scholarly journals The Initial Deposition Behavior of Silica Colloid and Amino-Modified Silica Colloid in Unsaturated Sand Columns

Water ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 2892
Author(s):  
Yosuke Fujita ◽  
Motoyoshi Kobayashi
Keyword(s):  
Deposition Rate ◽  
Salt Concentration ◽  
Rate Constants ◽  
Unsaturated Sand ◽  
Silica Colloid ◽  
Collector Efficiency ◽  
Initial Deposition ◽  
Water Saturated ◽  
Unsaturated Condition ◽  
Positively Charged

Colloid transport experiments focusing on the initial deposition stage in water-unsaturated sand columns were conducted. To examine the effect of electrostatic interaction in the unsaturated condition, negatively and positively charged silica colloids were used for column transport experiments under different salt concentrations. The results of the column experiments were analyzed based on the colloid filtration theory and the deposition rate constants, and the single collector efficiency was calculated. The deposition rate constants of both negatively and positively charged silica in a water-unsaturated condition are larger than those in a water-saturated condition at an equivalent salt concentration, because the interface between air and water acts as an additional deposition site. The negatively charged silica shows the salt concentration, above which electric double layer (EDL) repulsion can be neglected, and the salt concentration is called critical deposition concentration (CDC). The CDCs were almost the same values in water-saturated as well as unsaturated conditions. The deposition rate constants of the positively charged silica were slightly increased at 0.05 mM due to the EDL attractive forces in the saturated condition. However, we could not see the significant effects of the EDL attractive force in the unsaturated condition in this study. Also, the present results demonstrated that a correlation equation for calculating collector efficiency can be applied to the non-spherical collector particles.

scholarly journals GROUNDWATER SELF-CLEARING FROM 90SR WITHIN BACKGROUND AREA AND OWING TO ARTIFICIAL CONTAMINATION

2018 ◽  
pp. 100-106
Author(s):  
O. Shevchenko ◽  
V. Dolin
Keyword(s):  
Rate Constants ◽  
Water Exchange ◽  
Main Idea ◽  
Exclusion Zone ◽  
Well Drilling ◽  
90Sr Content ◽  
Waste Storage ◽  
Formal Kinetic ◽  
Unstable Process ◽  
Water Saturated

The main idea of the presented results is the determination of spatial-temporal regularities of 90Sr content in groundwaters within Chornobyl Exclusion Zone. Utilization of formal kinetic regularities (of I order for irreversible process) for monitoring data analyses has been substantiated. Rate constants of groundwater self-clearing from 90Sr in dependence of type of contamination are calculated by iteration method. Graphic interpretation of data has been realized using package for analysis of Microsoft Excel and Statistica software. Self-clearing of groundwaters is carried out owing to three main processes: sorption as function of water containing medium dispercity, dispersion due to water exchange, concentration dilution (dissolving) of radionuclides in specified volume, and physical decay. considered Self-clearing is considered to be an important element both for the security and vulnerability of groundwaters. Data on 90Sr content in groundwater of background areas, in affected zone of radioactive waste storage, zone of groundwater nutrition from cooling pond of Chornobyl NPP, spots of primarily radioactive contamination, and of groundwater secondary contamination owing to well drilling are discussed. Rate constants for groundwater self-clearing from 90Sr are calculated from experimental data both for non-stationary (rapid) and stationary (slow) processes. The “half-decontamination” period (in analogy to half-life) is less than 0.5 year. The rate constant for unstable process two times, and for established one time exceeds the decay constant. The rates of groundwater self-clearing from strontium-90 owing to water exchange and geochemically immobilization are determined. The equilibrium of sorption-desorption within water saturated zone is generally depended on the rate of water exchange and radionuclides concentration in upper stream, i.e. from concentration gradient.

Evaluation of initial deposition rate of electroless Ni–P layers by QCM method

2005 ◽  
Vol 50 (28) ◽  
pp. 5526-5532 ◽  
Author(s):  
H. Ashassi-Sorkhabi ◽  
A. Mirmohseni ◽  
H. Harrafi
Keyword(s):  
Deposition Rate ◽  
Initial Deposition ◽  
Electroless Ni

scholarly journals The Intrinsic Electrostatic Potential and the Intermediate Ring of Charge in the Acetylcholine Receptor Channel

2000 ◽  
Vol 115 (2) ◽  
pp. 93-106 ◽  
Author(s):  
Gary G. Wilson ◽  
Juan M. Pascual ◽  
Natasja Brooijmans ◽  
Diana Murray ◽  
Arthur Karlin
Keyword(s):  
Acetylcholine Receptor ◽  
Electrostatic Potential ◽  
Rate Constants ◽  
Xenopus Laevis Oocytes ◽  
Mouse Muscle ◽  
Α Subunit ◽  
Intermediate Ring ◽  
Acetylcholine Receptor Channel ◽  
Positively Charged ◽  
Receptor Channel

A ring of aligned glutamate residues named the intermediate ring of charge surrounds the intracellular end of the acetylcholine receptor channel and dominates cation conduction (Imoto et al. 1988). Four of the five subunits in mouse-muscle acetylcholine receptor contribute a glutamate to the ring. These glutamates were mutated to glutamine or lysine, and combinations of mutant and native subunits, yielding net ring charges of −1 to −4, were expressed in Xenopus laevis oocytes. In all complexes, the α subunit contained a Cys substituted for αThr244, three residues away from the ring glutamate αGlu241. The rate constants for the reactions of αThr244Cys with the neutral 2-hydroxyethyl-methanethiosulfonate, the positively charged 2-ammonioethyl-methanethiosulfonate, and the doubly positively charged 2-ammonioethyl-2′-ammonioethanethiosulfonate were determined from the rates of irreversible inhibition of the responses to acetylcholine. The reagents were added in the presence and absence of acetylcholine and at various transmembrane potentials, and the rate constants were extrapolated to zero transmembrane potential. The intrinsic electrostatic potential in the channel in the vicinity of the ring of charge was estimated from the ratios of the rate constants of differently charged reagents. In the acetylcholine-induced open state, this potential was −230 mV with four glutamates in the ring and increased linearly towards 0 mV by +57 mV for each negative charge removed from the ring. Thus, the intrinsic electrostatic potential in the narrow, intracellular end of the open channel is almost entirely due to the intermediate ring of charge and is strongly correlated with alkali-metal-ion conductance through the channel. The intrinsic electrostatic potential in the closed state of the channel was more positive than in the open state at all values of the ring charge. These electrostatic properties were simulated by theoretical calculations based on a simplified model of the channel.

Kinetics and mechanism of the decarboxylation of pyrimidine-2-carboxylic acid in aqueous solution

1977 ◽  
Vol 55 (13) ◽  
pp. 2478-2481 ◽  
Author(s):  
Gerald E. Dunn ◽  
Edward A. Lawler ◽  
A. Brian Yamashita
Keyword(s):  
Carbon Dioxide ◽  
Aqueous Solution ◽  
Carboxylic Acid ◽  
Rate Constants ◽  
Kinetics And Mechanism ◽  
First Order ◽  
Order Rate ◽  
Pseudo First Order ◽  
Positively Charged

Pseudo-first-order rate constants for the decarboxylation of pyrimidine-2-carboxylic acid have been determined at 65 °C in aqueous solution over the acidity range pH = 2 to H0 = −9.5. Rate constants increase rapidly from pH = 2 to H0 = −3, then remain constant. This behaviour can be accounted for by a Hammick-type mechanism in which monoprotonated pyrimidine-2-carboxylic acid loses carbon dioxide to form an ylide (stabilized by the adjacent positively charged nitrogens) which rapidly converts to pyrimidine.

scholarly journals Effect of cationized antibodies in performed immune complexes on deposition and persistence in renal glomeruli.

1982 ◽  
Vol 156 (3) ◽  
pp. 766-777 ◽  
Author(s):  
V J Gauthier ◽  
M Mannik ◽  
G E Striker
Keyword(s):  
Immune Complexes ◽  
Negative Charge ◽  
Binding Activity ◽  
Anionic Sites ◽  
Renal Glomeruli ◽  
Dense Deposits ◽  
Small Doses ◽  
Initial Deposition ◽  
Subendothelial Deposits ◽  
Positively Charged

To study the interaction of positively charged antibodies in immune complexes with the fixed negative charge on the glomerular capillary wall, chemical cationization of antibody was accomplished with the maintenance of antigen-binding activity. These cationized antibodies bound rapidly to glomeruli but did not persist. Large-latticed immune complexes formed with these cationic antibodies showed rapid deposition and persistence in renal glomeruli, even when administered in small doses. Electron-dense deposits were present at the anionic sites in the glomerular basement membrane at 1 min and 1 h, with extensive subendothelial deposits present from 12 to 72 h. By 14 d, the deposits were seen in the subepithelial region and the glomerular mesangium. The administration of small-latticed immune complexes prepared with cationized antibody revealed initial deposition without persistence in glomeruli in a manner similar to cationized antibodies alone. Thus, the positive charges on antibodies in immune complexes contribute to the deposition and persistence of the complexes in glomeruli, particularly in the subendothelial area.

scholarly journals Effect of pH on inhibition and spontaneous reactivation of acetylcholinesterase treated with esters of phosphorus acids and of carbamic acids

1967 ◽  
Vol 105 (1) ◽  
pp. 171-179 ◽  
Author(s):  
Elsa Reiner ◽  
W. N. Aldridge
Keyword(s):  
Rate Constants ◽  
Ph Optimum ◽  
Esters Of Phosphorus Acids ◽  
Ph Values ◽  
Order Rate ◽  
Alkaline Side ◽  
Group 2 ◽  
The One ◽  
Spontaneous Reactivation ◽  
Positively Charged

1. The second-order rate constants of inhibition, ka, of acetylcholinesterase were measured at pH values between 5·5 and 10·5 for two esters of phosphorus acids and five esters of carbamic acids. Two of the carbamates and one of the phosphates contained a quaternary nitrogen group. 2. For the three positively charged compounds the ka–pH plots are bell-shaped, with a pH optimum between 7·5 and 9·0. The changes in ka above and below the optimum pH fit theoretical curves for the dissociation of groups on the protein of pK 6·2 and 10·25. 3. For the uncharged compounds, the ka–pH plot on the alkaline side is identical with the one obtained for charged inhibitors. On the acid side they do not fit such a curve and the ka for two of the carbamates is independent of pH changes between 5·5 and 8·0. 4. The first-order rate constants, k+3, for spontaneous reactivation were measured at pH values between 5·0 and 11·0 for N-methylcarbamoylated, NN-dimethylcarbamoylated and di-(2-chloroeth)phosphorylated cholinesterase. For all three derivatives the k+3–pH plots are bell-shaped, with a pH optimum between 8·0 and 8·5. The changes in k+3 above and below the optimum fit theoretical curves for the dissociation of groups of pK 6·9 and 9·8. 5. The relevance of these results to binding, acylation and deacylation of both inhibitors and substrates is discussed.

scholarly journals State-dependent Accessibility and Electrostatic Potential in the Channel of the Acetylcholine Receptor

1998 ◽  
Vol 111 (6) ◽  
pp. 717-739 ◽  
Author(s):  
Juan M. Pascual ◽  
Arthur Karlin
Keyword(s):  
Electrostatic Potential ◽  
Rate Constants ◽  
Transmembrane Potential ◽  
Spatial Arrangement ◽  
Α Subunit ◽  
Closed State ◽  
State Dependent ◽  
Membrane Spanning ◽  
Positively Charged ◽  
Receptor Channel

Ion channel function depends on the chemical and physical properties and spatial arrangement of the residues that line the channel lumen and on the electrostatic potential within the lumen. We have used small, sulfhydryl-specific thiosulfonate reagents, both positively charged and neutral, to probe the environment within the acetylcholine (ACh) receptor channel. Rate constants were determined for their reactions with cysteines substituted for nine exposed residues in the second membrane-spanning segment (M2) of the α subunit. The largest rate constants, both in the presence and absence of ACh, were for the reactions with the cysteine substituted for αThr244, near the intracellular end of the channel. In the open state of the channel, but not in the closed state, the rate constants for the reactions of the charged reagents with several substituted cysteines depended on the transmembrane electrostatic potential, and the electrical distance of these cysteines increased from the extracellular to the intracellular end of M2. Even at zero transmembrane potential, the ratios of the rate constants for the reactions of three positively charged reagents with αT244C, αL251C, and αL258C to the rate constant for the reaction of an uncharged reagent were much greater in the open than in the closed state. This dependence of the rate constants on reagent charge is consistent with an intrinsic electrostatic potential in the channel that is considerably more negative in the open state than in the closed state. The effects of ACh on the rate constants for the reactions of substituted Cys along the length of αM2, on the dependence of the rate constants on the transmembrane potential, and on the intrinsic potential support a location of a gate more intracellular than αThr244.

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