Quantification Of Reaction Products Research Articles

Efficacy of functionalized sodium-montmorillonite in mitigating alkali-silica reaction

Alkali-silica reaction (ASR) is a fatal deterioration that can cause volume expansion, cracking, and premature failure of concrete. In this study, the efficacy of sodium montmorillonite (NaMt) organically functionalized with two non-ionic surfactants (ONaMts) in mitigating ASR is investigated by determining the expansion and cracking behavior of mortars containing reactive aggregates. The underlying mitigation mechanisms were analyzed through the quantification of reaction products and in-situ characterizations of ASR gels. The results revealed that, compared with raw NaMt, ASR-induced expansion and cracking can be more substantially mitigated in the presence of ONaMts, which is supported by the improved consumption of portlandite and reduced formations of both crystalline and amorphous ASR gels. The functionalized ONaMts appeared to further suppress the formation of Q3 polymerization sites, decrease the [K + Na]/Si atomic ratio and increase the Al/Ca in ASR gels.

Microstructure as a key parameter for understanding chloride ingress in alkali-activated mortars

This study aims to evaluate the influence of microstructural properties on the chloride diffusion resistance of alkali-activated materials (AAMs) based on blast furnace slag and/or fly ash, with variable activator doses (represented as Na2O%). Resistance to chloride penetration was tested using accelerated chloride penetration (NT BUILD 443) and chloride migration (NT BUILD 492) tests. Addition of slag to alkali-activated mortars mainly based on fly ash reduced porosity and chloride permeability. Chloride penetration decreased with increasing Na2O%, but porosity and pore structure did not follow the same trend. The pore threshold (dth) and critical pore radius (rcrit) determined by mercury intrusion porosimetry had a good correlation with the chloride diffusion coefficient. Both the quantification of reaction products and the correlation between chloride penetration and pore surface area indicated that physical chloride adsorption on the C-A-S-H/N-A-S-H gel surfaces predominated over chemical chloride binding.

Interactions of Ascorbic Acid, 5-Caffeoylquinic Acid, and Quercetin-3-Rutinoside in the Presence and Absence of Iron during Thermal Processing and the Influence on Antioxidant Activity.

Bioactive compounds in fruit and vegetables influence each other’s antioxidant activity. Pure standards, and mixtures of the common plant compounds, namely ascorbic acid, 5-caffeoylquinic acid, and quercetin-3-rutinoside (sum 0.3 mM), in the presence and absence of iron, were analyzed pre- and post-thermal processing in an aqueous solution. Antioxidant activity was measured by total phenolic content (TPC), 1,1-diphenyl-2-picrylhydrazyl (DPPH), and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (TEAC) radical-scavenging assays. Ionic ferrous iron (Fe2+) and ferric iron (Fe3+) were measured photometrically. For qualification and quantification of reaction products, HPLC was used. Results showed that thermal processing does not necessarily lead to a decreased antioxidant activity, even if the compound concentrations decreased, as then degradation products themselves have an antioxidant activity. In all used antioxidant assays the 2:1 ratio of ascorbic acid and 5-caffeoylquinic acid in the presence of iron had strong synergistic effects, while the 1:2 ratio had strong antagonistic effects. The pro-oxidant iron positively influenced the antioxidant activity in combination with the used antioxidants, while ferrous iron itself interacted with common in vitro assays for total antioxidant activity. These results indicate that the antioxidant activity of compounds is influenced by factors such as interaction with other molecules, temperature, and the minerals present.

Thermogravimetric analysis of the gasification of microalgae Chlorella vulgaris

The gasification of microalgae Chlorella vulgaris under an atmosphere of argon and water vapor was investigated by thermogravimetric analysis. The data were interpreted by using conventional isoconversional methods and also by the independent parallel reaction (IPR) model, in which the degradation is considered to happen individually to each pseudo-component of biomass (lipid, carbohydrate and protein). The IPR model allows obtaining the kinetic parameters of the degradation reaction of each component. Three main stages were observed during the gasification process and the differential thermogravimetric curve was satisfactorily fitted by the IPR model considering three pseudocomponents. The comparison of the activation energy values obtained by the methods and those found in the literature for other microalgae was satisfactory. Quantification of reaction products was performed using online gas chromatography. The major products detected were H2, CO and CH4, indicating the potential for producing fuel gas and syngas from microalgae.

A Method for the Determination of Soluble Arabinoxylan Released from Insoluble Substrates by Xylanases

The propensity for xylanase to convert insoluble to soluble arabinoxylan is an important parameter in many applications. Current methods for determining xylanase activity on insoluble substrates are nonspecific or utilize artificial substrates which may provide much different results from native substrates. Therefore, a new method for the determination of xylanase activity on insoluble substrates was developed. This method involved incubation of the enzyme with a material containing insoluble arabinoxylan. Arabinoxylan released by the enzyme was quantified as total pentose sugars colorimetrically by reaction with phloroglucinol upon heating in acetic–hydrochloric acid. Absorbance was determined at 552 nm, and interfering hexoses were accounted for by subtracting the absorbance at 510 nm. Because the method measured total pentose sugars released by the enzyme, (arabino)xylanase activity, rather than xylanase activity, was recommended for expressing results. The method was tested using two xylanases and six insoluble arabinoxylan-containing substrates. Sodium acetate and sodium citrate buffers (50 mM) were suitable for the reaction; sodium phosphate buffer substantially interfered with quantification of reaction products by reducing color development. The enzymic release of soluble arabinoxylan was linear for at least 5 min under all reaction conditions tested. Contaminating amylase and cellulase activity did not influence the results, despite the presence of starch and cellulose in many substrate sources. Relative standard deviations were <5% between reactions assayed on different days. Activity on substrates from different botanical origin differed by up to 100-fold, emphasizing the need for the use of application-specific substrates to obtain accurate estimations of enzyme activity.

Quantitative Mass Measurements from Mass Spectrometer Trend Data in a TG/MS System

Abstract The use of mass spectrometry (MS) in the identification of evolved gaseous species in thermogravimetric (TG) experiments is well established. The mass spectrometer can be attached directly to the outgas port of the thermogravimetric instrument. Mass spectrometers have the ability to detect species to 1 ppm or better, and the detection is done in real time as the TGA scans. Typically, the mass spectrometer is used for identification only. However, there are situations where it would be desirable to quantify the MS data. For example, when two or more species are evolved during a weight transition, the total weight loss is known from the TGA, but the weights for the individual components are unknown. Calibration techniques for quantifying MS data are already well established. Following one of these techniques, we show that trend data from a mass spectrometer can be used to approximate the amount of material evolved for low m/e ratio species such as water and carbon dioxide. The process involves first calibrating the system using a sample that only gives off the gaseous species of interest. Multiple runs at different initial weights provide the data for the calibration. A correlation between mass loss as measured by the TGA and ion current increase as measured by the MS is then constructed. In this study, the technique is applied not only to overlapping transitions but also to the quantification of reaction products from gases released during a TGA experiment. An attempt is also made to quantify the accuracy of the technique.

Both High Mobility Group (HMG)-boxes and the Acidic Tail of HMGB1 Regulate Recombination-activating Gene (RAG)-mediated Recombination Signal Synapsis and Cleavage in Vitro

RAG-1 and RAG-2 initiate V(D)J recombination through synapsis and cleavage of a 12/23 pair of V(D)J recombination signal sequences (RSS). RAG-RSS complex assembly and activity in vitro is promoted by high mobility group proteins of the "HMG-box" family, exemplified by HMGB1. How HMGB1 stimulates the DNA binding and cleavage activity of the RAG complex remains unclear. HMGB1 contains two homologous HMG-box DNA binding domains, termed A and B, linked by a stretch of basic residues to a highly acidic C-terminal tail. To identify determinants of HMGB1 required for stimulation of RAG-mediated RSS binding and cleavage, we prepared an extensive panel of mutant HMGB1 proteins and tested their ability to augment RAG-mediated RSS binding and cleavage activity. Using a combination of mobility shift and in-gel cleavage assays, we find that HMGB1 promotes RAG-mediated cleavage largely through the activity of box B, but optimal stimulation requires a functional A box tethered in the correct orientation. Box A or B mutants fail to promote RAG synaptic complex formation, but this defect is alleviated when the acidic tail is removed from these mutants.

Gaseous and Particulate Oxidation Products Analysis of a Mixture of α-pinene + β-pinene/O3/Air in the Absence of Light and α-pinene + β-pinene/NOx/Air in the Presence of Natural Sunlight

The gas and particle phase reaction products of a mixture of the atmospherically important terpenes α-pinene and β-pinene with the atmospheric oxidants O3 and OH/NOx were investigated using both gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC) for identification and quantification of reaction products. The nighttime oxidation of a mixture of α-pinene and β-pinene in the presence of O3/air, and the daytime oxidation of a mixture of α-pinene + β-pinene with NOx air in the presence of natural sunlight were carried out in the University of North Carolina's large outdoor smog chamber (190 m3) located in Chatham County, North Carolina. Mass balances for gaseous and aerosol reaction products are reported over the course of the reaction. More than twenty-nine products were identified and/or quantified in this study. On average, measured gas and particle phase products accounted for ∼74 to ∼80% of the reacted α-pinen/β-pinene mixture carbon. Measurements show that a number of reaction products were found in both O3 and NOx system [pinonaldehyde, pinic acid, pinonic acid, pinalic-3-acid, 4-hydroxypinalic-3-acid, 4-oxonopinone, 1-hydroxy-nopinone, 3-hydroxy-nopinone, and nopinone]. Pinonic acid, pinic acid, pinalic-3-acid, 4-hydroxypinalic-3-acid, and 10-hydroxypinonic acid were observed in the early stage in the aerosol phase and may play an important role in the early formation of secondary aerosols.

Mass Balance of Gaseous and Particulate Products from β-Pinene/O3/Air in the Absence of Light and β-Pinene/NOx/Air in the Presence of Natural Sunlight

The gas and particle phase products from the reaction of β-pinene with the atmospheric oxidants O3 and OH radicals in the presence of NOx were investigated using both gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC) for identification and quantification of reaction products. The nighttime oxidation of β-pinene in the presence of O3/air and the daytime oxidation of β-pinene in the presence of NOx/air and natural sunlight were carried out in the University of North Carolina large outdoor smog chamber (190 m3) located in Chatham County, North Carolina. A Scanning Mobility Particle Sizer system (3936, TSI) and a Condensation Particle Counter (3025A, TSI) were used to study the secondary organic aerosol (SOA) formation, and a filter pack/denuder sampling system was used for simultaneously collecting gas and particle phase products for analysis. A gas chromatograph coupled to a mass spectrometer (GC-EIMS or GC-CIMS) was used for the identification and quantification of gas and aerosol products. A HPLC method was used for the measurement of small carbonyl compounds (aldehydes and ketones) as their 2,4-dinitrophenylhydrazones (DNPH) derivatives. Mass balances for gaseous and aerosol reaction products were reported over the course of the reaction. More than sixteen products were identified and/or quantified in this study. On average, measured gas and particle phase products accounted for ∼57 to ∼71% of the reacted β-pinene carbon. Measurements showed that a number of reaction products were found in both O3 and NOx systems (pinic acid, pinalic-3-acid, 4-hydroxypinalic-3-acid, 4-oxonopinone, 1-hydroxynopinone, 3-hydroxynopinone, and nopinone). Pinic acid, pinalic-3-acid, and 4-hydroxypinalic-3-acid were observed in the early stage in the aerosol phase and may play an important role in the early formation of secondary aerosols. Detailed reaction schemes are presented to account for most of the observed reaction products.

Association-dissociation studies of bovine and rat liver glutamic dehydrogenase by high-performance liquid chromatography gel filtration

The concentration-dependent association-dissociation tendency of purified bovine liver and rat liver glutamic dehydrogenase (GDH) has been demonstrated by high-performance liquid Chromatographic gel filtration. In the concentration range of 100 to 1.0 μg bovine GDH/ml molecular species ranged from dimer and unimer to subunimeric forms. The dissociation process of the unimeric hexapeptide, consisting of six polypeptide chains, to the subunimeric tripeptide, consisting of three polypeptide chains, was irreversible without added ionic support, but reversible with added ionic support. In dilute Tris-HCl bovine liver GDH was dispersed to subunimeric sizes. Increasing the ionic strength in 20 m m phosphate as the mobile phase increased dissociation to a subunimeric tripeptide while sustaining as much as 80% of its activity. Activity of a eluting subunimer was verified by the inclusion of reaction substrates (NAD and glutamute) in the mobile phase and quantification of reaction products (NADH) in chromatograms. Gel filtration of GDH in the presence of GTP with NADH rendered a subunimeric tripeptide, largely independent of ionic strength or GDH concentration. Rat liver GDH, differing from bovine liver GDH, was dissociated by gel filtration to an active tripeptide independent of ionic or buffer conditions.