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

Biological N(2) fixation represents the major source of N input in agricultural soils including those in arid regions. The major N(2)-fixing systems are the symbiotic systems, which can play a significant role in improving the fertility and productivity of low-N soils. The Rhizobium-legume symbioses have received most attention and have been examined extensively. The behavior of some N(2)-fixing systems under severe environmental conditions such as salt stress, drought stress, acidity, alkalinity, nutrient deficiency, fertilizers, heavy metals, and pesticides is reviewed. These major stress factors suppress the growth and symbiotic characteristics of most rhizobia; however, several strains, distributed among various species of rhizobia, are tolerant to stress effects. Some strains of rhizobia form effective (N(2)-fixing) symbioses with their host legumes under salt, heat, and acid stresses, and can sometimes do so under the effect of heavy metals. Reclamation and improvement of the fertility of arid lands by application of organic (manure and sewage sludge) and inorganic (synthetic) fertilizers are expensive and can be a source of pollution. The Rhizobium-legume (herb or tree) symbiosis is suggested to be the ideal solution to the improvement of soil fertility and the rehabilitation of arid lands and is an important direction for future research.
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PMID:Rhizobium-legume symbiosis and nitrogen fixation under severe conditions and in an arid climate. 1058 71

The adsorption of tripsin and albumin on silicapolymetylsilocsan (SG-PMS) and its modified forms by cooper (II)--(SG-PMS (Cu)--from water-salt solutions were studied. It was determined difference in peculiarities of proteins sorption depending on its amino acids composition, chemistry of sorbent surface and acidity of medium. It was showed, that modified by cooper (II) sorbent have high affinity to tripsin than albumin in studied solutions. Influence of bearer modification degree on albumin immobilisation and interaction character of SG-PMS (Cu) active centres with function groups of enzyme and albumin have been showed.
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PMID:[Features of protein adsorption by silicopolymethylsiloxanes]. 1060 2

As part of a pilot study into the chemical and physical properties of Australian fine particles, a suite of aerosol samples was collected at Ti Tree Bend in Launceston, Tasmania, during June and July 1997. This period represents midwinter in the Southern Hemisphere, a period when aerosol sources in Launceston are dominated by smoke from domestic wood burning. This paper describes the results from this measurement campaign, with the aim of assessing the effect of wood smoke on the chemical and physical characteristics of ambient aerosol. A micro orifice uniform deposit impactor (MOUDI) was used to measure the size distributions of the aerosol from 0.05 to 20 microns aerodynamic diameter. Continuous measurements of fine particle mass were made using a PM2.5 tapered element oscillating microbalance (TEOM) and light scattering coefficients at 530 nm were measured with nephelometers. Mass size distributions tended to be bimodal, with the diameter of the dominant mode tending to smaller sizes with increases in total mass. Non-sea salt potassium and polycyclic aromatic hydrocarbons (PAHs) were used as chemical tracers for wood smoke. Wood smoke was found to increase absolute particle mass (enough to regularly exceed air quality standards), and to concentrate mass in a single mode below 1 micron aerodynamic diameter. The acid-base equilibrium of the aerosol was altered by the wood smoke source, with free acidity hydrogen ion, non-sea salt sulfate, and ammonium concentrations being higher and the concentration of all species, including nitrate (to differing extents), focused in the fine particle size ranges. The wood smoke source also heavily influenced the aerosol scattering efficiency, adding to a strong diurnal cycle in both mass concentration and light scattering.
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PMID:Size distribution and sources of aerosol in Launceston, Australia, during winter 1997. 1073 13

The empirical and mass balance approaches to setting critical loads of acidity for mineral soils have been evaluated using field data from forest sites in Wales. Using the Simple Mass Balance Equation (SMBE) with Sitka spruce as the biological target, critical loads ranged between 2.3 and 9.8 keq H+ ha(-1) year(-1) compared to mapped empirical critical loads which ranged between 0.2 and 0.5 keq H+ ha(-1) year(-1). At all sites the empirical critical load was exceeded with respect to deposited sulfur acidity. There were no exceeded sites for the SMBE critical loads. The big differences between the two methods arise from the large ANC leaching term in the SMBE model which is determined by the relatively low (Ca + Mg + K)/Al(crit) ratio for Sitka spruce, compared to other conifers, and the influence of the large deposition of sea salt base cations. The low value of the (Ca + Mg + K)/Al(crit) ratio for Sitka spruce implies that it is tolerant of very acidic soil conditions, however, the ratio is based on the results of only one solution culture study and may thus be uncertain under field conditions. Large sea salt base cation deposition directly influences SMBE critical loads because the predicted soil water base cation concentrations permit large concentrations of hydrogen ions and aluminium (low ANC values) before the critical chemical limit is transgressed. Where weathering rates are low, critical ANC leaching (ANC(lecrit)) becomes the dominant term in the SMBE, with the counter intuitive result that the critical load becomes a linear function of sea salt base cation deposition. Thus the current formulation of the SMBE may not be appropriate for low weathering rate areas receiving large amounts of sea salt base cation deposition.
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PMID:An evaluation of critical loads of soil acidity in areas of high sea salt deposition. 1084 40

The decarboxylation rate of the tetramethylguanidinium salt of 3-carboxy-6-nitrobenzisoxazole in 24 pure solvents and 36 dimethyl sulfoxide binary mixtures with diglyme, acetonitrile, benzene, dichloromethane, chloroform, and methanol was analyzed in the light of the SPP, SA, and SB pure solvent scales. The results allow one to rationalize the high sensitivity of this kinetics to the reaction medium and to assess the potential use of this compound as a probe in biochemical environments. The natural environment for comparison of this kinetics was found to be the gas phase rather than the aqueous medium. In the latter, the process is much faster owing to such high polarity, which, however, is strongly diminished by the high acidity of the medium. Based on our calculations, the rate constant for the decarboxylation kinetics in the gas phase must be in the region of 2 x 10(-10) s(-1) (i.e., 3 orders of magnitude smaller than in water).
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PMID:Effects of medium on decarboxylation kinetics: 3-carboxybenzisoxazoles and their potential use as environmental probes in biochemistry. 1084 24

The effect of ionic strength of the reaction medium on the pH optimum, specificity, and mechanism of action of the acid DNase isolated from mature eggs of the sea urchin Strongylocentrotus intermedius was studied. Changes in ionic strength of the reaction medium caused a displacement of the pH optimum of the enzyme to acidity or alkalinity. The region and range of this displacement depended on the buffer used and on the substrate structure. For single-stranded, duplex, and supercoiled forms of DNA, the pH optimum displacements were 1.0, 1.4, and 2.0 pH units, respectively. The pH optimum displacement changed the mechanism of action of the enzyme. Under optimum pH conditions, the enzyme cleaved supercoiled DNA only by the double-hit mechanism, and fragments of duplex DNA resulted due to the coincidence of breaks in opposite chains. On pH displacement to acidity, the enzyme acted by the mixed mechanism (single- and double-hit). And the quantitative ratio of products of the enzymatic hydrolysis of supercoiled DNA was significantly changed depending on the pH displacement to acidity or to alkalinity. The findings are explained by the effect of salt-dependent electrostatic interactions during the formation of a nonspecific DNA-enzyme complex.
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PMID:Effect of ionic strength on the pH optimum, specificity, and mechanism of action of acid DNase from mature eggs of the sea urchin Strongylocentrotus intermedius. 1100 89

Bilirubin, the yellow-orange tetrapyrrole pigment of jaundice, is essentially insoluble in pure water, but is much more soluble in solutions of bile salts such as sodium taurocholate. The biophysical chemistry of bilirubin in bile salt solutions is affected by changes in the pH of the solution in the range 5-9, suggesting that interactions with bile salt molecules and micelles may alter the acidity of the pigment. We have examined this possibility by determining the apparent pKa values for a series of carboxyl 13C-enriched model compounds, including the bilirubin analog mesobilirubin XIIIalpha, in solutions of sodium taurocholate and sodium taurodeoxycholate. Apparent pKa values were determined by 13C NMR titrations in dimethyl sulfoxide-water mixtures. The results show that the acidity of all compounds is decreased, or pKa increased, in micellar bile salt solution relative to pure water and that the effect is greatest for the larger, less water-soluble compounds. We have proposed a model to explain these results and discussed the implications of these findings for the biophysical chemistry of bilirubin in bile.
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PMID:Acid dissociation constants of bilirubin and related carboxylic acid compounds in bile salt solutions. 1101 23

Eight barrows (Yorkshire x [Finnish Landrace x Dutch Landrace]), initially 30 kg BW, were fitted with ileal cannulas to evaluate the effects of supplementing Ca benzoate (2.4%) and organic acids (OA) in the amount of 300 mEq acid/kg feed on dietary buffering capacity (BC), apparent digestibility and retention of nutrients, and manure characteristics. Swine were allotted in a 2 x 4 factorial arrangement of treatments according to a cyclic (8 x 5) changeover design. Two tapioca-corn-soybean meal-based diets were formulated without and with acidogenic Ca benzoate. Each diet was fed in combination with OA (none, formic, fumaric, or n-butyric acid). Daily rations were equal to 2.8 x maintenance requirement (418 kJ ME/BW(.75)) and were given in two portions. Chromic oxide (.25 g/kg) was used as a marker. On average, Ca benzoate lowered BC by 54 mEq/kg feed. This salt enhanced (P < .05) the ileal digestibility (ID) of DM, OM, arginine, isoleucine, leucine, phenylalanine, alanine, aspartic acid, and tyrosine (by up to 2.4 percentage units). Also, the total tract digestibility (TD) of DM, ash, Ca and GE, and Ca retention (percentage of intake) was greater (P < .05) in swine fed Ca benzoate, whereas N retention remained unaffected. Addition of all OA (formic and n-butyric acid, in particular) exerted a positive effect (P < .05) on the ID of amino acids (except for arginine, methionine, and cysteine). A similar effect (P < .05) was found for the TD of DM, OM, CP, Ca and total P and for the retention of N and Ca. In swine fed Ca benzoate, urinary pH decreased by 1.6 units (P < .001). In conclusion, dietary OA have a beneficial effect on the apparent ileal/total tract nutrient digestibilities, and Ca benzoate increased urine acidity, which could be effective against a rapid ammonia emission from manure of swine.
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PMID:The effects of calcium benzoate in diets with or without organic acids on dietary buffering capacity, apparent digestibility, retention of nutrients, and manure characteristics in swine. 1104 28

Two-electron reduction occurs when the Re(V) precursors ReOX3(PPh3)2 and ReO(OEt)X2(PPh3)2 are reacted with biimidazole (biimH2) in boiling chloroform, affording rhenium(III) cationic complexes of the type cis,trans-[ReX2(PPh3)2(biimH2)]X with X = Cl, Br, and I. Crystal structures are determined for the compounds with the three halogens, as well as for the [ReCl2(PPh3)2(biimH2)](benzoate) salt. In all cases, the counterion is attached to the complex cation via hydrogen bonding with the N-H groups of coordinated biimidazole. Variable-temperature 1H NMR spectroscopy shows that a mixture of [ReCl2(PPh3)2(biimH2)](benzoate) and [ReCl2(PPh3)2(biimH2)]Cl is in slow exchange below -50 degrees C in CD2Cl2, indicating that ion pairing is retained in solution. Both N-H groups can be deprotonated with sodium methoxide, and their acidities are evaluated from UV-visible spectra. Competition between monodeprotonated [ReCl2(PPh3)2(biimH)] and various carboxylic acids reveals that the acidity of the first N-H proton corresponds to that of acetic acid (pKa(aq) approximately 4.8). By a similar competitive reaction between bis-deprotonated [ReCl2(PPh3)2(biim)]- and phenols, the second acidity is estimated to be close to that of phenol (pKa(aq) approximately 9.8).
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PMID:Preparations, characterizations, and structures of (biimidazole)dihalobis(triphenylphosphine)rhenium(III) salts: strong ion-pairing and acid-base properties. 1119 66

Eight lake sites in central and south-west Scotland, north-west England and north Wales, forming part of the UK Acid Waters Monitoring Network (UKAWMN), have been studied with regard to the influence of marine ions on surface water chemistry. Since monitoring began in 1988 these sites have exhibited large and long-term variation in Cl concentration, which are consistent between regions and can be linked to inter-annual variations in wet deposition. Through regression analysis against Cl, the response of other solutes to these fluctuations has been assessed. Sites show a highly consistent pattern of Na, and Mg retention during periods of high Cl, in accordance with the 'sea-salt' mechanism of marine cation adsorption onto soil exchange sites following large marine inputs. An associated displacement of cations with non-marine sources is also observed, with one or more of non-marine Ca, labile Al and hydrogen ions exhibiting a positive relationship with Cl at all sites. The relative extent to which these are released appears not to follow a simple relationship to site acidity, and may be linked to site/region-specific geology and soil characteristics. In addition, an inverse relationship between non-marine SO4 and Cl is observed at five of the sites, and the possibility is considered that a sea-salt related process, with soil retention and subsequent release, may also operate for SO4. A mechanism that might explain this process is suggested. The impact of marine inputs on non-marine solutes, including important indicators of acidification such as pH, labile Al and non-marine SO4, has clear implications for the detection of long-term trends in acidity status and is, therefore, of particular relevance to the UKAWMN. Due to their unpredictability, and the long timescale over which they operate, fluctuations caused by marine inputs may be difficult to separate from acid deposition related long-term trends. Evidence from a longer Cl time series from mid-Wales shows that fluctuations in concentration could be linked to the North Atlantic Oscillation and might therefore be expected to exhibit a similar, decal periodicity. Currently, the UKAWMN dataset only appears long enough to represent one climatic cycle. Consequently, and since few surface water chemistry datasets in the UK extend over more than a decade, it is important that: (a) trend analyses of current data from marine-impacted areas take account of possible marine input cycles; and (b) long-term monitoring is maintained into the future so that the impact of these cycles can be better quantified, and distinguished from anthopogenically-induced long-term changes.
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PMID:Long-term variability in the deposition of marine ions at west coast sites in the UK Acid Waters Monitoring Network: impacts on surface water chemistry and significance for trend determination. 1122 59


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