Activation Parameters ΔH Research Articles

Diphosphine Isomerization and C−H and P−C Bond Cleavage Reactivity in the Triosmium Cluster Os3(CO)10(bpcd): Kinetic and Isotope Data for Reversible Ortho Metalation and X-ray Structures of the Bridging and Chelating Isomers of Os3(CO)10(bpcd) and the Benzyne-Substituted Cluster HOs3(CO)8(μ3-C6H4)[μ2,η1-PPhCC(PPh2)C(O)CH2C(O)

The coordination and reactivity of the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopentene-1,3-dione (bpcd) with Os3(CO)10(MeCN)2 (1) has been explored. The initial substitution product 1,2-Os3(CO)10(bpcd) (2b) undergoes a nondissociative, intramolecular isomerization to furnish the bpcd-chelated cluster 1,1-Os3(CO)10(bpcd) (2c) over the temperature range of 323−343 K. The isomerization reaction is unaffected by trapping ligands, yielding the activation parameters ΔH⧧ = 25.0(0.7) kcal/mol and ΔS⧧ = −2(2) eu. Thermolysis of 2c in refluxing toluene gives the hydrido cluster HOs3(CO)9[μ-(PPh2)CC{PPh(C6H4)}C(O)CH2C(O)] (3) and the benzyne cluster HOs3(CO)8(μ3-C6H4)[μ2,η1-PPhCC(PPh2)C(O)CH2C(O)] (4). Time−concentration profiles obtained from sealed-tube NMR experiments starting with either 2c or 3 suggest that both clusters are in equilibrium with the unsaturated cluster 1,1-Os3(CO)9(bpcd) and that the latter cluster serves as the precursor to the benzyne-substituted cluster 4. The product composition...

Kinetics of the oxidative degradation of d-xylose in the presence and absence of cationic and anionic surfactants

The oxidative degradation of d-xylose by cerium(IV) has been found to be slow in acidic aqueous solution with the evidence of autocatalysis. The reaction is accelerated in the cetyltrimethylammonium bromide (CTAB) micellar medium but sodium dodecyl sulfate (an anionic surfactant) has no effect. The pseudo first-order rate constants have been determined at different [reductant], [oxidant], [H2SO4], temperature, and [CTAB]. The reaction rate increased with increasing [d-xylose] and decreased with increase in [H2SO4]. The CTAB-micelle-catalyzed kinetic results can be interpreted by the pseudophase model. The kinetic parameters such as association constant (Ks), micellar medium rate constant (km), and activation parameters (Ea, ΔH# and ΔS#) are evaluated and the reaction mechanism is proposed. The reaction rate is inhibited by electrolytes and the results provide an evidence for the exclusion of the reactive species from the reaction site.

Excess Molar Volume and Viscosity of Isobutyric Acid + Water Binary Mixtures Near and Far Away from the Critical Temperature

The excess molar volume VE, shear viscosity deviation Δη and excess Gibbs energy of activation ΔG∗E of viscous flow have been investigated by using density (ρ) and shear viscosity (η) measurements for isobutyric acid + water (IBA+W) mixtures over the entire range of mole fractions at five different temperatures, both near and close to the critical temperature (2.055K ≤ (T−Tc)≤ 13.055K). The results were also fitted with the Redlich–Kister equation. This system exhibited very large negative values of VE and very large positive values of Δη due to increased hydrogen bonding interactions and correlation length between unlike molecules in the critical region and to very large differences between the molar volumes of the pure components at low temperatures. The activation parameters ΔH∗ and ΔS∗ have been also calculated and show that the critical region has an important effect on the volumetric properties.

Fast and precise access to enantiomerization rate constants in dynamic chromatography

An analytical solution of the unified equation to evaluate elution profiles of interconverting enantiomers in dynamic chromatography is presented. Rate constants k1 and k(-1) and Gibbs activation energies are directly obtained from the chromatographic parameters (retention times tR A and tR A of the interconverting enantiomers, the peak widths at half height wA and wB, and the relative plateau height hp), and the initial amounts A0 and B0 of the enantiomers without any iterative and time consuming computational step. Therefore, this equation is no longer limited to racemic analytes. The analytical solution presented here was validated by comparison with a dataset of 125,000 simulated elution profiles of enantiomerizations. Furthermore, it was found that the recovery rate from a defined dataset is on average 40% higher using the unified equation compared to evaluation methods based on iterative computer simulation. The new equation was applied to determine the enantiomerization rate constant of 1-n-butyl-2-tert-butyldiaziridine by enantioselective gas chromatography. The activation parameters (DeltaH(double dagger) = 112.6 +/- 2.5 kJ/mol and DeltaS(double dagger) = -27 +/- 2 J/(K mol) were obtained from temperature-dependent measurements between 100 degrees C and 140 degrees C in 10K steps.

Proton NMR Investigation of the Stoichiometry, Stability, and Exchange Kinetics of Tl+ Complexes with Hexacyclen and Hexamethylhexacyclen in N,N-Dimethylformamide Solutions. Observation of a Three-Site Exchange Process

Abstract 1H NMR spectroscopy was used to investigate the stoichiometry, stability, and exchange kinetics and mechanism of ligand interchange for Tl+ complexes with hexacyclen (HCY) and hexamethylhexacyclen (HMHCY) in dimethylformamide (DMF) solution. In both cases, a stable complex with a 1:1 stoichiometry was formed in solution. A complete line-shape analysis was used to evaluate the mean exchange times and exchange rates. The two-site chemical exchange between Tl+ and HCY proceeded via a dissociative ligand-interchange mechanism in the temperature range 250–310 K. However, the 1H NMR spectra of the Tl+–HMHCY complex system in DMF, in about the same temperature range, revealed the predominance of a three-site exchange process in the system. The type of exchange was dependent on the Tl+/HMHCY mole ratio, ρ. At ρ < 1, ligand exchange occurs via a dissociative mechanism, while at ρ > 1, a bimolecular metal exchange is the predominate mechanism. In this case, the main factors controlling the exchange rates are the conformational rearrangement of the ligand during a concerted partial decomplexation of a Tl+ cation and partial complexation of a second one. The activation parameters (Ea, ΔH‡, ΔS‡, and ΔG‡) for the exchange processes (i.e. the ligand exchange, metal exchange, and the conformational change of the complex) were determined and compared with those for a two-site exchange for the Tl+–HCY system.

Mechanism of Replacement of the Nitro Group and Fluorine Atom in meta-Substituted Nitrobenzenes by Phenols in the Presence of Potassium Carbonate

The relative mobilities of the nitro group and fluorine atom in 1,3-dinitrobenzene and 1-fluoro-3-nitrobenzene by the action of phenols in the presence of potassium carbonate in dimethylformamide at 95–125°C were studied by the competing reaction method. The rate constant ratios k(NO2)/k(F) were correlated with the differences between the corresponding activation parameters (ΔΔH≠ and ΔΔ S≠). The greater mobility of the nitro group was found to be determined by the entropy control of the reactivity of arenes. The activation parameters (ΔH≠ and ΔS≠) were calculated, and the enthalpy-entropy compensation effect was revealed. The reaction mechanism is discussed.

Inner‐Phase Reaction Dynamics: The Influence of Hemicarcerand Polarizability and Shape on the Potential Energy Surface of an Inner‐Phase Reaction

AbstractThe thermal decomposition of six phenyldiazirine (2) hemicarceplexes and the spectroscopic properties of these hemicarceplexes, as well as those of one spiro[cyclobutabenzene‐1(2H),3′‐diazirine] (1) and one p‐tolyldiazirine (3) hemicarceplex, have been investigated in order to determine the effect of a hemicarcerand on the potential energy surface of an inner‐phase reaction. These hemicarceplexes have pentyl or phenethyl feet groups, three tetramethylene linkers and differ in the nature of one linker group X as follows: 1: X = (CH2)5; 2: X = (CH2)n (n = 2, 3, 4), (S,S)‐CH2CH[OC(CH3)O]CHCH2 ­and ortho‐CH2C6H4CH2; 3: X = (CH2)4. The effect of the linker group X on the structure of the phenyldiazirine hemicarceplexes was analyzed by MM2 force field calculations and leads to a change in the bending of the inner phase, which increases in the order (S,S)‐CH2CH[OC(CH3)O]CHCH2 > (CH2)4 > (CH2)3 > (CH2)2 > ortho‐CH2C6H4CH2 and to a shortening of the center‐to‐center distance between the two cavitands of the host, which decreases in the order (S,S)‐CH2CH[OC(CH3)O]CHCH2 < (CH2)4 < (CH2)3 < (CH2)2 < ortho‐CH2C6H4CH2. All hemicarceplexes show large red shifts of the diazirine n‐π*‐transition in their UV/Vis absorption spectra. From the red shifts and from plots of the n‐π*‐excitation energy of the free diazirines against the solvent polarizability P, the inner‐phase polarizability was estimated. P ranges from 0.39 to 0.58 and is larger than the polarizabilities of common organic solvents. A comparison of the activation parameters ΔH‡, TΔS‡, and ΔG‡ for the diazirine decomposition in the inner phase with those in the bulk phase shows that the hemicarcerand stabilizes the inner‐phase transition states enthalpically by ΔΔH‡ = 1.9–2.8 kcal/mol and destabilizes the transition states entropically by ΔTΔS‡ = 0.2 to 3.0 kcal/mol. The enthalpic stabilization is explained with dispersion interactions between the stretched C–N bonds in the transition state and the highly electron‐rich aryl units of the hemicarcerand. This is consistent with the high polarizability of the inner phase. The entropic destabilization of the inner‐phase transition states is explained with a greater loss of vibrational degrees of freedoms as the transition state is reached in the inner phase as compared to the more mobile bulk solvent cage. Furthermore, the entropic destabilization decreases with an increased bending of the inner phase. This is explained with an induced‐fit model. An increased hemicarcerand bending leads to an improved fit between the inner phase and the bend transition states, which reduces the loss of vibrational degrees of freedom as the transition states are reached. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Investigation of kinetic and mechanism of triphenylphosphine addition to para‐naphthoquinone

AbstractThis work reports the results of a kinetic and mechanistic investigations of the addition reaction of triphenylphosphine to para‐naphtoquinone in 1,2‐dichloromethane as solvent. The order of reaction with respect to the reactants was determined using initial rate method, and the rate constant was obtained on the basis of pseudo‐first‐order method. Variable time method using Uv–Vis spectrophotometry (at 400 nm) was utilized for monitoring this addition reaction, for which the following Arrhenius equation was obtained: equation image The resulting activation parameters Ea, ΔH#, ΔG#, and ΔS# at 300 K were 13.63, 14.42, 18.75 kcal mol−1, and −14.54 cal mol−1K−1, respectively. The results suggest that the reaction is first order with respect to both triphenylphosphine and para‐naphthoquinone. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 427–433, 2005

Rate and Equilibrium Constants of Benzoyl Group Transfer between Pyridine N-Oxides

Kinetic characteristics of 19 transfer reactions of benzoyl group from N-benzoyloxypyridinium salts to pyridine N-oxides and 4-dimethylaminopyridine were studied in acetonitrile by the stopped-flow method. The rate of an identical reaction for 4-methoxypyridine was measured by dynamic NMR spectroscopy. For 5 other identical reactions the rates were estimated from Bronsted correlations. Equilibrium constants were estimated with the use of UV spectrophotometry (6), IR spectroscopy (2), from kinetic data (K ij = k ij /k ji ) (2), and in one case as logK i−j = logK i−x − logK j−x . The second order rate constants (k ij ) varied in the range 102–105 l mol−1 s−1, the equilibrium constants (K ij ) in the range 102–10−2; the activation parameters (ΔH ≠) were within 15–50 kJ mol−1, (−ΔS ≠) −20–110 J mol−1 K−1. The reactions under study occur in a single stage following the concerted SN2 mechanism through an early associative transition state. The benzoyl groups exchange rate and equilibrium are well described by simplified Marcus equation (omitting the quadratic term).

Platinum Complexes with Only One Purine Ligand (Guanine, Deoxyguanine, or Adenine) Flanked by Two cis‐NH(CH3) Groups – Informative Models for Assessing the Interaction of Purine C6 Substituents with cis‐Amines

Abstractsyn‐(R,S)‐Me3dienPtL complexes (Me3dien = N,N',N‐trimethyldiethylenetriamine; L = a guanine, a 6‐deoxyguanine, or an adenine derivative) represent useful models for assessing the influence of the purine C6 substituent on the rate of rotation about the Pt–N7 bond. Because of the unsymmetric nature of the syn‐(R,S)‐Me3dien carrier ligand with respect to the coordination plane (all N–Me groups on one side of this plane), two rotamers are possible; they are defined as endo or exo for the six‐membered ring of the purine on the same or opposite side of the coordination plane as the N–Me groups, respectively. The derivatives of guanine (Pen), 6‐deoxyguanine (deoxy‐Pen), and adenine (MeA) used are distinguished by their C6 substituent (O, H, or NH2, respectively). At ambient temperature the rate of rotation of the purine about the Pt–N7 bond is slow on the NMR time scale for all three complexes. However, for Pen and deoxy‐Pen, an increase of the temperature from 293 to 353 K led to coalescence of the 1H NMR signals, indicating fast interconversion between rotamers and allowing evaluation of the rate constants and activation parameters (ΔH≠ and ΔS≠) for rotation. In contrast, for MeA raising the temperature to 353 K caused only a very slight broadening of the NMR signals, thus precluding a kinetic analysis of this complex by NMR methods. The rate of interconversion between the rotamers was comparable for the Pen and deoxy‐Pen complexes, notwithstanding the greater bulk of the C6 substituent in the Pen complex. On the other hand, the far slower rate of rotation for MeA, as compared to Pen, cannot be explained solely on the basis of C6 substituent bulk. Activation parameters for rotation (average values for the two rotamers: ΔH≠ = 57 ± 4 and 108 ± 3 kJ·mol–1, ΔS≠ = –18 ± 11 and 170 ± 11 J·K–1·mol–1 for Pen and deoxy‐Pen, respectively) suggest a plausible explanation for the observed trend. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Four-Coordinate Titanium Alkylidene Complexes: Synthesis, Reactivity, and Kinetic Studies Involving the Terminal Neopentylidene Functionality

A series of titanium complexes containing a terminal neopentylidene functionality have been prepared by a one electron oxidatively induced α-hydrogen abstraction from the corresponding bis-neopentyl precursor (Nacnac)Ti(CH2tBu)2 (Nacnac- = [Ar]NC(CH3)CHC(CH3)N[Ar], Ar = 2,6-(CHMe2)2C6H3), among them (Nacnac)TiCHtBu(OTf) and (Nacnac)TiCHtBu(I). It was determined that bulky alkyl groups bound to titanium as well as a bulky coordinating anion from the oxidant are needed to promote α-hydrogen abstraction. Complex (Nacnac)TiCHtBu(OTf) serves as a template for other four-coordinate titanium neopentylidene complexes such as (Nacnac)TiCHtBu(X) (X- = Cl, Br, and BH4). Complexes (Nacnac)TiCHtBu(X) undergo cross-metathesis reactivity with the imine functionality of the Nacnac- ligand forming the imido complexes (HtBuCC(Me)CHC(Me)N[Ar])TiNAr(X) (X- = OTf, Cl, Br, I, BH4). In addition, C−H activation of two tertiary carbons also takes place to afford the titanacycles Ti[2,6-(CMe2)(CHMe2)C6H3]NC(Me)CHC(Me)N[2,6-(CMe2)(CHMe2)C6H3](X) (X- = OTf, Cl, Br and η2-BH4). Kinetic studies in C6D6 reveal the formation of (HtBuCC(Me)CHC(Me)N[Ar])TiNAr(I) from (Nacnac)TiCHtBu(I) to be independent of solvent (C6D6, Et2O−d10, THF-d8) and the reaction to be first order in titanium (k = 8.06 × 10-4 s-1 at 57 °C, with activation parameters ΔH⧧ = 21.3(2) kcal/mol, ΔS⧧ = −8(3) cal/mol K). Compound (Nacnac)TiCHtBu(OTf) reacts with various substrates to afford products in which the alkylidene functionality has been significantly transformed. When the alkylidene derivatives (NacnactBu)TiCHtBu(X) (X- = OTf, I; NacnactBu- = [Ar]NC(tBu)CHC(tBu)N[Ar]) were prepared, the intramolecular cross-metathesis transformation observed with (Nacnac)TiCHtBu(X) was inhibited completely.

Kinetic and mechanistic studies on the interaction of thymidine with the hydroxopentaaquarhodium(III) ion

The interaction of thymidine, a nucleoside, with hydroxopentaaquarhodium(III), [Rh(H2O)5(OH)]2+ ion in aqueous medium is reported and the possible mode of binding is discussed. The kinetics of interaction between thymidine and [Rh(H2O)5OH]2+ has been studied spectrophotometrically as a function of [Rh(H2O)5OH2+], [thymidine], pH and temperature. The reaction has been monitored at 298 nm, the λmax of the substituted complex, and where the spectral difference between the reactant and product is a maximum. The reaction rate increases with [thymidine] and reaches a limiting value at a higher ligand concentration. From the experimental findings an associative interchange mechanism for the substitution process is suggested. The activation parameters (ΔH‡=47.8 ± 5.7 kJ mol−1, ΔS‡=−173 ± 17 J K−1 mol−1) supports our proposition. The negative ΔG0 (−13.8 kJ mol−1) for the first equilibrium step also supports the spontaneous formation of the outer sphere association complex.

Zirconium‐Mediated Conversion of Amides to Nitriles: A Surprising Additive Effect.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Oxygen activation by a macrocyclic chromium complex. Mechanism of hydroperoxo-chromium(iii) to oxo-chromium(v) transformation

The transformation of the hydroperoxo complex L1(H2O)CrOOH2+ (L1 = 1, 4 8, 11-tetraazacyclotetradecane) to an oxo-chromium(v) species is a first-order process throughout the pH range examined, 1.7 < pH < 9.2. The pH dependence of the rate constant (k1) yielded an apparent pKa of 5.6 for L1(H2O)CrOOH2+. In the acidic range, (pH <4), the value of k1 is 0.191 s(-1). At the other extreme, pH >7.5, k(1)= 0.025 s(-1). No [H+]-dependence is observed within the two limiting regimes, clearly ruling out a simple attack by H+ at the hydroperoxo group. The temperature dependence of k1 in 0.020 M HClO4 yielded the activation parameters DeltaH++ = 53.7 kJ mol(-1) and DeltaS++ = -80.5 J mol(-1) K(-1).

Kinetic Study of Cysteine Oxidation by Potassium Hexacyanoferrate(III) in the Presence of Sodium Dioctylsulfosuccinate

The kinetic oxidation of cysteine (Cyst) by 0.001 M hexacyanoferrate(III) (Fe(CN)6 3−) in 0.06 M HCl at 25°C in aqueous and/or in and 0.005 M sodium dioctylsulfosuccinate (AOT) has been studied using optical absorption at 420 nm. The present data show that the reaction is first‐order with respect to [Cyst]T and Fe(CN)6 3−. Also, k obs is constant within the 0.05–0.10 M HCl range and decreases with increasing concentration of AOT up to 0.003 M, and then increases above 0.005 M AOT. The rate of the reaction in the presence of micelles can be explained using a pseudo‐phase model of the kinetics. Association constants of Cyst and Fe (CN)6 3− with AOT micelles are reported. The activation parameters ΔH # and ΔS # have also been obtained. The variation of the reaction rate with the nature of the salt is discussed.

Influence of acidity on the reaction between [PdCl(dien)]+ and L‐cysteine or glutathione in the presence of sodium dodecyl sulfate micelles

AbstractThe reaction mechanism and thermodynamic parameters of the complex formation between [PdCl(dien)]+ and sulfur‐containing ligands L‐cysteine and glutathione (GSH) were investigated in the presence of sodium dodecyl sulfate micelles in the pH range 0.5–3.5. The reaction rates were determined under pseudo‐first‐order conditions (ligand in excess) in the temperature range 276–299 K by using the stopped‐flow technique. A reaction mechanism was proposed that consisted of at least two parallel paths involving protonated and zwitterionic forms of thiols. The pH effects on reaction rate were interpreted in terms of the electrostatic interactions between the negatively charged micelle surface and different ionic forms of the ligand species. The calculation of pH‐dependent activation parameters (ΔH≠ and ΔS≠) revealed the considerable catalytic effects on the rate of complexation. The entropy of activation is strongly negative in the presence and absence of micelles, which is compatible with an associative reaction mechanism. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Preparation, X-ray Structure, and Reactivity of an Olefin-Carbene-Osmium Complex: α-Alkenylphosphine to α-Allylphosphine Transformation via an Osmaphosphabicyclopentane Intermediate

The isopropenyldi(isopropyl)phosphine complex (1) reacts at room temperature with phenyldiazomethane to give the olefin-carbene derivative Os(η5-C5H5)Cl(CHPh){PiPr2[C(CH3)CH2]} (2), which has been characterized by X-ray diffraction analysis. In toluene at 70 °C, complex 2 evolves into the osmaphosphabicyclopentane compound (3). Treatment of 3 with TlPF6 at room temperature leads to a 1:1 mixture of the α-allylphosphine complex (4) and its α-alkenyl-γ-(η3-benzyl)phosphine isomer (5). The heating of the mixture in tetrahydrofuran at 66 °C gives rise to the isomerization of 5 into 4, which has been also characterized by X-ray diffraction analysis. The hydride ligand of 4 is fairly acidic. Its deprotonation with NaOCH3 leads to an equilibrium mixture of the neutral osmium(II) α-allylphosphine (6), α-alkenyl-γ-(η3-benzyl)phosphine (7), and α-alkenyl-γ-carbenephosphine (8) isomers. Complex 2 also reacts with TlPF6. The reaction affords the hydride-carbyne derivative [OsH(η5-C5H5)(⋮CPh){PiPr2[C(CH3)CH2]}]PF6 (9), which evolves into 4. The isomerization is a first-order process with activation parameters of ΔH⧧ = 23 ± 3 kcal·mol-1 and ΔS⧧ = −4 ± 4 cal·K-1·mol-1. The hydride ligand of 9 is also fairly acidic. Its deprotonation with NaOCH3 leads to the neutral carbyne Os(η5-C5H5)(⋮CPh){PiPr2[C(CH3)CH2]} (10), which reacts with methanol to give the hydride-alkoxycarbene derivative OsH(η5-C5H5){C(OMe)Ph}{PiPr2[C(CH3)CH2]} (11). The carbene carbon atom of 2 has amphiphilic character, reacting with electrophiles and nucleophiles. The reaction with HBF4 leads to the hydride-benzylcyclopentadienyl derivative (14) via η1-benzyl intermediates, whereas the reaction with CH3Li gives the hydride-styrene compound OsH(η5-C5H5)(η2-CH2CHPh){PiPr2[C(CH3)CH2]} (15).

Nitro and Nitroso Metathesis Reactions with Monomeric Zirconium Imido Complexes

The bis(cyclopentadienyl)(tert-butylimido)zir-conium complex 1 undergoes ambient-temperature metathesis reactions with nitro- and nitrosoarenes, providing a rare nonphotochemical synthesis of cis-azoxy and cis-azo compounds, respectively. 2-Nitro-2-methylpropane also undergoes metathesis to give trans-(tert-butylazoxy)-2-methylpropane. This reaction was studied kinetically, and the rate was found to be first order in both 1 and substrate and inversely proportional to the concentration of tetrahydrofuran, with activation parameters DeltaH(double dagger) = 15 +/- 2 kcal mol(-1) and DeltaS(double dagger) = -26 +/- 3 cal mol(-1) K(-1).

1H NMR Study of Hindered Internal Rotation of Tetramethylthiuram Disulfide in Binary Dimethyl Sulfoxide‐Chloroform Mixtures

AbstractHindered internal rotation about the C‐N single bonds joining the thiuram disulfide was studied by 1H NMR complete line‐shaped analysis in different dimethyl sulfoxide‐chloroform (DMSO‐CDCl3) mixtures. From the temperature dependence of methyls proton spectra, activation parameters (Ea, ΔH≠, ΔS≠, and ΔG≠) were obtained. The Arrhenius plots showed a distinct isokinetic temperature at about 35 °C at which the exchange rate is more or less independent of the solvent composition. The resulting ΔH≠ against TΔS≠ plot showed a firmly good linear correlation, indicating the existence of an enthalpy‐entropy composition in an exchange process.

Kinetic behaviour and thermal inactivation of pectinlyase used in food processing

SummaryKinetic properties and thermal inactivation of pectinlyase (PL) were assayed in commercial pectinase preparations (Rapidase C80, Pectinase CCM, Pectinex 3XL and Grindamyl 3PA) by using apple pectin as substrate. The PL activity of Rapidase C80 showed substrate inhibition, while the other enzyme preparations followed typical Michaelis–Menten kinetics. The optimum pH and temperature values for PL activity lay within the range of 5.5–6.5 and 35–40 °C, respectively. PL was heat‐inactivated with simple first order kinetics. With respect to this, thermodynamic activation parameters (ΔH#, ΔS# and ΔG#) using a non‐linear Arrhenius plot were calculated. The Pectinase CCM and Pectinex 3XL PL showed a half‐life (t1/2) at 50 °C of 2.0 min and 11.8 min, respectively.