Organic phase enzyme electrodes based on organohydrogel

A dimethylformamide-polyhydroxyl cellulose organo-hydrogel has been prepared, and its applications for enzyme immobilization in construction of organic phase biosensors have been exploited. With horseradish peroxidase, tyrosinase, and bilirubin oxidase immobilized in the organohydrogel, enzyme electrodes can be operated in various situations, including aqueous buffer, oil/water mixtures, and anhydrous organic solvents, and even in dimethylformamide, to determine analytes of different solubilities, e.g., organic peroxides, phenolic compounds and bilirubin. Biosensing has no restrictions in terms of measuring media and solubilities of analytes.

Synthesis of Unstable Cyclic Peroxides for Chemiluminescence Studies

Cyclic four-membered ring peroxides are important high-energy intermediates in a variety of chemi and bioluminescence transformations. Specifically, alpha-peroxylactones (1,2-dioxetanones) have been considered as model systems for efficient firefly bioluminescence. However, the preparation of such highly unstable compounds is extremely difficult and, therefore, only few research groups have been able to study the properties of these substances. In this study, the synthesis, purification and characterization of three 1,2-dioxetanones are reported and a detailed procedure for the known synthesis of diphenoyl peroxide, another important model compound for the chemical generation of electronically excited states, is provided. For most of these peroxides, the complete spectroscopic characterization is reported here for the first time.

Synthesis of unstable cyclic peroxides for chemiluminescence studies

Cyclic four-membered ring peroxides are important high-energy intermediates in a variety of chemi and bioluminescence transformations. Specifically, α-peroxylactones (1,2-dioxetanones) have been considered as model systems for efficient firefly bioluminescence. However, the preparation of such highly unstable compounds is extremely difficult and, therefore, only few research groups have been able to study the properties of these substances. In this study, the synthesis, purification and characterization of three 1,2-dioxetanones are reported and a detailed procedure for the known synthesis of diphenoyl peroxide, another important model compound for the chemical generation of electronically excited states, is provided. For most of these peroxides, the complete spectroscopic characterization is reported here for the first time.

Development, characterization, and application of flowing atmospheric-pressure afterglow ionization for mass spectrometric analysis of ambient organic aerosols

Addressing current limitations of state-of-the-art instrumentation in aerosol research, the aim of this work was to explore and assess the applicability of a novel soft ionization technique, namely flowing atmospheric-pressure afterglow (FAPA), for the mass spectrometric analysis of airborne particulate organic matter. Among other soft ionization methods, the FAPA ionization technique was developed in the last decade during the advent of ambient desorption/ionization mass spectrometry (ADI–MS). Based on a helium glow discharge plasma at atmospheric-pressure, excited helium species and primary reagent ions are generated which exit the discharge region through a capillary electrode, forming the so-called afterglow region where desorption and ionization of the analytes occurs. Commonly, fragmentation of the analytes during ionization is reported to occur only to a minimum extent, predominantly resulting in the formation of quasimolecular ions, i.e. [M+H]+ and [M–H]– in the positive and the negative ion mode, respectively. Thus, identification and detection of signals and their corresponding compounds is facilitated in the acquired mass spectra. The focus of the first part of this study lies on the application, characterization and assessment of FAPA–MS in the offline mode, i.e. desorption and ionization of the analytes from surfaces. Experiments in both positive and negative ion mode revealed ionization patterns for a variety of compound classes comprising alkanes, alcohols, aldehydes, ketones, carboxylic acids, organic peroxides, and alkaloids. Besides the always emphasized detection of quasimolecular ions, a broad range of signals for adducts and losses was found. Additionally, the capabilities and limitations of the technique were studied in three proof-of-principle applications. In general, the method showed to be best suited for polar analytes with high volatilities and low molecular weights, ideally containing nitrogen- and/or oxygen functionalities. However, for compounds with low vapor pressures, containing long carbon chains and/or high molecular weights, desorption and ionization is in direct competition with oxidation of the analytes, leading to the formation of adducts and oxidation products which impede a clear signal assignment in the acquired mass spectra. Nonetheless, FAPA–MS showed to be capable of detecting and identifying common limonene oxidation products in secondary OA (SOA) particles on a filter sample and, thus, is considered a suitable method for offline analysis of OA particles. In the second as well as the subsequent parts, FAPA–MS was applied online, i.e. for real time analysis of OA particles suspended in air. Therefore, the acronym AeroFAPA–MS (i.e. Aerosol FAPA–MS) was chosen to refer to this method. After optimization and characterization, the method was used to measure a range of model compounds and to evaluate typical ionization patterns in the positive and the negative ion mode. In addition, results from laboratory studies as well as from a field campaign in Central Europe (F–BEACh 2014) are presented and discussed. During the F–BEACh campaign AeroFAPA–MS was used in combination with complementary MS techniques, giving a comprehensive characterization of the sampled OA particles. For example, several common SOA marker compounds were identified in real time by MSn experiments, indicating that photochemically aged SOA particles were present during the campaign period. Moreover, AeroFAPA–MS was capable of detecting highly oxidized sulfur-containing compounds in the particle phase, presenting the first real-time measurements of this compound class. Further comparisons with data from other aerosol and gas-phase measurements suggest that both particulate sulfate as well as highly oxidized peroxyradicals in the gas phase might play a role during formation of these species. Besides applying AeroFAPA–MS for the analysis of aerosol particles, desorption processes of particles in the afterglow region were investigated in order to gain a more detailed understanding of the method. While during the previous measurements aerosol particles were pre-evaporated prior to AeroFAPA–MS analysis, in this part no external heat source was applied. Particle size distribution measurements before and after the AeroFAPA source revealed that only an interfacial layer of OA particles is desorbed and, thus, chemically characterized. For particles with initial diameters of 112 nm, desorption radii of 2.5–36.6 nm were found at discharge currents of 15–55 mA from these measurements. In addition, the method was applied for the analysis of laboratory-generated core-shell particles in a proof-of-principle study. As expected, predominantly compounds residing in the shell of the particles were desorbed and ionized with increasing probing depths, suggesting that AeroFAPA–MS might represent a promising technique for depth profiling of OA particles in future studies.

Cystine-mediated oxidative defence in Lactobacillus reuteri BR11

Lactobacillus reuteri BR11 possesses an abundant cystine uptake (Cyu) ABC-transporter that was previously found to be involved in a novel mechanism of oxidative defence mediated by cystine. The current study aimed to elucidate this mechanism with a focus on the role of the co-transcribed cystathionine ã-lyase (Cgl). Growth studies of wild-type L. reuteri BR11 and mutants inactivated in cgl and the cystine-binding protein encoding gene cyuC showed that in contrast to the Cyu transporter, whose inactivation led to growth arrest in aerated cultures, Cgl is not crucial for oxidative defence. However, the role of Cgl in oxidative defence became apparent in the presence of severe oxidative damage and cysteine deprivation. Cysteine was found to be protective against oxidative stress, and the action of Cgl in both cysteine biosynthesis and degradation poses a seemingly futile pathway that deprives the intracellular cysteine pool. To further characterise the relationship between Cgl activity and cysteine and their roles in oxidative defence, enzymatic assays were performed on purified Cgl, and intracellular concentrations of cysteine, cystathionine and methionine were determined. Cgl was highly active towards cystine and cystathionine and less active towards cysteine in vitro, suggesting the main function of Cgl to be cysteine biosynthesis. Cysteine was found at high concentrations in the cell, but the levels were not significantly affected by inactivation of cgl or growth under aerobic conditions. It was concluded that both anabolic and catabolic activities of Cgl towards cysteine contribute to oxidative defence, the former by maintaining an intracellular reservoir of thiol analogous to glutathione, and the latter by producing H2S which is readily secreted, thus creating a reducing extracellular environment. The significance of the Cyu transporter to the physiology of L. reuteri BR11 prompted a phylogenetic study to determine its presence in bacteria. Orthologs of the Cyu transporter that are closest matches to the Cyu transporter are only limited to several species of Lactobacillus and Leuconostoc. Outside the Lactobacillales order, the closest matching orthologs belong to Proteobacteria, and there are more orthologs in Proteobacteria than non-Lactobacillales Firmicutes, suggesting that the Cyu transporter locus was present in the ancestor of the Proteobacteria and Firmicutes, and over evolutionary time has been lost or diverged in many Firmicutes. The clustering of the Cyu transporter locus with a gene encoding a Cgl family protein is even rarer. It was only found in L. reuteri, Lactobacillus vaginalis, Weissella paramesenteroides, the Lactobacillus casei group, and several Campylobacter sp. An accompanying phylogenetic study of L. reuteri BR11 using multi-locus sequence analysis showed that L. reuteri BR11 had diverged from more than 100 strains of L. reuteri isolated from various hosts and geographical locations. However, comparison with other Lactobacillus species supported the current classification of BR11 as L. reuteri. The most closely related species to L. reuteri is L. vaginalis or Lactobacillus antri, depending on the housekeeping gene used for analysis. The close evolutionary relationship of L. vaginalis to L. reuteri and the high degree of sequence identity between the cgl-cyuABC loci in both species suggest that the Cyu system is highly likely to perform similar functions in L. vaginalis. In search of other genes that function in oxidative defence, a number of mutants which were inactivated in genes that confer increased resistance to oxidative stress in other bacteria were constructed. The genes targeted were ahpC (peroxidase component of the alkyl hydroperoxide reductase system), tpx (thiol peroxidase), osmC (osmotically induced protein C), mntH (Mn2+/Fe2+ transporter), gshA (ã-glutamylcysteine synthetase) and msrA (methionine sulfoxide reductase). The ahpC and mntH mutants had slightly lower minimum inhibitory concentrations of organic peroxides, suggesting these genes might be involved in resistance to organic peroxides in L. reuteri. However, none of the mutants exhibited growth defects in aerated cultures, in stark contrast to the cyuC mutant. This may be due to compensatory functions of other genes, a hypothesis which cannot be tested until a robust protocol for constructing markerless multiple gene deletion mutants in L. reuteri is developed. These results highlight the importance of the Cyu transporter in oxidative defence and provide a foundation for extending the research of this system in other bacteria.

Thiol cofactors for selenoenzymes and their synthetic mimics

The importance of selenium as an essential trace element is now well recognized. In proteins, the redox-active selenium moiety is incorporated as selenocysteine (Sec), the 21st amino acid. In mammals, selenium exerts its redox activities through several selenocysteine-containing enzymes, which include glutathione peroxidase (GPx), iodothyronine deiodinase (ID), and thioredoxin reductase (TrxR). Although these enzymes have Sec in their active sites, they catalyze completely different reactions and their substrate specificity and cofactor or co-substrate systems are significantly different. The antioxidant enzyme GPx uses the tripeptide glutathione (GSH) for the catalytic reduction of hydrogen peroxide and organic peroxides, whereas the larger and more advanced mammalian TrxRs have cysteine moieties in different subunits and prefer to utilize these internal cysteines as thiol cofactors for their catalytic activity. On the other hand, the nature of in vivo cofactor for the deiodinating enzyme ID is not known, although the use of thiols as reducing agents has been well-documented. Recent studies suggest that molecular recognition and effective binding of the thiol cofactors at the active site of the selenoenzymes and their mimics play crucial roles in the catalytic activity. The aim of this perspective is to present an overview of the thiol cofactor systems used by different selenoenzymes and their mimics.

Processos de formação de ligações cruzadas de polietileno de alto peso molecular

No projeto desenvolvido, ligações cruzadas foram formadas no polietileno de alta densidade e alto peso molecular, grade HS5103, através dos processos reticulação por peróxidos e silanos, com o objetivo de se avaliar o efeito da introdução de ligações cruzadas nas propriedades térmicas e mecânicas deste PEAD. Misturas entre o HS5103 e os peróxidos orgânicos, 2,5-Dimetil-2,5-di(terc-butilperoxi)hexano (DHBP) e peróxido de dicumila (DCP), foram produzidas e analisadas para a avaliação do efeito dos tipos de peróxido na reticulação e propriedades do PEAD e para determinação da concentração e do tipo de peróxido a ser utilizado como agente iniciador de reticulação por silano. Ensaios de índice de fluidez (MFI), reometria capilar, extração de polímero por xileno (teor de gel), análise termogravimétrica (TGA), calorimetria diferencial de varredura (DSC) e tração foram realizados para caracterização das misturas com peróxidos. Os resultados indicaram aumento da viscosidade com o aumento da concentração de peróxido, sendo o DHBP o que apresentou maior índice de aumento; não houve mudanças relevantes nas propriedades mecânicas e, ocorreu aumento do grau de cristalinidade, sendo mais significativo nas amostras com DCP. Após avaliação dos resultados citados, para as amostras a serem reticuladas via silano, foi promovida a graftização de diferentes concentrações de viniltrimetóxisilano (VTMS) na presença de 0,01%p/p de DCP com a adição de 0,05%p/p de catalisador, posteriormente a reticulação foi promovida em água. As amostras produzidas foram caracterizadas por ensaios de teor de gel, análise dinâmico-mecânica (DMA), espectroscopia de absorção no infravermelho (FTIR), TGA, ensaios de desgaste por deslizamento e tração. Nas amostras com silano a formação de ligações cruzadas foi gradativa, apresentando de 8% de gel para amostra com 0,5%p/p de VTMS a 57 % para amostra com1,5% p/p de silano, maior concentração utilizada. A análise dinâmico-mecânica (DMA) realizada evidenciou que houve um aumento densidade de ligações cruzadas e do módulo de armazenamento após temperatura de fusão com o teor de silano, concordando com os resultados de teor de gel. As análises de FTIR mostraram que houve a graftização e a formação de ligações cruzadas no PEAD HS5103. Não se observou um aumento significativo para o limite de resistência para o PEAD modificado. E os testes de desgaste por deslizamento indicaram um aumento da resistência ao desgaste das amostras reagidas com VTMS.

Contamination des solutions d’hyper-alimentation intraveineuses (HAIV) néonatales, effet de l’ascorbylperoxyde au foie

Introduction : Chez les nouveau-nés prématurés, l’hyper-alimentation intraveineuse (HAIV) contribue à leur survie, mais elle est aussi une source importante de molécules oxydantes. L’absence d’une protection adéquate contre la lumière ambiante génère in vitro, via la photo-excitation de la riboflavine, du H2O2, des peroxydes organiques et un dérivé peroxydé de la vitamine C, l’ascorbylperoxyde (AscOOH). Plusieurs données du laboratoire associent l’infusion d’HAIV à des désordres lipidiques dans notre modèle animal. L’hypothèse est donc que l’AscOOH a un pouvoir oxydant et est responsable de certains des effets biologiques observés. Mes objectifs sont les suivants : 1) développer une méthode de dosage de l’AscOOH; 2) démontrer, à l’aide du modèle animal bien établi au laboratoire, des relations entre la concentration tissulaire de cette molécule et des paramètres métaboliques et l’état redox au foie et dans la circulation; et 3) confirmer l’effet physiologique de l’AscOOH dans un modèle cellulaire. Méthode : Différents étalons internes potentiels ont été testés pour le dosage de l’AscOOH par spectrométrie de masse après séparation sur HPLC (LC-MS). Les phases mobiles et conditions chromatographiques ont été optimisées. Pour l’objectif 2, des cobayes de 3 jours de vie (n=11) ont reçu par voie intraveineuse une dose d’AscOOH (entre 0 et 3,3mM). Les animaux ont été sacrifiés au 4e jour de traitement pour le prélèvement de tissus. Les concentrations tissulaires d’AscOOH ont été déterminées au LC-MS. La triglycéridémie et la cholestérolémie ont été mesurées à l’aide d’un kit commercial par spectrophotométrie. Le glutathion oxydé et réduit ont été mesurés par électrophorèse capillaire. Les relations linéaires obtenues sont exprimées par le ratio des carrés (r2), et traitées par ANOVA. Résultats : La validation du dosage de l’AscOOH par LC-MS a été réalisée. Chez les animaux, la concentration urinaire d’AscOOH par créatinine corrèle positivement avec la dose reçue, négativement avec la lipidémie, et négativement avec le redox sanguin et érythrocytaire, indiquant un milieu moins oxydé. Conclusion : La concentration urinaire d’AscOOH peut donc être un reflet de l’oxydation de l’HAIV en clinique. Nos données chez l’animal suggèrent une interaction de l’AscOOH avec le métabolisme hépatique produisant une chute de la concentration plasmatique de cholestérol et de triglycérides. Le modèle cellulaire n’a pas permis d’élucider le mécanisme moléculaire de l’action de l’AscOOH sur le métabolisme.

Direct Kinetic Observation of the Chemiexcitation Step in Peroxyoxalate Chemiluminescence

A high-energy intermediate in the peroxyoxalate reaction can be accumulated at room temperature under specific reaction conditions and in the absence of any reducing agent in up to micromolar concentrations. Bimolecular interaction of this intermediate, accumulated in the reaction of oxalyl chloride with hydrogen peroxide, with an activator (highly fluorescent aromatic hydrocarbons with low oxidation potential) added in delay shows unequivocally that this intermediate is responsible for chemiexcitation of the activator. Activation parameters for the unimolccular decomposition of this intermediate (Delta H(double dagger) = 11.2 kcal mol(-1); Delta S(double dagger) = -23.2 cal mol(-1) K(-1)) and for its bimolecular reaction with 9,10-diphenylanthracene (Delta H(double dagger) = 4.2 kcal mol(-1); Delta S(double dagger) = -26.9 cal mol(-1) K(-1)) show that this intermediate is much less stable than typical 1,2-dioxetanes and 1,2-dioxetanones and demonstrate its highly favored interaction with the activator. Therefore, it can be inferred that structural characterization of the high-energy intermediate in the presence of an activator must be highly improbable. The observed linear free-energy correlation between the catalytic rate constants and the oxidation potentials of several activators definitely confirms the occurrence of the chemically initiated electron-exchange luminescence (CIEEL) mechanism in the chemiexcitation step of the peroxyoxalate system.

Fenchyl substituted 1,2-dioxetanes as an alternative to adamantyl derivatives for bioanalytical applications

The synthesis and study of the chemiluminescence parameters and thermal stability of 1,2-dioxetanes containing a spirofenchyl substituent are reported. Three fenchyl-substituted 1,2-dioxetanes were synthesized by photooxygenation of the corresponding alkenes, obtained by Barton-Kellogg olefination of the readily available (-)-fenchone. The fenchyl-substituted 1,2-dioxetanes showed thermal stabilities similar to those of the corresponding spiroadamantyl-substituted derivatives, although being slightly more labile with respect to unimolecular decomposition than the latter derivatives, which are widely utilized as labels in a great variety of chemiluminescent immunoassays. Fluoride induced decomposition of one triggerable fenchyl 1,2-dioxetane derivative showed kinetic parameters similar to those of the corresponding adamantyl-substituted derivative. The chemiluminescence quantum yields in the one percent range are also similar to that of other widely utilized chemiluminescence systems as the luminol reaction. These results indicate that fenchyl-substituted 1,2-dioxetanes can potentially be utilized as a cheaper alternative to substitute the corresponding spiroadamantyl derivatives in bioanalytical applications. (C) 2010 Elsevier B.V. All rights reserved.

The chemiluminescent peroxyoxalate system: state of the art almost 50 years from its discovery

Almost fifty years after the discovery of the peroxyoxalate reaction by E. A. Chandross in the early nineteen sixties, this review article intends to give a general overview on mechanistic aspects of this system and to describe the principles of its analytical application. After a short general introduction on the principles of chemiluminescence and the history of peroxyoxalate discovery, mechanistic aspects of high-energy intermediate formation, its structure and its reaction with an activator in the peroxyoxalate system are discussed. Finally, analytical applications of peroxyoxalate chemiluminescence are exemplified using representative recent examples, including oxalic acid detection in biological samples.

Massenspektrometrische Untersuchungen und Nachweise von organischen Hydroperoxiden und höhermolekularen Verbindungen im biogenen sekundären organischen Aerosol

Atmosphärische Aerosole beeinflussen den Strahlungshaushalt und damit das Klima der Erde. Dies geschieht sowohl direkt (Streuung und Absorption), als auch indirekt (Wolkenkondensationskeime). Das sekundäre organische Aerosol (SOA) bildet einen wichtigen Bestandteil des atmosphärischen Aerosols. Seine Bildung erfolgt durch Reaktionen von Kohlenwasserstoffen mit atmosphärischen Oxidationsmitteln (z.B. Ozon, OH-Radikalen). Eine Klasse dieser Kohlenwasserstoffe sind die Terpene. Sie werden in großen Mengen durch die Vegetation emittiert und gelten als wichtige Vorläufersubstanzen des biogenen SOAs. In den Reaktionen von Monoterpenen und Sesquiterpenen mit atmosphärischen Reaktionspartnern wird eine große Vielfalt an multifunktionellen Reaktionsprodukten gebildet, von denen bis heute nur ein Bruchteil identifiziert werden konnte. In der vorliegenden Arbeit soll im Speziellen die Bildung von organischen Peroxiden und oligomeren Verbindungen im biogenen SOA untersucht und Nachweise einzelner Moleküle erbracht werden.rnFür eine Identifizierung von organischen Peroxiden aus der Oxidation einzelner Monoterpene und Sesquiterpene mit Ozon wurden die Reaktionsprodukte direkt in eine bei Atmosphärendruck arbeitende chemische Ionisationsquelle überführt und massenspektrometrisch untersucht (online-APCI-MS). Hierdurch konnten organische Hydroperoxide in der Partikelphase nachgewiesen werden, welche sich durch eine signifikante Abspaltung von H2O2 im Tandem-Massenspektrum (MS/MS) auszeichneten. Des Weiteren sollte die Bildung von höhermolekularen Verbindungen („Dimere“) im SOA des α-Pinens untersucht werden. Hierfür wurden zunächst die Reaktionsprodukte des Cyclohexens, das als einfache Modellverbindung des α-Pinens dient, mittels online-APCI-MS und offline durch Flüssigkeitschromatographie und Elektrospray-Ionenfallenmassenspektrometrie (HPLC/ESI-MS) untersucht. Verschiedene Produkte der Cyclohexen-Ozonolyse konnten hierbei als Esterverbindungen identifiziert werden, wobei eigens synthetisierte Referenzsubstanzen für die Identifizierung verwendet wurden. In einem weiteren Experiment, indem gleichzeitig Cyclohexen und α-Pinen mit Ozon umgesetzt wurden, konnten ebenfalls eine Bildung von höhermolekularen Estern nachgewiesen werden. Es handelte sich hierbei um „Mischester“, deren Struktur aus Reaktionsprodukten der beiden VOC-Vorläufermoleküle aufgebaut war. Durch diese neuen Erkenntnisse, über die Bildung von Estern im SOA des Cyclohexens, wurden die Dimer-Bildung einer reinen α-Pinen/Ozon-Reaktion online und offline massenspektrometrisch untersucht. Hier stellten sich als Hauptprodukte die Verbindungen mit m/z 357 und m/z 367 ([M-H]--Ionen) heraus, welche zudem erstmals auf einem Filter einer Realprobe aus Hyytiälä, Finnland nachgewiesen werden konnten. Aufgrund ihrer Fragmentierung in MS/MS-Untersuchungen sowie den exakten Summenformeln aus FT-MS Messungen konnte für die Struktur der höhermolekularen Verbindung mit m/z 367 ebenfalls ein Ester und für m/z 357 ein Peroxyhemiacetal vorgeschlagen werden. Die vorgeschlagene Struktur der Verbindung m/z 367 konnte im Anschluss über eine Reaktion aus Hydroxypinonsäure mit Pinsäure bestätigt werden. Die Identifizierung der Esterverbindung des α-Pinen-SOA erfolgte ebenfalls mit Hilfe von LC-MSn-Messungen.rnDie bisher diskutierten Ergebnisse, sowie die meisten in der Literatur beschriebenen Studien befassen sich jedoch mit einzelnen Vorläuferverbindungen, im Gegensatz zu den komplexen SOA-Proben aus den Emissionen der Vegetation. Im Rahmen einer Messkampagne am Forschungszentrum Jülich erfolgte eine massenspektrometrische Charakterisierung (online-APCI-MS) des SOAs aus direkten VOC-Emissionen von Pflanzen. Durch einen Vergleich der Produktverteilung dieser erhalten online-Massenspektren mit denen aus den Reaktionen einzelner VOCs, konnten Aussagen über die in den Reaktionen umgesetzten VOCs gemacht werden. Es konnte gezeigt werden, dass in stressbedingten Situationen die untersuchten Exemplare der Betula pendula (Birke) hauptsächlich Sesquiterpene, Picea abies (Fichte) eher Monoterpene und Eucalyptus (Eukalyptus) sowohl Sesquiterpene als auch Monoterpene emittieren. Um die atmosphärischen Prozesse, die zur Bildung der Produkte im SOA führen vollständig zu verstehen, müssen jedoch noch weitere Anstrengungen unternommen werden.rn

The electrochemical oxidation and reduction of nitrate ions in the room temperature ionic liquid [C(2)mim][NTf2]; the latter behaves as a 'melt' rather than an 'organic solvent'

The electrochemical oxidation of 1-butyl-3-methylimidazolium nitrate [C(4)mim][NO3] was studied by cyclic voltammetry in the room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide [C(2)mim][NTf2]. A sharp peak was observed on a Pt microelectrode (d = 10 mu m), and a diffusion coefficient at infinite dilution of ca. 2.0 x 10(-11) m(2) s(-1) was obtained. Next, the cyclic voltammetry of sodium nitrate (NaNO3) and potassium nitrate (KNO3) was studied, by dissolving small amounts of solid into the RTIL [ C2mim][ NTf2]. Similar oxidation peaks were observed, revealing diffusion coefficients of ca. 8.8 and 9.0 x 10(-12) m(2) s(-1) and solubilities of 11.9 and 10.8 mM for NaNO3 and KNO3, respectively. The smaller diffusion coefficients for NaNO3 and KNO3 (compared to [C(4)mim][NO3]) may indicate that NO3- is ion-paired with Na+ or K+. This work may have applications in the electroanalytical determination of nitrate in RTIL solutions. Furthermore, a reduction feature was observed for both NaNO3 and KNO3, with additional anodic peaks indicating the formation of oxides, peroxides, superoxides and nitrites. This behaviour is surprisingly similar to that obtained from melts of NaNO3 and KNO3 at high temperatures ( ca. 350 - 500 degrees C), and this observation could significantly simplify experimental conditions required to investigate these compounds. We then used X-ray photoelectron spectroscopy (XPS) to suggest that disodium( I) oxide (Na2O), which has found use as a storage compound for hydrogen, was deposited on a Pt electrode surface following the reduction of NaNO3.

Revision of Singlet Quantum Yields in the Catalyzed Decomposition of Cyclic Peroxides

The chemiluminescence of cyclic peroxides activated by oxidizable fluorescent dyes is an example of chemically initiated electron exchange luminescence (CIEEL), which has been used also to explain the efficient bioluminescence of fireflies. Diphenoyl peroxide and dimethyl-1,2-dioxetanone were used as model compounds for the development of this CIEEL mechanism. However, the chemiexcitation efficiency of diphenoyl peroxide was found to be much lower than originally described. In this work, we redetermine the chemiexcitation quantum efficiency of dimethyl-1,2-dioxetanone, a more adequate model for firefly bioluminescence, and found a singlet quantum yield (Phi(s)) of 0.1%, a value at least 2 orders of magnitude lower than previously reported. Furthermore, we synthesized two other 1,2-dioxetanone derivatives and confirm the low chemiexcitation efficiency (Phi(s) < 0.1%) of the intermolecular CIEEL-activated decomposition of this class of cyclic. peroxides. These results are compared with other chemiluminescent reactions, supporting the general trend that intermolecular CIEEL systems are much less efficient in generating singlet excited states than analogous intramolecular processes (Phi(s) approximate to 50%), with the notable exception of the peroxyoxalate reaction (Phi(s) approximate to 60%).