Steady-state Cl Research Articles

Effective and continuous removal of Cr(VI) from brackish wastewater by flow-electrode capacitive deionization (FCDI)

Effective treatment of Cr(VI)-containing wastewater is a great challenge faced by many industries with this situation further complicated by the coexistence of other ions such as Cl−. This study demonstrated the suitability and effectiveness of utilizing flow-electrode capacitive deionization (FCDI) for effective and continuous removal of Cr(VI) from brackish wastewaters. The effects of various influencing factors were systematically investigated, including applied current density, feed concentration of coexisting Cl−, hydraulic residence time (HRT), activated carbon loading, initial solution pH and other common coexisting anions. Results indicated that Cr(VI) was preferentially removed compared to Cl− with a high ion selectivity achievable, and Cr(VI) and Cl− had significantly different removal behaviors in many cases. The steady-state effluent Cl− concentration dropped almost linearly with the increase of current density, while the steady-state effluent Cr(VI) concentration dropped to a value under a small current density and decreased insignificantly in spite of the increase in current density. A larger HRT or activated carbon loading favorably contributed to a lower steady-state effluent concentrations of Cr(VI) and Cl−. Initial pH of feed water around 5–6 without pH adjustment was the most advantageous to the removal of Cr(VI). Different coexisting anions had inhibitory effects on the Cr(VI) removal to varying degrees and the carbonate species was found to have the greatest inhibitory effect. This study is of value in promoting FCDI as a viable technology for treatment of Cr(VI)-containing brackish wastewater.

Effective fluoride removal from brackish groundwaters by flow-electrode capacitive deionization (FCDI) under a continuous-flow mode

Herein, we demonstrated the suitability and effectiveness of utilizing flow-electrode capacitive deionization (FCDI) for treatment of fluoride-contaminated brackish groundwater. By comparing operational modes of short-circuited closed-cycle (SCC), isolated closed-cycle (ICC) and single cycle (SC), it was found that SCC mode was the most advantageous. In SCC configuration, the effects of different parameters on the removal of F− and Cl− were investigated including current density, hydraulic residence time (HRT), activated carbon (AC) loading and feed concentration of coexisting NaCl. Results indicated that the steady-state effluent Cl− concentration dropped with elevated applied current, and the decreasing rate got faster with the increase of HRT or AC loading. However, for the steady-state effluent F− concentration, it dropped to a value under a small applied current and maintained stable in spite of the increase in applied current, and both HRT and AC loading had insignificant effects on the steady-state effluent F− concentration. F− was preferentially removed from the treated water compared with Cl−, and a higher ion selectivity could be obtained at lower applied current and smaller HRT with the trade-off being that operation under these circumstances would generate outlet water with little change in conductivity compared to the influent. The removal efficiencies of F− and Cl− both decreased with increasing feed concentration of coexisting NaCl. This study should be of value in establishing FCDI as a viable technology for treatment of fluoride-contaminated brackish groundwater.

Long-term evaluation of the impact of urbanization on chloride levels in lakes in a temperate region

The application of road salts for winter de-icing of roadways in cold regions has been demonstrated to increase chloride (Cl) concentrations in nearby surface waters and have a negative impact on aquatic organisms and processes. In addition to toxicity to aquatic organisms, high concentrations of Cl in lakes can alter mixing processes, resulting in prolonged anoxic conditions and associated water quality degradation. Elevated concentrations of Cl in freshwater environments in cold regions is a well-documented phenomenon, but few studies have undertaken a long-term evaluation of the impact of urbanization on lakes. In this paper, nine lakes in the Halifax region of Nova Scotia, Canada, were monitored over 35 years to observe Cl concentrations prior to, during, and after urbanizing development. Cl concentrations were observed to increase in most study lakes over the monitoring period and all nine exhibited seasonal trending in response to winter de-icing activities. Six of the lakes achieved a steady-state Cl level after an initial increase in response to development activities, two are potentially still in transition, and one was unaffected by development activities. Watershed land use was found to be a good predictor of the springtime concentration of Cl and can help to inform decision-making surrounding development activities. When the percent of developed land was 25% or more, the Cl concentrations tended to exceed Canadian freshwater quality guidelines for the protection of aquatic life.

Effects of SAP on the properties and pore structure of high performance cement-based materials

Water-to-binder ratio (w/b) directly affects the pore structure and performance of concrete, and drying conditions enhance the influence of water-to-binder ratio. Superabsorbent polymer (SAP) is effective to adjust the water in the concrete. In this paper, the effect of SAP and extra water on drying shrinkage, pore structure and the permeability of high performance cement-based material with w/b from 0.18 to 0.24 were studied to reveal the adjusting role of SAP for the influence of water-binder ratio at a 60% of relative humidity (RH). The permeability was determined through the vacuum saturation method, the diffusion of steady-state Cl− ion and carbonation testing. The structure of harden mortar and SAP voids were evaluated by mercury intrusion porosimetry (MIP) and backscatter electronic microscopy (BSEM). At the same effective w/b, SAP reduces the strength, and raises the drying shrinkage and permeability. However, the effect of SAP on the above properties is exactly opposite when the same total w/b is used. The greater the SAP particle size is, the more obvious those favorable effects are. SAP can weaken the effect of total w/b. The addition of SAP also results in the formation of the hydration diffusion layer in SAP void and the refinement of pore structures.

A chemiluminescent aptasensor based on rolling circle amplification and Co2+/N-(aminobutyl)-N-(ethylisoluminol) functional flowerlike gold nanoparticles for Salmonella typhimurium detection

A sensitive steady-state chemiluminescent aptasensor based on rolling circle amplification (RCA) was fabricated for the detection of Salmonella typhimurium. The sensor utilized aptamer modified Fe3O4 magnetic nanoparticles (MNPs) as capture probes, aptamer as recognition molecules, and Co2+ enhanced N‑(aminobutyl)-N-(ethylisoluminol) (ABEI) functional flowerlike gold nanoparticles (AuNFs) and complementary strand (cDNA) complex (Co2+/ABEI-AuNFs-cDNA) as signal probes. And P-Iodophenol (PIP) was also added to form a typical ABEI- AuNFs-PIP-H2O2 steady-state CL system. By virtue of Fe3O4 MNPs based solid-phase RCA strategy, S. typhimurium can be first captured by the aptamer immobilized on the surface of Fe3O4 MNPs then complex with RCA products to form a sandwich complex. Co2+/ABEI-AuNFs-cDNA signal probes were then assembled on the RCA products to produce and enhance CL signals. Under optimal conditions, the logarithmic correlation between the concentration of S. typhimurium and the CL signal was found to be linear within the range of 32cfumL−1 to 3.2×106cfumL−1 (R2 =0.9921). The limits of detection of the developed method were found to be 10cfumL−1 for S. typhimurium. The method was also used to detect S. typhimurium in real pork samples. The results were compared with those obtained from the plate-counting methods and showed good consistency. Therefore, this detection aptasnesor can be a good candidate for sensitive and selective detection of S. typhimurium with simple and effective operations.

Groundwater age, mixing and flow rates in the vicinity of large open pit mines, Pilbara region, northwestern Australia

Determining groundwater ages from environmental tracer concentrations measured on samples obtained from open bores or long-screened intervals is fraught with difficulty because the sampled water represents a variety of ages. A multi-tracer technique (Cl, 14C, 3H, CFC-11, CFC-12, CFC-113 and SF6) was used to decipher the groundwater ages sampled from long-screened production bores in a regional aquifer around an open pit mine in the Pilbara region of northwest Australia. The changes in tracer concentrations due to continuous dewatering over 7 years (2008–2014) were examined, and the tracer methods were compared. Tracer concentrations suggest that groundwater samples are a mixture of young and old water; the former is inferred to represent localised recharge from an adjacent creek, and the latter to be diffuse recharge. An increase in 14C activity with time in wells closest to the creek suggests that dewatering of the open pit to achieve dry mining conditions has resulted in change in flow direction, so that localised recharge from the creek now forms a larger proportion of the pumped groundwater. The recharge rate prior to development, calculated from a steady-state Cl mass balance, is 6 mm/y, and is consistent with calculations based on the 14C activity. Changes in CFC-12 concentrations with time may be related to the change in water-table position relative to the depth of the well screen.

Comparison of the Average Lift Coefficient ͞CL and Normalized Lift ͞ηL for Evaluating Hovering and Forward Flapping Flight

The capability of flapping wings to generate lift is currently evaluated by using the lift coefficient C ¯ L , a dimensionless number that is derived from the basal equation that calculates the steady-state lift coefficient CL for fixed wings. In contrast to its simple and direct application to fixed wings, the equation for C ¯ L requires prior knowledge of the flow field along the wing span, which results in two integrations: along the wing span and over time. This paper proposes an alternate average normalized lift η ¯ L that is easy to apply to hovering and forward flapping flight, does not require prior knowledge of the flow field, does not resort to calculus for its solution, and its lineage is close to the basal equation for steady state CL. Furthermore, the average normalized lift η ¯ L converges to the legacy CL as the flapping frequency is reduced to zero (gliding flight). Its ease of use is illustrated by applying the average normalized lift η ¯ L to the hovering and translating flapping flight of bumblebees. This application of the normalized lift is compared to the same application using two widely-accepted legacy average lift coefficients: the first C ¯ L as defined by Dudley and Ellington, and the second lift coefficient by Weis-Fogh. Furthermore, it is shown that the average normalized lift η ¯ L has a physical meaning: that of the ratio of work exerted by the flapping wings onto the surrounding flow field and the kinetic energy available at the aerodynamic surfaces during the generation of lift. The working equation for the average normalized lift η ¯ L is derived and is presented as a function of Strouhal number, St.

Membrane efficiency and diffusive tortuosity of a dense prehydrated geosynthetic clay liner

In this study, a series of membrane/diffusion tests were conducted on specimens of a dense prehydrated geosynthetic clay liner (DPH GCL) subjected to KCl solutions (source concentration, Co = 8.7–160 mM) in rigid-wall cells. The source KCl solutions and de-ionized water (DIW) were circulated across the top and bottom specimen boundaries, respectively, and membrane efficiency coefficients, ω, were measured based on the differential pressures induced across the specimens due to prevention of liquid flux. Also, effective salt-diffusion coefficients, Ds∗, and apparent tortuosity factors, τa, were determined for each specimen based on the steady-state diffusive Cl− flux measured at the exit (bottom) boundary. The DPH GCL specimens exhibited higher ω and lower Ds∗ (and, likewise, lower τa) relative to conventional (granular, non-prehydrated) GCL specimens tested under similar conditions. The results were consistent with the lower hydraulic conductivities, k, measured for the DPH GCL specimens and are attributed primarily to the higher bentonite dry densities in the DPH GCL specimens (1.1 Mg/m3) relative to the conventional GCL specimens (∼0.4 Mg/m3), although differences in bentonite texture (powdered versus granular), bentonite type (treated versus untreated), and testing apparatus (rigid wall versus flexible wall) may have been contributing factors. Both the DPH GCL and the conventional GCL exhibited similar trends of decreasing τa with increasing ω. The τa values are considered to be a function of both a matrix tortuosity factor, τm, that accounts for the geometry of the interconnected pores, and a restrictive tortuosity factor, τr, that accounts for solute exclusion due to membrane behavior. Whereas the DPH GCL exhibited a lower τm relative to the conventional GCL, both GCLs exhibited similar trends of decreasing τr with increasing ω. The relationship between τr and ω for both GCLs is reasonably well represented by τr = 1 – ω, an expression that has been proposed for clay membranes in previous theoretical and experimental studies.

The primary and recycling sources of OH during the NACHTT‐2011 campaign: HONO as an important OH primary source in the wintertime

AbstractWe present OH observations from Nitrogen, Aerosol Composition, and Halogens on a Tall Tower 2011 (NACHTT‐11) held at the Boulder Atmospheric Observatory in Weld County, Colorado. Average OH levels at noon were ~ 2.7 × 106 molecules cm−3 at 2 m above ground level. Nitrous acid (HONO) photolysis was the dominant OH source (80.4%) during this campaign, while alkene ozonolysis (4.9%) and ozone photolysis (14.7%) were smaller contributions to OH production. To evaluate recycling sources of OH from HO2 and RO2, an observationally constrained University of Washington Chemical Mechanism (UWCM) box model (version 2.1) was employed to simulate ambient OH levels over several scenarios. For the base run, not constrained by observed HONO, the model significantly underestimated OH by a factor of 5.3 in the morning (9:00–11:00) and by a factor of 3.2 in the afternoon (13:00–15:00). The results suggest that known chemistry cannot constrain HONO and, subsequently, OH during the observational period. When HONO is constrained in the model by observations (< 50 m), the discrepancy between observation and model simulation improves to a factor of 1.3 in the morning and a factor 1.1 in the afternoon, within the 35% estimated instrumental uncertainty. However, the model produces both a morning and afternoon maximum in OH, in contrast to the observations, which show strong evidence for morning OH production but no distinct morning maximum. Two additional OH sources were also considered, although they do not improve the differences in modeled and measured temporal OH profiles. First, the impact of daytime HONO gradients near the ground surface (< 20 m) was evaluated. Strong HONO gradients were observed between 06:00 and 09:00 MST (mountain standard time), especially within 20 m of the surface. When constrained to HONO observed below 20 m (rather than 50 m), the model produced an even larger morning OH maximum, in contrast to the observations. Second, Cl atoms from ClNO2 photolysis producing RO2 from reaction with alkanes, while significant, produced steady state Cl atom levels (~ 103 atoms cm−3) that were too low to significantly perturb measured OH through reactions of organic peroxy radicals produced from Cl reactions with volatile organic compounds.

Efficacy of Synaptic Inhibition Depends on Multiple, Dynamically Interacting Mechanisms Implicated in Chloride Homeostasis

Chloride homeostasis is a critical determinant of the strength and robustness of inhibition mediated by GABAA receptors (GABAARs). The impact of changes in steady state Cl− gradient is relatively straightforward to understand, but how dynamic interplay between Cl− influx, diffusion, extrusion and interaction with other ion species affects synaptic signaling remains uncertain. Here we used electrodiffusion modeling to investigate the nonlinear interactions between these processes. Results demonstrate that diffusion is crucial for redistributing intracellular Cl− load on a fast time scale, whereas Cl−extrusion controls steady state levels. Interaction between diffusion and extrusion can result in a somato-dendritic Cl− gradient even when KCC2 is distributed uniformly across the cell. Reducing KCC2 activity led to decreased efficacy of GABAAR-mediated inhibition, but increasing GABAAR input failed to fully compensate for this form of disinhibition because of activity-dependent accumulation of Cl−. Furthermore, if spiking persisted despite the presence of GABAAR input, Cl− accumulation became accelerated because of the large Cl− driving force that occurs during spikes. The resulting positive feedback loop caused catastrophic failure of inhibition. Simulations also revealed other feedback loops, such as competition between Cl− and pH regulation. Several model predictions were tested and confirmed by [Cl−]i imaging experiments. Our study has thus uncovered how Cl− regulation depends on a multiplicity of dynamically interacting mechanisms. Furthermore, the model revealed that enhancing KCC2 activity beyond normal levels did not negatively impact firing frequency or cause overt extracellular K− accumulation, demonstrating that enhancing KCC2 activity is a valid strategy for therapeutic intervention.

Deep drainage and soil salt loads in the Queensland Murray - Darling Basin using soil chloride: comparison of land uses

Increases in deep drainage below the root-zone can lead to secondary salinity. Few data were available for drainage under dryland cropping and pastures in the Queensland Murray–Darling Basin (QMDB) before this study. Modelled estimates were available; however, without measured drainage these could not be validated. Soil chloride (Cl) mass-balance was used to provide an extensive survey of deep drainage. The method is ‘backward-looking’ and can detect low rates of drainage over longer times. Soil Cl and other soil properties were collated for a number of soils, mostly Vertosols and Sodosols, for paired native vegetation, cropped and sometimes pasture sites, from historical data and new soil sampling. Large amounts of salt and Cl had accumulated under native vegetation (Cl mean 25 t/ha, range 6–54, in 2.4 m depth), due to low rates of drainage. Steady-state Cl balances for native vegetation gave average drainage of 1.2 mm/year at wetter, eastern sites and 0.3 mm/year for Sodosols and Grey Vertosols in drier, western areas. Chloride profiles were mostly of a shape indicating matrix/piston flow. One site (Hermitage fallow trial) appeared to be affected by diffusion of Cl to a watertable. The Cl profiles from 14 longer term cropping sites (18–70 years), mainly used for winter cropping/summer fallow, indicate: (i) large losses of Cl since clearing (mean 50%, range 13-85% for 0–1.5 m soil); and (ii) drainage rates from transient Cl balance are a relatively low percentage of rainfall but are considerably higher than under native vegetation. Drainage averaged 8 mm/year and ranged from 2 to 18 mm/year. This variation is partly explained by rainfall (R2 = 0.63) (500–730 mm/year) and soil plant-available water capacity (R2 = 0.77) (80–300 mm). Deep drainage increases with increasing rainfall and with decreasing available water capacity. Drainage under pasture was less than under cropping but greater than under native vegetation. The deep drainage water (leachate) was of poor quality and will increase salinity if added to good quality groundwater. Leachate at nine sites was too saline to be used (undiluted) for irrigation (>2500 mg Cl/L) and was marginal at the remainder of sites (~800 mg Cl/L). Cropping areas in the QMDB have the precursors for secondary salinity development—high salt loads and an increase in drainage after clearing. The Vertosols and Sodosols studied occur in 90% of croplands in the QMDB. Salinisation will depend on the properties of the underlying regolith and groundwater systems.

The Brigalow Catchment Study revisited: Effects of land development on deep drainage determined from non-steady chloride profiles

Summary A large area of woodland in the brigalow bioregion in semi-arid central Queensland was cleared for agriculture from the 1960s to the 1980s. To assess the risk of salinity associated with land clearing, soil chloride (Cl) was monitored at the Brigalow Catchment Study (BCS), in brigalow ( Acacia harpophylla ) scrub, a cropped catchment and a pasture catchment before and after clearing in 1982. The monitoring sites include three landscape positions, two on clay soils and one on a sodic duplex (Sodosol), within each catchment. An earlier report of deep drainage, using the early soil Cl profiles and steady-state and transient chloride (SODICS) mass balance, was revisited after a further 13 yr and four more sampling times. Profile Cl mass changed little in 18.4 yr at scrub sites, justifying the use of native vegetation sites to represent pre-clearing Cl for paired cleared sites. Steady-state Cl mass balance (CMB) gave deep drainage of 0.13–0.34 mm/yr for nine pre-clearing scrub sites. Large losses of soil Cl occurred under cropping and smaller losses occurred under pasture. Transient CMB gave average deep drainage of 59 and 32 mm/yr for crop and pasture catchments, respectively, during the development phase (1981–1983) when the land was bare following clearing of native vegetation and prior to establishment of crops or pastures. In the 16.7 yr following establishment of agricultural land uses (1983–2000), transient CMB gave average deep drainage of 19.8 (range 3.3–50) and 0.16 (−2.2 to 1.4) mm/yr, respectively, in crop and pasture catchments. The drainage rate under pasture was similar to that under brigalow scrub. In the cropped catchment, drainage for modern farming systems (less tillage, more summer/opportunity crops) was about half that of older farming systems (wheat-summer fallow, more tillage, less stubble retention). Drainage was greater for the Sodosol than for the clay soils under cropping. Deep drainage occurred under cropping even though the soils are considered to have low permeability and the climate is semi-arid, with potential evaporation exceeding rainfall, on average, in all months. Increased drainage at cropped sites has driven a clear exponential loss of soil Cl, as predicted by the transient CMB theory. One cropped site is at or near a new steady-state and the others will reach a new steady-state 50–200 yr after clearing. The leachate is saline with an average Cl concentration of 7000 mg/L and would salinised any groundwater it entered. The salinity risk associated with the drainage is not well understood as yet and will depend on local hydrogeological conditions, which are poorly mapped in the Fitzroy. Effects of these losses of salts on sodicity, soil structure and permeability should also be investigated.

Chloride Homeostasis in Saccharomyces cerevisiae: High Affinity Influx, V-ATPase-dependent Sequestration, and Identification of a Candidate Cl− Sensor

Chloride homeostasis in Saccharomyces cerevisiae has been characterized with the goal of identifying new Cl− transport and regulatory pathways. Steady-state cellular Cl− contents (∼0.2 mEq/liter cell water) differ by less than threefold in yeast grown in media containing 0.003–5 mM Cl−. Therefore, yeast have a potent mechanism for maintaining constant cellular Cl− over a wide range of extracellular Cl−. The cell water:medium [Cl−] ratio is >20 in media containing 0.01 mM Cl− and results in part from sequestration of Cl− in organelles, as shown by the effect of deleting genes involved in vacuolar acidification. Organellar sequestration cannot account entirely for the Cl− accumulation, however, because the cell water:medium [Cl−] ratio in low Cl− medium is ∼10 at extracellular pH 4.0 even in vma1 yeast, which lack the vacuolar H+-ATPase. Cellular Cl− accumulation is ATP dependent in both wild type and vma1 strains. The initial 36Cl− influx is a saturable function of extracellular [36Cl−] with K1/2 of 0.02 mM at pH 4.0 and >0.2 mM at pH 7, indicating the presence of a high affinity Cl− transporter in the plasma membrane. The transporter can exchange 36Cl− for either Cl− or Br− far more rapidly than SO4 =, phosphate, formate, HCO3 −, or NO3 −. High affinity Cl− influx is not affected by deletion of any of several genes for possible Cl− transporters. The high affinity Cl− transporter is activated over a period of ∼45 min after shifting cells from high-Cl− to low-Cl− media. Deletion of ORF YHL008c (formate-nitrite transporter family) strongly reduces the rate of activation of the flux. Therefore, Yhl008cp may be part of a Cl−-sensing mechanism that activates the high affinity transporter in a low Cl− medium. This is the first example of a biological system that can regulate cellular Cl− at concentrations far below 1 mM.

Dietary sodium chloride intake independently predicts the degree of hyperchloremic metabolic acidosis in healthy humans consuming a net acid-producing diet

We previously demonstrated that typical American net acid-producing diets predict a low-grade metabolic acidosis of severity proportional to the diet net acid load as indexed by the steady-state renal net acid excretion rate (NAE). We now investigate whether a sodium (Na) chloride (Cl) containing diet likewise associates with a low-grade metabolic acidosis of severity proportional to the sodium chloride content of the diet as indexed by the steady-state Na and Cl excretion rates. In the steady-state preintervention periods of our previously reported studies comprising 77 healthy subjects, we averaged in each subject three to six values of blood hydrogen ion concentration ([H]b), plasma bicarbonate concentration ([HCO(3)(-)]p), the partial pressure of carbon dioxide (Pco(2)), the urinary excretion rates of Na, Cl, NAE, and renal function as measured by creatinine clearance (CrCl), and performed multivariate analyses. Dietary Cl strongly correlated positively with dietary Na (P < 0.001) and was an independent negative predictor of [HCO(3)(-)]p after adjustment for diet net acid load, Pco(2) and CrCl, and positive and negative predictors, respectively, of [H]b and [HCO(3)(-)]p after adjustment for diet acid load and Pco(2). These data provide the first evidence that, in healthy humans, the diet loads of NaCl and net acid independently predict systemic acid-base status, with increasing degrees of low-grade hyperchloremic metabolic acidosis as the loads increase. Assuming a causal relationship, over their respective ranges of variation, NaCl has approximately 50-100% of the acidosis-producing effect of the diet net acid load.

Anion Channels, Including ClC-3, Are Required for Normal Neutrophil Oxidative Function, Phagocytosis, and Transendothelial Migration

NADPH oxidase activity, phagocytosis, and cell migration are essential functions of polymorphonuclear leukocytes (PMNs) in host defense. The cytoskeletal reorganization necessary to perform these functions has been extensively studied, but the role of cell volume regulation, which is likely dependent upon anion channels, has not been defined. Mice lacking the anion channel ClC-3 (Clcn3(-/-)) died from presumed sepsis following intravascular catheter placement, whereas Clcn3(+/+) littermates survived. We hypothesized that ClC-3 has a critical role in host defense and reasoned that PMN function would be compromised in these mice. Clcn3(-/-) PMNs displayed markedly reduced NADPH oxidase activity in response to opsonized zymosan and modestly reduced activity after phorbol 12-myristate 13-acetate. Human PMNs treated with the anion channel inhibitors niflumic acid or 5-nitro-2-(3-phenylpropylamino)benzoic acid had a very similar defect. ClC-3 protein was detected in the secretory vesicles and secondary granules of resting PMNs and was up-regulated to the phagosomal membrane. Clcn3(-/-) PMNs and human PMNs lacking normal anion channel function both exhibited reduced uptake of opsonized zymosan at 1, 5, and 10 min in a synchronized phagocytosis assay. Niflumic acid-treated PMNs also had impaired transendothelial migration in vitro, whereas migration in vivo was not altered in Clcn3(-/-) PMNs. Selective inhibition of the swelling-activated chloride channel with tamoxifen profoundly reduced PMN migration but had no effect on NADPH oxidase activity. In summary, PMNs lacking normal anion channel function exhibited reduced NADPH oxidase activity, diminished phagocytosis, and impaired migration. ClC-3 was specifically involved in the respiratory burst and phagocytosis.

Defect assessment of Mg-doped GaN by beam injection techniques

The electronic recombination properties of Mg-doped GaN have been investigated by steady state and time-resolved cathodoluminescence (TRCL) in the scanning electron microscope, photocurrent (PC) spectroscopy, and optical beam induced current (OBIC). CL and OBIC maps reveal an inhomogeneous recombination activity in the investigated material. Deep levels giving rise to level-to-band transitions were detected by PC spectroscopy. A large PC quenching observed upon illumination with light of (2.65–2.85) eV is tentatively attributed to metastable traps within the band gap. CL spectra reveal the existence of emission bands centered at 85 K at 3.29, 3.20, 3.15, and 3.01 eV, respectively. Both time-resolved and steady-state CL measurements carried out under different excitation conditions indicate that the 3.15 and 3.01 eV emissions are likely related to donor-acceptor pair transitions. TRCL measurements also reveal different recombination kinetics for these bands and suggest that deep donors are involved in the mechanism responsible for the 3.01 eV emission.

Kinetics and Mechanism of the Gas-Phase Reaction of Cl Atoms and OH Radicals with Fluorobenzene at 296 K

Smog chamber/FTIR techniques were used to study the kinetics and mechanism of the reaction of Cl atoms and OH radicals with fluorobenzene, C6H5F, in 700 Torr of N2 or air diluent at 296 K. Reaction of Cl atoms with C6H5F proceeds via two pathways: H-atom abstraction to give HCl and the C6H4F radical and adduct formation to give the C6H5F−Cl adduct. At 296 K the rate constant for the abstraction channel is k5a(Cl + C6H5F) = (1.1 ± 0.1) × 10-17 cm3 molecule-1 s-1. The C6H5F−Cl adduct undergoes rapid (k ∼ 108 s-1) decomposition to reform C6H5F and Cl atoms and reaction with Cl atoms via a mechanism which, at least in part, leads neither to production of C6H5Cl nor to reformation of C6H5F. As the steady-state Cl atom concentration is increased, the fraction of the C6H5F−Cl adduct undergoing reaction with Cl atoms increases causing an increase in the effective rate constant for the reaction of C6H5F with Cl atoms. The equilibrium between Cl atoms, C6H5F, and the C6H5F−Cl adduct is established rapidly and has an equilibrium constant estimated to be K5b=[C6H5F−Cl]/[C6H5F][Cl] = (3.2 ± 2.4) × 10-18 cm3 molecule-1. An upper limit of k9 < 6 × 10-17 cm3 molecule-1 s-1 was established for the reaction of the C6H5F−Cl adduct with O2. The reaction of OH radicals with C6H5F was studied and a rate constant of k(OH + C6H5F) = (7.9 ± 2.2) × 10-13 cm3 molecule-1 s-1 was determined. The results are discussed with respect to the available literature concerning reaction of Cl atoms and OH radicals with aromatic compounds. As part of this work, rate constants for reaction of OH radicals with 2-, 3-, and 4-fluorophenol of (6.3 ± 1.3) × 10-12, (2.3 ± 0.5) × 10-11, and (2.5 ± 0.5) × 10-11 cm3 molecule-1 s-1 were determined.

ATP-driven, Na(+)-independent inward Cl- pumping in neuroblastoma cells.

In immature neurones, the steady-state intracellular Cl- concentration [Cl-](i) is generally higher than expected for passive distribution, and this is believed to be due to Na(+)-K(+)-2Cl(-) co-transport. Here, we show that N2a neuroblastoma cells, incubated in HEPES-buffered NaCl medium maintain a [Cl-](i) around 60 mm, two- to threefold higher than expected for passive distribution at a membrane potential of - 49 mV. When the cells were transferred to a Cl(-) -free medium, [Cl-](i) decreased quickly (t(1/2) < 5 min), suggesting a high Cl- permeability. When the intracellular ATP concentration was reduced to less than 1 mm by metabolic inhibitors, the initial rate of (36) Cl- uptake was strongly inhibited (60-65%) while steady-state [Cl-](i) decreased to 24 mm, close to the value predicted from the Nernst equilibrium. Moreover, after reduction of [ATP](i) and [Cl-](i) by rotenone, the subsequent addition of glucose led to a reaccumulation of Cl-, in parallel with ATP recovery. Internal bicarbonate did not affect Cl- pumping, suggesting that Cl-/HCO(3)(-) exchange does not significantly contribute to active transport. Likewise, Na(+) -K(+) -2Cl(-) co-transport also appeared to play a minor role: although mRNA for the NKCC1 form of the co-transporter was detected in N2a cells, neither the initial rate of (36)Cl- uptake nor steady-state [Cl-](i) were appreciably decreased by 10 microm bumetanide or replacement of external Na(+) by choline. These results suggest that a highly active ATP-dependent mechanism, distinct from Na(+) -K(+) -2Cl(-) co-transport, is responsible for most of the inward Cl- pumping in N2a cells.

Kinetics and Mechanism of the Gas-Phase Reaction of Cl Atoms with Benzene

The gas-phase reaction of Cl atoms with benzene has been studied using both experimental and computational methods. The bulk of the kinetic data were obtained using steady-state photolysis of mixtures containing Cl2, C6H6, and a reference compound in 120−700 Torr of N2 diluent at 296 K. Reaction of Cl atoms with C6H6 proceeds via two pathways; (a) H-atom abstraction and (b) adduct formation. At 296 K the rate constant for the abstraction channel is k1a = (1.3 ± 1.0) × 10-16 cm3 molecule-1 s-1. Phenyl radicals produced via H-atom abstraction from C6H6 react with Cl2 to give chlorobenzene. The main fate of the C6H6−Cl adduct is decomposition to reform C6H6 and Cl atoms. A small fraction of the C6H6−Cl adduct undergoes reaction with Cl atoms via a mechanism which does not lead to the production of C6H5Cl, or the reformation of C6H6. As the steady-state Cl atom concentration is increased, the fraction of the C6H6−Cl adduct undergoing reaction with Cl atoms increases causing an increase in the effective rate c...

Mechanisms of chloride transport in the proximal tubule.

The major fraction of filtered Cl- is reabsorbed in the proximal tubule. An important component of Cl- reabsorption is passive and paracellular, driven by the lumen-negative potential difference in the early proximal tubule and the outwardly directed concentration gradient for Cl- in the later proximal tubule. Evidence suggests that a significant additional component of NaCl reabsorption in the proximal tubule is active and transcellular. Cl-/formate and Cl-/oxalate exchangers have been identified as mechanisms of uphill Cl- entry across the apical membrane. For steady-state Cl- absorption to occur by these mechanisms, formate and oxalate must recycle from lumen to cell. Recent studies indicate that recycling of formate occurs by H(+)-coupled formate transport in parallel with Na+/H+ exchange, whereas oxalate recycling takes place by oxalate/sulfate exchange in parallel with Na(+)-sulfate cotransport. The predominant route for Cl- exit across the basolateral membrane is via Cl- channels. Unresolved issues include the adequacy of formate recycling to sustain Cl- absorption by Cl-/formate exchange, the existence and contributions of additional mechanisms for apical Cl entry and basolateral Cl- exit, and the relative magnitudes of transcellular and paracellular transport under physiological conditions. In addition, the molecular identification and mechanisms of regulation of the Cl-/formate and Cl-/oxalate exchangers remain to be defined.