Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The synthesis of (Dien)Pt(PMEA-N1), where Dien = diethylenetriamine and PMEA2- = dianion of 9-[2-(phosphonomethoxy)ethyl]adenine, is described. The acidity constants of the threefold protonated H3[(Dien)Pt(PMEA-N1)]3+ complex were determined and in part estimated (UV spectrophotometry and potentiometric pH titration): The release of the proton from the (N7)H+ site in H4[(Dien)Pt(PMEA-N1)]3+ occurs with a rather low pKa (= 0.52+/-0.10). The release of the proton from the -P(O)2(OH) group (pKa = 6.69+/-0.03) in H[(Dien)Pt(PMEA-N1)]+ is only slightly affected by the N1-coordinated (Dien)Pt2+ unit. Comparison with the acidic properties of the H[(Dien)Pt(PMEA-N7)]+ species provides evidence that in the (Dien)Pt(PMEA-N7) complex in aqueous solution an intramolecular, outer-sphere macrochelate is formed through hydrogen bonds between the -PO3(2-) residue of PMEA2- and a PtII-coordinated (Dien)NH2 group; its formation degree amounts to about 40%. The stability constants of the M[(Dien)Pt(PMEA-N1)]2+ complexes with M2+ = Mg2+, Ca2+, Ni2+, Cu2+ and Zn2+ were measured by potentiometric pH titrations in aqueous solution at 25 degrees C and I = 0.1 M (NaNO3). Application of previously determined straight-line plots of log K(M(R-PO3))M versus pK(H(R-PO3)H for simple phosph(on)ate ligands. R-PO3(2-), where R represents a non-inhibiting residue without an affinity for metal ions, proves that the primary binding site of (Dien)Pt(PMEA-N1) is the phosphonate group with all metal ions studied; in fact, Mg2+, Ca2+ and Ni2+ coordinate (within the error limits) only to this site. For the Cu[(Dien)Pt(PMEA-N1)]2+ and Zn[(Dien)Pt(PMEA-N1)]2- systems also the formation of five-membered chelates involving the ether oxygen of the -CH2-O-CH2-PO3(2-) residue could be detected; the formation degrees are about 60% and 30%, respectively. The metal-ion-binding properties of the isomeric (Dien)Pt(PMEA-N7) species studied previously differ in so far that the resulting M[(Dien)Pt(PMEA-N7)]2+ complexes are somewhat less stable, but again Cu2+ and Zn2+ also form with this ligand comparable amounts of the mentioned five-membered chelates. In contrast, both M[(Dien)Pt(PMEA-N1/N7)]2+ complexes differ from the parent M(PMEA) complexes considerably; in the latter instance the formation of the five-membered chelates is of significance for all divalent metal ions studied. The observation that divalent metal-ion binding to the phosphonate group of (Dien)Pt(PMEA-N1) and (Dien)Pt(PMEA-N7) is only moderately inhibited (about 0.2-0.4 log units) by the twofold positively charged (Dien)Pt2+ unit at the adenine residue allows the general conclusion, considering that PMEA is a nucleotide analogue, that this is also true for nucleotides and that consequently participation of, for example, two metal ions in an enzymatic process involving nucleotides is not seriously hampered by charge repulsion.
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PMID:Formation of ternary complexes by coordination of (diethylenetriamine)-platinum(II) to N1 or N7 of the adenine moiety of the antiviral nucleotide analogue 9. 1140 68

Two collected micro-orifice uniform deposit impactors (MOUDIs) and a filter-based sampler were used to measure the size distribution and chemical composition of atmospheric particulate matter at Bakersfield, CA, between January 14 and 23, 1999. The peak number concentration of airborne ultrafine particles measured was 1.45 x 10(11) m-3, which is a factor of approximately 3 higher than the peak airborne ultrafine-particle number concentration measured previously in Pasadena, CA. Chemical analysis revealed that airborne ultrafine particles (Dp < 0.1 micron) at Bakersfield contained significant amounts of water-soluble species, including calcium, sodium, ammonium ion, nitrate, and sulfate. Other chemical species detected in the ultrafine size range included potassium, iron, copper, zinc, and strontium. A balance of aqueous ions showed that ultrafine particles were alkaline in nature with calcium acting as the dominant cation. Bulk samples of airborne particles with diameter less than 2.0 microns (PM2.0) were essentially neutral, but particle acidity was found to be a strong function of particle size. The results of this experiment suggest that areas deep in the human lung that preferentially collect particles in the ultrafine size range could be exposed to locally acidic or alkaline conditions even if the integrated airborne particle complex is essentially neutral.
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PMID:Detection of alkaline ultrafine atmospheric particles at Bakersfield, California. 1141 17

2-(3,5,6-Trifluoro-2-hydroxy-4-methoxyphenyl)benzoxazole (3) and benzothiazole analogue (4) are prepared by the two-step procedures from the corresponding 2-(pentafluorophenyl)benzazoles. Benzoxazole 3 is applicable to a fluorescent probe sensing magnesium cation, and 4 is suitable for sensing zinc cation. Both fluorophores 3 and 4 are sensitive to the pH change at pH 7-8, resulting in large fluorescence enhancement under basic conditions. Their high sensitivity to pH and selectivity in metal cations are ascribed to the high acidity of the fluorophenol moiety.
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PMID:Application of 2-(3,5,6-trifluoro-2-hydroxy-4-methoxyphenyl)benzoxazole and -benzothiazole to fluorescent probes sensing pH and metal cations. 1168 45

Laboratory- and pilot-scale racemic polylactides (PLA50) were synthesized in the presence of stannous octoate (SnOct2) or zinc-metal as initiators in the absence of alcohol. The resulting polymers were processed by compression molding or injection molding depending on the batch scale. The hydrolytic degradation of compression-molded samples selected to be comparable was investigated first in order to show the influence of the initiator system. Differences in water uptake were found between PLA50-Zn (zinc-metal initiation) and PLA50-Sn (SnOct2 initiation). PLA50-Zn being much more hydrophilic. PLA50-Sn exhibited a slower molecular weight decrease and delayed onsets of weight loss, release of acidity and stereocomplex formation, with respect to PLA-Zn. The concentration in residual tin in PLA50-Sn increased from 306 to 795 ppm during aging. In the case of PLA50-Zn the residual metal remains constant at ca. 40 ppm. In a second series of experiments, high molecular weight PLA50 different in characteristics and in initiator, synthesized under pilot-scale, were compared. The effects of the initiator on the degradation of the polymers well agreed with laboratory-scale findings, differences in hydrophobicity being enlarged by the up scaling. PLA50-Sn polymers appeared much more degradation resistant than PLA50-Zn ones. Contributions of the other characteristics (e.g. molecular weight, purity, stereoregularity, processing) were shown to be important as well.
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PMID:Influence of polymerization conditions on the hydrolytic degradation of poly(DL-lactide) polymerized in the presence of stannous octoate or zinc-metal. 1179 33

A study of interception of chemicals at an ash plantation forest in southern-central England shows the modification of acidic pollution as it passes from precipitation, through the vegetation cover and the soil to generate surface runoff. Precipitation is highly acidic (pH 3.7-4.8, alkalinity -16 to -200 microEq/l) and it is enriched in the strong acid anions associated with acidification (sulfate and nitrate) as well as ammonium and the trace elements aluminium and zinc. The concentration of both sea-salt and pollutant components varies considerably over time and this is linked to washout from the atmosphere during precipitation events as marked by an inverse relationship between concentration and volume of catch. The catchment is also supplied by sea-salt and pollutant additions as dry deposition: gaseous inputs of SO(x) may also increase sulfate deposition. Through the vegetation, much of the acidity is neutralised and, particularly during the growth period, calcium, magnesium and potassium is cycled, while sodium and nitrate are partially removed. Within the catchment, weathering ensures that further base cation production occurs leading to enhanced neutralisation of acidity and the generation of positive alkalinities. As a result, surface runoff becomes buffered with alkalinity approximately 490 microEq/l and pH approximately 7.9. Thus, although the acidification input from the atmosphere is high, this does not translate to acidic runoff due to within-canopy and within-soil processes.
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PMID:Interception and attenuation of atmospheric pollution in a lowland ash forested site, Old Pond Close, Northamptonshire, UK. 1184 89

Sugar beet pulp, a common agricultural waste, was studied in the removal of metal ions from aqueous solutions. Potentiometric titrations were used to characterize the surface acidity of the polysaccharide. The acid properties of the material can be described by invoking three distinct types of surface functional groups with the intrinsic acidity constants (pKa(int)) values 3.43+/-0.1, 6.05+/-0.05, and 7.89+/-0.1, respectively. The contents of each functional group (i.e., the carboxyl and phenol moieties) were also determined. Then, a simple surface complexation model with the diffuse layer model successfully described the sorption of several metal ions (Cu2+, Zn2+, Cd2+, and Ni2+) onto the polysaccharide under various experimental conditions: pH ranging from 2 to 5.5, ionic strength from 0.01 to 0.1 M, metal concentration between 10(-4) and 10(-3) M, for a constant sorbent concentration equal to 2.5 g x L(-1). It was observed experimentally that the affinity of the polysaccharide was in the sequence of Cu2+ > Zn2+ > Cd2+ > Ni2+. Predictions of sorption in binary-metal systems based on single-metal data fits represented competitive sorption data reasonably well.
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PMID:Modeling of single and competitive metal adsorption onto a natural polysaccharide. 1203 36

Sulphate-reducing biofilm and suspension processes were studied for treatment of synthetic wastewater containing sulphate, zinc and iron. With lactate supplemented wastewater with 170-230mg/l Zn and 58mg/l Fe, the following precipitation rates were obtained: 250 and 350mg/l d for Zn in fluidized-bed (FBR) and upflow anaerobic sludge blanket reactors, respectively, and 80mg/l d for Fe in both reactors with hydraulic retention time of 16h. The effluent Zn and Fe concentrations remained at less than 0.1 mg/l. The alkalinity produced in lactate oxidation increased the initial pH of 2.5-3, resulting in effluent pH of 7.5-8.5. The highest sulphate reduction rate was over 2000 mg/l d. In terms of sulphate reduction, hydrogen sulphide production and effluent alkalinity, the start-up of the FBR with the 10% fluidization rate was superior to the FBRs with 20-30% fluidization rates. With increased loading rates, high recycling rate became an advantage. After process failure caused by intentional overloading, the sulphate reduction partially recovered within 2 weeks. Metal precipitates in the reactors were predominantly FeS2, ZnS and FeS. The metal mass balance was as follows: 73-86% of Zn and Fe accumulated into the reactors and water level adjustors, 14-23% of the metals were washed out as precipitates and 0.05-0.15% remained as soluble metals. Biomass yield in the sulphate-reducing processes was 0.039-0.054g dry biomass (VS or VSS) per g of lactate oxidized or 0.035-0.074g dry biomass per g of sulphate reduced. The results of this work demonstrate that the lactate supplemented sulphate-reducing processes precipitated the metals as sulphides and neutralized the acidity of the synthetic wastewater.
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PMID:Optimization of metal sulphide precipitation in fluidized-bed treatment of acidic wastewater. 1250 54

The factors governing the deprotonation ability of zinc(II)-water and zinc(II)-alcohol and nucleophilicity of the resultant zinc(II) hydroxide and zinc(II) alkoxide as complex models for zinc enzymes have been investigated through Hartree-Fock and density-functional theory methods with the 6-311++G(d,p) basis set. Our calculations showed that in these double-functionalized complexes (i.e., zinc complexes having both a zinc(II)-alcohol motif and a zinc(II)-water motif) zinc(II)-alcohol is preferred in deprotonation over zinc(II)-water (i.e., zinc(II)-alcohol has a much lower pK(a) than zinc-coordinated water in the same molecule). Natural bond orbital analysis revealed that zinc(II) alkoxides are more nucleophilic than their respective counterparts zinc(II) hydroxides. The analysis of the transition state in the transformation reaction from zinc(II) hydroxide species to zinc(II) alkoxide species indicates that zinc(II) alkoxides are the preferred deprotonated species not only thermodynamically but also kinetically. Further examination of the proposed mechanisms of the zinc(II) alkoxide-promoted transesterification path and the zinc(II) hydroxide-promoted hydrolysis path revealed the structures of the intermediates and energy diagrams in the reactions. These results, entitled double-functionalized complexes, for the first time, put a firm theoretical foundation of why the zinc(II)-alcoholic OH is a better model for hydrolytic zinc enzymes (having both stronger acidity and better nucleophilicity).
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PMID:Deprotonation of zinc(II)-water and zinc(II)-alcohol and nucleophilicity of the resultant zinc(II) hydroxide and zinc(II) alkoxide in double-functionalized complexes: theoretical studies on models for hydrolytic zinc enzymes. 1251 79

In this paper, extraction chromatography by which Co2+ can be separated from Cu2+, Cd2+, Mn2+, Zn2+, Fe3+ is developed. The chromatographic column was 17 mm i.d. x 520 mm, containing polymers synthesized by styrene, divinylbenzene and P204 (volume fraction was 40%), with particle size of 100-200 mesh. The effects of transformation of P204 from the H(+)-form to the Na(+)-form by NaAc solution, the eluent acidity, and eluent composition were investigated. The results indicated that this extraction chromatographic method is good to separate Co2+ from Cu2+, Cd2+, Mn2+, Zn2+ and Fe3+, and the condition of separation is simple and convenient. When the P204 is transformed from the H(+)-form to the Na(+)-form by pH 4.0 NaAc (0.5 mol/L), and the column is eluted with pH 2.5 ClCHCOOH-ClCHCOONa (0.1 mol/L), the separation can be completed effectively.
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PMID:[Study on the separation of Co2+ from Cu2+, Cd2+, Mn2+, Zn2+ and Fe3+ by extraction chromatography]. 1254 30

The Deckers Creek watershed in northern West Virginia (USA), containing a land area of 166 km2 (63 mi2), has a long history of industrial development and attendant environmental abuses from both land and water pollution practices. The water in Deckers Creek was sampled in 1974 at 29 locations along the main stem and resampled in 1999-2000 to determine water quality changes over this 25-year period. Water samples were analyzed for pH, acidity, alkalinity, iron, and calcium at both times, while aluminum, manganese, zinc, and fecal coliform (FC) bacteria densities were added in 1999-2000. Water at almost all sampling points showed lower acidity and metal contents in 1999-2000 compared with 1974. Water pH increased at the mouth from 5.4 in 1974 to 6.0 in 1999-2000. Acidity and iron concentrations were decreased an average of 70% in the upper stretches of the creek. However, one major untreated point source of water from an abandoned underground mining complex continues to degrade the quality of the creek in its lower stretches. In the upper section, the water quality in Deckers Creek has improved due to decreased surface and underground coal mining activities, reclamation of abandoned and recently permitted surface mined lands, and natural healing of past land use scars from timbering and mining over time. The decrease in mineral extraction activities and the reclamation of disturbed lands has occurred due to the passage and enforcement of water quality and land reclamation laws and regulations. More time and additional reclamation projects will continue to enhance the water quality in the creek. Improved water chemistry in the majority of the creek, however, shows the previously unnoticeable biological contamination from sewage inputs.
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PMID:Water quality changes in a polluted stream over a twenty-five-year period. 1270 90


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