Rate Constants For Hydrolysis Research Articles

Application of high-resolution ultrasonic spectroscopy for real-time monitoring of trypsin activity in β-casein solution

High-resolution ultrasonic spectroscopy (HR-US) was applied for real-time monitoring of β-casein hydrolysis by trypsin at various conditions for the first time. The technique is based on the precision measurement of hydration changes proportional to the number of peptide bond hydrolyzed. As HR-US exhibits ultrasonic transparency for most solution, the analysis did not require optical transparency like for 2,4,6-trinitrobenzenesulfonic acid (TNBS) assay. Appropriate enzymatic models were fitted with degree of hydrolysis (dh) profiles to provide kinetic and mechanistic description of proteolysis in terms of initial hydrolysis rate, r0, and rate constant of hydrolysis, kh, and enzyme inactivation, kd. Maximal r0 and dh were obtained at 45 °C and pH 8. The exponential dependence of kinetic parameters allowed determination of the activation (EA = 50.3 ± 7 kJ/mol) and deactivation (ED = 62.23 ± 3 kJ/mol) energies of hydrolysis. The ultrasonic assay provided rapid detection of trypsin activity even at sub-nanomolar concentration.

Potential bleach activators with improved imide hydrolytic stability

The commercially available bleach activator, N,N,N′,N′-tetraacetylethylenediamine (TAED), has been widely used in laundry detergents to enable efficient low-temperature bleaching. However, the competitive hydrolysis of TAED limits its use in liquid detergents. Herein we report the synthesis of two TAED derivatives, N,N,N′,N′-tetracetylpropylene-1,2-diamine (TA(Me)ED) and N,N,N′-triacetylpropylene-1,2-diamine (TriA(Me)ED), through the acetylation of propylene-1,2-diamine. The hydrolytic and perhydrolytic activity of the imide molecules were studied by HPLC to elucidate the structure–function relationship. Due to the increased steric hindrance imparted by the α-methyl group close to the imide, TA(Me)ED and TriA(Me)ED exhibited higher hydrolytic stability than TAED, with the hydrolytic rate constants (kH) at pH 8.0 decreased by 58% and 84% for TA(Me)ED and TriA(Me)ED, respectively. On the other hand, TA(Me)ED and TriA(Me)ED showed comparable perhydrolytic activity with TAED in the presence of peroxide, enabling similar bleaching effect of a model food dye at room temperature. These results suggest these TAED derivatives may have potential being used as improved bleach activators.

Effect of amino acids present at the carboxyl end of succinimidyl residue on the rate constants for succinimidyl hydrolysis in small peptides

Structural alterations of aspartyl and asparaginyl residues in various proteins can lead to their malfunction, which may result in severe health disorders. The formation and hydrolysis of succinimidyl intermediates are crucial in specific protein modifications. Nonetheless, only few studies investigating the hydrolysis of succinimidyl intermediates have been published. In this study, we established a method to prepare peptides bearing succinimidyl residues using recombinant protein l-isoaspartyl methyltransferase and ultrafiltration units. Using succinimidyl peptides, we examined the effect of amino acid residues on succinimidyl hydrolysis at the carboxyl end of succinimidyl residues and determined the rate constant of hydrolysis for each peptide. The rate constant of succinimidyl hydrolysis in the peptide bearing a Ser residue at the carboxyl side (0.50 ± 0.02 /h) was 3.0 times higher than that for the peptide bearing an Ala residue (0.17 ± 0.01 /h), whereas it was just 1.2 times higher for the peptide bearing a Gly residue (0.20 ± 0.01 /h). The rate constant of succinimidyl formation in the peptide bearing a Ser residue [(2.44 ± 0.11) × 10−3 /d] was only 1.2 times higher than that for the peptide bearing an Ala residue ([1.87 ± 0.09) × 10−3 /d], whereas 5.5 times higher for the peptide bearing a Gly residue [(10.2 ± 0.2) × 10−3 /d]. These results show that the Gly and Ser residues at the carboxyl end of the succinimidyl residue have opposing roles in succinimidyl formation and hydrolysis. Catalysis of Ser residue's hydroxyl group plays a crucial role in succinimidyl hydrolysis.

Kinetic study of oxytetracycline and chlortetracycline inhibition in the anaerobic digestion of dairy manure

This study was aimed to investigate the mechanisms of oxytetracycline (OTC) and chlortetracycline (CTC) inhibition in anaerobic digestion (AD) using four kinetic models. The results showed that the inhibition rate of OTC was faster than CTC at OTC and CTC between 0.04 and 1.28 g/L. Hydrolysis rate constant was linearly and positively correlated with OTC and increased from 0.172 to 0.193 d-1, 0.164 to 0.179 d-1 and 0.251 to 0.285 d−1 using first-order kinetic, Fitzhugh and Cone models, respectively, while the maximum specific methane production rate was linearly and negatively correlated with CTC and decreased from 0.028 to 0.016 L/gVS. Cone model was found to give the most satisfactory fitting results followed in descending order by first-order kinetic, Fitzhugh and modified Gompertz models. The kinetic modeling of methane yield helped explain the mechanism of OTC and CTC inhibition in the AD process and provided essential information for further process improvement.

Electrochemical oxidation of o-phenylenediamine and 1,3 dihydrospiro[benzo[d]imidazole-2,1′-cyclohexane]. A comprehensive study and introducing a novel case of CE mechanism

Electrochemical behavior of o-phenylenediamine (PDA) and 1,3-dihydrospiro[benzo[d]imidazole-2,1′-cyclohexane] (DBI) was extensively studied in water and water/ethanol mixture using different voltammetric techniques. Our data showed that the oxidation of PDA is highly dependent on pH, follows a complex pattern and participate in following chemical reactions such as polymerization. Unlike acidic and neutral solutions, in highly alkaline solutions (pH ≥ 11), however, PDA shows a simple reversible redox system. Contrary to PDA, the presence of the cyclohexyl group in the structure of DBI makes its oxidation pattern less complex than that of PDA and causes the molecule less susceptible to participate in the following chemical reactions. Our results showed that DBI in aqueous solutions is unstable and undergoes acid catalyzed hydrolysis to give PDA. The instability of DBI in acidic solutions is so high that it turns completely into PDA in the time scale of the voltammetric experiments. Different from acidic media, in alkaline solutions (pH ≥ 9.0), the hydrolysis rate is slow, so that DBI shows a reversible redox couple. The kinetic of DBI hydrolysis using differential pulse voltammetry method was studied and the apparent hydrolysis rate constants (khobs) were found by assuming the pseudo-first order rate kinetics. In addition, in this work, adsorption activity, diffusion coefficient and pKa values of DBI and PDA species were determined and the Pourbaix diagrams for these compounds were constructed. The most important part of this paper is devoted to introducing a rare type of mechanism in electrochemical reactions. In this way, the rarely studied mechanism has been introduced in relation to the reaction of PDA with cyclohexanone and the formation of DBI.

Engineering and Structural Analysis of a Covalent HRas Dimer

Ras is part of the major signaling cascade Ras/Raf/MEK/ERK which regulates cell proliferation. The dysregulation of this pathway through the mutation of Ras is highly implicated in up to 30% of human cancers. Pathway activation is dependent on the binding of Ras to Raf‐RBD and the subsequent dimerization of the Ras/Raf complex. This complex, however, is only robust in the presence of the membrane. In order to create a form of the Ras/Raf‐RBD dimer that is more stable in solution, we engineered mutations to promote covalent bonding at the dimer interface. Our data reveal the structure of a covalent HRas dimer in the absence of Raf‐RBD, and we present an analysis of the disulfide bonded dimer interface and its impact on allosteric connections to the active site. Going forward we plan to use crosslinking as a means to characterize the Ras/Raf‐RBD dimer biochemically, including affinity of the Ras dimer for Raf‐RBD and hydrolysis rate constants in the presence and absence of ligand binding at an allosteric site near the dimer interface.Support or Funding InformationNSFCHE‐1757078

The performance evaluation and kinetics response of advanced anaerobic digestion for sewage sludge under different SRT during semi-continuous operation

Sludge retention time (SRT) is vital for advanced anaerobic digestion (AD) to realize energy self-sufficient. However, the criteria on reasonable SRT has not been fully understood. This study investigated the performance and kinetics response of AD under different SRT in semi-continuous AD with microwave (MW) pretreatment, according to the long-term operation and methane production during one feeding interval. Results showed that modified Gompertz model better described the kinetics than first-order model. At short SRT (15 d), pretreatment coupled with two-stage AD preserved methane production with the high attainable methane potential (B0) of 257.98 mL/g VS and hydrolysis rate constant (khyd) of 0.075 h−1. But the acceptable decrease of methane production rate seems to be unavoidable, which was possibly derived from the evolution of methanogenesis pathway. This study emphasized the importance of improved methane production rate in semi-continuous AD under short SRT rather than methane production potential obtained from batch experiment.

ZnCl2 Enhanced Acid Hydrolysis of Pretreated Corncob for Glucose Production: Kinetics, Thermodynamics and Optimization Analysis

The biomass of agricultural wastes as a source of fermentable sugars for biofuels production will address the food security and environmental preservation issues. These wastes are rich in lignocellulosic materials which can be hydrolyzed into fermentable sugars. However, low sugar yield and high energy consumption are some of the challenges faced in the process of hydrolization. This study investigated the low-cost corncob substrate for glucose production by dilute sulphuric acid hydrolysis in the presence of ZnCl2 at temperatures below 100°C after pretreatment with 10% NaOH.Time dependent hydrolysis data were analyzed by Saeman model, and thermodynamic parameters were obtained using Erying and Arrhenius equations while Box-Behnken model (Design Expert 6.0 version) was used for experimental design. As the substrate concentration increased from 50 mg/L to 150 mg/L, glucose yield increased from 10.4 mg/g to 14.6 mg/g for pretreated corncob while an increase from 3.4 mg/g to 8.6 mg/g was noted for untreated corncob. The hydrolysis rate constant was two orders of magnitude higher than the degradation rate constant. Thermodynamic parameters revealed endothermic process with positive Gibb’s free energy of hydrolysis having average values of 84.76 kJ/mol and 79.87 kJ/mol for pretreated and untreated samples respectively. The optimum yield from the model was found to be 177.44 mg/g with 3.94% H2SO4 and 0.43 mol/L ZnCl2 for 200 g/L compared with optimum yield of 46.37 mg/g obtainable without ZnCl2. The results of this study showed that the alkaline pretreatment of corncob increased the accessibility of cellulose from the solid fraction and increased glucose production.

REGULARITIES OF HYDROLYSIS OF ALUMINUM ACTIVATED BY Ga-In-Sn EUTECTIC ALLOY AND ZINC

Aluminum is a promising metal for creating energy-storing substances (ESS) on its basis for hydrogen evolution from water as a result of its of activating aluminum and providing it with the ability to react with water, special attention is paid to methods of alloying it with additions of low-melting metals and alloys, in particular, the eutectic alloy of gallium, indium and tin is perspective alloy for alloying aluminum and obtaining ESS, capable of releasing hydrogen from water without additional heating. The temperature at which stable interaction of aluminum activated by low-melting metals and alloys with water begins to be determined by the temperature at which alloying metals on the surface of aluminum crystallites become liquid. The melting point of the four-component Ga61In25Sn13Zn1 eutectic is about 3 °C, what is about 8 °C lower than the melting point of the Ga-In-Sn eutectic. Therefore, in this work, aluminum was activated by the eutectic alloy of gallium, indium and tin, as well as zinc, and the regularities of the hydrolysis of the obtained EAPs were investigated.
 Comparative volumetric determinations of hydrogen, which was released during the hydrolysis of 95 wt.% Al + 5 wt.% Ga-In-Sn eutectic and 92 wt.% Al + 5 wt.% Ga-In-Sn eutectic + 3 wt.% Zn alloys, showed that the introduction of zinc into activated aluminum led to a significant acceleration of hydrogen evolution from water at low temperatures (25 and 40 °C). The effective rate constants of hydrolysis of the zinc-doped alloy, calculated using the modified Prout-Tompkins equation, were 1.33, 1.75, 2.19, and 2.58 min-1 at temperatures of 25, 40, 55, and 70 °C, respectively. The effective activation energy of the process, calculated from the temperature dependence of the effective rate constant, was 12.6 kJ·mol-1, which indicates diffuse control of the hydrolysis rate. An analysis of the X-ray diffraction pattern of the products of the hydrolysis of 92 wt.% Al + 5 wt.% Ga-In-Sn eutectic + 3 wt.% Zn alloy at the temperature of 55 °C showed that they contain boehmite, baerite and small amounts of alloying metals.

Extracting the Hydrolysis Rate Constant from a Single-Molecule Controlled Rotation Experimental Data on a F1-ATPase

The chemo-mechanical energy transduction of the ATP Synthase is at the heart of the biological function, and it can be elucidated by studying the water soluble F1-ATPase, focusing on the individual sub-steps of the reactions in the enzyme. In controlled rotation experiment single F1-ATPase molecules deposited on a microscope slide are rotated by magnetic tweezers. Simultaneously the individual ATP binding and ADP release events are monitored by single molecule fluorescence imaging in real time. Our goal is to extract the ATP hydrolysis and synthesis rate constants as a function of rotor angle from the single molecule binding and release data. This work requires advanced analysis because these processes occurring in the binding pocket are “hidden”, and not directly monitored. Our approach is based on the treatment of composite events developed by Volkan-Kacso and Marcus, for a constant rotation rate. We will use high-quality single-molecule trajectories provided by our experimentalist collaborator K. Adachi, who pioneered the method of controlled rotation. Preliminary results indicate that fluorescent Cy3-ATP hydrolyses about 100 times slower than the wild species (ATP), at rotor angle of 240 degrees, its rate is about 1.7 X 10⁻³ per seconds. We plan to extract the hidden hydrolysis and synthesis rates for the complete 360 degrees cycle.

Kinetic study on the digestibility of lactose and lactulose using small intestinal glycosidases

Lactose is mostly hydrolysed in the small intestine, whereas lactulose, recognised prebiotic carbohydrate, reaches the colon to be fermented by the intestinal microbiota. Digestibility of these substrates was investigated by an in vitro digestion model using a Rat Small Intestine Extract (RSIE). A kinetic study of lactose digestion showed levels of hydrolysis (82.8%) at 0.2 mg*mL−1 and the highest hydrolysis rate constant (kobt). Considering these conditions, lactulose showed high resistance to intestinal digestion by RSIE, resulting in low hydrolysis degrees (20.4%) after 5 h reaction. These results underline the suitability of these intestinal extracts under the studied conditions, as a reliable tool to evaluate carbohydrate digestion and support the evidences towards the higher resistance of galactosyl-fructose linkages during its intestinal degradation.

Synergistic effect from anaerobic co-digestion of food waste and Sophora flavescens residues at different co-substrate ratios.

When food waste (FW) undergoes anaerobic digestion, the hydrolysis rate is rapid, and thus causes system instability. Sophora flavescens residues (SFRs) are rich in complex hydrolysed substances, such as lignocellulosic material. When combined FW and SFRs can effectively improve the stability of digestion systems and increase biogas yields. In this work, batch anaerobic experiments were conducted at different co-substrate ratios to investigate the performance of co-digestion and the synergistic effect of FW and SFRs. The co-digestion of the two substrates exerted synergistic effects on biogas production and the highest synergy was 120.8%. After digestion, the ratio of hydrolysed chemical oxygen demand (COD) to the entire COD (RCODH) of the co-digestion group was 1.08 times that of the single FW group, which indicated the co-digestion promoted the hydrolysis of substrates. Moreover, the hydrolysis rate constant (kh) of co-digestion group increased by 4.10 times in comparison with that of the single FW group, which indicated the co-digestion increased the hydrolysis rate. In other words, the synergistic effect mainly occurred in the hydrolysis acidification process.

Natural Formation of Chloro- and Bromoacetone in Salt Lakes of Western Australia

Western Australia is a semi-/arid region known for saline lakes with a wide range of geochemical parameters (pH 2.5–7.1, Cl− 10–200 g L−1). This study reports on the haloacetones chloro- and bromoacetone in air over 6 salt lake shorelines. Significant emissions of chloroacetone (up to 0.2 µmol m−2 h−1) and bromoacetone (up to 1. 5 µmol m−2 h−1) were detected, and a photochemical box model was employed to evaluate the contribution of their atmospheric formation from the olefinic hydrocarbons propene and methacrolein in the gas phase. The measured concentrations could not explain the photochemical halogenation reaction, indicating a strong hitherto unknown source of haloacetones. Aqueous-phase reactions of haloacetones, investigated in the laboratory using humic acid in concentrated salt solutions, were identified as alternative formation pathway by liquid-phase reactions, acid catalyzed enolization of ketones, and subsequent halogenation. In order to verify this mechanism, we made measurements of the Henry’s law constants, rate constants for hydrolysis and nucleophilic exchange with chloride, UV-spectra and quantum yields for the photolysis of bromoacetone and 1,1-dibromoacetone in the aqueous phase. We suggest that heterogeneous processes induced by humic substances in the quasi-liquid layer of the salt crust, particle surfaces and the lake water are the predominating pathways for the formation of the observed haloacetones.

Improved Methane Production Using Lignocellulolytic Enzymes from Trichoderma koningiopsis TM3 Through Co-digestion of Palm Oil Mill Effluent and Oil Palm Trunk Residues

The efficacy of concentrated enzymes from Trichoderma koningiopsis TM3 in hydrolyzing palm oil mill effluent (POME) and oil palm trunk residues (OPTr) at 40 and 50 °C was evaluated prior to methane fermentation. POME hydrolysate containing total sugar concentration of 15.40 g L−1 was obtained from enzymatic hydrolysis using 15 Unit g−1 TVS at 50 °C for 18 h incubation with the hydrolysis yield of 0.35 g total sugars g−1 TVS. The OPTr hydrolysate contained slightly higher total sugar concentration (18.90 g L−1) with the hydrolysis yield of 0.85 g total sugars g−1 TVS under the same condition. Methane production from POME hydrolysate was 6.29% higher than the raw POME. Co-digestion of POME hydrolysate with OPTr gave the maximum methane yield (369 ml CH4 g−1 VS-added) with the increase of 9.28% compared to the raw POME. The methane production rate (Rmax) and the hydrolysis rate constant (kh) of the co-digestion of POME hydrolysate with OPTr were 1.2-fold higher than those of the POME hydrolysate. PCR-DGGE analysis revealed that Clostridium sp. and Petrimonas sp. were dominated bacteria while Methanosarcina sp. and Methanospirillum sp. played an important role in methane production. These results indicated that enzymatic pretreatment and co-digestion of POME hydrolysate with OPTr could improve methane yield from anaerobic fermentation of POME.

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English

Weakened adhesion force between extracellular polymeric substances of waste activated sludge caused by rhamnolipid leading to more efficient carbon release.

Rhamnolipid (RL), a biosurfactant produced by bacteria, is investigated to alter the physical characteristics of extracellular polymeric substance (EPS) of waste-activated sludge (WAS), and subsequently promotes hydrolysis and acidogenesis during anaerobic digestion for short chain fatty acids (SCFAs) production. The results revealed that RL could decrease the adhesion force of EPS from 13.46 nN to 1.08 nN, resulting in EPS disintegration layer by layer, decreasing the median particle size by 31.57 μm and releasing abundant soluble organic matter. The cell number of living bacteria remained stable after RL pretreatment (2.59 × 109 vs. 2.66 × 109), indicating that RL has a minimal impact on microbial cells (only ~2% bacterial lysis was observed). The kinetic studies of ammonia nitrogen release and SCFA production suggested that, in the RL-pretreated WAS, the reaction rate constants for hydrolysis and acidogenesis were respectively 2-fold and 1.5-fold higher than those of the control group.

Modeling & simulation studies on batch anaerobic digestion of hydrodynamically cavitated tannery waste effluent for higher biogas yield.

This study describes the efficacy of the pretreatment method of tannery waste effluent (TWE) by hydrodynamic cavitation (HC) prior to anaerobic digestion (AD) using a slit venturi cavitating device operated at 5 bar pressure for 2 h. The HC effect caused faster disintegration and solubilization of larger organic molecules into smaller ones, so that it could be easily digested by the microbial cells resulting in higher degradation rates, lower acclimatization time, higher COD reduction of the TWE and higher biogas generation. The biogas yield and % COD reduction was almost twice higher in HC treated TWE compared to raw TWE. Biogas yield of 68.57 mL/g volatile solids with 43.17% COD reduction was obtained during AD of HC treated TWE in 2 L bioreactor with 10% seed dosage. 'AD' Simulator developed in MATLAB represented the AD performance for both raw and HC treated TWE feed and predicted for concentrations of organic polymers, monomers, VFA and biogas produced, in which model parameter optimization was done by validations using methane production data from bioreactors. The AD simulator estimated higher hydrolysis rate constants for HC treated TWE than for raw TWE as observed in the experiments. Biogas production increased up to 7.8 and 11.8 folds for raw and HC treated TWE samples respectively by adding food waste to TWE feed with organic loading rate of 48 h. Cost estimations proved that cost of excess biogas produced by anaerobic digestion of HC treated TWE mixed with food waste, recovers the extra cost of HC pretreatment when compared to raw TWE alone, establishing HC as an effective pre-treatment tool prior to AD.

Kinetic modeling of the conversion and losses of isoflavones during soybean soaking

The objective of this study was to solve the first-order kinetic models of interconversion and losses of isoflavones, expressed as differential equations, by Laplace transform method. The kinetic models were applied to investigate the changes in the contents of different forms of isoflavone (malonylglucosides, β-glucosides, and aglycones) during soybean soaking at various temperatures (25 °C, 40 °C, 55 °C, and 70 °C). Soaking at 25 °C did not influence the contents of isoflavones of the daidzein, glycitein, and genistein series. A higher hydrolysis rate constant, which corresponds to the conversion of β-glucosides to aglycones, was observed at 55 °C due to the action of endogenous β-glucosidase. However, at 70 °C, there was a decrease in the hydrolysis rate. All isoflavone forms of the genistein and daidzein series were thermally stable during soybean soaking at 70 °C. A mathematical modelling of the kinetics provided better insights into the mechanisms of interconversion and losses of the isoflavones.

The reactivity of propyl esters of 2-(benzoylamino)(1-R-2-oxoindoline-3-ylidene) acetic acids

Aim. To study the reactivity of esters of 2-(benzoylamino)(1-R-2-oxoindoline-3-ylidene) acetic acids.Results and discussion. The reaction rate constants of alkaline hydrolysis of esters of 2-(benzoylamino) (1-R-2-oxoindoline-3-ylidene) acetic acids depend on the structure and the length of the hydrocarbon chain at the heterocyclic nitrogen atom. Introduction of hydrocarbon radicals to the structure of the heterocycle slows down the reaction, while the chain extension accelerates it. The effect of the electronic nature of the substituents on the reactivity of propyl esters was quantitatively assessed by Hammett equation. The data obtained suggest that the values of the reaction parameter ρ are positive in the temperature range studied; it is additionally confirmed by the ВАС2 mechanism of this reaction.Experimental part. The concentration of NaOH in the solution was determined by potentiometric titration on an EV-74 ionomer using the standard aqueous HCl solution. The reaction kinetics was performed in triplicates, the experiments contained 6-8 measurements (the depth of the change was not less than 80 %). The accuracy of the results obtained was assessed by the methods of mathematical statistics of small samples with statistical significance of 0.95.Conclusions. The reaction kinetics of alkaline hydrolysis of biologically active propyl esters of 2-(benzoylamino)(1-R-2-oxoindoline-3-ylidene) acetic acids has been studied in a wide temperature range; its ВАС2 mechanism has been proven with formation of a highly symmetrical intermediate. The effect of the substituents at the heterocyclic nitrogen atom on the numerous kinetic and activation parameters of the reaction has been analyzed; isokineticity and synchronicity of the reaction have been proven using independent tests.

Hydrolytic stability of ternary and quaternary urethane end-capped oligoesters

The hydrolytic stability was evaluated for a series of oligoesters comprised of three or four different monomers. The oligoesters were prepared from adipic acid (AA) and isophthalic acid (IPA) with six different diols, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 2-methyl-1,3-propanediol, 2-butene-1,4-diol, and one triol, trimethylolpropane. The hydroxyl-terminated ternary and quaternary oligoesters were end-capped using phenyl isocyanate. The hydrolysis rate constants were obtained from acid number. The flexibility of diacids had a determinative effect on the hydrolytic stability of the carbamate end-capped oligoesters.