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Maleimide
Selected AbstractsSevering of F-actin by yeast cofilin is pH-independentCYTOSKELETON, Issue 9 2006Dmitry Pavlov Abstract Cofilin plays an important role in actin turnover in cells by severing actin filaments and accelerating their depolymerization. The role of pH in the severing by cofilin was examined using fluorescence microscopy. To facilitate the imaging of actin filaments and to avoid the use of rhodamine phalloidin, which competes with cofilin, ,-actin was labeled with tetramethylrhodamine cadaverine (TRC) at Gln41. The TRC-labeling inhibited actin treadmilling strongly, as measured by ,ATP release. Cofilin binding, detected via an increase in light scattering, and the subsequent conformational change in filament structure, as detected by TRC fluorescence decay, occurred 2,3 times faster at pH 6.8 than at pH 8.0. In contrast, actin filaments severing by cofilin was pH-independent. The pH-independent severing by cofilin was confirmed using actin labeled at Cys374 with Oregon Green® 488 maleimide. The depolymerization of actin by cofilin was faster at high pH. Cell Motil. Cytoskeleton 2006. © 2006 Wiley-Liss, Inc. [source] Attachment of Amine- and Maleimide-Containing Ferrocene Derivatives onto Self-Assembled Alkanethiol and Alkanedithiol Monolayers: Voltammetric Evaluation of Cross-Linking Efficiencies and Surface Coverage of Electroactive GroupsELECTROANALYSIS, Issue 21 2004Yunfeng Wang Abstract Ferrocene derivatives containing primary amines and maleimide groups were attached covalently onto N -hydrosuccinimidyl (NHS)-terminated alkanethiol self-assembled monolayers (SAMs) and SAMs of alkanedithiol. The surface coverage and efficiencies of the two cross-linking reactions were evaluated with cyclic voltammetry. All the ferrocene derivatives attached onto the alkanethiol or alkanedithiol SAMs exhibit reversible redox waves. The surface coverage of the aminated ferrocene groups was compared to that of N -hydrosuccinimidyl (NHS)-terminated alkanethiol SAM. The covalent attachment of ,-ferrocenylethylamine onto a 11,11,-dithio-bis(succinimidylundecanoate) SAM yielded an efficiency as high as 63.1%. The cross-linking efficiency of this reaction was found to increase with the nucleophilicity of the amino groups. SAMs of longer alkyl chains favor the attachment of a greater number of ferrocene derivatives. As for the Michael-type electrophilic addition between the sulfhydryl groups of the alkanedithiol SAMs and the ferrocenyl maleimide, the cross-linking efficiencies were found to range from 6.5% to 25.7%, depending on the alkanedithiol chain length. The difference in the efficiencies between the two types of cross-linking reactions might be partially attributable to the steric hindrance imposed by the SAMs and the relative sizes of the functional groups. [source] Thiol-reactive dyes for fluorescence labeling of proteomic samplesELECTROPHORESIS, Issue 14 2003Kamala Tyagarajan Abstract Covalent derivatization of proteins with fluorescent dyes prior to separation is increasingly used in proteomic research. This paper examines the properties of several commercially available iodoacetamide and maleimide dyes and discusses the conditions and caveats for their use in labeling of proteomic samples. The iodoacetamide dyes BODIPY TMR cadaverine IA and BODIPY Fl C1 -IA were highly specific for cysteine residues and showed little or no nonspecific labeling even at very high dye:thiol ratios. These dyes also showed minimal effects on pI's of standard proteins. Some iodoacetamide dyes, (5-TMRIA and eosin-5-iodoacetamide) and some maleimide dyes (ThioGlo I and Rhodamine Red C2 maleimide) exhibited nonspecific labeling at high dye:thiol ratios. Labeling by both iodoacetamide and maleimide dyes was inhibited by tris(2-carboxyethyl)phosphine (TCEP); interactions between TCEP and dye were also observed. Thiourea, an important component of sample solubilization cocktails, inhibited labeling of proteins with iodoacetamide dyes but not with maleimide dyes. Maleimide dyes may serve as an alternative for labeling proteins where it is essential to have thiourea in the solubilization buffer. Covalent derivatization by BODIPY TMR cadaverine IA, BODIPY Fl C1 -IA or Rhodamine Red C2 maleimide was also demonstrated to be compatible with in-gel digestion and peptide mass fingerprinting by matrix assisted laser desorption/ionization-mass spectrometry and allowed successful protein identification. [source] Bifunctional Thiourea-Catalyzed Asymmetric Addition of Anthrones to MaleimidesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7 2010Alex Zea Abstract For the first time, the addition of anthrones to maleimides catalyzed by bifunctional thiourea catalysts is reported. The thiourea moiety is able to activate the maleimide and the tertiary amine deprotonates the anthrone, furnishing the final Diels,Alder or Michael adducts in excellent yields and enantioselectivities. [source] Thermal and dielectric properties of bismaleimide-triazine resins containing octa(maleimidophenyl)silsesquioxaneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Hongwei Cao Abstract Octa(maleimidophenyl)silsesquioxane (OMPS) was synthesized, characterized, and employed to modify the BT resin which composed of 4,4,-bismaleimidodiphenylmethane (BMI) and 2,2,-bis(4-cyanatophenyl)propane (BCE). The curing reaction between OMPS and BT resin was first investigated. It was found that OMPS accelerate the curing reaction of BCE, and the onset temperature of the cyclotrimerization was reduced up to 95.5°C (by DSC). As demonstrated by DSC and FTIR, there was no evidence that indicated the coreaction between maleimide and cyanate ester. 2,2,-diallyl bisphenol A (DBA) and diglycidyl ether of bisphenol A (E-51) (Wuxi Resin Factory, Jiangsu Province, China) were also used to enhance the toughness of BT resin, and the formulated BTA (containing DBA) and BTE (containing E-51) resins were obtained. The thermal properties of BT, BTA, and BTE resins incorporated with OMPS were then investigated. The results of DMA and TG showed that the BT, BTA, and BTE resins containing 1 wt % of OMPS exhibit enhanced thermal properties in comparison with their pristine resins respectively, while more contents of OMPS may impair the thermal properties of the polymer matrix, though the effect of OMPS was slight. Finally, the dielectric constant of these hybrid materials were detected, and their dielectric constant were distinctly reduced by the incorporation of OMPS, while overmuch contents of OMPS were disadvantageous for dielectric constant because of the aggregation of OMPS. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source] Graft copolymerization of methyl methacrylate with an N -substituted maleimide,liquid-crystalline copolymer by atom transfer radical polymerizationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008T. Çak Abstract The synthesis of novel copolymers consisting of a side-group liquid-crystalline backbone and poly (methyl methacrylate) grafts were realized by the use of atom transfer radical polymerization (ATRP). In the first stage, the bromine-functional copolymers 6-(4-cyanobiphenyl-4,-oxy)hexyl acrylate and (2,5-dioxo-2,5-dihydro-1H -pyrrole-1-yl)methyl 2-bromopropanoate were synthesized by free-radical polymerization. These copolymers were used as initiators in the ATRP of methyl methacrylate to yield graft copolymers. Both the macroinitiator and graft copolymers were characterized by 1H-NMR, gel permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis. The ATRP graft copolymerization was supported by an increase in the molecular weight of the graft copolymers compared to that of the macroinitiator and also by their monomodal molecular weight distribution. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Synthesis of isomeric 2,3,5-trisubstituted perhydropyrrolo[3,4-d]-isoxazole-4,6-diones via 1,3-dipolar cycloaddition reactionsJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2010Hamdi Özkan A series of isoxazolidine derivates (isomeric 2,3,5-trisubstitutedperhydropyrrolo[3,4-d]isoxazole-4,6-diones) used as anti-inflammatory, immunosuppressive, antibacterial agent, and inhibitor for some enzymes were synthesized. These compounds were prepared by 1,3-dipolar cycloaddition of N -methyl maleimide and N -phenyl maleimide with nitrones. Diastereomeric products obtained in this reaction were separated by column chromatography and recrystallized. All compounds synthesized were characterized by elemental analysis and spectroscopic methods (1H NMR, 13C NMR, and FTIR). J. Heterocyclic Chem., (2010). [source] Solid-phase biotinylation of antibodies,JOURNAL OF MOLECULAR RECOGNITION, Issue 3 2004Elizabeth Strachan Abstract Biotinylation is an established method of labeling antibody molecules for several applications in life science research. Antibody functional groups such as amines, cis hydroxyls in carbohydrates or sulfhydryls may be modified with a variety of biotinylation reagents. Solution-based biotinylation is accomplished by incubating antibody in an appropriate buffered solution with biotinylation reagent. Unreacted biotinylation reagent must be removed via dialysis, diafiltration or desalting. Disadvantages of the solution-based approach include dilution and loss of antibody during post-reaction purification steps, and difficulty in biotinylation and recovery of small amounts of antibody. Solid-phase antibody biotinylation exploits the affinity of mammalian IgG-class antibodies for nickel IMAC (immobilized metal affinity chromatography) supports. In this method, antibody is immobilized on a nickel-chelated chromatography support and derivitized on-column. Excess reagents are easily washed away following reaction, and biotinylated IgG molecule is recovered under mild elution conditions. Successful solid phase labeling of antibodies through both amine and sulfhydryl groups is reported, in both column and mini-spin column formats. Human or goat IgG was bound to a Ni-IDA support. For sulfhydryl labeling, native disulfide bonds were reduced with TCEP, and reduced IgG was biotinylated with maleimide,PEO2 biotin. For amine labeling, immobilized human IgG was incubated with a solution of NHS,PEO4 biotin. Biotinylated IgG was eluted from the columns using a buffered 0.2,M imidazole solution and characterized by ELISA, HABA/avidin assay, probing with a streptavidin,alkaline phosphatase conjugate, and binding to a monomeric avidin column. The solid phase protocol for sulfhydryl labeling is significantly shorter than the corresponding solution phase method. Biotinylation in solid phase is convenient, efficient and easily applicable to small amounts of antibody (e.g. 100,,g). Antibody biotinylated on-column was found to be equivalent in stability and antigen-recognition ability to antibody biotinylated in solution. Solid-phase methods utilizing Ni-IDA resin have potential for labeling nucleic acids, histidine-rich proteins and recombinant proteins containing polyhistidine purification tags, and may also be applicable for other affinity systems and labels. Copyright © 2004 John Wiley & Sons, Ltd. [source] Poly(ethylene glycol)-thioxanthone prepared by Diels,Alder click chemistry as one-component polymeric photoinitiator for aqueous free-radical polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2010Hakan Akat Abstract Novel water-borne macrophotoinitiator containing thioxanthone (TX) end group was successfully synthesized by using Diels,Alder (DA) [4 + 2] click chemistry strategy. For this purpose, thioxanthone-anthracene (TX-A) and maleimide end-functionalized poly(ethylene glycol) (PEG-MI) were reacted in toluene at reflux temperature for 48 h. The final polymer (PEG-TX) and the intermediates were characterized in detail by spectral analysis. PEG-TX possesses absorption characteristics similar to the parent TX. The one-component photoinitiating nature of the photointiator was demonstrated by photopolymeization of several hydrophilic vinyl monomers, such as acrylic acid, acrylamide, 2-hydroxyethyl acrylate, and 1-vinyl-2-pyrrolidone. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2109,2114, 2010 [source] A paradigm for the mechanisms and products of spontaneous polymerizationsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2009H. K. Hall Jr. Abstract In spontaneous vinyl and ring-opening copolymerizations, polar and resonance effects on the intermediates from bond-forming initiation offer a continuous spectrum of reactivities and polymer structures. In bond-forming initiation, an electron-rich donor monomer forms a bond to an acceptor monomer. The donor monomer may be a vinyl monomer with O, N, or aryl substituent or it may be an aza- or oxacycle. The acceptor monomer may be a vinyl monomer carrying CN, COOR, or SO2R substituent or it may be a cyclic anhydride or maleimide. Beyond this, the donor may have a ,-like strained single bond, whereas the acceptor may be an electrophilic quinodimethane. Lewis acids may be used to enhance the electrophilicity of acceptor monomers. Reaction rates and polymer composition are determined by systematically varying the stability of the first intermediate, designated P (for polymethylene). The nature of the intermediate will vary from a highly reactive trans biradical, which initiates chain alternating copolymerization, to a cis/gauche zwitterion, which can initiate chain ionic homopolymerization, to an extremely stabilized zwitterion, which cannot add monomer, but builds up in concentration and terminates by combination, forming alternating copolymer. This model embraces the existing literature for a wide variety of monomers and possesses predictive power. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009 [source] Heterograft copolymers via double click reactions using one-pot techniqueJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2008Aydan Dag Abstract The double click reactions (Cu catalyzed Huisgen and Diels,Alder reactions) were used as a new strategy for the preparation of well-defined heterograft copolymers in one-pot technique. The synthetic strategy to the various stages of this work is outlined: (i) preparing random copolymers of styrene (St) and p -chloromethylstyrene (CMS) (which is a functionalizable monomer) via nitroxide mediated radical polymerization (NMP); (ii) attachment of anthracene functionality to the preformed copolymer by the o -etherification procedure and then conversion of the remaining CH2Cl into azide functionality; (iii) by using double click reactions in one-pot technique, maleimide end-functionalized poly(methyl methacrylate) (PMMA-MI) via atom transfer radical polymerization (ATRP) of MMA and alkyne end-functionalized poly (ethylene glycol) (PEG-alkyne) were introduced onto the copolymer bearing pendant anthryl and azide moieties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6969,6977, 2008 [source] Use of fluorinated maleimide and telechelic bismaleimide for original hydrophobic and oleophobic polymerized networksJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2008Aurélien Soules Abstract The syntheses of original fluorinated maleimide and telechelic bismaleimide bearing C6F13 and C6F12 groups, respectively, and their use as reactive additives in photopolymerizable formulations of telechelic poly(propylene glycol) bismaleimide (PPGBMI) are presented. Fluorinated maleimide was synthetized in five steps in 63% overall yield from C6F13C2H4I precursor, whereas the fluorinated bismaleimide was prepared in six steps in 14% overall yield from IC6F12I. These latter led to fluorinated azido and diazido intermediates that were reduced into the fluorinated amine and diamines in two steps. The condensation of amine and diamine onto maleic anhydride offered an amic acid and a diamic acid, which were subsequently cyclized into fluorinated maleimide and bismaleimide. Formulations of telechelic PPGBMI containing a low concentration of these fluorinated maleimide and bismaleimide were UV cured and the surface properties of the resulting films were investigated. A deep modification of the surface properties was noted when the monomaleimide was used. In all the cases, a selective enrichment of the fluorinated monomer at the film surface was observed. The dependence of the surface properties on the fluorinated maleimide and bismaleimide concentrations were also studied, and showed an asymptotic behavior of the contact angle with only 1.5 wt % of fluorinated maleimide additive, whatever the conditions. This monomaleimide led to better hydrophobic and oleophobic properties of the resulting material than that containing the telechelic one. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3214,3228, 2008 [source] A Diels-Alder/retro Diels-Alder strategy to synthesize polymers bearing maleimide side chainsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2007Tugba Dispinar Abstract Polymers containing thiol-reactive maleimide groups on their side chains have been synthesized by utilization of a novel methacrylate monomer containing a masked maleimide. Diels-Alder reaction between furan and maleimide was adapted for the protection of the reactive maleimide double bond prior to polymerization. AIBN initiated free radical polymerization was utilized for synthesis of copolymers containing masked maleimide groups. No unmasking of the maleimide group was evident under the polymerization conditions. The maleimide groups in the side chain of the polymers were unmasked into their reactive form by utilization of retro Diels-Alder reaction. This cycloreversion was monitored by thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), and 1H and 13C NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4545,4551, 2007 [source] Synthesis of comb-like polystyrene with poly(N -phenyl maleimide- alt-p -chloromethyl styrene) as macroinitiatorJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2006Yan Shi Abstract The copolymerization of N -phenyl maleimide and p -chloromethyl styrene via reversible addition,fragmentation chain transfer (RAFT) process with AIBN as initiator and 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate as RAFT agent produced copolymers with alternating structure, controlled molecular weights, and narrow molecular weight distributions. Using poly(N -phenyl maleimide- alt - p -chloromethyl styrene) as the macroinitiator for atom transfer radical polymerization of styrene in the presence of CuCl/2,2,-bipyridine, well-defined comb-like polymers with one graft chain for every two monomer units of backbone polymer were obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2069,2075, 2006 [source] Preparation and properties of high performance epoxy,silsesquioxane hybrid resins prepared using a maleimide,alkoxysilane compound as a modifierJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2005Ying-Ling Liu Abstract An alkoxysilane compound possessing maleimide moiety (MSM) was prepared from N-(4-hydroxyphenyl)maleimide and 3-glycidoxypropyltrimethoxysilane and was used as a modifier of epoxy resins. In situ curing epoxy resins with MSM resulted in epoxy resins with good homogeneity. Just 5,10 wt % of MSM is sufficient to yield high glass transition temperature (165 °C), good thermal stability above 360 °C, and high flame retardancy (LOI = 30) to bisphenol-A-based epoxy resins. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5787,5798, 2005 [source] Polymerization of n -phenyl maleimide by lanthanide complexesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2005Bei Zhao Abstract N -Phenyl maleimide (N -PMI) was successfully polymerized by divalent rare-earth complexes (ArO)2Sm(THF)4 (ArO = 2,6-di- tert -butyl-4-methyl phenoxo-; THF = tetrahydrofuran) and (Ar,O)2Ln(THF)3 (Ar,O = 2,6-di- tert -butyl phenoxo-; Ln = Sm, Yb, or Eu). The central metals greatly affected the reactivity, and the reactivity order was Sm(II) > Yb(II) > Eu(II). The activity of (Ar,O)2Sm(THF)3 was higher than that of (ArO)2Sm(THF)4. The polymerization yields were higher in THF than in other solvents, and the maximum yields were obtained around 25 °C. A proposed mechanism is discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3966,3972, 2005 [source] Stabilization of vinyl chloride/vinylidene chloride copolymers using N-substituted maleimides,JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 3 2006Bob A. Howell As a consequence of their excellent barrier properties, vinyl chloride/vinylidene chloride copolymers have long been prominent in the flexible packaging market. While these polymers possess a number of superior characteristics, they tend to undergo thermally induced degradative dehydrochlorination at process temperatures. This degradation must be controlled to permit processing of the polymers. Three series of N-substituted maleimides (N -alkyl-, N -aralkyl-, and N -aryl-) have been synthesized, characterized spectroscopically, and evaluated as potential stabilizers for a standard vinyl chloride/vinylidene chloride (85 wt%) copolymer. As surface blends with the polymer, these compounds are ineffective as stabilizers. However, significant stabilization may be achieved by pretreatment of the polymer with N-substituted maleimides. The most effective stabilization of the polymer is afforded by N -aralkyl- or N -arylmaleimides, most notably, N -benzylmaleimide and N -(p -methoxyphenyl)maleimide. J. VINYL. ADDIT. TECHNOL. 12:88,97, 2006. © 2006 Society of Plastics Engineers. [source] Polymers from Multifunctional Isocyanates, 15,MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 8 2007A Novel Alternating Copolymer Containing an Isocyanate, a Cyanate Group in the Repeating Unit Abstract N -(4-cyanatophenyl)maleimide and 2-isocyanato propene were copolymerised to give an alternating copolymer, which is the first example of a polymer having an isocyanate as well as a cyanate reactive functional group in the repeating unit. The polymer analogous reaction with methanol proceeded selectively at the isocyanate groups. Crosslinking of the cyanate-urethane copolymers by cyclotrimerisation of cyanate groups occurred at elevated temperature. Reaction with dibutylamine at 20,°C led to complete reaction of both the cyanate and isocyanate moieties in a non-selective manner. [source] UV-Curable Azobenzene Polymer Bearing Photo-Crosslinkable Moiety for Stabilization of Photo-Fabricated Surface Relief StructureMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 16 2002Tatsumi Kimura Abstract In order to find a new class of photo-processable liquid crystalline (LC) aligning material, five kinds of new maleimide-based copolymers bearing both azobenzene and cinnamate moieties with different functionalization ratio have been synthesized. The properties of these five copolymers were compared regarding physical and chemical properties that are required for our aim. The photo-induced surface relief (PSR) gratings could be fabricated on the films of these copolymers using an Ar+ laser (,,=,488 nm), and were successfully immobilized and bleached by UV-light irradiation that causes photo-crosslinking of the cinnamate moiety and photo-degradation of the azobenzene moiety, respectively. The PSR inscription rate and the thermal stability have been investigated regarding the functionalization ratio between cinnamate and azobenzene side chain. The residual ratio of the PSR structure after UV-curing was increased with increasing photo-crosslinkable moiety. It was confirmed that the UV-cured PSR grating structure becomes transparent at visible wavelength and was able to align LC molecules parallel to the grating direction. Polarized optical microscope image of LC cell aligned by the PMPDC 21-18 film with UV-cured PSR structure (0°). [source] Pyrene Excimer Fluorescence of Yeast Alcohol Dehydrogenase: A Sensitive Probe to Investigate Ligand Binding and Unfolding Pathway of the EnzymePHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2006Manas Kumar Santra ABSTRACT The cysteine residues of yeast alcohol dehydrogenase (YADH) were covalently modified by N-(1-pyrenyl) maleimide (PM). A maximum of 3.4 cysteines per YADH monomer could be modified by PM. The secondary structure of PM-YADH was found to be similar to that of the native YADH using far-UV circular dichroism. The covalent modification of YADH by PM inhibited the enzymatic activity indicating that the active site of the enzyme was altered. PM-YADH displayed maximum excimer fluorescence at an incorporation ratio of 2.6 mol of PM per monomeric subunit of YADH. Nucleotide adenine dinucleotide (NAD) divalent zinc and ethanol reduced the excimer fluorescence of PM-YADH indicating that these agents induce conformational changes in the enzyme. Guani-dinium hydrochloride (GdnHCl)-induced unfolding of YADH was analyzed using tryptophan fluorescence, pyrene excimer fluorescence and enzymatic activity. The unfolding of YADH was found to occur in a stepwise manner. The loss of enzymatic activity preceded the global unfolding of the protein. Further, changes in tryptophan fluorescence with increasing GdnHCl suggested that YADH was completely unfolded by 2.5 M GdnHCl. Interestingly, residual structures of YADH were detected even in the presence of 5 M GdnHCl using the excimer fluorescence of PM-YADH. [source] Facile synthesis and characterization of star-shaped polystyrene: self-condensing atom transfer radical copolymerization of N -[4-(,-bromoisobutyryloxy)phenyl]maleimide and styrenePOLYMER INTERNATIONAL, Issue 10 2008Yun Cao Abstract BACKGROUND: Generation of stars around in situ formed cores provides a facile approach to star-shaped polymers. Therefore the self-condensing atom transfer radical copolymerization (SCATRCP) of N -[4-(,-bromoisobutyryloxy)phenyl]maleimide (BiBPM) and a large excess of styrene (St) was investigated. RESULTS: BiBPM and St formed a charge transfer complex (CTC), which underwent the SCATRCP, leading to the branched core initiating the atom transfer radical polymerization of St, finally giving star-shaped polystyrene (PS). Kinetic and structural study showed that a higher dosage of BiBPM resulted in an enhanced polymerization rate, a higher degree of branching and a larger number of short PS arms. Differential scanning calorimetry suggested that the glass transition temperature of the star-shaped PS decreased with molecular weight. Melt rheometry showed that even a slightly branched architecture of the PS led to a significantly lower viscosity; both the melt flow index and the activation energy increased with the degree of branching. CONCLUSION: Due to the preferential consumption of BiBPM and formation of a CTC, even a very low dosage of BiBPM could lead to star-shaped PS, which, in comparison with linear analogues, could possess much better melt fluidity. Copyright © 2008 Society of Chemical Industry [source] Synthesis and characterization of optically active star-shaped poly (N -phenylmaleimide)s with a calixarene corePOLYMER INTERNATIONAL, Issue 6 2007Liping Lou Abstract Two N -phenylmaleimide derivatives bearing a chiral oxazoline group, N -[o -(4-phenyl-4,5-dihydro-1,3-oxazol-2-yl)phenyl]maleimide [(R)-PhOPMI] and N -[o -(4-isopropyl-4,5-dihydro-1,3-oxazol-2-yl)phenyl]maleimide [(S)-PriOPMI], were polymerized using in situ generated calixarene-based phenates as initiators to yield optically active polymers. The formation of star-shaped architectures was strongly dependent on both polymerization conditions and calixarene moieties. In the case of polymerization conducted in toluene at 80,100 °C, the arm-chain numbers achieved their respective maxima for the polymers with these multifunctional initiators. In contrast, the polymers obtained in polymerizations at lower temperature possessed fewer arm chains. The structure and chiroptical properties were investigated on the basis of 13C NMR, multiangular laser light scattering, gel permeation chromatography, and circular dichroism for the macromolecules with calixarene cores. Copyright © 2006 Society of Chemical Industry [source] Preparation and thermal properties of bismaleimide blends based on hydroxyphenyl maleimidePOLYMER INTERNATIONAL, Issue 8 2005BS Rao Abstract N -(4-hydroxyphenyl)maleimide was melt-blended with the glycidyl ether of bisphenol-A and various mole percentages of 4, 4,-(diaminodiphenylsulfone) bismaleimide. The cure behaviour of the resins was evaluated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The blends showed distinct reductions in the onset of cure (To) and peak exothermic (Texo) temperatures. The blends cured at low temperatures exhibited glass transition temperatures (Tgs) higher than the cure temperatures. The cured blends showed high moduli, glass transition temperatures in excess of 250 °C and good thermal stabilities up to 400 °C. Copyright © 2005 Society of Chemical Industry [source] Low loss second-order non-linear optical crosslinked polymers based on a phosphorus-containing maleimidePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 10 2004Chih-Ping Chen Abstract A series of crossslinked organic and organic/inorganic polymers based on maleimide chemistry have been investigated for second-order non-linear optical (NLO) materials with excellent thermal stability and low optical loss. Two reactive chromophores (maleimide-containing azobenzene dye and alkoxysilane-containing azobenzene dye) were incorporated into a phosphorus-containing maleimide polymer, respectively. The selection of the phosphorus-containing maleimide polymer as the polymeric matrices provides enhanced solubility and thermal stability, and excellent optical quality. Moreover, a full interpenetrating network (IPN) was formed through simultaneous addition reaction of the phosphorus-containing maleimide, and sol-gel process of alkoxysilane dye (ASD). Atomic force microscopy (AFM) results indicate that the inorganic networks are distributed uniformly throughout the polymer matrices on a nano-scale. The silica particle sizes are well under 100,nm. Using in situ contact poling, the r33 coefficients of 2.2,17.0,pm/V have been obtained for the optically clear phosphorus-containing NLO materials. Excellent temporal stability (100°C) and low optical loss (0.99,1.71,dB/cm; 830,nm) were also obtained for these phosphorus-containing materials. Copyright © 2004 John Wiley & Sons, Ltd. [source] Novel ferrocenyl phosphonate derivatives.APPLIED ORGANOMETALLIC CHEMISTRY, Issue 10 2010Inhibition of serine hydrolases by ferrocene azaphosphonates Abstract Owing to their unique properties, ferrocene compounds are gaining increasing interest for biological applications, particularly as enzyme inhibitors. Phosphonate derivatives including a ferrocenyl moiety were synthesized by reaction of dimethyl- and diphenylphosphite with ferrocenyl methyl maleimide. The ferrocenyl diphenyl phosphonate complex was characterized by X-ray diffraction. The ability of these organometallic compounds to inhibit the enzymatic activity of the serine esterases acetyl- and butyrylcholinesterase was investigated. It appeared that the new ferrocenyl phosphonates inhibited both enzymes by competitive, mixed or non competitve mechanisms with inhibition constants in the range 35,1000 µM. Both compounds also behave as slow time-dependent inactivators of butyrylcholinesterase. The presence of the ferrocenyl entity seems then to have a dramatic effect on the biochemical behavior of the systems. Copyright © 2010 John Wiley & Sons, Ltd. [source] Determination of glutathione disulfide levels in biological samples using thiol,disulfide exchanging agent, dithiothreitolBIOMEDICAL CHROMATOGRAPHY, Issue 2 2009Burhan Ates Abstract A reverse-phase HPLC method incorporating dithiothreitol (DTT) reduction for quantitative determination of oxidized glutathione (GSSG) in biological samples is described here. This method is based on our previous enzymatic reduction technique that uses N-1-(pyrenyl) maleimide (NPM) as a derivatizing agent. In our earlier method, glutathione disulfide (GSSG) was measured by first reducing it to GSH with glutathione reductase (GR) in the presence of NADPH. However, this is a very costly and time-consuming technique. The method described here employs a common and inexpensive thiol,disulfide exchanging agent, DTT, for reduction of GSSG to GSH, followed by derivatization with NPM. The calibration curves are linear over a concentration range of 25,1250 nm (r2 > 0.995). The coefficients of variations for intra-run precision and inter-run precision range from 0.49 to 5.10% with an accuracy range of 1.78,6.15%. The percentage of relative recovery ranges from 97.3 to 103.2%. This new method provides a simple, efficient, and cost-effective way of determining glutathione disulfide levels with a 2.5 nm limit of detection per 5 µL injection volume. Copyright © 2008 John Wiley & Sons, Ltd. [source] Separation and quantification of N -acetyl- l -cysteine and N -acetyl-cysteine-amide by HPLC with fluorescence detectionBIOMEDICAL CHROMATOGRAPHY, Issue 5 2006Wei Wu Abstract N- acetyl- l -cysteine (NAC) is a well-known antioxidant that is capable of facilitating glutathione (GSH) biosynthesis and replenishing intracellular GSH under oxidatively challenging circumstances. N- acetyl-cysteine-amide (NACA), the amide form of NAC, is a newly designed and synthesized thiol-containing compound which is believed to be more lipophilic and permeable through cell membranes than NAC. The metabolic and antioxidant effects of these compounds in vitro and in vivo are under investigation. However, an analytical method that can separate and quantify both compounds simultaneously is not yet available, to the best of our knowledge. Because of their structural similarities, the two compounds are difficult to separate using earlier HPLC methods which were designed for NAC quantification. Therefore, the goal of this work was to develop an HPLC method with fluorescence detection for simultaneous quantification of NAC and NACA in biological blood and tissue samples. A gradient HPLC program with fluorescence detection (,ex = 330 nm, ,em = 376 nm) using N -(1-pyrenyl)maleimide (NPM) as the derivatizing agent was developed. The calibration curves were linear over a concentration range of 25,5000 nm (r2 > 0.997). The coefficients of variation for within-run precision and between-run precision ranged from 0.67 to 5.23% and for accuracy ranged from 0.98 to 10.54%; the percentage relative recovery ranged from 94.5 to 102.8%. This new method provides satisfactory separation of NAC and NACA, along with other biological thiols, in 20 min with a 5 nm limit of detection (LOD) per 5 µL injection volume. Copyright © 2005 John Wiley & Sons, Ltd. [source] Maleimide-Modified Phosphonium Ionic Liquids: A Template Towards (Multi)Task-Specific Ionic LiquidsCHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2010Jocelyn Abstract The synthesis and characterization of several compounds representing a new class of multitask-specific phosphonium ionic liquids that contain a maleimide functionality is reported. The maleimide moiety of the ionic liquid (IL) is shown to undergo Michael-type additions with substrates containing either a thiol or amine moiety, thus, serving as a template to introduce wide structural diversity into the IL. Multitask-specific ILs are accessible by reaction of the maleimide with Michael donors that are capable of serving some function. As a model example to illustrate this concept, a redox active ferrocenyl thiol was incorporated and examined by cyclic voltammetry. Because the maleimide moiety is highly reactive to additions, the task-specific ionic liquids (TSILs) are prepared as the furan-protected Diels,Alder maleimide. The maleimide moiety can then be liberated when required by simple heating. [source] Catalytic Asymmetric 1,3-Dipolar Cycloaddition of ,-IminonitrilesCHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2010Rocío Robles-Machín Improving the structural scope: A catalytic asymmetric 1,3-dipolar cycloaddition involving ,-iminonitriles as azomethine precursors has been developed. In the presence of AgOAc/Taniaphos as the catalyst system the reaction of ,-iminonitriles with dimethyl fumarate and N -methyl maleimide affords 2-cyanopyrrolidines with good endo selectivity and enantioselectivity (68,,99,%,ee; see scheme). [source] Size-Tunable Highly Luminescent SiO2 Particles Impregnated with Number-Adjusted CdTe NanocrystalsCHEMPHYSCHEM, Issue 4 2010Ping Yang Dr. Abstract Highly luminescent SiO2 particles impregnated with CdTe nanocrystals (NCs) are prepared by a sol,gel procedure. Partial ligand exchange from thioglycolic acid to 3-mercaptopropyltrimethoxysilane (MPS) on the NCs enables retention of the initial photoluminescence (PL) efficiency of the NCs in water, while the simultaneous addition of a poor solvent (ethanol) results in regulated assembly of the NCs through condensation of hydrolyzed MPS. The SiO2 particles thus prepared have, for example, a diameter of 16 nm and contain three NCs each. The PL efficiency of these particles is 40,%, while the initial efficiency is 46,% in a colloidal solution. The redshift and narrowed spectral width in PL observed after impregnation indicate that the concentration of NCs in these nearly reaches the ultimate value (on the order of 1021 particles per liter). The porosity of these particles is investigated by means of N2 adsorption,desorption isotherms. Due to the SiO2 shell, these particles have higher stability in phosphate-buffered saline buffer solution than the initial NCs. Their potential use for labeling in bio-applications is investigated by conjugating biotinylated immunoglobulin G to them by using streptavidin maleimide as linker. Successful conjugation is confirmed by electrophoresis in agarose gel. This preparation method is an important step towards fabricating intensely emitting biocompatible SiO2 particles impregnated with semiconductor NCs. [source] | ||||||||||||||||