Kinetics Of Hydrolysis Reaction Research Articles

Intrinsic GTP hydrolysis is observed for a switch 1 variant of Cdc42 in the presence of a specific GTPase inhibitor

ABSTRACTThe Ras-related protein Cell division cycle 42 (Cdc42) is important in cell-signaling processes. Protein interactions involving Cdc42 occur primarily in flexible “Switch” regions that help regulate effector binding. We studied the kinetics of intrinsic GTP hydrolysis reaction in the absence and presence of a biologically active peptide derivative of a p21-activated kinase effector (PBD46) for wt Cdc42 and compared it to the Switch 1 variant Cdc42(T35A). While the binding of PBD46 to wt Cdc42 results in complete inhibition of GTP hydrolysis, this interaction in Cdc42(T35A) does not. Comparison of the crystal structure of wt Cdc42 in the absence of effector (1AN0.pdb), as well as the NMR structure of wt Cdc42 bound to an effector in the Switch 1 region (1CF4.pdb) (www.rcsb.org) suggests that the orientation of T35 with bound Mg2+ changes in the presence of effector, resulting in movement of GTP away from the catalytic box leading to the inhibition of GTP hydrolysis. For Cdc42(T35A), molecular dynamics simulations and structural analyses suggest that the nucleotide does not undergo the conformational shift observed for the wt Cdc42-effector interaction. Our data suggest that change in dynamics in the Switch 1 region of Cdc42 caused by the T35A mutation (Chandrashekar, et al. 2011, Biochemistry, 50, p. 6196) fosters a conformation for this Cdc42 variant that allows hydrolysis of GTP in the presence of PBD46, and that alteration of the conformational dynamics could potentially modulate Ras-related over-activity.

DFT study of the hydrolysis reaction in atranes and ocanes: the influence of transannular bonding.

Thermochemical kinetics of hydrolysis reactions of compounds with transannular intramolecular M…N bonds, i.e., atranes RM(OCH2CH2)3N and ocanes R2M(OCH2CH2)2NH (M = Si, Ge; R = F, Cl, Me), is studied at the B3LYP/aug-cc-pVDZ theoretical level. Several DFT methods are assessed for the reproduction of the experimental activation barrier for the Si-O bond cleavage of 1-methylsilatrane. Activation barriers for atranes and ocanes show the tendency for their growth with the decrease of the electronegativity of a substituent R on going from F to Me and their decrease from Si to Ge. Hydrolysis activation barriers of atranes and ocanes are compared with those of their acyclic analogs RM(OCH3)3 and R2M(OCH2)2NH in order to study the role of transannular M…N bonds in the stability of these molecules to hydrolysis. Substantially larger barriers for atranes support the opinion that stability of atranes may be explained by the formation of intramolecular bonds; however, the strengthening of transannular M…N bonds results in lower M-O cleavage barriers. It was proposed that the M-O cleavage barrier height is determined not by a weak M…N bonding itself, but rather by the contribution of a nitrogen lone pair to the antibonding orbitals of M-O bonds. The NBO analysis show that this interaction increases with the decrease of the electronegativity of a substituent R and decreases on going from atranes to ocanes. In ocanes, the presence of M…N bonds does not kinetically hinder the hydrolytic process; M-O cleavage activation barriers for acyclic analogs are higher. M-Hal cleavage barriers are substantially higher than those for M-O cleavage for R = F, but lower for R = Cl. Graphical Abstract The experimental barrier height of the Si-O bond cleavage in 1-methylsilatrane is well reproduced when three explicit water molecules are included in the B3LYP/aug-cc-pVDZ theoretical model.

The influence of an acid catalyst on the morphology, wettabillity, adhesion and chemical structure properties of TiO2 and ZrO2 sol–gel thin films

Abstract The proper selection of synthesis parameters and the way of preparing materials is of crucial importance in successful sol–gel synthesis, hence high quality of coatings is essential. The pH value of the sol–gel reaction mixture, which is dependent on the used catalyst, influences the hydrolysis and condensation reaction and also affects the form and structure of the received materials. Acids contribute to protonate alkoxide groups and intensify the hydrolysis reaction kinetics. Moreover, during condensation the pH affects the structure of the produced polymeric chains. Acid-catalyzed reaction is preferentially directed to the end of chains and leads to the achievement of less branched and more extended structures. The studies presented in this paper, focused on the influence of a catalyst type used in the acid catalysis for the preparation of thin films. TiO 2 and ZrO 2 thin films have been investigated due to the ability to form crystalline structure at relatively low temperatures. The influence of the used acid catalyst (HCl, HNO 3 , H 2 SO 4 , H 3 PO 4 ) on physicochemical properties was considered. SEM examination of the obtained materials was carried out to check the influence of different catalysts on the surface morphology and topography. The impact of the type of the used catalyst on the chemical structure of material has been investigated by Raman and Infrared Spectroscopy. Wettability measurements were conducted to verify the catalyst and materials structure effect on surface properties of the obtained materials. All described results have proved that sol–gel process of zirconia materials is much more sensitive to the pH value of a reaction in comparison with titania materials.

Templating Influence of Molecular Precursors on Pr(OH)3 Nanostructures.

Four new praseodymium alkoxo and amido compounds ([Pr3(μ3-OtBu)2(μ2-OtBu)3(OtBu)4(HOtBu)2] (1), [Pr{OC(tBu)3}3(THF)] (2), [PrCl{N(SiMe3)2}2(THF)]2 (3), and [PrCl{OC(tBu)3}2(THF)]2 (4)) were synthesized and structurally characterized by single-crystal X-ray diffraction analysis. Application of these compounds in solvothermal synthesis of praseodymium oxide/hydroxide nanostructures showed their templating influence on the morphology and phase composition of the resulting solid-state materials. Differential reactivity of the chosen alkoxide ligands toward water and the different arrangements of metal-oxygen units in the studied precursor compounds strongly influenced the kinetics of hydrolysis and cross-condensation reactions as manifested in the morphological changes and phase composition of the final products. Thermal decomposition studies of 1-4 confirmed their conversion into the corresponding oxide phases. Activation of compounds 1, 2, and 4 by either a base or a stoichiometric amount of water showed the distinct influence of their chemical configuration on the obtained nanopowders: whereas 1 solely produced nanorods of Pr(OH)3, 2 predominantly formed a mixture of rod-shaped and spherical particles. The solvothermal decomposition of 4 resulted in Pr(OH)2Cl or PrOCl due to the presence of Cl ligands in the molecular precursor. The resultant materials were thoroughly characterized to demonstrate the relationship between precursor chemistry and the processing parameters that are clearly manifested in the morphology and phase of the final ceramics.

Cellulose Hydrolysis in Acidified LiBr Molten Salt Hydrate Media

We screened nine acidified molten salt hydrates (solutions with water to salt molar ratio equal or less than the coordination number of the cation) as reaction media for cellulose hydrolysis, and we found that cellulose can be efficiently hydrolyzed in LiBr acidified MSH under mild conditions (>90% yield to water-soluble products in 0.05 M H2SO4 at 85 °C for 30 min). The effect of various factors (temperature as well as acid and initial cellulose concentrations) on the kinetics of hydrolysis reaction was also investigated. At the lowest temperatures examined (70 and 85 °C) low amounts of degradation products have been observed, and glucose appears to be in equilibrium with its dimers and possibly other oligomers. Higher temperatures (100–115 °C) enhanced the formation of degradation products (organic acids and humins). Analysis of the kinetic data indicate that hydrolysis rates are first order in cellulose and in H2SO4 concentration, and the initial hydrolysis rates have an apparent activation energy ∼123...

Magnetic immobilization and characterization of α-amylase as nanobiocatalyst for hydrolysis of sweet potato starch

Magnetic immobilization of enzymes became emerging method for efficient recovery of biocatalyst under magnetic field. Sweet potato (Ipomoea batatas) root starch is abundantly produced in tropical countries. Thus the present work was focused on immobilizing α-amylase on to magnetic nanoparticles and use as biocatalyst for hydrolysis of sweet potato starch into glucose. The hydrolysis of sweet potato starch using immobilized α-amylase was investigated and the maximum glucose yield of 42.89mg/g was obtained using 3% (w/v) of sweet potato starch concentration with an initial pH 4 at 40°C in 80min reaction time. The optimal concentration of immobilized α-amylase for maximum glucose yield was found as 1% (w/v). The kinetics of hydrolysis reaction was studied using Michaelis–Menten equation. The sweet potato starch was found to have more affinity towards magnetically immobilized α-amylase with substrate affinity constant (Km) of 0.16mg/ml and the maximum reaction rate (Vmax) of 3.63×10−3μmol/mls. The magnetically immobilized nanocomposite of α-amylase can be easily recovered and reused for maximum utilization.

A dynamic supramolecular polymer with stimuli-responsive handedness for in situ probing of enzymatic ATP hydrolysis.

Design of artificial systems, which can respond to fluctuations in concentration of adenosine phosphates (APs), can be useful in understanding various biological processes. Helical assemblies of chromophores, which dynamically respond to such changes, can provide real-time chiroptical readout of various chemical transformations. Towards this concept, here we present a supramolecular helix of achiral chromophores, which shows chiral APs responsive tunable handedness along with dynamically switchable helicity. This system, composing of naphthalenediimides with phosphate recognition unit, shows opposite handedness on binding with ATP compared with ADP or AMP, which is comprehensively analysed with molecular dynamic simulations. Such differential signalling along with stimuli-dependent fast stereomutations have been capitalized to probe the reaction kinetics of enzymatic ATP hydrolysis. Detailed chiroptical analyses provide mechanistic insights into the enzymatic hydrolysis and various intermediate steps. Thus, a unique dynamic helical assembly to monitor the real-time reaction processes via its stimuli-responsive chiroptical signalling is conceptualized.

Kinetics and genetic algorithm study of acid catalysed hydrolysis of water hyacinth biomass

Industrialization has elevated our energy demand during the last century by many a folds, to deal with the rapid social growth. Non-renewable energy sources, like petroleum being the main source of energy, have become scarce due to their overuse and limited available reserve. Water hyacinth can be considered as a good source of lignocellulosic biomass. Cellulose and hemi-cellulose derived from water hyacinth via effective bioprocess can be converted to bioethanol. Production of liquid fuel from biomass can only be made economically viable and sustainable only if the de-polymerization of the recalcitrant hemi-cellulosic fraction of the biomass can be optimally utilized. The study aims to obtain an in-depth mechanistic understanding of the catalytic reaction involved in dilute sulphuric acid pre-treatment of water hyacinth biomass. Acid catalysed hemi-cellulose hydrolysis reaction kinetics in water hyacinth was studied based on a bi-phasic model. Arrhenius equation was used to study the kinetic modelling in a greater depth. A distinct relationship of soaking time of the biomass in the acid before hydrolysis on the activation energy and frequency factor was observed. A maximum xylose yield of 76.96% was predicted by the genetic algorithm based model for the optimum operating conditions; operating temperature (135.8 °C), concentration of sulphuric acid (5.6%), treatment time (17.45 min), and soaking time (3.99 h).

The role of microemulsions in lipase‐catalyzed hydrolysis reactions

The kinetics of the p-nitrophenyl butyrate hydrolysis reaction, catalyzed by Candida rugosa lipase in the water-in-oil microemulsion cetyltrimethylammonium bromide/water/pentanol/hexane, was investigated. The results described in the present manuscript reveal two peculiar characteristics of the reaction: (i) the initial rate of hydrolysis is very fast and (ii) by decreasing the water content of the microemulsion, the reaction rate approaches the typical behavior of reactions performed in aqueous solution. In particular, for microemulsion systems with a high water content, the end points of the reactions are dictated by the shape stability of the microemulsion. For these systems, our methodological approach shows that the process follows a second-order kinetics equation, indicative of the dual role played by water, which is involved both as a component of the microemulsion, i.e., relevant for the microemulsion stability and as a reagent of the hydrolysis reaction. In contrast, for microemulsions containing a small amount of water, after the hydrolysis reaction the system seems to fall in the no existence range of the microemulsion. Accordingly, the kinetics results are more complex: in the initial stage, the reaction follows a zero-order kinetics equation, while for longer reaction times a first-order kinetics equation fits the experimental data, as would be expected for an enzymatic reaction in a homogeneous system.

Kinetics of Hydrolysis Reaction of Chitin Using Chitinase Purified from Marine Bacterium Alteromonas marina

Kinetics of Hydrolysis Reaction of Chitin Using Chitinase Purified from Marine Bacterium <I>Alteromonas marina</I>

Synthesis, structural characterization, and hydrolysis of Ammonia Borane (NH3BH3) as a hydrogen storage carrier

In the present study, synthesis, structural characterization, and hydrolysis of the promising hydrogen storage carrier ammonia borane (NH3BH3), were investigated. NH3BH3 was prepared by one-pot chemical reaction between sodium borohydride (NaBH4) and different ammonia salts [NH4X, X: SO4, CO3, Cl] in the presence of solvent, tetrahydrofurane (THF). Synthesizes with different temperatures (20–40 °C), reaction times (30–130 min), amount of added THF volume (50–200 ml) and NaBH4/(NH4)2SO4 input molar ratios (0.47–0.75) were performed in order to find the optimum reaction conditions for obtaining maximum product yield. The characterization of NH3BH3 products was carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (RS), elemental analysis (C, H, N, O) and NMR spectroscopy. Characterization results indicated that NH3BH3 as a crystalline powder at 98% purity was achieved with 92.18% production yield. Additionally, hydrolysis of product NH3BH3 in the presence of amorphous Co–B catalyst at 22–80 °C under magnetic stirring (700 rpm) was performed. The maximum hydrogen generation rate was 5447.80 ml min−1 g cat−1 and the hydrolysis reaction kinetics were clarified based on zero-order, first-order and Langmuir–Hinshelwood kinetic models.

Reaction kinetics study of α-amylase in the hydrolysis of starch size on cotton fabrics

The hydrolysis reaction kinetics of α-amylase on the starch size of cotton fabrics followed the first-order reaction in the initial stage that α-amylase hydrolyzed on the surface of cotton fabrics; desizing ratios of more than 95% were obtained in the initial stage, which are acceptable, and the hydrolysis time for the initial stage shortened sharply as the temperature increased. The increase of α-amylase dosage enhanced the reaction rate constant as well as speeded up the first-order reaction rate in the initial stage, both treated at the same treatment temperature. The hydrolysis action of α-amylase on starch size on the surface of cotton fabrics speeded up significantly as the temperature increased. Also, the treatment time needed to obtain an acceptable desizing ratio (> 95%) shortened sharply from 6 to 1/12 h as the treatment temperature increased from 20 to 100 °C.

Catalysis and hydrolysis properties of perovskite hydride NaMgH3

• The formation of NaMgH 3 in the NaH doped MgH 2 improves the hydrogen sorption kinetics of MgH 2 . • The catalytic role of NaMgH 3 is related with its perovskite structure. • The NaMgH 3 shows fast hydrolysis reaction kinetics without any passivation. The addition of NaH by ball milling is shown to greatly improve the hydrogen storage properties and the hydrolysis properties of MgH 2 , which is related to the formation of ternary hydride NaMgH 3 with specific perovskite structure. The MgH 2 –10%NaH mixture exhibits better hydriding and dehydriding kinetics than the MgH 2 –10%LiH mixture, in which the LiMgH 3 with perovskite structure could not be formed. The catalytic role of NaMgH 3 is attributed to fast hydrogen mobility in the perovskite structure, which provides fast hydrogen diffusion pathways for the hydriding and dehydriding of MgH 2 . The NaMgH 3 also shows fast hydrolysis reaction kinetics without any passivation. Our work shows that such perovskite-type hydride demonstrates great potential as efficient catalysts for the high-capacity hydrides for whether reversible or irreversible hydrogen storage.

Kinetics of Bamboo Fiber Hydrolysis Reaction in Saturated Formic Acid

Kinetic models can have practical applications for the optimization of the process and performance analysis, or economic estimations, so investigate the bamboo fiber kinetics is necessary. In this paper, effects of temperature and time on bamboo fiber hydrolysis in saturated formic acid with 4% hydrochloric acid solution reaction kinetics have been investigated. The rate constants, average apparent activation energy and frequency factors were evaluated according to the Arrhenius equation. The results showed that the hydrolysis velocities of bamboo fiber were 1.63×10-2 h-1 at 55 °C, 2.59×10-2 h-1 at 60 °C, 4.56×10-2 h-1 at 65 °C, 6.75×10-2 h-1 at 70 °C and 0.10 h-1 at 75 °C in formic acid solution with 4 % hydrochloric acid. The degradation velocities of glucose were 6.57×10-3 h-1 at 55 °C, 1.98×10-2 h-1 at 60 °C, 2.53×10-2 h-1 at 65 °C, 7.47×10-2 h-1 at 70 °C and 0.14 h-1 at 75 °C. The pre-exponential factor of Arrhenius equation of bamboo fiber hydrolysis reaction and glucose decomposition was 1.48×1014 h-1 and 2.32×1020 h-1 respectively. The activation energy of bamboo fiber hydrolysis was 87.65kJ/mol, and the activation energy of glucose degradation was 141.44kJ/mol.

Preparation of a carbon‐based material derived from coking industry solid waste–phenol residue and its performance as hydrolysis catalysts

ABSTRACTA carbon‐based solid acid was successfully synthesized by sulfonating a carbon precursor from pyrolysis of phenol residue, which is a solid waste from coking industry and contains higher phenols. The unit structures of the phenolic residual‐based solid acid are fused aromatic rings bearing CH3 side chains besides phenolic‐OH, COOH and SO3H groups. The direct pyrolysis and carbonization process of phenol residue abounding in phenolic hydroxyl groups avoids the loss of sulfonic acid groups instead of low temperature carbonization in concentrated sulfuric acid. Reaction kinetics of sucrose heterogeneous hydrolysis over the solid acid was studied to assess its catalytic activity and stability. The results indicate that the carbonization temperature for the preparation of carbon precursor significantly affects the catalytic performance of the solid acid because of the difference in the compact degree of carbon skeleton. The activation energy calculated is 74.67 kJ mol−1, which reveals good catalytic activity. And the catalyst is fairly stable after repeatedly being used five times. It can substitute enzymes and sulfuric acid in sucrose hydrolysis. © 2012 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Determination of reaction kinetics of hydrolysis of tilapia (Oreochromis niloticus) protein for manipulating production of bioactive peptides with antioxidant activity, angiotensin‐I‐converting enzyme inhibitory activity and Ca‐binding properties

SummaryTo manipulate enzymatic hydrolysis of tilapia (Oreochromis niloticus) muscle protein for production of bioactive peptides, its reaction kinetics was intensively studied. The study showed that the production of peptides with different bioactive properties including antioxidant activity, angiotensin‐I‐converting enzyme (ACE) inhibition and Ca‐binding property and their kinetics were affected by the degree of hydrolysis and substrate concentration. A comparative study on reaction kinetics found that the kinetic parameters for the production of each bioactive peptide are unique, that is, the maximum initial velocity, Vmax, for hydrolysis of protein was as high as 1.07 mg mL−1 min−1, but that for the production of peptides with antioxidant activity and Ca‐binding property were very low, range of 7.14–66.7 μg mL−1 min−1, and that for the production of peptides with ACE inhibitory activity was the lowest, at 2.57 μg mL−1 min−1. This knowledge of reaction kinetics of protein hydrolysis would be useful for manipulating and optimising the production of peptides with desired bioactive properties.

Steam flow effects on hydrolysis reaction kinetics in the Cu–Cl cycle

Abstract In this paper, the effects of an inert carrier gas and steam flow on the reaction kinetics of a CuCl2 hydrolysis reactor are examined for the thermochemical copper-chlorine (Cu–Cl) cycle of hydrogen production. Experimental data from two packed bed reactors, at three separate vapour pressures of H2O in the gaseous input stream, are investigated in terms of the transient conversion efficiencies and reaction kinetics. The results show that the transient reaction rate reduces by over 75% as the reaction progresses and physical resistances develop in the reactor. The effects of system temperature and reactant flowrate on the reaction rate are also investigated with experimental data. The results of this paper show that by reducing the steam density, the variability in reaction rate can be decreased. These results can be used to predict the reaction kinetics, allowing residence time and transport properties to be more effectively considered.

Microtubules: Sizing Up the GTP Cap

The 'GTP cap' of the microtubule has long been postulated to exist, but a recent experiment gives us the first quantitative measurements of the cap size in thecell.

Estimating the Microtubule GTP Cap Size In Vivo

Microtubules (MTs) polymerize via net addition of GTP-tubulin subunits to the MT plus end, which subsequently hydrolyze to GDP-tubulin in the MT lattice. Relatively stable GTP-tubulin subunits create a "GTP cap" at the growing MT plus end that suppresses catastrophe. To understand MT assembly regulation, we need to understand GTP hydrolysis reaction kinetics and the GTP cap size. In vitro, the GTP cap has been estimated to be as small as one layer (13 subunits) or as large as 100-200 subunits. GTP cap size estimates in vivo have not yet been reported. Using EB1-EGFP as a marker for GTP-tubulin in epithelial cells, we find on average (1) 270 EB1 dimers bound to growing MT plus ends, and (2) a GTP cap size of ∼750 tubulin subunits. Thus, in vivo, the GTP cap is far larger than previous estimates in vitro, and ∼60-fold larger than a single layer cap. We also find that the tail of a large GTP cap promotes MT rescue and suppresses shortening. We speculate that a large GTP cap provides a locally concentrated scaffold for tip-tracking proteins and confers persistence to assembly in the face of physical barriers such as the cell cortex.

Reaction kinetics of hydrothermal hydrolysis of hesperidin into more valuable compounds under supercritical carbon dioxide conditions

A kinetic model and reaction mechanism of hydrothermal hydrolysis of hesperidin aided with supercritical carbon dioxide were elucidated. Experiments were carried out at 25MPa, reaction temperatures of 110–140°C and reaction time of 1–4h. Results were presented in terms of the concentration change (with time) of the major components namely hesperidin, hesperetin-β-glucoside and hesperetin. Experimental results showed that pressurized carbon dioxide could serve as a catalyst for the hydrothermal degradation of hesperidin that follows first-order rate kinetics. The pathways for the degradation reaction compose of complex reactions. The one involves consecutive reactions that take hesperetin-β-glucoside as an intermediate product followed by its degradation to hesperetin. Parallel to that is a reaction that directly cleaves the glycosidic bond of hesperidin to form hesperetin. The kinetic parameters of the hydrolysis reaction were estimated by least squares approximation methods, and the proposed model fitted well with the experimental data. The values of activation energies calculated based on Arrhenius equation may suggest that the cleavage of rhamnosidic bond takes lesser energy than the cleavage of glycosidic bond of hesperidin.