Labeled 15NO experiments for the study of NOx reduction over Pt-Ba/Al2O3 LNT catalyst

Labelled 15NO study on N2 and N2O formation over Pt-Ba/Al2O3 LNT catalysts

Effective collision strengths for fine-structure forbidden transitions among the 2s22p3 levels of S x

Effective collision strengths for electron-impact excitation of the N-like ion S x are calculated in the close-coupling approximation using the multichannel R-matrix method. Specific attention is given to the 10 astrophysically important fine-structure forbidden transitions among the ⁴S^O, ²D^o and ²P^o levels in the 2s²2p³ ground configuration. The total (e^- + ion) wavefunction is expanded in terms of the 11 lowest LS eigenstates of S x, and each eigenstate is represented by extensive configuration-interaction wavefunctions. The collision strengths obtained are thermally averaged over a Maxwellian distribution of velocities, for all 10 fine-structure transitions, over the range of electron temperatures log T(K) = 4.6-6.7 (the range appropriate for astrophysical applications). The present effective collision strengths are the only results currently available for these fine-structure transition rates.

Effective collision strengths for fine-structure forbidden transitions among the 3s 23p 3 levels of Ar IV

The multichannel R-matrix method is used to compute electron impact excitation collision strengths in Ar IV for all fine-structure transitions among the ⁴S°, ²D° and ²P° levels in the 3s ²3p ³ ground configuration. Included in the expansion of the total wavefunction are the lowest 13 LS target eigenstates of Ar iv formed from the 3s ²3p ³, 3s3p ⁴ and 3s ²3p ²3d configurations. The effective collision strengths, obtained by averaging the electron collision strengths over a Maxwellian distribution of electron velocities, are presented for all 10 fine-structure transitions over a wide range of electron temperatures of astrophysical interest (T _e = 2000-100 000 K). Comparisons are made with an earlier 7-state close-coupling calculation by Zeippen, Butler & Le Bourlot, and significant differences are found to occur for many of the forbidden transitions considered, in particular those involving the ⁴S° ground state, where discrepancies of up to a factor of 3 are found in the low-temperature region. © 1997 RAS.

Síntese e transformações de compostos do tipo pirazol e 1,2,3-triazol

Compostos do tipo pirazol e 1,2,3-triazol encontram-se presentes em inúmeras moléculas biologicamente ativas. Muitos fármacos atualmente comercializados ou em fase de estudos clínicos contêm na sua estrutura base núcleos de pirazol ou 1,2,3-triazol. Por isso, estes compostos têm sido alvo de intensa pesquisa na procura de novas moléculas com potenciais aplicações medicinais e agroquímicas. Nesta dissertação são descritas novas vias de síntese de novos compostos do tipo pirazol e 1,2,3-triazol. No primeiro capítulo apresenta-se uma breve revisão bibliográfica sobre a atividade biológica, ocorrência natural e métodos de síntese de pirazóis e seus derivados. O segundo capítulo foca-se na síntese de (E)-2-estiril-3-halo-4H-cromen-4-onas e sua transformação em 3(5)-aril-5(3)-[2-(2-hidroxifenil)-2-oxoetil-1H-pirazóis. Em primeiro lugar faz-se uma revisão bibliográfica sobre as (E)-2-estiril-4H-cromen-4-onas e a sua semelhança estrutural com as flavonas, a sua importância e ocorrência natural e métodos de síntese. São ainda abordadas as metodologias mais utilizadas para a síntese de derivados halogenados de (E)-2-estiril-4H-cromen-4-onas. Seguidamente são apresentados e discutidos os resultados da síntese de (E)-3-bromo-2-estiril-4H-cromen-4-onas através da reação de 5-aril-3-hidroxi-1-(2-hidroxifenil)penta-2,4-dien-1-onas com NBS, sob irradiação com micro-ondas, tendo sido estabelecida uma nova metodologia mais eficiente, rápida e regiosseletiva para a síntese de (E)-3-bromo-2-estiril-4H-cromen-4-onas, na ausência de solvente. São igualmente apresentados os resultados da síntese regiosseletiva de (E)-2-estiril-3-iodo-4H-cromen-4-onas através da reação de 5-aril-3-hidroxi-1-(2-hidroxifenil)penta-2,4-dien-1-onas com NIS e TFA/TFAA/NaOAc. Em ambos os métodos de halogenação desenvolvidos, obtiveram-se como produtos secundários as (E)-2-estiril-4H-cromen-4-onas correspondentes. Seguidamente é apresentado o estudo da reação de (E)-2-estiril-3-halo-4H-cromen-4-onas com hidrato de hidrazina. Ao contrário do esperado, obtiveram-se os 3(5)-aril-5(3)-[2-(2-hidroxifenil)-2-oxoetil-1H-pirazóis através de uma reação de adição conjugada 1,6-, de hidrazina à posição C- da cromona com consequente abertura do anel, seguida de uma adição conjugada 1,4- intramolecular. Estes resultados demonstraram que esta reação segue um mecanismo diferente daquele que está reportado na literatura para a reação de (E)-2-estiril-4H-cromen-4-onas não halogenadas em C-3 com hidrato de hidrazina. No terceiro capítulo apresenta-se uma breve revisão bibliográfica sobre as propriedades, aplicações e metodologias de síntese de 1,2,3-triazóis, dando mais relevância às reações de cicloadição 1,3-dipolar e de “click-chemistry”. Seguidamente descrevem-se os resultados obtidos na reação de (E)-5(3)-estiril-3(5)-(2-hidroxifenil)-1H-pirazóis com a azida de sódio para obtenção de díades pirazol-1,2,3-triazol. No entanto esta reação deu origem a novos 5(3)-(2-aril-2-azidoetil)-3(5)-(2-hidroxifenil)-1H-pirazóis e não às díades pirazol-1,2,3-triazol pretendidas. Como o resultado não foi o esperado, desenvolveu-se outra metodologia de síntese, que envolve, num primeiro, a reação de (E)-2-estiril-4H-cromen-4-onas com azida de sódio, dando origem a 5(4)-aril-4(5)-(cromon-2-il)-1H-1,2,3-triazóis. No passo seguinte, efetuou-se a reação destes compostos com hidrato de hidrazina tendo ocorrido a formação das diades 5(4)-aril-4(5)-[3(5)-(2-hidroxifenil)-1H-pirazol-5(3)-il]-1H-1,2,3-triazol pretendidas. No quarto capítulo, estudou-se a reatividade de (E)-5(3)-estiril-3(5)-(2-hidroxifenil)-1H-pirazóis em reações de iodação com vista à obtenção de 4-iodo-1H-pirazóis. Apresenta-se uma breve revisão bibliográfica sobre os diferentes métodos descritos na literatura para a iodação de compostos heterocíclicos aromáticos, nomeadamente para a obtenção de 4-iodo-1H-pirazóis. Dos vários sistemas de iodação testados, o sistema oxidativo I2/CAN foi o que deu melhores resultados na iodação dos (E)-5(3)-estiril-3(5)-(2-hidroxifenil)-1H-pirazóis. Este método permitiu iodar a posição C-4 do núcleo de pirazol apenas para os derivados que possuem o grupo nitro ou o átomo de cloro no anel do grupo estirilo, obtendo-se o 3(5)-(2-hidroxifenil)-4-iodo-5(3)-(4-nitrofenil)vinil-1H-pirazol e o 5(3)-(4-clorofenil)vinil)-3(5)-(2-hidroxi-5-iodofenil)-4-iodo-1H-pirazol; no entanto, para os restantes derivados, verificou-se apenas a iodação nas posições ativadas do anel fenólico. Todos os novos compostos sintetizados foram caraterizados estruturalmente recorrendo a estudos de espetroscopia de ressonância magnética nuclear (RMN) mono e bidimensionais. Sempre que possível, para uma caraterização estrutural mais completa, foram efetuados espetros de massa (EM) e análises elementares ou espetros de massa de alta resolução (EMAR) para todos os novos compostos sintetizados. Finalmente são apresentadas as conclusões gerais deste trabalho e perspetivas futuras.

Orientation of Non-Native 2-Monosubstituted and 2,3-Disubstituted 1,4-Naphthoquinones in the A1 binding site of PSI and the effect on the rate of electron transfer : an electron paramagnetic resonance spectroscopy study

The proce-ss ofoxygenic photosynthesis is vital to life on Earth. the central event in photosynthesis is light induced electron transfer that converts light into energy for growth. Ofparticular significance is the membrane bound multisubunit protein known as Photosystem I (PSI). PSI is a reaction centre that is responsible for the transfer of electrons across the membrane to reduce NADP+ to NADPH. The recent publication ofa high resolution X-ray structure of PSI has shown new information about the structure, in particular the electron transfer cofactors, which allows us to study it in more detail. In PSI, the secondary acceptor is crucial for forward electron transfer. In this thesis, the effect of removing the native acceptor phylloquinone and replacing it with a series of structurally related quinones was investigated via transient electron paramagnetic resonance (EPR) experiments. The orientation of non native quinones in the binding site and their ability to function in the electron transfer process was determined. It was found that PSI will readily accept alkyl naphthoquinones and anthraquinone. Q band EPR experiments revealed that the non-native quinones are incorporated into the binding site with the same orientation of the headgroup as in the native system. X band EPR spectra and deuteration experiments indicate that monosubstituted naphthoquinones are bound to the Al site with their side group in the position occupied by the methyl group in native PSI (meta to the hydrogen bonded carbonyl oxygen). X band EPR experiments show that 2, 3- disubstituted methyl naphthoquinones are also incorporated into the Al site in the same orientation as phylloquinone, even with the presence of a halogen- or sulfur-containing side chain in the position normally occupied by the phytyl tail ofphylloquinone. The exception to this is 2-bromo-3-methyl --.- _. -. - -- - - 4 _._ _ _ - _ _ naphthoquinone which has a poorly resolved spectrum, making determination of the orientation difficuh. All of the non-native quinones studied act as efficient electron acceptors. However, forward electron transfer past the quinone could only be demonstrated for anthraquinone, which has a more negative midpoint potential than phylloquinone. In the case of anthraquinone, an increased rate of forward electron transfer compared to native PSI was found. From these results we can conclude that the rate ofelectron transfer from Al to Fx in native PSI lies in the normal region ofthe Marcus Curve.

Stille reactions of 2,3-bis(stannyl)butenoates: an unexpected regioselectivity

The palladium-catalyzed cross-coupling reaction of methyl (Z)-2,3-bis(tributylstannyl)butenoate with aryl iodides is regioselective, leading to 2-aryl-3-stannylated products; this selectivity is the opposite to that observed in the reaction between halides and 3,4-bis(stannyl)furan-2(5H)-one. Since the resulting butenoates can be converted into the corresponding furanones, the method provides useful flexibility in the preparation of functionalized butenoates and furanones.

Synthesis and crystal structure characterization of iron(II), cobalt(II) and nickel(II) complexes with 1,3-bis(2-pyridylmethylthio)propane

Three new mononuclear complexes of nitrogen-sulfur donor sets, formulated as (Fe-II(L)Cl-2] (1), [Co-II(L)Cl-2] (2) and [Ni-II(L)Cl-2] (3) where L = 1,3-bis(2-pyridylmethylthio)propane, were synthesized and isolated in their pure form. All the complexes were characterized by physicochemical and spectroscopic methods. The solid state structures of complexes I and 3 have been established by single crystal X-ray crystallography. The structural analysis evidences isomorphous crystals with the metal ion in a distorted octahedral geometry that comprises NSSN ligand donors with trans located pyridine rings and chlorides in cis positions. In dimethylformamide solution, the complexes were found to exhibit Fe-II/Fe-III, co(II)/co(III) and Ni-II/Ni-III quasi-reversible redox couples in cyclic voltammograms with E-1/2 values (versus Ag/AgCl at 298 K) of +0.295, +0.795 and +0.745 V for 1, 2 and 3, respectively. (C) 2009 Elsevier Ltd. All rights reserved.

Coordination modes of 3-aminosalicylic and 3-hydroxyanthranilic acids in palladium(II), platinum(II) and rhenium(V) complexes. The crystal structure of cis-[Pt(HsalNH)(PPh3)(2)] (.) 0.25C(2)H(5)OH

New Pd(II), Pt(II) and Re(V) complexes of 3-aminosalicylic acid (H(2)salNH(2)) and 3-hydroxyantranilic acid (HantOH) have been prepared, cis-[Pt (HsalNH)(PPh3)(2)] center dot 0.25C(2)H(5)OH (1), trans-[PdCl(salNH(2))(PPh3)(2)](2), trans-[ReOI2(HsalNH(2))(PPh3)] center dot (CH3)(2)CO (3), cis-[Pt(HantO)(PPh3)(2)] (4), trans-[PdCl(antOH)(PPh3)(2)] center dot 4H(2)O (5), [PdCl(antOH)(bipy)] center dot C2H5OH (6), [PdCl2(HantOH)(2)] (7) and trans-[ReOI(HantO)(PPh3)(2)] center dot (CH3)(2)CO (8). The crystal structure of complex I was determined showing chelation of HsalNH(2-) through the adjacent nitrogen and oxygen atoms of the amino and phenolate groups. Infrared and H-1 NMR spectroscopic data for the complexes are presented. (c) 2005 Elsevier Ltd. All rights reserved.

Different supramolecular hydrogen bond structures and significant changes in magnetic properties in dinuclear mu(2)-1,1-N-3 copper(II) complexes with very similar tridentate Schiff base blocking ligands

Three new basal-apical, mu(2)-1,1-azide bridged complexes, [CuL1(N-3)](2) (1), [CuL2(N-3)](2) (2) and [CuL3(N-3)]2 (3) with very similar tridentate Schiff base blocking ligands [L-1=N-(3-aminopropyl) salicylaldimine, L-2=7-amino-4-methyl-5-azahept-3-en-2-one and L-3=8-amino-4-methyl-5-azaoct-3-en-2-one) have been synthesised and their molecular structures determined by X-ray crystallography. In complex 1, there is no inter-dimer H-bonding. However, complexes 2 and 3 form two different supramolecular structures in which the dinuclear entities are linked by strong H-bonds giving one-dimensional systems. Variable-temperature (300-2 K) magnetic susceptibility measurements and magnetization measurements at 2 K reveal that complexes 1 and 2 have antiferromagnetic coupling while 3 has ferromagnetic coupling which is also confirmed by EPR spectra at 4-300 K. Magnetostructural correlations have been made taking into consideration both the azido bridging ligands and the existence of intermolecular hydrogen bonds in complexes 2 and 3.

Marked influence of the bridging carbonyl ligands on the photo- and electrochemistry of the clusters [Ru-3(CO)(8)(mu-CO)(2)-(alpha-diimine)] (alpha-diimine = 2,2 '-bipyridine, 4,4 '-dimethyl-2,2 '-bipyridine and 2,2 '-bipyrimidine)

Bonding, photochemical and electrochemical properties of the clusters [Ru-3(CO)(8)(mu-CO)(2)(alpha-diimine)] (alpha-diimine=2,2'-bipyridine (1), 4,4'-dimethyl-2,2'-bipyridine (2) and 2,2'-bipyrimidine (3)) are strongly influenced by the presence of bridging carbonyl ligands. Irradiation at 471 nm initially results in the population of a sigma(Ru-3)pi*(alpha-diimine) excited state. From this state, fast decay takes place to the optically hardly directly accessible pi(Ru/mu-CO) pi*(alpha-diimine) lowest excited state. These assignments agree with theoretical (TD-DFT) results, resonance Raman and picosecond time-resolved infrared spectra. The involvement of the bridging carbonyl ligands in the electron transfer increases the energetic barrier for the formation of open-structure photoproducts such as biradicals and zwitterions. Zwitterions were therefore only obtained in strongly coordinating media such as pyridine at 250 K. The bridging carbonyl ligands also stabilize the radical anions produced upon one-electron reduction of the clusters [Ru-3(CO)(8)(mu-CO)(2)(alpha-diimine)] and observed with cyclic voltammetry, EPR and IR spectroelectrochemistry (for alpha-diimine=2,2'-bipyrimidine). In contrast, open-triangle intermediates formed along the reduction path to [Ru(CO)(2)(alpha-diimine)](n) and [Ru-2(CO)(8)](2-) are more reactive than their triosmium analogues.

Synthesis of the first-membered ring compound containing three tin atoms and one oxygen. The crystal structure of the species [O{Sn(C6H3Et2-2,6)2}3]

Aerial oxidation of the novel homocyclic tetratin species [{SnAr2}3SnArBr] (1) [1] (Ar  C6H3Et2-2,6) affords the tritin heterocycle [O{Sn(C6H3Et2-2,6)2}3] (2), which has been crystallographically characterised; 2 is the first reported oxatristannacyclobutane, and the first heterocyclic tin species having both tintin and tinheteroatom bonds.

Reaction of 2-methyl-1,4-naphthoquinone and its 3-substituted derivatives with active methylene group anions and with diazo compounds

The reaction of 2-chloro-3-methyl-1,4-naphthoquinone (3) with the anion of ethyl cyanoacetate led to a mixture of two epimeric fused-ring cyclopropane compounds, characterised as exo- and endo-1-cyano-1 -ethoxycarbonyl-1a-methyl-1a,7a-dihydro-1H-cyclopropa[b]naphthalene-2,7-dione (8) and (9). Various hydrolysis products of these were prepared and an X-ray crystallographic analysis was carried out on one of them, 1-carbamoyl-1 -carboxy-1a-methyl-1a,7a-dihydro-1H-cyclopropa[b]-naphthalene-2,7-dione (17). The reaction of 2-methyl-1,4-naphthoquinone (1) with ethyl diazoacetate gave a fused pyrazoline derivative, 3-ethoxycarbonyl-4-hydroxy-9a-methyl-1,9a-dihydro-benz[f]indazol-9-one (22), while reaction of 2-methyl-3-nitro-1,4-naphthoquinone (5) with diazomethane led to a fused Δ2-isoxazoline N-oxide, 3a-methyl-3,3a-dihydroisoxazolo[3,4-b]naphthalene-4,9-dione 1-oxide (26).

Reaction of 4-phenylbut-3-en-2-one with cyanoacetamide in 2:1 ratio

The reaction of 4-phenylbut-3-en-2-one with cyanoacetamide is not confined to a 1 : 1 reaction [which results in formation of 3-cyano-6-methyl-4-phenylpyridin-2(1H)-one]. The reaction of 2 mole equivalents of 4-phenylbut-3-en-2-one with one of cyanoacetamide also takes place, the products being 1-cyano-6-hydroxy-6-methyl-4-methylene-8,9-diphenyl-3-azabicyclo[3.3.1]nonan-2-one and 3-cyano-6-methyl-3-(3-oxo-1-phenylbutyl)-4-phenyl-3,4-dihydropyridin-2(1H)-one. The latter compound cyclises in acid medium to form 6-acetyl-4-cyano-1-methyl-5,8-diphenyl-2-azabicyclo[2.2.2]octan-3-one. X-Ray crystal structures of the 3-azabicyclo[3.3.1]nonan-2-one and the 3-azabicyclo[2.2.2]octan-2-one derivatives are described.

Structural variations in self-assembled coordination complexes of Zn(II) with hexamethylenetetramine and isomeric 2-, 3- and 4-nitrobenzoates

Three new zinc(II)-hexamethylenetetramine (hmt) complexes [Zn-2(4-nbz)(4)(mu(2)-hmt)(OH2)(hmt)] (1). [Zn-2(2-nbz)(4)(mu(2)-hmt)(2)](n) (2) and [Zn-3(3-nbz)(4)(mu(2)-hmt)(mu(2)-OH)(mu(3)-OH)](n) (3) with three isomeric nitrobenzoate, [4-nbz = 4-nitrobenzoate, 2-nbz = 2-nitrobenzoate and 3-nbz = 3-nitrobenzoate] have been synthesized and structurally characterized by X-ray crystallography. Their identities have also been established by elemental analysis: IR, NMR, UV-Vis and mass spectral studies. 1 is a dinuclear complex formed by bridging hmt with mu(2) coordinating mode. The geometry around the Zn centers in 1 is distorted tetrahedral. Paddle-wheel centrosymmetric Zn-2(2-nbz)(4) units of complex 2 are interconnected by mu(2)-hmt forming a one-dimensional chain with square-pyramidal geometries around the Zn centers. Compound 3 contains a mu(2)/mu(3)-hydroxido and mu(2)-hmt bridged 1D chain. In this complex, varied geometries around the Zn centers are observed viz, tetrahedral, square pyramidal and trigonal bipyramidal. Various weak forces, i.e. lone pair-pi, pi-pi and CH-pi interactions, play a key role in stabilizing the observed structures for complexes 1,2 and 3. This series of complexes demonstrates that although the nitro group does not coordinate to the metal center, its presence at the 2-, 3- or 4-position of the phenyl ring has a striking effect on the dimensionality as well as the structure of the resulted coordination polymers, probably due to the participation of the nitro group in 1.p.center dot center dot center dot pi and/or C-H center dot center dot center dot pi interactions.