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The synthesis of a new series of photoluminescent compounds, namely 5,8-diaryl quinoxaline derivatives (aryl = phenyl, 4-fluorophenyl, 4-methoxyphenyl, and 4-cyanophenyl), was achieved by a direct Suzuki cross-coupling reaction with the employment of a NCP-pincer palladacycle. The electrochemical and photophysical properties of these compounds were also investigated. Four new 4,8-diaryl-2,1,3-benzothiadiazoles were also synthesized in order to enable a comparison between the two types of nitrogen-containing π-extended heterocycles. The substitution of a hydrogen atom at the 4-position of the aryl that is groups attached to the quinoxaline or benzothiadiazole base by either elec-

Uma série de líquidos iônicos 1-alquil éter (e 1-alquil)-3-metilimidazólio 2-4 ([C x O y MIm] + [Ânion] ou [C x MIm] + [Ânion] , onde MIm = 3-metilimidazólio; C x O y = 1-alquil éter, C 7 O 3 = -(CH 2 ) 2 O(CH 2 ) 2 O(CH 2 ) 2 OCH 3 (A), C 3 O 1 = -(CH 2 ) 2 OCH 3 (B); C x = 1-alquil, C 10 = C 10 H 21 (C), C 4 = C 4 H 9 (D); e [Ânion] = H 3 CSO 3 (2), BF 4 (3) ou PF 6 (4)) foram preparados e caracterizados. A força da ligação de hidrogênio entre o cátion e o ânion dos líquidos iônicos 2-4 depende principalmente do ânion e diminui na ordem H 3 CSO 3 > BF 4 > PF 6 . Todos os líquidos iônicos metanosulfonatos 2 possuem uma forte desblindagem para o próton H 2 do ciclo imidazólio. Os líquidos iônicos funcionalizados com um grupo 1-alquil éter mostram densidades mais altas em comparação com seus equivalentes do grupo 1-alquil. Os sais 2a-b, 3a-d e 4a-b são líquidos iônicos à temperatura ambiente. E, todos os líquidos iônicos 1-alquil éter funcionalizados (exceto 4b) são completamente amorfos. As maiores faixas líquidas foram obtidas com os líquidos iônicos tetrafluoroborato devido as suas solidificações a temperaturas baixas e excelente estabilidade térmica. Estes dados fornecem informações importantes para o entendimento sobre possíveis aplicações e a preparação de líquidos iônicos com tarefas específicas.A set of 1-alkyl ether (and 1-alkyl)-3-methylimidazolium ionic liquids 2-4 ([C x O y MIm] + [Anion] or [C x MIm] + [Anion] , where MIm = 3-methylimidazolium; C x O y = 1-alkyl ether, C 7 O 3 = -(CH 2 ) 2 O(CH 2 ) 2 O(CH 2 ) 2 OCH 3 (A), C 3 O 1 = -(CH 2 ) 2 OCH 3 (B); C x = 1-alkyl, C 10 = C 10 H 21 (C), C 4 = C 4 H 9 (D); and [Anion] = H 3 CSO 3 (2), BF 4 (3) or PF 6 (4)) was prepared and characterized. The cation-anion hydrogen bonding strength showed to be mainly anion dependent and decreased in the order H 3 CSO 3 > BF 4 > PF 6 . All methanesulfonate ionic liquids 2 possessed a strongly deshielded H 2 imidazolium ring proton. 1-Alkyl ether functionalized ionic liquids showed higher densities in comparison to their 1-alkyl equivalents. The salts 2a-b, 3a-d and 4a-b are room-temperature ionic liquids. All 1-alkyl ether functionalized ionic liquids (except 4b) are completely amorphous. The widest liquid ranges were obtained with the tetrafluoroborate ionic liquids due to their late solidification and excellent thermal stability. These data provide important information for the understanding of their application scope and the preparation of task-specific ionic liquids.Keywords: imidazolium ionic liquids, ether-functionalized, hydrogen bonding, physicochemical properties, task-specific IntroductionRoom-temperature ionic liquids (RTILs), ionic salts that melt at and below ambient temperature, typically comprise of an organic cation and an organic or inorganic anion. The class of imidazolium RTILs is used in a wide variety of applications due to their attractive physical and chemical properties, 1-3 which include: air and moisture stability, low flammability, thermal stability, a neglectable vapor pressure, bei...

A janela eletroquímica do líquido iônico trifluoroacetato de 1-n-butil-3-metilimidazólio foi estudada sobre eletrodos de carbono vítreo e platina em condições estática e dinâmica. Observouse uma drástica diminuição da janela eletroquímica ao trocar o eletrodo de carbono vítreo (4.50 V) pelo de platina (2.50 V). A variação da velocidade de rotação do eletrodo e da velocidade de varredura não afetaram o perfil dos voltamogramas, porém alteraram as densidades de corrente dos picos referentes aos processos anódicos e catódicos. A adsorção do cátion imidazólio durante o processo de transferência de carga na região catódica foi evidenciada, principalmente para baixas velocidades de rotação do eletrodo.The 1-n-butyl-3-methylimidazolium trifluoroacetate ionic liquid electrochemical windows have been investigated at vitreous carbon and platinum disc electrodes under static and dynamic conditions. The electrochemical window abruptly decreases by changing vitreous carbon (4.50 V) by platinum electrode (2.50 V). Electrode rotation and potential sweep rate did not affect the current-potential profiles but alter the current values of both anodic and cathodic peaks. The adsorption of imidazolium cation involved in the charge transfer process during the cathodic sweep rate was evidenced, mainly at low electrode rotation.Keywords: platinum electrode, vitreous carbon electrode, ionic liquid, imidazolium cation IntroductionRoom temperature molten salts or ionic liquids have been historically considered as liquid electrolytes composed entirely of ions. However, new evidences in the last years pointed out that these compounds, specially those based upon N,N'-dialkyl substituted imidazolium cations, are better described as liquid compounds that display ioniccovalent structures.1 In the light of their promising physical and chemical properties, room temperature ionic liquid systems attract increasing attention for applications as solvents in organic synthesis, transition metal two-phase catalysis, liquid-liquid extraction and electrochemical devices.1-3 Some characteristics that make these liquids so versatile and promising as novel solvents are (i) the high thermal stability and wide range of liquid phase, 4 (ii) their ability to act as solvents for many organic and inorganic materials, since it has been shown that they have micro heterogeneities that induce to act either as highly or weakly polar liquids, 5 (iii) the considerable conductivity, which commends their use in the study of electrochemical processes without using supporting electrolytes, and (iv) the negligible vapor pressure in contrast with conventional organic solvents, permitting their study under conditions of high vacuum. From the ecological point of view, the easier recovery of these solvents and its negligible vapor pressure, which avoid vapor emissions, makes these solvents environmental friendly. 1We have recently showed that the ionic liquids obtained from the combination of 1-n-butyl-3-methylimidazolium cation with tetrafluoroborate and hexafluorophosphate are ...

This study's aim was to evaluate the degradation rate of hydrogen peroxide (H2O2) and to quantify its penetration in tooth structure, considering the residence time of bleaching products on the dental enamel. For this study, bovine teeth were randomly divided according to the bleaching product received: Opalescence Xtra Boost 38%, White Gold Office 35%, Whiteness HP Blue 35%, Whiteness HP Maxx 35%, and Lase Peroxide Sensy 35%. To analyze the degradation of H2O2, the titration of bleaching agents with potassium permanganate was used, while the penetration of H2O2 was measured via spectrophotometric analysis of the acetate buffer solution, collected from the artificial pulp chamber. The analyses were performed immediately as well as 15 minutes, 30 minutes, and 45 minutes after product application. The data of degradation rate of H2O2 were submitted to analysis of variance (ANOVA) and Tukey tests, while ANOVA and Fisher tests were used for the quantification of H2O2, at the 5% level. The results showed that all products significantly reduced the concentration of H2O2 activates at the end of 45 minutes. It was also verified that the penetration of H2O2 was enhanced by increasing the residence time of the product on the tooth surface. It was concluded that the bleaching gels retained substantial concentrations of H2O2 after 45 minutes of application, and penetration of H2O2 in the dental structure is time-dependent.

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