Home About us Contact
|
Home About us Contact | ||
|
|
||
Basic Conditions (basic + condition)
Selected AbstractsReinvestigation of the Mechanism of gem -Diacylation: Chemoselective Conversion of Aldehydes to Various gem -Diacylates and Their Cleavage under Acidic and Basic ConditionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2005Veerababurao Kavala Abstract The mechanism of gem -diacylate formation has been studied extensively using tetrabutylammonium tribromide (TBATB) as the catalyst. The reaction proceeds by a nucleophilic attack of an anhydride on an aldehydic carbonyl group, nucleophilic attack of the hemiacylate intermediate on a second molecule of the anhydride, followed by an intermolecular attack of a second acetate group to regenerate the anhydride. gem -Diacylates of various aliphatic and aromatic aldehydes were obtained directly from the reaction of a variety of aliphatic and aromatic acid anhydrides in the presence of a catalytic quantity of tetrabutylammonium tribromide (TBATB) under solvent-free conditions. A significant electronic effect was observed during its formation as well as deprotection to the corresponding aldehyde. Chemoselective gem -diacylation of the aromatic aldehyde containing an electron-donating group has been achieved in the presence of an aldehyde containing an electron-withdrawing group. Deprotection of the gem -diacylate to the parent carbonyl compound can be accomplished in methanol in presence of the same catalyst. Here again, chemoselective deprotection of the gem -diacylate of a substrate containing an electrondonating group has been achieved in the presence of a substrate containing an electron-withdrawing group. Both the acid and base stability order of the various gem -diacylates examined follow a similar order. The stability order determined from the present study is: gem -dibenzoate > gemdipivalate > gem -diisobutyrate > gem -diacetate > gem -dipropionate. All the gem -diacylals are more stable under basic conditions than acidic condition. No correlation was found between the stability order and the pKa's of the corresponding acids; rather, the stability order is directly related to the steric crowding around the carbonyl carbon. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Intermolecular Reactions of Chlorohydrine Anions: Acetalization of Carbonyl Compounds under Basic Conditions.CHEMINFORM, Issue 51 2006Michal Barbasiewicz Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] "Syn-Effect" in the Isomerization of (E)-,-Fluorovinylic Sulfones to the Corresponding Allylic Sulfones under Basic Conditions.CHEMINFORM, Issue 1 2003Tetsuya Nakamura Abstract For Abstract see ChemInform Abstract in Full Text. [source] An Unusual N -Boc Deprotection of Benzamides under Basic ConditionsCHINESE JOURNAL OF CHEMISTRY, Issue 9 2009Biaolin Yin Abstract For the first time, an unusal cleavage of N-tert -butyloxycarbonyl (N -Boc) protection from N -Boc-protected benzamide under basic conditions in excellent yields is reported. The deprotection involves the N -Boc emigration from the benzamide to form 2- O -Boc group followed by O -Boc deprotection on the phenyl ring. [source] Well-defined diblock and triblock copolymers for KrF lithographyJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Ting-Yu Lee Abstract One of the major components of a photoresist formulation is polymer resin. Well-defined diblock and random copolymer of tert -butyl acrylate (tBA) and 4-acetoxystyrene (StyOAc), as well as triblock and random tertpolymer of tBA, StyOAc, and Sty were prepared by reversible addition fragmentation chain transfer polymerization (RAFT) process. The polymers all possess Mw about ten thousand and PDI less than 1.23. After hydrolysis under basic condition, the hydroxystyrene (StyOH) analogs are obtained and then are formulated as photoresist. Lithographic evaluation under KrF excimer laser shows that random copolymer based photoresist exhibits better S/L patterns according to SEM images. However, the lithographic performance of the terpolymer based resists is similar. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Synthesis and characterization of the PEG-based nonionic surfactants endowed with carboxylic acid moiety at the hydrophobic terminalJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2008Hiroshi Morikawa As a new class of stimulus-responsive surfactants, a series of ,-methyl-,-alkyl PEGs endowed with a carboxylic acid moiety at the hydrophobic terminal was successfully synthesized with 56,97% yields. They were characterized by IR, NMR spectroscopic and MALDI-TOF MS analyses. It is suggested by DLS measurement that the collapse of the micelle-like aggregation occurred under basic condition. This synthetic procedure would be applicable to surfactants with sufficient hydrophilic and lipophilic balances, allowing precise control of pH-responsive micellar systems. [source] A Polymer-Bound Oxidovanadium(IV) Complex Prepared from an L -Cysteine-Derived Ligand for the Oxidative Amination of StyreneEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2008Mannar R. Maurya Abstract The ligand H2sal-cys (I) derived from salicylaldehyde and L -cysteine has been covalently bonded to chloromethylated polystyrene cross-linked with 5,% divinylbenzene. Upon treatment with [VO(acac)2] in dimethylformamide (DMF) the polystyrene-bound ligand PS-H2sal-cys (II) gave the oxidovanadium(IV) complex, PS-[VO(sal-cys)·DMF] (1). The corresponding neat complex, [VO(sal-eta)]2 (2), has also been prepared similarly in methanol. These complexes have been characterised by IR, electronic, EPR spectroscopic studies, magnetic susceptibility measurements and thermal as well as scanning electron micrographs studies. Complex [VO(sal-eta)]2 exhibits a medium intensity band at 980 cm,1 in the IR spectrum due to ,(V=O) stretch. Broad features of the EPR spectrum for the neat complex along with magnetic susceptibility studies suggest the presence of antiferromagnetic exchange interaction between two vanadium centers in close proximity. Both complexes catalyze the oxidative amination of styrene, in mild basic conditions, with secondary amines (diethylamine, imidazole, and benzimidazole) and gave a mixture of two aminated products in good yields. Amongst the two aminated products, the anti-Markovnikov product is favored over the Markovnikov one due to the steric hindrance posed by the secondary amines. The polymer-anchored heterogeneous catalyst is free from leaching during catalytic action and recyclable.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Reinvestigation of the Mechanism of gem -Diacylation: Chemoselective Conversion of Aldehydes to Various gem -Diacylates and Their Cleavage under Acidic and Basic ConditionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2005Veerababurao Kavala Abstract The mechanism of gem -diacylate formation has been studied extensively using tetrabutylammonium tribromide (TBATB) as the catalyst. The reaction proceeds by a nucleophilic attack of an anhydride on an aldehydic carbonyl group, nucleophilic attack of the hemiacylate intermediate on a second molecule of the anhydride, followed by an intermolecular attack of a second acetate group to regenerate the anhydride. gem -Diacylates of various aliphatic and aromatic aldehydes were obtained directly from the reaction of a variety of aliphatic and aromatic acid anhydrides in the presence of a catalytic quantity of tetrabutylammonium tribromide (TBATB) under solvent-free conditions. A significant electronic effect was observed during its formation as well as deprotection to the corresponding aldehyde. Chemoselective gem -diacylation of the aromatic aldehyde containing an electron-donating group has been achieved in the presence of an aldehyde containing an electron-withdrawing group. Deprotection of the gem -diacylate to the parent carbonyl compound can be accomplished in methanol in presence of the same catalyst. Here again, chemoselective deprotection of the gem -diacylate of a substrate containing an electrondonating group has been achieved in the presence of a substrate containing an electron-withdrawing group. Both the acid and base stability order of the various gem -diacylates examined follow a similar order. The stability order determined from the present study is: gem -dibenzoate > gemdipivalate > gem -diisobutyrate > gem -diacetate > gem -dipropionate. All the gem -diacylals are more stable under basic conditions than acidic condition. No correlation was found between the stability order and the pKa's of the corresponding acids; rather, the stability order is directly related to the steric crowding around the carbonyl carbon. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Synthesis and Rearrangement of N -Organyloxy ,-Lactams Derived from a (4+2)/(3+2) Sequential Cycloaddition Reaction Involving Enol Ethers and Nitro AlkenesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2004Leon W. A. van Berkom Abstract The synthesis of N -organyloxy ,-lactams 2 by treatment of nitroso acetals 1 with a base is discussed. Based on the formation of a by-product, a mechanism for the rearrangement to N -organyloxy ,-lactams is proposed. This mechanism is supported by trapping of the intermediate acyl nitro compound 8 with dimethylamine. Furthermore, it was discovered that upon more forcing basic conditions these N -organyloxy ,-lactams can rearrange further to 3-organyloxy ,-lactams. By using a series of structurally diverse N -organyloxy ,-lactams the generality of this novel rearrangement is demonstrated. A mechanism for the conversion of N -organyloxy ,-lactams to 3-organyloxy ,-lactams is proposed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] A Fast Access to Non-Symmetrically Substituted 1,3-Alternate Conformers of Calix[4]arenesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2004Arjan W. Kleij Abstract A simple and direct protocol is reported for the synthesis of the first non-symmetrically substituted 1,3-alternate conformers of calix[4]arenes by selective mono-deacylation of a tribenzoyl precursor under basic conditions, followed by dialkylation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Total Synthesis without Protection: Three-Step Synthesis of Optically Active Clavicipitic Acids by a Biomimetic RouteEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2004Yuusaku Yokoyama Abstract A three-step synthesis of a mixture of optically active cis - and trans -clavicipitic acids 6, which are ergot alkaloids, was achieved, starting from 4-bromoindole (7) and dl -serine (dl - 2). This short synthesis was made possible by omitting the protection and deprotection steps from the synthetic route. The key step was the spontaneous cyclization of 4-vinyltryptophan (10) formed from the Heck reaction of 4-bromotryptophan (8) with 2-methyl-3-buten-2-ol (9) in aqueous media. During this investigation, we also found that the palladium-catalyzed reaction of 8 with 9 showed an interesting pH dependence; under strongly basic conditions, the Heck reaction occurred to give a C4 -vinylated product 10, whereas an N -allylated product 19b was formed under neutral or weakly basic conditions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Gene expression profiling of the pH response in Shigella flexneri 2aFEMS MICROBIOLOGY LETTERS, Issue 1 2007Fan Cheng Abstract The pH response of Shigella flexneri 2a 301 was identified by gene expression profiling. Gene expression profiles of cells grown in pH 4.5 or 8.6 were compared with the profiles of cells grown at pH 7.0. Differential expression was observed for 307 genes: 97 were acid up-regulated, 102 were acid down-regulated, 91 were base up-regulated, and 86 were base down-regulated. Twenty-seven genes were found to be both acid and base up-regulated, and 29 genes were both acid and base down-regulated. This study showed that (1) the most pH-dependent genes regulate energy metabolism; (2) the RpoS-dependent acid-resistance system is induced, while the glutamate-dependent acid resistance system is not; (3) high pH up-regulates some virulence genes, while low pH down-regulates them, consistent with Shigella infection of the low gut; and (4) several cross-stress response genes are induced by pH changes. These results also illustrate that many unknown genes are significantly regulated under acid or basic conditions, providing researchers with important information to characterize their function. [source] A metapopulation perspective for salmon and other anadromous fishFISH AND FISHERIES, Issue 4 2007Nicolas Schtickzelle Abstract Salmonids are an important component of biodiversity, culture and economy in several regions, particularly the North Pacific Rim. Given this importance, they have been intensively studied for about a century, and the pioneering scientists recognized the critical link between population structure and conservation. Spatial structure is indeed of prime importance for salmon conservation and management. At first glance, the essence of the metapopulation concept, i.e. a population of populations, widely used on other organisms like butterflies, seems to be particularly relevant to salmon, and more generally to anadromous fish. Nevertheless, the concept is rarely used, and barely tested. Here, we present a metapopulation perspective for anadromous fish, assessing in terms of processes rather than of patterns the set of necessary conditions for metapopulation dynamics to exist. Salmon, and particularly sockeye salmon in Alaska, are used as an illustrative case study. A review of life history traits indicates that the three basic conditions are likely to be fulfilled by anadromous salmon: (i) the spawning habitat is discrete and populations are spatially separated by unsuitable habitat; (ii) some asynchrony is present in the dynamics of more or less distant populations and (iii) dispersal links populations because some salmon stray from their natal population. The implications of some peculiarities of salmon life history traits, unusual in classical metapopulations, are also discussed. Deeper understanding of the population structure of anadromous fish will be advanced by future studies on specific topics: (i) criteria must be defined for the delineation of suitable habitats that are based on features of the biotope and not on the presence of fish; (ii) the collection of long-term data and the development of improved methods to determine age structure are essential for correctly estimating levels of asynchrony between populations and (iii) several key aspects of dispersal are still poorly understood and need to be examined in detail: the spatial and temporal scales of dispersal movements, the origin and destination populations instead of simple straying rates, and the relative reproductive success of immigrants and residents. [source] The Limits of Unilateral Migration Control: Deportation and Inter-state Cooperation1GOVERNMENT AND OPPOSITION, Issue 2 2008Antje Ellermann Despite the recent proliferation of policy initiatives designed to curb illegal immigration, advanced industrialized states have made little headway towards the goal of effective migration control. Examining the case of deportation in Germany and the European Union, this article contends that one of the most fundamental reasons underlying this failure is a unilateral policy bias that fails to take into account two related conditions. First, policies of migration control directly and substantially impinge upon the interests of foreign governments. Secondly, the cooperation of foreign officials is an essential condition for policy implementation. To the extent that they disregard these basic conditions, then, migration control policies are bound to fail. By examining the implementation of deportation policy, the article illustrates the limited efficacy of control measures that are dominated by the interests of advanced industrialized states to the exclusion of the concerns of foreign governments. [source] Structural Evolution of Self-Assembling Nanohybrid Thin Films from Functionalized Urea Precursors,ADVANCED FUNCTIONAL MATERIALS, Issue 18 2007I. Karatchevtseva Abstract Hybrid organic-inorganic thin films exhibiting patterned structuring on the nanometer scale have been prepared through the controlled hydrolysis-condensation of enantiomerically pure chiral urea-based silyl compounds. The thin films are obtained by spin-coating of sols obtained via acid- or base-catalyzed hydrolytic condensation of these molecular precursors. A self-templating process is demonstrated via atomic force and transmission electron microscopy, showing the formation of nanometer size aggregates consisting of interconnected spherulates under acidic condition and of assembled fibers under basic conditions. [source] Facile and Sensitive Spectrophotometric Determination of Propoxur in Formulations and Environmental SamplesHELVETICA CHIMICA ACTA, Issue 5 2005Kailasa, Suresh Kumar A facile, rapid, and sensitive spectrophotometric method for the determination of propoxur in insecticidal formulations, fortified water, vegetables, agricultural wastewater, and agricultural soil samples has been elaborated. The proposed method is based on the hydrolysis of propoxur under basic conditions, followed by instantaneous azo coupling of the resulting 2-isopropoxyphenol with the anilines 2a,c. This yielded the orange-red chromophore 3a (,max=at 470,nm), the pale-red coupling product 3b (490,nm), or the red derivative 3c (478,nm), which are stable for 46,h, 38,h, and 24,h, respectively, and could be readily analyzed spectrophotometrically. [source] Chemo- and Stereodivergent Preparation of Terminal Epoxides and Bromohydrins through One-Pot Biocatalysed Reactions: Access to Enantiopure Five- and Six-Membered N-HeterocyclesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Fabricio Abstract Different enantiopure terminal epoxides or bromohydrins have chemoselectively been synthesised in one-pot starting from the corresponding ,-bromo ketones through alcohol dehydrogenase (ADH)-catalysed processes adding an organic co-solvent and tuning appropriately the medium pH and the temperature. Thus, at neutral pH enantiopure bromohydrins were obtained while using basic conditions (pH,9.5,10) epoxides were isolated as the main product. Furthermore, by simple selection of the biocatalyst, chemo- and stereodivergent transformations were achieved to obtain, e.g., enantiopure prolinol or piperidin-3-ol. [source] Novel [Ruthenium(substituted-tetramethylcyclopentadiene) (2-quinolinecarboxylato)(allyl)] Hexafluorophosphate Complexes as Efficient Catalysts for Highly Regioselective Nucleophilic Substitution of Aliphatic Allylic SubstratesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2008Hui-Jun Zhang Abstract Stable [ruthenium(R-substituted-tetramethylcyclopentadiene)(2-quinolinecarboxylato)(1-R,-substituted-allyl) hexafluorophosphate (R=Me, R,=H, Me, n- Pr, Ph; R=t- Bu, R,=Me) and [ruthenium(pentamethylcyclopentadiene)(2-quinolinecarboxylato)(1- n -propylallyl)] tetrafluoroborate (4,a), as allylruthenium(IV) complexes, have been synthesized in one step, starting from [ruthenium(R-substituted-tetramethylcyclopentadiene)tris(acetonitrile) hexafluorophosphate or tetrafluoroborate complexes, quinaldic acid, and allylic alcohols. Single stereoisomers are obtained and the X-ray single crystal structure determinations of 3b (R=t- Bu, R,=Me) and 4,a allow one to specify the preferred arrangement. Complexes 3a (R=R,=Me) and 3b are involved as precatalysts favoring the formation of branched products in regioselective nucleophilic allylic substitution reactions, starting from ethyl 2- (E) -hexen-1-yl carbonate and chlorohexene as unsymmetrical aliphatic allylic substrates. Phenols, dimethyl malonate, and primary (aniline) and secondary (pyrrolidine, piperidine) amines have been used as nucleophiles under mild basic conditions. For the first time, the regioselectivity in favor of the branched product obtained from purely aliphatic allylic substrates is close to the high regioselectivity previously reached starting from cinnamyl-type substrates in the presence of ruthenium catalysts. [source] Chemoselective Palladium-Catalyzed Reaction in Aqueous Media: Selectivity in the Reaction of Haloanilines with 1,1-Dimethylallyl AlcoholADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4-5 2007Yuusaku Yokoyama Abstract Palladium-catalyzed reactions of various haloanilines with 1,1-dimethylallyl alcohol were carried out in the presence of a hydrophilic ligand, 3,3,,3,,-phosphinidyne tris(benzenesulfonic acid) trisodium salt (TPPTS), or a lipophilic phosphine ligand, 1,1,-bis(diphenylphosphino)ferrocene (DPPF). The reactions proceeded chemoselectively in aqueous solvent to give C -vinylated products under basic conditions or N -allylated products under neutral conditions in practical yields (up to 79,%). The use of an aqueous solvent played an important role in this chemoselectivity and allowed the development of a one-pot synthesis of 3-methylindole. This chemoselectivity is synthetically useful because the reactive position of haloanilines can be controlled simply by changing the basicity of the reaction medium, which eliminates the need to protect the amino group during the reaction. [source] Synthesis and alkylation of 5-(3-chlorobenzo[b]thien-2-yl)-4H -1,2,4-triazole-3-thiol under classical and microwave conditions.JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 6 2006AM1 semiemperical calculations for investigating the regioselectivity of alkylation Under microwave irradiation (MWI), 5-(3-chlorobenzo[b]thien-2-yl)-4H -1,2,4-triazole-3-thiol (3) was synthesized in a good yield by intramolecular cyclization of the carbonyl thiosemicarbazide 2. A regioselective S-alkylation of 3 with benzyl chloride or allyl bromide has been achieved by using triethylamine as a base, while other different basic conditions led to a mixture of bis(alkylated) derivatives N4, S- and S, N2 -, under both of classical and MWI conditions. The relative stabilities, charge densities, dipole moments and electronic energies of reactants, transition states and intermediates were calculated by the AM1 method and used for investigating the regioselectivity. [source] Synthesis of MMP inhibitor radiotracers [11C]methyl-CGS 27023A and its analogs, new potential PET breast cancer imaging agentsJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 6 2002Xiangshu Fei Abstract [11C]Methyl-CGS 27023A (1a) and its analogs [11C]methyl-2-picolyl-CGS 27023A (1b), [11C]methyl-benzyl-CGS 27023A (1c), [11C]methyl-2-nitro-CGS 27023A (1d), [11C]methyl-3-nitro-CGS 27023A (1e), and [11C]methyl-4-nitro-CGS 27023A (1f), novel radiolabeled matrix metalloproteinase (MMP) inhibitors, have been synthesized for evaluation as new potential positron emission tomography (PET) breast cancer imaging agents. The appropriate precursors for radiolabeling were obtained in four to five steps from starting material amino acid D -valine with moderate to excellent chemical yields. Precursors were labeled by [11C]methyl triflate through 11C,O-methylation method at the aminohydroxyl position under basic conditions and isolated by solid-phase extraction (SPE) purification to produce pure target compounds in 40,60% radiochemical yields (decay corrected to end of bombardment), in 20,25 min synthesis time. Copyright © 2002 John Wiley & Sons, Ltd. [source] Quantitative analysis of EO9 (apaziquone) and its metabolite EO5a in human plasma by high-performance liquid chromatography under basic conditions coupled to electrospray tandem mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2006Liia D. Vainchtein A sensitive and specific LC-MS/MS assay for the quantitative determination of EO9 and its metabolite EO5a is presented. A 200-µl human plasma aliquot was spiked with a mixture of deuterated internal standards EO9- d3 and EO5a- d4 and extracted with 1.25 ml ethyl acetate. Dried extracts were reconstituted in 0.1 M ammonium acetate,methanol (7 : 3, v/v) and 25 µl-volumes were injected into the HPLC system. Separation was achieved on a 150 × 2.1 mm C18 column using an alkaline eluent (1 mM ammonium hydroxide,methanol (gradient system)). Detection was performed by positive ion electrospray followed by tandem mass spectrometry. The assay quantifies a range from 5 to 2500 ng/ml for EO9 and from 10 to 2500 ng/ml EO5a using 200 µl of human plasma samples. Validation results demonstrate that EO9 and EO5a concentrations can be accurately and precisely quantified in human plasma. This assay will be used to support clinical pharmacologic studies with EO9. Copyright © 2006 John Wiley & Sons, Ltd. [source] Tetrahedral intermediates in reactions of carboxylic acid derivatives with nucleophiles,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2005Martin Adler Abstract Transacylation reactions of carboxylic acids, carboxylic acid esters, carboxylic acid amides and other carboxylic acid derivatives are among the most widespread and most important reactions in chemistry and biochemistry. Already in 1887, Claisen suggested a tetrahedral intermediate in transformations of carboxylic acid derivatives with nucleophiles. A historical overview gives insight into the studies to detect possible tetrahedral intermediates in such reactions. However, only in recent years has detailed information concerning the structures of such species become available. In this review, neutral, cationic and anionic tetrahedral intermediates are described which serve as models for transacylations under neutral, acid-catalysed or basic conditions. The characteristically different structures correspond nicely with experimental experience with reactions of carboxylic acid derivatives and with quantum chemical model calculations on tetrahedral intermediates. Finally, by means of model calculations, an explanation is given for the fast reactions of Weinreb amides, RC(O)N(CH3)OCH3, with organolithium and even with Grignard reagents: the reactions are determined by comparatively stable chelate transition states. Copyright © 2004 John Wiley & Sons, Ltd. [source] Synthesis of hyperbranched degradable polymers by atom transfer radical (Co)polymerization of inimers with ester or disulfide groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2009Nicolay V. Tsarevsky Abstract Degradable hyperbranched polymers with multiple alkyl halide chain ends were synthesized by the atom transfer radical polymerization of inimers containing ester (2-(2,-bromopropionyloxy)ethyl acrylate) or disulfide (2-(2,-bromoisobutyryloxy)ethyl 2,,-methacryloyloxyethyl disulfide) groups. Both the homo- and copolymerizations (with styrene in the former case and methyl methacrylate in the latter) were studied. The hyperbranched polymers derived from the ester-type inimer were hydrolytically degradable under basic conditions, whereas those derived from the disulfide-containing inimer could be efficiently degraded in the presence of reducing agents such as tributylphosphine. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009 [source] New environmentally responsive fluorescent N -isopropylacrylamide copolymer and its application to DNA sensingJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2006Chang-Chung Yang Abstract We report two novel multifunctional copolymers consisting of a temperature-responsive poly(N -isopropylacrylamide) (PNIPAA) segment and a fluorescent fluorene-containing acrylic polymer segment with pH responsiveness and/or DNA-sensing ability. The functional acrylic monomer with a fluorene dimer side group substituted with amino units was synthesized first. Then, it was copolymerized with N -isopropylacrylamide to result in a new water-soluble, fluorescent PNIPAA copolymer (P1). The fluorescent properties of P1 under neutral and acidic conditions did not change with the temperature. However, significant variation was observed under basic conditions. The protonation of the amino moiety at a low pH improved the solubility and prevented aggregation for fluorescence quenching, but not under the basic conditions. Although aggregation of the fluorene units was significant at room temperature under basic conditions, the aggregation was resolved at a temperature above the lower critical solution temperature. These findings indicated the pH- and temperature-responsive characteristics of P1. Moreover, after the amino groups were quaternized, the obtained polymer could be used as a biosensor because the fluorescence intensity was quenched with the addition of DNA. This study demonstrates that multifunctional materials with pH- and temperature-sensing characteristics and biological molecules could be realized by the incorporation of a functional fluorene-containing moiety with PNIPAA. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5495,5504, 2006 [source] Anionic grafting polymerization of propylene sulfide onto human hair in waterJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2006Hisatoyo Morinaga Abstract Natural human hair was modified by the graft polymerization of propylene sulfide in an aqueous medium. The amount of the polymer grafted onto the reduced hair was 0.15,0.19 g on 1.0 g of hair. The grafted polymer was isolated by the hydrolysis of the hair in the polymer-grafted hair under basic conditions and was confirmed to be poly(propylene sulfide) by 1H NMR, 13C NMR, and Fourier transform infrared spectra. The number-average molecular weights of the isolated polymers from the grafted products were 10,000,12,000. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3778,3786, 2006 [source] Characterization of ring-opening polymerization of genipin and pH-dependent cross-linking reactions between chitosan and genipinJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2005Fwu-Long Mi Abstract In this study, a novel chitosan-based polymeric network was synthesized by crosslinking with a naturally occurring crosslinking agent,genipin. The results showed that the crosslinking reactions were pH-dependent. Under basic conditions, genipin underwent a ring-opening polymerization prior to crosslinking with chitosan. The crosslink bridges consisted of polymerized genipin macromers or oligomers (7 , 88 monomer units). This ring-opening polymerization of genipin was initiated by extracting proton from the hydroxyl groups at C-1 of deoxyloganin aglycone, followed by opening the dihydropyran ring to conduct an aldol condensation. At neutral and acidic conditions, genipin reacted with primary amino groups on chitosan to form heterocyclic amines. The heterocyclic amines were further associated to form crosslinked networks with short chains of dimmer, trimer, and tetramer bridges. An accompanied reaction of nucleophilic substitution of the ester group on genipin by the primary amine group on chitosan would occur in the presence of an acid catalysis. The extent in which chitosan gels crosslinked with genipin was significantly dependent on the crosslinking pH values: 39.9 ± 3.8% at pH 5.0, 96.0 ± 1.9% at pH 7.4, 45.4 ± 1.8% at pH 9.0, and 1.4 ± 1.0% at pH 13.6 (n = 5, p < 0.05). Owing to the different crosslinking extents and different chain lengths of crosslink bridges, the genipin-crosslinked chitosan gels showed significant difference in their swelling capability and their resistance against enzymatic hydrolysis, depending on the pH conditions for crosslinking. These results indicated a direct relationship between the mode of crosslinking reaction, and the swelling and enzymatic hydrolysis properties of the genipin-crosslinked chitosan gels. The ring-opening polymerization of genipin and the pH-dependent crosslinking reactions may provide a novel way for the preparation and exploitation of chitosan-based gels for biomedical applications. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1985,2000, 2005 [source] Facile synthesis, characterization, and potential applications of two kinds of polymeric pH indicators: Phenolphthalein formaldehyde and o -cresolphthalein formaldehydeJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2005Zhihong Liu Abstract Two kinds of applicable polymeric pH indicators were synthesized by the reaction of phenolphthalein and o -cresolphthalein with formaldehyde under alkaline conditions by a one-pot method. The synthesized products were fully characterized with Fourier transform infrared, 1H NMR, ultraviolet,visible spectroscopy, and gel permeation chromatography. The results indicated that the reaction was a typical phenol formaldehyde reaction. The dosage of formaldehyde and the reaction time were well controlled to obtain soluble polymers, instead of crosslinked products. The polymeric-pH-indicator-immobilized poly(vinyl alcohol) (PVA) membranes were easily fabricated and had good long-term stability under highly basic conditions and a fast equilibrium response. Moreover, the phenolphthalein formaldehyde immobilized PVA membrane had a linear response from pH 10.0 to 14.0, and so it has promise as a optical transducer for high pH value determinations. The o -cresolphthalein formaldehyde immobilized PVA membrane had a nonlinear response from pH 9.0 to 13.0. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1019,1027, 2005 [source] Synthesis and characterization of alkylated N -vinylformamide monomers and their polymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2004Lianjun Shi Abstract N -alkyl- N -vinylformamide monomers (alkyl: n -butyl, hexyl, decyl, and dodecyl) are synthesized in two steps: first, preparation of N -vinylformamide potassium salt by the reaction of N -vinylformamide (NVF) with potassium t -butoxide, then reaction with alkyl bromide. All four monomers are liquid and are characterized by IR, 1H NMR, 13C NMR, and mass spectra. They exist as rotomers in solution and a 2D NOE experiment on the N -hexyl containing polymer shows the E isomer to be favored. The polymerizability of the four monomers is from good to fair, depending upon the length of alkyl chain on the N -atom--the longer the chain length, the lower lower the polymerizability of monomer. The hydrolysis of poly(N -hexyl- N -vinylformamide) and poly(N -dodecyl- N -vinylformamide) under acidic and basic conditions was examined. Studies show that hydrolytic cleavage of formyl groups of poly (N -alkylated- N -vinylformamide) depends on the hydrophobicity of the alkyl substituent on the N -atom under acidic conditions; both polymers were hydrolyzed to only a minor extent under alkaline conditions. The N -alkylated monomers can copolymerize with NVF and demonstrate amphiphilic properties. The copolymers demonstrate a critical aggregation concentration above which they can solubilize a water insoluble dye; the N -hexyl containing copolymer stabilizes a castor oil-in-water emulsion. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4994,5004, 2004 [source] Synthesis and ring-opening (co)polymerization of L -lysine N -carboxyanhydrides containing labile side-chain protective groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2003Juan Rodríguez Hernández Abstract This contribution describes the synthesis and ring-opening (co)polymerization of several L -lysine N -carboxyanhydrides (NCAs) that contain labile protective groups at the ,-NH2 position. Four of the following L -lysine NCAs were investigated: N, -trifluoroacetyl- L -lysine N -carboxyanhydride, N, -(tert -butoxycarbonyl)- L -lysine N -carboxyanhydride, N, -(9-fluorenylmethoxycarbonyl)- L -lysine N -carboxyanhydride, and N, -(6-nitroveratryloxycarbonyl)- L -lysine N -carboxyanhydride. In contrast to the harsh conditions that are required for acidolysis of benzyl carbamate moieties, which are usually used to protect the ,-NH2 position of L -lysine during NCA polymerization, the protective groups of the L -lysine NCAs presented here can be removed under mildly acidic or basic conditions or by photolysis. As a consequence, these monomers may allow access to novel peptide hybrid materials that cannot be prepared from ,-benzyloxycarbonyl- L -lysine N -carboxyanhydride (Z-Lys NCA) because of side reactions that accompany the removal of the Z groups. By copolymerization of these L -lysine NCAs with labile protective groups, either with each other or with ,-benzyl- L -glutamate N -carboxyanhydride or Z-Lys NCA, orthogonally side-chain-protected copolypeptides with number-average degrees of polymerization ,20 were obtained. Such copolypeptides, which contain different side-chain protective groups that can be removed independently, are interesting for the synthesis of complex polypeptide architectures or can be used as scaffolds for the preparation of synthetic antigens or protein mimetics. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1167,1187, 2003 [source] | ||||||||||||||||||||||||||||||||||