ABC patterns assignable to two N-invertomers; a single time-averaged ABC pattern is observed at 158.9°C. The static parameters extracted from the spectra in the temperature range from –40.3 to 23.2°C and from the high-temperature spectrum permit the calculation of the thermodynamic quantities ΔH0 = ?475±20 cal mol?1 (?1.987 ± 0.084 kJ mol?1) and ΔS0 = 0.43±0.08 cal mol?1 K?1 (1.80±0.33 J mol?1 K?1) for the cis ? trans equilibrium. Bandshape analysis of the spectra broadened by non-mutual three-spin exchange in the temperature range from 39.4–137.8°C yields the activation parameters ΔHtc = 17.52±0.18 kcal mol?1 (73.30±0.75 kJ mol?1), ΔStc = ?2.08±0.50 cal mol?1 K?1 (?8.70±2.09 J mol?1 K?1) and ΔGtc (300 K) = 18.14±0.03 kcal mol?1 (75.90±0.13 kJ mol?1) for the transcis isomerization. An attempt is made to rationalize the observed entropy data in terms of the principles of statistical thermodynamics.  相似文献   

6.
The kinetics of the interaction of adenosine with cis‐[Pt(cis‐dach)(OH2)2]2+ (dach = diaminocyclohexane) was studied spectrophotometrically as a function of [cis‐[Pt(cis‐dach)(OH2)2]2+], [adenosine], and temperature at a particular pH (4.0), where the substrate complex exists predominantly as the diaqua species and the ligand adenosine exists as a neutral molecule. The substitution reaction shows two consecutive steps: the first is the ligand‐assisted anation followed by a chelation step. The activation parameters for both the steps have been evaluated using Eyring equation. The low negative value of ΔH1 (43.1 ± 1.3 kJ mol?1) and the large negative value of ΔS1 (?177 ± 4 J K?1 mol?1) along with ΔH2 (47.9 ± 1.8 kJ mol?1) and ΔS2 (?181 ± 6 J K?1 mol?1) indicate an associative mode of activation for both the aqua ligand substitution processes. The kinetic study was substantiated by infrared and electrospray ionization mass spectroscopic analysis. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 219–229, 2011  相似文献   

7.
This paper reports the computed O2 binding to heme, which for the first time explains experimental enthalpies for this process of central importance to bioinorganic chemistry. All four spin states along the relaxed Fe? O2‐binding curves were optimized using the full heme system with dispersion, thermodynamic, and scalar‐relativistic corrections, applying several density functionals. When including all these physical terms, the experimental enthalpy of O2 binding (?59 kJ mol?1) is closely reproduced by TPSSh‐D3 (?66 kJ mol?1). Dispersion changes the potential energy surfaces and leads to the correct electronic singlet and heptet states for bound and dissociated O2. The experimental activation enthalpy of dissociation (~82 kJ mol?1) was also accurately computed (~75 kJ mol?1) with an actual barrier height of ~60 kJ mol?1 plus a vibrational component of ~10 and ~5 kJ mol?1 due to the spin‐forbidden nature of the process, explaining the experimentally observed difference of ~20 kJ mol?1 in enthalpies of binding and activation. Most importantly, the work shows how the nearly degenerate singlet and triplet states increase crossover probability up to ~0.5 and accelerate binding by ~100 times, explaining why the spin‐forbidden binding of O2 to heme, so fundamental to higher life forms, is fast and reversible.  相似文献   

8.
The kinetics of the interaction of L ‐asparagine with [Pt(ethylenediamine)(H2O)2]2+ have been studied spectrophotometrically as a function of [Pt(ethylenediamine)(H2O)22+], [L ‐asparagine], and temperature at pH 4.0, where the substrate complex exists predominantly as the diaqua species and L ‐asparagine as the zwitterion. The substitution reaction shows two consecutive steps: the first step is the ligand‐assisted anation and the second one is the chelation step. Activation parameters for both the steps have been calculated using Eyring equation. The low ΔH1 (43.59 ± 0.96 kJ mol?1) and large negative values of ΔS1 (?116.98 ± 2.9 J K?1 mol?1) as well as ΔH2 (33.78 ± 0.51 kJ mol?1) and ΔS2 (?221.43 ± 1.57 J K?1 mol?1) indicate an associative mode of activation for both the aqua ligand substitution processes. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 252–259, 2003  相似文献   

9.
Restricted rotation about the naphthalenylcarbonyl bonds in the title compounds resulted in mixtures of cis and trans rotamers, the equilibrium and the rotational barriers depending on the substituents. For 2,7-dimethyl-1,8-di-(p-toluoyl)-naphthalene (1) ΔH° = 3.66 ± 0.14 kJ mol?1, ΔS° = 1.67 ± 0.63 J mol?1 K?1, ΔHct = 55.5 ± 1.3 kJ mol?1, ΔHct = 51.9 ± 1.3 kJ mol?1, ΔSct = ?41.3±4.1 J mol?1 K?1 and ΔSct = ?42.9±4.1 J mol?1 K?1. The rotation about the phenylcarbonyl bond requires ΔH = ?56.9±4.4 kJ mol?1 and ΔS = ?20.5±15.3 J mol?1 K?1 for the cis rotamer, and ΔH = 43.5Δ0.4 kJ mol?1 and ΔS =± ?22.4Δ1.3 J mol?1 K?1 for the trans rotamer. The role of electronic factors is likely to be virtually the same for both these rotamers but steric interaction between the two phenyl rings occurs in the cis rotamer only. Hence, the difference of the activation enthalpies obtained for the cis and trans rotamers, ΔΔH?1 = 13.4 kJ mol?1, provides a basis for the estimation of the role of steric factors in this rotation. For the tetracarboxylic acid 2 and its tetramethyl ester 3 the equilibrium is even more shifted towards the trans form because of enhanced steric and electrostatic interactions between the substituents in the cis form. The barriers for the rotation around the phenylcarbonyl bond and the cis-trans isomerization are lowered; an explanation for this result is presented.  相似文献   

10.
The heat of reaction for SnJ2 (c)+J2 (c)+4045 CS2 (l)=[SnJ4; 4045 CS2] (sol) has been determined to be (?41.12±0.55) kJ mol?1, [(?9.83±0.13) kcal mol?1] by isoperibol solution calorimetry. Combining this result with the heat of formation of SnJ4 in CS2 determined in a previous investigation11 the value (?153.9±1.40) kJ mol?1, [(?36.9±0.33) kcal mol?1] has been derived for the heat of formation, ΔH f ι (SnJ2;c; 298.15 K), of tin diiodide.  相似文献   

11.
IntroductionZincisanessentialtraceelementtothelife .Manydiseasesarousedfromadeficiencyofzincelementhavere ceivedconsiderableattention .L α Aminoacidsarebasicunitsofproteins .L α Trytophanisoneoftheeightspeciesofaminoacidsindispensableforlife ,whichhastobeab sorbedfromfoodbecauseitcannotbesynthesizedinthehumanbody .InviewofthecomplexesofL α trytophanandessentialelementsasaddictiveswidelyusedinsuchfieldsasfoodstuff,medicineandcosmetic ,1 3theyhaveabroadenprospectforapplications .Briefly ,ab…  相似文献   

12.

Ligand substitution of trans-[CoIII(en)2(Me)H2O]2+ was studied for pyrazole, 1,2,4-triazole and N-acetylimidazole as entering nucleophiles. These displace the coordinated H2O molecule trans to the methyl group to form trans-[Co(en)2(Me)azole]. Stability constants at 18°C for the substitution of H2O by pyrazole, 1,2,4-triazole and N-acetylimidazole are 0.7 ± 0.1, 13.8 ± 1.4 and 1.7 ± 0.2 M?1, respectively. Second order rate constants at the same temperature for the reaction of trans-[CoIII(en)2(Me)H2O]2+ with pyrazole, 1,2,4-triazole and N-acetylimidazole are 161 ± 12, 212 ± 11 and 12.9 ± 1.6 M?1 s?1, respectively. Activation parameters (ΔH, ΔS) are 67 ± 6 kJ mol?1, + 27 ± 19 J K?1 mol?1; 59 ± 2 kJ mol?1, + 1 ± 6 J K?1 mol?1 and 72 ± 4 kJ mol?1, + 23 ± 14 J K?1 mol?1 for reactions with pyrazole, 1,2,4-triazole and N-acetylimidazole, respectively. Substitution of coordinated H2O by azoles follows an Id mechanism.  相似文献   

13.
The kinetics of decomposition of [Alg · Mn VIO42?] intermediate complex have been investigated spectrophotometrically at a constant ionic strength of 0.5 mol dm?3. The decomposition reaction was found to be first-order in the intermediate concentration. The results showed that the rate of reaction was base-catalyzed. The kinetic parameters have been evaluated and found to be ΔS? = ?103.88±6.18 J mol?1 K?1, ΔH? = 51.61 ± 1.02 kJ mol?1, and ΔG? = 82.57 ± 2.86 kJ mol?1, respectively. A reaction mechanism consistent with the results is discussed. © 1993 John Wiley & Sons, Inc.  相似文献   

14.
The rate of the fastest ene reaction between 4-phenyl-1,2,4-triazoline-3,5-dione (1) and 2,3-dimethyl-2-butene (2) is studied by means of stopped flow in solutions of benzene (k 2 = 55.6 ± 0.5 and 90.5 ± 1.3 L mol?1 s?1 at 23.3 and 40°C) and 1,2-dichloroethane (335 ± 9 L mol?1 s?1 at 23.5°C). The enthalpy of reaction (?139.2 ± 0.6 kJ/mol in toluene and ?150.2 ± 1.4 kJ/mol in 1,2-dichloroethane) and the enthalpy (20.0 ± 0.5 kJ/mol) and entropy (144 ± 2 J mol?1 K?1) of activation are determined. A clear correlation is observed between the reaction rate and ionization potential in a series of ene reactions of 4-phenyl-1,2,4-tri-azoline-3,5-dione with acyclic alkenes.  相似文献   

15.
In order to investigate the gas‐phase mechanisms of the acid catalyzed degradation of ascorbic acid (AA) to furan, we undertook a mass spectrometric (ESI/TQ/MS) and theoretical investigation at the B3LYP/6‐31 + G(d,p) level of theory. The gaseous reactant species, the protonated AA, [C6H8O6]H+, were generated by electrospray ionization of a 10?3 M H2O/CH3OH (1 : 1) AA solution. In order to structurally characterize the gaseous [C6H8O6]H+ ionic reactants, we estimated the proton affinity and the gas‐phase basicity of AA by the extended Cooks's kinetic method and by computational methods at the B3LYP/6‐31 + G(d,p) level of theory. As expected, computational results identify the carbonyl oxygen atom (O2) of AA as the preferred protonation site. From the experimental proton affinity of 875.0 ± 12 kJ mol?1 and protonation entropy ΔSp 108.9 ± 2 J mol?1 K?1, a gas‐phase basicity value of AA of 842.5 ± 12 kJ mol?1 at 298 K was obtained, which is in agreement with the value issuing from quantum mechanical computations. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

16.
The synthesis, structure, and solution‐state behavior of clothespin‐shaped binuclear trans‐bis(β‐iminoaryloxy)palladium(II) complexes doubly linked with pentamethylene spacers are described. Achiral syn and racemic anti isomers of complexes 1 – 3 were prepared by treating Pd(OAc)2 with the corresponding N,N′‐bis(β‐hydroxyarylmethylene)‐1,5‐pentanediamine and then subjecting the mixture to chromatographic separation. Optically pure (100 % ee) complexes, (+)‐anti‐ 1 , (+)‐anti‐ 2 , and (+)‐anti‐ 3 , were obtained from the racemic mixture by employing a preparative HPLC system with a chiral column. The trans coordination and clothespin‐shaped structures with syn and anti conformations of these complexes have been unequivocally established by X‐ray diffraction studies. 1H NMR analysis showed that (±)‐anti‐ 1 , (±)‐anti‐ 2 , syn‐ 2 , and (±)‐anti‐ 3 display a flapping motion by consecutive stacking association/dissociation between cofacial coordination planes in [D8]toluene, whereas syn‐ 1 and syn‐ 3 are static under the same conditions. The activation parameters for the flapping motion (ΔH and ΔS) were determined from variable‐temperature NMR analyses as 50.4 kJ mol?1 and 60.1 J mol?1 K?1 for (±)‐anti‐ 1 , 31.0 kJ mol?1 and ?22.7 J mol?1 K?1 for (±)‐anti‐ 2 , 29.6 kJ mol?1 and ?57.7 J mol?1 K?1 for syn‐ 2 , and 35.0 kJ mol?1 and 0.5 J mol?1 K?1 for (±)‐anti‐ 3 , respectively. The molecular structure and kinetic parameters demonstrate that all of the anti complexes flap with a twisting motion in [D8]toluene, although (±)‐anti‐ 1 bearing dilated Z‐shaped blades moves more dynamically than I‐shaped (±)‐anti‐ 2 or the smaller (±)‐anti‐ 3 . Highly symmetrical syn‐ 2 displays a much more static flapping motion, that is, in a see‐saw‐like manner. In CDCl3, (±)‐anti‐ 1 exhibits an extraordinary upfield shift of the 1H NMR signals with increasing concentration, whereas solutions of (+)‐anti‐ 1 and the other syn/anti analogues 2 and 3 exhibit negligible or slight changes in the chemical shifts under the same conditions, which indicates that anti‐ 1 undergoes a specific heterochiral association in the solution state. Equilibrium constants for the dimerizations of (±)‐ and (+)‐anti‐ 1 in CDCl3 at 293 K were estimated by curve‐fitting analysis of the 1H NMR chemical shift dependences on concentration as 26 M ?1 [KD(racemic)] and 3.2 M ?1 [KD(homo)], respectively. The heterochiral association constant [KD(hetero)] was estimated as 98 M ?1, based on the relationship KD(racemic)=1/2 KD(homo)+1/4 KD(hetero). An inward stacking motif of interpenetrative dimer association is postulated as the mechanistic rationale for this rare case of heterochiral association.  相似文献   

17.
Perovskite-type KTaO3 powder was synthesized by an alternative solid-state method at low temperature. Stoichiometric ammonium tantalum hydroxide, K2C2O4 and KF were mixed in water and then dried at room temperature. The crude product was formed by calcining the dried mixture at different temperatures. Pyrochlore-free KTaO3 powder was successfully synthesized after treating the crude product with water. KF plays an important role to inhibit the formation of pyrochlore K2Ta2O6 during the calcination process of ammonium tantalum hydroxide/K2C2O4/KF mixture. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, UV-vis diffuse reflectance (UV-vis) spectroscopy and thermogravimetric (TG) analysis were used to characterize the precursor compound and as-prepared samples. XRD results show that pyrochlore-free KTaO3 powder can be obtained at 600 °C. SEM results reveal that the as-prepared products are agglomerated and each of the agglomerations consists of many small grains with 10-30 nm in diameter.  相似文献   

18.
Cyclohexane and piperidine ring reversal in 1-(3-pentyloxyphenylcarbamoyloxy)-2-dialkylaminocyclohexanes was investigated by 13C NMR. An unusually low conformational energy ΔG = 0.59 kJ mol?1 and activation parameters ΔG218 = 43.8 ± 0.4 kJ mol?1, ΔH = 48.9 ± 2.5 kJ mol?1 and ΔS = 23 ± 9 J mol?1 K?1 were found for the diequatorial to diaxial transition of the cyclohexane ring in the trans-pyrrolidinyl derivative. In the trans-piperidinyl derivative, ΔG222 = 44.7 ± 0.5 KJ mol?1, ΔH = 55.7 ± 6.3 kJ mol?1 and ΔS = 51 ± 21 J mol?1 K?1 was found for the piperidine ring reversal from the non-equivalence of the α-carbons.  相似文献   

19.
2D 1H-1H EXSY NMR spectroscopy show that the free energy of activation ΔG in six 3-allyl-3-borabicyclo[3.3.1]nonane derivatives is significantly higher (72–86 kJ mol?1) than that in typical allylboranes (48–66 kJ mol?1). For the first member of the series, viz., 3-allyl-3-borabicyclo[3.3.1]nonane, the activation parameters of the permanent allylic rearrangement were also determined (ΔH = 82.7±3.4 kJ mol?1, ΔS = ?11.8±10.3 J mol?1 K?1, E A = 85.5±3.4 kJ mol?1, lnA = 29.2±1.2).  相似文献   

20.
The surface segregation of In and S from a dilute Cu(In,S) ternary alloy were measured using Auger electron spectroscopy coupled with a linear programmed heater. The alloy was linearly heated and cooled at constant rates. Segregation data of a linear heat run showed surface segregation of In that reached a maximum surface coverage of 25% followed by S, which reached a coverage of 30%. It was found that after In had reached a maximum surface coverage, it started to desegregate as soon as the S enriched the surface until In was completely replaced by S. The segregation parameters, namely, the pre‐exponential factor (D0), activation energy (Q), segregation energy (ΔG?) and interaction energy (Ω) were extracted from the measured segregation data for both In and S segregation in Cu by simulating the measured segregation data with a theoretical segregation model (modified Darken model). The segregation parameters obtained for In segregation in Cu are D0 = 1.8 ± 0.5 × 10?5 m2 s?1, Q = 184.3 ± 1.0 kJ.mol?1, ΔG? = ?61.4 ± 1.4 kJ.mol‐1, ΩCu?In = 3.0 ± 0.4 kJ.mol?1; for S segregation in Cu the parameters are D0 = 8.9 ± 0.5 × 10?3 m2 s?1, Q = 212.8 ± 3.0 kJ.mol?1, ΔG? = ?120.0 ± 3.5 kJ.mol?1, ΩCu?S = 23.0 ± 2.0 kJ mol?1 and the In and S interaction parameter is ΩIn?S = ?4.0 ± 0.5 kJ.mol?1. The initial parameters used for the Darken calculations were extracted from fits performed with the Fick's and Guttmann model. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

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