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

The role of acidity in determining and restricting plant distribution and performance is discussed. In soils especially, a key effect of H+ ion concentration is on the solubility of potentially toxic heavy metals such as aluminum, managenese, zinc, iron, copper, and nickel. Al has been reported from many studies since the 1920's as the key determining toxic factor in acid soils. Some acid-tolerant species have been shown to be especially tolerant of Al, and mechanisms of tolerance have been suggested. Mn is also a commonly toxic factor at soil pH less than 5.0. Calcium has been shown to alleviate Mn toxicity. Low pH soils are also generally low in Ca, K, Na, and P; all essential major elements for plant growth. In lakes and marine situations acidic waters are uncommon as the waters are buffered. Calcium is again ameliorative of metal toxicities. The pH, redox, and valency state are critical in determining nutrient availability and metal speciation. Recent increases in the H+ ion content of precipitation have caused increased acidities of freshwater lakes in Scandinavia and eastern North America, which have depleted biota, including fish populations.
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PMID:Effect of H+ ion activity and Ca2+ on the toxicity of metals in the environment. 3 Dec 77

Aqueous solutions of polysorbate 20 undergo autoxidation on storage, with the peroxide number increasing and subsequently decreasing again, the acidity increasing continuously, the pH and surface tension falling and tending to level off, and the cloud point dropping sharply until turbidity begins at room temperature. The changes are accelerated by light, elevation of temperature, and a copper sulfate catalyst. At the same time, hydrolysis occurs, liberating lauric acid. Analysis of the alterations in these properties leads to the conclusion that hydrolysis has the major influence near room temperature and that oxyethylene undergoes chain shortening at temperatures above 40 degrees. However, evidence of degradation is detectable even in previously unopened commercial samples of polysorbates 20, 40, and 60, warranting attention to the stability of and standards for these surfactants as compared with the solid alkyl ether type of nonionic surfactant.
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PMID:Autoxidation of polysorbates. 3 49

A simple preconcentration procedure for mercury and copper was examined in the activation analysis of water samples. The preconcentration using pure activated carbon has been reported in several papers. The authors found that the carbon powder for emission spectroscopic analysis showed the high purity equivalent to pure activated carbon. The influence of various parameters in adsorption conditions was studied by radioactive tracers 197Hg and 64Cu. It was confirmed that 100% of these elements were adsorbed on carbon powders as pyrrolidine dithiocarbonate complexes at an acidity of pH 6--8, the temperature of 50 degrees C and the stirring time of 30 minutes. This method was applied to the activation analysis of the river water samples taken from the upper stream area of the Arakawa river and the ground water samples taken from the upper stream area of the Arakawa river and the ground water samples taken from the wells of the environs of Tokyo Megapolis. The carbon powders which adsorbed these elements were filtered, dried and analyzed by instrumental neutron activation analysis. The Hg concentrations of 0.01--0.1 ppb in river water and 0.03--1.4 ppb in ground water were obtained as well as the Cu concentrations of 0.3--3.0 ppb in ground water. The limits of determination of this method are 0.01 ppb Hg and 0.2 ppb Cu in the case of 11 sample of fresh water.
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PMID:[Determination of mercury and copper in water samples by activation analysis using preconcentration on emission spectroscopic carbon powder (author's transl)]. 70 56

Six experiments were conducted with male broiler chicks kept in battery brooders to investigate the effects of feeding diets high in copper on the integrity of the gizzard lining. Conventional and corn starch-soy basal diets were used. Slight improvements in body weight gain and/or feed efficiency were observed when the diets were supplemented with 250 p.p.m. copper as as CuSO4-5HSO, but higher levels (500 to 1000 p.p.m.) depressed growth and decreased feed efficiency. Little or no gizzard erosion was seen in birds fed the practical ration without added copper. Gizzard erosion was observed with 250 p.p.m. copper and the severity of the condition increased with higher levels. With the same level of copper supplementation, severity of gizzard erosion was greater when chicks were fed the corn starch-soy diet than when fed the practical diet. Adding 0.5 p.p.m. selenium to the practical diet containing 1000 p.p.m. copper slightly improved the appearance of the gizzard lining, although the subjective scoring index was significantly (P less than 0.05) lower in only one of two experiments. The addition of zinc, vitamin E, and vitamin B12 did not prevent the gizzard damage caused by high copper levels. Severity of gizzard erosion was significantly reduced by adding 0.35% cholic acid to the semipurified diet with 500 p.p.m. copper, but not to the practical diet with 100 p.p.m. copper. There was no correlation between acidity of the gizzard contents and severity of the erosion.
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PMID:Effect of high dietary copper on gizzard integrity of the chick. 93 76

After immersion of unpolished and polished high copper amalgam in saliva with different pH values for up to 12 weeks, the elements mercury, tin, copper, silver and antimony were analysed in the solution. Unpolished amalgam corroded more than polished amalgam. Corrosion increased with the time of immersion and the acidity of the solution. The values calculated to a maximum of clinical application not imply any toxicologic risk.
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PMID:[Toxicological assessment of amalgam components released in immersion tests]. 181 27

We have studied the mechanism by which liver Golgi apparatus maintains the acidity of its contents, using a subcellular fraction from rat liver highly enriched in Golgi marker enzymes. Proton accumulation (measured by quenching of acridine-orange fluorescence) and anion-dependent ATPase were characterized and compared. Maximal ATPase and proton accumulation required ATP; GTP and other nucleotides gave 10% to 30% of maximal activity. Among anions, Cl- and Br- approximately doubled the activities; others were much less effective. Half-maximal increase of ATPase and H+ uptake required 55 mmol/L and 27 mmol/L Cl-, respectively. In predominantly chloride media, SCN- and NO3- markedly inhibited H+ uptake. Nitrate competitively inhibited both the chloride-dependent ATPase (apparent Ki 6 mmol/L) and proton uptake (apparent Ki 2 mmol/L). Nitrate and SCN- also inhibited uptake of 36Cl. Replacing K+ with Na+ had no effect on the initial rate of proton uptake but somewhat reduced the steady state attained. Replacement of K+ with NH4+ and choline reduced proton uptake without affecting ATPase. The ATPase and H+ uptake were supported equally well by Mg2+ or Mn2+. The ATPase was competitively inhibited by 4-acetamido-4'-isothiocyano-stilbene-2,2'-disulfonic acid (apparent Ki 39 mumol/L). Other agents inhibiting both H+ uptake and ATPase were N-ethylmaleimide, N,N'-dicyclohexylcarbodiimide, chlorpromazine, diethylstilbestrol, Zn2+, Co2+ and Cu2+. In the Cl- medium, accumulated protons were released by ionophores at the relative rates, monensin = nigericin greater than valinomycin greater than carbonyl cyanide mchlorophenylhydrazone; the last of these also reduced ATPase activity. In the absence of Cl-, monensin and valinomycin both stimulated the ATPase. These results show a close association between ATPase activity and acidification of liver Golgi vesicles. They support a role for Cl- that depends on its uptake as a counter ion for H+ and suggest that it may also stimulate proton transport by a more direct effect on a component of the transport system.
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PMID:Proton accumulation and ATPase activity in Golgi apparatus-enriched vesicles from rat liver. 184 95

The objective of this study was to determine the in vitro corrosion products that resulted from crevice corrosion of low- and high-copper dental amalgams. Specimens were potentiostatically polarized in a chloride-containing electrolyte while set against a PTFE surface to form a crevice. After 16 h, corrosion products were examined by light microscopy, SEM, EDS, and XRD. Analysis showed the presence of three previously reported products [Sn4(OH)6Cl2, SnO, and Cu2O] and a new product, CuCl, which formed on high-copper, gamma 2-free amalgams. Thermodynamic considerations show that CuCl is stable for the reported in vivo potentials of amalgam restorations and the high acidity and high chloride ion concentration associated with crevice corrosion.
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PMID:Crevice corrosion products of dental amalgam. 206 90

This study evaluated the cytotoxic effects of three common restorative materials on early passage cultured cells derived from human gingiva (HG cells). Other early passage cultured cells derived from human dental pulp tissues (HP cells) and L cells established obtained from mouse subcutaneous tissues, were also examined. Cytotoxicity was assessed according to the uptake of neutral red and dye exclusion with nigrosin. The cytotoxicity was in the order of glass ionomer cement (highest), light cured composite resin and dental amalgam. HG cells were the least sensitive to the materials tested. Both filtration of extracts and addition of serum into the extract affected the cytotoxicity. Glass ionomer cement increased the acidity of the extract, but the two other materials did not. Dissolution of metal ions, aluminium, tin, copper, mercury and zinc occurred from the materials. The extract of the composite resin had a different absorbance. This study disclosed differences in the cellular reaction to the restorative materials. Thus, utilization of early passage cultured cells is necessary for biological evaluation of the dental materials in vitro.
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PMID:[Cytotoxic effects of restorative materials on early passage cultured cells derived from human gingiva (in vitro)]. 213 20

The superoxide dismutase (SOD) mimetic reactivity of Cu(II)EDTA was studied in the pH range of 6.0 to 8.0. Cu(II)EDTA disproportionated superoxide without inhibiting superoxide production by xanthine oxidase, as a result of bonding sites becoming available on the copper complex with increasing acidity. This disproportionation by Cu(II)EDTA is offered as evidence that the addition of EDTA to biological preparations for the purpose of complexing copper and thereby inhibiting copper-dependent superoxide disproportionation and promoting superoxide-dependent reactions is not a valid practice.
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PMID:Copper(II)ethylenediaminetetraacetate does disproportionate superoxide. 282 69

The proton nuclear magnetic resonance spectrum of azurin from Alcaligenes denitrificans at pH 6.0 and 309 K is reported. Proton signals from all methionine and histidine residues (among them the copper ligands) have been assigned. The data have been used to study the pH behaviour of His35 and to establish the electron self-exchange rate of the protein. His35 appears to be protonated at pH less than 4.5, possibly after rupture of a salt bridge. No effects of this protonation on the tertiary structure around the copper site are observed, however, contrary to the case of Pseudomonas aeruginosa azurin. The electron self-exchange rate amounts to 4 x 10(5) M-1 S-1 at pH 6.7 and 297 K. The data support the conclusion that the electron self-exchange takes place by way of the hydrophobic surface patch around His117, and that His35 is not involved in this reaction. Oxidation of azurin increases the acidity of the freely titrating His32 and His83 by 0.07 and 0.25 pKa units, respectively. The data can be used to test the theory of electrostatic interactions in proteins. The optical extinction coefficient at 625 nm was experimentally determined and amounts to 4.8(+/- 0.1) x 10(3) M-1 cm-1.
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PMID:1H nuclear magnetic resonance study of the protonation behaviour of the histidine residues and the electron self-exchange reaction of azurin from Alcaligenes denitrificans. 283 76


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