Chloride Binding Research Articles

Effect of sub-zero versus sub-freezing temperature on chloride diffusion and binding in concrete

Effect of temperature on chloride diffusion in concrete has been extensively studied by others and it is found to follow Arrhenius law. However, the lowest exposure temperature studied to date has been −4 °C, but due to supercooling the concrete pore solution is not expected to freeze at −4 °C. It is hypothesized here that below the supercooling temperature, some of the pore water will freeze and pore ice will form, which increases the pores tortuosity, and reduces their connectivity, resulting in reduced diffusivity. To test this hypothesis, concrete samples are subjected to natural diffusion in a 10% NaCl solution under 5, 0, −5, or −15 °C for 3 and 6 months. It is discovered that Arrhenius law can capture the effect of temperature on chloride diffusion, but when the temperature falls below the supercooling temperature, the effect of pore ice must be also considered. A method is proposed for capturing the latter effect. The diffusion coefficients of the frozen specimens computed by the proposed method differ maximum 15% from the corresponding experimental values.

Durability of clinker reduced shotcrete: Ca2+ leaching, sintering, carbonation and chloride penetration

The reduction of clinker use is mandatory to lower the negative environmental impact of concrete. In shotcrete mixes, similarly to the case of conventional concrete, the use of supplementary cementitious materials (SCMs) and proper mix design allow for the substitution of clinker without compromising the mechanical properties. However, the impact of the substitution on the durability of shotcrete needs to be further assessed and understood. The results from the present study, obtained from real-scale sprayed concrete applications, show a reduction of the Ca2+ leaching and sintering potential of clinker-reduced shotcrete mixes due to the presence of SCMs. This positive effect, crucial for low maintenance costs of tunnels, is mainly related to a reduced portlandite content, which on the other hand negatively affects the carbonation resistance of shotcrete. Additionally, the hydration of SCMs positively influences the chloride penetration resistance presumably due to a combination of microstructural changes and changes in the chloride binding capacity. Differences found in the pore size distribution of the various mixes have low impact on the determined durability parameters, in particular compared to the effect of inhomogeneities produced during shotcrete application.

Chloride permeability and chloride binding capacity of nano-modified concrete

Chloride permeability and chloride binding capacity are two important factors for assessment of the rebar corrosion risk in reinforced concrete structures. In this work, the chloride permeability and chloride binding capacity of concrete modified with nano-SiO2 (NS), nano-CaCO3 (NC), multi-walled carbon nanotubes (CNT) were evaluated. The results demonstrate that incorporation of nanomaterials significantly decreases the chloride diffusion coefficients by refining the pore structure and reducing the pore volume. The experimental data strongly suggest the existence of a percolation threshold (critical porosity), below which the chloride permeability decreases dramatically. Addition of NS compromises the chloride binding capacity due to decreased pH value of pore solution, which results in dissolution of Friedel's salt. XRD suggests that adding NC restrains the formation of AFm phase, which is mainly responsible for the chemical binding. TG/DTG analyses confirm that adding CNT facilitates the formation of more amount of hydrates, thus enhancing the chloride binding. Addition of NS and NC leads to a decreased amount of Friedel's salt and thereby weakens the chemical binding.

Numerical investigation of external sulfate attack and its effect on chloride binding and diffusion in concrete

Reinforced concrete (RC) structures may suffer from serious durability problems during long-term service. To investigate the deterioration of RC structures subjected to the dual attacks of chlorides and sulfates, this study proposes a coupled model for external sulfate attack (ESA) and its effect on chloride binding and diffusion. To account for the influence of sulfate attack on chloride binding, a reduction function is proposed. The effect of sulfate-induced damage on the chloride diffusion and chloride binding is considered through a damage function. The coupled model is validated against third-party experimental data from multiple perspectives. Some important factors such as solution concentration, immersion time, curing time and water-cement ratio, as well as how these factors affect the impact of sulfate attack on chloride transport, were elaborated. The findings may bring insights to the durability design of RC structures serving in harsh environments.

Possible Involvement of Muscarinic Receptor Blockade in Mirabegron Therapy for Patients with Overactive Bladder.

The selective β 3-adrenoceptor agonist mirabegron, an established alternative to antimuscarinic therapy for patients with overactive bladder, induces additional effects against receptors, transporters, and hepatic enzymes. The present study aimed to elucidate the effects of mirabegron on muscarinic receptors in the rat bladder using radioligand binding and functional assays. Mirabegron (0.1-100 μM) inhibited specific [N-methyl-3H]scopolamine methyl chloride binding in the bladder and other tissues of rats in a concentration-dependent manner. Binding affinity in the bladder was similar to that in the heart and significantly higher than those in the submaxillary gland and brain. Mirabegron induced the concentration-dependent relaxation of carbachol-induced contractions in the rat isolated bladder. Further analyses using a two-site model revealed that the relative quantities of high- and low-affinity components for mirabegron were 44.5% and 55.5%, respectively. Respective pEC50 values were 7.06 and 4.97. Based on the receptor binding affinity and pharmacokinetics of mirabegron, muscarinic receptor occupancy in the human bladder for 24 hours after the administration of a single oral dose of 50 mg mirabegron was 37%-76%. The present results demonstrate for the first time that mirabegron may relax the detrusor smooth muscle not only by β 3-adrenoceptor activation but also muscarinic receptor blockade. SIGNIFICANCE STATEMENT: Mirabegron, the first selective β 3-adrenoceptor agonist, represents an alternative to antimuscarinic agents for management of overactive bladder (OAB). The present study aimed to clarify whether mirabegron directly binds to muscarinic receptors and affects cholinergic agonist-induced contractions in rat urinary bladder and to predict muscarinic receptor occupancy in human bladder after oral administration of mirabegron. The results demonstrated that mirabegron therapy for patients with OAB may be due not only to β 3-adrenoceptor activation but also muscarinic receptor blockade.

Calmodulin binds to the STAS domain of SLC26A5 prestin with a calcium-dependent, one-lobe, binding mode

SLC26A5 transporter prestin is fundamental for the higher hearing sensitivity and frequency selectivity of mammals. Prestin is a voltage-dependent transporter found in the cochlear outer hair cells responsible for their electromotility. Intracellular chloride binding is considered essential for voltage sensitivity and electromotility. Prestin is composed by a transmembrane domain and by a cytosolic domain called STAS. There is evidence of a calcium/calmodulin regulation of prestin mediated by the STAS domain. Using different biophysical techniques, namely SEC, CD, ITC, MST, NMR and SAXS, here we demonstrate and characterize the direct interaction between calmodulin and prestin STAS. We show that the interaction is calcium-dependent and that involves residues at the N-terminal end of the “variable loop”. This is an intrinsically disordered insertion typical of the STAS domains of the SLC26 family of transporters whose function is still unclear. We derive a low-resolution model of the STAS/CaM complex, where only one lobe of calmodulin is engaged in the interaction, and build a model for the entire dimeric prestin in complex with CaM, which can use the unoccupied lobe to interact with other regions of prestin or with other regulatory proteins. We show that also a non-mammalian STAS can interact with calmodulin via the variable loop. These data start to shed light on the regulatory role of the STAS variable loop of prestin.

The Stability and Chloride Entrapping Capacity of ZnAl-NO2 LDH in High-Alkaline/Cementitious Environment

In this work, the ZnAl-NO2 LDH (layered double hydroxide) is investigated as a possible additive for mitigating the chloride-induced corrosion of steel in reinforced concrete. The investigation focused on the stability and chloride binding capacity of this LDH in the pH range typical of cementitious materials. Until pH = 12.5 the material was stable and effective in capturing chloride ions from the surrounding aqueous environment. For higher pH, precisely that of hydrated cement, the LDH was partially dissolved and OH− preferentially entrapped instead of Cl−. These results suggested that ZnAl-NO2 has excellent chloride entrapping capability at neutral pH, but this is reduced with increasing pH. However, when the LDH was incorporated into mortars, the chloride ingress was delayed, signifying that the dissolution of LDH leads to a secondary mechanism responsible for chloride capture.

Chloride binding and transport characteristic of phosphoaluminate cement-based marine sand coating subjected to marine environment

Marine sand with more or less aggressive Cl− has received considerable attention because of the depletion of river sand resources; however, it should be treated to avoid harmful effects on reinforced concrete. Phosphoaluminate cement (PAC)-based coating is a promising method to treat marine sand, and it can potentially solidify Cl−. In the experiment, the characteristics of Cl− binding and transport of PAC-based coating material were thoroughly investigated. The results indicated that the characteristic of prohibiting Cl− transport by PAC was more effective than using Portland cement in terms of erosion depth and free surface Cl− concentration. The PAC-based coating material can bind large amounts of Cl− efficiently by chemical bonding and improve the electrochemical performance of steel bar. In concrete, Cl− can be bonded by PAC-based marine sand coating. Further, PAC-based marine sand coating can prohibit the transport of Cl−, and significantly improve the resistance to chloride penetration of concrete.

Sequestration and release of nitrite and nitrate in alkali-activated slag: A route toward smart corrosion control

Intercalating the corrosion inhibitive ions in hydrotalcite is a promising approach to improve the long-term efficiency of inhibitors in corrosion protection of steel in reinforced concrete. In this work, the potential of autogenously generating nitrite- and nitrate-intercalated hydrotalcite in alkali-activated slag (AAS) is investigated. The results show that the added nitrite and nitrate ions are preferably uptaken in the interlayer structure of hydrotalcite in AAS, and the sequestered nitrite and nitrate are released upon chloride exposure in seawater and NaCl solution. The incorporation of nitrite and nitrate has little detrimental effects on the chloride binding capacity of AAS but slightly enhances the chloride ingress due to the pore coarsening effect. Similar to ordinary Portland cement (OPC), AAS is more permeable to the chloride in seawater than NaCl solution. However, unlike the release of bound chloride contributed by ettringite formation in seawater-exposed OPC, the enhanced chloride ingress in seawater-exposed AAS is primarily attributed to the aggravated pH reduction at the exposure front due to brucite formation. This study contributes to the design of alkali-activated binders with a smart inhibitor releasing ability for mitigating corrosion of steel in concrete.

The effect of chloride ingress in reinforced geopolymer concrete exposed in the marine environment

Determining the durability of geopolymer materials in a real field environment is important to enhance the feasibility of their use in concrete production.. This paper investigates the durability of slag-based geopolymer concrete (SGPC-M) exposed in the spray/splash zone of the marine environment. Properties of SGPC-M in the marine environment including chloride resistance, absorption characteristics, and the scaling effect were examined and compared with ordinary Portland Cement concrete (OPC-M) properties in the same environment. The test results indicate that the SGPC-M has a lower resistance to chloride penetration than the OPC- M concrete. Compared to the OPC-M, higher values of diffusion coefficient and lower values of chloride binding capacity were obtained for the SGPC-M concrete. Besides, the study on the pore characteristics and absorption behaviour of the concrete indicates that the SGPC-M possesses more pores than the OPC-M, which is related to the lower resistance to chloride penetration in the marine environment. Furthermore, the microstructural changes due to chloride attack in the SGPC-M are different than the changes in the OPC-M concrete, which was identified from the SEM and XRD analysis.

Influence of pH on chloride binding isotherms for cement paste and its components

In this paper, chloride (Cl−) binding isotherms are developed for cement hydration compounds, specifically, calcium-silicate-hydrates (CSH) and AFm phases including mono-sulfate aluminate, hydroxy-AFm, monocarbonate-AFm, and hemicarbonate-AFm, in simulated concrete pore solutions to account for the effect of pH and the presence of other ions. pH and the presence of other ions have a strong influence on the Cl− binding capacity of cement compounds, which have not been taken into consideration in previous research. A novel experimental technique is developed to characterize the binding capacity from very low (1 mM) to very high concentrations (5 M). To overcome the existing challenges of measuring both low and high Cl− concentrations without significant dilution and in the presence of SO42− and OH− ions, a potentiometric method was used. The amorphous CSH in the hydrated cement paste; thus, the heterogeneity of the hydrated components of the cement paste was also quantified and accounted for in this study.

Chloride binding and desorption properties of the concrete containing corn stover ash

This study investigates the performance of binary blended concrete mixtures containing ordinary Portland cement (OPC) and corn stover ash (CSA) in terms of chloride ingress, chloride binding capacity, and resistance to chloride desorption. Concrete mixtures with water-to-cementitious material ratios of 0.45 and 0.54, and CSA replacement levels of 5 and 20% by mass of cement were prepared and exposed to various chloride solution concentrations ranging from 0.1 to 2 mol/L after 28 and 112 d of curing. Results show that pretreated CSA can improve the long-term chloride resistance of concrete, mainly due to its positive influence on promoting pozzolanic reactions. The results demonstrate that CSA concrete has a lower chloride binding capacity than OPC. However, the chloride desorption testing results in a low-pH environment suggest that CSA concrete is more durable than OPC concrete, and fewer chlorides disassociate from a drop in pH of the exposure solution.

On the relationship between anion binding and chloride conductance in the CFTR anion channel

Mutations at many sites within the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel pore region result in changes in chloride conductance. Although chloride binding in the pore – as well as interactions between concurrently bound chloride ions – are thought to be important facets of the chloride permeation mechanism, little is known about the relationship between anion binding and chloride conductance. The present work presents a comprehensive investigation of a number of anion binding properties in different pore mutants with differential effects on chloride conductance. When multiple pore mutants are compared, conductance appears best correlated with the ability of anions to bind to the pore when it is already occupied by chloride ions. In contrast, conductance was not correlated with biophysical measures of anion:anion interactions inside the pore. Although these findings suggest anion binding is required for high conductance, mutations that strengthened anion binding had very little effect on conductance, especially at high chloride concentrations, suggesting that the wild-type CFTR pore is already close to saturated with chloride ions. These results are used to support a revised model of chloride permeation in CFTR in which the overall chloride occupancy of multiple loosely-defined chloride binding sites results in high chloride conductance through the pore.

Effect of temperature on the chloride binding capacity of cementitious materials

The effect of temperature on the chloride binding capacity (CBC) of cementitious materials was investigated. A reactive transport model including thermodynamic equilibrium, kinetic control and surface complexation was applied to investigate this effect. The surface complexation model was completed by introduction of the equilibrium constant of calcium silicate hydrate (C–S–H) complexation reactions at different temperatures (5, 21 and 35°C). In order to validate the developed numerical model, the results were compared with experimental data obtained from the literature. Good agreement was found between the numerical and experimental CBCs. The effect of temperature on the CBC of cementitious materials was evaluated and is discussed in this paper. The van 't Hoff equation of C–S–H surface complexation reactions (SCRs) and variation of the standard thermodynamic properties of the SCR (ΔrHT0 (kJ/K) and ΔrST00) at the reference temperature of T0 = 25°C and p0 = 1·1013 × 105 Pa are also presented.

Hydration and counterion binding of aqueous acetylcholine chloride and carbamoylcholine chloride.

The hydration and Cl- ion binding of the neurot†ransmitter acetylcholine (ACh+) and its synthetic analogue, carbamoylcholine (CCh+), were studied by combining dilute-solution conductivity measurements with dielectric relaxation spectroscopy and statistical mechanics calculations at 1D-RISM and 3D-RISM level. Chloride ion binding was found to be weak but not negligible. From the ∼30 water molecules coordinating ACh and CCh+ only ∼1/3 is affected in its rotational dynamics by the cation, with the majority - situated close to the hydrophobic moieties - only retarded by a factor of ∼2.5. At vanishing solute concentration cations and the ∼3-4 H2O molecules hydrogen bonding to the CO group of the solute exhibit similar rotational dynamics but increasing concentration and temperature markedly dehydrates ACh+ and CCh+.

Synthesis and crystal structure of the simultaneous binding of Ni(ii) cation and chloride by the protonated 2,4,6 tris-(2-pyridyl)-1,3,5 triazine ligand: theoretical investigations of anion⋯π, π⋯π and hydrogen bonding interactions

A new octahedral Ni(ii) complex of a protonated 2,4,6-tris(2-pyridyl)-1,3,5-triazine ligand has been synthesized and X-ray analysis exhibited cooperative anion–π and H-bonding interactions.

Study of Blood Serum Biochemical Profile and Pathological Changes in <i>Haemonchosis</i> Experimentally Induced in Goats

<i>Haemonchus contortus</i> (<i>H. contortus</i>) parasite causes various functional derangements in the host body. This experimental study was established to appraise the remedial effect of <i>Balanites aegyptiaca</i> fruit’s ethanolic extract (BAF-EE) on experimentally induced haemonchosis in goats. Blood serum biochemical parameters and pathological changes were perused. Twelve male goats were randomly divided into 4 equal groups, G1 (infected-untreated), G2 (infected- BAF-EE treated), G3 (infected-albendazole treated) and G4 (uninfected-BAF-EE treated). Experimental infection was conducted with a single oral dose of 10x³ infective third larval stage (L3) of <i>H. contortus</i> at 0-time, whereas treatment with BAF-EE and albendazole was given at a single oral dose of 9g and 5mg/kg body wieght respectively in the 5^th week post infection (PI). Blood samples were drawn on zero time, 3^rd week PI and then biweekly till the 9^th week for serum biochemical analyses. At the end of the experiment, all animals were slaughtered to estimate histopathological alterations in the abomasal and hepatic tissues. Serum biochemistry of infected animals showed significant depression of total serum protein (TP), albumin, albumin/globulin (A/G) ratio, total antioxidant capacity (TAC) and calcium (Ca) levels compared to uninfected goats. Significant elevation was observed in values of aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma-glutamyl transferase (γGT), cholesterol, urea and creatinine of infected animals, while no significant differences were recorded in levels of inorganic phosphorus (P), potassium (K), sodium (Na), chloride (Cl) and total iron binding capacity (TIBC). Histopathological studies conducted on abomasa of infected-untreated animals revealed inflammation, necrosis, petechial hemorrhages and intense cellular infiltration. Liver showed bile duct hyperplasia, degeneration of hepatocytes and cell infiltration. Histopathological alterations in tissues of infected – treated animals were lower in intensity than those of infected-untreated goats. Results of the present experiment demonstrated that BAF-EE has an anti-parasitic and hepatoprotective effects as well as it improves serum biochemical alterations and oxidative stress in goats infected with <i>H. contortus </i>parasite. The present findings nominate the use of this plant as a novel safe natural anthelmintic agent.

A single point mutation converts a proton-pumping rhodopsin into a red-shifted, turn-on fluorescent sensor for chloride.

The visualization of chloride in living cells with fluorescent sensors is linked to our ability to design hosts that can overcome the energetic penalty of desolvation to bind chloride in water. Fluorescent proteins can be used as biological supramolecular hosts to address this fundamental challenge. Here, we showcase the power of protein engineering to convert the fluorescent proton-pumping rhodopsin GR from Gloeobacter violaceus into GR1, a red-shifted, turn-on fluorescent sensor for chloride in detergent micelles and in live Escherichia coli. This non-natural function was unlocked by mutating D121, which serves as the counterion to the protonated retinylidene Schiff base chromophore. Substitution from aspartate to valine at this position (D121V) creates a binding site for chloride. The binding of chloride tunes the pKa of the chromophore towards the protonated, fluorescent state to generate a pH-dependent response. Moreover, ion pumping assays combined with bulk fluorescence and single-cell fluorescence microscopy experiments with E. coli, expressing a GR1 fusion with a cyan fluorescent protein, show that GR1 does not pump ions nor sense membrane potential but instead provides a reversible, ratiometric readout of changes in extracellular chloride at the membrane. This discovery sets the stage to use natural and laboratory-guided evolution to build a family of rhodopsin-based fluorescent chloride sensors with improved properties for cellular applications and learn how proteins can evolve and adapt to bind anions in water.

A photoswitchable strapped calix[4]pyrrole receptor: highly effective chloride binding and release.

A stiff-stilbene strapped calix[4]pyrrole receptor can be reversibly switched by light between a strong chloride-binding Z-isomer and a very weakly binding E-isomer. The light-induced switching process is monitored by UV-Vis and 1H NMR spectroscopy and chloride binding is studied in detail using both 1H NMR and ITC titrations in DMSO and MeCN. In DMSO, at millimolar concentrations, switching from a fully bound to an almost fully unbound state can be triggered. Quantification of the binding constants in MeCN reveals an extraordinary 8000-fold affinity difference between the Z- and E-isomer. Single crystal X-ray crystallographic analysis gives insight into the structure of the photogenerated E-isomer and the geometry of the chloride-bound receptors is optimized by DFT calculations. The highly effective control of binding affinity demonstrated in this work opens up new prospects for on demand binding and release in extractions and photocontrol of membrane transport processes, among other applications.

Improving the Chloride Binding Capacity of Alkali Activated Slag by Calcium and Aluminium Containing Phases

Improving the Chloride Binding Capacity of Alkali Activated Slag by Calcium and Aluminium Containing Phases