Activation Energy For Hydrolysis Research Articles

The effect of various factors on the hydrogen generation by hydrolysis reaction of potassium borohydride

Potassium borohydride (KBH 4) reacted very slowly with water to liberate 4 mol of hydrogen/mol of compound at room temperature. The hydrolysis and stability conditions of KBH 4 investigated depend on KBH 4 concentrations, concentration of alkaline solutions, temperatures and electrical field intensity. Yield of produced hydrogen by self-hydrolysis of KBH 4 increases as the temperature increased and it produced 53.9% yield at the end of 300 min at 60 °C. The reaction rate order of hydrolysis of KBH 4 in aqueous solution is found at about 0.7–0.8 and the activation energy for hydrolysis is calculated as 14,700 kJ/mol. Potassium borohydride is stable both in room temperature and in aqueous alkaline solution. In this study, the electrical field that is not needed for catalytic activity was used for the hydrolysis of KBH 4 aqueous solution. It was found that 6 mol of hydrogen/mol of potassium borohydride was liberated in the presence of electrical field, whereas 4 mol of hydrogen was produced in the absence of electrical field per mol of potassium borohydride.

Rate of hydrolysis and degradation of the cyanogenic glycoside – dhurrin – in soil

Cyanogenic glycosides are common plant toxins. Toxic hydrogen cyanide originating from cyanogenic glycosides may affect soil processes and water quality. In this study, hydrolysis, degradation and sorption of dhurrin (4-hydroxymandelonitrile-β- d-glucoside) produced by sorghum has been studied in order to assess its fate in soil. The log K ow of dhurrin was −1.18 ± 0.08 (22 °C). Hydrolysis was a first-order reaction with respect to dhurrin and hydroxyl ion concentrations. Half lives ranged from 1.2 h (pH 8.6; 25 °C) to 530 d (pH 4; 25 °C). The activation energy of hydrolysis was 112 + 9 kJ. At pH 5.8 and room temperature, addition of humic acids (50 g l −1) increased the rate of hydrolysis tenfold, while addition of kaolinite or goethite (100–250 g l −1) both decreased the rate considerably. No significant sorption to soil components could be observed. The degradation rates of dhurrin in top and subsoils of Oxisols, Ultisols, Alfisols and Mollisols were studied at 22 °C (25 mg l −1, soil:liquid 1:1 (w:V), pH 3.8–8.1). Half-lives were 0.25–2 h for topsoils, and 5–288 h in subsoils. Hydrolysis in solution explained up to 45% of the degradation in subsoils whereas the contribution in topsoils was less than 14%, indicating the importance of enzymatic degradation processes. The highest risk of dhurrin leaching will take place when the soil is a low activity acid shallow soil with low content of clay minerals, iron oxides and humic acids.

Characterization of Cold- and High-Pressure-Active Polygalacturonases from a Deep-Sea Yeast,Cryptococcus liquefaciensStrain N6

A deep-sea yeast, Cryptococcus liquefaciens strain N6, produces two polygalacturonases, p36 and p40 (N6-PGases). These N6-PGases were highly active at 0-10 degrees C in comparison to a PGase from Aspergillus japonicus. The hydrolytic activity of these N6-PGases remained almost unchanged up to a hydrostatic pressure of 100 MPa at 24 degrees C with a very small activation volume of -1.1 ml/mol. At 10 degrees C, however, the activation volume increased to 3.3 or 5.4 ml/mol (p36 and p40, respectively), suggesting that the enzyme-substrate complexes can expand at their transition states. We speculate that such a volume expansion upon forming the enzyme-substrate complexes contributes to decreasing the activation energy for hydrolysis. This can account for the high activity of N6-PGases at low-temperature.

Silicate Glass and Mineral Dissolution: Calculated Reaction Paths and Activation Energies for Hydrolysis of a Q3 Si by H3O+ Using Ab Initio Methods

Molecular orbital energy minimizations were performed with the B3LYP/6-31G(d) method on a [((OH)3SiO)3SiOH-(H3O+).4(H2O)] cluster to follow the reaction path for hydrolysis of an Si-O-Si linkage via proton catalysis in a partially solvated system. The Q3 molecule was chosen (rather than Q2 or Q1) to estimate the maximum activation energy for a fully relaxed cluster representing the surface of an Al-depleted acid-etched alkali feldspar. Water molecules were included in the cluster to investigate the influence of explicit solvation on proton-transfer reactions and on the energy associated with hydroxylating the bridging oxygen atom (Obr). Single-point energy calculations were performed with the B3LYP/6-311+G(d,p) method. Proton transfer from the hydronium cation to an Obr requires sufficient energy to suggest that the Si-(OH)-Si species will occur only in trace quantities on a silica surface. Protonation of the Obr lengthens the Si-Obr bond and allows for the formation of a pentacoordinate Si intermediate ([5]Si). The energy required to form this species is the dominant component of the activation energy barrier to hydrolysis. After formation of the pentacoordinate intermediate, hydrolysis occurs via breaking the [5]Si-(OH)-Si linkage with a minimal activation energy barrier. A concerted mechanism involving stretching of the [5]Si-(OH) bond, proton transfer from the Si-(OH2)+ back to form H3O+, and a reversion of [5]Si to tetrahedral coordination was predicted. The activation energy for Q3Si hydrolysis calculated here was found to be less than that reported for Q3Si using a constrained cluster in the literature but significantly greater than the measured activation energies for the hydrolysis of Si-Obr bonds in silicate minerals. These results suggest that the rate-limiting step in silicate dissolution is not the hydrolysis of Q3Si-Obr bonds but rather the breakage of Q2 or Q1Si-Obr bonds.

Hydrolysis of Fluorosilanes: A Theoretical Study

Hydrolysis and condensation of simple trifluorosilanes, HSiF3 and MeSiF3, was studied by quantum mechanical methods. Hydrolysis of fluorosilanes is highly endothermic. The Gibbs free energy of the first reaction step in the gas phase is 31.4 kJ/mol, which corresponds to an equilibrium constant of 10(-6). Hydrolysis of the subsequent fluorine atoms in trifluorosilanes is thermodynamically more unfavorable than the first step of substitution. No significant difference in thermodynamics of hydrolysis was found between HSiF3 and MeSiF3. The activation energy for hydrolysis by a water dimer is significantly lower than that for hydrolysis by a water monomer. The former reaction is also less unfavorable thermodynamically, due to a high binding energy of the HF-H2O complex formed as a product of hydrolysis. Self-consistent reaction field (SCRF) calculations show that hydrolysis of trifluorosilanes in aqueous medium has lower activation energy than in the gas phase. It is also thermodynamically less unfavorable, due to better solvation of the products. Homofunctional condensation of HSiF2OH is thermodynamically favored. The equilibrium mixture for hydrolysis/condensation of RSiF3 in water is predicted to contain ca. 2.3% disiloxane (HF2Si)2O, if 100-fold excess of water relative to silane is assumed. Further hydrolysis of (HF2Si)2O is negligible. The thermodynamics of fluorosilane hydrolysis contrasts with that of chlorosilanes, where both hydrolysis and condensation are strongly favorable. Moreover, in the case of trichlorosilanes each subsequent hydrolysis step is more facile, leading to the product of full hydrolysis, RSi(OH)3.

Michaelis-menten kinetics for determining enzymatic activity of lysostaphin.

The rate of lysostaphin-catalyzed lysis of staphylococci follows the Michaelis-Menten equation at [E](0) << [S](0), i.e., the activity of the enzyme is proportional to its concentration. This equation is proposed for determining the specific activity of lysostaphin. The apparent activation energy of hydrolysis of pentaglycine bridges in Staphylococcus peptidoglycan is 77.9 kJ/mol.

Stability studies on diloxanide furoate: effect of pH, temperature, gastric and intestinal fluids

The degradation of the amoebicide diloxanide furoate in alkaline medium at different temperatures was investigated using both a spectrophotometric and a developed HPLC method. In solutions, the drug was found to undergo decomposition, i.e., temperature and pH dependent. The pH-rate profile at pH between 7.6 and 9.6 indicated a first-order dependence of K obs on [ –OH]. Arrhenius plot obtained at pH 8 was linear between 40 and 63 °C. The estimated activation energy of hydrolysis was found to be 18.25 kcal degree.mol –1. The effect of simulated gastric and intestinal fluids on the drug was also investigated. A new thin-layer chromatographic (TLC) procedure for the fractionation of the drug and its alkaline hydrolysis products has been developed and was found to compare favorably with that of the British Pharmacopoeia. Three hydrolysis products of a basic methanolic solution of the drug, namely furoic acid, diloxanide and methylfuroate could be identified by the use of TLC, HPLC, infrared and mass spectrometry.

In vitro hydrolysis of poly(l-lactide) crystalline residues as extended-chain crystallites: II. Effects of hydrolysis temperature.

The effects of hydrolysis temperature on the hydrolysis behavior and mechanism of poly(l-lactide) crystalline residues or extended-chain crystallites were investigated in phosphate-buffered solution (50-97 degrees C), using gel permeation chromatography and differential scanning calorimetry (DSC). The hydrolysis of the crystalline residues proceeded from their surface composed of very short chains with a free end along the chain direction, irrespective of hydrolysis temperature, but the hydrolysis from their lateral surface could not be traced. The activation energy of hydrolysis for the crystalline residues (extended-chain crystallites) was evaluated to be 18.0 kcal mol(-1) (75.2 kJ mol(-1)). The monotonic melting temperature (T(m)) and crystallinity decreases occurred after their initial very small increases, excluding the monotonic crystallinity decrease at 97 degrees C with no initial increase. The T(m) decrease reflects the decreased thickness of the crystalline residues. The equilibrium T(m) of the crystalline residues (extended-chain crystallites) was estimated to be 464.5-464.9 K. The free energy values for the surface composed of very short chains with a free end, which are neighboring the air (or nitrogen during DSC scanning), were calculated to be 55.6-56.4 erg cm(-2) for heat of fusion per unit mass = 135 J g(-1). The obtained surface free energy values are significantly higher than that for the surface composed of folding chains, tie chains, and the chains with a free end, which are neighboring the same kind of amorphous chains (39.9 erg cm(-2)).

Spectroscopy of Hydrothermal Reactions. 27. Simultaneous Determination of Hydrolysis Rate Constants of Glycylglycine to Glycine and Glycylglycine−Diketopiperazine Equilibrium Constants at 310−330 °C and 275 bar

Hydrolysis rate constants of glycylglycine to glycine and equilibrium constants between glycylglycine and diketopiperazine were determined simultaneously in situ using an FT-IR spectroscopy flow reactor at 310−330 °C and 275 bar. The hydrolysis of the peptide bond in neutral hydrothermal solution follows the first-order (or pseudo-first-order) rate law. The cyclization of dipeptides is very prominent at high temperatures. Pressure affects the hydrolysis rate and the enthalpy of cyclization of the dipeptide. Specifically, the activation energy for hydrolysis of the dipeptide is reduced by about 50 kJ/mol and the standard enthalpy change of cyclization of the dipeptide is increased by about 50 kJ/mol when pressure is increased from a steam pressure of 1−16 bar to a solution pressure of 275 bar. The data analysis method used in this work is general and could be applied to other dipeptides provided the decomposition rate of the free amino acid product of hydrolysis is monitored.

Characterization of Extra- and Intracellular Phytases from Bacteria Proliferating during Tempe Production

Bacteria species Streptococcus faecium and Streptococcus dysgalactiae, proliferating during tempe (fermented soybeans) production produced both extra- and intracellular phytases. The enzymes were isolated from growth media and the cultured bacteria and partially purified by acetone fractionation. Extracellular phytase activities were higher than that of the intracellular enzymes. The extra- and intracellular phytases of S. faecium and S. dysgalactiae acted over a nerrow pH range at 4.1 – 4.3 and the maximum activity at 45, 45, 45, and 40-c, respectively. Among the estimated K values, the value of 1.0 x I Mfor the intracellular phytase of S. dysgalactiae was the lowest, indicating strong affinity of the enzyme for the substrate. V.valties were 0.005 and 0.007 nimole P,. liberated/min/ml enzyme for the extra- and intracellular phytases of S. faeciwn, while the extra- and intracellular phytases of dysgalactiae had V. values of 0.003 and 0.003 nimole P. iberated/min/ml enzyme, respectively. The activation energy for hydrolysis of phytic acid by extra- and intracellular phytases of S. faecium and S. dysgalactiae were calculated by the Arrhenius equation to be 3,400; 3,600; 14,600 and 7,100 cal/mole, respectively.

Characterizing and Modeling the Hydrolysis of Polyamide-11 in a pH 7 Water Environment

Multiangle laser light scattering (MALLS) is used to monitor changes in molecular weight during solid state aging of polyamide-11 (PA-11). A mathematical model is presented which successfully describes the degradation kinetics of PA-11 in pH 7 water. The MALLS results demonstrate that there is a recombination reaction in the solid state, which may be described as a cage effect during hydrolysis−degradation of the amide bond. During aging, the competing recombination and hydrolysis reactions lead to the formation of an equilibrium molecular weight. The equilibrium molecular weight is surprisingly high at about 26 000 in pH 7 water, a value close to the ductile−brittle transition. The activation energy of hydrolysis is 81 to 87 kJ/mol, close to the values of previous acid degradation studies and a recent value of 96 kJ/mol for hydrolysis of the peptide amide bond.

カラムスイッチング高速液体クロマトグラフィーによる銅電解液中のにかわ分析

A new method for determination of concentrations of trace glue in copper electrolyte solutions, and the molecular weight distribution of the glue, and its change with time using a combination of the size exclusion chromatography (SEC) and the column-switching methods was developed. Trace amount of glue can be separated from a large amount of copper sulfate and sulfuric acid in the electrolyte solutions by pretreatment of the SEC resin column. Then, only a fraction containing the glue could be introduced into an analytical column by the column-switching technique, and the determination of concentrations of glue and the molecular weight distribution of the glue could be analyzed. This method was applied to electrolyte solutions containing mg L-1 level glue to determine concentrations and molecular weight distributions of the glue of molecular weight larger than about 2, 500.Degradation behavior of the glue in the electrolyte solutions was also investigated. The velocities speed of the hydrolysis reaction are depended on the concentrations of sulfuric acid. By the temperature dependency of the hydrolysis reaction rate constant of glue, the apparent activation energy of hydrolysis was estimated to be 65kJ/mol using an Arrhenius plot.

Hydrolysis of Chitin-Glucan Complex of Aspergillus niger Fungus with Phosphoric Acid

The kinetic parameters of hydrolysis of chitin-glucan complex of Aspergillus niger fungus with 85% phosphoric acid were studied at three temperatures. The activation energies of hydrolysis of chitin and glucan components of the complex were determined.

Acid hydrolysis of chitosans

The hydrolysis of the O-glycosidic linkages (depolymerization) and the N-acetyl linkage (de- N-acetylation) of partially N-acetylated chitosans were studied in dilute and concentrated HCl. The rate of hydrolysis of the glycosidic linkages was found to be equal to the rate of de- N-acetylation in dilute acid, while the glycosidic linkages was hydrolysed more than 10 times faster than the N-acetyl linkage in concentrated HCl. This can be explained by assuming that the hydrolysis of the N-acetyl linkage is a S N2 reaction (rate-limiting step: addition of water to the carbonium ion) while the hydrolysis of the glycosidic linkages is a S N1 reaction where the rate-limiting step is the formation of the carbonium ion. The specificity of the acid-catalysed cleavage of the different chitosan glycosidic linkages in concentrated HCl was such that the linkages between two acetylated units ( A–A) and between an acetylated and a deacetylated unit ( A–D) was cleaved with about equal rate and three orders of magnitude faster than the other two linkages ( D–A and D–D). The activation energies for acid hydrolysis of two almost fully de- N-acetylated chitosans ( F A=0.002 and F A<0.0003) were determined to be 152.2±8.1 and 158.1±9.8 kJ mol −1, respectively, representing the activation energy for hydrolysis of the D–D glycosidic linkage in chitosans. The activation energies for acid hydrolysis of two partially N-acetylated chitosans ( F A=0.47 and F A=0.62) were determined to be 130.4±2.5 and 134.3±3.1 kJ mol −1, respectively, representing the activation energy for hydrolysis of the A–A and A–D glycosidic linkage in chitosans.

Rates of alkoxylation and hydrolysis of alkoxyl groups on silica surfaces

The rate of reactions on silica surfaces was investigatedfor the alkoxylation and hydrolysis of alkoxyl groups. Silica gel particles were contacted with vapors of several alcohols and water in a flow-type reactor at various temperatures. The surface concentrations of alkoxyl groups were measured by thermogravimetric analyses to determine the rates of reactions. The apparent rate constants could be calculated by applying the progressivereaction model. The apparent rates based on the total number of surface groups were determined for alkoxylation reactions. Among the alcohols investigated, alkoxylation with methanol showed the smallest activation energy and the largest rate constant. The rates of hydrolysis of alkoxyl groups were also measured on samples which had been alkoxylatedto about 10% of the initial surface groups. The activation energy of hydrolysis was almost constant for all alkoxyl groups. However, the hydrolysis of methoxy groups showed the largest rate constant. The influence of preheating treatment on the rate of alkoxylation was examined for the reaction with 1-butanol. Even when the reaction temperature was the same, the rate constant increased with increasing preheating temperature. The increase in the rate constant could be attributed to the increase in the frequency factor, since the preheating treatment increased the activation energy.

PURIFICATION AND CHARACTERIZATION OF PROTEASES FROM HEPATOPANCREAS OF CRAWFISH (PROCAMBARVS CLARKII)

Four trypsin-like enzymes (CP-I, II, III and IV in order of elution on DEAE-Sepharose chromatography), purified from the hepatopancreas of crawfish, were inhibited by protease inhibitors such as phenyl methyl suifonyl fluoride (PMSF), soybean trypsin inhibitor (SBTI), aprotinin and tosyl lysine chloromethyl ketone (TICK). The molecular weights of CP-I, II, III and IV were determined to be 35.0, 41.2, 37.9 and 39.5 kDa, respectively, using sodium dodecyl sulfate polyacryl-amide gel electrophoresis (SDS-PAGE), These proteases had optimal esterase activity at pH 8.0–8.5 and showed the highest activity at 60–70C. Crawfish proteases were rich in acidic amino acids. Activation energies for hydrolysis of tosyl arginine methyl ester (TAME) by these proteases were 6.98 – 8.34 kcal/mole. Unlike other serine proteases, the activities of CP-I and CP-II were activated by mercury while CP-HI and IV were inhibited.

Comparisons of Phosphorothioate and Phosphate Monoester Transfer Reactions: Activation Parameters, Solvent Effects, and the Effect of Metal Ions

The thermodynamics, pH dependency, solvent effects, and the effect of divalent metal ions have been examined for the hydrolysis reactions of the phosphorothioate monoester p-nitrophenyl phosphorothioate (pNPPT) and compared with those of the corresponding phosphate monoester, p-nitrophenyl phosphate (pNPP). The pH dependency for pNPPT hydrolysis mirrors that for typical phosphate monoesters, with the monoanion being the most reactive species. The ratio of the rate constants for pNPPT hydrolysis to that for pNPP is 1380 for the monoanion reactions and 12.6 for the dianion reactions at 39 °C. The free energy of activation for hydrolysis of the pNPPT dianion in water is 27.9 kcal/mol versus 29.5 kcal/mol for pNPP; for the monoanion reactions the values are 22.2 kcal/mol for pNPPT and 26.8 kcal/mol for pNPP. The free energies of solvation for pNPPT and pNPP are within 0.1 kcal/mol of each other despite the poorer hydrogen bonding ability of sulfur versus oxygen. This minimal difference in ground-state energie...

Cold-active serine alkaline protease from the psychrotrophic bacterium Shewanella strain ac10: gene cloning and enzyme purification and characterization.

The gene encoding serine alkaline protease (SapSh) of the psychrotrophic bacterium Shewanella strain Ac10 was cloned in Escherichia coli. The amino acid sequence deduced from the 2,442-bp nucleotide sequence revealed that the protein was 814 amino acids long and had an estimated molecular weight of 85,113. SapSh exhibited sequence similarities with members of the subtilisin family of proteases, and there was a high level of conservation in the regions around a putative catalytic triad consisting of Asp-30, His-65, and Ser-369. The amino acid sequence contained the following regions which were assigned on the basis of homology to previously described sequences: a signal peptide (26 residues), a propeptide (117 residues), and an extension up to the C terminus (about 250 residues). Another feature of SapSh is the fact that the space between His-65 and Ser-369 is approximately 150 residues longer than the corresponding spaces in other proteases belonging to the subtilisin family. SapSh was purified to homogeneity from the culture supernatant of E. coli recombinant cells by affinity chromatography with a bacitracin-Sepharose column. The recombinant SapSh (rSapSh) was found to have a molecular weight of about 44,000 and to be highly active in the alkaline region (optimum pH, around 9.0) when azocasein and synthetic peptides were used as substrates. rSapSh was characterized by its high levels of activity at low temperatures; it was five times more active than subtilisin Carlsberg at temperatures ranging from 5 to 15 degreesC. The activation energy for hydrolysis of azocasein by rSapSh was much lower than the activation energy for hydrolysis of azocasein by the subtilisin. However, rSapSh was far less stable than the subtilisin.

Influence of global ischemia on the sarcolemmal ATPases in the rat heart.

To elucidate the effect of global ischemia on the energy utilizing processes, regarding the molecular principles, the kinetic and thermodynamic properties of the sarcolemmal ATPases were investigated in the rat heart. The activation energy for hydrolysis of ATP during ischemia was higher when the reaction was catalyzed by Ca-ATPase or Mg-ATPase. For the Na,K-ATPase reaction, no changes in the activation energy were observed. With respect to the enzyme kinetics, ischemia in a time-dependent manner induced important alterations in KM and Vmax values of Na,K-ATPase, Ca-ATPase and Mg-ATPase. The Vmax value decreased significantly already after 15 min of ischemia, and it also remained low after 30, 45 and 60 min for all 3 enzymes. The significant diminution of KM values occurred later in the 30th min for Ca-ATPase, in the 45th min for Na,K-ATPase. The observed drop in KM indicates the increase in the affinity of the enzymes to substrate, suggesting thus the adaptation to ischemic conditions on the molecular level. This effect could be attributed to some conformational changes of the protein molecule in the vicinity of the ATP-binding site developing after longer duration of ischemia.

Hydrolytic thermal degradation of poly(naphthoyleneimide benzimidazole) in concentrated sulfuric acid

AbstractTranslational diffusion in 96% H2SO4 and intrinsic viscosity of poly(naphthoyleneimide benzimidazole) (PNIB) have been investigated in different stages of its degradation in solution in the temperature range from 65 to 120°C. The degradation rate constant k has been determined from the change in molecular weight M of degraded products with time at the fixed temperature of solution. The activation energy of the process E was calculated from the temperature dependence of k. The difference in E values at low and high temperatures was found. At degradation temperatures above 90°C, the activation energy of hydrolysis was obtained as E = 133 kJ/mol, which coincides with that of aromatic polyamides in sulfuric acid. The data obtained are compared with the results of the investigations of optical properties of products of PNIB degradation in solution and PNIB stability in the solid state. An explanation of anomalies observed during PNIB degradation at low temperatures is suggested. © 1995 John Wiley &amp; Sons, Inc.