Activation Energy For Hydrolysis Research Articles

Catalyzed hydrolysis of polyethylene terephthalate melts

AbstractThe effect of zinc catalysts on the hydrolytic depolymerization of polyethylene terephthalate (PET) melts in excess water was studied using a 2‐L stirred pressure reactor at temperatures of 250, 265, and 280°C. The main products of the reaction were found to be terephthalic acid, ethylene glycol, and diethylene glycol. Rate constants were calculated from initial rate data at each temperature and found to be about 20% greater than the corresponding rate constants for uncatalyzed hydrolysis. The catalytic effect of zinc, as well as sodium, salts is attributed to the electrolytic destabilization of the polymer‐water interface during hydrolysis. The depolymerization rate data at 265°C were found to fit a kinetic model proposed earlier for the uncatalysed hydrolysis of PET. The effect of zinc and sodium salts on the activation energy of hydrolysis, or on the formation of ethylene glycol monomer is unclear. © 1994 John Wiley & Sons, Inc.

The effect of pH, temperature, and D 2O on the activity of porcine synovial collagenase and gelatinase

The pH dependence of V max and V max K m for hydrolysis of DnpProLeuGlyLeuTrpAla dArgNH 2 at the GlyLeu bond by porcine synovial collagenase and gelatinase was determined in the pH range 5–10. Both enzymes exhibited bell-shaped dependencies on pH for these two kinetic parameters, indicating that activity is dependent on at least two ionizable groups, one of which must be unprotonated and the other protonated. For collagenase, V max K m data indicate that in the substrate-free enzyme, these groups have apparent p K values of 7.0 and 9.5, while the V max profile indicates similar p K values of 6.8 and 10.1 for the enzyme-substrate complex. The corresponding pH profiles of gelatinase were similar to those of collagenase, indicating the importance of groups with apparent p K values of 5.9 and 10.0 for the free enzyme and 5.9 and 11.1 for the enzyme-substrate complex. When these kinetic constants were determined in D 2O using the peptide substrate, there was no significant effect on V max or K m for collagenase or K m for gelatinase. However, there was a deuterium isotope effect of ~1.5 on V max for gelatinase. These results indicate that a proton transfer step is not involved in the rate-limiting step for collagenase, but may be limiting with gelatinase. The Arrhenius activation energies for peptide bond hydrolysis of the synthetic peptide as well as the natural substrates were also determined for both enzymes. The activation energy (81 kcal) for hydrolysis of collagen by collagenase was nine times greater than that determined for the synthetic substrate (9.2 kcal). In contrast, the activation energy for hydrolysis of gelatin by gelatinase (26.3 kcal) was only 2.4 times greater than that for the synthetic substrate (11 kcal).

Comparison of the acid stability of azithromycin and erythromycin A

In acidic aqueous media, erythromycin A is rapidly degraded via intramolecular dehydration to form erythromycin-6.9-hemiketal and then anhydroerythromycin, both of which possess little antimicrobial activity. Azithromycin, a new azalide antibiotic, has a methyl-substituted nitrogen in place of the carbonyl at the 9a position of the aglycone ring, thus blocking the internal dehydration pathway. As a result, azithromycin decomposition occurs primarily via acid-catalysed hydrolysis of the ether bond to the neutral cladinose sugar. Rate constants and the time for 10% decay (T1/10) were determined for both azithromycin and erythromycin A at pH2 using various levels of acetonitrile cosolvent and constant ionic strength. Semi-log plots of the decay rate constants versus the reciprocal of the solution dielectric constants were used to extrapolate to totally aqueous conditions. In solution at 37 degrees C and pH2 with ionic strength mu = 0.02, azithromycin was degraded with a T1/10 of 20.1 min while erythromycin underwent 10% decay in only 3.7 sec. The activation energy for hydrolysis of the ether bond connecting cladinose to azithromycin was 25.3 kcal/mol while the internal dehydration reaction of erythromycin had an activation energy of 15.6 kcal/mol. A solution stability profile was generated for azithromycin over the pH range of 1.0 to 4.1 at 30 degrees C. Stability was found to improve ten-fold for each unit increase in pH.

Kinetic studies of the hydrolysis of platinum-DNA complexes by nuclease S1

The antitumor agent cis-diamminedichloroplatinum(II) ( cis-DDP) reacts covalently with DNA and disrupts its secondary structure. Damaged DNA, but not native DNA, is readily digested by S1 nuclease, an endonuclease specific for single stranded polynucleotides. We have measured S1 nuclease digestion of platinated DNA by the release of platinum-DNA adducts and compared it with digestion of unplatinated DNA. The rate of hydrolysis of damaged substrate from platinum-DNA complexes was less than the overall rate of digestion of nucleotides. Similar results were observed for platinum-DNA complexes in native, denatured or renatured conformations. The hydrolysis of denatured platinum-DNA complexes, r b = 0.075 platinum per nucleotide, obeyed Michaelis-Menten kinetics. Taking into account the level of DNA damage, V m for the release of platinated adducts was 0.6 times smaller than for digestion of unplatinated DNA. K m values and competition experiments indicated that the enzyme bound equally well to platinated and unplatinated substrates. Similar results were obtained for denatured DNA complexes with trans-DDP while [PtCl(diethylenetriamine)]Cl had no influence on nuclease digestion. These results suggest that bifunctional platinum-DNA lesions have contradictory effects on the hydrolysis of double stranded DNA by S1 nuclease. On one hand they create nuclease sensitive substrate by disrupting DNA secondary structure. On the other, they inhibit digestion of the damaged strand by increasing the activation energy for hydrolysis.

Alkaline Phosphatase and Other Hydrolyases Produced by Cenococcum graniforme , an Ectomycorrhizal Fungus

Cell extracts of Cenococcum graniforme have been found to contain the following hydrolytic enzymes: protease, esterase, alpha-d-galactopyranosidase, beta-d-galactopyranosidase, alpha-d-mannopyranosidase, beta-d-xylopyranosidase, alpha-d-glucopyranosidase, beta-d-glucopyranosidase, and alkaline phosphatase. Sulfatase, inorganic pyrophosphatase, and beta-d-mannopyranosidase were not detected in the extracts. beta-d-Xylopyranosidase and alpha-d-mannopyranosidase were most active in the neutral pH range, protease and phosphatase were most active in the alkaline pH range, and other enzymes were most active in the acidic pH range. These enzymes showed a high association with cell wall material, and the release of enzymes from the cells into the culture fluid appeared to occur only when the cells were undergoing autolysis. Alkaline phosphatase in C. graniforme is a constitutive enzyme, and examination of the alkaline phosphatase following a purification of 265-fold produced the following characteristics: pH optimum of 9.5, M(r) of 60,000, K(m) of 2.1 x 10 M for p-nitrophenylphosphate, and activation energy for hydrolysis of the substrate at 9.9 kcal (1 cal = 4.184 J)/mol.

Sol-gel kinetics of tetraethylorthosilicate (TEOS) in acid catalyst

Hydrolysis and condensation of tetraethylorthosilicate (TEOS) were measured under various pH ranges. Differential temperature analysis was used to determine the hydrolysis rate constant and the activation energy of hydrolysis. A kinetic model was established on the basis of hydrolysis, esterification and water-alcohol forming condensation. Each reaction rate constant could be obtained from gas chromatography analysis and the kinetic model. Hydrolysis rate constants were in proportion to acid concentration. Also the esterification reaction should not be neglected during the sol-gel transition of TEOS in alcoholic solvent.

Continuous production of maltotetraose using immobilized Pseudomonas stutzeri amylase

A continuous production process of maltotetraose was investigated by using immobilized maltotetraose (G(4))- forming amylase (1,4-alpha-D-glucan maltotetraohydrolase, EC3.2.1.60) from Pseudomonas stutzeri adsorbed on a macroporous hydrophobic resin. The maximum reaction rate was obtained at 55 degrees C and the activation energy of hydrolysis by immobilized G(4)-forming amylase was calculated to be 8.45 kcal/mol. The maltotetraose yield was greatly influenced by the flow rate of substrate solution, its concentration, and the immobilized enzyme activity. The newly defined factor "specific space velocity" was successfully introduced to normalize the operating parameters. Using this factor, the immobilized enzyme reactor then can be simulated and the operating dynamics can be determined.

Micellar catalysis by perfluorooctanoic acid

AbstractRates of acidic hydrolysis of hexano‐, octano‐, and decanohydroxamic acids and of 4‐bromophenylaceto‐ and phenylacetohydroxamic acids have been determined in aqueous perfluorooctanoic acid—a reactive counterion surfactant system. Typical micellar catalysis was observed for the hydrolyses of the n‐alkyl hydroxamic acids but not for the arylacetohydroxamic acids. The Arrhenius activation energy for hydrolysis of octano‐hydroxamic acid is smaller above the cmc of the surfactant than it is below the cmc.

Apo C-IIのLipoprotein lipase活性化機構

The effect of apolipoprotein C-II (apo C-II) on the bovine milk lipoprotein lipase (LPL)-catalysed hydrolysis of a homogeneous series of saturated phosphatidylcholines (PC) was examined with respect to the fatty acyl chain length of the substrates. Dilauryl-, dimyristoyl-, dipalmitoyl-, and distearoylphophatidylcholine (diC12PC, diC14PC, diC16PC and diC18PC, respectively) solubilized by Triton X-100 were used as substrates. The maximal rate of the LPL-catalysed hydrolysis of each of these lipids was determined in the absence and presence of apo C-II. The activation factor (the ratio of enzyme activity with apo C-II to that without the activator protein) increased with increasing mol ratio of apo C-II to LPL and was maximal at a ratio of about 50. At all apo C-II/ LPL mol ratio tested, the activation factor increased as a function of fatty acyl chain length.When LPL activities were determined between 16C and 40C, no systematic relationship between substrate fatty acyl chain length and either the rates or the activation energies for hydrolysis in the presence or absence of apo C-II was observed. However, there was a linear relationship between fatty acyl chain length and both the logarithm of the activation factor and the difference in activation energy in the presence and absence of apo C-II.These relationship were not the result of an alteration in the physical form of the substrate, since a mixture of diC14PC and diC16PC gave activation factors for each PC which were the same as those obtained for each individual lipid. From the temperature dependence of the activation factor, thermodynamic functions of the apo C-II-induced change in the reaction pathway were calculated. The free energy of activation decreased linearly with increasing chain length as the result of a linear increase in activation entropy which more than offset the unfavorable increase in activation enthalpy. We propose that the apo C-II mediated increase in the rate of LPL-catalysed hydrolysis of phosphatidylcholine is associated with transfer of a fatty acyl chain of the substrate or product to a more hydrophobic environment within the transition state complex.

Mechanisms of reaction of benzo(a)pyrene-7,8-diol-9,10-epoxide with DNA in aqueous solutions.

The physical and chemical reaction pathways of the metabolite model compound benzo(a)pyrene-7,8-diol-9,10-epoxide (BPDE) in aqueous (double-stranded) DNA solutions was investigated as a function of temperature (0-30 degrees C), pH (7.0-9.5), sodium chloride concentration (0-1.5M) and DNA concentration in order to clarify the relationships between the multiple reaction mechanisms of this diol epoxide in the presence of nucleic acids. The reaction pathways are (1) noncovalent intercalative complex formation with DNA, characterized by the equilibrium constant K, and Xb the fraction of molecules physically bound; (2) accelerated hydrolysis of BPDE bound to DNA; (3) covalent binding to DNA; and (4) hydrolysis of free BPDE(kh). The DNA-induced hydrolysis of BPDE to tetraols and the covalent binding to DNA are parallel pseudo-first-order reactions. Following the rapid (millisecond time scale) noncovalent complex formation between BPDE and DNA, a much slower (approximately minutes) H+-dependent (either specific or general acid catalysis) formation of a DNA-bound triol carbonium ion (rate constant k3) occurs. At pH 7.0 the activation energy of k3 is 8.7 +/- 0.9 kcal/mol, which is lower than the activation energy of hydrolysis of free BPDE in buffer solution (14.2 +/- 0.7 kcal/mol), and which thus partially accounts for the acceleration of hydrolysis of BPDE upon complexation with DNA. The formation of the triol carbonium ion is followed by a rapid reaction with either water to form tetraols (rate constant kT), or covalent binding to DNA (kc). The fraction of BPDE molecules which undergo covalent binding is fcov approximately equal to kc/(kc + kT) = 0.10 and is independent of the overall BPDE reaction rate constant k = kh(1 - Xb) + k3Xb if Xb----1.0, or is independent of Xb as long as k3Xb much greater than kh(1 - Xb). Thus, at Xb = 0.9, fcov is independent of pH (7.0-9.5) even though k exhibits a 70-fold variation in this pH range and k----kh above pH 9 (k3 = kh). Similarly, fcov is independent of temperature (0-30 degrees C), while k varies by a factor of approx. 3. In the range of 0-1.5 M NaCl, fcov decreases from 0.10 to 0.04. These variations are attributed to a combination of salt-induced variations in the factors k3, Xb and the ratio kc/kT.

Effect of apolipoprotein C-II on the temperature dependence of lipoprotein lipase-catalyzed hydrolysis of phosphatidylcholines. A hydrophobic model for the mechanism.

The lipoprotein lipase-catalyzed hydrolysis of diacylphosphatidylcholines (PC) in mixed micelles of Triton X-100/PC was studied as a function of temperature in the presence and absence of apolipoprotein C-II (apo-C-II), the activator protein for lipoprotein lipase. Dilauroyl-, dimyristoyl-, dipalmitoyl-, and distearoyl-phosphatidylcholine (di-C12-PC, di-C14-PC, di-C16-PC, and di-C18-PC, respectively) were used as substrates. No systematic relationship between substrate fatty acyl chain length and either the rates of the activation energies for hydrolysis in the presence or absence of apo-C-II was observed. However, there was a linear relationship between fatty acyl chain length and both the logarithm of the activation factor (the ratio of enzyme activity with apo-C-II to that without apo-C-II) and the difference in activation energy in the presence and absence of apo-C-II. These relationships were not the result of an alteration in the physical form of the substrate, since a mixture of di-C14-PC and di-C16-PC gave activation factors for each PC which were the same as those obtained for each individual lipid. From the temperature dependence of the activation factor, thermodynamic functions of the apo-C-II-induced change in the reaction pathway were calculated. The free energy of activation decreased linearly with increasing chain length as the result of a linear increase in activation entropy which more than offset the unfavorable increase in activation enthalpy. We propose that the apo-C-II-mediated increase in the rate of the lipoprotein lipase-catalyzed hydrolysis of phosphatidylcholine is associated with transfer of a fatty acyl chain of the substrate or product to a more hydrophobic environment within the transition state complex.

The hydrolysis of polyester-ether homologs by an alkali.

The rate of hydrolysis of aromatic polyester-ether homologs in an aqueous caustic soda solution was investigated at temperatures of 60°C to 90°C, and the activation energy for the reaction was determined. The results indicate that the polyester-ether homologs have higher alkali resistances than poly(ethylene terephthalate). The activation energy for hydrolysis of poly (ethylene 1, 2-diphenoxyethane-p, p′-dicarboxylate) [B type polyester-ether] was estimated as high as 22.6kcal/mole.

Amylases: enzymatic mechanisms.

Many types of amylases are found throughout the animal, vegetable and microbial kingdoms. They have evolved along different pathways to enable the organism to convert insoluble starch (or glycogen) into low molecular weight, water soluble dextrins and sugars. Alpha amylases are dextrinogenic and can attack the interior of starch molecules. The products retain the alpha anomeric configuration. Beta amylases act only at the non-reducing chain ends and liberate only beta maltose. Both alpha and beta amylases exhibit multiple (repetitive) attack, that is, after the initial catalytic cleavage, the enzyme may remain attached to the substrate and lead to several more cleavages before dissociation of the enzyme-substrate complex. Amylases have extended substrate binding sites, in the range 4-9 glucose units. This enables the enzyme to stress the substrate and lower the activation energy for hydrolysis. Similarly the enzyme exerts a torsion on the glucose unit at the catalytic site, inducing a transition state conformation (oxycarbonium ion). Alpha and beta amylases differ in the stereospecific hydration of the oxycarbonium ion, in the sequence of liberation of the right-hand vs the left-hand product, and the direction of motion of the retained substrate to give multiple attack.

Effect of external mass transfer of activation energy of hydrolysis of BAEE and casein by trypsin immobilized on molecular sieve type 4A

AbstractIn this investigation, the activation energies of the hydrolysis of N‐(α)‐benzol‐L‐arginine ethyl ester (BAEE) and casein have been determined using trypsin immobilized on molecular sieve type 4A. There is a complete absence of intraparticle diffusion in the system, and the temperature dependence of the reaction has been studied only under external diffusional limitation. While the hydrolysis of BAEE by bound trypsin in found to be controlled by external diffusion, that of casein is kinetically controlled.

The chemistry of some quaternary derivatives of the 10,11-dihydrodibenzo[b,f]phosphepin system. The kinetics of alkaline hydrolysis, and products of betaine collapse, and a comparison with other phosphonium salts

Alkaline hydrolysis of 10,11-dihydro-5-methyl-5-phenyldibenzo[b,f]phosphepinium iodide (1; R = Ph) proceeds with cleavage of the exocyclic phenyl group at a rate fifty times faster than that observed for the ring-opening, hydrolysis of the 5,5-dimethyl analogue (1; R = Me). Comparison of the rate data and activation energies for hydrolysis of these seven-membered ring salts with those for the acyclic salts [PMePh3][I] and [PMe2Ph2][I] indicates the existence of a ‘seven-membered-ring effect’, which may be due to the preferential occupation by the ring of diequatorial positions in intermediate trigonal-bipyramidal phosphoranes. Hydrolysis of these seven-membered-ring salts proceeds much more slowly than those of related five-membered-ring salts, indicating that relief of ring strain on phosphorane formation is of little importance for the seven-membered-ring compounds. The betaine (9) derived from 10,11-dihydro-5-phenyldibenzo[b,f]phosphepin and styrene oxide collapses in refluxing ethanol to form styrene and the related cyclic phosphine oxide (5; R = Ph); no rearrangement products are formed, in contrast to the reactions of the corresponding betaine derived from triphenylphosphine.

Kinetics of hydrolysis, acetylation, and deamination reactions on polyamide fibers in homogeneous medium

AbstractChemical reactions on polymers in homogeneous medium were used to characterize the structure of the macromolecules. The polymer was in the form of polyamide fibers dissolved in m‐cresol to give a fairly highly concentrated solution (approximately 6%). Kinetic studies of hydrolysis, acetylation, and deamination reactions on the polyamide fibers were carried out in homogeneous medium at different temperatures. All the three reactions studied followed first‐order kinetics. Rate constants and apparent activation energies were determined for these reactions, which show two rates—an initial fast rate followed by a slow one. A new microfibrillar model of the polymer dissolved in m‐cresol is proposed, and the existence of two rates is explained on the basis of the two‐phase structure of the proposed microfibril. The fast rate is attributed to the free chain segments, and the slow rate is shown to correspond to the regions which are strongly hydrogen bonded and which hold the various chains together to give the microfibrillar structure of the polymer in the homogeneous phase. The apparent activation energy for hydrolysis was 3.20 and 0.18 kcal/mole for the fast and slow rates, respectively. The apparent activation energy values for acetylation were 1.50 and 0.80 kcal/mole, while those for the apparent deamination reaction were 6.90 and 4.60 kcal/mole, respectively. Lower values of apparent activation energies are attributed to the ease of reaction in the difficult‐to‐penetrate regions of the microfibril due to the role played by the solvent of the homogeneous phase in carrying the reacting species inside these regions while simultaneously breaking the hydrogen bonds between the polypeptide chains. The apparent deamination reaction is shown to be a resultant reaction of simultaneous deamination and “amination” through hydrolytic breakdown of the polypeptide chain.

STABILITY AND ENZYMATIC PROPERTIES OF ?-GALACTOSIDASE FROM KLUYVEROMYCES FRAGILIS

Kluyveromyces fragilis β-galactosidase purified to electrophoretic, chromatographic and immunochemical homogeneity was used. The enzyme specifically required potassium ions for stability; MnCl2 increased the stability. The enzyme was maximally stable at pH 6.5 to 7.5; stability was markedly less at pH's below 6.5 and above pH 8.5 at 37°C. Temperature denaturation followed first order kinetics with an activation energy for denaturation of 56 kcal/mol. Maximum activity was achieved in the presence of 5mM KCl. In potassium phosphate buffer, the enzyme was further activated by Mn2+, Mg2+, Co2+ and Zn2+; Mn2+, at 0.1 mM, gave the highest activation. None of these ions activated the enzyme in Tris buffer and> 0.1 mM Zn2+ caused complete loss of activity. Activity was completely inhibited by ethylenediaminetetraacetate and partially restored by addition of MnCl2. p-Chloromercuribenzoate caused rapid loss of activity which could be restored by dithiothreitol. Iodoacetamide, N-ethylmaleimide and sodium tetrathionate did not inactivate the enzyme. The enzyme was specific for β-galactosides. Km's for o-nitrophenyl β-D-galactopyranoside and lactose were 2.72 and 13.9 mM, respectively, at pH 6.6 D-Galactono-1, 4-lactone was a good competitive inhibitor (Ki=0.17 mM). pH optimum for hydrolysis of o-nitrophenyl β-D-galactopyranoside was 6.2–6.4. Vmax for this substrate was dependent on two ionizable groups of pKa of 6.13 and 6.51 while Vmax/Km was dependent on two ionizable groups of pKa of 6.39 and 7.23. Activation energy for hydrolysis of o-nitrophenyl β-D-galactopyranoside at pH 7.0 was 9.1 kcal/mol in the range 20–40°C.

Reactive polymers XIV. Hydrolysis of the epoxide groups of the copolymer glycidylmethacrylate — ethylenedimethacrylate

AbstractHydrolysis of the epoxide groups of the copolymer glycidylmethacrylate ‐ ethylenedi‐methacrylate in variously concentrated sulphuric acid solutions was studied. An approximate activation energy of hydrolysis, 41 kJ mol−1, was determined from the temperature dependences. For the sake of comparison the effect of pH on the degree of hydrolysis over the whole range of pH values was examined, and the importance of the results with respect to other reactions of the copolymer used was discussed.

Interaction of Hydrochloric Acid with Cyclodextrin

AbstractThe first order rate constant for the hydrochloric acid catalyzed hydrolysis of β‐cyclodextrin increases during the reaction, because the α‐1,14‐bonds present in the macrocycle and in linear dextrins (formed by opening of the macrocycles) are split at different rates. The activation energy for hydrolysis of the glycosidic bond of maltose is 30,5 kcal/mole, while the opening of the cyclodextrin macroring is characterized with a value of 34,2 kcal/mole. At lower temperatures and higher HCl concentrations a rather stable crystalline HCl‐cyclodextrin complex is formed with good yield. This complex contains 1,8 molecules of HCl per cyclodextrin unit. After storage at room temperature for one year it still retains 1 mole of HCl. Storing the product in sealed vials for one year leads to no change in the composition.

Kinetics of hydrolysis, acetylation, and deamination reactions on polyamide fibers in heterogeneous medium

The kinetics of reactions, namely, hydrolysis, acetylation, and deamination, on polyamide fibers has been studied at different temperatures. Rate constants and apparent activation energies of these reactions were determined. All the three reactions studied show two rates, the initial fast rate, followed by the slow one. The existence of two rates has been explained on the basis of two-phase structure of the polyamide fibers, the fast rate corresponding to the weakly hydrogen-bonded regions and the slow rate corresponding to the regions which are strongly hydrogen bonded in the regular fashion. For hydrolysis, the fast rate was 38 times faster than the slow one, while the fast rate of acetylation reaction was about 162 times that of the slow rate. The ratio between the fast and slow rates was constant at all the temperatures studied in case of the hydrolysis and acetylation reactions. This ratio, however, was found to be extremely temperature sensitive for the deamination reaction. The hydrolysis and acetylation reactions were found to be strongly temperature dependent leading to the increase in the extent of modification with increase in temperature. Deamination, on the other hand, showed negative temperature dependence giving progressive decrease in the modification with increase in temperature. All the three modifications studied observed first-order kinetics. The apparent activation energy for hydrolysis was 1.38 and 1.05 kcal/mole corresponding to the fast and slow rates, respectively. The apparent activation energy values for acetylation were 2.53 and 3.29 kcal/mole, while those for deamination reaction were −8.28 and −46.0 kcal/mole, respectively. The apparent activation energy values for the deamination reaction bore negative signs possibly because of the negative temperature dependence of this reaction. The apparent activation energy for slow reactions in case of acetylation and deamination was found to be higher than that of the fast rate, while the reverse was true in case of hydrolysis, showing that the acetylation and deamination reactions, being the chemical modification of polyamide fibers at the NH2 groups, proceed by altogether different mechanisms than the hydrolytic breakdown of the polyamide linkage.