Rate Constants For Hydrolysis Research Articles

Mineral- and Base-Catalyzed Hydrolysis of Organophosphate Flame Retardants: Potential Major Fate-Controlling Sink in Soil and Aquatic Environments.

The ubiquitous occurrence of organophosphate flame retardants (OPFRs) in aquatic and soil environments poses significant risks to human health and ecosystems. Here, we report on the hydrolysis of six OPFRs and three structural analogues in the absence and presence of metal (hydr)oxide minerals. Eight of the target compounds showed marked degradation in alkaline solutions (pH 9-12) with half-lives ranging from 0.02-170 days. Kinetics follow a second-order rate law with apparent rate constants for base-catalyzed hydrolysis (kB) ranging from 0.69-42 000 M-1 d-1. Although hydrolysis in homogeneous solution at circumneutral pH is exceedingly slow (t1/2 > 2 years, except for tris(2,2,2-trichloroethy) phosphate), rapid degradation is observed in the presence of metal (hydr)oxide minerals, with half-lives reduced to <10 days for most of the target OPFRs in mineral suspensions (15 m2/L mineral surface area loading). LC-qToF-MS analysis of transformation products confirmed ester hydrolysis as the active degradation pathway. Values of kB for individual OPFRs are highly variable and correlate with acid dissociation constants (pKa) of the corresponding alcohol leaving groups. In contrast, kinetic parameters for mineral-catalyzed reactions are much less sensitive to OPFR structure, indicating that other factors like mineral-OPFR interactions are rate controlling. Given the documented recalcitrance of OPFRs to biodegradation and photodegradation, these results suggest that mineral-catalyzed hydrolysis may be a major fate-controlling sink in natural environments.

Kinetics of the hydrolysis of xylan based on ether bond cleavage in subcritical water

In this study, the rate of xylan hydrolysis was investigated. The hydrolysis of tulip poplar was conducted in subcritical water from 180 to 220 °C for 1–240 min. An equation for estimating the hydrolysis of ether bonds in both xylan and xylooligosaccharide from the yield of xylan and xylooligosaccharide was derived, and the rate constant of ether bond hydrolysis was calculated using the derived equation. It was found that our kinetic study can be applied to subcritical water treatment of various lignocellulosic biomass. In addition, linearity between the apparent activation energy and the logarithmic value of the apparent pre-exponential factor was observed. An equation for the apparent reaction rate constant was derived by introducing a factor, α, that reflects the changes in the reaction rate arising from various factors.

Valorizing waste iron powder in biogas production: Hydrogen sulfide control and process performances

Biogas is composed of different gases including hydrogen sulfide (H2S), which is a hazardous gas that damages pipes and generators in anaerobic digestion system. The objective of this study was to control H2S by waste iron powder produced by laser cutting machine in a steel and iron industry. Waste iron powder was mixed with dairy manure at a concentration between 2.0 and 20.0 g/L in batch experiments, while the concentration was varied between 1.0 and 4.0 g/L in bench experiment. In batch experiment, a reduction of up to 93% of H2S was observed at waste iron powder of 2.0 g/L (T1), while the reduction was of more than 99% at waste iron powder beyond 8.0 g/L (T4 ∼ T6). The total sulfide concentration (ST) increased together with waste iron powder concentration and was fitted with a quadratic equation with a maximum ST of 208.0 mg/L at waste iron powder of 20.2 g/L. Waste iron powder did not have significant effect on methane yield in batch and bench experiments. However, hydrolysis rate constant was increased by almost 100%, while the lag-phase period was reduced to half in test digesters compared to that in control digester. In bench experiment, H2S concentration was reduced by 89% at 2.0 g/L, while 50% at 1.0 g/L. Therefore, waste iron powder was effectively removed H2S and did not affect negatively anaerobic digestion process.

Thermo-carbide slag pretreatment of turfgrass pruning: Physical-chemical structure changes, reducing sugar production, and enzymatic hydrolysis kinetics

Alkaline pretreatment shows a good effect on delignification of lignocellulosic biomass, and carbide slag, an alkaline industrial waste, was first applied to pretreat turfgrass pruning. Three thermo-alkaline pretreatment methods were compared to evaluate their ability to destroy the biomass structure and to enhance the enzymatic hydrolysis efficiency of turfgrass pruning, namely thermo-NaOH pretreatment, thermo-lime pretreatment, and thermo-carbide slag pretreatment. Results showed that the maximum net reducing sugar yield of 269.55 mg/g raw biomass was achieved by thermo-carbide slag pretreatment. Compared with raw biomass, the lignin and hemicellulose content of turfgrass pruning after thermo-carbide slag pretreatment reduced by 35.57% and 62.40%, respectively. SEM and FTIR analyses showed that the surface structure and chemical groups of turfgrass pruning were obviously destroyed by thermo-carbide slag pretreatment. There was a high positive correlation between the enzymatic hydrolysis efficiency and cellulose content of substrate. However, a high negative correlation was observed between the enzymatic hydrolysis efficiency and lignin content of substrate. The enzymatic hydrolysis kinetics with different pretreatments were well described by the fractal-like kinetics model, and the rate constant of enzymatic hydrolysis of thermo-alkali pretreated turfgrass pruning was about three times of that of the unpretreated turfgrass pruning. Overall, carbide slag is an ideal pretreatment material for enzymatic hydrolysis of turfgrass pruning in terms of hydrolysis efficiency and waste reuse.

Towards predicting protein hydrolysis by bovine trypsin

Abstract The extent of protein enzymatic hydrolysis is considered to be mostly determined by protease specificity and the number of cleavage sites (CS) on the substrate. However, this theoretical maximum is typically not reached. The limited hydrolysis of certain CS may be due to the differences in enzyme preference resulting from neighbouring amino acids (AA) of the CS (secondary specificity). This study aims to find the link between enzyme secondary specificity and the relative hydrolysis rate constants (selectivity) of individual CS in a protein, to better predict the maximum experimental degree of hydrolysis. Bovine tryptic hydrolysis of α-lactalbumin and β-casein showed that ≥50% of the CS were inefficiently hydrolysed. The selectivity depended on the number of charged AA at P2 and P2′ positions of a CS. Trypsin efficiently cleaves CS with neutral AA at these two positions. The selectivity towards 12 out of 18 (67%) CS in β-lactoglobulin was correctly predicted. The predicted maximum degree of hydrolysis is within ∼13% error of the experimental value, which is ∼5 times better than the prediction based only on enzyme specificity. This work helps to estimate the extent of hydrolysis and the peptide formation of bovine tryptic hydrolysis of other substrates.

Development of a novel fractal-like kinetic model for elucidating the effect of particle size on the mechanism of hydrolysis and biogas yield from ligno-cellulosic biomass

Abstract The effect of particle size on hydrolysis and biogas production kinetics from a typical ligno-cellulosic biomass was assessed by studying the anaerobic co-digestion of fixed amount of rice husk and cow dung mixture using a newly developed fractal-like kinetic model. British Standard (BS) sieves were used to obtain varying particles size fractions ranging from 0.150 to 0.212 mm, 0.212–0.300 mm, 0.300–0.600 mm, 0.600–1.000 mm and 1.000–1.700 mm from oven dried, milled rice husk and pulverized, dried cow dung respectively. These particle size fractions from both biomass were mixed in a ratio of 1:1 after which, they were loaded into batch reactors and digested anaerobically at ambient conditions for 75 days. Hydrolysis of ligno-cellulosic biomass was observed to depend on the fractal exponent (h), which indexed the presence of inaccessible regions in ligno-cellulosic biomass. Also, hydrolysis was observed to depend on two other intrinsic factors that comprised of the initial hydrolytic rate ( X o Y k o ′ ) and overall affinity constant ( k o ′ S o ) . Larger particle size fractions were associated with higher affinity but lower initial hydrolysis rate while, smaller particle size fractions were associated with lower affinity but higher initial hydrolysis rate. In addition, the fractal model compared favorably with the popular modified Gompertz equation.

Correlation between hydrolysis rate constant and chemical composition of energy crops

Besides biogas yield, the kinetic of biogas production in a biomethane potential (BMP) test also provides important information for feedstock characterization. In this study, fodder analysis and BMP tests with high temporal resolution were performed in order to identify statistical correlations between the hydrolysis rate constant (kh) and the chemical composition of various energy crops. Different species and cultivars of energy crops were analyzed in order to develop a broadly applicable regression model for the prediction of kh. Two independent datasets (222 samples in total) were used, one for the calibration of the model and one for its validation. The results indicated that the analytical parameters non-fiber carbohydrates and crude protein were statistically suitable for a multiple linear regression model for the prediction of kh. Furthermore, a first-order kinetic model and the proposed regression models can be utilized for the prediction of the biogas production in a BMP test. The proposed approach offers a fast and reliable prediction of the biogas production rate and allows a feedstock assessment according to their biogas potential.

Theoretical analysis of municipal solid waste treatment by leachate recirculation under anaerobic and aerobic conditions

Long-term emissions of Municipal Solid Waste (MSW) landfills are a burden for future generations because of the required long-term aftercare. To shorten aftercare, treatment methods have to be developed that reduce long-term emissions. A treatment method that reduces emissions at a lysimeter scale is re-circulation of leachate. However, its effectiveness at the field scale still needs to be demonstrated. Field scale design can be improved by theoretical understanding of the processes that control the effectiveness of leachate recirculation treatment. In this study, the simplest and most fundamental sets of processes are distilled that describe the emission data measured during aerobic and anaerobic leachate recirculation in lysimeters. A toolbox is used to select essential processes with objective performance criteria produced by Bayesian statistical analysis. The controlling processes indicate that treatment efficiency is mostly affected by how homogeneously important reactants are spread through the MSW during treatment. A more homogeneous spread of i.e. oxygen or methanogens increases the total amount of carbon degraded. Biodegradable carbon removal is highest under aerobic conditions, however, the hydrolysis rate constant is lower which indicates that hydrolysis is not enhanced intrinsically in aerobic conditions. Controlling processes also indicate that nitrogen removal via sequential nitrification and denitrification is plausible under aerobic conditions as long as sufficient biodegradable carbon is present in the MSW. Major removal pathways for carbon and nitrogen are indicated which are important for monitoring treatment effectiveness at a field scale. Optimization strategies for field scale application of treatments are discussed.

The computational analysis and modelling of substitution effects on hydrolysis of formanilides in acidic aqueous solutions

Various para, meta and ortho substituted formanilides have been theoretically studied. For trans and cis-isomers of non-substituted formanilide, the calculated B3LYP vibration normal modes were analyzed. Substituent effect on the selected normal modes was described and the comparison with the available experimental data is presented. The calculated B3LYP proton affinities were correlated with Hammett constants, Fujita-Nishioka equation and the rate constants of the hydrolysis in 1MHCl. Found linear dependences allow predictions of dissociation constants (pKBH+) and hydrolysis rate constants. Obtained results indicate that protonation of amide group may represent the rate determining step of acid catalyzed hydrolysis.

Kinetic Study on Alkaline Hydrolysis of 2‐Pyridyl and 4‐Pyridyl X‐substituted‐Benzoates: Effects of Benzoyl Substituent X and Leaving‐Group Basicity on Reactivity and Reaction Mechanism

Second‐order rate constants for alkaline hydrolysis of 2‐pyridyl X‐substituted‐benzoates (4a–4l) and 4‐pyridyl X‐substituted‐benzoates (5a–5l) are reported. The Hammett plots are nonlinear, e.g., substrates possessing a weak electron‐withdrawing group (EWG) or an electron‐donating group (EDG) in the benzoyl moiety deviate negatively from the linear Hammett plots composed of substrates bearing a strong EWG. In contrast, the Yukawa–Tsuno plots exhibit excellent linearity with ρX = 1.57, r = 0.43, and R2 = 0.998 for the reactions of 4a–4l and ρX = 1.47, r = 0.41, and R2 = 0.999 for those of 5a–5l, indicating that the nonlinear Hammett plots are not due to a change in the rate‐determining step (RDS) but are caused by ground‐state (GS) stabilization through resonance interactions. The ρX values found for the reactions of 4a–4l and 5a–5l are similar to those reported previously for reactions that proceed through a stepwise mechanism with formation of an intermediate being the RDS. Small βlg values (e.g., −0.2 ~ −0.3) calculated from the Brønsted‐type correlation of rate constants with leaving‐group basicity also indicate that the reactions proceed through a stepwise mechanism, in which expulsion of the leaving group occurs after the RDS.

Graphene oxide reduces the hydrolytic degradation in polyamide-11

Graphene oxide (GO) was incorporated into polyamide-11 (PA11) via in-situ polymerization. The GO-PA11 nano-composite had elevated resistance to hydrolytic degradation. At a loading of 1 mg/g, GO to PA11, the accelerated aging equilibrium molecular weight of GO-PA11 was higher (33 and 34 kg/mol at 100 and 120 °C, respectively) compared to neat PA11 (23 and 24 kg/mol at 100 and 120 °C, respectively). Neat PA11 had hydrolysis rate constants (kH) of 2.8 and 12 ( × 10−2 day−1) when aged at 100 and 120 °C, respectively, and re-polymerization rate constants (kP) of 5.0 and 23 ( × 10−5 day−1), respectively. The higher equilibrium molecular weight for GO-PA11 loaded at 1 mg/g was the result of a decreased kH, 1.8 and 4.5 ( × 10−2 day−1), and an increased kP, 10 and 17 ( × 10−5 day−1) compared with neat PA11 at 100 and 120 °C, respectively. The decreased rate of degradation and resulting 40% increased equilibrium molecular weight of GO-PA11 was attributed to the highly asymmetric planar GO nano-sheets that inhibited the molecular mobility of water and the polymer chain. The crystallinity of the polymer matrix was similarly affected by a reduction in chain mobility during annealing due to the GO nanoparticles' chemistry and highly asymmetric nano-planar sheet structure.

Nitrofurantoin hydrolytic degradation in the environment

Occurrence of pharmaceuticals, especially antibiotics in the environment increased attention to their environmental fate. Hydrolysis is one of two abiotic processes by which compounds are degraded in the environment. According to authors knowledge this is the first study investigating hydrolytic degradation of nitrofurantoin at pH-values normally found in the environment. Nitrofurantoin hydrolytic degradation appeared to be much slower at acidic (pH 4) solution compared to neutral (pH 7) and alkaline (pH 9) solutions at all three investigated temperatures (20 °C, 40 °C and 60 °C). In all cases nitrofurantoin hydrolysis followed the first-order kinetics with half-lives ranged from 0.5 days at pH 9 and 60 °C to 3.9 years at pH 4 and 20 °C. Temperature dependence of the hydrolysis rate constant was quantified by Arrhenius equation; obtained Ea values were as follows: 100.7 kJ mol−1 at pH 4, 111.2 kJ mol−1 at pH 7 and 102.3 kJ mol−1 at pH 9. Increase in hydrolysis rate constants for each 10 °C increase in temperature were 3.4, 3.9 and 3.5 at pH 4, pH 7 and pH 9, respectively. The structures of hydrolytic degradation products were determined and degradation pathways were suggested. Three main processes occurred depending on pH-values: protonation of the nitrofurantoin followed by cleavage of the NN single bond, heterocyclic non-aromatic ring cleavage, and reduction of the non-aromatic heterocyclic ring.

Glycosyl Cations versus Allylic Cations in Spontaneous and Enzymatic Hydrolysis.

Enzymatic prenyl and glycosyl transfer are seemingly unrelated reactions that yield molecules and protein modifications with disparate biological functions. However, both reactions employ diphosphate-activated donors and each proceed via cationic species: allylic cations and oxocarbenium ions, respectively. In this study, we explore the relationship between these processes by preparing valienyl ethers to serve as glycoside mimics that are capable of allylic rather than oxocarbenium cation stabilization. Rate constants for spontaneous hydrolysis of aryl glycosides and their analogous valienyl ethers were found to be almost identical, as were the corresponding activation enthalpies and entropies. This close similarity extended to the associated secondary kinetic isotope effects (KIEs), indicating very similar transition state stabilities and structures. Screening a library of over 100 β-glucosidases identified a number of enzymes that catalyze hydrolysis of these valienyl ethers with kcat values up to 20 s-1. Detailed analysis of one such enzyme showed that ether hydrolysis occurs via the analogous mechanisms found for glycosides, and through a very similar transition state. This suggests that the generally lower rates of enzymatic cleavage of the cyclitol ethers reflects evolutionary specialization of these enzymes toward glycosides rather than inherent reactivity differences.

Study of dichlorotriazine reactive dye hydrolysis in siloxane reverse micro-emulsion

The dyeing ability of the dichlorotriazine dye on cotton fiber in siloxane media was investigated using a water/oil emulsion system. Compared with traditional water base dyeing, a deeper color depth of fabric and 90% fixation rate of dye could be achieved without using salts in siloxane reverse micro-emulsion system. The hydrolysis mechanism of dichlorotriazine dye, which deeply affects the dyeing performance, was analyzed using high performance liquid chromatography and mass spectrometric methods. In siloxane reverse micro-emulsion dyeing system, the lower hydrolysis of dye is probably due to the grasping water ability of surfactant, the reaction between fiber and dye, and the dye aggregation under a high concentration of dye. Furthermore, the hydrolysis model shows that the hydrolysis rate constants in traditional water base was about three to four times faster than the one in siloxane reverse micro-emulsion system. The dye hydrolysis mechanism in siloxane reverse micro-emulsion system in this study could successfully guide the siloxane reverse micro-emulsion dyeing technology.

Investigation of acid phosphatase variants for the synthesis of phosphate monoesters.

The major drawback of using phosphatases for transphosphorylation reactions lies in product depletion caused by the natural hydrolytic activity of the enzymes. Variants of PhoC-Mm from Morganella morganii and NSAP-Eb from Escherichia blattae were studied for their ability to maintain a high product level in the transphosphorylation of various primary alcohols. A single amino acid exchange delivered phosphatase variant PhoC-Mm G92D, which was able to catalyze the phosphorylation of primary alcohols without any major hydrolysis of the formed phosphate esters. The mutation mostly improved the affinity of the enzyme for alcohols, while rate constants of transphosphorylation and hydrolysis were decreased, overall resulting in a superior catalytic efficiency in transphosphorylation compared to hydrolysis. The presence of residual substrate alcohol at a given concentration was crucial to suppress phosphate ester hydrolysis. The present work extends the synthetic applicability of phosphatase variants beyond the previously reported nucleosides and allows preparative-scale production of various primary phosphate esters (yields up to 42%) with high enzyme productivity (TONs up to ∼66,000). Biotechnol. Bioeng. 2017;114: 2187-2195. © 2017 Wiley Periodicals, Inc.

Hydrolysis of radicals and molecules of ethers

Radiolysis of aqueous solutions of diisopropyl and methyl tert-butyl ethers under γ-irradiation has been studied. The effect of pH on the products yield has been investigated. It has been shown that the rate constants of ether radicals hydrolysis are ~109 times higher than these of ether molecules in acidic as well as basic medium.

PH Dependence of Chitosan Enzymolysis.

As a means of making chitosan more useful in biotechnological applications, it was hydrolyzed using pepsin, chitosanase and α-amylase. The enzymolysis behavior of these enzymes was further systematically studied for its effectiveness in the production of low-molecular-weight chitosans (LMWCs) and other derivatives. The study showed that these enzymes depend on ion hydronium (H3O+), thus on pH with a pH dependence fitting R2 value of 0.99. In y = 1.484 + 0.114, the equation of pH dependence, when increases by one, y () increases by 1.484. From the temperature dependence study, the activation energy (Ea) and pre-exponential factor (A) were almost identical for two of the enzymes, but a considerable difference was observed in comparison with the third enzyme. Chitosanase and pepsin had nearly identical Ea, but α-amylase was significantly lower. This serves as evidence that the hydrolysis reaction of α-amylase relies on low-barrier hydrogen bonds (LBHBs), which explains its low Ea in actual conditions. The confirmation of this phenomenon was further derived from a similarly considerable difference in the order magnitudes of A between α-amylase and the other two enzymes, which was more than five. Variation of the rate constants of the enzymatic hydrolysis of chitosan with temperature follows the Arrhenius equation.

Acidic and alkaline bimolecular hydrolysis of substituted formanilides. Computational analysis and modelling of substitution effects

Abstract In this article, the study of 67 compounds representing various para-, meta- and ortho- substituted formanilides is presented. These molecules and the products of their acidic and alkaline hydrolysis were studied using DFT quantum chemical methods in order to calculate the reaction enthalpies. These enthalpies are correlated with the hydrolysis rate constants, kH, published for the acid-catalysed acyl cleavage bimolecular (AAC2) mechanism and the modified base-catalysed acyl cleavage bimolecular (BAC2) mechanism. The found linear dependences can be used for the prediction of rate constants of non-synthesised formanilide derivatives.

Hydrolysis mechanism of (N, N) chelated cytotoxic Pt/Pd(II)-dichloro complexes: A theoretical approach

Two cytotoxic complexes cis-[Pt(MAMP)Cl2], 1 and cis-[Pd(MAMP)Cl2], 2 (where, MAMP=2-[(Methylamino)methyl]pyridine) have been considered to explore their hydrolysis mechanism through Density Functional Theory. The stationary states on potential energy surfaces are optimized and characterized. Activation parameters and rate constants for hydrolysis of the complexes have been calculated in CPCM model and compared with that of renowned anticancer drugs. Second step is the rate-determining step with greater activation energy for both the complexes. Time Dependent Density Functional Theory is performed in order to understand the nature of electronic transition in the complexes.

Balance of Conformational States Affect the Intrinsic Hydrolysis of NRas When Compared to Other Ras Isoforms

Ras GTPases are small proteins that are involved in various signal transduction pathways that regulate cellular proliferation, survival, migration, and apoptosis. Although the first crystal structure of Ras was determined more than two decades ago, biochemical and structural differences in the G‐domain of the three isoforms, H‐, K‐ and N‐Ras is only now beginning to emerge. Each isoform functions as a molecular switch where guanine nucleotide exchange factors (GEFs) facilitate the exchange of guanosine diphosphate (GDP) for guanosine triphosphate (GTP) turning its signal on. Ras signaling is turned off via intrinsic hydrolysis or through the aid of GTPase activating proteins (GAP). Ras mutants are involved in 20% of human cancers, yet there are no inhibitors that target these proteins effectively. Most of the effort was originally focused on HRas as the classical representative of all three isoforms and more recently on KRas, the most frequently mutated in cancers. Thus, the structural biology and biochemistry of NRas have been largely overlooked. We have determined hydrolysis rate constants for NRas and determined the crystal structure of wild‐type NRas bound to GppNHp (GNP), a non‐hydrolyzable analogue of GTP, for comparison with H‐Ras and K‐Ras. Although each of the three isoforms follow a one‐step mechanism of hydrolysis, K‐ and NRas have lower rates than HRas, with structural features that promote disorder in switch II near the active site. N‐Ras mutants at G12 and Q61 are commonly found in melanoma tumors. These conserved residues are found in the phosphate‐binding loop (G12) and switch II (Q61) that help make up the active site of NRas. The structures of NRas mutants reveal distinct mechanisms through which they affect catalysis, consistent with lower hydrolysis rate constants found for G12D, G12S, Q61H, and Q61K compared to wild‐type NRas. Biochemical and structural understanding of NRas mutants will help further influence the development of novel therapeutic targets of NRas mutant melanoma.Support or Funding InformationThis research was funded by NSF Grant Number MCB‐1517295.