Miniprojeto para ensino de Química Orgânica Experimental baseado no acoplamento catalítico N-C promovido por micro-ondas

This paper describes a three-week mini-project for an Experimental Organic Chemistry course. The activities include N-C cross-coupling synthesis of N-(4-methoxyphenyl) benzamide in an adapted microwave oven by a copper catalyst (CuI). Abilities and concepts normally present in practical organic chemistry courses are covered: use of balances, volumetric glassware, separation of mixtures (liquid-liquid extraction and filtration), chromatographic techniques, melting point determination and stoichiometric calculations.

Voltammetric oxidation of drugs of abuse I. Morphine and metabolites

A detailed study of the electrochemical oxidative behavior of morphine in aqueous solution is reported. Through the synthesis of several metabolites and derivatives, pseudomorphine, morphine N-oxide, normorphine, dihydromorphine and 2-(N,N-dimethylaminomethyl)morphine, and their voltammetric study it was possible to identify the oxidation peaks for morphine. The anodic waves are related with the oxidation of phenolic and tertiary amine groups. It is also possible to verify that a poorly defined peak observable during morphine oxidation is not a consequence of further oxidation of pseudomorphine but due to formation of a dimer during phenolic group oxidation. The results obtained and especially those regarding the formation of a new polymer based on a C O coupling could be useful for clarifying the discoloration phenomenon occurring during storage of morphine solutions as well as leading to a better understanding of its oxidative metabolic pathways.

Methyl syringate: An efficient phenolic mediator for bacterial and fungal laccases

The aim of the present work is to provide insight into the mechanism of laccase reactions using syringyl-type mediators. We studied the pH dependence and the kinetics of oxidation of syringyl-type phenolics using the low CotA and the high redox potential TvL laccases. Additionally, the efficiency of these compounds as redox mediators for the oxidation of non-phenolic lignin units was tested at different pH values and increasing mediator/non-phenolic ratios. Finally, the intermediates and products of reactions were identified by LC-MS and H-1 NMR. These approaches allow concluding on the (1) mechanism involved in the oxidation of phenolics by bacterial laccases, (2) importance of the chemical nature and properties of phenolic mediators, (3) apparent independence of the enzyme's properties on the yields of non-phenolics conversion, (4) competitive routes involved in the catalytic cycle of the laccase-mediator system with several new C-O coupling type structures being proposed.

Synthesis and properties of d6 metal complexes of bidentate and tridentate ‘super donor’ ligands

La polyvalence de la réaction de couplage-croisé C-N a été explorée pour la synthèse de deux nouvelles classes de ligands: (i) des ligands bidentates neutres de type N^N et (ii) des ligands tridentates neutres de type N^N^N. Ces classes de ligands contiennent des N-hétérocycles aromatiques saturés qui sont couplés avec hexahydropyrimidopyrimidine (hpp). Les ligands forment de cycles à six chaînons sur la coordination du centre Ru(II). Ce fait est avantageux pour améliorer les propriétés photophysiques des complexes de polypyridyl de Ru(II). Les complexes de Ru(II) avec des ligands bidentés ont des émissions qui dépendent de la basicité relative des N-hétérocycles. Bien que ces complexes sont électrochimiquement et photophysiquement attrayant, le problème de la stereopurité ne peut être évité. Une conception soigneuse du type de ligand nous permet de synthétiser un ligand bis-bidentate qui est utile pour surmonter le problème de stereopurité. En raison de la spécialité du ligand bis-bidentate, son complexe diruthénium(II,II) présente une grande diastéréosélectivité sans séparation chirale. Alors que l'unité de hpp agit comme un nucléophile dans le mécanisme de C-N réaction de couplage croisé, il peut également agir en tant que groupe partant, lorsqu'il est activé avec un complexe de monoruthenium. Les complexes achiraux de Ru(II) avec les ligands tridentés présentent des meilleures propriétés photophysiques en comparason avec les prototypes [Ru(tpy)2]2+ (tpy = 2,2′: 6′, 2′′-terpyridine). L’introduction de deux unités de hpp dans les ligands tridentates rend le complexe de Ru(II) en tant que ‘absorbeur noir’ et comme ‘NIR émetteur’ (NIR = de l’anglais, Near Infra-Red). Cet effet est une conséquence d'une meilleure géométrie de coordination octaédrique autour de l'ion Ru(II) et de la forte donation sigma des unités hpp. Les complexes du Re(I) avec des ligands tridentates présentent un comportement redox intéressant et ils émettent dans le bleu. L'oxydation quasi-réversible du métal est contrôlée par la donation sigma des fragments hpp, tandis que la réduction du ligand est régie par la nature électronique du motif N-hétérocycle central du ligand lui-même. Cette thèse presente également l'auto-assemblage des métal-chromophores comme ‘métallo-ligands’ pour former des espèces supramoléculaires discretes utilisant des complexes neutres. Les synthèses et propriétés des métaux-chromophores précités et les supramolécules sont discutées.

Discovery of two distinct red clumps in NGC 419: a rare snapshot of a cluster at the onset of degeneracy

Colour-magnitude diagrams (CMDs) of the Small Magellanic Cloud (SMC) star cluster NGC 419, derived from Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) data, reveal a well-delineated secondary clump located below the classical compact red clump typical of intermediate-age populations. We demonstrate that this feature belongs to the cluster itself, rather than to the underlying SMC field. Then, we use synthetic CMDs to show that it corresponds very well to the secondary clump predicted to appear as a result of He-ignition in stars just massive enough to avoid e(-)-degeneracy settling in their H-exhausted cores. The main red clump instead is made of the slightly less massive stars which passed through e(-) degeneracy and ignited He at the tip of the red giant branch. In other words, NGC 419 is the rare snapshot of a cluster while undergoing the fast transition from classical to degenerate H-exhausted cores. At this particular moment of a cluster`s life, the colour distance between the main-sequence turn-off and the red clump(s) depends sensitively on the amount of convective core overshooting, Lambda(c). By coupling measurements of this colour separation with fits to the red clump morphology, we are able to estimate simultaneously the cluster mean age (1.35(-0.04)(+0.11) Gyr) and overshooting efficiency (Lambda(c) = 0.47(-0.04)(+0.14)). Therefore, clusters like NGC 419 may constitute important marks in the age scale of intermediate-age populations. After eye inspection of other CMDs derived from HST/ACS data, we suggest that the same secondary clump may also be present in the Large Magellanic Cloud clusters NGC 1751, 1783, 1806, 1846, 1852 and 1917.

Search for ZZ and z gamma* production in p(p)over-bar collisions at root s=1.96 TeV and limits on anomalous ZZZ and ZZ gamma* couplings

We present a study of mu mu mu mu, eeee, and mu mu ee events using 1 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron p (p) over bar Collider at root s = 1.96 TeV. Requiring the lepton pair masses to be greater than 30 GeV, we observe one event, consistent with the expected background of 0.13 +/- 0.03 events and with the predicted standard model ZZ and Z gamma(*) production of 1.71 +/- 0.15 events. We set an upper limit on the ZZ and Z gamma(*) cross section of 4.4 pb at the 95% C.L. We also derive limits on anomalous neutral trilinear ZZZ and ZZ gamma(*) gauge couplings. The one-parameter 95% C.L. coupling limits with a form-factor scale Lambda = 1.2 TeV are -0.28 < f(40)(Z)< 0.28, -0.31 < f(50)(Z)< 0.29, -0.26 < f(40)(gamma)< 0.26, and -0.30 < f(50)(gamma)< 0.28.

Estudo e caracterização da eletropolimerização de moléculas nanoestruturadas a Base de Schiff

Pós-graduação em Química - IBILCE

Stereoselectivity of Additions to N-Methyl Acetonitrilium Fluorosulfonate

Alkoxy-N-methyl-acetiminium salts were prepared by addition of CH3OH and C2H5OH to N-methyl acetonitrilium fluorosulfonate at low temperature. Analysis of the (5)J(HH) and (3)J(13)C-H coupling constants in the NMR spectra showed an anti addition with a diastereoselectivity of >9596. Deprotonation of these salts with (Z)-configuration gave the corresponding N-methyl-alkoxyacetimines with very high (E)-configuration. Upon protonation at -78 degrees C, these iminoesters gave the corresponding alkoxy-N-methyl-acetirninium salts with (E)-configuration. Computational analyses of the iminoesters and the corresponding iminium cations including the conformations give insight into the relative stability. Nitrilium salts can be used as reagents, exemplified by some esterifications between simple acids and alcohols.

Heterogeneous catalysts for environmentally sustainable reactions

This PhD work deals with problems of synthetic organic chemistry with particular attention to the development of environmentally friendly processes. In particular, new synthetic strategies have been studied based on the use of low cost heterogeneous catalysts, non-toxic reagents and mild operating conditions that do not involve, when possible, the use of solvents. The catalysts examined are both basic and acids, commercial or prepared by hetereogenization of homogeneous catalysts synthesized by tethering or impregnation. In particular it will be discussed the catalytic activity of oxides (Al2O3 and TiO2), supported sulphonic acids and hydrotalcites for the reactions of selective monoesterificazion of dicarboxylic acids, dehydrogenation of butane in gas phase, esterification of levulinic acid, Friedel-Craft acylations, C-C and C-P coupling. The use of these materials has allowed the development of simple processes with low environmental impact. The operating conditions are in fact mild and reaction times short. The selectivity for the desired products is in all reported cases very high and the catalysts can be recycled maintaining their optimum performances.

Junções moleculares e agregados de nanobastões de ouro: um estudo SERS

A Espectroscopia Raman Intensificada pela Superfície (SERS) é um efeito de intensificação da intensidade Raman de uma molécula adsorvida numa superfície metálica nanoestruturada. Esta característica permite a utilização do SERS na caracterização vibracional de sistemas como junções moleculares (JM) (JM são sistemas constituídos de fios moleculares sintetizados em junções do tipo metal|fiomolecular|metal) e, no entendimento de quais características morfológicas de agregados metálicos mais influenciariam no sinal SERS obtido. Portanto, esta tese apresenta os seguintes objetivos: (a) síntese e caracterização de substratos SERS ativos, nanoesferas (AuNE) e nanobastões (AuNB) de ouro e eletrodo de ouro ativado eletroquimicamente; (b) síntese e caracterização SERS de fios moleculares em JM; (c) estudo do acoplamento plasmônico entre as superfícies metálicas em JM; (d) correlação entre SERS - morfologia de agregados individuais de AuNB. Os fios moleculares estudados foram os da família das oligofeniliminas (OPI) e, no melhor do nosso entendimento, esta foi a primeira vez que fios moleculares desta família foram caracterizados por Raman e SERS. As JM apresentaram um comportamento SERS não esperado. Enquanto para o modo vibracional, v(CS), a intensidade da banda se apresentou constante com o aumento do espaçamento entre as nanoestruturas metálicas (para distâncias de até 5 nm), o modo vibracional, β(CH), teve a intensidade de sua banda aumentada. Este comportamento foi explicado considerando a diferente natureza da interação dos plasmons nas JM, sendo estas interações do tipo, ressonância de plasmon de superfície (LSPR) - dipolo imagem, para ambos os modos. No entanto, para o modo β(CH) existe também uma intensificação extra devido ao aumento da polarizabilidade dos fios moleculares com o aumento do número de unidades. A correlação SERS - morfologia dos agregados de AuNB indicam que, para agregados onde predominam interações ponta a ponta, os espectros SERS apresentavam uma maior intensidade quando comparados com aqueles em que interações lado a lado predominavam. No entanto, este comportamento não foi observado para agregados contendo mais do que cinco nanopartículas onde estes dois tipos de interações ocorrem indicando que deve existir um acoplamento dos plasmons destes dois tipos de interações contribuindo para maiores valores de intensidade SERS.

Screening of highly modular sugar-based ligand libraries in the enantioselective C-C coupling reactions

Projecte de recerca elaborat a partir d’una estada a la University of Nottingham, Gran Bretanya, entre març i abril del 2007. Aquest treball s’ha centrat en l’aplicació de compostos derivats de la D-(+)-glucosa, de la D-(+)-fructosa i la D-galactosa com a lligands de catalitzadors homogenis quirals en dos reaccions asimètriques: addició 1,2 a aldehids catalitzada per níquel i addició 1,4 conjugada catalitzada per coure.(veure figura adjunta al final del document). En primer lloc, s’ha estudiat l’aplicació dels compostos L1-L6 a les reaccions d’addició 1,2 a aldehids catalitzades per níquel. S’ha observat que la selectivitat del procés depèn principalment del grup funcional unit a l’esquelet del lligand, de les propietats estèriques del substituent en la funció oxazolina i de l’estructura del substrat. S’ha obtingut fins a un 59% d’excés enantiomèric utilitzant el precursor de catalitzador que conté el lligand L3a. En segon lloc, aquest treball descriu l’aplicació de les tres famílies de compostos (L1-L11) com a lligands en la reacció d’addició 1,4 catalitzada per coure de compostos organometàl•lics a diferents enones amb diferents propietats estèriques. L’ús de les llibreries de compostos fosfit-oxazolina (L1-L5) i fosfit-fosforamidit (L6) han proporcionat bones enantioselectivitats (fins a 80%) en l’addició de reactius de trialquilalumini a diferents enones. En canvi, la llibreria de compostos monofosfit (L7-L11) ha mostrat bones activitats però enantioselectivitats fins a 57%.

mitoKATP channel activation in the postanoxic developing heart protects E-C coupling via NO-, ROS-, and PKC-dependent pathways.

Whereas previous studies have shown that opening of the mitochondrial ATP-sensitive K(+) (mitoK(ATP)) channel protects the adult heart against ischemia-reperfusion injury, it remains to be established whether this mechanism also operates in the developing heart. Isolated spontaneously beating hearts from 4-day-old chick embryos were subjected to 30 min of anoxia followed by 60 min of reoxygenation. The chrono-, dromo-, and inotropic disturbances, as well as alterations of the electromechanical delay (EMD), reflecting excitation-contraction (E-C) coupling, were investigated. Production of reactive oxygen species (ROS) in the ventricle was determined using the intracellular fluorescent probe 2',7'-dichlorofluorescin (DCFH). Effects of the specific mitoK(ATP) channel opener diazoxide (Diazo, 50 microM) or the blocker 5-hydroxydecanoate (5-HD, 500 microM), the nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 50 microM), the antioxidant N-(2-mercaptopropionyl)glycine (MPG, 1 mM), and the PKC inhibitor chelerythrine (Chel, 5 microM) on oxidative stress and postanoxic functional recovery were determined. Under normoxia, the baseline parameters were not altered by any of these pharmacological agents, alone or in combination. During the first 20 min of postanoxic reoxygenation, Diazo doubled the peak of ROS production and, interestingly, accelerated recovery of ventricular EMD and the PR interval. Diazo-induced ROS production was suppressed by 5-HD, MPG, or L-NAME, but not by Chel. Protection of ventricular EMD by Diazo was abolished by 5-HD, MPG, L-NAME, or Chel, whereas protection of the PR interval was abolished by L-NAME exclusively. Thus pharmacological opening of the mitoK(ATP) channel selectively improves postanoxic recovery of cell-to-cell communication and ventricular E-C coupling. Although the NO-, ROS-, and PKC-dependent pathways also seem to be involved in this cardioprotection, their interrelation in the developing heart can differ markedly from that in the adult myocardium.

C-H and C-D interbond coupling in CHDCl2

Laser photoacoustic spectra of vapour phase CHDCl2 reveal the presence of an interaction which has been ascribed to interbond coupling between C-H and C-D local modes. The absolute value of the interbond coupling parameter for the CHD group, determined from a fit of a model local mode hamiltonian to the experimental data, is shown to be given approximately by the geometric mean of the interbond coupling parameters of the CH2 and CD2 groups recently derived from similar studies of CH2Cl2 and CD2Cl2. Such behaviour is understood in terms of a simple analysis in which kinetic coupling effects dominate. It is suggested that C-H stretch/bend Fermi resonance is responsible for some weaker features in the spectra and modelling calculations are described which allow an order of magnitude estimate of the size of the coupling parameter involved.