Intermediates of chemical assembling of oligoorganosiloxanes in hydrolysis of organochlorosilanes

The mechanism of the formation of oligoorganosiloxanes during the hydrolysis of organochlorosilanes was considered. A comparative estimation of a relationship of the degree of conversion of the monomer vs. degree of conversion of functional groups in the homo- and heterofunctional condensation and partial hydrolysis of organochlorosilanes was performed for the first time. In the hydrolysis of diorganodichlorosilanes with either an excess or a deficiency of water, the homofunctional condensation of diorganosilanediols is not the main mode for the chemical assembling of oligoorganosiloxanes. The main intermediates in the route of oligoorganosiloxane formation during organochlorosilane hydrolysis are the incomplete hydrolysis products (organochlorohydroxysilanes). Experimental data suggest that the chemical assembling of oligoorganosiloxanes occurs via the mechanism of organochlorohydroxysilane heterocondensation under usually used conditions of organochlorosilane hydrolysis.     

Interactive influence and optimization of reaction parameters in the hydrolysis of olive and coconut triacylglycerols byC. cylindracea andR. javanicus lipases in reverse micellar media

The four reaction parameters—pH, reaction temperature, molar ratio (R) of water to surfactant, and Aerosol-OT concentration—have significant linear, quadratic., and interactive effects on the initial rate and the degree of hydrolysis for lipase-mediated hydrolysis of triacylglycerols (TAG) in Aerosol-OT/iso-octane reverse micellar media. Reaction temperature and pH had the most significant influence on the rate and the degree of hydrolysis, whereas Aerosol-OT concentration had the least influence on those parameters. The initial rate was most influenced by the interactive effect of pH with all other variables, whereas the degree of hydrolysis was the most influenced by the interactive effect of reaction temperature with other variables. Lowerlevel variable combinations were favorable over higher-level variable combinations to TAG hydrolysis in reverse micellar media. Regression models, developed for the initial rate and the degree of hydrolysis as a function of reaction variables, accounted for up to 96% of the variation in the two responses. The optimum reaction condition ranges were determined based on maximization of both the rate and the degree of hydrolysis. The differences in the physicochemical characteristics of substrates had no significant effect on the optimum condition ranges. However, the noticeable differences were observed for these ranges between the systems withRhizopus javanicus andCandida cylindracea lipases. Lipase-catalyzed hydrolysis of TAG in Aerosol-OT/iso-octane reverse micellar media was optimum at about 22‡C, 140 mM Aerosol-OT concentration, pH 6.8, andR value of 14.     

Nonenzymatic Hydrolysis of Cocaine via Intramolecular Acid Catalysis

The spontaneous hydrolysis of the methyl-ester group of cocaine ( 1 ) in vivo contributes to the metabolic clearance of the drug in man. Neighboring-group participation by the tropane N-atom of cocaine in this hydrolysis was suggested by the normal stability of the methyl-ester groups of pseudococaine and N-acylnorcocaine. For cocaine, the relative rate of methyl-ester to benzoyl-ester hydrolysis was ca. 10:1 at pH≤7.4, and, although absolute rates increased with increasing pH, their ratio collapsed at pH>pK_a (8.6). These data are consistent with intramolecular acid catalysis of alkaline hydrolysis of the cocaine methyl-ester group under physiologic conditions.     

Ionic liquid aqueous solvent-based microwave-assisted hydrolysis for the extraction and HPLC determination of myricetin and quercetin from Myrica rubra leaves

An ionic liquid aqueous solvent‐based microwave‐assisted hydrolysis (ILAS‐MAH) approach was proposed for the rapid extraction and accurate determination of myricetin and quercetin from Myrica rubra (M. rubra) leaves for the first time. The effects of the ionic liquid class and concentration, liquid–solid ratio, hydrolysis temperature and time were investigated to obtain the optimal ILAS‐MAH conditions. The optimized conditions were 2.0 mol/L [bmin][HSO4] or 2.5 mol/L acidified [bmin]Br solution, liquid–solid ratio 30:1 (mL : g), hydrolysis temperature 70°C and hydrolysis time 10 min. Under these conditions, the recoveries of myricetin and quercetin were in the range of 86.3–107.3% with relative standard deviation lower than 5.8%. Compared with conventional heating hydrolysis and regular MAH, the proposed approach reduced hydrolysis time and improved yields. The mechanism of ILAS‐MAH was also investigated. Copyright © 2010 John Wiley & Sons, Ltd.     

A DFT study on the hydrolysis mechanism of NH‐tautomeric antitumors of [HL][trans‐RuCl4L(dmso‐S)]

The hydrolysis process of Ru (III) complex [Htrz][trans‐RuCl₄(1‐H‐1,2,4‐triazole)(dmso‐S)] 1 , a potential antitumor complex similar to the well‐known anticancer agent [ImH][trans‐RuCl₄(Im)(dmso‐S)] (NAMI‐A), has been investigated by using density functional theory (DFT) method, and the solvent effect was also considered and calculated by conductor‐like polarizable calculation model (CPCM). Meanwhile, the hydrolysis process of the NH‐tautomeric isomer, [Htrz][trans‐RuCl₄(4‐H‐1,2,4‐triazole)(dmso‐S)] 2 , was also modeled and predicted by the same methods. The structural characteristics and the detailed energy profiles for the hydrolysis processes of two isomers have been obtained. The analysis of thermodynamic and kinetic characteristics of hydrolysis reaction suggests the following: for the first hydrolysis step, the Complex 1 has lower hydrolysis rate than the reported anticancer drug NAMI‐A, and the result is in accordance with experimental one. However, Complex 1 has obviously higher hydrolysis rate than its isomer Complex 2 , and the result was reasonably explained in theory. For the second hydrolysis step, the formation of cis‐diaqua species is thermodynamic preferred to that of trans isomers. In addition, the trend in nucleophilic attack abilities (A) of hydrolysis products by pertinent biomolecules was revealed and predicted. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Heterogeneous dilute acid hydrolysis of cellulose: A kinetic model for the hydrolysis of the difficultly accessible portion of cellulose based on donnan's theory of membrane equilibria

The effect of adding an electrolyte on the rate of the heterogeneous dilute acid hydrolysis of cellulose was studied using 1.3M hydrochloric acid containing varying amounts of sodium chloride up to 0.17M. A general increase in the rate of hydrolysis was observed. In particular, a linear relationship was observed between the rate of hydrolysis of the later portion of the hydrolysis curve and the concentration of added electrolyte, thus confirming that Donnan's theory of membrane equilibria can be applied to the heterogeneous hydrolysis of cellulose in dilute acid. A kinetic model, based on this theory and whose predictions are consistent with the above experimental results is presented.     

Some considerations of the kinetics of the acid hydrolysis of poly- and oligosaccharides. Part III. The disaccharides 2-O-(α-D-glucopyranosyluronic acid)-D-xylose, 2-O-(4-O-methyl-α-D-glucopyrano-syluronic acid)-D-xylose,and 2-O-(4-O-methyl-α-D-glucopyranosyl)-D-xylitol

Rate equations have been formulated for the formation and depletion of the hydrolysis product(s) of the title disaccharides. They are based on the assumptions that (1) the rate of acid hydrolysis of the disaccharides is according to first order, and (2) the rate of depletion of the hydrolysis product(s) is constant in the early periods while it approaches first order in the more advanced stages of the reactions. By using experimental rate data from the literature the rate constants of the hydrolysis of the disaccharides and of the depletion of the hydrolysis product(s) have been computed. The validity of the assumptions underlying the rate equations advanced has been confirmed by (a) the agreement between experimental and calculated values and (b) the similar values for the rate constant of the depletion of xylose formed in the hydrolysis of the two biouronic acids. Also discussed are some implications arising from the magnitude of the hydrolysis rate constant of methylaldobiouronic acid and of the depletion rate constant of xylose in relation to complete hydrolysis of polysaccharides.     

Solvation Effects in Hydrolysis of 2-Toluenesulfonyl Halides in Aqueous Dioxane. Catalysis with Water Molecules in Cyclic Transition States

The activation parameters of hydrolysis of 2-toluenesulfonyl chloride in aqueous dioxane in the range of dioxane mole fractions X ₂ 0-0.33 were determined. As for the previously studied hydrolysis of 2-toluenesulfonyl bromide, the dependences of the activation parameters on X ₂ are essentially nonmonotonic, with minima in the ranges of X ₂ 0.005-0.010 and 0.10-0.12. The kinetic data were discussed taking into account the concepts of the effect of nonelectrolyte on the water structure and the results of previous PM3 calculations of benzenesulfonyl chloride hydrolysis in the gas phase and in water clusters. A scheme of catalytic hydrolysis of sulfonyl halides with water molecules in cyclic transition states was suggested.     

Polyethylenimine catalysts containing an isolated apolar binding site: Solovolysis of p-nitrophenyl esters

The preparation dodecane-block-poly[ethylenimine-graft-4(5)-methylimidazole] copolymers and related model compounds has been described and such polymers have been described and such polymers have been demonstrated to be efficient catalysts for the hydrolysis of activated phenyl esters in aqueous solutions. Polymeric catalysts that contain isolated apolar blocks exhibited enhanced catalytic activity for the hydrolysis of the p-nitrophenyl esters of acetate and butyrate compared with polymer model compounds. This rate enhancement was atributed to the apolar binding of substrate within the apolar polymer regime. Twenty-to 100-fold increases in the second-order rate constants were observed for the hydrolysis of the longer-chain p-nitrophenyl esters. This is indicative of a significant hydrophobic interaction. The contribution of the apolar block to the hydrophobic interaction was masked in the hydrolysis of the p-nitrophenyl caproate and p-nitrophenyl laurate substrates. In both instances the dominant contribution to the hydrophobic interactions was ascribed to a substrate-imidazole intermediate rather than the apolar block of the catalyst. The pH-rate profiles for the hydrolysis of p-nitrophenyl esters by the various catalysts indicated an absence of any cooperative interactions between imidazole residues or amine groups.     

Enzymatic resolution of flavanone oximes

The optically active (R)- and (S)-flavanones were prepared by an enzymatically enantioselective hydrolysis of (±)-flavanone oxime O-acylates employing lipases, followed by hydrolysis with acid.     

Hydrolysis of Cephanone in SDS／n－C5H11OH／H2O System

The hydrolysis of cephanone in SDS micelle and SDS/n-C5H11-OH/H2O O/W microemulsion was studied through Uv-vis ab-sorption spectroscopy. The change of pH value in the hydrolysis of cephanone was determined. The result shows that pH value decreases in the process of the hydrolysis, and that the SDS ml-celle and SDS/n-C5H11OH/H2O O/W microemulsion accelerate the hydrolysis of cephanone compared with water.     

Competition between thermal decomposition and hydrolysis of 2,2'-azobis(2-amidinopropane) in aqueous solution

The thermal decomposition and hydrolysis of 2,2′-azobis(2-amidinopropane) were examined as functions of pH. The rate of decomposition decreased with increasing pH. The specific rates at 60°C were 3.85 × 10^?5 1/sec at pH 0.90 and 2.5 × 10^?5 1 see at pH ≥ 8.5. The hydrolysis in alkaline solution yielded 2,2′-azobis(2-carbamylpropane) which was stable to thermal decomposition. The relation between the specific rate of hydrolysis k_h′ and the concentration of hydroxyl ion was obtained as k_h′ = 4.0 × 10^?2 [OH]^0.50 1/sec at 60°C. In alkaline solution, the rate of hydrolysis was considerably larger than that of thermal decomposition. A mechanism for this hydrolysis is propesed.     

The Inhibition of the Hydrolysis of Cephanone by CTAB/n‐C5H11OH/H2O Microemulsion

Abstract

The hydrolysis of cephanone in water, cetyl trimethyl ammonium bromide (CTAB) micelle, and CTAB/n‐C₅H₁₁OH/H₂O O/W microemulsion was studied through UV‐VIS absorption spectroscopy. The mechanism of the hydrolysis and the effects of both the acidity of the media and the composition of O/W microemulsion on the hydrolysis were studied. The results show that the hydrolysis rate of cephanone increases with the acidity. Compared with water, CTAB micelle and CTAB/n‐C₅H₁₁OH/H₂O O/W microemulsion suppress this hydrolysis. The inhibition of the hydrolysis of cephanone by CTAB micelle and CTAB/n‐C₅H₁₁OH/H₂O O/W microemulsion is related to the location of cephanone in the interphases of CTAB micelles and CTAB/n‐C₅H₁₁OH/H₂O O/W microemulsion droplets.     

Effect of Chain Length on Enzymatic Hydrolysis of p-Nitrophenyl Esters in Supercritical Carbon Dioxide

The effect of chain length on the enzymatic hydrolysis of various p-nitrophenyl esters was investigated. Specifically, the hydrolysis of various esters p-nitrophenyl butyrate (PNPB), p-nitrophenyl caprylate (PNPC), p-nitrophenyl laurate (PNPL), p-nitrophenyl myristate (PNPM) and p-nitrophenyl palmitate (PNPP) was studied in supercritical carbon dioxide (ScCO₂) with lipase (Novozym 435). This indicates that the conversion of nitrophenyl esters decreases with increasing chain length. The effect of various parameters such as amount of water added, temperature, and enzyme loading was studied. The optimum temperature for the hydrolysis of PNPB and PNPC was 50°C but was 55°C for PNPL, PNPM, and PNPP in ScCO₂. The reactions were also conducted in acetonitrile as the solvent, and it was found that the reactions reach equilibrium much faster in ScCO₂ than in acetonitrile. The kinetics of the hydrolysis reactions were modeled using a Ping Pong Bi Bi model.     

Kinetics of hydrolysis of procaine in aqueous and micellar media

The kinetics of alkaline hydrolysis of procaine under the pseudo–first‐order condition ([OH^?] ? [procaine]) has been carried out. N,N‐Diethylaminoethanol and p‐aminobenzoate anion were obtained as the hydrolysis product. The rate of hydrolysis was found to be linearly dependent upon [NaOH]. The addition of cationic cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DDTAB) and tetradecyltrimethylammonium bromide, and anionic sodium dodecyl sulfate (SDS) micelles inhibited the rate of hydrolysis. The maximum inhibitive effect on the reaction rate was observed for SDS micelles, whereas among the cationic surfactants, CTAB inhibited most. The variation in the rate of hydrolysis of procaine in the micellar media is attributed to the orientation of a reactive molecule to the surfactant and the binding constant of procaine with micelles. The rate of hydrolysis of procaine is negligible in DDTAB micelles. The observed results in the presence of cationic micelles were treated on the basis of the pseudophase ion exchange model. The results obtained in the presence of anionic micelles were treated by the pseudophase model, and the various kinetic parameters were determined. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 1–9, 2013     

The influence of methacryloxypropyltrimethoxysilane on the sol-gel process of TEOS

The influence of MPS on the hydrolysis and condensation process of TEOS is studied by means of hydrolysis time (t _H) and gelation time (t _G) curves. The addition of MPS to a mixture of TEOS, ethanol and water results in a substantial increase in t _G. The increase is most pronounced when adding takes place in the acid step of the sol-gel process of TEOS.In acid environment hydrolysis of MPS will be dominant compared to hydrolysis of TEOS. This results in an effective decrease of the amount of water available for the hydrolysis of TEOS. However, this decrease in water concentration cannot explain the complete effect of the addition of MPS. The hydrolysed MPS will also be incorporated in the gel network and will strongly influence the cross-linking ability. The lesser functionality of MPS compared to TEOS and the steric hindrance of the acrylate group results in a large increase in t _G.     

Reactions of Thorium Oxide Clusters with Water: The Effects of Oxygen Content

Thorium oxide has many important applications in industry. In this article, theoretical calculations have been carried out to explore the hydrolysis reactions of the ThO_n (n=1–3) clusters. The reaction mechanisms of the O-deficient ThO and the O-rich ThO₃ are compared with the stoichiometric ThO₂. The theoretical results show good agreement with the prior experiments. It is shown that the hydrolysis mainly occurred on the singlet potential surface. The overall reactions consist of two hydrolysis steps which are all favourable in energy. The effects of oxygen content on the hydrolysis are elucidated. Interestingly, among them, the peroxo group O₂²⁻ in ThO₃ is converted to the HOO− ligand, behaving like the terminal O²⁻ in the hydrolysis which is transformed into the HO− groups. In addition, natural bond orbital (NBO) analyses were employed to further understand the bonding of the pertinent species and to interpret the differences in hydrolysis.     

Enzymatic hydrolysis by Humicola lanuginosa lipase of polycaprolactone monolayers

The enzymatic hydrolysis by Humicola lanuginosa lipase (HLL) of spread insoluble monolayers of polycaprolactone with various molecular weights was studied by measuring the decrease in surface area and in surface potential, in a barostat surface balance. The interfacial hydrolysis under the action of enzymes leads to the progressive fragmentation of the polymer molecules and to the appearance at the interface of charged insoluble and small soluble products. The solubilization of the small soluble fragments was detected by measuring the decrease in surface area during hydrolysis. An independent study showed that, in contrast to poly(lactic-co-glycolic acid) (PLAGA) oligomers, this solubilization is not instantaneous. Taking into account the solubilization rates, one can determine the kinetics of enzymatic hydrolysis. The specific catalytic activity of HLL was estimated in the framework of the random-scission model and compared to those obtained for the hydrolysis of monolayers built up of PLAGA or of simple di- and triglyceride molecules. Received: 25 July 2000 Revised: 28 November 2000 Accepted: 29 November 2000     

Enzymatic Hydrolysis of Soy Protein Isolates. DSC study

The aim of this work was to analyze the possible use of differential scanning calorimetry (DSC) as a method to study the process of protein modifications during enzymatic hydrolysis. Results of the enzymatic hydrolysis of soy protein showed significant differences in the values of maximum deflection temperature (T _p), heat of reaction (ΔH), and width at half peak height (ΔT _1/2), between DSC curves corresponding to the substrate, or zerotime of hydrolysis, and those of the hydrolysates obtained by the action of cucurbita and pomiferin enzymes. DSC curve changes mentioned were explained by the use of gel-filtration chromatography, denaturing electrophoresis and surface hydrophobicity of the hydrolysis products obtained at 30 min of reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Studies on the reaction kinetics and the mechanism of hydrolysis of bis(4-nitrophenyl) phosphate (BNPP) catalyzed by oxamido-bridged dinuclear copper(II) complexes in micellar solution

Oxamido-bridged dinuclear copper(II) complexes, used as symmetric two-center catalysts for the cleavage of BNPP, were synthesized and characterized. The reaction kinetics and the mechanism of hydrolysis of BNPP catalyzed by metallomicelles, made from complex (A) or (B) and a surfactant (LSS or CTAB), were investigated. A kinetic mathematical model for BNPP cleavage was also proposed. The results showed that the reaction rate for the catalytic hydrolysis of BNPP, compared with spontaneous hydrolysis of BNPP, increased by a factor of ca. 1 × 10⁶ due to the synergistic effect of two copper ions in the complex and the local concentration effect of the micelle. The study indicates that the metallomicelle-containing oxamido-bridged dinuclear copper(II) complex may be a potential catalyst for the hydrolysis of BNPP.