Global ETD Search

11	Exposition prénatale aux pesticides organophosphorés et neurodéveloppement chez les jeunes enfants Ntantu Nkinsa, Patrick 05 1900 (has links) No description available. pesticides organophosphorés (OP) dialkyl phoshates (DAP) neurodéveloppement exposition prénatale organophsphates pesticides (OP) neurodevelopment prenatal exposure
12	The synthesis of new phenylhydroxyiodonium phosphates from (diacetoxyiodobenzene) and dialkyl phosphates and their use in the α-phosphorylation of ketones to mono-ketol phosphates Keita, Ousainou Ansumana 12 May 2008 (has links) No description available. Chemistry, Organic phenylhydroxyiodonium phosphates (diacetoxyiodo) benzene dialkyl phosphates diphenyl phosphate phosphate esters phosphotriesters bis-ketol phosphates hypervalent iodine reagents
13	Compostos de coordenação envolvendo aroil(n,n-dialquil-calcogenoureias) monopodais e bipodais Schwade, Vânia Denise 24 January 2014 (has links) Conselho Nacional de Desenvolvimento Científico e Tecnológico / This work presentes the study realized with monopodal and bipodal aroyl(N,N-dialkylchalcogenoureas) involving different metallic ions to obtain mononuclear, dinuclear and trinuclear compounds. The compounds were characterized by X-ray diffraction, 1H NMR, I.R., ESI+ MS and elemental analysis. In the first part, the chemistry of aroyl(N,N-dialkylchalcogenoureas) with {ReVO}3+ was investigated, where mononuclear and dinuclear compounds were obtained. In the second part, the chemistry of isophthaloylbis(N,N-diethylchalcogenoureas) was investigated against different metallic ions. Dinuclear complexes of AuI, CuII, HgII and InIII, and polymeric compounds with PbII and SnII were obtained. Compounds were also obtained with CuI and TeII. The structural analysis of the AuI, CuII, PbII and InIII compounds with isophthaloylbis(N,N-diethylthiourea), H2L1, have shown that the ligand can exhibit different orientations of the arms‟ to make bis(bidentate) chelate coordination, by the oxygen and sulphur atoms, or bis(monodentate), by the sulphur atoms. These orientations occur due the metal characteristics, as geometry or the influency of the lone pair of electrons. The third part was focused in exploring the synthesis of trinuclear compounds using combinations of metals with dipicolinoylbis(N,N-diethylchalcogenoureas). With the derivatized ligand, 4-chlorodipicolinoylbis(N,N-diethylthiourea), H2L4, trinuclear [MIIBaIIMII] and [MIIGdIIIMII] (where MII = Mn, Co) compounds were obtained; and with the dipicolinoylbis(N,N-diethylselenourea), H2L5, the compounds [MnIIBaIIMnII] and [MIISmIIIMII] (MII = Mn, Co) were obtained. The composition of these compounds for the charge compensation follows that observed for the known compounds with the dipicolinoylbis(N,N-diethylthiourea) ligand, H2L2, in the way that, depending on the combination of metals used, two or three bis(chalcogenourea) anions are involved, where also acetate and/or chloride anions can be involved. The derivatization (additional Cl atom in the pyridine ring of the ligand molecule) led to the connection of the trinuclear molecules due to Ba∙∙∙Cl interactions, verified by the structural analysis of one compound. With the H2L2 and H2L4 ligands the incorporation of PbII in the trinuclear systems was explored, and [PbIIBaIIPbII] compounds were obtained. In these compounds the PbII metallic centers are located in the border positions by the chelate S,O coordination of three bis(thioureato) anions. On the other hand, [MIIPbIIMII] compounds were obtained for MII = Mn and Ni with H2L2, in which PbII is located in the central cavity formed by the S,O chelate coordination to the MnII and NiII metallic centers. However, from the combination PbII/NiII, a tetranuclear compound was also obtained, leading to a discussion of radius ratio between the metals as an aspect to be considered to obtain trinuclear systems, seeking the alignment of the metallic centers in the complexes. / Este trabalho apresenta um estudo realizado com aroil(N,N-dialquil-calcogenoureias) monopodais e bipodais envolvendo diferentes íons metálicos, na obtenção de compostos mononucleares, dinucleares e trinucleares. Os compostos foram caracterizados por difração de raios X, 1H RMN, I.V., IES+ EM e análise elementar. Na primeira parte, foi investigada a química de aroil(N,N-dialquilcalcogenoureias) envolvendo núcleos de {ReVO}3+, onde foram obtidos compostos mononucleares e dinucleares. Na segunda parte, foi investigada a química de isoftaloilbis(N,N-dietilcalcogenoureias) frente a diferentes íons metálicos. Foram obtidos complexos dinucleares de AuI, CuII, HgII e InIII, e poliméricos com PbII e SnII. Também foram obtidos compostos envolvendo CuI e TeII. A análise estrutural dos compostos de AuI, CuII, PbII e InIII com isoftaloilbis(N,N-dietiltioureia), H2L1, mostrou que o ligante pode apresentar diferentes orientações dos braços‟ para coordenação quelato bis(bidentada), pelos átomos de oxigênio e enxofre, ou bis(monodentada), pelo átomo de enxofre. Estas orientações ocorrem devido às características dos metais, como geometria ou influência do par isolado de elétrons. Na terceira parte explorou-se a síntese de compostos trinucleares utilizando-se combinações de metais, com dipicolinoilbis(N,N-dietilcalcogenoureias). Com o ligante derivatizado, 4-clorodipicolinoilbis(N,N-dietiltioureia), H2L4, foram obtidos compostos trinucleares [MIIBaIIMII] e [MIIGdIIIMII] (onde MII = Mn, Co); já com o ligante dipicolinoilbis(N,N-dietilselenoureia), H2L5, foram obtidos os compostos [MnIIBaIIMnII] e [MIISmIIIMII] (MII = Mn, Co). A composição destes compostos para o balanceamento de cargas segue à observada para os compostos conhecidos com o ligante dipicolinoilbis(N,N-dietiltioureia), H2L2, de forma que, dependendo da combinação de metais utilizada, são envolvidos dois ou três ânions bis(calcogenoureatos), podendo ainda estar envolvidos ânions acetato e/ou cloreto. A derivatização (átomo de Cl adicional no anel piridínico da molécula do ligante) levou à conexão de moléculas trinucleares a partir de interações Ba∙∙∙Cl, verificada pela análise estrutural de um dos compostos. Com os ligantes H2L2 e H2L4 foi explorada a incorporação de PbII em sistemas trinucleares, sendo obtidos compostos [PbIIBaIIPbII]. Nestes, os centros metálicos de PbII localizam-se nas posições das extremidades, pela coordenação quelato S,O de três ânions bis(tioureatos). Por outro lado, compostos [MIIPbIIMII] foram obtidos para MII = Mn e Ni com H2L2, nos quais PbII localiza-se na cavidade central formada pela coordenação quelato S,O aos centros metálicos de MnII e NiII. Porém, da combinação PbII/NiII, um composto tetranuclear também foi obtido, o que levou à uma discussão de razão de raios entre os metais como aspecto a ser considerado para a obtenção de sistemas trinucleares, buscando o alinhamento dos centros metálicos nos complexos. Aroil(N,N-dialquilcalcogenoureias) M-aroilbis(N,N-dialquil calcogenoureias) Compostos Mononucleares e Multinucleares Aroyl(N,N-dialkylchalcogenoureas) M-aroylbis(N,N-dialkyl-chalcogenoureas) Mononuclear and Multinuclear Compounds
14	Tribological Performance of Novel Boron Dithiocarbamate Lubricant Additives Taher, Mamoun January 2011 (has links) Different lubricant additives such as dialkyldithiophosphates (DTPs) of different metals have been extensively used as multifunctional additives to control wear and friction in mechanical systems. These additives can produce protective films on steel rubbing surfaces and, therefore, control friction and reduce wear. On the other hand, these additives contain large amounts of metals, phosphorus and sulfur, which can adversely affect the environment by degrading catalytic converters in automobiles. Boron based additives are recognized as friction modifiers, corrosion inhibitors, antioxidants, and effective antiwear additives. These additives are emerging as attractive alternatives for the additives already used in lubricants. The aim of the project is to investigate the tribological performance of some novel alkylborate dithiocarbamates.This project was performed in the following steps:1- Chemical synthesis of three different borated dialkyl dithiocarbamate additives with alkyl chains of different lengths.2- Tribological tests of novel compounds using a four ball tribometer.3- Surface analysis using an optical profiler (Veeco WYkO NT 1100) and Scanning Electron Microscopy coupled with X-ray Energy Dispersive Spectroscopy (SEM/EDS).The effect of the alkyl chain length in both DTC and the borate molecular moities of three B-DTC compounds on the tribological performance was studied. An increase in the alkyl chain length at the borate side improves antiwear properties in steel-steel contact. It was found that cyclo-N,N-alkylenedithiocarbamato-S-alkyl-di-n-alkyl-borate previously synthesized and studied [1], has the best antiwear performance compared with the other compounds synthesized in this work. All the novel additives were able to stabilize friction coefficient over a wide concentration range of the additives in the base oil. B-DTC additives with long alkyl chains show greater reduction in friction compared to the one with short alkyl chains. A possible explanation of this phenomenon is that longer chains have improved deposition process of additives on surfaces leading to a thicker and more stable tribofilm. EDS spectra show the presence of sulfur atoms on the rubbing surfaces lubricated by the base oil with B-DTC additives. / <p>Validerat; 20111001 (anonymous)</p> Physics Chemistry Maths Boron based additives borated dialkyl dithiocarbamate Tribofilm Tribology wear Friction Fysik Kemi Matematik
15	A Holocene temperature (brGDGT) record from Garba Guracha, a high-altitude lake in Ethiopia Bittner, Lucas, De Jonge, Cindy, Gil-Romera, Graciela, Lamb, Henry F., Russell, James M., Zech, Michael 22 February 2024 (has links) Eastern Africa has experienced strong climatic changes since the last deglaciation (15 000 years ago). The driving mechanisms and teleconnections of these spatially complex climate variations are yet not fully understood. Although previous studies on lake systems have enhanced our knowledge of Holocene precipitation variation in eastern Africa, relatively few studies have reconstructed the terrestrial temperature history of eastern Africa from lake archives. Here, we present (i) a new branched glycerol dialkyl glycerol tetraether (brGDGT) temperature calibration that includes Bale Mountains surface sediments and (ii) a quantitative record of mean annual air temperature (MAT) over the past 12 ka cal BP using brGDGTs in a sediment core collected from Garba Guracha (3950ma.s.l.) in the Bale Mountains. After adding Bale Mountains surface sediment (n = 11) data (Baxter et al., 2019) to the existing East African lake dataset, additional variation in 6-methyl brGDGTs was observed, which necessitated modifying the MBT'5ME calibration (MBT denotes methylation of branched tetraethers) by adding 6-methyl brGDGT IIIa0 (resulting in the MBT Bale Mountains index, r² = 0:93, p < 0:05). Comparing the MBT'5ME and the new MBT Bale Mountains index, our high-altitude Garba Guracha temperature record shows that warming occurred shortly after the Holocene onset when the temperature increased by more than 3.0°C in less than 600 years. The highest temperatures prevailed between 9 and 6 ka cal BP, followed by a temperature decrease until 1.4 ka cal BP. The reconstructed temperature history is linked to supraregional climatic changes associated with insolation forcing and the African Humid Period (AHP), as well as with local anomalies associated with catchment deglaciation and hydrology. info:eu-repo/classification/ddc/570 ddc:570 info:eu-repo/classification/ddc/550 ddc:550
16	Messung und Modellierung der Initiatoreffektivität organischer Peroxide in der Ethen-Hochdruckpolymerisation / Measurement and modelling of the initiator efficiency of organic peroxides in the high-pressure ethene polymerization Hinrichs, Stefan 30 June 2005 (has links) No description available. 540 Chemie Mathematics and Computer Science Initiatoreffektivität Hochdruck-Polymerisation Dialkylperoxid <i>tert</i>-Alkylperoxyester Polyethylen Ethen Ethylen Initiator efficiency high-pressure polymerization dialkyl peroxide <i>tert</i>-alkylperoxyester polyethylene ethene ethylene 35.80
17	N alpha -Arensulfonyl-Aminosäurechloride / Kupplung sterisch stark gehinderter Komponenten in der Peptidsynthese Henklein, Petra 24 July 2000 (has links) Obwohl die methodische Entwicklung der Peptidsynthese gewöhnlich eine automatisierte Herstellung erlaubt, sind für die Herstellung einer Reihe von Peptiden auch gegenwärtig Grenzen gesetzt. Einerseits kann eine im Verlauf der Kettenverlängerung auftretende Bildung intra- und /oder intermolekularer Wasserstoffbrücken zu einer begrenzten Solvatation und damit Zugänglichkeit der zu acylierenden Aminokomponente am Syntheseharz führen, andererseits kommt es beim Einbau sterisch anspruchsvoller Aminosäuren zu ungenügenden Acylierungsausbeuten. Urethangeschützte Aminosäurefluoride haben sich für den Einbau von alpha, alpha-Dialkylaminosäuren als geeignet erwiesen. Die reaktiveren urethangeschützten Aminosäurechloride sind zwar herstellbar, besitzen aber in Gegenwart einer Hilfsbase, die zum Abfangen der während ihrer Reaktion gebildeten HCl notwendig ist, eine zu geringe Stabilität (Oxazolonbildung, Abspaltung der Schutzgruppen). Erst die Verwendung von N(alpha)-Schutzgruppen, die keinen reaktionsfähigen Carbonylkohlenstoff enthalten, wie Arensulfonyl- Schutzgruppen, ermöglichen die volle Ausschöpfung der hohen Reaktivität der Aminosäurechloride. Mit Hilfe dieser Schutzgruppen gelang ein erster Vergleich der Reaktivität der Aminosäurechloride und -fluoride. Bei den durchgeführten Reaktionen wurde keine Stereomutation beobachtet. Unter Verwendung von Arensulfonylschutzgruppen war es erstmals möglich, zwei aufeinanderfolgende N-Alkyl-alpha, alpha-dialkylaminosäuren in Peptide einzubauen. Weiterhin konnten wir zeigen, daß derart geschützte Aminosäuren sich für in situ Aktivierungen mit Thionylchlorid eignen. Als Fänger für überschüssiges Aktivierungsreagenz wurden tertiäre Alkohole bzw. Amine eingesetzt. Arensulfonyl-geschützte Aminosäurechloride haben wir darüber hinaus erfolgreich in der Festphasenpeptidsynthese verwendet. In Kombination von Arensylfonyl-Schutz mit der Standard-Fmoc-Strategie gelang die Synthese eines biologisch aktiven Analogen des CRF, eines 41-mer Peptides mit einer eingefügten Tetrapeptidsequenz -Ala-MeAib-MeAib-Aib-. / Despite its wide field of application automatic peptide synthesis is still limited in certain cases. One of the limiting factors is the possibility of intra- or intermolecular hydrogen bond formation during the elongation of the peptide chain. This causes decreased solvation and thus reduced accessibility to the resin-bound amino component. Another limitation is the incorporation of sterically hindered amino acids that usually give rise to insufficient yields of acylation. Urethane protected amino acid fluorides have been shown suitable for the incorporation of alpha,alpha-dialkyl amino acids. Though the more reactive urethane protected amino acid chlorides can be readily synthesized, they do not possess the necessary stability in the presence of an auxiliary base that must be used for trapping of the hydrochloric acid formed during the reaction. Formation of oxazolons and deprotection of formerly protected functional groups would occur. Only the advent of protecting groups for the amino acid N-alpha that do not have a reactive carbonyl function - like arene sulfonyl groups - allowed to take full advantage of the high reactivity of the amino acid chlorides. These protecting groups enabled us to compare the reactivities of amino acid chlorides and fluorides for the first time. We didn't observe any stereo mutation in our experiments. The use of arene sulfonyl protecting groups permitted the consecutive incorporation of two N-alkyl-alpha,alpha-dialkyl amino acids into a peptide for the first time. Furthermore we could show, that amino acids protected in this way, are suitable for in situ activation with thionyl chloride. Tertiary alcohols and amines were used as scavenger for excessive activating reagent. Arene sulfonyl protected amino acids were also successfully used in solid phase peptide synthesis. By combining this protecting concept with the standard Fmoc approach we were able to synthesize a biologically active analogue of CRF, a peptide containing 41 residues into which we inserted the tetrapeptide Ala-MeAib-MeAib-Aib. Aminosäurefluorid Aminosäurechlorid Arensulfonyl-Schutzgruppen N-Alkyl-alpha alpha-dialkylaminosäuren Oxazolonbildung Peptidsynthese SPPS CRF amino acid fluorid amino acid chlorid arene sulfonyl protecting group N-alkyl-alpha alpha-dialkyl amino acids oxazolon peptide synthesis solid phase peptide synthesis CRF 30 Chemie VK 8567 ddc:540
18	Investigations into cyclopropanation and ethylene polymerization via salicylaldiminato copper (II) complexes Boyd, Ramon Cornell 23 January 2007 Two distinct overall research objectives are in this Masters thesis. Very little relates the two chapters apart from the ligands. The first chapter addresses diastereoselective homogeneous copper catalyzed cyclopropanation reactions. Cyclopropanation of styrene and ethyl diazoacetate (EDA) is a standard test reaction for homogeneous catalysts. Sterically bulky salicylaldimine (SAL) ligands should select for the ethyl trans-2-phenylcyclopropanecarboxylate diastereomer. Steric bulk poorly influences trans:cis ratios. Salicylaldiminine ligands do not posses the correct symmetry to affect diastereoselectivity. The SAL ligand belongs to the Cs point group in the solid state. Other ligand motifs are more effective at altering the trans:cis ratios. The second chapter addresses the general route toward successful copper(II) ethylene polymerization catalysts. Catalytic activity of the copper(II) complexes is very low. Polymer chain growth from a copper catalyst is very unlikely. Copper-carbon bonds decompose by homolytic cleavage or C-H activation. Copper-alkyls and aryls readily decompose into brown colored oils and salts with different colors. Ligand transfer to trimethylaluminum (TMA) appears to explain low yield ethylene polymerization. bulky migratory insertion mechanism coordination/insertion methodology d-block metal late transition metal phenolic ring coordination number ketimine precatalysts ketimine nitrogen bis(salicylaldiminato)copper(II) ratio cyclopropane steric bulk salicylaldiminato TMA salt trimethylaluminum aryl oil alkyl copper-aryls copper-alkyls C-H activation homolytic homolytic cleavage copper(II) polymerization ethylene cis trans symmetry diastereomer salicylaldimine SAL EDA ethyl diazoacetate styrene cyclopropanation copper diastereoselective steric protection stable CH(SiMe3)2 intermediate catalytic activity associated TMA free TMA vacant coordination site hydrolysis Lewis acid halogen anionic anionic ligand donor ligand monodentate anionic ligand aluminum(III) monodentate polymer chain polymer chain aluminum-carbon bond bulky SAL ligand open coordination site first row transition metal PE paramagnetic high molecular weight polyethylene alkylate methylaluminoxane MAO anionic ligands arylate aluminum carbon aluminum carbon bond beta-hydrogen elimination beta hydrogen elimination Aufbau reaction Aufbau neutral dialkyl aluminum aluminum-alkyl aluminum alkyl copper(0)
19	Investigations into cyclopropanation and ethylene polymerization via salicylaldiminato copper (II) complexes Boyd, Ramon Cornell 23 January 2007 (has links) Two distinct overall research objectives are in this Masters thesis. Very little relates the two chapters apart from the ligands. The first chapter addresses diastereoselective homogeneous copper catalyzed cyclopropanation reactions. Cyclopropanation of styrene and ethyl diazoacetate (EDA) is a standard test reaction for homogeneous catalysts. Sterically bulky salicylaldimine (SAL) ligands should select for the ethyl trans-2-phenylcyclopropanecarboxylate diastereomer. Steric bulk poorly influences trans:cis ratios. Salicylaldiminine ligands do not posses the correct symmetry to affect diastereoselectivity. The SAL ligand belongs to the Cs point group in the solid state. Other ligand motifs are more effective at altering the trans:cis ratios. The second chapter addresses the general route toward successful copper(II) ethylene polymerization catalysts. Catalytic activity of the copper(II) complexes is very low. Polymer chain growth from a copper catalyst is very unlikely. Copper-carbon bonds decompose by homolytic cleavage or C-H activation. Copper-alkyls and aryls readily decompose into brown colored oils and salts with different colors. Ligand transfer to trimethylaluminum (TMA) appears to explain low yield ethylene polymerization. bulky migratory insertion mechanism coordination/insertion methodology d-block metal late transition metal phenolic ring coordination number ketimine precatalysts ketimine nitrogen bis(salicylaldiminato)copper(II) ratio cyclopropane steric bulk salicylaldiminato TMA salt trimethylaluminum aryl oil alkyl copper-aryls copper-alkyls C-H activation homolytic homolytic cleavage copper(II) polymerization ethylene cis trans symmetry diastereomer salicylaldimine SAL EDA ethyl diazoacetate styrene cyclopropanation copper diastereoselective steric protection stable CH(SiMe3)2 intermediate catalytic activity associated TMA free TMA vacant coordination site hydrolysis Lewis acid halogen anionic anionic ligand donor ligand monodentate anionic ligand aluminum(III) monodentate polymer chain polymer chain aluminum-carbon bond bulky SAL ligand open coordination site first row transition metal PE paramagnetic high molecular weight polyethylene alkylate methylaluminoxane MAO anionic ligands arylate aluminum carbon aluminum carbon bond beta-hydrogen elimination beta hydrogen elimination Aufbau reaction Aufbau neutral dialkyl aluminum aluminum-alkyl aluminum alkyl copper(0)

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