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Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The long-term leachability of heavy metals from municipal solid waste incinerator (MSWI) bottom ash is of concern because of its potential use as a secondary construction material. Calcite is the most important long-term buffer in MSWI bottom ash as it buffers solutions during percolation and is an important factor in the control of heavy-metal mobility. It has been argued that biodegradation of residual organic material in the MSWI is a significant source of acidity. Model calculations have therefore been carried out to determine the influence of biodegradation on the longevity of the calcite buffer. Using the program STEADYQL, which couples thermodynamic equilibrium with kinetically controlled reactions, solution composition was estimated at steady state. The concentration of Ca dissolved from calcite was estimated in the presence and absence of gypsum as a function of the reaction rate of a number of slow reactions: aerobic, ferrogenic, sulfogenic, and methanogenic biodegradation; diffusion of O2 into the system; degassing of CO2 out of the system; and dissolution of Ca silicate. It was found that, independent of the rate, the biodegradation of organic matter had little influence on the longevity of the calcite buffer (between 2,000 and 3,000 yr for a deposit of 1 m in depth), that anaerobic biodegradation may have a slight retarding effect, and that calcite dissolution due to acid input via precipitation was negligible (around 3% of the total at reference conditions for rainwater with a pH value of 4.3).
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PMID:Influence of biodegradation processes on the duration of CaCO3 as a pH buffer in municipal solid waste incinerator bottom ash. 1182 54

The kinetics, reaction pathways and product distribution of oxidation of tetrachloroethylene (PCE) by potassium permanganate (KMnO4) were studied in phosphate-buffered solutions under constant pH, isothermal, completely mixed and zero headspace conditions. Experimental results indicate that the reaction is first-order with respect to both PCE and KMnO4 and has an activation energy of 9.3+/-0.9 kcal/mol. The second-order rate constant at 20 degrees C is 0.035+/-0.004 M(-1) s(-1), and is independent of pH and ionic strength (I) over a range of pH 3-10 and I approximately 0-0.2 M, respectively. The PCE-KMnO4 reaction may proceed through further oxidation and/or hydrolysis reaction pathways, greatly influenced by the acidity of the solution, to yield CO2(g), oxalic acid, formic acid and glycolic acid. Under acidic conditions (e.g., pH 3), the further oxidation pathway will dominate and PCE tends to be directly mineralized into CO2 and chloride. Under neutral (e.g., pH 7) and alkaline conditions (e.g., pH 10), the hydroxylation pathway dominates the reaction and PCE is primarily transformed into oxalic acid prior to complete PCE mineralization. Moreover, all chlorine atoms in PCE are rapidly liberated during the reaction and the rate of chloride production is very close to the rate of PCE degradation.
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PMID:Kinetics and mechanism of oxidation of tetrachloroethylene with permanganate. 1192 62

Luminol and 1,10-phenanthroline are widely used chemiluminescent (CL) reagents for the analysis of a wide range of metals and inorganic and organic complexes. While the fundamental mechanism for luminol and 1,10-phenantholine chemiluminescence is understood, the analytical application of these reagents is largely empirical and often poorly described mechanistically. For example, CL signals observed from metal-luminol systems are strongly dependent on the pH of the sample, even though the final pH of the reaction mixture is controlled to a narrow range by a buffer. Other investigators report significant changes in CL signal due to freshness and the acidity of reagents. Our work shows that many of these effects are due to dissolved CO2 present or formed in the analytical system. The hypothesis that carbon dioxide plays a pivotal role in enhancing luminol CL is supported by direct manipulation of CO2(aq) concentrations by the addition of CO2(g) or carbonic anhydrase. In contrast, Cu(II) analysis using the CL reagent 1,10-phenanthroline is completely quenched in the presence of CO2(aq). A plausible mechanism for these observations involves the reaction between superoxide, produced in these analytical systems, and CO2(aq) to form the peroxycarbonate radical, *C04-. The formation of *CO4- has very important analytical implications since this species appears to enhance or quench the CL signal from luminol and 1,10-phenanthroline, respectively.
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PMID:Carbon dioxide effects on luminol and 1,10-phenanthroline chemiluminescence. 1203 28

The optimised biodegradability test system "O2/CO2 Headspace Test with GC-TCD" is used for the assessment of synthetic ester lubricants. The effects of both additives and usage on biodegradability are examined and discussed. Ester based cutting fluids and hydraulic fluids with and without additives are used under defined conditions at machine tools and hydraulic and plain bearing test benches. The lubricants are characterised additionally with respect to kinematic viscosity, acidity and elemental composition. Furthermore, a formulated mineral oil is characterised before and after usage at an hydraulic test bench. The results clearly show that the mineral oil is far less biodegradable than the ester oils and that their biodegradability is not affected by usage. Biodegradability of the ester oils is mainly depending on the characteristics of the base fluids and not affected by the additives. Antioxidants are influencing stability respectively biodegradability indirectly, since they prevent oxopolymerisation effects. Other effects of usage on biodegradation are not detected. In this context, the antioxidants ensure ready biodegradability and have a positive effect on the environmental fate of synthetic ester lubricants.
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PMID:Biodegradability testing of synthetic ester lubricants--effects of additives and usage. 1213 62

The magnitude and extent of Crassulacean acid metabolism (CAM) activity in two Clusia species was manipulated to investigate the regulation of the distinct CAM phases. First, in response to leaf-air vapor pressure deficit at night, changes in leaf conductance altered on-line carbon-isotope discrimination throughout the theoretical range for dark CO2 uptake during CAM. These ranged from the limit set by phosphoenolpyruvate carboxylase (PEPc) (-6[per mille (thousand) sign], [delta]13C equivalent of -2[per mille (thousand) sign]) to that imposed by diffusion limitation (+4[per mille (thousand) sign], [delta]13C equivalent of -12[per mille (thousand) sign]), but the lowest carbon-isotope discrimination occurred when P[square root]pa was only 0.7. Second, when the availability of external or internal sources of CO2 was reduced for both field- and greenhouse-grown plants, CO2 uptake by day via PEPc during phase II largely compensated. Third, by reducing the dark period, plants accumulated low levels of acidity, and CO2 uptake occurred throughout the subsequent light period. Discrimination switched from being dominated by PEPc (phase II) to ribulose 1,5-bisphosphate carboxylase/oxygenase (phase III), with both enzymes active during phase IV. Under natural conditions, photochemical stability is maintained by extended PEPc activity in phase II, which enhances acid accumulation and delays decarboxylation until temperature and light stress are maximal at midday.
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PMID:Discrimination Processes and Shifts in Carboxylation during the Phases of Crassulacean Acid Metabolism. 1222 74

Diel courses of net CO2 exchange of leaves were studied in Clusia uvitana (Clusiaceae), a tropical Crassulacean acid metabolism (CAM) hemiepiphyte, growing in the crown of a 47-m tall kapok tree on Barro Colorado Island, Panama. Measurements on days without precipitation showed that net uptake of atmospheric CO2 occurred at night, a feature of CAM, as well as in the early morning and late afternoon. During 36 h of almost continuous rainfall, nocturnal net CO2 uptake was abolished and the diel pattern of net CO2 exchange became similar to that of a C3 plant. Exposing well-watered, potted plants of Clusia in the laboratory to temperatures and photosynthetic photon flux densities similar to those during the tropical rainstorm also abolished nocturnal net CO2 uptake. In contrast, Kalanchoe pinnata (Crassulaceae), an obligate CAM plant, still showed net CO2 dark fixation following the same low-light and moderate-temperature conditions, albeit at decreased rates. During these 12-h photoperiods, titratable acidity in Clusia increased slightly above its high level measured at the end of the previous dark period, whereas in Kalanchoe, the acid content decreased by about 40%. A survey among outer canopy leaves of Clusia on Barro Colorado Island showed that leaves that exhibited little or no nocturnal acidification maintained high levels of H+ at dawn and dusk. Progressively lower levels of H+ at dusk were accompanied by progressively higher nocturnal increases in H+. The data suggest that in C. uvitana the rapid switching between CAM- and C3-type carbon fixation that may occur within 24 h in response to environmental changes is controlled by the acidity status of the leaves in the light. Nocturnal CO2 fixation is enhanced by conditions that decrease the organic acid content during the light period.
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PMID:Short-Term Regulation of Crassulacean Acid Metabolism Activity in a Tropical Hemiepiphyte, Clusia uvitana. 1223 70

An attempt was made to isolate human strains of Bifidobacteria, all together 36, from fecal samples of 15 breast-fed infants ages 1-6 mo. These isolates were checked for their ability to grow in the presence of 1-3% bile, 0.2-0.4% phenol, and low pH (3.0-5.0) in vitro, to evaluate their capacity to grow under hostile and unfavorable conditions of the human digestive tract. Because milk is to be used as a carrier medium, their ability to grow in 10% sterile skim milk was also evaluated. The bifidobacteria count of the cultured milk samples (0, 24, and 48 h) was taken on tryptone yeast extract agar after 48 h of incubation in the presence of 10% CO2 at 37 degrees C. The changes in pH and developed titratable acidity were also recorded up to 96 h of incubation. The results indicated that all the isolates obtained had reasonable resistance to pH, bile, and phenol and were capable of growing well in milk. Among the 36 isolates, Bifidobacterium bifidum (isolates no. 4, 8, and 17) and B. breve (isolates no. 25 and 26) were the most tolerant to unfavorable conditions, and they may therefore be recommended for use in fermented milk or baby food formulations as probiotic dietary adjuncts.
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PMID:Selection of human isolates of Bifidobacteria for their use as probiotics. 1239 13

The induction of CAM in Pedilanthus tithymaloides (Euphorbiaceae) under water-limited conditions was evaluated by following diurnal oscillations of CO2 fixation, titratable acidity and malic acid content in the leaf extracts. CAM induction was assessed by measuring the activities of phosphoenolpyruvate carboxylase (PEPC), NADH-malate dehydrogenase (MDH) and phosphoenolpyruvate caroxykinase (PEPCK) in the leaves as well. Drought resulted in large increases in the nocturnal acid accumulation and rates of CO2 uptake in the leaves of P. tithymaloides. The drought-induced CAM activity tended to be reversible after re-watering. Nevertheless, under well-watered conditions, plants of P. tithymaloides showed day time CO2 uptake patterns with less pronounced diurnal oscillations of organic acids. Our data indicate that although P. tithymaloides is a CAM plant, environmental variables like drought induce photosynthetic flexibility in this species. This type of plasticity in CAM and metabolic versatility in P. tithymaloides should be an adaptation for prolonged survival under natural adverse edaphic and microclimate situations.
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PMID:Photosynthetic flexibility in Pedilanthus tithymaloides poit, a CAM plant. 1268 49

H(+) is maintained constant in the internal environment at a given body temperature independent of external environment according to Bernard's principle of "milieu interieur". But CO2 relates to ventilation and H(+) to kidney. Hence, the title of the chapter. In order to do this, sensors for H(+) in the internal environment are needed. The sensor-receptor is CO2/H(+) sensing. The sensor-receptor is coupled to integrate and to maintain the body's chemical environment at equilibrium. This chapter dwells on this theme of constancy of H(+) of the blood and of the other internal environments. [H(+)] is regulated jointly by respiratory and renal systems. The respiratory response to [H(+)] originates from the activities of two groups of chemoreceptors in two separate body fluid compartments: (A) carotid and aortic bodies which sense arterial P(O2) and H(+); and (B) the medullary H(+) receptors on the ventrolateral medulla of the central nervous system (CNS). The arterial chemoreceptors function to maintain arterial P(O2) and H(+) constant, and medullary H(+) receptors to maintain H(+) of the brain fluid constant. Any acute change of H(+) in these compartments is taken care of almost instantly by pulmonary ventilation, and slowly by the kidney. This general theme is considered in Section 1. The general principles involving cellular CO2 reactions mediated by carbonic anhydrase (CA), transport of CO2 and H(+) are described in Section 2. Since the rest of the chapter is dependent on these key mechanisms, they are given in detail, including the role of Jacobs-Stewart Cycle and its interaction with carbonic anhydrase. Also, this section deals briefly with the mechanisms of membrane depolarization of the chemoreceptor cells because this is one mechanism on which the responses depend. The metabolic impact of endogenous CO2 appears in the section with a historical twist, in the context of acclimatization to high altitude (Section 3). Because low P(O2) at high altitude stimulates the peripheral chemoreceptors (PC) increasing ventilation, the endogenous CO2 is blown off, making the internal milieu alkaline. With acclimatization however ventilation increases. This alkalinity is compensated in the course of time by the kidney and the acidity tends to be restored, but the acidification is not great enough to increase ventilation further. The question is what drives ventilation during acclimatization when the central pH is alkaline? The peripheral chemoreceptor came to the rescue. Its sensitivity to P(O2) is increased which continues to drive ventilation further during acclimatization at high altitude even when pH is alkaline. This link of CO2 through the O2 chemoreceptor is described in Section 4 which led to hypoxia-inducible factor (HIF-1). HIF-1 is stabilized during hypoxia, including the carotid body (CB) and brain cells, the seat of CO2 chemoreception. The cells are always hypoxic even at sea level. But how CO2 can affect the HIF-1 in the brain is considered in this section. CO2 sensing in the central chemoreceptors (CC) is given in Section 5. CO(2)/H(+) is sensed by the various structures in the central nervous system but its respiratory and cardiovascular responses are restricted only to some areas. How the membranes are depolarized by CO2 or how it works through Na(+)/Ca(2+) exchange are discussed in this section. It is obvious, however, that CO2 is not maintained constant, decreasing with altitude as alveolar P(O2) decreases and ventilation increases. Rather, it is the [H(+)] that the organism strives to maintain at the expense of CO2. But then again, [H(+)] where? Perhaps it is in the intracellular environment. Gap junctions in the carotid body and in the brain are ubiquitous. What functions they perform have been considered in Section 6. CO2 changes take place in lung alveoli where inspired air mixes with the CO2 from the returning venous blood. It is the interface between the inspired and expired air in the lungs where CO2 change is most dramatic. As a result, various investigators have looked for CO2 receptors in the lung, but none have been found in the mammals. Instead, CO2/H(+) receptors were found in birds and amphibians. However, they are inhibited by increasing CO2/H(+), instead of stimulated. But the afferent impulses transmitted to the brain produced stimulation in the efferents. This reversal of afferent-efferent inputs is a curious situation in nature, and this is considered in Section 7. The NO and CO effects on CO2 sensing are interesting and have been briefly mentioned in Section 8. A model for CO2/H(+) sensing by cells, neurons and bare nerve endings are also considered. These NO effects, models for CO2/H(+) and O2-sensitive cells in the CNS have been considered in the perspectives. Finally, in conclusion, the general theme of constancy of internal environment for CO2/H(+) is reiterated, and for that CO2/H(+) sensors-receptors systems are essential. Since CO2/H(+) sensing as such has not been reviewed before, the recent findings in addition to defining basic CO2/H(+) reactions in the cells have been briefly summarized.
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PMID:CO2/H(+) sensing: peripheral and central chemoreception. 1281 38

In an effort to understand the mechanisms that sustain rootless atmospheric plants, the modulation of Crassulacean acid metabolism (CAM) in response to variations in irradiance and water supply was investigated in the epiphyte Tillandsia usneoides. Plants were acclimated to three light regimes, i.e. high, intermediate and low, with integrated photon flux densities (PFD) of 14.40, 8.64 and 4.32 mol m-2 d-1 equivalent to an instantaneous PFD of 200, 100, and 50 mumol m-2 s-1, respectively. Daily watering was then withdrawn from half of the plants at each PFD for 7 d prior to sampling. In response to the three PFD treatments, chlorophyll content increased in plants acclimated to lower irradiances. Light response curves using non-invasive measurements of chlorophyll fluorescence demonstrated that photosystem II efficiency (phi PSII) was maintained in high PFD acclimated plants, as they exhibited a larger capacity for non-photochemical dissipation (NPQ) of excess light energy than low PFD acclimated plants. Net CO2 uptake increased in response to higher PFD, reflecting enhanced carboxylation capacity in terms of phosphoenolpyruvate carboxylase (PEPc) and ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activities. After water was withdrawn, nocturnal net CO2 uptake and accumulated levels of acidity declined in all PFD treatments, concomitant with increased respiratory recycling of malate. Examining the strategies employed by epiphytes such as T. usneodies to tolerate extreme light and water regimes has demonstrated the importance of physiological mechanisms that allow flexible carboxylation capacity and continued carbon cycling to maintain photosynthetic integrity.
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PMID:Physiological responses of the CAM epiphyte Tillandsia usneoides L. (Bromeliaceae) to variations in light and water supply. 1287 84


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