The use of binary mixtures of 1-butyl-1-methylpyrrolidinium bis{(trifluoromethyl)sulfonyl}imide and aliphatic nitrile solvents as electrolyte for supercapacitors

Abstract The development of high voltage electrolytes is one of the key aspects for increasing both energy and power density of electrochemical double layer capacitors (EDLCs). The usage of blends of ionic liquids and organic solvents has been considered as a feasible strategy since these electrolytes combine high usable voltages and good transport properties at the same time. In this work, the ionic liquid 1-butyl-1-methylpyrrolidinium bis{(trifluoromethyl)sulfonyl}imide ([Pyrr14][TFSI]) was mixed with two nitrile-based organic solvents, namely butyronitrile and adiponitrile, and the resulting blends were investigated regarding their usage in electrochemical double layer capacitors. Both blends have a high electrochemical stability, which was confirmed by prolonged float tests at 3.2 V, as well as, good transport properties. In fact, the butyronitrile blend reaches a conductivity of 17.14 mS·cm−1 and a viscosity of 2.46 mPa·s at 20 °C, which is better than the state-of-the-art electrolyte (1 mol·dm−3 of tetraethylammonium tetrafluoroborate in propylene carbonate).

Binary Mixtures of 1-Butyl-1-Methylpyrrolidinium Bis{(trifluoromethyl)Sulfonyl}Imide and Aliphatic Nitrile Solvents As Electrolyte for Electrochemical Double Layer Capacitors (Invited).

Electrochemical double layer capacitors (EDLCs), also known as supercapacitors, are promising energy storage devices, especially when considering high power applications [1]. EDLCs can be charged and discharged within seconds [1], feature high power (10 kW·kg-1) and an excellent cycle life (>500,000 cycles). All these properties are a result of the energy storage process of EDLCs, which relies on storing energy by charge separation instead of chemical redox reactions, as utilized in battery systems. Upon charging, double layers are forming at the electrode/electrolyte interface consisting of the electrolyte’s ions and electric charges at the electrode surface.In state-of-the-art EDLC systems activated carbons (AC) are used as active materials and tetraethylammonium tetrafluoroborate ([Et4N][BF4]) dissolved in organic solvents like propylene carbonate (PC) or acetonitrile (ACN) are commonly used as the electrolyte [2]. These combinations of materials allow operative voltages up to 2.7 V - 2.8 V and an energy in the order of 5 Wh·kg-1[3]. The energy of EDLCs is dependent on the square of the operative voltage, thus increasing the usable operative voltage has a strong effect on the delivered energy of the device [1]. Due to their high electrochemical stability, ionic liquids (ILs) were thoroughly investigated as electrolytes for EDLCs, as well as, batteries, enabling high operating voltages as high as 3.2 V - 3.5 V for the former [2]. While their unique ionic structure allows the usage of neat ILs as electrolyte in EDLCs, ILs suffer from low conductivity and high viscosity increasing the intrinsic resistance and, as a result, a lower power output of the device. In order to overcome this issue, the usage of blends of ionic liquids and organic solvents has been considered a feasible strategy as they combine high usable voltages, while still retaining good transport properties at the same time.In our recent work the ionic liquid 1-butyl-1-methylpyrrolidinium bis{(trifluoromethyl)sulfonyl}imide ([Pyrr14][TFSI]) was combined with two nitrile-based organic solvents, namely butyronitrile (BTN) and adiponitrile (ADN), and the resulting blends were investing regarding their usage in electrochemical double layer capacitors [4,5]. Firstly, the physicochemical properties were investigated, showing good transport properties for both blends, which are similar to the state-of-the-art combination of [Et4N][BF4] in PC. Secondly, the electrochemical properties for EDLC application were studied in depth revealing a high electrochemical stability with a maximum operative voltage as high as 3.7 V. In full cells these high voltage organic solvent based electrolytes have a good performance in terms of capacitance and an acceptable equivalent series resistance at cut-off voltages of 3.2 and 3.5 V. However, long term stability tests by float testing revealed stability issues when using a maximum voltage of 3.5 V for prolonged time, whereas at 3.2 V no such issues are observed (Fig. 1).Considering the obtained results, the usage of ADN and BTN blends with [Pyrr14][TFSI] in EDLCs appears to be an interesting alternative to state-of-the-art organic solvent based electrolytes, allowing the usage of higher maximum operative voltages while having similar transport properties to 1 mol∙dm-3 [Et4N][BF4] in PC at the same time.

E-cigarette puffing patterns associated with high and low nicotine e-liquid strength: effects on toxicant and carcinogen exposure

Contrary to intuition, use of lower strength nicotine e-liquids might not offer reduced health risk if compensatory puffing behaviour occurs. Compensatory puffing (e.g. more frequent, longer puffs) or user behaviour (increasing the wattage) can lead to higher temperatures at which glycerine and propylene glycol (solvents used in e-liquids) undergo decomposition to carbonyl compounds, including the carcinogens formaldehyde and acetaldehyde. This study aims to document puffing patterns and user behaviour associated with using high and low strength nicotine e-liquid and associated toxicant/carcinogen exposure in experienced e-cigarette users (known as vapers herein).

Síntese, extração e caracterização de biopolímeros de origem microalgal para desenvolvimento de nanofibras

Pesquisas com microalgas estão crescendo devido aos possíveis bioprodutos oriundos de sua biomassa, bem como as suas diferentes aplicabilidades. Microalgas podem ser cultivadas para a produção de biopolímeros com características de biocompatibilidade e biodegradabilidade. Nanofibras produzidas por electrospinning a partir de poli-β-hidroxibutirato (PHB) geram produtos com aplicabilidade na área de alimentos e médica. O objetivo deste trabalho foi selecionar microalgas com maior potencial para síntese de biopolímeros, em diferentes meios de cultivo, bem como purificar poli-β-hidroxibutirato e desenvolver nanofibras. Este trabalho foi dividido em cinco artigos: (1) Seleção de microalgas produtoras de biopolímeros; (2) Produção de biopolímeros pela microalga Spirulina sp. LEB 18 em cultivo com diferentes fontes de carbono e redução de nitrogênio; (3) Síntese de biopolímeros pela microalga Spirulina sp. LEB 18 em cultivos autotróficos e mixotróficos; (4) Purificação de poli-β- hidroxibutirato extraído da microalga Spirulina sp. LEB 18; e (5) Produção de nanofibras a partir de poli-β-hidroxibutirato de origem microalgal. Foram estudadas as microalgas Cyanobium sp., Nostoc ellipsosporum, Spirulina sp. LEB 18 e Synechococcus nidulans. Os biopolímeros foram extraídos nos tempos de 5, 10, 15, 20 e 25 d de cultivo a partir de digestão diferencial. Para os experimentos com diferentes nutrientes, foi utilizado como fonte de carbono, bicarbonato de sódio, acetato de sódio, glicose e glicerina modificando-se as concentrações de nitrogênio e fósforo. Os cultivos foram realizados em fotobiorreatores fechados de 2 L. A concentração inicial de inóculo foi 0,15 g.L-1 e os ensaios foram mantidos em estufa termostatizada a 30 ºC com iluminância de 41,6 µmolfótons.m -2 .s -1 e fotoperíodo 12 h claro/escuro. Para a purificação de PHB, foi utilizada a biomassa da cianobactéria Spirulina sp. LEB 18, cultivada em meio Zarrouk. Após a extração do biopolímero bruto, a amostra foi desengordurada com hexano e purificada com 1,2-carbonato de propileno. Foram determinadas as purezas e as propriedades térmicas no PHB purificado. O biopolímero utilizado para produzir as nanofibras apresentava 70 % de pureza. A técnica para produção de nanofibras foi o electrospinning. As microalgas que apresentaram máxima produtividade foram Nostoc ellipsosporum e Spirulina sp. LEB 18 com rendimento de biopolímero 19,27 e 20,62 % em 10 e 15 d, respectivamente, na fase de máximo crescimento celular. O maior rendimento de biopolímeros (54,48 %) foi obtido quando se utilizou 8,4 g.L-1 de NaHCO3, 0,05 g.L-1 de NaNO3 e 0,1 g.L-1 de K2HPO4. A condição que proporcionou maior pureza do PHB foi a 130 ºC e 5 min de contato entre o solvente (1,2-carbonato de propileno) e o PHB. As análises térmicas para todas as amostras foram semelhantes em relação ao PHB padrão (Sigma-Aldrich). A purificação com 1,2-carbonato de propileno foi eficiente para o PHB extraído de microalga, alcançando pureza acima de 90 %. A condição que apresentou menores diâmetros de nanofibras foi ao utilizar solução contendo 20 % de biopolímero solubilizado em clorofórmio. As condições do electrospinning que apresentou nanofibras com diâmetros de 470 e 537 nm foram, vazão 150 µL.h-1 , diâmetro do capilar 0,45 mm e voltagens entre 24,1 e 29,6 kV, respectivamente. A microalga Spirulina sp. LEB 18 produz PHB ao utilizar menores concentrações de nutrientes no meio de cultivo, que pode ser purificado com 1,2-carbonato de propileno. Este biopolímero possui aplicabilidade para produção de nanofibras.

Effects of Ageratum Conyzoides on Semen Characteristics and Sperm Morphology in Rats Exposed to Sodium Arsenite

Arsenite is a major environmental toxicant that is well known to cause reproductive injury. The sperm protective potential of Ageratum conyzoides Linn in arsenic-treated rats was carried out in this study taking advantage of the antioxidant constituents and its androgenic activities. Twenty-four male albino rats aged 16 weeks, weighing 225 to 228g were used. They were grouped into 4(A-Da) with each group containing 6 rats. Group A was orally treated with 100mg/kg ethanol leaf extract of Ageratum conyzoides L., daily for 14 days, group B (single oral dose of sodium arsenite 2.5 mg/kg body weight), C (Ageratum conyzoides extract daily for 14 days and sodium arsenite (SA) given on the 14th day) and group D (Propylene glycol as negative control). It was observed that group B had a more lower (p<0.05) percentage motility (26.7±6.67%) when compared across the groups while group A had a significantly higher (p<0.05) mean value (63.3±3.33%). The sperm motility of rats in group D was significantly higher (p<0.05) than groups B and C. This implies that A. conyzoides extract had no adverse effect on the sperm motility of the rats and also ameliorates the adverse effect of arsenite on sperm motility. The mean value obtained for sperm liveability, semen volume and Sperm concentration followed a similar pattern although, the differences were not significant (p>0.05) for semen volume and the Sperm concentration of rats across the groups. The total sperm abnormality obtained across the groups ranges between 10.44 and 14.27% with group B treated with sodium arsenite (SA) having the highest value when compared with groups A and D, although, the differences were not significant (P>0.05). The study concluded that ethanol leaf extract of Ageratum conyzoides has no negative effect on sperm motility, liveability characteristics and morphology and also protected spermatozoa against arsenic reproductive toxicity in wistar strain albino rats..

The Use of Mucoadhesive Polymers to Enhance the Hypotensive Effect of a Melatonin Analogue, 5-MCA-NAT, in Rabbit Eyes

Purpose.: 5-Methoxy-carbonylamino-N-acetyltryptamine (5-MCA-NAT, a melatonin receptor agonist) produces a clear intraocular pressure (IOP) reduction in New Zealand White rabbits and glaucomatous monkeys. The goal of this study was to evaluate whether the hypotensive effect of 5-MCA-NAT was enhanced by the presence of cellulose derivatives, some of them with bioadhesive properties, as well as to determine whether these formulations were well tolerated by the ocular surface. Methods.: Formulations were prepared with propylene glycol (0.275%), carboxymethyl cellulose (CMC, 0.5% and 1.0%) of low and medium viscosity and hydroxypropylmethyl cellulose (0.3%). Quantification of 5-MCA-NAT (100 μM) was assessed by HPLC. In vitro tolerance was evaluated by the MTT method in human corneal-limbal epithelial cells and normal human conjunctival cells. In vivo tolerance was analyzed by biomicroscopy and specular microscopy in rabbit eyes. The ocular hypotensive effect was evaluated measuring IOP for 8 hours in rabbit eyes. Results.: All the formulations demonstrated good in vitro and in vivo tolerance. 5-MCA-NAT in CMC medium viscosity 0.5% was the most effective at reducing IOP (maximum IOP reduction, 30.27%), and its effect lasted approximately 7 hours. Conclusions.: The hypotensive effect of 5-MCA-NAT was increased by using bioadhesive polymers in formulations that are suitable for the ocular surface and also protective of the eye in long-term therapies. The use of 5-MCA-NAT combined with bioadhesive polymers is a good strategy in the treatment of ocular hypertension and glaucoma.

Improvement of carbon materials performance by nitrogen functional groups in electrochemical capacitors in organic electrolyte at severe conditions

N-doped activated carbon fibers have been synthesized by using chemically polymerized aniline as source of nitrogen. Commercial activated carbon fibers (A20) were chemically modified with a thin film of polyaniline (PANI) inside the microporosity of the carbon fibers. The modified activated carbon fibers were carbonized at 600 and 800 °C, respectively. In this way, activated carbon fibers modified with surface nitrogen species were prepared in order to analyze their influence in the performance of electrochemical capacitors in organic electrolyte. Symmetric capacitors were made of activated carbon fibers and N-doped activated carbon fibers and tested in a two-electrode cell configuration, using triethylmethylammonium tetrafluoroborate/propylene carbonate (TEMA-BF4/PC) as electrolyte. The effect of nitrogen species in the degradation or stabilization of the capacitor has been analyzed through floating durability tests using a high voltage charging (3.2 V). The results show higher stabilizing effect in carbonized samples (N-ACF) than in non-carbonized samples and pristine activated carbon fibers, which is attributed to the presence of aromatic nitrogen group, especially positively charged N-functional groups.

Síntese e caracterização de nanocompósitos magnéticos empregando polimerização radicalar em meios homogêneo (blk) e heterogêneo (miniemulsão)

Tese (doutorado)—Universidade de Brasília, Instituto de Química, Curso de Pós-Graduação em Química, 2016.

Mechanisms of Chloroperoxidase-catalyzed Enantioselective Reactions as Probed by Site-directed Mutagenesis and Isotopic Labeling

Chloroperoxidase (CPO) is a heme-containing glycoprotein secreted by the marine fungus Caldariomyces fumago. Chloroperoxidase contains one ferriprotoporphyrin IX prosthetic group per molecule and catalyzes a variety of reactions, such as halogenation, peroxidation and epoxidation. The versatile catalytic activities of CPO coupled with the increasing demands for chiral synthesis have attracted an escalating interest in understanding the mechanistic and structural properties of this enzyme. In order to better understand the mechanisms of CPO-catalyzed enantioselective reactions and to fine-tune the catalytic properties of chloroperoxidase, asparagine 74 (N74) located in the narrow substrate access channel of CPO was replaced by a bulky, nonpolar valine and a polar glutamine using site-directed mutagenesis. The CPO N74 mutants displayed significantly enhanced activity toward nonpolar substrates compared to wild-type CPO as a result of changes in space and polarity of the heme distal environment. More interestingly, N74 mutants showed dramatically decreased chlorination and catalase activity but significantly enhanced epoxidation activity as a consequence of improved kinetic perfection introduced by the mutation as reflected by the favorable changes in kcat and kcat/KM of these reactions. It is also noted that the N74V mutant is capable of decomposing cyanide, the most notorious poison for many hemoproteins, as judged by the unique binding behavior of N74V with potassium cyanide. Histidine 105 (H105) was replaced by a nonpolar amino acid alanine using site-directed mutagenesis. The CPO H105 mutant (H105A) displayed dramatically decreased chlorination and catalase activity possibly because of the decreased polarity in the heme distal environment and loss of the hydrogen bonds between histidine 105 and glutamic acid 183. However, significantly increased enantioselectivity was observed for the epoxidation of bulky styrene derivatives. Furthermore, my study provides strong evidence for the proposed histidine/cysteine ligand switch in chloroperoxidase, providing experimental support for the structure of the 420-nm absorption maximum for a number of carbon monoxide complexes of heme-thiolate proteins. For the NMR study, [dCPO(heme)] was produced using 90% deuterated growth medium with excess heme precursors and [dCPO(Phe)] was grown in the same highly deuterated medium that had been supplemented with excess natural phenylalanine. To make complete heme proton assignments, NMR spectroscopy has been performed for high-resolution structural characterization of [dCPO(heme)] and [dCPO(Phe)] to achieve unambiguous and complete heme proton assignments, which also allows important amino acids close to the heme active center to be determined.