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Side-chain
Terms modified by Side-chain Selected AbstractsStructure of Lipopolysaccharide Side-chain of Pseudomonas syringae pv. lachrymans Strain NCPPB 1096, in Relation to O-serogroupJOURNAL OF PHYTOPATHOLOGY, Issue 11-12 2000M. Spitali [source] Mixed-Ligand Oxidovanadium(V) Complexes with N, -Salicylidenehydrazides: Synthesis, Structure, and 51V Solid-State MAS NMR Investigation,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2008Simona Nica Abstract The synthesis and spectroscopic characterization of a series of three oxidovanadium(V) complexes with 8-hydroxyquinoline and Schiff-base ligands derived from salicylaldehyde and ,-hydroxy-functionalized carbohydrazides with different chain lengths are reported. The complex with the hydrazone ligand containing the shortest chain length was crystallographically characterized. This complex crystallizes in the triclinic space group P with two structurally similar but crystallographically independent oxidovanadium(V) complexes. Each vanadium atom is six-coordinate in a distorted-octahedral geometry. The two molecules are assembled through hydrogen-bonding interactions between the hydroxyl groups of the side-chain substituted Schiff-base ligand and the oxido group of one of the two complexes. Electrochemical measurements performed in acetonitrile solution reveal two reversible one-electron reduction steps. The observed pre-wave feature of the second reduction step indicates the presence of dissociation equilibria related to the 8-hydroxyquinoline coligand. Magic-angle spinning solid-state 51V NMR spectroscopy allowed to characterize the full series of complexes with alkyl and hydroxy alkyl-substituted hydrazone ligands that were used. The quadrupolar coupling constants are small with a value of about 4 MHz and show little variation within the series. The asymmetry of the chemical shift tensor indicates a rather axial symmetric environment around the vanadium(V) center. The isotropic chemical shifts observed in the solid state occur at about 30 ppm, which is in the same order of magnitude as the solvent induced variations, about 10 ppm, found for different solvents.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Regiospecific Cyclometalation of Diphenyl(2-substituted phenyl)phosphane with Methyltetrakis(trimethylphosphane)cobalt(I)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2003Hans-Friedrich Klein Abstract The pre-chelate molecules 2-(diphenylphosphanyl)- N,N -dimethylaniline, [2-(diphenylphosphanyl)benzyl]dimethylamine, 1-(diphenylphosphanyl)-2-ethylbenzene, 1-(diphenylphosphanyl)-2-isopropylbenzene, and 2-(diphenylphosphanyl)benzonitrile, in a reaction with [CoMe(PMe3)4], eliminate methane to afford the selectively 6- ortho -metalated complexes 1,5 that contain four-membered metallacycles. The molecular structure of 3 shows a tbp-coordinated cobalt atom, with axial C and PMe3 donor groups. Metalation in the aliphatic side-chain occurs with 2-(diphenylphosphanyl)toluene, giving complex 6 that contains a five-membered metallacycle. Benzyldiphenylphosphane is selectively ortho -metalated in the benzyl group, affording 7. As shown by the molecular structures, complex 7 is a true ligand isomer of 6. Substitution of a trimethylphosphane group in compounds 4 and 6 by ethene gives the pentacoordinate complexes 8 and 9, respectively. The ethene ligand is ,-coordinated in the equatorial plane of a trigonal bipyramid. Under 1 bar of CO, complex 6 forms monocarbonyl complex 10. Carbonylation of complexes 3 and 4 proceeds by insertion of CO into the Co,C bond under ring expansion, affording the aroylcobalt complexes 11 and 12, respectively. Complex 6 reacts with iodomethane in an oxidative substitution reaction yielding a structurally characterized octahedral complex mer - 13, which eliminates a methyl group in THF at 20 °C to form a pentacoordinate cobalt(II) complex 14. Complex 3 oxidatively adds iodomethane in a stereoselective cis addition to give the cobalt(III) complex mer - 15, which retains its four-membered metallacycle and the CoCH3 group. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Chemoenzymatic Synthesis of (Protected) Psymberic AcidEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2009Jörg Pietruszka Abstract Two alternative approaches to the side-chain of psymberin (1), psymberic acid (5), have been developed starting from either racemic or enantiopure acetal 6. A five-step chemoenzymatic route provided the PMB-protected acid (S,S)- 16 required for the coupling that should ultimately lead to the natural product 1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Transition-Metal-Free Synthesis of Perdeuterated Imidazolium Ionic Liquids by Alkylation and H/D ExchangeEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2008Ralf Giernoth Abstract Economic, transition-metal-free syntheses of partially or completely deuterated imidazolium ionic liquids (ILs) were developed. Double alkylation starting from imidazole afforded side-chain deuterated imidazolium ionic liquids, which subsequently were fully deuterated by H/D-exchange on the cation ring. Isotopic exchange was studied for a range of ionic liquids, solvents and bases. Here, the presence of small amounts of basic impurities was found to significantly affect the exchange behaviour.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] A Chemoenzymatic, Enantioconvergent, Asymmetric Total Synthesis of(R)-Fridamycin EEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2005Bernhard J. Ueberbacher Abstract A chemoenzymatic, asymmetric total synthesis of the anti-biotic (R)-fridamycin E has been accomplished following a biocatalytic deracemization procotol. The key step comprises the construction of the chiral side-chain from a functionalized rac -2,2-disubstituted oxirane via a kinetic resolution/stereoinversion sequence without formation of the undesiredstereoisomer. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] High resolution X-ray analysis of two mutants of a curaremimetic snake toxinFEBS JOURNAL, Issue 5 2000Jean-François Gaucher A previous mutational analysis of erabutoxin a (Ea), a curaremimetic toxin from sea snake venom, showed that the substitutions S8G and S8T caused, respectively, 176-fold and 780-fold affinity decreases for the nicotinic acetylcholine receptor (AchR). In view of the fact that the side-chain of Ser8 is buried in the wild-type toxin, we wondered whether these affinity changes reflect a direct binding contribution of S8 to the receptor and/or conformational changes that could have occurred in Ea as a result of the introduced mutations. To approach this question, we solved X-ray structures of the two mutants S8G and S8T at high resolution (0.18 nm and 0.17 nm, with R factors of 18.0% and 17.9%, respectively). The data show that none of the mutations significantly modified the toxin structure. Even within the site where the toxin binds to the receptor the backbone conformation remained unchanged. Therefore, the low affinities of the mutants S8T and S8G cannot be explained by a large conformational change of the toxin structure. Although we cannot exclude the possibility that undetectable structural changes have occurred in the toxin mutants, our data support the view that, although buried between loop I and II, S8 is part of the functional epitope of the toxin. [source] Ultrathin Multilayered Films Assembled from "Charge-Shifting" Cationic Polymers: Extended, Long-Term Release of Plasmid DNA from Surfaces,ADVANCED MATERIALS, Issue 23 2007J. Zhang Ultrathin multilayered films can be designed to release plasmid DNA for three months by using side-chain functionalized ,charge-shifting' cationic polymers. Slow hydrolysis of the side chains of these polymers facilitates film disruption and release of DNA over periods longer than films fabricated using degradable cationic polymers, and suggests approaches to the fabrication of thin films for the localized and long-term release of DNA, proteins, or other agents from surfaces. [source] Electronic structure and physicochemical properties of selected penicillinsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2007Catalina Soriano-Correa Abstract Traditionally, penicillins have been used as antibacterial agents due to their characteristics and widespread applications with few collateral effects, which have motivated several theoretical and experimental studies. Despite the latter, their mechanism of biological action has not been completely elucidated. We present a theoretical study at the Hartree,Fock and density functional theory (DFT) levels of theory of a selected group of penicillins such as the penicillin-G, amoxicillin, ampicillin, dicloxacillin, and carbenicillin molecules, to systematically determine the electron structure of full ,-lactam antibiotics. Our results allow us to analyze the electronic properties of the pharmacophore group, the aminoacyl side-chain, and the influence of the substituents (R and X) attached to the aminoacyl side-chain at 6, (in contrast with previous studies focused at the 3, substituents), and to corroborate the results of previous studies performed at the semiempirical level, solely on the ,-lactam ring of penicillins. Besides, several density descriptors are determined with the purpose of analyzing their link to the antibacterial activity of these penicillin compounds. Our results for the atomic charges (fitted to the electrostatic potential), the bond orders, and several global reactivity descriptors, such as the dipole moments, ionization potential, hardness, and the electrophilicity index, led us to characterize: the active sites, the effect of the electron-attracting substituent properties and their physicochemical features, which altogether, might be important to understand the biological activity of these type of molecules. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Structure,Activity Relationship Studies in Single-Site Esterase Peptide DendrimersISRAEL JOURNAL OF CHEMISTRY, Issue 1 2009Sacha Javor We recently reported on peptide dendrimers with a single catalytic site at the dendrimer core catalyzing the hydrolysis of acetoxy- and butyryloxy-pyrene trisulfonate 1a/b in aqueous buffer with Michaelis,Menten kinetics. Substrate binding is mediated by a pair of protonated arginine or histidine residues in the first generation branch, and esterolysis is performed by the imidazole side-chain of a histidine residue in the core acting as a general base or nucleophile. Herein we report on a structure,activity relationship study searching for an optimal combination between amino acid sequence and catalytic machinery. Installation of histidine residues onto the aromatic dendrimer framework "R" leads to 10-fold higher rate acceleration up to kcat/kuncat = 1.5 * 103 at pH 5.5 with dendrimers RG3H (AcYT)8 (BWG)4 (BHS)2BHS and RMG3H (AcYT)8(BWG)4(BHSG)2BHS (one-letter codes for L -amino acids; Ac = acetyl, B = L -2,3-diaminopropionic acid branching point, C-terminus is amide -CONH2). These dendrimers reach the compactness of a native folded protein. [source] Hypersensitivity reactions to penicillins: studies in a group of patients with negative benzylpenicillin G skin testJOURNAL OF CLINICAL PHARMACY & THERAPEUTICS, Issue 3 2009H.-L. Qiao MD PhD Summary Background:, Although skin tests are usually employed to evaluate current penicillin allergy status, a negative result does not exclude hypersensitivity. There is a need for accurate in vitro tests to exclude hypersensitivity. A radioallergosorbent test (RAST) is a potentially good supplementary approach, but there is little information on the suitability of this method to diagnose penicillin hypersensitivity in subjects with a negative skin test to benzylpenicillin. Methods:, A total of 133 patients with a negative skin test to benzylpenicillin G (PG) and all of whom developed allergic reactions to PG were studied. RAST was used to detect eight kinds of specific IgE antibodies to penicillins in serum, which included four kinds of major and minor antigenic determinants to four penicillin drugs. The combination sites for the specific IgE antibodies were studied by RAST inhibition test. Results:, The rate of positive reactions for the specific IgE antibodies was 59·40% (79/133). Of the eight kinds of antigenic determinants, the positive rates for specific IgE against the major and minor determinants were 39·10% (52) and 42·86% (57) respectively. Of the four drugs, positive cases only to PG were 10 (7·5%), were significantly fewer than the cross-reacting positive cases (36) to PG (P < 0·01). In the RAST inhibition studies all drugs exhibited good inhibitory potencies, and in some instances the side-chain of the penicillins could induce specific responses with a variable degree of cross-reactivity among the different penicillins. Conclusion:, Radioallergosorbent test is a good complementary test in persons who are skin-test negative with PG, and the sensitivity of RAST increaes with increasing specificity of IgE antibodies to be detected. 6-APA and the groups, making part of the different side-chains on penicillins, all contributed to the cross-reactivity. [source] Investigation of tyrosine nitration in proteins by mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2001Ann-Sofi Petersson Abstract In vivo nitration of tyrosine residues is a post-translational modification mediated by peroxynitrite that may be involved in a number of diseases. The aim of this study was to evaluate possibilities for site-specific detection of tyrosine nitration by mass spectrometry. Angiotensin II and bovine serum albumin (BSA) nitrated with tetranitromethane (TNM) were used as model compounds. Three strategies were investigated: (i) analysis of single peptides and protein digests by matrix-assisted laser desorption/ionization (MALDI) peptide mass mapping, (ii) peptide mass mapping by electrospray ionization (ESI) mass spectrometry and (iii) screening for nitration by selective detection of the immonium ion of nitrotyrosine by precursor ion scanning with subsequent sequencing of the modified peptides. The MALDI time-of-flight mass spectrum of nitrated angiotensin II showed an unexpected prompt fragmentation involving the nitro group, in contrast to ESI-MS, where no fragmentation of nitrated angiotensin II was observed. The ESI mass spectra showed that mono- and dinitrated angiotensin II were obtained after treatment with TNM. ESI-MS/MS revealed that the mononitrated angiotensin II was nitrated on the side-chain of tyrosine. The dinitrated angiotensin II contained two nitro groups on the tyrosine residue. Nitration of BSA was confirmed by Western blotting with an antibody against nitrotyrosine and the sites for nitration were investigated by peptide mass mapping after in-gel digestion. Direct mass mapping by ESI revealed that two peptides were nitrated. Precursor ion scanning for the immonium ion for nitrotyrosine revealed two additional partially nitrated peptides. Based on the studies with the two model compounds, we suggest that the investigation of in vivo nitration of tyrosine and identification of nitrated peptides might be performed by precursor ion scanning for the specific immonium ion at m/z 181.06 combined with ESI-MS/MS for identification of the specific nitration sites. Copyright © 2001 John Wiley & Sons, Ltd. [source] Synthesis of linear and cyclic phosphopeptides as ligands for the N -terminal SH2-domain of protein tyrosine phosphatase SHP-1JOURNAL OF PEPTIDE SCIENCE, Issue 7 2005Dr Diana Imhof Abstract Linear and cyclic phosphopeptides related to the pY2267 binding site of the epithelial receptor tyrosine kinase Ros have been synthesized as ligands for the amino-terminal SH2 (src homology) domain of protein tyrosine phosphatase SHP-1. The synthesis was accomplished by Fmoc-based solid-phase methodology using side-chain unprotected phosphotyrosine for the linear and mono-benzyl protected phosphotyrosine for the cyclic peptides. According to molecular modelling, the incorporation of a glycine residue between Lys (position pY,1 relative to phosphotyrosine) and Asp or Glu (position pY+2) was recommended for the cyclic candidates. The preparation of these peptides was successfully performed by the incorporation of a Fmoc-Xxx(Gly-OAll)-OH (Xxx = Asp, Glu) dipeptide building block that was prepared in solution prior to SPPS. The cyclization was achieved with PyBOP following Alloc/OAll-deprotection. This study demonstrates the usefulness of allyl-type protecting groups for the generation of side-chain cyclized phosphopeptides. Alloc/OAll-deprotection and cyclization are compatible with phosphorylated tyrosine. Copyright © 2004 European Peptide Society and John Wiley & Sons, Ltd. [source] Efficient synthesis and comparative studies of the arginine and N,,N, -dimethylarginine forms of the human nucleolin glycine/arginine rich domainJOURNAL OF PEPTIDE SCIENCE, Issue 1 2005Dr Sotir Zahariev Abstract The Gly- and Arg-rich C -terminal region of human nucleolin is a 61-residue long domain involved in a number of protein,protein and protein,nucleic acid interactions. This domain contains 10 aDma residues in the form of aDma-GG repeats interspersed with Phe residues. The exact role of Arg dimethylation is not known, partly because of the lack of efficient synthetic methods. This work describes an effective synthetic strategy, generally applicable to long RGG peptides, based on side-chain protected aDma and backbone protected dipeptide Fmoc-Gly-(Dmob)Gly-OH. This strategy allowed us to synthesize both the unmodified (N61Arg) and the dimethylated (N61aDma) peptides with high yield (,26%) and purity. As detected by NMR spectroscopy, N61Arg does not possess any stable secondary or tertiary structure in solution and N,,N, -dimethylation of the guanidino group does not alter the overall conformational propensity of this peptide. While both peptides bind single-stranded nucleic acids with similar affinities (Kd = 1.5 × 10,7M), they exhibit a different behaviour in ssDNA affinity chromatography consistent with the difference in pKa values. It has been previously shown that N61Arg inhibits HIV infection at the stage of HIV attachment to cells. This study demonstrates that Arg-dimethylated C -terminal domain lacks any inhibition activity, raising the question of whether nucleolin expressed on the cell-surface is indeed dimethylated. Copyright © 2004 European Peptide Society and John Wiley & Sons, Ltd. [source] Solid-phase synthesis of cyclic analogues related to the hypoglycaemic peptide hGH[6,13]: Comparison of two i,i+4 lactam cyclization proceduresJOURNAL OF PEPTIDE SCIENCE, Issue 10 2001Vittoria Cavallaro Abstract The use of 1,3-diisopropylcarbodiimide (DIC) for the synthesis of cyclic analogues of the hypoglycaemic peptide fragment derived from the N -terminus of human growth hormone (hGH), namely hGH[6,13], is described. Different strategies were examined to achieve improved yields for the on resin side-chain to side-chain cyclization of the corresponding linear peptides containing reverse , - turn motifs. When compared with the more reactive Castro's reagent, the results confirm that DIC in the presence of HOBt can be successfully employed to minimize the formation of intermolecular oligomeric by-products associated with the preparation of cyclic hGH[6,14] peptide analogues based on an i,(i+4)Lys,Glu or Glu,Lys cyclization strategy. Copyright © 2001 European Peptide Society and John Wiley & Sons, Ltd. [source] A new amino acid derivative with a masked side-chain aldehyde and its use in peptide synthesis and chemoselective ligationJOURNAL OF PEPTIDE SCIENCE, Issue 10 2001Jane C. Spetzler Abstract A new amino acid derivative with a diol side-chain, ,,-2-amino-4,5-dihydroxy-pentanoic acid (Adi), has been prepared from ,,-allylglycine by suitable protection, for use in peptide synthesis, as Fmoc-,,-Adi(Trt)2. This building block enables the introduction of a side-chain aldehyde at any position in a given peptide sequence without use of specialized side-chain protection schemes. The aldehyde is revealed by mild oxidation with sodium periodate, circumventing the problematic release of reactive peptidic aldehydes in TFA solution. Peptides with aldehyde side-chains are useful for chemo-selective ligation, reacting selectively with oxyamines to yield oxime links, while all other peptide functions can be left unprotected. The utility of the new building block has been demonstrated by the synthesis of peptide dimers and a cyclo-peptide. Copyright © 2001 European Peptide Society and John Wiley & Sons, Ltd. [source] Highly potent side-chain to side-chain cyclized enkephalin analogues containing a carbonyl bridge: synthesis, biology and conformationJOURNAL OF PEPTIDE SCIENCE, Issue 3 2001Danuta Pawlak Abstract Six novel cyclic enkephalin analogues have been synthesized. Cyclization of the linear peptides containing basic amino acid residues in position 2 and 5 was achieved by treatment with bis(4-nitrophenyl)carbonate. It was found that some of the compounds exibit unusually high µ -opioid activity in the guinea pig ileum (GPI) assay. The 18-membered analogue cyclo(N,,N,, -carbonyl-,,-Lys2,Dap5)enkephalinamide turned out to be one of the most potent µ-agonists reported so far. NMR spectra of the peptides were recorded and structural parameters were determined. The conformational space was exhaustively examined for each of them using the electrostatically driven Monte Carlo method. Each peptide was finally described as an ensemble of conformations. A model of the bioactive conformation of this class of opioid peptides was proposed. Copyright © 2001 European Peptide Society and John Wiley & Sons, Ltd. [source] Applications of model ,-hairpin peptidesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 12 2004Carol E. Stotz Abstract In recent years, ,-hairpin peptides have been studied in great detail. Much of the focus has been on the thermodynamic stability of ,-hairpin structure. Structural measurements have been conducted with nuclear magnetic resonance, with additional information obtained from circular dichroism, Fourier transform infrared, and molecular dynamic simulation studies. Point mutations, both in the ,-strands and in the turn region, have systematically explored the role of turn sequence, side-chain,side-chain interactions, intramolecular hydrogen bonding, and ,-strand length on ,-hairpin peptide conformational stability. In addition to studying the elements of structural stability independently, the cooperative nature of the individual components to combine to form the overall structure has also been investigated. Because the ,-hairpin peptides often spontaneously form their conformation, they have begun to serve as models for studying peptide binding and therapeutic agents. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:2881,2894, 2004 [source] Novel, cell-penetrating molecular transporters with flexible backbones and permanently charged side-chainsJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 8 2007N. Bodor Various cell-penetrating peptides have been discovered recently that can translocate across plasma membranes and can even carry large cargo molecules into the cells. Because under physiological conditions most of these peptides carry considerable positive charges due to the presence of basic amino acids such as arginine, we decided to investigate whether molecular transporters composed of permanently charged side-chains also possess such cell penetrating ability. Arginine-rich oligomers that have a backbone with increased flexibility due to incorporation of non-,-amino acids (,-aminocaproic acid) have been found to be effective molecular transporters. Here, we report the preparation of analogue structures by replacing the arginine residues with the quaternary form of a novel redox amino acid (Nys+) that contain a trigonelline moiety; it has already been shown possible to replace the original basic amino acid side-chain of neuropeptides without significant activity-loss due to the sufficiently close steric and electronic analogy between the new Nys+ and the original side-chains (in their protonated form, e.g., Arg+, Lys+). A nonamer analogue showed transporter activity resulting in increased cellular uptake in human carcinoma (HeLa) cells. [source] Effect of side-chain end groups on the optical, electrochemical, and photovoltaic properties of side-chain conjugated polythiophenesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2006Erjun Zhou Abstract Three new side-chain conjugated polythiophene derivatives, poly{3-[2-(3-methoxy-4-octyloxy-phenyl)-vinyl]-thiophene} (P3MOPVT), poly{3-[2-(3,5-dimethoxy-4-octyloxy-phenyl)-vinyl]-thiophene} (P3DMOPVT), and poly{3-[2-(3,4-dioctyloxy-phenyl)-vinyl]-thiophene} (P3DOPVT), were synthesized by Wittig-Hornor reaction and GRIM method and compared with poly{3-[2-(4-octyloxy-phenyl)-vinyl]-thiophene} (P3OPVT) for investigating the effect of the end groups of the conjugated side-chain on the properties of the polymers. Owing to the electron-donating ability of methoxy groups, the visible absorption peaks of P3MOPVT and P3DMOPVT solutions and films become stronger and red-shifted compared with P3OPVT. The electrochemical bandgaps of the four polymers are 2.15 eV for P3OPVT, 1.99 eV for P3MOPVT, 1.85 eV for P3DMOPVT, and 2.36 eV for P3DOPVT, respectively, which indicate that the electron-donating ability of the methoxy end group on the conjugated side chain of P3MOPVT and P3DMOPVT and the large steric hindrance of the two octyloxy end groups on the conjugated side chain of P3DOPVT have obvious influence on the electrochemical properties of the side-chain conjugated polythiophenes. Polymer solar cells were fabricated with a structure of ITO/PEDOT:PSS/Polymer:PCBM/LiF/Al. The best device, based on P3DMOPVT, shows a power conversion efficiency of 1.63% under the illumination of AM1.5, 80 mW/cm2. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4916,4922, 2006 [source] Synthesis of azobenzene-containing polythiophenes and photoinduced anisotropyJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2004Francois Aubertin Abstract Three new polythiophenes containing an azobenzene moiety in the side-chain were synthesized and characterized. Two of them, which are slightly soluble in tetrahydrofuran to allow the preparation of thin films from solution casting, were used to investigate the photoinduced anisotropy arising from the photoisomerization of azobenzene in this type of polymer. The results show that, unlike other amorphous azobenzene polymers, only an extremely small anisotropy can be induced on excitation with an Ar+ laser at 488 nm in these azobenzene-containing polythiophenes, and that this photoinduced anisotropy is observable only by heating the polymer to some temperatures below glass transition temperature. It is suggested that the inability for azobenzene polythiophenes to display a significant photoinduced anisotropy may be caused by some structural constraints and/or a severe interference from conjugated thiophene chains that absorb strongly in the visible region. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3445,3455, 2004 [source] Bioconversion of 3,-acetoxypregna-5,16-diene-20-one to androsta-1,4-diene-3,17-dione by mixed bacterial cultureLETTERS IN APPLIED MICROBIOLOGY, Issue 2 2002S. Patil Aims:,To isolate a bacterium capable of degrading 3,-acetoxypregna-5,16-diene-20-one (16-DPA) to androsta-1,4-diene-3,17-dione (ADD) and to decipher the biodegradation pathway. Methods and Results:,Isolation on mineral salt agar containing 16-DPA as sole carbon source yielded two bacteria identified as Pseudomonas diminuta and Comamonas acidovorons. These bacteria failed to degrade 16-DPA individually in pure cultures but converted 16-DPA to ADD in a mixed culture. The intermediates accumulated during the bioconversion were identified as pregna-4,16-diene-3,20-dione and pregna-1,4,16-triene-3,20-dione. Conclusions:,The degradation pattern of 16-DPA by mixed bacterial culture revealed the reaction sequence as (i) cleavage of C-3 acetyl function, (ii) dehydrogenation at C-1 and C-2 positions and (iii) cleavage of C-17 side-chain. Significance and Impact of the Study:,The present work opens a new approach towards the production of a female sex hormone precursor and elucidates the biodegradation pathway of 16-DPA by mixed bacterial culture. [source] Promising Optoelectronic Materials: Polymers Containing Phosphorescent Iridium(III) ComplexesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 9-10 2010Qiang Zhao Abstract As one of the most promising optoelectronic materials, polymers that contain phosphorescent IrIII complexes have attracted more and more interest in recent years. They are a class of well-known electroluminescent materials with excellent performance. So far, efficient green-, red-, and white-emitting polymer light-emitting diodes based on polymers with on-chain IrIII complexes have been realized successfully. For the realization of this class of polymer material, IrIII complexes (as energy guest) can be introduced into the main-chain or side-chain of polymers (as energy host). In this article, we summarize the design principles, synthetic routes, structure,property relationships, and applications in optoelectronic devices of polymers that contain phosphorescent IrIII complexes. [source] Structure elucidation and 3D solution conformation of the antibiotic enduracidin determined by NMR spectroscopy and molecular dynamicsMAGNETIC RESONANCE IN CHEMISTRY, Issue 8 2005F. Castiglione Abstract Enduracidin and ramoplanin belong to the large family of cyclodepsipeptide antibiotics, highly effective against Gram-positive bacteria. The primary and 3D solution structure of ramoplanin is already well known, and the primary structure of enduracidin has been determined by a combination of chemical and NMR spectroscopic methods. Both antibiotics share a similar peptide core of 17 amino acids and differ mainly in the length of the acyl chain and the presence of two D -mannose moieties in ramoplanin. Based on the high sequence homology with ramoplanin, the structure in solution of enduracidin is modeled as a cyclic peptide. The tertiary structure thus obtained was refined through molecular dynamics (MD) simulation, in which the interatomic NOE-derived distance restraints were imposed. MD simulations yielded a family of representative 3D structures (RMSD = 0.89), which highlighted a backbone geometry similar to that of ramoplanin in its ,-hairpin arrangement. In contrast, enduracidin displays a different arrangement of the side-chain and of the residues forming the hydrophobic core. Copyright © 2005 John Wiley & Sons, Ltd. [source] Characterization of reduced iso-,-acids derived from hops (Humulus lupulus) by NMRMAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2003Lars I. Nord Abstract Reduced forms of iso-,-acids (isohumulones), used in modern beer brewing were separated and characterized by 1H and 13C NMR spectroscopy. Components from mixtures of rho-iso-,-acids, tetrahydro-iso-,-acids, and hexahydro-iso-,-acids were isolated using high-performance liquid chromatography (HPLC) and analyzed by use of one- and two-dimensional NMR experiments. The data presented assign the identities of the main peaks in the HPLC traces for the reduced iso-,-acids. Previous tentative assignments regarding the cis and trans configurations and the structures of the acyl residues of the reduced iso-,-acids were confirmed and extensive NMR assignments were made. Furthermore, the previously unknown stereochemistry in the C-4 side-chain of the rho- and hexahydro-iso-,-acids was assigned. Copyright © 2003 John Wiley & Sons, Ltd. [source] Characterization of two Pseudomonas putida lipopeptide biosurfactants, putisolvin I and II, which inhibit biofilm formation and break down existing biofilmsMOLECULAR MICROBIOLOGY, Issue 1 2004Irene Kuiper Summary Pseudomonas putida strain PCL1445 was isolated from roots of plants, grown on a site polluted with polycyclic aromatic hydrocarbons. PCL1445 produces biosurfactant activity at the end of the exponential growth phase. High-performance liquid chromatography (HPLC) analysis of supernatant extracts of PCL1445 showed two peaks with surface-tension reducing activity, tentatively assigned as biosurfactants putisolvin I and putisolvin II and was followed by structural analyses. A transposon mutant of PCL1445, strain PCL1436, which lacks the two surface-active peaks appeared to be mutated in an open reading frame (ORF) with amino acid homology to various lipopeptide synthetases. Structural analyses of the two biosurfactants of PCL1445 revealed that both are novel cyclic lipodepsipeptides with a hexanoic lipid chain connected to the N-terminus of a 12-amino-acid peptide moiety, in which the C-terminal carboxylic acid group forms an ester with the hydroxyl side-chain of Ser9. The difference between the two structures is located in the second amino acid from the C-terminus, being valine for putisolvin I, and leucine/isoleucine for putisolvin II. We show that these novel compounds lower the surface tension and influence the biofilm development on polyvinyl chloride (PVC). Biofilm formation of the bio-synthetic mutant PCL1436 was strongly increased containing more cells, which formed aggregates earlier as compared with wild-type PCL1445 biofilms. Using purified putisolvin I and II it was shown that biofilm formation of different Pseudomonas strains was inhibited and most interestingly, that both putisolvins are also able to break down existing Pseudomonas biofilms. [source] Structure,activity relationship study of alkynyl ether insecticide synergists and the development of MB-599 (verbutin),PEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 4 2003Béla Bertók Abstract Structure,activity relationships of aryl alkynyl synergists of the general formula of Ar,Q,R, where Q represents a bridging structure, were studied using a standardised testing system and Relative Potency values. Ethers, esters, oxime ethers, amides and amines were prepared and evaluated. The length of the R-alkynyl chain, the role of the bridge and the substitution of the aromatic ring were examined systematically. The most potent compounds possessed an aromatic ring connected via a bridge of three atoms to an alkynyl chain, forming together a linear side-chain of six atoms. Several highly potent compounds were synthesised of which one (MB-599; proposed common name verbutin) was selected for development as a selective insecticide synergist in crop protection. Its high potential at practical insecticide:synergist ratios makes possible the reduction of the total amount of insect-control chemicals applied, and its use as an additive to produce new formulations of existing insecticides makes it highly advantageous in resistance management, giving a new tool to sustain the effectiveness of a wide range of insecticides. A product containing a (1,+,1) mixture of verbutin and beta-cypermethrin was launched in Hungary in 2002. © 2003 Society of Chemical Industry [source] Effect of side-chain length of succinic anhydride on coefficient of thermal expansion behavior of epoxy resinsPOLYMER INTERNATIONAL, Issue 11 2006Fan-Long Jin Abstract The effect of an alkenyl side-chain of succinic anhydride (SA) on the thermal behavior and the coefficient of thermal expansion (CTE) of diglycidylether of bisphenol A (DGEBA) epoxy resins was studied. The number of carbons in the side-chain of SA was varied from 6 to 14 and N,N -Dimethylbenzylamine was used as an accelerator. As a result, the reactivity of SA with epoxide groups was decreased on increasing the length of the alkenyl side-chain of SA. The thermal stabilities of cured DGEBA/SA samples were approximately constant with varying alkenyl side-chain of SA. Also, the CTE of the systems was increased as the length of the alkenyl side-chain of SA increased. This could be attributed to the increased motion of the chain segments in the epoxy network structure induced by the longer alkenyl side-chain of SA. The effect of amount anhydride, thermoplastics, and fillers on the CTE of the epoxy resins was also discussed. Copyright © 2006 Society of Chemical Industry [source] Syntheses and properties of polyurethanes containing side-chain azobenzene groupsPOLYMER INTERNATIONAL, Issue 5 2003Mi-Ra Kim Abstract Polymers containing azobenzene groups have the characteristic reaction of photo-induced cis,trans isomerism. The study of new materials for optical information storage has prompted making use of these photo-isomerizations. In this study, we report the syntheses and properties of four different polyurethanes (DR-PUns) containing azobenzene groups in the side-chains. The structurally similar polyurethanes (DR-PUns) were synthesized by the polycondensation reaction of Disperse Red 19 (DR 19) and four different diisocyanates in dimethylformamide. By introducing of DR 19 into the polymer, we obtained polymers containing a photochromic group in the side-chain. The weight-average molecular weights of the DR-PUns were in the range 5500,12,900. The Tgs of the DR-PUns range from 119.5,°C to 157.0,°C, depending on the structure of the diisocyanate. Optical properties and solubilities of the polyurethanes were compared. The diffraction efficiencies of films were measured as a function of the reaction time. Typically, the diffraction efficiencies of the DR-PU1 film prepared from toluene 2,4-diisocyanate were observed up to a level of 0.25%. For the DR-PU1 film, the effect of the intensity of the induced laser beam on the diffraction efficiency is also discussed. © 2003 Society of Chemical Industry [source] Synthesis, characterization, and electroluminescence of new conjugated PPV derivatives bearing triphenylamine side-chain through a vinylene bridgePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 12 2007Zhan'ao Tan Abstract Three new conjugated poly(p -phenylene vinylene) (PPV) derivatives bearing triphenylamine side-chain through a vinylene bridge, poly(2-(4,-(diphenylamino)phenylenevinyl)-1,4-phenylene-vinylene) (DP-PPV), poly(2-(3,-(3,,7,-dimethyloctyloxy)phenyl)-1,4-phenylenevinylene- alt -2-(4,- (diphenylamino)phenylenevinyl)-1,4-phenylenevinylene) (DODP-PPV), and poly(2-(4,-(diphenylamino)phenylenevinyl)-1,4-phenylenevinylene-co-2-(3,,5,-bis(3,,7,-dimethyloctyloxy)-1,4-phenylenevinylene) (DP-co-BD-PPV), were synthesized according to the Gilch or Wittig method. Among the three polymers, the copolymer DP-co-BD-PPV is soluble in common solvents with good thermal stability with 5% weight loss at temperatures higher than 386°C. The weight-average molecular weight (Mw) and polydispersity index (PDI) of DP-co-BD-PPV were 1.83,×,105 and 2.33, respectively. The single-layer polymer light-emitting diodes (PLEDs) with the configuration of Indium tin oxide (ITO)/poly (3,4-ethylenedioxythiophene): poly(4-styrene sulfonate)(PEDOT:PSS)/DP-co-BD-PPV/Ca/Al were fabricated. The PLED emitted yellow-green light with the turn-on voltage of ca. 4.9,V, the maximum luminance of ca. 990,cd/m2 at 15.8,V, and the maximum electroluminescence (EL) efficiency of 0.22,cd/A. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||||||||||||||