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Hydrolysis
Kinds of Hydrolysis Terms modified by Hydrolysis Selected AbstractsHYDROLYSIS OF ISOFLAVONE GLYCOSIDES IN SOY MILK BY ,-GALACTOSIDASE AND ,-GLUCOSIDASEJOURNAL OF FOOD BIOCHEMISTRY, Issue 1 2009THUY T. PHAM ABSTRACT The objective of this study was to assess the potential of pure ,-galactosidase and ,-glucosidase for hydrolyzing isoflavone glycosides to aglycones in soy milk. Both pure ,-galactosidase and ,-glucosidase were added at various concentrations (0.5, 1.0, 2.0 and 4.0 U/mL) to soy milk made from 4% soy protein isolate and incubated at 37C for up to 240 min. Isoflavones were quantified using high-performance liquid chromatography. The isoflavone contents of soy milk before and after autoclaving were also compared. ,-Glucosidase and ,-galactosidase were both able to hydrolyze the ,-glucosidic linkages in isoflavone glycosides. A range of 43.3 to 77.2% of the total isoflavone glycosides was hydrolyzed at various ,-galactosidase concentrations. The ,-glucosidase hydrolyzed isoflavone glycosides more efficiently than ,-galactosidase. At the most diluted ,-glucosidase concentration (0.5 U/mL), 86.6% of isoflavone glycosides were hydrolyzed to aglycones at 240 min. PRACTICAL APPLICATIONS Isoflavone glycosides, which are mainly found in the bean family, are the inactive forms of isoflavones. However, aglycones, which are the nonsugar component of a glycoside molecule that results from hydrolysis of the isoflavone glycosides, are the biologically active forms. Because of their similarity to female hormone, they are considered a "natural way" to relieve the menopausal symptoms as they prevent certain cancers and improve bone health. Only a small amount of the total isoflavones, however, exists in the aglycone forms in nature. A novel method to produce aglycones from natural isoflavones is highly important. ,-Glucosidase has been claimed to be the only enzyme which is able to hydrolyze isoflavone glycosides to aglycones. However, other enzymes could hydrolyze isoflavone glycosides more efficiently and could be easier to produce. This paper investigates the ability of ,-galactosidase to biotransform isoflavone glycosides to aglycones, as the source of the enzyme is abundant. [source] OPTIMIZATION OF PERMEABILIZATION PROCESS FOR LACTOSE HYDROLYSIS IN WHEY USING RESPONSE SURFACE METHODOLOGYJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2009GURPREET KAUR ABSTRACT To overcome the permeability barrier and prepare whole cell biocatalysts with high activities, permeabilization of Kluyveromyces marxianus var. lactis NCIM 3566 in relation to, -galactosidase activity was optimized using cetyltrimethylammonium bromide (CTAB) as permeabilizing agent. Permeabilized whole cells can be advantageous over pure enzyme preparations in terms of cost-effectiveness and increased stability maintained by the intracellular environment. Response surface methodology (RSM) was applied to optimize concentration of CTAB, temperature and the treatment time for maximum permeabilization of yeast cells. The optimum operating conditions for permeabilization process to achieve maximum enzyme activity obtained by RSM were 0.06% (w/v) CTAB concentration, 28C temperature and process duration of 14 min. At these conditions of process variables, the maximum value of enzyme activity was found to be 1,334 IU/g. The permeabilized yeast cells were highly effective and resulted in 90.5% lactose hydrolysis in whey. PRACTICAL APPLICATION , -Galactosidase is one of the most promising enzymes, which has several applications in the food, fermentation and dairy industry. However, the industrial applications of , -galactosidase have been hampered by the costs involved in downstream processing. The present investigation was focused on developing the low-cost technology for lactose hydrolysis based on permeabilization process. Disposal of lactose in whey and whey permeates is one of the most significant problems with regard to economics and environmental impact faced by the dairy industries. Keeping this in view, lactose hydrolysis in whey has been successfully performed using permeabilized Kluyveromyces marxianus cells. Hydrolysis of lactose using , -galactosidase converts whey into a potentially very useful food ingredient, which has immense applications in food industries. Its use has increased significantly in recent years, mainly in the dairy products and in digestive preparations. Lactose hydrolysis causes several potential changes in the manufacture and marketing of dairy products, including increased solubility, sweetness and broader fermentation possibilities. [source] ENZYMATIC HYDROLYSIS OF SOYBEAN FOR SOLVENT AND MECHANICAL OIL EXTRACTIONJOURNAL OF FOOD PROCESS ENGINEERING, Issue 4 2000PRAVEEN C. BARGALE ABSTRACT Due to inefficient extractability of its low oil content, soybeans are often bypassed in village-scale processing. Soygrits, flakes, and expanded collets were hydrolyzed by proteases, cellulases, and pectinases before oil extraction by solvent and static mechanical pressure. Driselase with multi-enzyme activity and two proteases improved solvent extraction rates but only Driselase enhanced mechanical pressing. Up to 58% of seed oil was pressed from enzyme-hydrolyzed flakes but 88% was pressed from Driselase-treated collets. Either pretreatment is a feasible adjunct to mechanical pressing in small batch operations. [source] Complex Formation in the Region of Metal Hydrolysis and M(OH)2 Precipitation.ELECTROANALYSIS, Issue 7 2006(AMPSO)x, (OH)y, (OH)y Systems, A Glass Electrode Potentiometric, Polarographic Study of Cd Abstract The interaction between cadmium or zinc and AMPSO was investigated by DCP and GEP, at fixed total ligand to total metal concentration ratios and various pH values, at 25.0,°C and 0.1,M KNO3 ionic strength. For Cd,(AMPSO)x,(OH)y system, CdL and CdL(OH) species, were identified, with stability constants values set to (as log,,): 2.1±0.1 and 6.2±0.2, respectively. For Zn,(AMPSO)x,(OH)y system, the proposed final model with stability constants set to (as log,,) is: ZnL=2.5±0.1 and ZnL(OH)2=12.9±0.2. For both systems, the fact that AMPSO deprotonation occurs in the metal hydrolysis and M(OH)2 precipitation and the complexes formed are not too strong added a real challenge to data interpretation. [source] Electrophoretically mediated microanalysis for the evaluation of interspecies variation in cholinesterase metabolismELECTROPHORESIS, Issue 14 2010Joana Moura Abstract This study describes an electrophoretically mediated microanalysis method, suitable for the preclinical evaluation of the hydrolysis of ester drugs by the serum of different animals and for further characterization of human,animal correlation. Dog, cat, cow, horse, sheep, rat and human serum were diluted (25%) in the appropriate buffer and replaced the enzyme solution usually used in electrophoretically mediated microanalysis methods for the study of enzyme kinetics. They were then compared in terms of the ability to hydrolyze acetylthiocholine and butyrylthiocholine (0.25,mM) by in-capillary reaction. Human serum afforded the highest conversion rates (52% butyryltiocholine and 34% acetylthiocholine) followed by horse (31 and 35%), dog (26 and 24%), cat (22 and 14%), rat (11 and 15%) and sheep (8 and 8%). Hydrolysis by bovine serum was negligible. The method is fast (under 8,min including rinsing steps), sensitive (under 25,,M substrate could be quantified) and repeatable (RSD,2%), only requiring minute amounts of sample. [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] Anion-Directed Template Synthesis and Hydrolysis of Mono-Condensed Schiff Base of 1,3-Pentanediamine and o -Hydroxyacetophenone in NiII and CuII ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2008Pampa Mukherjee Abstract Bis(o -hydroxyacetophenone)nickel(II) dihydrate, on reaction with 1,3-pentanediamine, yields a bis-chelate complex [NiL2]·2H2O (1) of mono-condensed tridentate Schiff baseligand HL {2-[1-(3-aminopentylimino)ethyl]phenol}. The Schiff base has been freed from the complex by precipitating the NiII as a dimethylglyoximato complex. HL reacts smoothly with Ni(SCN)2·4H2O furnishing the complex [NiL(NCS)] (2) and with CuCl2·2H2O in the presence of NaN3 or NH4SCN producing [CuL(N3)]2 (3) or [CuL(NCS)] (4). On the other hand, upon reaction with Cu(ClO4)2·6H2O and Cu(NO3)2·3H2O, the Schiff base undergoes hydrolysis to yield ternary complexes [Cu(hap)(pn)(H2O)]ClO4 (5) and [Cu(hap)(pn)(H2O)]NO3 (6), respectively (Hhap = o -hydroxyacetophenone and pn = 1,3-pentanediamine). The ligand HL undergoes hydrolysis also on reaction with Ni(ClO4)2·6H2O or Ni(NO3)2·6H2O to yield [Ni(hap)2] (7). The structures of the complexes 2, 3, 5, 6, and 7 have been confirmed by single-crystal X-ray analysis. In complex 2, NiII possesses square-planar geometry, being coordinated by the tridentate mono-negative Schiff base, L and the isothiocyanate group. The coordination environment around CuII in complex 3 is very similar to that in complex 2 but here two units are joined together by end-on, axial-equatorial azide bridges to result in a dimer in which the geometry around CuII is square pyramidal. In both 5 and 6, the CuII atoms display the square-pyramidal environment; the equatorial sites being coordinated by the two amine groups of 1,3-pentanediamine and two oxygen atoms of o -hydroxyacetophenone. The axial site is coordinated by a water molecule. Complex 7 is a square-planar complex with the Ni atom bonded to four oxygen atoms from two hap moieties. The mononuclear units of 2 and dinuclear units of 3 are linked by strong hydrogen bonds to form a one-dimensional network. The mononuclear units of 5 and 6 are joined together to form a dimer by very strong hydrogen bonds through the coordinated water molecule. These dimers are further involved in hydrogen bonding with the respective counteranions to form 2-D net-like open frameworks. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Dinuclear Titanium(IV) Complexes Bearing Phenoxide-Tethered N-Heterocyclic Carbene Ligands with cisoid Conformation through Control of HydrolysisEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 30 2007Dao Zhang Abstract In situ generated N-heterocyclic carbene salt derivative Na2(L) of 1,3-bis(4,6-di- tert -butyl-2-hydroxybenzyl)imidazolium bromide, [H3(L)]Br, reacted with 1 equiv. of TiBr4 at ,78 °C to give a titanium complex of the composition [(L)TiBr2(thf)] (1), while the reaction in a 2:1 ratio under the same conditions afforded bisligand titanium complex [(L)2Ti] (2). Two oxygen-bridged titanium dimers, {[(L)TiBr]2(,-O)} (4) and {[(L)Ti(,-O)]2} (5), were obtained by control of hydrolysis of 1 and [(L)Ti(CH2Ph)2] (3) in tetrahydrofuran and diethyl ether. The molecular structures of 2, 4, and 5 have been confirmed by X-ray single-crystal analysis. The phenoxide-functionalized NHC ligand adopts transoid conformation in mononuclear complex 2 but rare cisoid conformation in dinuclear complexes 4 and 5. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Transition Metal-Assisted Hydrolysis of Pyrazole-Appended Organooxotin Carboxylates Accompanied by Ligand TransferEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2007Vadapalli Chandrasekhar Abstract The reaction of the potentially multi-site coordination ligands [{nBu2SnO2CL}2O]2 (1), [{nBu2SnO2CL,}2O]2 (2), [nBuSn(O)O2CL]6 (3), and [nBuSn(O)O2CL,]6 (4), (L = (Pz)2CH-); L, = (3,5-Me2Pz)2CH-; Pz = pyrazolyl) with hydrated metal salts leads to the hydrolysis of the organotin carboxylates accompanied by the formation of insoluble organotinoxide/hydroxides and metal complexes. The in situ generated LCOO and L,COO ligands bind to the metal ions. The complexes [Cu(LCOO)2(NO3)2(nBu2Sn((H2O)2)]n[Cu(LCOO)2] (5), [Mg(L,COO)2] (6), [Cu(LCOO)2] (7), and [{(Cu(L,COO)2(Cu(MeOH))3}{ClO4}2]n (8) were isolated and structurally characterized. The solid-state structure of 5 reveals that two discrete molecules are present in the same asymmetric unit; a heterobimetallic coordination polymer, [Cu(LCOO)2(NO3)2(nBu2Sn((H2O)2)]n and a discrete coordination complex, [Cu(LCOO)2]. The cationic portion of the heterobimetallic compound contains alternate six-coordinate SnIV and CuII centers bridged by the carboxylate oxygen atoms of the LCOO ligand.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Water-Soluble Arene Ruthenium Complexes Containing a trans -1,2-Diaminocyclohexane Ligand as Enantioselective Transfer Hydrogenation Catalysts in Aqueous SolutionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2005Jérôme Canivet Abstract The cationic chloro complexes [(arene)Ru(H2N,NH2)Cl]+ (1: arene = C6H6; 2: arene = p -MeC6H4iPr; 3: arene = C6Me6) have been synthesised from the corresponding arene ruthenium dichloride dimers and enantiopure (R,R or S,S) trans -1,2-diaminocyclohexane (H2N,NH2) and isolated as the chloride salts. The compounds are all water-soluble and, in the case of the hexamethylbenzene derivative 3, the aqua complex formed upon hydrolysis [(C6Me6)Ru(H2N,NH2)OH2]2+ (4) could be isolated as the tetrafluoroborate salt. The molecular structures of 3 and 4 have been determined by single-crystal X-ray diffraction analyses of [(C6Me6)Ru(H2N,NH2)Cl]Cl and [(C6Me6)Ru(H2N,NH2)OH2][BF4]2. Treatment of [Ru2(arene)2Cl4] with the monotosylated trans -1,2-diaminocyclohexane derivative (TsHN,NH2) does not yield the expected cationic complexes, analogous to 1,3 but the neutral deprotonated complexes [(arene)Ru(TsN,NH2)Cl] (5: arene = C6H6; 6: arene = p -MeC6H4iPr; 7: arene = C6Me6; 8: arene = C6H5COOMe). Hydrolysis of the chloro complex 7 in aqueous solution gave, upon precipitation of silver chloride, the corresponding monocationic aqua complex [(C6Me6)Ru(TsHN,NH2)(OH2)]+ (9) which was isolated and characterised as its tetrafluoroborate salt. The enantiopure complexes 1,9 have been employed as catalysts for the transfer hydrogenation of acetophenone in aqueous solution using sodium formate and water as a hydrogen source. The best results were obtained (60 °C) with 7, giving a catalytic turnover frequency of 43 h,1 and an enantiomeric excess of 93,%. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Carboxy Ester Hydrolysis Promoted by a Dicopper(II) Macrocyclic Polyamine Complex with Hydroxypropyl Pendant GroupsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2004Jin Huang Abstract A dinuclear CuII complex containing a hexaaza macrocyclic ligand bearing two 2-hydroxypropyl pendants, 3,6,9,16,19,22-hexaaza-6,19-bis(2-hydroxypropyl)tricyclo[22.2.2.211,14]triaconta-1,11,13,24,27,29-hexaene (L), was synthesized. The title complex [Cu2(H,2L)Cl2]·6.5H2O was isolated as a blue crystal, orthorhombic, space group Fddd, with a = 16.4581(12), b = 32.248(2), c = 35.830(2) Å, V = 19017(2) Å3, Z = 16, R1 = 0.0690, and wR2 = 0.1546 [I > 2,(I)]. The protonation constants of Cu2L were determined by potentiometric titration, and it was found that the alcoholic hydroxypropyl group of the complex Cu2L exhibits low pKa values of pKa1 = 7.31, pKa2 = 7.83 at 25 °C. The hydrolysis kinetics of 4-nitrophenyl acetate (NA) promoted by the title complex have also been studied. The pH-rate profile for Cu2L gave a sigmoidal curve and showed a second-order rate constant of 0.39 ± 0.02 M,1 s,1 in 10% CH3CN/H2O(v/v), which is greater than that of the dinuclear CuII complex formed by a hexaaza macrocycle without pendants. The reason for the higher catalytic activity of the title complex is discussed. We found that the volume of nucleophile RO, can effect the hydrolysis of the carboxy ester, the nucleophilicity of RO, and the Lewis acidity of the metal macrocycle also affect the carboxy ester hydrolysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] (4-Acyl-5-pyrazolonato)titanium Derivatives: Oligomerization, Hydrolysis, Voltammetry, and DFT StudyEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2003Francesco Caruso Abstract Twenty 4-acyl-5-pyrazolonato (Q) titanium derivatives of varied nuclearity have been synthesized from Ti(OR)4 or TiCl4 and characterized with spectroscopic methods (IR, NMR, ESI-MS). While Ti,(,-diketonato) cleavage is not seen in isolated solids, Ti,O(alkoxy) (or Ti,Cl) bonds cleave upon hydrolysis, leading to several structural forms, including oligomers. Ionic Q species with no Ti, i.e., obtained after Ti,Q cleavage, are seen for some Ti,Q derivatives by ESI-MS, which also indicates a varied nuclearity for a given species, e.g., the isolated polynuclear [Q2Ti-,-O]n has several "n" values. Mononuclear Ti complexes are obtained under rigorous anhydrous conditions. The cis structures of the mononuclear species (QT)2Ti(OCH3)2, QT = 3-methyl-4-(neopentylcarbonyl)-1-phenylpyrazol-5-onato have been analyzed with DFT methods. A trans influence is a major driving force that accounts for several sets of Ti,O bonds. One of the cis stereoisomers is 56 kcal/mol higher in energy than the other two. In contrast, all (QT)2TiCl2cis isomers show similar energies. Voltammetry of the mononuclear species (QT)2Ti(OnPr)2 and the antitumor tetranuclear compound [(QB)2Ti-,-O]4, (QB = 4-benzoyl-3-methyl-1-phenylpyrazol-5-onato) indicate that the TiIV is less prone to reduction to TiIII in the latter (Epc for the TiIV/TiIII couple is ,1.71 V and ,1.46 V versus Fc+/Fc, respectively). Potential antitumor compounds having a Ti/Q ratio of 1:1 do not disproportionate, unlike the equivalent acetylacetonato derivatives, and are water-soluble. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Synthesis of Monodisperse Silica Nanoparticles Dispersable in Non-Polar Solvents,ADVANCED ENGINEERING MATERIALS, Issue 5 2010Eoin Murray Three synthetic routes to hydrophobic silica nanoparticles are compared in this paper. First, the established synthetic method based on the Stöber process was examined. Monodisperse colloidal silica particles with diameters of 15,25,nm were prepared via the hydrolysis of tetraethyl orthosilicate (TEOS) by aqueous ammonia in ethanol. The surfaces of these particles were rendered hydrophobic with octadecyltrimethoxysilane (ODTMS) after the reaction or, more conveniently, during the growth phase. Secondly, silica particles with diameters of 15,50,nm were prepared using a one-pot synthesis in which TEOS was hydrolyzed by an amino acid and the resulting particles were coated with ODTMS. Lastly a novel, direct approach to the synthesis of hydrophobic organosilica nanoparticles was developed using ODTMS as the single silica source. Hydrolysis of the ODTMS by aqueous ammonia in ethanol yielded monodisperse colloidal organosilica particles with diameters of 15,30,nm. [source] Improved Synthesis and Isolation of 2,- O -Methyladenosine: Effective and Scalable Enzymatic Separation of 2,/3,- O -Methyladenosine RegioisomersEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2009Saúl Martínez-Montero Abstract An efficient separation of a mixture of 2,/3,- O -methyladenosine regioisomers (1 + 2; 1:1) has been developed by selective enzymatic acylation using immobilized Pseudomonas cepacia lipase (PSL-C) in combination with acetonoxime levulinate as acyl donor. The 3,-hydroxy group of 2,- O -methyladenosine (1) was acylated with high selectivity (ca. 70,%), whereas an equal amount of 3,- O -methyladenosine (2) in the same solution resulted in minor acylation of 5,-hydroxy group (ca. 8,%). The differential behavior of both regioisomers towards enzymatic acylation allowed to develop a separation protocol. Upon extraction of the acylated products, the 3,- O -methyladenosine was isolated in 81,% yield and 97,% purity from the aqueous layer. Hydrolysis of acylated products in organic layer furnished 2,- O -methyladenosine in 67,% yield and 99,% purity. The separation process was successfully applied to the crude reaction mixture of methylated products (ca. 3:1 of 1/2) on 5-g scale. We also report on the use of methyl p -toluenesulfonate as a safe reagent for 2,- O -methylation of adenosine.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] A Versatile Synthesis of 5,-Functionalized Nucleosides Through Regioselective Enzymatic Hydrolysis of Their Peracetylated PrecursorsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 12 2009Teodora Bavaro Abstract We describe a chemo-enzymatic synthesis of modified nucleosides through lipase-catalyzed hydrolysis of their peracetylated precursors. It was found from screening of a large number of substrates that these enzymes' regioselectivities were affected by the sugar and the nucleobase structures. By selecting the best enzyme for each substrate in terms of activity and regioselectivity, we prepared a small library of differently monodeprotected purine and pyrimidine nucleosides useful as intermediates for the synthesis of high-value nucleosides and mononucleotides. By this approach, the chemo-enzymatic preparation of doxifluridine (14) anduridine 5,-monophosphate (5,-UMP, 15) from peracetylated uridine 1 was carried out. Elimination of many of the processing stages associated with existing methods was achieved, and higher yields and products of increased purity were generated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Regioselective C-6 Hydrolysis of Methyl O -Benzoyl-pyranosides Catalysed by Candida Rugosa LipaseEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2009Aslan Esmurziev Abstract Hydrolysis of six methyl O -benzoyl-pyranosides has been investigated using Candida rugosa lipase in dioxane/buffer mixtures. The lipase catalysed the hydrolysis of all substrates in a regiospecific manner at C-6. The rate of reaction was dependent on pyranoside structure, reaction temperature and scale, dioxane concentration and agitation speed. Starting from their C-6 O -benzoyl precursors, the methyl 2,3,4-tri- O -benzoyl-pyranosides of ,- D -galactose, ,- D -galactose, ,- D -glucose, and methyl 2,3-di- O -benzoyl-,- D -galactopyranoside could be isolated in 85,96,% yield. In hydrolysis of methyl 2,3,4,6-tetra- O -benzoyl-,- D -glucopyranoside and methyl 2,3,4,6-tetra- O -benzoyl-,- D -galactopyranoside substrate inhibition were observed, which in part could be overcome by increasing the reaction volume. Methyl 2,3,4,6-tetra- O -benzoyl-,- D -glucopyranoside and methyl 2,3,4,6-tetra- O -benzoyl-,- D -mannopyranoside were poor substrates for Candida rugosa lipase and low degree of conversion towards products were obtained under all conditions. No acyl migration was detected in any of the products.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Hydrolysis of Toxic Natural Glucosides Catalyzed by Cyclodextrin DicyanohydrinsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 4 2008Jeannette Bjerre Abstract The hydrolysis of toxic 7-hydroxycoumarin glucosides and other aryl and alkyl glucosides, catalyzed by modified ,- and ,-cyclodextrin dicyanohydrins, was investigated using different UV, redox, or HPAEC detection assays. The catalyzed reactions all followed Michaelis,Menten kinetics, and an impressive rate increase of up to 7569 (kcat/kuncat) was found for the hydroxycoumarin glucoside substrate 4-MUGP. Good and moderate degrees of catalysis (kcat/kuncat) of up to 1259 were found for the natural glucosides phloridzin and skimmin. By using a newly developed catechol detection UV-assay, a weak degree of catalysis was also found for the toxic hydroxycoumarin esculin. A novel synthesized diaminomethyl ,-cyclodextrin showed a weak catalysis of p -nitrophenyl ,- D -glucopyranoside hydrolysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Synthesis of Both Enantiomers of Conduritol C Tetraacetate and of meso -Conduritol D Tetraacetate by Oxidation of Benzoquinone Bis(ethylene acetal)EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2007Martin Lang Abstract Epoxidation of p -benzoquinone bis(ethylene acetal) (1) with m -chloroperbenzoic acid or hydrogen peroxide/benzonitrile afforded corresponding monoepoxide 2, which was converted into p -benzoquinone mono(ethylene acetal) monoepoxide 5 with perchloric acid. Dihydroxylation of 1 with osmium tetroxide or ruthenium trichloride/sodium periodate afforded corresponding cis -diol 6, which was subsequently acetylated to give diacetate 7. One ethyleneacetal moiety in 7 could be selectively hydrolyzed with silica gel/ferric chloride under solvent-free conditions to give ketone 8, which, upon reduction with sodium borohydride and subsequent acetylation of the formed alcohol group, afforded two diastereomeric triacetates 10. Hydrolysis of the remaining acetal functions in the two diastereomers 10, followed by reduction of the second carbonyl group as described above, afforded racemic conduritol C and meso -conduritol D tetraacetates 12 and 13, respectively. Enzymatic resolution of the racemic arabino -configured triacetate 10 with Lipozym failed, while the ribo -configured counterpart reacted smoothly to give enantiomerically pure D - ribo - and L - ribo -configured triacetates 10. The latter pair of enantiomerically pure triacetates were converted into both enantiomers of conduritol C tetraacetate 13 as described for the racemic compounds. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] The Mechanism of Hydrolysis of Aryl Ether Derivatives of3-HydroxymethyltriazenesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2005Emília Carvalho Abstract 1-Aryl-3-aryloxymethyl-3-methyltriazenes hydrolyse to the corresponding anilines and phenols by specific-acid-catalysed, general-acid-catalysed and pH-independent mechanisms. All compounds studied exhibit specific- and general acid catalysis, though for 5a general acid catalysis was not observed below a pH of approximately 4, while for compounds 5e,f, such catalysis was absent above a pH of approximately 5. The pH-independent pathway is observed only for those compounds, 5d,f, that contain good aryloxy nucleofugic groups. The specific-acid-catalysed pathway is supported by a solvent deuterium isotope effect (SDIE) of 0.64, consistent with a mechanism involving protonation of the substrate followed by rate-determining unimolecular decomposition of the protonated species. The kH+ values gave rise to a Hammett , value of ,0.93, reflecting the competing effect of the substituents on the protonation of the substrate and the cleavage of the aryl ether. Correlation of kH+ with the pKa of the phenol leaving group affords a ,lg of 0.3. Decomposition of the protonated intermediate proceeds via a triazenyliminium ion that can be trapped by methanol. The general-acid-catalysed process exhibits an SDIE of 1.43 and Hammett , values of 0.49, 0.84 and 1.0 for reactions catalysed by chloroacetic, formic and acetic acids, respectively. Correlation of kA with the pKa of the acid gave Brønsted , values that diminish from 0.6 for O -aryl systems that are poor nucleofuges (5a,b) to 0.2 for the best nucleofuge (5f), reflecting the different extents of proton transfer required to expel each phenol. Compounds containing powerful nucleofuges exhibit a pH-independent reaction that has an SDIE of 1.1, a Hammett , value of 3.4 and a Brønsted ,lg value of 1.4. These imply a mechanism involving displacement of the aryloxide leaving group to form a triazenyliminium ion intermediate that again was trapped as a methyl ether. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Highly Enantioselective Synthesis of No-Carrier-Added 6-[18F]Fluoro- L -dopa by Chiral Phase-Transfer AlkylationEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2004Christian Lemaire Abstract [18F]Fluoro- L -dopa, an important radiopharmaceutical for positron emission tomography (PET), has been synthesized using a phase-transfer alkylation reaction. A chiral quaternary ammonium salt derived from a Cinchona alkaloid served as phase-transfer catalyst for the enantioselective alkylation of a glycine derivative. The active methylene group of this Schiff-base substrate was deprotonated with cesium hydroxide and rapidly alkylated by the 2-[18F]fluoro-4,5-dimethoxybenzyl halide (X = Br, I). The reaction proceeded with high yield (> 90%) at 0 °C or room temperature in various solvents such as toluene or dichloromethane. Preparation of the [18F]alkylating agent on a solid support was developed. After labelling, the labeled [18F]fluoroveratraldehyde was trapped on a tC18 cartridge and then converted on the cartridge into the corresponding benzyl halide derivatives by addition of aqueous sodium borohydride and gaseous hydrobromic or -iodic acid. Hydrolysis and purification by preparative HPLC made 6-[18F]fluoro- L -dopa ready for human injection in a 25,30% decay-corrected radiochemical yield in a synthesis time of 100 min. The product was found to be chemically, radiochemically and enantiomerically pure (ee > 95%). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Facile Cleavage of Si,C Bonds during the Sol-Gel Hydrolysis of Aminomethyltrialkoxysilanes , A New Method for the Methylation of Primary AminesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 12 2004Augustin Adima Abstract The reaction of chloromethyltriethoxysilane with (1R,2R)-bis(methylamino)cyclohexane (1) afforded the corresponding bis-silylated compound 2. The sol-gel hydrolysis of 2 did not give the expected bridged silsesquioxane owing to quantitative Si,C-bond cleavage. Instead, silica and (1R,2R)-bis(dimethylamino)cyclohexane (3) were obtained. This reaction was exploited to propose a new route for the methylation of amines. Such methylation reaction of amines could be extended to other amines and provides a new method for the selective monomethylation of primary amines. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Stereoselective Hydrolysis of Quaternary Quinuclidinium Benzoates Catalyzed by ButyrylcholinesteraseEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2003Ines Primoz Abstract Four chiral, quaternary, N -methyl and N -benzyl derivatives of (R)- and (S)-quinuclidin-3-yl benzoates were synthesized and studied as substrates of horse serum butyrylcholinesterase (BChE). The kcat for the substrates decreased in the order (R)- N -methyl > (R)- N -benzyl (2.3-fold slower) >> (S)- N -methyl (70.5-fold slower reaction), while for the (S)- N -benzyl ester inhibition of the enzyme was observed. The kinetics of inhibition (Ka = 3.3 ,M) indicated that binding to the catalytic site of BChE occurred. From the ratio of the kcat/KM values of both enantiomers an enantiomeric excess of 95% was calculated for N -methyl derivatives. Thus, BChE is suitable as a biocatalyst for the resolution of racemic quaternary quinuclidinium esters. In order to explain the experimental data, combined quantum chemical (HF/3,21G*) and semiempirical (PM3) calculations within the ONIOM scheme of the stable species in the acylation step were performed. Geometry optimizations were carried out for all benzoate esters for an assumed active site model of BChE. It was confirmed that hydrolysis is affected to an appreciable extent by a proper geometrical orientation of substrates at the choline subsite. The energies of the optimized systems were in good agreement with the experimental data. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Hydrolysis of acetylthiocoline, o -nitroacetanilide and o- nitrotrifluoroacetanilide by fetal bovine serum acetylcholinesteraseFEBS JOURNAL, Issue 7 2009María F. Montenegro Besides esterase activity, acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) hydrolyze o -nitroacetanilides through aryl acylamidase activity. We have reported that BuChE tetramers and monomers of human blood plasma differ in o -nitroacetanilide (ONA) hydrolysis. The homology in quaternary structure and folding of subunits in the prevalent BuChE species () of human plasma and AChE forms of fetal bovine serum prompted us to study the esterase and amidase activities of fetal bovine serum AChE. The kcat/Km values for acetylthiocholine (ATCh), ONA and its trifluoro derivative N -(2-nitrophenyl)-trifluoroacetamide (F-ONA) were 398 × 106 m,1·min,1, 0.8 × 106 m,1·min,1, and 17.5 × 106 m,1·min,1, respectively. The lack of inhibition of amidase activity at high F-ONA concentrations makes it unlikely that there is a role for the peripheral anionic site (PAS) in F-ONA degradation, but the inhibition of ATCh, ONA and F-ONA hydrolysis by the PAS ligand fasciculin-2 points to the transit of o -nitroacetalinides near the PAS on their way to the active site. Sedimentation analysis confirmed substrate hydrolysis by tetrameric 10.9S AChE. As compared with esterase activity, amidase activity was less sensitive to guanidine hydrochloride. This reagent led to the formation of 9.3S tetramers with partially unfolded subunits. Their capacity to hydrolyze ATCh and F-ONA revealed that, despite the conformational change, the active site architecture and functionality of AChE were partially retained. [source] The presence of phosphate at a catalytic site suppresses the formation of the MgADP-inhibited form of F1 -ATPaseFEBS JOURNAL, Issue 1 2002Noriyo Mitome F1 -ATPase is inactivated by entrapment of MgADP in catalytic sites and reactivated by MgATP or Pi. Here, using a mutant ,3,3, complex of thermophilic F1 -ATPase (,W463F/,Y341W) and monitoring nucleotide binding by fluorescence quenching of an introduced tryptophan, we found that Pi interfered with the binding of MgATP to F1 -ATPase, but binding of MgADP was interfered with to a lesser extent. Hydrolysis of MgATP by F1 -ATPase during the experiments did not obscure the interpretation because another mutant, which was able to bind nucleotide but not hydrolyse ATP (,W463F/,E190Q/,Y341W), also gave the same results. The half-maximal concentrations of Pi that suppressed the MgADP-inhibited form and interfered with MgATP binding were both ,,20 mm. It is likely that the presence of Pi at a catalytic site shifts the equilibrium from the MgADP-inhibited form to the enzyme,MgADP,Pi complex, an active intermediate in the catalytic cycle. [source] Inactivation of Aeromonas hydrophila metallo-,-lactamase by cephamycins and moxalactamFEBS JOURNAL, Issue 13 2001Astrid Zervosen Incubation of moxalactam and cefoxitin with the Aeromonas hydrophila metallo-,-lactamase CphA leads to enzyme-catalyzed hydrolysis of both compounds and to irreversible inactivation of the enzyme by the reaction products. As shown by electrospray mass spectrometry, the inactivation of CphA by cefoxitin and moxalactam is accompanied by the formation of stable adducts with mass increases of 445 and 111 Da, respectively. The single thiol group of the inactivated enzyme is no longer titrable, and dithiothreitol treatment of the complexes partially restores the catalytic activity. The mechanism of inactivation by moxalactam was studied in detail. Hydrolysis of moxalactam is followed by elimination of the 3, leaving group (5-mercapto-1-methyltetrazole), which forms a disulfide bond with the cysteine residue of CphA located in the active site. Interestingly, this reaction is catalyzed by cacodylate. [source] [Ru(0)]@SiO2 and [RuO2]@SiO2 Hybrid Nanomaterials: From Their Synthesis to Their Application as Catalytic Filters for Gas SensorsADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Victor Matsura Abstract [Ru(0)]@SiO2 and [RuO2]@SiO2 hybrid nanomaterials are produced following a facile method consisting of the synthesis of size-controlled ruthenium nanoparticles as elemental bricks. This route takes advantage of the organometallic approach and the use of a bifunctional ligand for the synthesis of ruthenium nanoparticles from [Ru(COD)(COT)](COD,=,1,3-cyclooctadiene, COT,=,1,3,5-cyclooctatriene) as metal precursor and (PhCH2)2N(CH2)11O(CH2)3Si(OEt)3 (benzenemethanamine) as stabilizer. Hydrolysis and polycondensation steps via a sol,gel approach lead to the formation of the silica materials containing the metal nanoparticles. A final calcination step in air at 400,°C yields the [RuO2]@SiO2 nanocomposites. Such hybrid nanomaterials display a good dispersion of the nanoparticles inside the silica matrix and interesting porosity properties making them attractive materials for catalytic applications. This is shown by using [RuO2]@SiO2 hybrid nanomaterials as catalytic filters for gas sensors. [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] Tuning and Transcription of the Supramolecular Organization of a Fluorescent Silsesquioxane Precursor into Silica-Based Materials through Direct Photochemical Hydrolysis,Polycondensation and MicropatterningADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Xavier Sallenave Abstract A new fluorescent silsequioxane precursor with tuned optical properties and controlled aggregation properties is designed. The two cyclohexyl moieties introduced in the molecular structure allow the formation of very good quality films. The J-aggregated structure is transcribed into the solid by photoacid-catalyzed hydrolysis,polycondensation. Aggregation of the chromophores is reduced and highly fluorescent materials are obtained. The photoacid generator lies on the surface of the homogeneous layer of the sol,gel precursor. This phase separation presents several advantages, including UV protection of the chromophore and easy removal of the PAG. The first example of chemical amplification in the photolithography of the conjugated silsesquioxane precursor is demonstrated. As hydrolysis,polycondensation could be achieved in a controlled way by UV exposure, chemically amplified photolithography is achieved by irradiating a composite film (,110,nm thick) on silicon wafer by using a copper TEM grid as shadow mask. The pattern is produced uniformly on a miscroscopic scale of 3,mm, the photopatterned pixels remaining highly fluorescent. The sizes of the photolithographed pixels correspond to the sizes of the rectangular holes of the 300,×,75 mesh grid (hole: 63,<$>,<$>m,×,204,<$>,<$>m). [source] Synthesis and Enzymic Hydrolysis of Oligoribonucleotides Incorporating 3-Deazaguanosine: The Importance of the Nitrogen-3 Atom of Single Conserved Guanosine Residues on the Catalytic Activity of the Hammerhead RibozymeHELVETICA CHIMICA ACTA, Issue 8 2003Frank Seela Four base-modified hammerhead ribozyme/substrate complexes were constructed in which single guanosine (1) residues were replaced by 3-deazaguanosine (2) in the positions G5, G8, GL2.1, and G12. The base-modified ribozyme complexes were prepared by solid-phase synthesis of oligoribonucleotides employing the novel phosphoramidite 3 derived from 2. Phosphoramidite 3 carried a phenoxyacetyl group at the amino function and a diphenylcarbamoyl residue at the oxo group of the nucleobase. The 2,-hydroxy group was blocked with a triisopropylsilyl residue. Kinetic analysis of the phosphodiester hydrolysis showed a moderate decrease of the ribozyme catalytic activity when the residues G5 or G8 were replaced by 3-deazaguanosine and a 200-fold decrease when G12 was substituted. A 6-fold catalytic increase occurred when 3-deazaguanosine was replacing GL2.1 in the loop region. The data indicate that the N(3) atom of compound 2, in particular at position G12 is critical for the ribozyme activity. [source] Hydrolysis of diphenylmethyltin(iv) chloride in different aqueous solutions of ethanolHETEROATOM CHEMISTRY, Issue 7 2008Sima Mehdizadeh The hydrolysis of [(Ph)2MeSn(IV)]+ has been studied spectrophotometrically at 25,C and constant ionic strength of 0.1 mol dm,3 sodium perchlorate. Over a wide pH range, 1,11, the investigation has been performed in different aqueous solutions of ethanol. The species formed together with their formation constants have been determined using the computer program Squad. The hydrolysis constants at different media were analyzed in terms of Kamlet and Taft's parameters. A single-parameter correlation of the formation constants, K1-1 and K1-2, versus , (hydrogen-bond donor acidity), , (hydrogen-bond acceptor basicity), and ,* (dipolarity/polarizability) for both cases are relatively poor in all solutions, but multiparameter correlation represents significant improvement with regard to the single-parameter models. In this work, we have also used the normalized polarity parameter, E, alone and in combination with the Kamlet,Taft's parameters to find a better correlation of the formation constants in different aqueous solutions of ethanol. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:654,660, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20484 [source] | ||||||||||||||||||||||||||||||||||||||||||||||