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Hydrolysis Reaction (hydrolysis + reaction)
Selected AbstractsAnatase Titanium Dioxide Crystallization by a Hydrolysis Reaction of Titanium Alkoxide without AnnealingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2006Kunio Funakoshi The crystallization of anatase titanium dioxide (TiO2) was achieved by a hydrolysis reaction of titanium alkoxide without annealing. The hydrolysis reaction rates of tetraethyl orthotitanate were indicated by a function of the concentration of acetylacetone added. The degree of crystallinity of the product particles was influenced by the amounts of acetylacetone and seed crystals. Anatase TiO2 was crystallized by restraining the rapid increase in supersaturation of TiO2 and the consequent nucleation of amorphous TiO2. The degree of crystallinity of the product particles also changed with the types of seed crystals used, and was strongly influenced by the specific surface areas of the seed crystals. [source] Kinetics of Bis(p -nitrophenyl)phosphate (BNPP) Hydrolysis Reactions with Trivalent Lanthanide Complexes of N -Hydroxyethyl(ethylenediamine)- N,N,,N, -triacetate (HEDTA),EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2009C. Allen Chang Abstract Kinetic studies of hydrolysis reactions of BNPP [sodium bis(p -nitrophenyl)phosphate] with trivalent lanthanide (Ln3+) complexes of HEDTA [HEDTA = N -hydroxyethyl(ethylenediamine)- N,N,,N, -triacetate] were performed at pH 6.96,11.34 and 25 °C by a spectrophotometric method and by HPLC analysis. The reaction rates increase with increasing atomic number of lanthanide and solution pH from PrHEDTA to EuHEDTA and then decrease for heavier LnHEDTA complexes. Plots of pseudo-first-order rate constants (kobs) vs. pH could be fitted to the equation kobs = kLnL(OH)[LnL]T/{1,+,exp[,2.303(pH,,,pKh)]}, where kLnL(OH) is the rate constant for the reaction of LnHEDTA(OH), with BNPP, Kh is the hydrolysis constant of LnHEDTA, and [LnL]T is the total concentration of LnHEDTA. The pKh values obtained by the kinetic method are in the range 8.2,10.3 and are similar to those measured by potentiometric methods. At [LnL]T = 10,70 mM and pH 10.5, most of the observed pseudo-first-order rate constants could be fitted to a simple saturation kinetic model, kobs = k1K[LnHEDTA(OH),]/{1 + K[LnHEDTA(OH),]}, where K is the equilibrium constant for the formation for LnHEDTA(OH),BNPP and is in the range 2,147 M,1. The k1 values are in the range 1.12,×,10,5,2.71,×,10,3 s,1. The kobs data for TbHEDTA and HoHEDTA were fitted to a quadratic equation. It was observed that the dinuclear species are more reactive. ESI mass spectrometry confirmed that the reaction between BNPP and EuHEDTA is a simple hydrolysis but not a transesterification, presumably because the three inner-sphere coordinated water molecules are far away from the coordinated hydroxyethyl group. Hydrolysis is likely to occur by proton transfer from one inner-sphere coordinated water molecule to the deprotonated ethyl oxide group followed by nucleophilic attack of the resulting hydroxide ion on the bonded BNPP anion.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Sodium Borohydride Hydrolysis as Hydrogen Generator: Issues, State of the Art and Applicability Upstream from a Fuel CellFUEL CELLS, Issue 3 2010U. B. Demirci Abstract Today there is a consensus regarding the potential of NaBH4 as a good candidate for hydrogen storage and release via hydrolysis reaction, especially for mobile, portable and niche applications. However as gone through in the present paper two main issues, which are the most investigated throughout the open literature, still avoid NaBH4 to be competitive. The first one is water handling. The second one is the catalytic material used to accelerate the hydrolysis reaction. Both issues are objects of great attentions as it can be noticed throughout the open literature. This review presents and discusses the various strategies which were considered until now by many studies to manage water and to improve catalysts performances (reactivity and durability). Published studies show real improvements and much more efforts might lead to significant overhangs. Nevertheless, the results show that we are still far from envisaging short-term commercialisation. [source] A DFT study on the hydrolysis mechanism of NH-tautomeric antitumors of [HL][trans -RuCl4L(dmso- S)]INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2010Jin Can Chen Abstract 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 [source] ONIOM quantum chemistry study of cyclic nucleotide recognition in phosphodiesterase 5INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 12 2007Kerrie A. O'Brien Abstract Cyclic nucleotide phosphodiesterases (PDEs) are enzymes that contribute to the regulation of cyclic nucleotides in the cell by catalyzing the hydrolysis reaction of the O3,-phosphorous bond, yielding the noncyclic nucleotide as the product. The principal substrates are cyclic 3,,5,-adenosine and -guanosine monophosphate (cAMP and cGMP). PDE5, an important target of drug inhibition, is known to be highly selective for hydrolysis of cGMP. We use all-quantum hybrid calculations to accurately describe the binding interactions between PDE5 and cAMP/cGMP for the first time. The main reasons for cGMP preference in PDE5 are found to be to the fixed orientation of a conserved glutamine residue (Gln 817) together with the fixed orientation of a nonconserved glutamine residue (Gln 775). We report ONIOM(B3LYP/6-31g(d):PM3MM) binding energies, which reflect favorable guanine alignment with Gln 817 and steric crowding of adenine by Gln 775. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] The effect of water on particle size, porosity and the rate of drug release from implanted titania reservoirsJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2010Tessy Lopez Abstract The implantation of controlled drug release devices represents a new strategy in the treatment of neurodegenerative disorders. Sol,gel titania implants filled with valproic acid, have been used for this purpose to treat induced epilepsy in rats. The kinetics of the drug release depend on: (a) porosity, (b) chemical interactions between valproic acid and surface hydroxyl groups of titania, (c) particle size, and (d) particle size agglomerates. The concentration of water used in the hydrolysis reaction is an important variable in the degree of porosity, hydroxylation, and structural defects of the nanostructured titanium oxide reservoir. The titanium n -butoxide/water ratio was systematically varied during the sol,gel synthesis, while maintaining the amount of valproic acid constant. Characterization studies were performed using DTA-TGA, FTIR, Raman, TEM, SEM, BET, and in vitro release kinetic measurements. The particle agglomerate size and porosity were found to depend on the amount of water used in the sol,gel reaction. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2010 [source] Hsp90: Chaperoning signal transductionJOURNAL OF CELLULAR PHYSIOLOGY, Issue 3 2001Klaus Richter Hsp90 is an ATP dependent molecular chaperone involved in the folding and activation of an unknown number of substrate proteins. These substrate proteins include protein kinases and transcription factors. Consistent with this task, Hsp90 is an essential protein in all eucaryotes. The interaction of Hsp90 with its substrate proteins involves the transient formation of multiprotein complexes with a set of highly conserved partner proteins. The specific function of each component in the processing of substrates is still unknown. Large ATP-dependent conformational changes of Hsp90 occur during the hydrolysis reaction and these changes are thought to drive the chaperone cycle. Natural inhibitors of the ATPase activity, like geldanamycin and radicicol, block the processing of Hsp90 substrate proteins. As many of these substrates are critical elements in signal transduction, Hsp90 seems to introduce an additional level of regulation. © 2001 Wiley-Liss, Inc. [source] Improved Method for Determining Food Protein Degree of HydrolysisJOURNAL OF FOOD SCIENCE, Issue 5 2001P.M. Nielsen ABSTRACT When producing hydrolyzed proteins, it is important to determine the degree of hydrolysis (DH). The trinitro-benzene-sulfonic acid (TNBS) method is well established with regard to enzymatic hydrolysis. However, this method is laborious, cannot be used to follow a hydrolysis reaction continuously, and includes hazardous and unstable chemicals. This paper describes a method based on the reaction of primary amino groups with o-phthaldialdehyde (OPA). The conclusion is that the OPA method of analyzing the DH of protein hydrolyses is more accurate, is easier and faster to carry out, has a broader application range, and is environmentally safer than the TNBS method. [source] The sequential syntheses of [76Br]FBAU 3,,5,-dibenzoate and [76Br]FBAUJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 13 2001Chih-Hao K. Kao Abstract Thymidine analogs labeled with positron emitting radionuclides are potential proliferation markers for positron emission tomography (PET). Bromine-76 (T1/2=16.2 h) is our choice of radionuclide, because it allows for maximal DNA incorporation of the tracer. Following the literature descriptions, 76Br was produced using the 75As (3He, 2n) 76Br reaction. We then recovered 76Br from the target in the form of [76Br]NH4Br with a yield of 60±12% (n=32). Peracetic acid was used as the oxidant for electrophilic bromodestannylation to prepare [76Br]FBAU 3,,5,-dibenzoate (71.2±12.1%, RCY) and a basic hydrolysis of the dibenzoate then yielded [76Br]FBAU. The yield of the hydrolysis reaction was 53.1±9.2% when heated at 100°C for 15 min or quantitative (decay corrected) when left at room temperature overnight. The sequential synthesis of [76Br]FBAU 3,,5,-dibenzoate and [76Br]FBAU allowed us to perform a side-by-side comparison of their metabolic stabilities. While [76Br]FBAU 3,,5,-dibenzoate was hydrolyzed to [76Br]FBAU within 10 minutes by hepatocyte at 37°C, [76Br]FBAU was stable and no [76Br]Br, was released from either radiopharmaceutical. Both compounds are potential proliferation markers for PET. Copyright © 2001 John Wiley & Sons, Ltd. [source] Determination of binding sites in carboplatin-bound cytochrome c using electrospray ionization mass spectrometry and tandem mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 8 2005Gaosheng Yang Abstract Interaction of carboplatin with cytochrome c (Cyt. c) has been investigated by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). ESI-MS studies revealed that the ring-opened adducts of carboplatin with Cyt. c were formed in the stoichiometric ratio of 1 : 1 and 2 : 1 at pH 5.0 and 37 °C and in the stoichiometric ratio of 1 : 1 only at pH 7.0 and 37 °C. It was also found that Cyt. c could be cleaved by carboplatin at pH 2.5 and 50 °C. The cleaved fragments of Cyt. c were determined by ESI-MS and MS/MS analysis to be Glu66,Met80, Ac-Gly01,Met65, Glu66,Glu104, Ac-Gly01,Met80 and Ile81,Glu104. The carboplatin prefers to anchor to Met65 first, then to Met80. To further confirm the binding site of Met, AcMet-Gly was used as the model molecule to investigate its interaction with carboplatin and its hydrolysis reaction. On the basis of species detected during the reaction monitored by ESI-MS, a possible pathway of the cleavage reaction was proposed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Poly(tetramethylene ether) glycol containing acetal linkages: New PTMG-based polyol for chemically recyclable polyurethane thermoplastic elastomerJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2008Tamotsu Hashimoto To develop new chemically recyclable polyurethane elastomers, the poly(tetramethylene ether) glycol (PTMG) containing acetal linkages (PTMG-Acetal-OH) was prepared and subjected to the polyurethane synthesis with 4,4(-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BD; chain-extender). The obtained polyurethane (PTMG-Acetal-PU) shows very similar mechanical and thermal properties to those of the conventional PTMG-based thermoplastic polyurethane elastomers (PTMG-PU). The acid treatment of PTMG-Acetal-PU at room temperature caused hydrolysis reaction of their acetal units to regenerate PTMG as a degradation product. [source] Controlled polymerizations of 2-(dialkylamino)ethyl methacrylates and their block copolymers in protic solvents at ambient temperature via ATRPJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2004Baowei Mao Abstract Very well-controlled polymerizations of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and 2-(diethylamino)ethyl methacrylate (DEAEMA) in aqueous and methanolic solutions via atom transfer radical polymerization (ATRP) at ambient temperature were demonstrated. Poly(DMAEMA) and poly(DEAEMA) of low polydispersity index (PDI) of ,1.07 were obtained using the p -toluenesulfonyl chloride/CuCl/1,1,4,7,10,10-hexamethyl-triethylenetetramine (p -TsCl/CuCl/HMTETA) system. Excellent control of polymerization was achieved even in pure methanol. This is in contrast with the very poor control of DMAEMA ATRP in methanol reported previously using a different intiator/catalyst/ligand system. The initiator p -TsCl underwent hydrolysis reaction in aqueous methanolic solutions with a second-order rate constant of 6.1 × 10,4 dm3 mol,1 s,1 at 25 °C. Both poly(DMAEMA) and poly(DEAEMA) retained almost full chlorine-functionization at the chain ends. Well-defined block copolymers of DEAEMA and DMAEMA were successfully obtained by starting with either macroinitiators of DEAEMA or DMAEMA. Other well-defined diblock copolymers could be prepared using these macroinitiators. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5161,5169, 2004 [source] Anatase Titanium Dioxide Crystallization by a Hydrolysis Reaction of Titanium Alkoxide without AnnealingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2006Kunio Funakoshi The crystallization of anatase titanium dioxide (TiO2) was achieved by a hydrolysis reaction of titanium alkoxide without annealing. The hydrolysis reaction rates of tetraethyl orthotitanate were indicated by a function of the concentration of acetylacetone added. The degree of crystallinity of the product particles was influenced by the amounts of acetylacetone and seed crystals. Anatase TiO2 was crystallized by restraining the rapid increase in supersaturation of TiO2 and the consequent nucleation of amorphous TiO2. The degree of crystallinity of the product particles also changed with the types of seed crystals used, and was strongly influenced by the specific surface areas of the seed crystals. [source] New Process for the Preparation of Monodispersed, Spherical Silica ParticlesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2002Ki Do Kim A new method is presented for preparing highly monodispersed silica particles using a two-stage semibatch/batch hydrolysis reaction of Si(OC2H5)4. The slower rate of hydrolysis of the tetraethylorthosilicate (TEOS) that occurred during the semibatch process resulted in larger silica particles with a higher yield and narrower size distribution. This was in direct contrast to the batch process. In addition, the ability of four different mixed processes to produce silica particles with good packing density, narrower particle-size distribution, and higher yield were evaluated. These were batch/batch (B-B), batch/semibatch (B-S), semibatch/batch (S-B), and semibatch/semibatch (S-S) processes. The S-S system produced the largest particles with the highest yields. The size of the silica particles obtained by the S-B method decreased with increasing reaction time, while the particles obtained by the B-S process had the best particle-size distribution and packing density. In conclusion, a mixed batch/semibatch system was the best way to produce an extremely narrow particle-size distribution and a good packing density. [source] Polymerization compounding of HDPE/Kevlar composites.POLYMER COMPOSITES, Issue 2 2006The aim of this work is to perform the polymerization compounding to improve the properties of Kevlar/PE composites. The approach consists in involving the surface of a reinforcement in a polymerization process of a polymer to be used either as a matrix in the final composite or as a special surface treatment to enhance solid/polymer interface properties in the composite. The polymerization compounding process is illustrated here with the polyaramid fibers as reinforcements and polyethylene as a matrix. The number of active sites on the fiber surface, initially insufficient to anchor the catalyst, were increased by a hydrolysis reaction prior to the polymerization. The anchored catalyst was subsequently used to conduct the Ziegler,Natta polymerization reaction of ethylene. The modified fibers were incorporated into the polyethylene resin to produce composites at fiber concentrations as high as 15 wt%. The morphology of the fibers and the composites was tested using electron microscopy. Finally, the mechanical properties of the composites (in impact and tensile tests) were measured to characterize the properties of model composites. Polym. Compos. 27:129,137, 2006. © 2006 Society of Plastics Engineers. [source] Synthesis and properties of room temperature curable trimethoxysilane-terminated polyurethane and their dispersionsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 8 2007Sankaraiah Subramani Abstract The purpose of this research is to study the synthesis and characterization of stable aqueous dispersions of externally chain extended polyurethane/urea compositions terminated by hydrolyzable or hydrolyzed trialkoxysilane groups incorporated through secondary amino groups. These dispersions with excellent storage stability are substantially free from organic solvents which cure to water and solvent resistant, tough, scratch resistant, preferably light stable (non-yellowing) silylated polyurethane (SPU) films. The films were characterized by FT-IR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), tensile strength and water contact angle measurements, nanoindentation, gel content, water and xylene swellability tests. The properties of the films were discussed and correlated in detail by changing length of soft segment, diisocyanates, NCO/OH ratio and chain extender, ethylenediamine (EDA). From the results, it was found that the particle size and viscosity are lower whereas the gel content and thermal stability are higher for SPUs. Modulus, hardness and tensile properties of SPU films are superior compared to EDA-PU film. Higher water contact angle and residual weight percentage of SPU films confirm silylation of PU by [3-(phenylamino)propyl]trimethoxysilane (PAPTMS). Increase in NCO/OH ratios consumes more quantity of PAPTMS which makes PU with superior mechanical properties. Higher PAPTMS content in SPU results in effective crosslinking of the functional silanol groups formed by hydrolysis reaction of trimethoxysilane groups. Overall, SPUs synthesized at 1.4 NCO/OH ratio using Poly-(oxytetramethylene)glycol (PTMG)-2000 and isophorone diisocyanate (or) toluene-2,4-diisocyanate have excellent properties compared to SPUs prepared using PTMG-1000 and at 1.2 and 1.6 NCO/OH ratios. SPUs prepared at 1.6 NCO/OH ratio are brittle due to higher crosslinking density. In addition, the crosslinking density of the films can be modified through silane end-group modification to produce SPUs with a wide range of physical properties. Copyright © 2007 John Wiley & Sons, Ltd. [source] Re-examining the role of Lys67 in class C ,-lactamase catalysisPROTEIN SCIENCE, Issue 3 2009Yu Chen Abstract Lys67 is essential for the hydrolysis reaction mediated by class C ,-lactamases. Its exact catalytic role lies at the center of several different proposed reaction mechanisms, particularly for the deacylation step, and has been intensely debated. Whereas a conjugate base hypothesis postulates that a neutral Lys67 and Tyr150 act together to deprotonate the deacylating water, previous experiments on the K67R mutants of class C ,-lactamases suggested that the role of Lys67 in deacylation is mainly electrostatic, with only a 2- to 3-fold decrease in the rate of the mutant vs the wild type enzyme. Using the Class C ,-lactamase AmpC, we have reinvestigated the activity of this K67R mutant enzyme, using biochemical and structural studies. Both the rates of acylation and deacylation were affected in the AmpC K67R mutant, with a 61-fold decrease in kcat, the deacylation rate. We have determined the structure of the K67R mutant by X-ray crystallography both in apo and transition state-analog complexed forms, and observed only minimal conformational changes in the catalytic residues relative to the wild type. These results suggest that the arginine side chain is unable to play the same catalytic role as Lys67 in either the acylation or deacylation reactions catalyzed by AmpC. Therefore, the activity of this mutant can not be used to discredit the conjugate base hypothesis as previously concluded, although the reaction catalyzed by the K67R mutant itself likely proceeds by an alternative mechanism. Indeed, a manifold of mechanisms may contribute to hydrolysis in class C ,-lactamases, depending on the enzyme (wt or mutant) and the substrate, explaining why different mutants and substrates seem to support different pathways. For the WT enzyme itself, the conjugate base mechanism may be well favored. [source] Microwave-assisted specific chemical digestion for rapid protein identificationPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 2 2006Lin Hua Abstract We have developed a rapid microwave-assisted protein digestion technique based on classic acid hydrolysis reaction with 2% formic acid solution. In this mild chemical environment, proteins are hydrolyzed to peptides, which can be directly analyzed by MALDI-MS or ESI-MS without prior sample purification. Dilute formic acid cleaves proteins specifically at the C-terminal of aspartyl (Asp) residues within 10,min of exposure to microwave irradiation. By adjusting the irradiation time, we found that the extent of protein fragmentation can be controlled, as shown by the single fragmentation of myoglobin at the C-terminal of any of the Asp residues. The efficacy and simplicity of this technique for protein identification are demonstrated by the peptide mass maps of in-gel digested myoglobin and BSA, as well as proteins isolated from Escherichia coli,K12 cells. [source] A three-dimensional AlIII/NaI metal,organic framework resulting from dimethylformamide hydrolysisACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009Agnieszka Plutecka The three-dimensional metal,organic framework poly[bis(dimethylammonium) [hexa-,2 -formato-,12O:O,-aluminium(III)sodium(I)]], {(C6H8N)2[AlNa(HCOO)6]}n, was obtained serendipitously and has been characterized by X-ray diffraction. The product has arisen as a result of a hydrolysis reaction of dimethylformamide (DMF) and contains dimethylammonium (DMA) cations included in structural voids formed by a three-dimensional [AlNa(HCOO)6], network. This study provides evidence that, in the presence of traces of aluminium, DMF stored in a glass bottle can be hydrolysed to formate and dimethylamine with simultaneous extraction of Na+ cations from the glass. It also demonstrates that care must be taken regarding the metal and water content when DMF is not freshly distilled, since the hydrolysis of amide can occur. [source] Structure of aminopeptidase N from Escherichia coli complexed with the transition-state analogue aminophosphinic inhibitor PL250ACTA CRYSTALLOGRAPHICA SECTION D, Issue 8 2009Marie-Claude Fournié-Zaluski Aminopeptidase N (APN; EC 3.4.11.2) purified from Escherichia coli has been crystallized with the optically pure aminophosphinic inhibitor PL250, H3N+ -CH(CH3)-P(O)(OH)-CH2 -CH(CH2Ph)-CONH-CH(CH2Ph)CO2,, which mimics the transition state of the hydrolysis reaction. PL250 inhibits APN with a Ki of 1.5,2.2,nM and its three-dimensional structure in complex with E. coli APN showed its interaction with the S1, S,1 and S,2 subsites of the catalytic site. In this structure, the Zn ion was shown to be pentacoordinated by His297, His301 and Glu320 of APN and the two O atoms of the phosphinic moiety of PL250. One of these O atoms is also involved in a hydrogen bond to Tyr381, supporting the proposed role of this amino acid in the stabilization of the transition state of the enzymatic process. The strength of the phosphinic zinc binding and the occupancy of the S,2 subsite account for the 100-fold increase in affinity of PL250 compared with the dipeptide-derived inhibitor bestatin (Ki = 4.1 × 10,6,M). Accordingly, the removal of the C-terminal phenylalanine of PL250 resulted in a large decrease in affinity (Ki = 2.17 × 10,7,M). Furthermore, it was observed that the C-terminal carboxyl group of the inhibitor makes no direct interactions with the amino acids of the APN active site. Interestingly, PL250 exhibits the same inhibitory potency for E. coli APN and for mammalian enzymes, suggesting that the structure of the complex could be used as a template for the rational design of various human APN inhibitors needed to study the role of this aminopeptidase in various pathologies. [source] Enhancement of cellulose saccharification kinetics using an ionic liquid pretreatment stepBIOTECHNOLOGY & BIOENGINEERING, Issue 5 2006Anantharam P. Dadi Abstract Hydrolysis of cellulose to glucose in aqueous media catalyzed by the cellulase enzyme system suffers from slow reaction rates due in large part to the highly crystalline structure of cellulose and inaccessibility of enzyme adsorption sites. In this study, an attempt was made to disrupt the cellulose structure using the ionic liquid (IL), 1- n -butyl-3-methylimidazolium chloride, in a cellulose regeneration strategy which accelerated the subsequent hydrolysis reaction. ILs are a new class of non-volatile solvents that exhibit unique solvating properties. They can be tuned to dissolve a wide variety of compounds including cellulose. Because of their extremely low volatility, ILs are expected to have minimal environmental impact on air quality compared to most other volatile solvent systems. The initial enzymatic hydrolysis rates were approximately 50-fold higher for regenerated cellulose as compared to untreated cellulose (Avicel PH-101) as measured by a soluble reducing sugar assay. © 2006 Wiley Periodicals, Inc. [source] Development of New and Selective Trypanosoma cruzi trans-Sialidase Inhibitors from Sulfonamide Chalcones and Their DerivativesCHEMBIOCHEM, Issue 15 2009Jin Hyo Kim Abstract A series of sulfonamide-containing hydroxylated chalcone (4,7) and quinolinone (8, 9) derivatives was synthesised and tested for inhibition of the trans-sialidase from Trypanosoma cruzi (TcTS). IC50 values for these inhibitors ranged from 0.6 to 7.3 ,M, with the dihydroxylated (catechol) derivatives being the tightest binders. Full kinetic analyses of inhibition were performed for these catechol derivatives, both for the transglycosylation reaction in the presence of lactose and for the hydrolysis reaction in its absence. Competitive inhibition was seen in each case with Ki values for 5, 7 and 9 of 2.0, 2.2 and 0.2 ,M, respectively, in the absence of lactose, and 4.6, 3.7 and 0.4 ,M in its presence. None of the compounds tested showed any significant inhibition of the human sialidase Neu2, at concentrations up to 200 ,M. [source] The Molecular Mechanism of Tropospheric Nitrous Acid Production on Mineral Dust SurfacesCHEMPHYSCHEM, Issue 10 2008R. Joel Gustafsson Dr. Tropospheric model: The formation of tropospheric nitrous acid on mineral surfaces does not involve an N2O4 intermediate. Well-defined surface conditions achievable under ultra-high vacuum are utilised to show that the hydrolysis reaction involves dissociated water (see figure). [source] Kinetics of Bis(p -nitrophenyl)phosphate (BNPP) Hydrolysis Reactions with Trivalent Lanthanide Complexes of N -Hydroxyethyl(ethylenediamine)- N,N,,N, -triacetate (HEDTA),EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2009C. Allen Chang Abstract Kinetic studies of hydrolysis reactions of BNPP [sodium bis(p -nitrophenyl)phosphate] with trivalent lanthanide (Ln3+) complexes of HEDTA [HEDTA = N -hydroxyethyl(ethylenediamine)- N,N,,N, -triacetate] were performed at pH 6.96,11.34 and 25 °C by a spectrophotometric method and by HPLC analysis. The reaction rates increase with increasing atomic number of lanthanide and solution pH from PrHEDTA to EuHEDTA and then decrease for heavier LnHEDTA complexes. Plots of pseudo-first-order rate constants (kobs) vs. pH could be fitted to the equation kobs = kLnL(OH)[LnL]T/{1,+,exp[,2.303(pH,,,pKh)]}, where kLnL(OH) is the rate constant for the reaction of LnHEDTA(OH), with BNPP, Kh is the hydrolysis constant of LnHEDTA, and [LnL]T is the total concentration of LnHEDTA. The pKh values obtained by the kinetic method are in the range 8.2,10.3 and are similar to those measured by potentiometric methods. At [LnL]T = 10,70 mM and pH 10.5, most of the observed pseudo-first-order rate constants could be fitted to a simple saturation kinetic model, kobs = k1K[LnHEDTA(OH),]/{1 + K[LnHEDTA(OH),]}, where K is the equilibrium constant for the formation for LnHEDTA(OH),BNPP and is in the range 2,147 M,1. The k1 values are in the range 1.12,×,10,5,2.71,×,10,3 s,1. The kobs data for TbHEDTA and HoHEDTA were fitted to a quadratic equation. It was observed that the dinuclear species are more reactive. ESI mass spectrometry confirmed that the reaction between BNPP and EuHEDTA is a simple hydrolysis but not a transesterification, presumably because the three inner-sphere coordinated water molecules are far away from the coordinated hydroxyethyl group. Hydrolysis is likely to occur by proton transfer from one inner-sphere coordinated water molecule to the deprotonated ethyl oxide group followed by nucleophilic attack of the resulting hydroxide ion on the bonded BNPP anion.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Stability studies of oxazolidine-based compounds using 1H NMR spectroscopyJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2010Gerard P. Moloney Abstract A series of oxazolidine-based compounds with a variety of substituents in positions 2 and 3 was synthesized and their stability studied. Ring opened intermediates formed on addition of limiting amounts of D2O to oxazolidine solutions, as observed by NMR. As the hydrolysis reactions proceeded, a series of novel dimeric ,-amino alcohol compounds formed via an internal reaction between ephedrine and the ring opened intermediates. 2-Phenyl substituted oxazolidine compounds containing electron withdrawing nitro substituents were more rapidly hydrolyzed than the unsubstituted derivative and methoxy substituted compounds, with the nitro substituents appearing to stabilize the ring opened intermediates. Two oxazolidine derivatives, with a methyl and proton at position 2, were found to be more stable to oxazolidine hydrolysis than the 2-phenyl substituted compounds. Oxazolidines incorporating phenyl substituents at position 3 were synthesized and found to be less stable than those incorporating a methyl substituent at position 3. These fundamental structure,activity relationships may be useful when choosing oxazolidine derivatives as synthetic intermediates and as prodrugs for the delivery of compounds containing either ,-amino alcohol or aldehyde components. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:3362,3371, 2010 [source] Computational chemistry study of the environmentally important acid-catalyzed hydrolysis of atrazine and related 2-chloro- s -triazinesPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 8 2002Phillip Sawunyama Abstract Many chlorine-containing pesticides, for example 2-chloro- s -triazines, are of great concern both environmentally and toxicologically. As a result, ascertaining or predicting the fate and transport of these compounds in soils and water is of current interest. Transformation pathways for 2-chloro- s -triazines in the environment include dealkylation, dechlorination (hydrolysis), and ring cleavage. This study explored the feasibility of using computational chemistry, specifically the hybrid density functional theory method, B3LYP, to predict hydrolysis trends of atrazine (2-chloro- N4 -ethyl- N6 -isopropyl-1,3,5-triazine-2,4-diamine) and related 2-chloro- s -triazines to the corresponding 2-hydroxy- s -triazines. Gas-phase energetics are described on the basis of calculations performed at the B3LYP/6-311++G(d,p)//B3LYP/6-31G* level of theory. Calculated free energies of hydrolysis (,hG298) are nearly the same for simazine (2-chloro- N4,N6 -diethyl-1,3,5-triazine-2,4-diamine), atrazine, and propazine (2-chloro- N4,N6 -di-isopropyl-1,3,5-triazine-2,4-diamine), suggesting that hydrolysis is not significantly affected by the side-chain amine-nitrogen alkyl substituents. High-energy barriers also suggest that the reactions are not likely to be observed in the gas phase. Aqueous solvation effects were examined by means of self-consistent reaction field methods (SCRF). Molecular structures were optimized at the B3LYP/6-31G* level using the Onsager model, and solvation energies were calculated at the B3LYP/6-311++G(d,p) level using the isodensity surface polarizable continuum model (IPCM). Although the extent of solvent stabilization was greater for cationic species than neutral ones, the full extent of solvation is underestimated, especially for the transition state structures. As a consequence, the calculated hydrolysis barrier for protonated atrazine is exaggerated compared with the experimentally determined one. Overall, the hydrolysis reactions follow a concerted nucleophilic aromatic substitution (SNAr) pathway. Published in 2002 for SCI by John Wiley & Sons, Ltd [source] High-performance liquid chromatography/mass spectrometric and proton nuclear magnetic resonance spectroscopic studies of the transacylation and hydrolysis of the acyl glucuronides of a series of phenylacetic acids in buffer and human plasmaRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 20 2010Elin S. Karlsson The use of high-performance liquid chromatography/mass spectrometry (HPLC/MS) and proton nuclear magnetic resonance (1H NMR) spectroscopy for the kinetic analysis of acyl glucuronide (AG) isomerisation and hydrolysis of the 1-,- O -acyl glucuronides (1-,- O -AG) of phenylacetic acid, (R)- and (S)-,-methylphenylacetic acid and ,,,-dimethylphenylacetic acid is described and compared. Each AG was incubated in both aqueous buffer, at pH 7.4, and control human plasma at 37°C. Aliquots of these incubations, taken throughout the reaction time-course, were analysed by HPLC/MS and 1H NMR spectroscopy. In buffer, transacylation reactions predominated, with relatively little hydrolysis to the free aglycone observed. In human plasma incubations the calculated rates of reaction were much faster than for buffer and, in contrast to the observations in buffer, hydrolysis to the free aglycone was a significant contributor to the overall reaction. A diagnostic analytical methodology based on differential mass spectrometric fragmentation of 1-, -O- AGs compared to the 2-, 3- and 4-positional isomers, which enables selective determination of the former, was confirmed and applied. These findings show that HPLC/MS offers a viable alternative to the more commonly used NMR spectroscopic approach for the determination of the transacylation and hydrolysis reactions of these AGs, with the major advantage of having the capability to do so in a complex biological matrix such as plasma. Copyright © 2010 John Wiley & Sons, Ltd. [source] "Enzyme Test Bench," a high-throughput enzyme characterization technique including the long-term stabilityBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2009Kirill Rachinskiy Abstract A new high throughput technique for enzyme characterization with specific attention to the long term stability, called "Enzyme Test Bench," is presented. The concept of the Enzyme Test Bench consists of short term enzyme tests in 96-well microtiter plates under partly extreme conditions to predict the enzyme long term stability under moderate conditions. The technique is based on the mathematical modeling of temperature dependent enzyme activation and deactivation. Adapting the temperature profiles in sequential experiments by optimal non-linear experimental design, the long term deactivation effects can be purposefully accelerated and detected within hours. During the experiment the enzyme activity is measured online to estimate the model parameters from the obtained data. Thus, the enzyme activity and long term stability can be calculated as a function of temperature. The engineered instrumentation provides for simultaneous automated assaying by fluorescent measurements, mixing and homogenous temperature control in the range of 10,85,±,0.5°C. A universal fluorescent assay for online acquisition of ester hydrolysis reactions by pH-shift is developed and established. The developed instrumentation and assay are applied to characterize two esterases. The results of the characterization, carried out in microtiter plates applying short term experiments of hours, are in good agreement with the results of long term experiments at different temperatures in 1 L stirred tank reactors of a week. Thus, the new technique allows for both: the enzyme screening with regard to the long term stability and the choice of the optimal process temperature regarding such process parameters as turn over number, space time yield or optimal process duration. The comparison of the temperature dependent behavior of both characterized enzymes clearly demonstrates that the frequently applied estimation of long term stability at moderate temperatures by simple activity measurements after exposing the enzymes to elevated temperatures may lead to suboptimal enzyme selection. Thus, temperature dependent enzyme characterization is essential in primary screening to predict its long term behavior. Biotechnol. Bioeng. 2009;103: 305,322. © 2008 Wiley Periodicals, Inc. [source] Redirecting the inactivation pathway of penicillin amidase and increasing amoxicillin production via a thermophilic molecular chaperoneBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2009Lisa M. Bergeron Abstract We have previously shown that a single-subunit thermosome from Methanocaldococcus jannaschii (rTHS) can stabilize enzymes in semi-aqueous media (Bergeron et al., 2008b). In the present study, rTHS was used to stabilize penicillin amidase (PGA) in methanol,water mixtures. Including methanol in the reaction medium for amoxicillin synthesis can suppress unwanted hydrolysis reactions but inactivate PGA. Inactivation and reactivation pathways proposed for PGA illustrate the predictability of enzyme stabilization by rTHS in co-solvents. Calcium was necessary for reversible dissociation of the two PGA subunits in methanol,water and the presence of calcium resulted in an enhancement of chaperone-assisted stabilization. rTHS also acted as a stabilizer in the enzymatic synthesis of the ,-lactam antibiotic amoxicillin. rTHS stabilized PGA, increasing its half-life in 35% methanol by fivefold at 37°C. Stabilization by rTHS was enhanced but did not require the presence of ATP. Including rTHS in fed-batch reactions performed in methanol,water resulted in nearly 4 times more amoxicillin than when the reaction was run without rTHS, and over threefold higher selectivity towards amoxicillin synthesis compared to aqueous conditions without rTHS. The thermosome and other thermophilic chaperones may thus be generally useful for stabilizing enzymes in their soluble form and expanding the range of conditions suitable for biocatalysis. Biotechnol. Bioeng. 2009;102: 417,424. © 2008 Wiley Periodicals, Inc. [source] The effect of ethanol on the kinetics of lipase-mediated enantioselective esterification of 4-methyloctanoic acid and the hydrolysis of its ethyl esterBIOTECHNOLOGY & BIOENGINEERING, Issue 3 2001Nicole W. J. T. Heinsman Abstract The Novozym 435® catalyzed esterification and hydrolysis reactions of 4-methyloctanoic acid (ethyl ester) were investigated. In both the hydrolysis and esterification reactions, the increase of ethanol concentration led to an increase in enantiomeric ratio (E). For hydrolysis of the ethyl ester, the E -value increased from 5.5 [0% (v/v) EtOH] up to 12 [20% (v/v) EtOH]. In case of esterification, the E -value was already 16 [14% (v/v) EtOH] and rose to 57 [73% (v/v) EtOH]. When combining these results of esterification and hydrolysis, an enantiomeric ratio of 350 can be estimated for the sequential kinetic resolution of 4-methyloctanoic acid. In this way, enantiopure 4-methyloctanoic acid could be obtained after two consecutive reaction steps. © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 76: 193,199, 2001. [source] | |||||||||||||||||||||||||