Extracting Turnover Frequencies of Electron Transfer in Heterogeneous Catalysis: A Study of IrO2-TiO2 Anatase for Water Oxidation Using Ce4+ Cations

Within the context of electron transfer during the catalytic water oxidation reaction, the Ir-based system is among the most active. The reaction, mimicking photosynthesis II, requires the use of an electron acceptor such the Ce4+ cation. This complex reaction, involving adsorbed water at the interface of the metal cation and Ce4+, has mostly been studied in homogenous systems. To address the ambiguity regarding the gradual transformation of a homogenous system into a heterogeneous one, we prepared and studied a heterogeneous catalyst system composed of IrO2, with a mean particle size ranging from about 5 Å to 10 Å, dispersed on a TiO2 anatase support, with the objective of probing into the different parameters of the reaction, as well as the compositional changes and rates. The system was stable for many of the runs that were conducted (five consecutive runs with 0.18 M of Ce4+ showed the same reaction rate with TON > 56,000) and, equally importantly, was stable without induction periods. Extraction of the reaction rates from the set of catalysts, with an attempt to normalize them with respect to Ir loading and, therefore, to obtain turnover frequencies (TOF), was conducted. While, within reasonable deviations, the TOF numbers extracted from TPR and XPS Ir4f were close, those extracted from the particle shape (HR-STEM) were considerably larger. The difference indicates that bulk Ir atoms contribute to the electron transfer reaction, which may indicate that the reaction rate is dominated by the reorganization energy between the redox couples involved. Therefore, the normalization of reaction rates with surface atoms may lead to an overestimation of the site activity.

Risk Factors for Postinduction Hypotension among Elderly Patients Undergoing Elective Non-Cardiac Surgery under General Anesthesia

Objective: We aimed to determine risk factors for hypotension occurring after induction among elderly patients (aged 65 years and older). We hypothesized that the dosage of intravenous anesthesia drugs as well as the type of inhalation agent have an effect on hypotension during post-induction periods. We aimed to test this hypothesis to determine risk factors for hypotension after induction among elderly patients who underwent non-cardiac surgery.Material and Methods: This retrospective cohort study analyzed data from 580 patients between December 2017 and July 2018 at a tertiary university hospital in the south of Thailand. Hypotension is defined as a more than 30.0% decrease in mean arterial pressure from baseline after induction and within 20 minutes of the use of a vasopressor agent to treat hypotension. The intraoperative parameters were blood pressure and heart rate immediately after arrival at the operating room, immediately after intubation, and 5, 10, 15, and 20 minutes after intubation.Results: The median age was 72.5 (68, 78) years. The association of post-induction hypotension was raised with a diuretic drug as preoperative medication (p-value=0.025), and the degree of hypertension immediately after arrival at the operating room (p-value<0.001). Increasing fentanyl dosage during induction was associated with hypotension (p-value<0.010). There was no statistically significant difference in the increase of the propofol dosage.Conclusion: The degree of hypertension immediately after arrival at the operating room coupled with higher fentanyl dosage were significant risk factors for postinduction hypotension in elderly patients.

Impact of plum processing on the quality and oxidative stability of cold-pressed kernel oil

Plum kernels of the “Čačanska rodna” variety, by-products from plum brandy production, were collected before and after fermentation and distillation, and used for cold-pressed oil production. Fatty acid and tocopherol contents were determined by capillary GC and HPLC, while the oxidation stability of the resulting cold-pressed oils was tested by the Rancimat method. The results showed that oleic fatty acid was dominant in the oil samples with a content of 56.6 to 61.8%, regardless of the plum kernels’ origin. The fermentation and distillation processes had a pronounced effect on the tocopherol content and oxidative stability of the resulting kernel oils. Tocopherol contents were 61.8 mg·100g-1, 87.4 mg·100g-1, 79.6 mg·100g-1 of oil, while the induction periods were 38.7, 44.4 and 33.6 hours for samples before fermentation, after fermentation and distillation, respectively. Based on the results, it could be concluded that the fermentation process increased the content of tocopherols in kernel oil whereas the high temperature during the distillation process adversely affected the tocopherol content and oxidative stability of the obtained kernel oil.

Efficiency of different additives in improvement of oxidation stability of fatty acid methyl esters with different properties

This study evaluates six formulations in improving oxidation stability of different fatty acid methyl esters (MEs). Two MEs differed in the unsaturation levels as they were synthesized from different feedstocks: a blend of soybean and sunflower oils (SoSuME), and waste cooking oil (WCOME); they did not fulfill the requirements of the EN 14214 standard concerning the oxidation stability (~0.6 h) and some impurities. The third MEs (SoSuME-EN) were fully compliant with the standard. Five formulations were phenolic-based, containing single or mixed antioxidant compounds of different molecular structures; one was amine-based. Different dosages of the formulations were added to the ME samples (corresponding to the addition range ~50-48300 ppm). The MEs stability expressed as induction periods, IPs, determined by the Rancimat method, were used for calculation of stabilization factors, SFs, indicating the efficiency of the applied formulation. The formulation containing TBHQ was the most efficient concerning the lowest consumption rate and the highest SF achieved for the low quality ME. 2,2?-methylene-bis-(4-methyl-6-tert-butylphenol) was linked with higher antioxidant potency than amine-based formulation and the phenolic com-pounds with two bulky tert-butyl groups. Among 4 selected phenolic additives, BHT and 2,2?-methylene-bis-(4-methyl-6-tert-butylphenol) proved similar efficiency in SoSuME-EN (at ~500 ppm they produced SF~2), while it took twice of this amount for mixed butylphenols to achieve the same effect.

Production of lipids and natural antioxidants from passion fruit seeds

The wild passion fruit species Passiflora setacea, Passiflora alata, and Passiflora tenuifila are native to the Brazilian biomass. The seed waste generated from the extraction of passion fruit juice contains functional polyunsaturated fatty acids and phenolic compounds. The aims of this study were to obtain lipids and natural antioxidants from passion fruit seeds. Passion seed oils were extracted using a lab-scale continuous press and their oxidative stability was evaluated using the Rancimat® method. Higher antioxidant extract capacity was observed when using an ethanol-water solution (70:30) at 45 ºC. In these cases, the total phenolic contents expressed as gallic acid equivalents from P. setacea, P. alata, and P. tenuifila cakes were approximately 1800, 600 and 900 mg·100g−1 of extract. Induction periods increased up to two-fold when adding these extracts to their respective seed oil. Therefore, passion fruit seed extract can contribute to increasing the oxidative stability of polyunsaturated oils.

Use of Isothermal and Isoperibolic Calorimetry to Study the Effect of Zinc on Hydration of Cement Blended with Fly Ash

Increasing utilization of secondary raw materials and alternative fuels results in increasing contents of metals in cements. Zinc is one of these elements. It comes to cement with secondary raw materials such as slag or fly ash or by the utilization of used tires as an alternative fuel. Zinc ions significantly prolong the hydration process in cement. This work deals with the influence of zinc ions in the form of very poorly soluble ZnO salt and easily soluble ZnCl2 and Zn(NO3)2 on the hydration of cement blended with fly ash. Zinc was dosed in the range of 0.05%, 0.1%, 0.5% and 1% of cement weight. The effect of zinc on hydration was monitored by isothermal and isoperibolic calorimetry. A 15% addition of fly ash to cement mainly causes further retardation of hydration reactions due to the reactions of fly ash particles with Ca2+ ions from cement. The strongest effect on the hydration retardation from all investigated compounds showed in ZnO as it dissolves very slowly. On the contrary, for the dosage of 1% of zinc in the form of ZnCl2 significant acceleration of hydration occurred. In this work, a synergistic effect on the prolongation of hydration with a combination of cement, zinc and fly ash was demonstrated. The lengths of induction periods were assessed from detected calorimetric curves and from these lengths the curves were gained by fitting with the exponential function. Final products were next analyzed using X-ray diffraction.

Thermoresponsive Polymers of Poly(2-(N-alkylacrylamide)ethyl acetate)s

Thermoresponsive poly(2-(N-alkylacrylamide) ethyl acetate)s with different N-alkyl groups, including poly(2-(N-methylacrylamide) ethyl acetate) (PNMAAEA), poly(2-(N-ethylacrylamide) ethyl acetate) (PNEAAEA), and poly(2-(N-propylacrylamide) ethyl acetate) (PNPAAEA), as well as poly(N-acetoxylethylacrylamide) (PNAEAA), were synthesized by solution RAFT polymerization. Unexpectedly, it was found that there are induction periods in the RAFT polymerization of these monomers, and the induction time correlates with the length of the N-alkyl groups in the monomers and follows the order of NAEAA < NMAAEA < NEAAEA < NPAAEA. The solubility of poly(2-(N-alkylacrylamide) ethyl acetate)s in water is also firmly dependent on the length of the N-alkyl groups. PNPAAEA including the largest N-propyl group is insoluble in water, whereas PNMAAEA and PNEAAEA are thermoresponsive in water and undergo the reversible soluble-to-insoluble transition at a critical solution temperature. The cloud point temperature (Tcp) of the thermoresponsive polymers is in the order of PNEAAEA < PNAEAA < PNMAAEA. The parameters affecting the Tcp of thermoresponsive polymers, e.g., degree of polymerization (DP), polymer concentration, salt, urea, and phenol, are investigated. Thermoresponsive PNMAAEA-b-PNEAAEA block copolymer and PNMAAEA-co-PNEAAEA random copolymers with different PNMAAEA and/or PNEAAEA fractions are synthesized, and their thermoresponse is checked.

Dynamic Ion Speciation During Hydrolysis of Aryltrifluoroborates

<p>Organotrifluoroborates serve as a coupling partner during transmetallation in the Suzuki-Miyaura reaction but require hydrolysis prior to the coupling reaction. Their anionic nature allows study of their hydrolysis by electrospray ionization mass spectrometry (ESI-MS) by real-time monitoring, complemented by pH analysis. Induction periods varied according to the borates employed, and a dynamic series of equilibria for numerous ions was observed during hydrolysis. We found that the induction periods and reaction rates were sensitive to the R group of the borates, the shape of reaction vessel, and stir rate, and that after complete decay of all of the aryltrifluoroborate ion the solution contained a variety of partially hydrolyzed species.</p>

Dynamic Ion Speciation During Hydrolysis of Aryltrifluoroborates

<p>Organotrifluoroborates serve as a coupling partner during transmetallation in the Suzuki-Miyaura reaction but require hydrolysis prior to the coupling reaction. Their anionic nature allows study of their hydrolysis by electrospray ionization mass spectrometry (ESI-MS) by real-time monitoring, complemented by pH analysis. Induction periods varied according to the borates employed, and a dynamic series of equilibria for numerous ions was observed during hydrolysis. We found that the induction periods and reaction rates were sensitive to the R group of the borates, the shape of reaction vessel, and stir rate, and that after complete decay of all of the aryltrifluoroborate ion the solution contained a variety of partially hydrolyzed species.</p>

Effect of Calcium Chloride on Hydration Kinetics and Pore Structure of Hydrated Tricalcium Silicate

Chemical admixtures are frequently used to regulate the setting and strength development of concrete materials. In this study, tricalcium silicate (C3S) was used as a model of the cement system, and the influence of calcium chloride, an extremely useful accelerator, on C3S hydration and the pore structure of hardened C3S paste were investigated by the combination of the techniques of differential scanning calorimetry (DSC) and the N2 adsorption (BET). The results indicated that the addition of calcium chloride would significantly shorten the pre-induction and induction periods and enhance the specific surface area and porosity of hardened C3S paste. However, the presence of CaCl2 has little effect on the pores, with a width ranging from 2.5 nm to 5 nm. DSC technique has an advantage of measuring continuously the process of C3S hydration by changes of free water in hydrated C3S.