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Master's Dissertation
DOI
10.11606/D.75.2009.tde-26082009-105920
Document
Author
Full name
Gustavo Metzker
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 2009
Supervisor
Committee
Franco, Douglas Wagner (President)
Toledo Junior, José Carlos
Iamamoto, Yassuko
Title in Portuguese
Nitrosilo complexos de rutênio(II) como captores de radicais de interesse biológico
Keywords in Portuguese
nitrosilo de rutênio
óxido nítrico
radicadis superóxido e hidroxila
Abstract in Portuguese
Os complexos trans-[Ru(NO)(NH3)4(L)](X)3 (1), [Ru(NO)(Hedta)] (2) e seus precursores sintéticos trans-[Ru(H2O)(NH3)4(L)](X)2 (3), trans-[Ru(SO4)(NH3)4(L)](X) (4) , onde L = isn, nic, imN, 4-pic, py, P(OEt) e X = PF6 - e BF4 -, foram testados como captadores dos radicais livres DPPHo, OHo e O2 -o em meio aquoso. O potencial de oxidação do centro metálico nos complexos (1) foram estimados utilizando eletrodo de diamante dopado com boro como eletrodo de trabalho, estando situados em meio aquoso acima de 2,0 V vs. ECS (CH+ = 1,0 x 10-3, µ = 0,1 mol L-1). Os complexos (1) e (2) mostraram-se incapazes de reagir com o radical DPPHo, exceto o complexo trans-[Ru(NO)(NH3)4(P(OEt)3)]3+, que reagiu apenas em grande excesso (50 vezes) em relação ao radical DPPHo. Os complexos (3) reagiram quando em excesso ou em proporção estequiométrica. O mecanismo pelo qual esta reação ocorre é predominantemente o de transferência de elétrons. O radical OHo foi captado pelos complexos (1), sendo provavelmente o mecanismo predominante o de transferência de elétrons pela oxidação do centro metálico [Ru(NO)]3+ a [Ru(NO)]4+, compatível com o potencial de oxidação do radical OHo (acima de 2,8 V vs. ECS) reportado na literatura para este radical. As constantes de velocidade específica para estas reações foram estimadas como estando no intervalo de 108 a 1010 M-1 s-1. Não foi observada reação entre o radical OHo e os complexos (4). Os complexos (1) e (2) captam o radical O2 -o pela redução do ligante NO+ com constantes de velocidade específicas no intervalo de 2,0 ± 1,0 x 104 a 4,2 ± 1,0 x 105 M-1 s-1, em medidas efetuadas via cinética de competição com citocromo c. Após a redução, a liberação de NO foi acompanhada via eletrodo seletivo a NO e espectrofotometricamente pela reação do NO com o citocromo c. Nas condições experimentais utilizadas, não se observou a formação do íon peroxinitrito (ONOO-). Os complexos (3) e (4) não reagiram com o radical O2 -o.
Title in English
Ruthenium(II) nitrosyls as radical scavenger
Keywords in English
nitric oxide
radicals superoxide and hydroxyl
ruthenium nitrosyls
Abstract in English
The complexes trans-[Ru(NO)(NH3)4(L)](X)3 (1), [Ru(NO)(Hedta)] (2) and their synthetic precursors trans-[Ru(H2O)(NH3)4(L)](X)2 (3), trans-[Ru(SO4)(NH3)4(L)](X) (4) , where L = isn, nic, imN, 4-pic, py, P(OEt) e X = PF6 - and BF4 -, were tested as scavengers for the radicals DPPHo, OHo e O2 -o in aqueous media. The redox potential for the metal center in the complexes (1) were obtained a using boron doped diamond electrode as working electrode. The redox potentials values for ruthenium nitrosyl complexes were higher than 2,0 V vs. SCE. The complexes (1) and (2) were unable to reduce the radical DPPHo, excepted the complex ion trans-[Ru(NO)(NH3)4(P(OEt)3)]3+. The complexes (3) react with DPPHo in stoichometric proportion. Electron transfer from the oxidation of the ruthenium(II) center seems to be the reaction pathway. The OHo radical reacts with ruthenium nitrosyls, predominantly oxidizing the metal center, yielding the fragment [Ru(NO)]4+. This reaction is exothermic since the redox potential of the OHo is around 2.8 V vs. SCE. From competition kinetics the rate constant for this reaction were estimated in the range of 108 a 1010 M-1 s-1. Since the reaction between OHo radical and the complexes (4) was not observed, the hydrogen atom transfer mechanism for the scavenger of OHo by the nitrosyl complexes ca be ruled out. The complexes (1) and (2) scavenge the radical O2 -o by the reduction of the coordinated nitrosyl with specific rate constants ranging from 2,0 ± 1,0 x 104 to 4,2 ± 1,0 x 105 M-1 s-1 as probed by competitive kinetics using cytochrome c. After reduction, nitric oxide dissociation were probed ampherometricaly using a selective NO electrode or spectrophotometrically using cytochrome c as probe. Reduction of the complexes (3) by superoxide ion was not observed and may suggest the coordinated nitrosonium as the reaction site for reduction.
 
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Publishing Date
2009-12-18
 
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