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Group Leads (group + lead)
Selected AbstractsFluorinated ,-Diketones for the Extraction of Lanthanide Ions: Photophysical Properties and Hydration Numbers of Their EuIII ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2006Anne-Sophie Chauvin Abstract Tris(,-diketonato)europium(III) with a series of variably fluorinated ligands derived from 3,5-heptanedione were synthesised with the aim of determining their hydration state under extraction conditions. The number of coordinated water molecules was determined by measuring the lifetime of the Eu(5D0) excited level in water and deuterated water. The hydration gain (,q = q , q0) after shaking chloroform solutions during 10 min with 0.1 M NaClO4 aqueous solutions depends on the fluorination extent of the diketonates: fluorination of one methyl group leads to a decrease in ,q of ca. 0.5 unit, while fluorination of one ethyl group results in a decrease of ca. 1.3 units. Highly fluorinated complexes (i.e with hexafluoroacetylacetonate and related ligands) display a hydration number close to one while poorly fluorinated compounds (or nonfluorinated ones, such as the acetylacetonate complex) have a hydration state close to two. Photophysical properties of the EuIII ,-diketonates are also described and the synthesis of the fluorinated ,-diketones is re-investigated and discussed in details. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Synthesis, Structure and Spectroscopic Properties of Novel9,10-Bis{[6-(diphenylphosphanyl)-2-pyridylmethyl]propylaminomethyl}anthracene-Bridged Group 11 Metal (M = CuI and AgI) Dinuclear ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2005Hu Xu Abstract Dinuclear complexes [M2(,-BPNNAn)]X2 (M = CuI, X = ClO4,1, X = BF4,2; M = AgI, X = BF4,3, X = ClO4,4) have been prepared by treating 9,10-bis{[6-(diphenylphosphanyl)-2-pyridylmethyl]propylaminomethyl}anthracene (BPNNAn) with M(CH3CN)4X in CH2Cl2. The structures of complexes 1, 2 and 3 have been determined by single-crystal X-ray diffraction studies. In the complexes, BPNNAn acts as a chelating ligand and two metal ions riding on two bridgehead carbon atoms in the anthracene group leads to the deformation of the anthracenyl ring. The Cu,Arene charge transfer interaction is observed from the nonfluorescent emission of Cu complex 1, while the Ag complex 3 exhibits dual emission at high concentrations in a CH2Cl2 solution. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Dithiocarbamate mediated controlled/living free radical polymerization of methyl acrylate under 60Co ,-ray irradiation: Conjugation effect of N -groupJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2004Daoben Hua Abstract The free radical polymerizations of methyl acrylate have been studied under ,-ray irradiation in the presence of the dithiocarbamates with different N -groups. The results indicate that the conjugation structure of the N -group of dithiocarbamate plays an important role in living free radical polymerization. The polymerizations reveal good living characteristics in the presence of dithiocarbamates (benzyl 1H-imidazole-1-carbodithioate, benzyl 1H-pyrrole-1-carbodithioate, benzyl 1H-indole-1-carbodithioate, and benzyl 9H-carbazole-9-carbodithioate) with N -aryl group. In contrast, the polymerization with benzyl N,N -diethyldithiocarbamate cannot be controlled, and the obtained polymer has a broad molecular weight distribution or even crosslink occurs. Moreover, polymerization rate is influenced by the conjugation structure of the N -group of dithiocarbamate, and the aromatic polycyclic structure of the N -group leads to slow polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5670,5677, 2004 [source] Synthesis of a New Macromonomer from 2-(Dimethylamino)ethyl Methacrylate Bearing 1-(Isopropenylphenyl)-1,1-dimethylmethyl Isocyanate GroupMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 5 2004Cyril Boyer Abstract Summary: The telomerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA) with 2-mercaptoethanol in acetonitrile shows that the telogen can react with the monomer by nucleophilic addition. It is to say that the tertiary amino group leads to nucleophilic addition rather than telomerization. The oligomers thus obtained were functionalized with 1-(isopropenylphenyl)-1,1-dimethylmethyl isocyanate (TMI) in anhydrous toluene to afford macromonomers. These macromonomers were copolymerized with styrene and the r1, r2 ratio was determined according to Jaacks and Macret's methods. It was thereby demonstrated that the r1 value for this type of monomer is close to zero. Structure of the model molecule. [source] Sulfonamide bond cleavage in benzenesulfonamides and rearrangement of the resulting p -aminophenylsulfonyl cations: application to a 2-pyrimidinyloxybenzylaminobenzenesulfonamide herbicideRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2005Hao-Yang Wang The gas-phase fragmentation/rearrangement reactions of compound 1, [2-(4,6-dimethoxypyrimidin-2-yloxy)-benzyl]-[4-(piperidine-1-sulfonyl)phenyl]amine, have been examined by Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). The analyses reveal that under sustained off-resonance irradiation collision-induced dissociation (SORI-CID) conditions in the FTICR cell, protonated 1 undergoes two competitive pathways initiated by different protonation positions. The first pathway is initiated by protonation on the amino group and yields only one fragment ion due to loss of the entire benzenesulfonamide moiety. In the second pathway, protonation of the sulfonamide group leads to cleavage of a sulfonamide bond with loss of the neutral piperidine, followed by loss of SO via a sulfonyl cation rearrangement. An intramolecular SNAr mechanism is proposed to rationalize the rearrangement of the p -aminophenylsulfonyl cation and the resulting SO loss. To test the generality of this process, SORI-CID spectra of protonated sulfamethoxazole and of the p -aminophenylsulfonyl cation (SBN) were obtained. For the SBN ion, SORI-CID experiments as well as density functional theory (B3LYP) calculations show that rearrangement, assigned as a SNAr reaction of the sulfonyl cation group, can account for the observed SO loss process. Candidate transition state structures were optimized at the B3LYP/6-31+G (d, p) level of theory using the Gaussian98 molecular modeling package. The computational results show that the barrier for SO loss from SBN is much lower than that for SO2 loss, which satisfactorily rationalizes the SORI-CID experimental results for SBN. Moreover, it is proposed that a fragment ion at m/z 196 in the MS/MS spectrum of protonated 1 is formed via the ion resulting from SO loss via a second intramolecular SNAr mechanism. Copyright © 2005 John Wiley & Sons, Ltd. [source] High-resolution structure of the antibiotic resistance protein NimA from Deinococcus radioduransACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 6 2008Hanna-Kirsti S. Leiros Many anaerobic human pathogenic bacteria are treated using 5-nitroimidazole-based (5-Ni) antibiotics, a class of inactive prodrugs that contain a nitro group. The nitro group must be activated in an anaerobic one-electron reduction and is therefore dependent on the redox system in the target cells. Antibiotic resistance towards 5-Ni drugs is found to be related to the nim genes (nimA, nimB, nimC, nimD, nimE and nimF), which are proposed to encode a reductase that is responsible for converting the nitro group of the antibiotic into a nonbactericidal amine. A mechanism for the Nim enzyme has been proposed in which two-electron reduction of the nitro group leads to the generation of nontoxic derivatives and confers resistance against these antibiotics. The cofactor was found to be important in the mechanism and was found to be covalently linked to the reactive His71. In this paper, the 1.2,Å atomic resolution crystal structure of the 5-nitroimidazole antibiotic resistance protein NimA from Deinococcus radiodurans (DrNimA) is presented. A planar cofactor is clearly visible and well defined in the electron-density map adjacent to His71, the identification of the cofactor and its properties are discussed. [source] Sequence-specific Methyltransferase- Induced Labeling of DNA (SMILing DNA)CHEMBIOCHEM, Issue 3 2004Goran Pljevalj Abstract A new concept for sequence-specific labeling of DNA by using chemically modified cofactors for DNA methyltransferases is presented. Replacement of the amino acid side chain of the natural cofactor S -adenosyl- L -methionine with an aziridine group leads to a cofactor suitable for DNA methyltransferase-catalyzed sequence-specific coupling with DNA. Sequence-specifically fluorescently labeled plasmid DNA was obtained by using the DNA methyltransferase from Thermus aquaticus (M.TaqI) as catalyst and attaching a fluorophore to the aziridine cofactor. First results suggest that all classes of DNA methyltransferases with different recognition sequences can be used. In addition, this novel method for DNA labeling should be applicable to a wide variety of reporter groups. [source] Intramolecular Energy Transfer in Pyrene,Bodipy Molecular Dyads and TriadsCHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2005Raymond Ziessel Dr. Abstract Molecules bearing a 4,4-difluoro-8-(aryl)-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza- s -indacene (bodipy) core and 1-pyrenyl-1-phenyl-4-(1-ethynylpyrene), or 1-phenyl-4-[1-ethynyl-(6-ethynylpyrene)pyrene] units were constructed in a step-by-step procedure based on palladium(0)-promoted cross-coupling reactions with the required preconstructed modules. X-ray structures of single crystals reveal a twisted arrangement of the two chromophores. In one case, an almost perfect orthogonal arrangement is found. These dyes are strongly luminescent in solution and display rich electrochemistry in which all redox processes of the bodipy and pyrene fragments are clearly resolved. The absorption spectra indicate that the bodipy and pyrene chromophores are spectrally isolated, thereby inducing a large "virtual" Stokes shift. The latter is realised by efficient transfer of intramolecular excitation energy by the Förster dipole,dipole mechanism. The rate of energy transfer depends on the structure of the dual-dye system and decreases as the centre-to-centre separation increases. The energy transfer efficiency, however, exceeds 90,% in all cases. The linkage of two pyrene residues by an ethyne group leads to a decrease in the energy-transfer efficiency, with the two polycycles acting as a single chromophore. The directly linked bodipy,pyrene dual dye binds to DNA and operates as an efficient solar concentrator when dispersed in plastic. De nouvelles molécules comprenant un c,ur 4,4-difluoro-8-(aryl)-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (appelé bodipy) et des fragments 1-pyrènyl, 1-phényl-4-(1-éthynylpyrène), ou 1-phényl-4-[1-éthynyl-(6-éthynylpyrène)pyrène] ont été synthétisées par le biais de couplage croisés entre des modules pré-construits. Ces réactions ont été catalysées par du palladium sous-ligandé dans des conditions anaérobiques. Dans deux cas typiques la structure moléculaire déterminée par diffraction aux rayons X sur monocristal révèle un arrangement quasi perpendiculaire des deux sous-unités bodipy et pyrène. L'ensemble des composés sont très fluorescents en solution et dévoilent une voltammétrie cyclique riche en signaux réversibles. L'ensemble des processus d'oxydation et de réduction localisés sur les sous-unité pyrène et bodipy sont bien résolus. De plus ces deux fragments sont spectroscopiquement différenciées ce qui permet d'obtenir des déplacements de Stokes important lorsque la partie pyrène est excitée et que la fluorescence de la partie bodipy est observée. Le processus responsable de ce phénomène est un transfert d'énergie ayant lieu par résonance (mécanisme dit de Förster par interaction dipôle-dipôle). La vitesse de ce transfert d'énergie dépends de la structure moléculaire et décroît en augmentant la distance ente les deux chromophores. L'efficacité de ce transfert est supérieur à 90,% dans l'ensemble des cas étudiés. Cependant la connexion par une liaison triple des motifs bodipy et pyrène diminue l'efficacité de ce transfert. La molécule comportant un pyrène directement connecté au bodipy se lie fortement à l'ADN et se comporte comme un concentrateur de photons lorsque dispersé dans des plastiques rigides. [source] | |||||||||||||