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Concept: Acid dissociation constant

170

The comparison of volumes of cells and subcellular structures with the pH values reported for them leads to a conflict with the definition of the pH scale. The pH scale is based on the ionic product of water, K(w) = [H(+)]×[OH(-)].We used K(w) [in a reversed way] to calculate the number of undissociated H(2)O molecules required by this equilibrium constant to yield at least one of its daughter ions, H(+) or OH(-) at a given pH. In this way we obtained a formula that relates pH to the minimal volume V(pH) required to provide a physical meaning to K(w), [Formula: see text] (where N(A) is Avogadro’s number). For example, at pH 7 (neutral at 25°C) V(pH) = 16.6 aL. Any deviation from neutral pH results in a larger V(pH) value. Our results indicate that many subcellular structures, including coated vesicles and lysosomes, are too small to contain free H(+) ions at equilibrium, thus the definition of pH based on K(w) is no longer valid. Larger subcellular structures, such as mitochondria, apparently contain only a few free H(+) ions. These results indicate that pH fails to describe intracellular conditions, and that water appears to be dissociated too weakly to provide free H(+) ions as a general source for biochemical reactions. Consequences of this finding are discussed.

Concepts: Acid, PH indicator, Chemistry, Atom, Activity, Equilibrium constant, Acid dissociation constant, PH

138

Separation of volatile fatty acids (VFAs) from fermented wastewater is challenging, due to low VFA concentrations in mineral-rich streams. As a result, separation capacity and selectivity with traditional solvents and adsorbents are both compromised. In this study, using a complex artificial model solution mimicking real fermented wastewaters, it is shown that a simple and robust adsorption-based separation technique can retain a remarkable capacity and selectivity for VFAs. Four types of polystyrene-divinylbenzene-based resins (primary, secondary, and tertiary amine-functionalized, and nonfunctionalized) were examined as the adsorbents. The presence of chloride, sulfate, and phosphate salts resulted in coadsorption of their acidic forms HCl, H2SO4, and H3PO4 on amine-functionalized adsorbents, and severely reduced the VFA capacity. With the nonfunctionalized adsorbent, almost no mineral acid coadsorption was observed. This together with a high total VFA capacity of up to 76 g/kg in equilibrium with the model solution containing a total VFA concentration of 1 wt % resulted in a very high selectivity for the VFAs. Nitrogen-stripping with various temperature profiles was applied to regenerate the adsorbent, and study the potential for fractionation of the VFAs during regeneration. Butyric acid (HBu) was obtained in mole fractions of up to 0.8 using a stepwise increase in the stripping temperature from 25 °C via 120 to 200 °C. During four successive adsorption-regeneration cycles, no reduction in the adsorption capacity was observed.

Concepts: Acid dissociation constant, Chlorine, Water, Salt, Butyric acid, Carbon dioxide, Acid, Phosphoric acid

96

Thioesters and thioacetic acid (TAA) have been invoked as key reagents for the origin of life as activated forms of acetate analogous to acetyl-CoA. These species could have served as high-energy group-transfer reagents and allowed carbon insertions to form higher molecular weight compounds such as pyruvate. The apparent antiquity of the Wood-Ljungdahl CO2 fixation pathway and its presence in organisms which inhabit hydrothermal (HT) environments has also led to suggestions that there may be a connection between the abiotic chemistry of compounds similar to TAA and the origins of metabolism. These compounds' apparent chemical simplicity has made their prebiotic availability assumed, however, although the kinetic behavior and thermochemical properties of TAA and analogous esters have been preliminarily explored in other contexts, the geochemical relevance of these compounds merits further evaluation. Therefore, the chemical behavior of the simplest thiolated acetic acid derivatives, TAA and methylthioacetate (MTA) were explored here. Using laboratory measurements, literature data, and thermochemical models, we examine the plausibility of the accumulation of these compounds in various geological settings. Due to the high free energy change of their hydrolysis and corresponding low equilibrium constants, it is unlikely that these species could have accumulated abiotically to any significant extant.

Concepts: Gibbs free energy, Life, Molecule, Carbon dioxide, Carboxylic acid, Chemistry, Acid dissociation constant, Acetic acid

72

The International Society of Sports Nutrition (ISSN) provides an objective and critical review of the mechanisms and use of beta-alanine supplementation. Based on the current available literature, the conclusions of the ISSN are as follows: 1) Four weeks of beta-alanine supplementation (4-6 g daily) significantly augments muscle carnosine concentrations, thereby acting as an intracellular pH buffer; 2) Beta-alanine supplementation currently appears to be safe in healthy populations at recommended doses; 3) The only reported side effect is paraesthesia (tingling), but studies indicate this can be attenuated by using divided lower doses (1.6 g) or using a sustained-release formula; 4) Daily supplementation with 4 to 6 g of beta-alanine for at least 2 to 4 weeks has been shown to improve exercise performance, with more pronounced effects in open end-point tasks/time trials lasting 1 to 4 min in duration; 5) Beta-alanine attenuates neuromuscular fatigue, particularly in older subjects, and preliminary evidence indicates that beta-alanine may improve tactical performance; 6) Combining beta-alanine with other single or multi-ingredient supplements may be advantageous when supplementation of beta-alanine is high enough (4-6 g daily) and long enough (minimum 4 weeks); 7) More research is needed to determine the effects of beta-alanine on strength, endurance performance beyond 25 min in duration, and other health-related benefits associated with carnosine.

Concepts: Buffering agent, Effects unit, Paresthesia, Effect, Acid dissociation constant, Nutrition, Buffer solution, PH

28

The importance of the effective membrane charge on the electrophoretic behavior of a soft spherical particle comprising a rigid core and a charge-regulated membrane layer, mimicking both inorganic and biological colloids, is investigated. The mobility of the particle is simulated under various conditions by varying the double layer thickness, the bulk solution pH, and the charged conditions of the membrane layer. Several interesting electrophoretic behaviors that are of practical significance, are observed. For example, the particle mobility can be controlled by adjusting its properties such as the ratios of (acidic equilibrium constant/basic equilibrium constant) and (concentration of acidic functional groups/that of basic functional groups). Double layer polarization (DLP) is found to render the soft particle having behaviors different from those of the corresponding rigid particle. For instance, DLP can either be intensified or weakened, depending upon the strength of the hydrodynamic force and the electric force acting on the membrane layer. As the bulk electrolyte concentration increases in a certain range, because double layer shrinks into the membrane layer, its effective charge density increases, so is the particle mobility.

Concepts: Acid dissociation constant, Density, Psychology, Fundamental physics concepts, Zeta potential, Electromagnetism, PH, Electric charge

28

Controlling pH is essential for a variety of biopharmaceutical process steps. The chemical stability of biologics such as monoclonal antibodies is pH-dependent and slightly acidic conditions are favorable for stability in a number of cases. Since control of pH is widely provided by added buffer salts, the current study summarizes the buffer characteristics of acetate, citrate, histidine, succinate and phosphate buffers. Experimentally derived values largely coincide with values calculated from a model that had been proposed in 1922 by van Slyke. As high concentrated protein formulations become more and more prevalent for biologics, the self-buffering potential of proteins becomes of relevance. The current study provides information on buffer characteristics for pH ranges down to 4.0 and up to 8.0 and shows that a monoclonal antibody at 50 mg/ml exhibits similar buffer capacity as 6 mM citrate or 14 mM histidine (pH 5.0-6.0). Buffer capacity of antibody solutions scales linearly with protein concentration up to more than 200 mg/ml. At a protein concentration of 220 mg/ml, the buffer capacity resembles the buffer capacity of 30 mM citrate or 50 mM histidine (pH 5.0-6.0). The buffer capacity of monoclonal antibodies is practically identical at the process relevant temperatures 4°C, 25°C and 40°C. Changes in ionic strength of ΔI = 0.15, in contrast, can alter the buffer capacity up to 35 %. In conclusion, due to efficient self-buffering by antibodies in the pH range of favored chemical stability, conventional buffer excipients could be dispensable for pH stabilization of high concentrated protein solutions. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 2013.

Concepts: Salt, Chemistry, Acid dissociation constant, Buffering agent, Protein, Acid, PH, Buffer solution

28

A stable, label-free optical biosensor based on a porous silicon-carbon (pSi-C) composite is demonstrated. The material is prepared by electrochemical anodization of crystalline Si in an HF-containing electrolyte to generate a porous Si template, followed by infiltration of poly(furfuryl) alcohol (PFA) and subsequent carbonization to generate the pSi-C composite as an optically smooth thin film. The pSi-C sensor is significantly more stable toward aqueous buffer solutions (pH 7.4 or 12) compared to thermally oxidized (in air, 800 °C), hydrosilylated (with undecylenic acid), or hydrocarbonized (with acetylene, 700 °C) porous Si samples prepared and tested under similar conditions. Aqueous stability of the pSi-C sensor is comparable to related optical biosensors based on porous TiO(2) or porous Al(2)O(3). Label-free optical interferometric biosensing with the pSi-C composite is demonstrated by detection of rabbit IgG on a protein-A-modified chip and confirmed with control experiments using chicken IgG (which shows no affinity for protein A). The pSi-C sensor binds significantly more of the protein A capture probe than porous TiO(2) or porous Al(2)O(3), and the sensitivity of the protein-A-modified pSi-C sensor to rabbit IgG is found to be ∼2× greater than label-free optical biosensors constructed from these other two materials.

Concepts: Acid, Optical fiber, Chemistry, Acid dissociation constant, Buffer solution, Electrochemistry, PH, Biosensor

27

A simple, selective and stability-indicating high-pressure liquid chromatographic method was developed for the analysis of ribavirin. Chromatographic separation was achieved by using a CPS Hypersil cyano column (4.6 × 250 mm, 5 µm particle size) with isocratic elution of the mobile phase, which was composed of 50 mM phosphate buffer, adjusted at pH 4 with phosphoric acid. The mobile phase was pumped at a flow rate of 0.8 mL/min. The detector was set at 240 nm and quantification of the analyte was based on peak area measurement. The method was validated with respect to linearity, range, precision, accuracy, selectivity, robustness, limit of detection and limit of quantitation. The calibration curve was linear in the range of 5-200 µg/mL with correlation coefficient > 0.999. Ribavirin was subjected to forced degradation studies under two conditions: mild and extensive stress testing. These studies included the effects of hydrolysis (neutral, acidic and alkaline) and oxidation, photolysis and dry heat). The proposed method was proved to be stability-indicating by the resolution of the drug from its forced degradation products, making use of the diode array detector as a tool for confirmation of peak identity and purity. Moreover, the kinetics of alkaline degradation of ribavirin were investigated, an Arrhenius plot was constructed and the activation energy was calculated. The developed method was also extended to analyze ribavirin in capsules and in human plasma with good recovery values.

Concepts: Detection limit, Acid dissociation constant, Phosphoric acid, Acid, Measurement, PH, Chromatography, Analytical chemistry

27

This article describes the production of an anti-citrinin antibody that showed a high affinity constant (Ka) of 6.28 × 10(9) and good tolerance to organic solvent and low pH, the synthesis of a Cu (II)-embedded polymer that showed strong binding with this antibody and the preparation of packing material for an immunoaffinity column (IAC) that show good stability. Most of the IACs reported either use harsh elution conditions and are used only once or use gentle elution conditions and are reused many times. Here, through the combined use of a strong-affinity antibody and packing material with good stability, high recoveries during clean-up and yet simultaneously good stability of the IAC were successfully achieved. Under optimised conditions of 80% methanol (pH 3), the IACs were used to clean-up the extracts of Monascus colour and red yeast rice samples, followed by HPLC detection. The recoveries of citrinin from spiked samples at levels of 50-200 μg kg(-1) were in the range of 84-97%.

Concepts: Acid dissociation constant, Acetic acid, Red yeast rice, Methanol, PH, Monascus purpureus, Solvent, Ethanol

27

Bimetallic iron nanoparticles have mostly been applied to the degradation of chlorinated compounds in the aqueous phase. In this study, the degradation of pentachlorophenol (PCP) spiked into sandy soil is considered as a first exploratory step for remediating PCP in real contaminated soil using a commercial preparation of bimetallic iron (Trade name BioCAT). After 21 days of treatment a PCP removal efficiency of 90% was achieved, along with 70% dechlorination efficiency, for a dosage of 600mg BioCAT slurry/kg soil. Degradation of PCP by BioCAT follows first order kinetics in PCP. Stepwise dechlorination is the main pathway of PCP elimination from soil slurries contacted with BioCAT. Such dechlorination is confirmed by the appearance of intermediate products, as well as by release of chlorides. Additionally, the increasing pH value and the rapid decrease of the oxidation/reduction potential (ORP) also attest to the reductive dechlorination of PCP. The reaction products comprehend lower chlorinated phenols, including three TeCP isomers, four TrCP isomers, four DCP isomers, two MCP isomers and phenol. These findings indicate that BioCAT could be applied for field treatment of PCP-contaminated soil under ambient conditions.

Concepts: Hydrochloric acid, Enzyme, Environmental chemistry, Acid dissociation constant, Phenols, Environmental remediation, Anthocyanin, Water