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Query: UMLS:C0033036 (APC)
 10,214 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Proton inventory studies of the thrombin-catalyzed fibrinogen activation to fibrinopeptide A are most consistent with a two-proton bridge forming at the transition state probably between Ser195 OgammaH and His57 Nepsilon2 and His57 Ndelta1 and Asp102 COObeta- at the active site, with fractionation factors 0.66 +/- 0.03 under enzyme saturation with substrate and 0.64 +/- 0.03 at fibrinogen concentration at 0.2 Km, at pH 8.0, pD 8.6, and 25.0 +/- 0.1 degrees C. Strongly inverse solvent isotope effects (SIEs) result from inverse lag times and maximal slopes of blood clotting plots, which are also anion and cation dependent. The blood clot is much coarser in D2O, as indicated in clotting curves with 3-9 times shorter lag time and steeper slopes with respect to H2O. The finer the particles, the weaker the H-bonds interlocking the fibrin mesh and/or in water structure around fibrin. Proton inventories of inverse lag times and maximal slopes of blood clotting curves in buffers containing Na+ and Cl- ions give the best fit to an exponential dependence on deuterium content in the buffer and give fractionation factors 5.6 +/- 0.5 and 7.8 +/- 0.6 at pH 8.0 and 25.0 +/- 0.1 degrees C. The thrombin-catalyzed activation of protein C (PC) to APC is associated with inverse kinetic SIEs (KSIEs) of 0.75 +/- 0.09 and 1.02 +/- 0.06 in 0.3 M NaCl and 0.3 M choline chloride, respectively, at substrate concentrations = 0.2 Km. In comparison, thrombin-catalyzed hydrolysis of chromogenic substrates gives greater KSIEs (Enyedy, E. I.; Kovach. I. M J. Am. Chem. Soc. 2004, 126, 6017-6024) and more complex proton inventories than the ones reported here for the first time for natural substrates. The present study illuminates differences in the character of the rate-determining transition state for the initial phase of the two physiological reactions catalyzed by thrombin.
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PMID:Full and partial deuterium solvent isotope effect studies of alpha-thrombin-catalyzed reactions of natural substrates. 1577 10

The ecotoxicological effects of aluminum (Al)-based coagulants are of concern because of their wide-ranging applications in wastewater treatment and water purification. As important Al-based coagulants, AlCl(3) and PAC (polyaluminum-chloride) were selected as examples to examine the toxic effects on representative vegetables including the cabbage Brassica chinensis and the radish Raphanus sativus over a range of exposure concentrations in neutral (pH 7.00) and acidic (pH 4.00) conditions, using seed germination and root elongation in the early-growth stage as indicators of toxicity. The results showed that root elongation of the two vegetables was a more sensitive indicator than was seed germination for evaluating the toxicity of Al. As a single influencing factor, H(+) had no significant direct effects on root elongation of Brassica chinensis and Raphanus sativus under the experimental conditions. The toxicity of Al played the main role in inhibiting root elongation and seed germination and was strongly related to changes in pH. There was a markedly positive relationship between the inhibitory rate of root elongation, seed germination, and the concentration of Al at pH 4.00 (p < 0.01). The toxic effect of AlCl(3) on Brassica chinensis was less with a neutral pH than at pH 4.00, but Raphanus sativus was more susceptible to AlCl(3) toxicity at a neutral pH than at pH 4.00. Both Raphanus sativus and Brassica chinensis had a more toxic response to a low concentration (<64 mg . L(-1)) of PAC in a neutral condition than in an acidic condition. Undoubtedly, the Al toxicity caused by Al-based coagulants at a neutral pH is relevant when treatment solids are used in agriculture.
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PMID:Toxic effects of Al-based coagulants on Brassica chinensis and Raphanus sativus growing in acid and neutral conditions. 1579 23

The purpose of this study was to assess the effect of light-tip distance on the shear bond strength and failure site of brackets cured with three different light curing units: a high-intensity halogen (Astralis 10, 10-second curing), a light-emitting diode (LED, e-Light, six-second curing), and a plasma arc (PAC System, four-second curing). One hundred and thirty-five bovine permanent mandibular incisors were randomly allocated to nine groups of 15 specimens each. Stainless steel brackets were bonded with a composite resin to the teeth, and each curing light was tested at zero, three, and six mm from the bracket. After bonding, all samples were stored in distilled water at room temperature for 24 hours and subsequently tested for shear bond strength. When the three light curing units were compared at a light-tip distance of zero mm, the three lights showed no significantly different shear bond strengths. At light-tip distances of three and six mm, no significant differences were found between the halogen and plasma arc lights, but both lights showed significantly higher shear bond strengths than the LED light. When evaluating the effect of the light-tip distance on each light curing unit, the halogen light showed no significant differences between the three distances. However, the LED light produced significantly lower shear bond strengths at a greater light-tip distance, and the plasma arc lamp showed significantly higher shear bond strengths at a greater light-tip distance. In hard-to-reach areas, the use of PAC system is suggested, whereas the LED evaluated in this study is not recommended.
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PMID:Effect of light-tip distance on the shear bond strengths of composite resin. 1589 77

Poly-aluminum-chloride-sulfate(PACS) with different SO4(2-)/Al3+ mole ratios and bacicity(y) of 2.0 was synthesized using AlCl3 x 6H2O, Al2 (SO4 )3 x 18H2O and Na2CO3 as raw materials. The effect of SO4(2-)/Al3+ ratio on the performance of PACS for removal of natural organic matter(NOM) with humic-rich actual water was examined. It was found that PACS with SO4(2-)/Al3+ mole ratio of 0.0664 achieved the best NOM removal results and was selected to investigate its performance in comparison with PAC, FeCl3 and alum (Al2 (SO4)3 x 18H2O). The experimental results showed that the optimum NOM removals were achieved at pH 5.0-8.2 and the dose of about 5.0 mg/L as Al both for the selected PACS and PAC, at pH 5.0-6.0 and the dose of about 7.0 mg/L as Fe for FeCl3, and at pH 5.0-7.0 and the dose of about 7.0 mg/L as Al for alum, respectively. At the optimum conditions, the selected PACS achieved the best NOM removal result, followed by PAC, FeCl3, and then alum. The concentration of residual aluminum in treated water by the selected PACS and PAC under the optimum coagulant conditions was approximately 115 microg/L, which can completely comply with the regulated limits.
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PMID:Natural organic matter (NOM) removal from surface water by coagulation. 1590 Jul 72

This work studies the effect of water content on the aging of APC residues, with a liquid to solid ratio (L/S) of 0.25 or 10, aged with or without exposure to ambient air. After the residue was mixed with water, CaSO4 and (Na,K)Al3(SO4)2(OH)6 in the raw sample yielded ettringite. When CO2 were available, this ettringite was further transformed to gypsum, calcite and possibly gibbsite. Experimental data revealed that the concentrations of Pb, Zn, Cd, Hg, and Cu fell with age, whereas that of Cr increased. Given L/S=10, excess Ca2+ ions were present in the suspension, so a precipitate of primarily calcite crystals of sizes under 5 microm formed on the air-water surface. This layer significantly reduced the rates of decline of Pb, Zn, Cd and Hg contents, and also reduced the increasing rate of Cr content in the suspension. This result follows from the mass transfer barrier of CO2 added at the air-water surface and the occurrence of subsequent chemical reactions in the suspension. An estimate of the mass transfer rate revealed that the rate-controlling step with L/S=10 was the dissolution and diffusion of CO2 in the bulk solution. However, at L/S=0.25, the rate-limiting step was the dissolution of metals from ash particles. Water content is a very important process factor, whose distribution in the sample, and the resulting competition between carbonate ion flux and heavy metal flux, govern the reaction time required during the natural aging process.
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PMID:Aging of air pollution control residues from municipal solid waste incinerator: role of water content on metal carbonation. 1600 25

This study focuses on the experimental investigation to identify the effect of PAC at high concentrations on the fouling of membranes. A pilot-scale experimental apparatus was installed at a water treatment plant located downstream of Nakdong river basin, Korea. Effluent of rapid sand filter was used as influent of the system, which consists of PAC bio-reactor, submerged membrane module (hollow fiber with pore size 0.1 m) and air supply facility. PAC was dosed at 40 g/L initially and it was not replaced during the operation period. Suction type filtration was carried out at intervals of 12 min. suction and 3 min. idling. At the initial flux 0.36 m/d, the system could be operated stably for around 90 days at target trans-membrane pressure (TMP) of 40 kPa. Among total resistance of membrane filtration, cake and gel layer resistance, Rc+Rg, was the dominant fraction (more than 90% of the total) to increase the filtration pressure, which means that the filtration resistance could be controlled by the PAC cake layer and then irreversible membrane fouling could be prevented. Three minutes air backwashing every 3 days could extend the operation period to 127 days. Organics were analyzed in terms of molecular weight structure. The influent of the system consists of 15.0% and 74.4% of hydrophobic and hydrophilic natural organic matter (NOM), respectively. Hydrophobic and hydrophilic (electrostatic) interaction was the main factor on fouling of the membrane in the reactor. Hydrophobic fraction decreased slightly in the effluent, which means hydrophobic NOM removal in the reactor by adsorption. Organics accumulated in the membrane were extracted for analysis after a certain period of operation. The fraction of hydrophobic and hydrophilic organics was 41.4% and 38.9%, respectively. On the basis of the experimental results, the hydrophobic organics were the major materials causing the fouling of the membrane, which should be changed to other types of material.
Water Sci Technol 2005
PMID:The fouling characterization and control in the high concentration PAC membrane bioreactor HCPAC-MBR. 1600 64

Two pilot-scale powdered activated carbon-microfiltration (PAC-MF) reactors were operated using river water pretreated by a biofilter. A high permeate flux (4 m/d) was maintained in two reactors with different particle sizes of PAC. High concentration (20 g/L) in the PAC adsorption zone demonstrated 60-80% of organic removal rates. Analysis on the PAC cake fouling demonstrated that attached metal ions play more important role than organic matter attached on PAC to the increase of PAC cake resistance. Effects of factors which may cause PAC cake fouling in PAC-MF process were investigated and evaluated by batch experiments, further revealing that small particulates and metal ions in raw water impose prominent influence on the PAC cake layer formation. Fe (II) precipitates after being oxidized to Fe (III) during PAC adsorption and thus Fe(ll) colloids display more significant effect than other metal ions. At a high flux, PAC cake layer demonstrated a higher resistance with larger PAC due to association among colloids, metals and PAC particles, and easy migration of small particles in raw water into the void space in the PAC cake layer. Larger PAC possesses much more non-uniform particle size distribution and larger void space, making it easier for small colloids to migrate into the voids and for metal ions to associate with PAC particles by bridge effect, hence speeding up and intensifying the of PAC cake fouling on membrane surface.
Water Sci Technol 2005
PMID:Factors causing PAC cake fouling in PAC-MF (powdered activated carbon-microfiltration) water treatment systems. 1600 82

A study was carried out on a hybrid (AS-SBF) membrane bioreactor (HMBR) for the municipal wastewater reclamation and reuse at Chengfengzhuang WWTP in Daqing City, Heilongjiang Province. It was found that the effects of DO and water temperature on performance of the HMBR was significant. Under the conditions of water temperature in range of 10-14 degrees C, pH of 6.6- 7.0, DO of 4-6 mg/l and HRT of 7 h, the HMBR exhibited removal efficiencies for CODcr, BOD5, NH3-N and TN of 96.7%, 98.9%, 93.7% and 60.5% respectively. The turbidity of effluent from HMBR was below 1 NTU. The effluent of HMBR meets the standard of wastewater reclamation for oil exploitation. PAC was added into the bioreactor at the second operating stage, in order to further research parameters variation. The flux was improved by 53.2%, compared to the membrane without PAC-addition, due to formation of a PAC pre-coat layer on the membrane surface, with lots of advantages such as larger granules, higher porosity, non-compressibility, higher filterability and easy removal, compared with pure biomass layer. In addition, the performance of HMBR was further improved, due to adsorption and degradation of SMPs, the average removal of CODcr and TN was further improved by 5.1% and 13.5% respectively. Biomass in the HMBR was quantitatively measured, of which the biofilm played a major role in pollutants removal.
Water Sci Technol 2005
PMID:Performance improvement of hybrid membrane bioreactor with PAC addition for water reuse. 1645 13

An investigation of dye decolorization from synthetic dye solutions using the non-ionic, water-soluble, high molecular weight seed gums Ipomoea dasysperma and guar gum as coagulants was undertaken. The use of galactomannans derived from plants in this system presents a sustainable method of textile effluent treatment. These natural coagulants extracted from plants proved to be workable alternatives to conventional coagulants like polyaluminum chloride, as they are biodegradable, safe to human health, are cost effective when compared to imported chemicals and have a wider effective dosage range for flocculation of various colloidal suspensions. Coagulant dose and coagulation pH are important factors influencing the mechanism of coagulation. Also the type and chemical structure of the dye plays an important role in the coagulation process. The seed gums alone were found to be effective for decolorization of direct dye and in combination with PAC their coagulation efficiency was well extended even for reactive and acid dyes.
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PMID:Ipomoea dasysperma seed gum: an effective natural coagulant for the decolorization of textile dye solutions. 1654 36

A new packing for deep bed filtration using Flexible Fibers has been proposed and developed on a very large scale for tertiary treatment of wastewater. The purpose of this study is to check the possibility of using this technology for the production of drinking water from surface water. In this study, the feasibility of the fiber filter application on water treatment was examined and the removal efficiency of fiber filter was improved using an in-line coagulant injection method. The experiments were carried out at pilot scale. The filter was packed with bundles of polyamide fibers with a bed porosity of 93%. Nak-dong River was used as the filter influent water and alum, PSOM, and PAC were used as the coagulants. The coagulants were injected by the in-line injection method. Small dosages (1-5 mg/L) of the polymeric coagulants (PSOM and PAC) showed an increase of removal efficiency compared to the operation without coagulants. Specifically, 1 mg/L of PAC showed the longest filtration time. Considering filtration time, filtrate quality, and filtered volume, the filtration velocity of 120 m/hr was chosen as an optimum value. For long-term operations, the effluent quality was 0.4 NTU and the removal efficiency was stable for the given optimum conditions.
Water Sci Technol 2006
PMID:Enhancing flexible fiber filter (3FM) performance using in-line coagulation. 1675 65


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