931 resultados para radical ligands
Resumo:
The radicals formed on gamma-radiolysis of a series of copolymers of methacrylic acid and acrylonitrile have been investigated by ESR spectroscopy. This series of copolymers spanned the full composition range and the study was carried out at 77 K and ambient temperature. The radicals formed in the copolymers at 77 and 303 K were found to be similar to those found in the two homopolymers, but in the intermediate composition range the presence of acrylonitrile propagation radicals was also detected. These radicals were not observed to be formed in significant quantities on the radiolysis of polyacrylonitrile. They are believed to result from a scission of the main chain at methacrylic acid/acrylonitrile diad sequences following loss of the methacrylic acid carboxyl group. At 77 K, the copolymers with high methacrylic acid contents were found to be more sensitive to radical formation than the methacrylic acid homopolymer, but this enhanced sensitivity was not evident at ambient temperature, where the G-values for radical formation for the copolymers were slightly less than the values for the homopolymers. (C) 2003 Society of Chemical Industry.
Resumo:
The kinetics of chain reactions of octanedithiol with styrene, thermally initiated with TX29B50 (a 50:50 wt% solution of TX29 diperoxy initiator in a phthalate plasticizer), have been studied over a range of initiator concentrations, a range of mixture formulations and a range of temperatures. This system has been investigated as a model system for the reactions of polyfunctional thiols with divinyl benzene. The reactions have been shown to follow first-order kinetics for both the thiol and the ene species and to be characterized by a dependence on the initiator concentration to the power of one half. The kinetic rate parameters have been shown to adhere to Arrhenius behaviour. A kinetic model for the chain reactions for this system has been proposed. (C) 2003 Society of Chemical Industry.
Resumo:
Di-2-pyridyl ketone isonicotinoyl hydrazone (HPKIH) and a range of its analogues comprise a series of monobasic acids that are capable of binding iron (Fe) as tridentate (N,N,O) ligands. Recently, we have shown that these chelators are highly cytotoxic, but show selective activity against cancer cells. Particularly interesting was the fact that cytotoxicity of the HPKIH analogues is maintained even after complexation with Fe. To understand the potent anti-tumor activity of these compounds, we have fully characterized their chemical properties. This included examination of the solution chemistry and X-ray crystal structures of both the ligands and Fe complexes from this class and the ability of these complexes to mediate redox reactions. Potentiometric titrations demonstrated that all chelators are present predominantly in their charge-neutral form at physiological pH (7.4), allowing access across biological membranes. Keto-enol tautomerism of the ligands was identified, with the tautomers exhibiting distinctly different protonation constants. Interestingly, the chelators form low-spin (diamagnetic) divalent Fe complexes in solution. The chelators form distorted octahedral complexes with Fe-II, with two tridentate ligands arranged in a meridional fashion. Electrochemistry of the Fe complexes in both aqueous and non-aqueous solutions revealed that the complexes are oxidized to their ferric form at relatively high potentials, but this oxidation is coupled to a rapid reaction with water to form a hydrated (carbinolamine) derivative, leading to irreversible electrochemistry. The Fe complexes of the HPKIH analogues caused marked DNA degradation in the presence of hydrogen peroxide. This observation confirms that Fe complexes from the HPKIH series mediate Fenton chemistry and do not repel DNA. Collectively, studies on the solution chemistry and structure of these HPKIH analogues indicate that they can bind cellular Fe and enhance its redox activity, resulting in oxidative damage to vital biomolecules.
Resumo:
O paradigma terapêutico para o CEC do andar inferior da boca sofreu modificações em decorrência da sobrevida. OBJETIVO: Estudo comparativo do esvaziamento cervical radical e seletivo. MATERIAL E MÉTODO: Análise de 460 pacientes atendidos no Depto. de CCP e ORL do Hospital Heliópolis, de 1978 a 2002. Para esvaziamento radical foram avaliados os padrões de metastatização dos níveis IV e V, para o seletivo a ocorrência e localização das recidivas. O método estatístico utilizado foi o teste do qui-quadrado. RESULTADOS: Nos esvaziamentos radicais a taxa de metastatização nos níveis IV e V foram 5,8% e 4,6%, nos pacientes cNO e de 9,9% (nível IV) e 5,9% (nível V) para cN+, enquanto o nível I isolado estava comprometido em 11,0% nos cN0 e 5,5% nos cN+. Nos esvaziamentos seletivos ocorreram 4 recidivas (4,1%) em 97 esvaziamentos nos pN0 e 2 (10,0%) em 20 esvaziamentos. Nos casos pN+, não houve vantagens na indicação de radioterapia sobre os não irradiados (5,6% e 5,7% respectivamente). CONCLUSÃO: É possível realizar esvaziamento seletivo no tratamento das metástases do andar inferior de boca.
Resumo:
O tratamento do carcinoma da laringe tem como desafio a cura do paciente e a preservação do órgão. OBJETIVO: A avaliação dos subsítios na disseminação do carcinoma e a sua influência no tratamento cirúrgico da laringe, no controle local e na sobrevida. MATERIAL E MÉTODO: Cento e sessenta pacientes tratados na Escola Paulista de Medicina - Hospital São Paulo, no período de janeiro de 1998 a dezembro de 2004, foram compilados para análise da disseminação do carcinoma dos subsítios da laringe. Foram incluídos pacientes com seguimento mínimo de 2 anos, após diagnóstico e tratamento. A avaliação estatística foi: Teste X2, Teste de Fisher e a Curva de Kaplan-Meier. Forma de Estudo: Estudo de Coorte Histórica Longitudinal (Trabalho Clínico Retrospectivo). RESULTADOS: A comissura posterior e a infraglote, respectivamente, foram significantes para a laringectomia total: tumores glóticos AC: (p=0,03) AP: (p=0,0001); AC: (p=0,0007) AP: (p<0,0001). A infraglote foi significante nos tumores G+SG na AP: (p=0,04), e na taxa de óbitos AP: (p=0,03). CONCLUSÃO: A laringectomia total é o tratamento de eleição na presença de alto comprometimento da comissura posterior e da infraglote. Esta última pode comprometer a sobrevida, conforme a invasão local, mesmo na presença de margens cirúrgicas livres.
Resumo:
A cada dia surgem mais provas da importância da inovação radical ou revolucionária na determinação do sucesso das empresas, em longo prazo, no mercado competitivo atual. Embora esse reconhecimento tenha estado presente em muitas empresas sólidas, existem dúvidas no que diz respeito à maneira segundo a qual a inovação deve ser implementada. O presente artigo baseia-se em um estudo longitudinal de 12 projetos de inovação radical em 10 empresas maduras de grande porte, no período de seis anos. O ciclo de vida dos projetos de inovação radical é diferente daquele de projetos incrementais, devido ao grande número de incertezas e descontinuidades. Tais características exigem que os projetos de inovação radical sejam gerenciados de forma diversa daquela aplicada aos projetos incrementais. Demonstramos sete fatores estratégicos decisivos para realizar-se a implementação bem-sucedida da inovação radical.
Resumo:
Este artigo oferece uma análise da aprendizagem nas organizações em condições de mudança radical, em que a reestruturação da organização foi motivada por uma mudança na ideologia e na propriedade. Discute-se que, nessas circunstâncias, a aprendizagem não representa necessariamente uma melhoria para o coletivo como um todo. A fonte empírica para este artigo é um estudo de caso da Telemig, uma das principais companhias brasileiras de telecomunicações. A pesquisa empregou múltiplos métodos e fontes permitindo uma investigação do conteúdo e do processo de aprendizagem, e de seus agentes ao longo do tempo. O estudo elabora e ilustra o conceito de "aprendizagem contestada", concluindo que este necessita ser incorporado à teoria da aprendizagem nas organizações.
Resumo:
Four cationic ruthenium(II) complexes with the formula [Ru(eta(5)-C5H5)(PPh3)(2)](+), with L = 5-phenyl-1H-tetrazole (TzH) 1, imidazole (ImH) 2, benzo[1,2-b; 4,3-b'] dithio-phen-2-carbonitrile (Bzt) 3, and [5-(2-thiophen-2-yl)-vinyl]-thiophene-2-carbonitrile] (Tvt) 4 were prepared and characterized in view to evaluate their potentialities as antitumor agents. Studies by Circular Dichroism indicated changes in the secondary structure of ct-DNA. Changes in the tertiary structure of pBR322 plasmid DNA were also observed in gel electrophoresis experiment and the images obtained by atomic force microscopy (AFM) suggest strong interaction with pBR322 plasmid DNA; the observed decreasing of the viscosity with time indicates that the complexes do not intercalate between DNA base pairs. Compounds 1, 2, and 3 showed much higher cytotoxicity than the cisplatin against human leukaemia cancer cells (HL-60 cells).
Resumo:
The new potentially N-4-multidentate pyridyl-functionalized scorpionates 4-((tris-2,2,2-(pyrazol-1-ypethoxy)methyl)pyridine (TpmPy, (1)) and 4-((tris-2,2,2-(3-phenylpyrazol-1-yl)ethoxy)methyl)pyridine (TpmPy(Ph), (2)) have been synthesized and their coordination behavior toward Fe-II, Ni-II, Zn-II, Cu-II, Pd-II, and V-III centers has been studied. Reaction of (1) with Fe(BF4)(2)center dot 6H(2)O yields [Fe(TpmPy)(2)](BF4)(2) (3), that, in the solid state, shows the sandwich structure with trihapto ligand coordination via the pyrazolyl arms, and is completely low spin (LS) until 400 K. Reactions of 2 equiv of (1) or (2) with Zn-II or Ni-II chlorides give the corresponding metal complexes with general formula [MCl2(TpmPy*)(2)] (M = Zn, Ni; TpmPy* = TpmPy, TpmPy(Ph)) (4-7) where the ligand is able to coordinate through either the pyrazolyl rings (in case of [Ni(TpmPy)(2)Cl-2 (5)) or the pyridyl-side (for [ZnCl2(TpmPy)(2)] (4), [ZnCl2(TpmPy(Ph))(2)] (6) and [NiCl2(TpmPy(Ph))(2)] (7)). The reaction of (1) with VCl3 gives [VOCl2(TpmPy)] (8) that shows the N-3-pyrazolyl coordination-mode. Moreover, (1) and react with cis-[PdCl2(CH3CN)(2)] to give the disubstituted complexes [PdCl2(TprnPy)(2)] (9) and [PdCl2(TpmPy(Ph))(2)] (10), respectively, bearing the scorpionate coordinated via the pyridyl group. Compounds (9) and (10) react with Fe(BF4)(2) to give the heterobimetallic Pd/Fe systems [PdCl2(mu-TpmPy)(2)-Fe](BF4)(2) (11) and [PdCl2(mu-TpmPy(Ph))(2)Fe-2(H2O)(6)]BF4)(4) (13), respectively. Compound (11) can also be formed from reaction of (3) with cis-[PdCl2(CH3CN)(2)], while reaction of (3) with Cu(NO3)(2).2.5H(2)O generates [Fe(mu-TpmPy)(2)-Cu(NO3)(2)](BF4)(2) (12), confirming the multidentate ability of the new chelating ligands. The X-ray diffraction analyses of compounds (1), (3), (4), (5), and (9) are also reported.
Resumo:
The reactions of [ReCl2{eta(2)-N2C(O)Ph}(PPh3)(2)](1) with 2-aminopyrimidine (H(2)Npyrm), 2,2'-bipyridine (bpy) and tetraethylthiuram disulfide (tds), in MeOH upon reflux, lead to the new eta(1)-(benzoyldiazenido)-rhenium(III) complexes [ReCl{eta(1)-N2C(O)Ph}(HNpyrm)(PPh3)(2)](2)and [ReCl2{eta(1)-N2C(O)Ph}(bpy)(PPh3)] (3), and the known oxo(diethyldithiocarbamato)dirhenium(v)complex [Re2O2(mu O){Et2NC(S)S}(4)](4), respectively. The Et2NC(S)S ligands in 4 result from S-S bond rupture of tds molecules. The obtained compounds have been characterized by IR, H-1, P-31{H-1} and C-13{H-1} NMR spectroscopies, FAB(+)-MS, elemental and single-crystal X-ray diffraction (for 2 and 4)analyses. Complex 2 represents the first structurally characterized Re compound derived from 2-aminopyrimidine. Besides, the redox behaviour of 2-4 in CH2Cl2 solution has been studied by cyclic voltammetry, and the Lever electrochemical ligand parameter (E-L)has been estimated, for the first time, for HNpyrm. The electrochemical results are discussed in terms of electronic properties of the Re centres and the ligands.
Resumo:
Novel [Ru(eta(6)-p-cymene)(kappa(2)-L)X] and [Ru(eta(6)-p-cymene)(kappa(3)-L)]X center dot nH(2)O complexes (L = bis-, tris-, or tetrakis-pyrazolylborate; X = Cl, N-3, PF6, or CF3SO3) are prepared by treatment of [Ru(eta(6)-p-cymene)Cl-2](2) with poly-(pyrazolyl)borate derivatives [M(L)] (L in general; in detail L = Ph(2)Bp = diphenylbis-(pyrazol-1-yl)borate; L = Tp = hydrotris(pyrazol-1-yl)borate; L = pzTp = tetrakis(pyrazol-1-yl)borate; L = Tp(4Bo) = hydrotris(indazol-1-yl)borate, L = T-p4Bo,T-5Me = (5-methylindazol-1-yl)borate; L = Tp(Bn,4Ph) = hydrotris(3-benzyl-4-phenylpyrazol-1-yl)borate; M = Na, K, or TI) and characterized by analytical and spectral data (IR, ESIMS, H-1 and C-13 NMR). The structures of [Ru(eta(6)-p-cymene)(Ph(2)Bp)Cl] (1) and [Ru(eta(6)-p-cymene)(Tp)Cl] (3) have been established by single-crystal X-ray diffraction analysis. Electrochemical studies allowed comparing the electron-donor characters of Tp and related ligands and estimating the corresponding values of the Lever E-L ligand parameter. The complexes [Ru(eta(6)-p-cymene)-(kappa(2)-L)X] and [Ru(eta(6)-p-cymene)(kappa(3)-L)]X center dot nH(2)O act as catalyst precursors for the diastereoselective nitroaldol reaction of benzaldehyde and nitroethane to the corresponding beta-nitroalkanol (up to 82% yield, at room temperature) with diastereoselectivity toward the formation of the threo isomer.