Home About us Contact
|
Home About us Contact | ||
|
|
||
Organic Media (organic + media)
Selected AbstractsCandida antarctica Lipase B (CAL-B)-Catalyzed Carbon-Sulfur Bond Addition and Controllable Selectivity in Organic MediaADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2008Feng-Wen Lou Abstract A novel enzymatic, promiscuous protocol for Candida antarctica lipase B (CAL-B)-catalyzed carbon-sulfur bond addition is described. Some control experiments have been designed to demonstrate the catalytic specificity of CAL-B. Selectivity between anti-Markovnikov addition and Markovnikov addition was achieved in different organic media. A series of thioether-containing ester functional groups was synthesized under the catalysis of CAL-B at 50,°C. All the products were characterized by spectroscopic methods (IR, NMR, ESI-MS). [source] Promiscuous Acylases-Catalyzed Markovnikov Addition of N-Heterocycles to Vinyl Esters in Organic MediaADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4-5 2006Wei-Bo Wu Abstract Three acylases, including D -aminoacylase from Escherichia coli, acylase "Amano" from Aspergillus oryzae and immobilized penicillin G acylase from Escherichia coli have been found to possess novel activity to catalyze the Markovnikov addition reaction of N-heterocycles to vinyl esters. The aza-Markovnikov addition reactions of 4-nitroimidazle to vinyl acetate catalyzed by D -aminoacylase, acylase "Amano" and immobilized penicillin G acylase were up to 1260-fold, 720-fold and 320-fold faster than the respective non-enzymatic reaction. Some control experiments have been designed to demonstrate the catalytic specificity of acylases. Under the catalysis of these promiscuous acylases, a number of N-heterocycles, including some pentacyclic N-heterocycles, pyrimidines and purines, were successfully added to a series of vinyl esters in moderate to excellent yields to prepare N-heterocycle derivatives. The acylase-catalyzed Markovnikov addition reaction has provided a new strategy to perform the Markovnikov addition and expanded the application of biocatalysts. [source] Systematic Approach for Dispersion of Silicon Nitride Powder in Organic Media: I, Surface Chemistry of the PowderJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2000Liwu Wang To develop novel dispersants for submicrometer-sized Si3N4 powder, the surface chemistry of a powder has been investigated using thermodesorption, carrier-gas heat extraction, X-ray photoelectron spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and zeta potential measurements. This study indicates that the powder surface is composed mainly of silanol groups and exhibits acidic behavior. Furthermore, the interaction affinity of various surface probe molecules with the powder surface has been studied using adsorption isotherms. The detailed description of the surface chemistry can be used as a guide for designing efficient dispersants, as will be presented in part II. [source] Systematic Approach for Dispersion of Silicon Nitride Powder in Organic Media: II, Dispersion of the PowderJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2000Liwu Wang A novel dispersant,O-(2-aminopropyl)-O,-(2-methoxyethyl)-polypropylene glycol (AMPG),was developed to disperse submicrometer-sized Si3N4 powder in nonaqueous media, based on the surface chemistry of the powder. The dispersing phenomena and mechanisms have been studied systematically, both in model systems (using atomic force microscopy and ellipsometry) and in powder systems (using rheological behavior and adsorption isotherms). The results from the model systems correlated well with those from wet powder systems. It is demonstrated that highly concentrated (with a solids volume fraction of >0.50) and colloidally stable nonaqueous Si3N4 suspensions can be realized using AMPG. [source] Zinc(II) Containing ,-Keggin Sandwich-Type Silicotungstate: Synthesis in Organic Media and Oxidation Catalysis,ANGEWANDTE CHEMIE, Issue 35 2010Yuji Kikukawa Zink macht den Unterschied: Das Polyoxometallat 1 reagiert mit Zn2+ -Ionen in Aceton nahezu quantitativ zum neuartigen Sandwich-artigen POM 2. Die Oxidation sekundärer Alkohole mit H2O2 verläuft mit 2 effizient, und zwar mit Aktivitäten und Chemoselektivitäten, die sich von denen wolframhaltiger Katalysatoren einschließlich 1 erheblich unterscheiden (siehe Schema; grün,Zn). [source] Layer-by-Layer Growth of Polymer/Quantum Dot Composite Multilayers by Nucleophilic Substitution in Organic Media,ANGEWANDTE CHEMIE, Issue 2 2010Bokyoung Lee Beständig photolumineszierende Nanokomposit-Multischichten enthalten Quantenpunkte (siehe Bild) und werden durch eine nucleophile Substitution erzeugt. Die Anordnung funktioneller Nanopartikel in einem unpolaren Lösungsmittel kann die selektive Abscheidung ermöglichen und eine hydrophobe Oberfläche mit einem Wasser-Kontaktwinkel über 115° ergeben, was die Photolumineszenz der Nanokompositfilme deutlich stabilisiert. [source] Enzymatic Redox Cofactor Regeneration in Organic Media: Functionalization and Application of Glycerol Dehydrogenase and Soluble Transhydrogenase in Reverse MicellesBIOTECHNOLOGY PROGRESS, Issue 4 2005Hirofumi Ichinose An enzymatic system for the regeneration of redox cofactors NADH and NADPH was investigated in nanostructural reverse micelles using bacterial glycerol dehydrogenase (GLD) and soluble transhydrogenase (STH). Catalytic conversion of NAD+ to NADH was realized in the sodium dioctylsulfosuccinate (AOT)/isooctane reverse micellar system harboring GLD and a sacrificial substrate, glycerol. The initial rate of NADH regeneration was enhanced by exogenous addition of ammonium sulfate into the reverse micelles, suggesting that NH4+ acts as a monovalent cationic activator. STH was successfully entrapped in the AOT/isooctane reverse micelles as well as GLD and was revealed to be capable of catalyzing the stoichiometric hydrogen transfer reaction between NADP+ and NADPH in reverse micelles. These results indicate that GLD and STH have potential for use in redox cofactor recycling in reverse micelles, which allows the use of catalytic quantities of NAD(P)H in organic media. [source] Recovery of Homogeneous Polyoxometallate Catalysts from Aqueous and Organic Media by a Mesoporous Ceramic Membrane without Loss of Catalytic ActivityCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2006Sankhanilay Roy Chowdhury Dr. Abstract The recovery of homogeneous polyoxometallate (POM) oxidation catalysts from aqueous and non-aqueous media by a nanofiltration process using mesoporous ,-alumina membranes is reported. The recovery of Q12[WZn3(ZnW9O34)2] (Q=[MeN(n -C8H17)3]+) from toluene-based media was quantitative within experimental error, while up to 97,% of Na12[WZn3(ZnW9O34)2] could be recovered from water. The toluene-soluble POM catalyst was used repeatedly in the conversion of cyclooctene to cyclooctene oxide and separated from the product mixture after each reaction. The catalytic activity increased steadily with the number of times that the catalyst had been recycled, which was attributed to partial removal of the excess QCl that is known to have a negative influence on the catalytic activity. Differences in the permeability of the membrane for different liquid media can be attributed to viscosity differences and/or capillary condensation effects. The influence of membrane pore radius on permeability and recovery is discussed. [source] Organic Phase PPO Biosensors Prepared by Multilayer Deposition of Enzyme and Alginate Through Avidin-Biotin InteractionsELECTROANALYSIS, Issue 24 2004S. Cosnier Abstract Films of electrogenerated polypyrrole and hydrophilic alginate, both functionalized with biotin moieties, were used to allow for the transfer of polyphenol oxidase activity in organic media. Enzyme electrodes, based on multilayered structures, were protected at the molecular level by the affinity binding of alginate as a hydrophilic additive, and were then transferred into chlorobenzene, dichloromethane, chloroform, ethyl acetate or acetonitrile. The biosensor performance for the detection of catechol at ,0.2,V was investigated, highlighting the main influence of the hydrophobicity of the solvent and, to a lesser extent, the dielectric constant. The effect of the substrate hydrophobicity on the biosensor response was examined in chlorobenzene. [source] Synthesis and Binding Properties of Dendritic Oxybathophenanthroline Ligands towards Copper(II)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2005Holger Stephan Abstract Dendritic oxybathophenanthroline ligands (generation 0 to 3) have been synthesized by treatment of 4,7-bis(4,-hydroxyphenyl)-1,10-phenanthroline with the corresponding Fréchet-type dendrons carrying a benzylic bromide function at the focal point. The complexation of copper(II) has been studied by liquid,liquid extraction using the radioisotope 64Cu and time-resolved laser-induced fluorescence spectroscopy (TRLFS) in organic media indicating the formation of 1:3 complexes (Cu:dendritic ligand). Electronic and EPR spectroscopy were used to characterize the copper(II) chromophore, which is shown to have the expected distorted square-planar geometry with two phenanthroline donors coordinated to the copper(II) center. The third dendritic ligand therefore is proposed to be bound by secondary interactions. The stability constants of the 1:3 complexes were found to be in the order of log K , 16 in CHCl3. On the other hand, increasing generation of the dendritic Fréchet-type branches leads to enhanced shielding of the copper ion from the environment. Additional information about this behaviour was obtained by the fluorescence lifetimes, which are much less influenced upon addition of copper(II) salt to solutions of the higher generation ligands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Tuning Carbon Materials for Supercapacitors by Direct Pyrolysis of SeaweedsADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Encarnación Raymundo-Piñero Abstract The sea provides a large variety of seaweeds that, because of their chemical composition, are fantastic precursors of nanotextured carbons. The carbons are obtained by the simple pyrolysis of the seaweeds under a nitrogen atmosphere between 600 and 900,°C, followed by rinsing the product in slightly acidic water. Depending on the origin of the seaweed and on the pyrolysis conditions, the synthesis may be oriented to give an oxygen-enriched carbon or to give a tuned micro/mesoporous carbon. The samples with a rich oxygenated surface functionality are excellent as supercapacitor electrodes in an aqueous medium whereas the perfectly tuned porous carbons are directly applicable for organic media. In both cases, the specific surface area of the attained carbons does not exceed 1300 m2 g,1, which results in high-density materials. As a consequence, the volumetric capacitance is very high, making these materials more interesting than activated carbons from the point of view of developing small and compact electric power sources. Such versatile carbons, obtained by a simple, ecological, and cheap process, could be well used for environment remediation such as water and air treatment. [source] Candida antarctica Lipase B (CAL-B)-Catalyzed Carbon-Sulfur Bond Addition and Controllable Selectivity in Organic MediaADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2008Feng-Wen Lou Abstract A novel enzymatic, promiscuous protocol for Candida antarctica lipase B (CAL-B)-catalyzed carbon-sulfur bond addition is described. Some control experiments have been designed to demonstrate the catalytic specificity of CAL-B. Selectivity between anti-Markovnikov addition and Markovnikov addition was achieved in different organic media. A series of thioether-containing ester functional groups was synthesized under the catalysis of CAL-B at 50,°C. All the products were characterized by spectroscopic methods (IR, NMR, ESI-MS). [source] Preparation and applications of novel fluoroalkyl end-capped sulfonic acid oligomers,silica gel polymer hybridsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Kazuo Sasazawa Abstract Fluoroalkyl end-capped 2-methacryloxyethanesulfonic acid homo-oligomer [RF,(MES)n,RF] and 2-methacryloxyethanesulfonic acid,N,N -dimethylacrylamide co-oligomers [RF,(MES)x,(DMAA)y,RF] reacted with tetraethoxysilane (TEOS) under acidic conditions to afford RF,(MES)n,RF homo-oligomer,SiO2 polymer hybrid and RF,(MES)x,(DMAA)y,RF co-oligomer,SiO2 polymer hybrid, respectively. Thermogravimetric,mass spectra showed that the thermal stability of RF,(MES)n,RF homo-oligomer,SiO2 polymer hybrid was superior to that of traditionally well-known perfluorinated ion exchange polymers such as Nafion 112 (TR). The sol solutions of the fluorinated co-oligomer,SiO2 polymer hybrid were applied to the surface modification of glass to exhibit not only a strong oleophobicity imparted by fluorine but also a good hydrophilicity on the glass surface. On the other hand, RF,(MES)x,(DMAA)y,RF co-oligomer reacted with TEOS in the presence of a variety of silica nanoparticles (mean diameters: 11,95 nm) under alkaline conditions to afford fluoroalkyl end-capped oligomers,silica nanoparticles (mean diameters: 32,173 nm) with a good dispersibility and stability in methanol. Similarly, a variety of fluorinated oligomers containing sulfo groups,silica nanoparticles were prepared by the homo- and co-oligomerizations of fluoroalkanoyl peroxides with 2-methacryloxyethane sulfonic acid (MES) and comonomers such as N,N -dimethylacrylamide (DMAA) and acryloylmorpholine (ACMO) in the presence of silica nanoparticles. Interestingly, these isolated fluorinated particle powders were found to afford nanometer size-controlled colloidal particles with a good redispersibility and stability in aqueous and organic media such as methanol. These fluorinated nanoparticles containing sulfo groups were also applied to an excellent heterogeneous catalyst for Bronsted acid-catalyzed transformations. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 110,117, 2007 [source] An investigation of the 125I-radioiodination of colchicine for medical purposesJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 1 2009K. M. El-Azony Abstract A procedure for radioiodination of colchicine with iodine-125 is carried out via an electrophilic substitution reaction. The reaction parameters studied were colchicine concentration, pH of the reaction mixture, reaction time, temperature, different oxidizing agents and different organic media to optimize the conditions for the labeling of colchicine and to obtain a high radiochemical yield of the 125I-colchicine (125I-Col). Using 3.7,MBq of Na125I, 1.25,mM of colchicine as substrate, 1.1,mM of chloramine-T (CAT) as oxidizing agent in ethanol at 60°C for 5,min, a maximum radiochemical yield of 125I-Col (60%) was obtained. The specific activity of 125I-Col obtained was 44.4,MBq/0.5,mmol, and the labeled compound was not completely separated and purified from Col by means of high-pressure liquid chromatography (HPLC), so the uncertainty in the purity may affect the distribution and clearance routes due to the expected competition between 125I-Col and Col. The biological distribution in normal mice indicates the suitability of radioiodinated colchicine for imaging of muscles. Copyright © 2008 John Wiley & Sons, Ltd. [source] Probing the limits of molecular imprinting: strategies with a template of limited size and functionalityJOURNAL OF MOLECULAR RECOGNITION, Issue 1 2009Miruna Petcu Abstract A series of polymers molecularly imprinted with the general anaesthetic propofol were synthesized using both semi- and non-covalent approaches. The polymers were evaluated with respect to template rebinding in both aqueous and organic media. In aqueous media, the observed propofol binding in these polymer systems was largely hydrophobic and non-specific in nature. In non-polar solvents such as hexane, electrostatic (hydrogen bonding) interactions dominate resulting in some selectivity. The implication of these results, in conjunction with those obtained using structures of similar size in other studies, is that propofol, a template possessing limited functionality and size, appears to define the lower limit for template size and degree of functionalization that can be used for the creation of ligand-selective recognition sites in molecularly imprinted polymers. Furthermore, studies with alternative ligands indicate that the steric crowding of a ligand's functionality to the polymer contributes to the extent of polymer,ligand recognition. Copyright © 2008 John Wiley & Sons, Ltd. [source] Ionic liquids in the synthesis and modification of polymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2005Przemys, aw Kubisa Abstract Ionic liquids are organic salts that are liquid at ambient temperatures, preferably at room temperature. They are nonvolatile, thermally and chemically stable, highly polar liquids that dissolve many organic, inorganic, and metallo-organic compounds. Many combinations of organic cations with different counterions are already known, and the properties of ionic liquids may be adjusted by the proper selection of the cation and counterion. In the last decade, there has been increasing interest in using ionic liquids as solvents for chemical reactions. The interest is stimulated not only by their nonvolatility (green solvents) but also by their special properties, which often affect the course of a reaction. In recent years, ionic liquids have also attracted the attention of polymer chemists. Although the research on using ionic liquids in polymer systems is still in its infancy, several interesting possibilities have already emerged. Ionic liquids are used as solvents for polymerization processes, and in several systems they indeed show some advantages. In radical polymerization, the kp/kt ratio (where kp is the rate constant of propagation and kt is the rate constant of termination) is higher than in organic media, and thus better control of the process can be achieved. Ionic liquids, as electrolytes, have also attracted the attention of researchers in the fields of electrochemical polymerization and the synthesis of conducting polymers. Finally, the blending of ionic liquids with polymers may lead to the development of new materials (ionic liquids may act as plasticizers, electrolytes dispersed in polymer matrices, or even porogens). In this article, the new developments in these fields are briefly discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4675,4683, 2005 [source] Kinetic analysis of bacterial bioluminescence in water,organic mediaLUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 4 2001I. E. Sukovataya Abstract The interaction of luciferases from two types of luminous bacteria, Photobacterium leiognathi and Vibrio harveyi, with their substrates [the photorecovered FMNH2 and long-chain aldehydes,decanal (C10), dodecanal (C12) and tetradecanal (C14)] in water,organic media was analysed using kinetic graphical methods. Moderate concentrations of organic solvents have been demonstrated to activate the bioluminescence, while higher concentrations inhibit it. The interactions of these effectors with luciferases show different types of kinetics, which depend on concentrations of solvents, kinds of enzymes and substrates. The apparent value of the Michaelis constant, Km, for C14 of both luciferases and for C10 of luciferase V. harveyi is enhanced with increasing concentration of the organic solvent, but Km for C12 and C10 of luciferase P. leiognathi decreases. Obviously, at the specific binding of aldehydes with luciferases in the first case, hydrophobic interactions are realized, but in second, the electrostatic interactions are realized. The series of changes in parameters of bioluminescence reaction catalysed by different luciferases is obviously determined by their structural peculiarities. Copyright © 2001 John Wiley & Sons, Ltd. [source] Facile Access to an Efficient Solid-Supported Click Catalyst System Based on Poly(ethyleneimine)MACROMOLECULAR RAPID COMMUNICATIONS, Issue 1 2009Lies Bonami Abstract A novel heterogeneous copper(I) catalyst system, which is based on readily available poly(ethyleneimine), has been used as a recyclable catalyst for Cu(I) catalyzed "click" 1,3 dipolar cycloaddition reactions of azides and alkynes in organic media. Branched poly(ethyleneimine) was first methylated and then cross-linked with 1,9-dibromononane. Subsequently, after the immobilization of Cu(I)Br, this system was applied for heterogeneous copper catalyzed click chemistry of a few model reagents and polymeric compounds. [source] Supramolecular Structure of Self-assembled Synthetic Zinc-131 -oxo-chlorins Possessing a Primary, Secondary or Tertiary Alcoholic 31 -Hydroxyl Group: Visible Spectroscopic and Molecular Modeling Studies,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2001Shiki Yagai ABSTRACT Zinc-chlorin 3 (see Fig. 2 in text) possessing a tertiary 31 -hydroxyl group and a 13-keto group was synthesized as a model for the antenna chlorophylls of green bacteria. Self-aggregation of 3 in nonpolar organic media was examined and compared to 1 and 2 possessing a primary and secondary 31 -hydroxyl group, respectively. Zinc-chlorin 3 self-aggregated in 1 vol% CH2Cl2,hexane to form oligomers and showed a red-shifted Qy maximum at 704 nm compared to the monomer (648 nm in CH2Cl2). This red-shift is larger than that of 2S (648 , 697 nm) and comparable to that of 2R (648 , 705 nm), but smaller than that of 1 (648 , 740 nm), indicating that while a single 31 -methyl group (prim -OH ,sec -OH) suppressed close and/or higher aggregation, the additional 31 -methyl group (sec -OH ,tert -OH) did not further suppress aggregation. The relative stability of the aggregates was in the order 1 > 2R, 3 > 2S as determined by visible spectral analyses. Molecular modeling calculations on dodecamers of zinc-chlorins 1, 2R and 3 gave similar well-ordered energy-minimized structures, while 1 stacked more tightly than 2R and 3. In contrast, 2S gave a relatively disordered (twisted) structure. The calculated dodecameric structures could explain the visible spectral data of 1,3 in nonpolar organic media. [source] Electrochemical behaviour and electrochemical polymerization of fluoro-substituted anilinesPOLYMER INTERNATIONAL, Issue 8 2002Atilla Cihaner Abstract The electrochemical behaviour of three fluoro-substituted aniline monomers, 2-fluoroaniline (2FAN), 3-fluoroaniline (3FAN) and 4-fluoroaniline (4FAN), was investigated in aqueous acidic and organic media by means of cyclic voltammetry (CV) studies. Constant potential electrolysis (CPE) of the monomers in acetonitrile,water mixture (1:1 by volume) using NaClO4 as supporting electrolyte yielded soluble polymers. The mechanism of electrochemical polymerization was investigated using in situ electron spin resonance (ESR) and in situ UV,VIS spectroscopic techniques for one of the monomers (4FAN). Both CV and in situ UV,VIS measurements indicated that the polymers obtained are in the emeraldine base form. In situ ESR studies indicated that electrochemical polymerization involves a radical-cation as an intermediate. Characterization of polymer products have been carried out using FTIR and NMR spectroscopic techniques, and thermal behaviour was studied using differential scanning calorimetry (DSC). It was found that conductivity can be imparted to as-synthesized polyfluoroanilines via iodine doping. © 2002 Society of Chemical Industry [source] Fabrication of multilayer ceramic membranesASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009V.V. Zyryanov Abstract The development of multilayer mixed conducting oxide membranes on macroporous dead-end tubular composite glass/ceramic substrates is presented. Sol modification of glass/ceramic substrate enhances the performance of catalytic membrane reactor (CMR) with reduced thickness of ceramic layers. The shrinkage misfit between support and ceramic layers can be regulated by different processing steps including sol modification of substrate and preliminary annealing of ceramic powders. Nanopowders of compatible complex perovskites as membrane materials were obtained by mechanochemical synthesis. Porous and dense ceramic layers were supported onto the internal wall of substrate by slip casting of slurries comprised of the narrow fractions of agglomerated powders dispersed in organic media with addition of surfactants. For SrFeO3 -based dense perovskite ceramics, both dynamics of oxygen loss at high temperatures and mechanical properties were found to be affected by the presence of SrSO4 surface inclusions formed due to sulfur admixture in starting reactants. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Adsorption, absorption, and biological degradation of ammonia in different biofilter organic mediaBIOTECHNOLOGY & BIOENGINEERING, Issue 3 2007Estela Pagans Abstract A tailor-made apparatus called ammoniometer, which is a batch mode respirometer applied to the study of ammonia biodegradation in biofilter media, has been used to evaluate adsorption, absorption, and biodegradation in five different organic materials (compost, coconut fibre, bark, pruning wastes, and peat) obtained from full-scale biofilters in operation in several waste treatment plants. The results showed that absorption could be represented by a Henry's law linear equation, with values of the Henry coefficient significantly higher (from 1,866 to 15,320) than that of pure water (1,498). Adsorption data were successfully fitted to Langmuir and Freundlich isotherms and maximum adsorption capacity varies from 1.06 to 1.81 mg NH3/g dry media. Ammonia biodegradation rates for each organic material were also calculated. Biodegradation rates varied from 0.67 to 7.82 mg NH3/kg media/d depending on the material tested. The data obtained showed important differences in the behaviour of the biofilter organic media, which has important implications in the design and modelling of these systems. Biotechnol. Bioeng. 2007;97: 515,525. © 2006 Wiley Periodicals, Inc. [source] Altering lipase activity and enantioselectivity in organic media using organo-soluble bases: Implication for rate-limiting proton transfer in acylation stepBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2006Chun-Chi Chen Abstract With the hydrolytic resolution of (R,S)-naproxen 2,2,2-trifluoroethyl esters via a partially purified papaya lipase (PCPL) in water-saturated isooctane as the model system, the enzyme activity, and enantioselectivty is altered by adding a variety of organo-soluble bases that act as either enzyme activators (i.e., TEA, MP, TOA, DPA, PY, and DMA) or enzyme inhibitors (i.e., PDP, DMAP, and PP). Triethylamine (TEA) is selected as the best enzyme activator as 2.24-fold increase of the initial rate for the (S)-ester is obtained when adding 120 mM of the base. By using an expanded Michaelis,Menten mechanism for the acylation step, the kinetic analysis indicates that the proton transfer for the breakdown of tetrahedral intermediates to acyl-enzyme intermediates is the rate-limiting step, or more sensitive than that for the formation of tetrahedral intermediates when the enzyme activators of different pKa are added. However, no correlation for the proton transfers in the acylation step is found when adding the bases acting as enzyme deactivators. © 2006 Wiley Periodicals, Inc. [source] Enzymatic Redox Cofactor Regeneration in Organic Media: Functionalization and Application of Glycerol Dehydrogenase and Soluble Transhydrogenase in Reverse MicellesBIOTECHNOLOGY PROGRESS, Issue 4 2005Hirofumi Ichinose An enzymatic system for the regeneration of redox cofactors NADH and NADPH was investigated in nanostructural reverse micelles using bacterial glycerol dehydrogenase (GLD) and soluble transhydrogenase (STH). Catalytic conversion of NAD+ to NADH was realized in the sodium dioctylsulfosuccinate (AOT)/isooctane reverse micellar system harboring GLD and a sacrificial substrate, glycerol. The initial rate of NADH regeneration was enhanced by exogenous addition of ammonium sulfate into the reverse micelles, suggesting that NH4+ acts as a monovalent cationic activator. STH was successfully entrapped in the AOT/isooctane reverse micelles as well as GLD and was revealed to be capable of catalyzing the stoichiometric hydrogen transfer reaction between NADP+ and NADPH in reverse micelles. These results indicate that GLD and STH have potential for use in redox cofactor recycling in reverse micelles, which allows the use of catalytic quantities of NAD(P)H in organic media. [source] Preparation of Bismuth Oxide Quantum Dots and their Photocatalytic Activity in a Homogeneous SystemCHEMCATCHEM, Issue 9 2010Prof. Hua Zhang Abstract Colloidal oil-soluble Bi2O3 quantum dots (QDs) are synthesized through an alcoholysis route in organic media. Water-soluble Bi2O3 QDs are then obtained from the initial oil-soluble QDs through phase transfer by surface modification with mercaptopropionic acid. X-ray diffraction and transmission electron microscopy studies show that the crystallinity is enhanced and particles grow larger after phase transfer. The water-soluble Bi2O3 QDs exhibit excellent photocatalytic activity for the degradation of methyl orange at a wide range of pH values. After several cycles, the Bi2O3 QDs retain high degradation efficiency. Simulation according to the first-order reaction dynamics indicates that the degradation reaction may follow complicated quasi-homogeneous photocatalysis. [source] Conformational Structure and Energetics of 2-Methylphenyl(2,-methoxyphenyl)iodonium Chloride: Evidence for Solution ClustersCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2010Dr. Yong-Sok Lee Abstract Diaryliodonium salts allow the efficient incorporation of cyclotron-produced [18F]fluoride ions into electron-rich and electron-deficient arenes to provide potential radiotracers for molecular imaging in vivo with positron emission tomography (PET). This process (ArI+Ar,+18F,,Ar18F+Ar,I) is still not well understood mechanistically. To better understand this and similar reactions, it would be valuable to understand the structures of diaryliodonium salts in organic media, where the reactions are typically conducted. In this endeavor, the X-ray structure of a representative iodonium salt, 2-methylphenyl(2,-methoxyphenyl)iodonium chloride (1), was determined. Our X-ray structure analysis showed 1 to have the conformational M,P dimer as the unit cell with hypervalent iodine as a stereogenic center in each conformer. With the ab initio replica path method we constructed the inversion path between the two enantiomers of 1, thereby revealing two additional pairs of enantiomers that are likely to undergo fast interconversion in solution. Also LC,MS of 1 showed the presence of dimeric and tetrameric anion-bridged clusters in weak organic solution. This observation is consistent with the energetics of 1, both as monomeric and dimeric forms in MeCN, calculated at the B3LYP/DGDZVP level. These evidences of the existence of dimeric and higher order clusters of 1 in solution are relevant to achieve a deeper general understanding of the mechanism and outcome of reactions of diaryliodonium salts in organic media with nucleophiles, such as the [18F]fluoride ion. [source] Dendritic Porphyrin,Fullerene Conjugates: Efficient Light-Harvesting and Charge-Transfer EventsCHEMISTRY - A EUROPEAN JOURNAL, Issue 45 2009Sebastian Schlundt Abstract A novel dendritic C60 -H2P-(ZnP)3 (P=porphyrin) conjugate gives rise to the successful mimicry of the primary events in photosynthesis, that is, light harvesting, unidirectional energy transfer, charge transfer, and charge-shift reactions. Owing, however, to the flexibility of the linkers that connect the C60, H2P, and ZnP units, the outcome depends strongly on the rigidity/viscosity of the environment. In an agar matrix or Triton X-100, time-resolved transient absorption spectroscopic analysis and fluorescence-lifetime measurements confirm the following sequence. Initially, light harvesting is seen by the peripheral C60 -H2P- *(ZnP)3 conjugate. Once photoexcited, a unidirectional energy transfer funnels the singlet excited-state energy to H2P to form C60 -*(H2P)-(ZnP)3, which powers an intramolecular charge transfer that oxidizes the photoexcited H2P and reduces the adjacent C60 species. In the correspondingly formed (C60)., -(H2P).+ -(ZnP)3 conjugate, an intramolecular charge-shift reaction generates (C60)., -H2P-(ZnP)3.+, in which the radical cation resides on one of the three ZnP moieties, and for which lifetimes of up to 460,ns are found. On the other hand, investigations in organic media (i.e., toluene, THF, and benzonitrile) reveal a short cut, that is, the peripheral ZnP unit reacts directly with C60 to form (C60)., -H2P-(ZnP)3.+. Substantial configurational rearrangements, placing ZnP and C60 in proximity to each other,are, however, necessary to ensure the required through space interactions (i.e., close approach). Consequently, the lifetime of (C60)., -H2P-(ZnP)3.+ is as short as 100,ps in benzonitrile. [source] Functional Polymeric Micelles Formed from a Novel Cationic Star Block CopolymerCHEMPHYSCHEM, Issue 10 2003Ren-Hua Jin Dr. Flowers made from stars: A star polymer, which consists of a porphyrin center to which four arms with cationic poly(ethyleneimine) (PEI) and hydrophobic poly(phenyloxazoline) (PPOZ) segments were attached, was synthesized and shown to form micelles in both aqueous and organic media (see picture). In aqueous media, the star formed a micelle in which a hydrophobic PPOZ core was surrounded by cationic corona PEI. The porphyrin moieties enclosed in the micellar core can effectively communicate with an ionic substrate enriched in the cationic corona. In organic media, the star gave a flowerlike micelle in which the ionomer segment PEI assembled to form a core and the nonionic PPOZ segments formed a looplike corona coating the core. [source] | ||||||||||||||||||||||||||||