A new post-treatment process for attaining Ca 2+, Mg 2+, SO 42− and alkalinity criteria in desalinated water

We have studied the molecular determinants of ion permeation through the TRPV4 channel (VRL-2, TRP12, VR-OAC, and OTRPC4). TRPV4 is characterized by both inward and outward rectification, voltage-dependent block by Ruthenium Red, a moderate selectivity for divalent versus monovalent cations, and an Eisenman IV permeability sequence. We identify two aspartate residues, Asp(672) and Asp(682), as important determinants of the Ca(2+) sensitivity of the TRPV4 pore. Neutralization of either aspartate to alanine caused a moderate reduction of the relative permeability for divalent cations and of the degree of outward rectification. Neutralizing both aspartates simultaneously caused a much stronger reduction of Ca(2+) permeability and channel rectification and additionally altered the permeability order for monovalent cations toward Eisenman sequence II or I. Moreover, neutralizing Asp(682) but not Asp(672) strongly reduces the affinity of the channel for Ruthenium Red. Mutations to Met(680), which is located at the center of a putative selectivity filter, strongly reduced whole cell current amplitude and impaired Ca(2+) permeation. In contrast, neutralizing the only positively charged residue in the putative pore region, Lys(675), had no obvious effects on the properties of the TRPV4 channel pore. Our findings delineate the pore region of TRPV4 and give a first insight into the possible architecture of its permeation pathway.

A cost effective method for improving the quality of inland desalinated brackish water destined for agricultural irrigation

The rat mesenteric vasculature contains high affinity binding sites specific for [3H]Arg8-vasopressin which mediate its vasoconstrictor action. We have investigated the in vitro effect of monovalent and divalent cations and guanine nucleotides on the interactions between [3H]Arg8-vasopressin and its receptor in this preparation. Binding was increased by divalent cations from fourfold in the presence of Mg2+ at 5 mM to ninefold in the presence of Mn2+ at 5 mM. The potency order of divalent cations to increase binding was Mn2+ greater than Co2+ greater than Ni2+ greater than Mg2+ greater than Ca2+ approximately equal to control without cations. Addition of Na2+ or other monovalent cations (K+, Li+, and NH4+) in the presence or absence of divalent cations reduced binding significantly. Analysis of saturation binding curves showed a single high affinity site. In the presence of 5 mM Mn2+, binding capacity (Bmax) increased to 139 +/- 23 fmol/mg protein. Receptor affinity was enhanced (KD decreased to 0.33 +/- 0.07 nM). In presence of 5 mM Mg2+ or 150 mM Na+, Bmax and affinity were reduced. The addition of 100 microM GTP or its nonhydrolyzable analogue, Gpp(NH)p, reduced receptor affinity in the presence of Mn2+ + Na+, Mg2+, and Mg2+ + Na+, but not in the presence of Mn2+ alone. Computer modeling of competition binding curves demonstrated that in contrast with saturation studies, the data were best explained by a two-site model with high affinity, low capacity sites and low affinity, high capacity sites. Mn2+ or Mn2+ + Na+ with or without guanine nucleotides resulted in a predominance of high affinity sites. GTP or Gpp(NH)p in the presence of Mg2+ or Mg2+ + Na+ induced a reduction of affinity of the high affinity binding sites and the number of these sites. In the presence of Mg2+ + Na+ and guanine nucleotides, high affinity sites were maximally decreased. An association kinetic study indicated that the association rate constant (K+1) was increased by divalent cations and reduced by guanine nucleotides, without change in the dissociation rate constant (K-1). The equilibrium dissociation constant (KD) calculated with these rate constants (K-1/K+1) was similar to that obtained in saturation experiments at steady state. Dissociation kinetics were biphasic, indicating the presence of two receptor states, one of high and one of low affinity, associated with a slow and a rapid dissociation rate. Cations and guanine nucleotides interact with one or more sites closely associated with vasopressin receptors, including possibly with a GTP-sensitive regulatory protein, to modulate receptor affinity for vasopressin.

The recent supply of large volumes of seawater desalinated water in Israel prompted both the development of new water quality standards and the development of a novel post treatment process, designed to comply with the new standards at a cost effective price. The new process is designed to supply water with alkalinity, Ca2 + and calcium carbonate precipitation potential values as required in the new criteria, along with the addition of a threshold Mg2 + concentration recently recommended by the WHO. The current paper describes the process in general, and focuses in particular on attaining these criteria while maintaining a low total hardness concentration (120 mg/L as CaCO3). The process is based on dissolving calcite using H2SO4 and replacing the excess calcium ions generated in this process by Mg2 + ions (using a specific cation exchange resin—Amberlite) and by Na+ (using a second cation exchange resin—chabazite, from the zeolite group). Once exhausted the resins are re-loaded with Mg2 + and Na+ by the brine generated in the RO process, thus no unwanted brines are generated. A case study is presented for which operational costs were approximated at 0.034 $US/m3 product water.

Selective capillary electrophoresis separation of mono and divalent cations within a high-surface area-to-volume ratio multi-lumen capillary

An extraction technique was used to estimate the radionuclide available fraction in two mineral soils, with loam-sandy and loamy textures, which had been contaminated by an aerosol containing 85Sr and 134Cs. A set of extractant solutions, including monovalent and divalent cations, and the experimental conditions (extraction time, ratio of volume of extractant solution to mass of soil, single or successive extractions, use of an ionic adsorbent) were tested. When applying single extractions, radiostrontium was less sensitive to changes in the extractant solutions. For radiocaesium, the desorption yields were higher with monovalent cations, although successive extractions suggested a potential collapsing effect of monovalent cations in the loam-sandy soil, since the divalent cation led to a higher desorption yield. In general, the higher the solution/soil ratios and time of extraction, the higher were the desorption yields, although a dependence on the type of radioactive contamination (aerosol and soluble) was noticed for radiostrontium. It was difficult to choose a common procedure to quantify the available fraction for all the radionuclides, but overnight extraction with a monovalent cation is suggested. Predictions of radionuclide mobility based on the available fraction alone depended on whether single or successive extractions were taken into account, and also on whether divalent or monovalent cations were considered. The comparison with vertical migration data suggested that an overnight extraction with a monovalent cation could also be chosen for prediction purposes.

Dialkylglycine decarboxylase (DGD) is a tetrameric pyridoxal phosphate (PLP)-dependent enzyme that catalyzes both decarboxylation and transamination in its normal catalytic cycle. Its activity is dependent on cations. Metal-free DGD and DGD complexes with seven monovalent cations (Li(+), Na(+), K(+), Rb(+), Cs(+), NH(4)(+), and Tl(+)) and three divalent cations (Mg(2+), Ca(2+), and Ba(2+)) have been studied. The catalytic rate constants for cation-bound enzyme (ck(cat) and ck(cat)/bK(AIB)) are cation-size-dependent, K(+) being the monovalent cation with the optimal size for catalytic activity. The divalent alkaline earth cations (Mg(2+), Ca(2+), and Ba(2+)) all give approximately 10-fold lower activity compared to monovalent alkali cations of similar ionic radius. The Michaelis constant for aminoisobutyrate (AIB) binding to DGD-PLP complexes with cations (bK(AIB)) varies with ionic radius. The larger cations (K(+), Rb(+), Cs(+), NH(4)(+), and Tl(+)) give smaller bK(AIB) ( approximately 4 mM), while smaller cations (Li(+), Na(+)) give larger values (approximately 10 mM). Cation size and charge dependence is also found with the dissociation constant for PLP binding to DGD-cation complexes (aK(PLP)). K(+) and Rb(+) possess the optimal ionic radius, giving the lowest values of aK(PLP). The divalent alkaline earth cations give aK(PLP) values approximately 10-fold higher than alkali cations of similar ionic radius. The cation dissociation constant for DGD-PLP-AIB-cation complexes (betaK(M)z+) was determined and also shown to be cation-size-dependent, K(+) and Rb(+) yielding the lowest values. The kinetics of PLP association and dissociation from metal-free DGD and its complexes with cations (Na(+), K(+), and Ba(2+)) were analyzed. All three cations tested increase PLP association and decrease PLP dissociation rate constants. Kinetic studies of cation binding show saturation kinetics for the association reaction. The half-life for association with saturating Rb(+) is approximately 24 s, while the half-life for dissociation of Rb(+) from the DGD-PLP-AIB-Rb(+) complex is approximately 12 min.

The impact of ions on hydrogel strength is not well understood, in particular with regards to specific ion effects for cations. Herein, we find that divalent and monovalent cations in most cases reduce the modulus and melting temperature while increasing the gelation time of gelatin hydrogels. This behavior is in contrast to the well-known stiffening effect of trivalent metals. The melting temperature, the logarithm of the gelation time, and the logarithm of the amplitude of the complex modulus were found to follow a power law dependence on ionic strength: kI x. The power law exponent, x, was found to be universal within the groups of monovalent and divalent cations. The prefactor k depended linearly on the ionic radius, which was used as a proxy for ion polarizability. The slope of this linear dependence was different for monovalent and divalent cations.

Membrane potential of single asymmetric nanopores: Divalent cations and salt mixtures

The effects of monovalent (Na+, Li+, K+, Rb+) and divalent (Ca2+, Mg2+, Mn2+) cations on dihydropyridine calcium antagonist binding sites in brain and cardiac membranes were investigated using a low ionic strength buffer (5 mM Tris-HCl, pH 7.4), and the dihydropyridine, [3H]-nitrendipine. At 25 degrees C, the monovalent cations Na+, Li+, and K+ (100 mM) but not Rb+ significantly decreased the apparent dissociation constant (KD) but had no effect on the maximum binding site capacity (Bmax) of [3H]-nitrendipine in brain. The divalent cations Ca2+, Mg2+, and Mn2+ (2 mM) significantly increased the Bmax, but did not affect the KD of [3H]-nitrendipine. The effects of cations were concentration-dependent (EC50 monovalent cations 10-25 mM; EC50 divalent cations 50-200 microM) and demonstrated brain region selectivity. The effect of Ca2+, but not Mg2+ or Mn2+ on [3H]-nitrendipine binding was described by a two-site model. At 25 degrees C, neither mono- nor divalent cations altered the characteristics of [3H]-nitrendipine binding to rat cardiac membranes. At 37 degrees C, Na+ (100 mM) but not K+ (100 mM) significantly increased the Bmax of [3H]-nitrendipine in rat brain membranes. Ca2+ (2 mM) significantly increased the Bmax of [3H]-nitrendipine binding to rat brain membranes to a greater extent than at 25 degrees C. Both Na+ and K+ had no effect on [3H]-nitrendipine binding to cardiac membranes, while Ca2+ (2 mM) significantly decreased the KD of [3H]-nitrendipine. It is suggested that the selective effects of mono- and divalent cations on [3H]-nitrendipine binding to rat brain and cardiac membranes may be associated with differences in the calcium current blocking activity of dihydropyridine calcium antagonists in brain and cardiac tissues.

Dlvo and hydration forces between mica surfaces in Mg 2+, Ca 2+, Sr 2+, and Ba 2+ chloride solutions

The two-phase extraction technique has been used to study the equilibrium between A23187, metal cations, and H+. Under these conditions the ionophore forms charge neutral isostoichiometric complexes with divalent cations in which both carboxylate groups of the 2:1 A23187:M2+ complexes are deprotonated. In ethanol, however, the methyl ester of A23187 also binds divalent cations indicating that protonated complexes between A23187 and cations should also exist. With monovalent cations, A23187 forms two charge-neutral complexes of stoichiometries and relative stabilities: A2HM greater than AM. Examination of energy utilization K+ and H+ movements, and light scattering capacity of mitochondria in the presence of divalent cation chelators, A23187, and valinomycin demonstrates that A23187 can act as a nigericin type K+ ionophore under appropriate conditions. Formation constants for the A2HM complexes with monovalent cations indicate that with appropriate conditions transport of Li+ and Na+ mediated by A23187 would also be expected. The binding constant data and associated free energies of complex formation are compared as a function of ionic radius and of cation charge. The data indicate that lack of conformational mobility in A23187 is responsible for the high cation size selectivity of this compound. To explain the transport selectivity of A23187 for divalent cations, it is proposed that this ionophore forms a family of five complexes, isostoichiometric between cations of different valence but of which only charge-neutral species are permeant to membranes. The charge of a given complex is in turn determined by that of the cation. The concept is consistent with the divalent cation transport specificity of A23187, explains the observed monovalent cation transport, and is useful in rationalizing the differences in charge selectivity between A23187 and X-537A.

Characteristic responses of a 1,2-dioleoyl-sn-glycero-3-phosphocholine molecular layer to monovalent and divalent metal cations

Light scattering measurements were used to assess the effects of selected divalent and monovalent cations on alginate aggregation in vitro. Alginate, formed with either strontium, calcium or cobalt was partially dissolved with sodium. Calcium-alginate was also partially dissolved with two other monovalent cations, lithium and potassium. Phosphate, when added to a solution containing calcium-alginate, scrubbed algin-ate-bound calcium as well as free calcium in solution. These findings provide an explanation for an alternative approach for breaking down cell wall alginate.

The present work reports results from the interactions of monovalent (Na+, NH4+, and K+) and divalent (Ca2+ and Sr2+) cations, nitrate was the counterion, with negatively charged poly(methyl methacrylate) particles decorated with poly(ethylene glycol) (PMMA/PEG). Particle characterization was performed with dynamic light scattering, ζ-potential measurements, and scanning electron microscopy (SEM). Phase separation analyses were performed in the salt concentration range of 0.01 to 1.0 mol L–1. Among the monovalent cations at 1.0 mol L–1, the colloidal stability order was Na+ > K+ > NH4+ and only NH4+ bound specifically to PEG oligomers, causing the largest instability for concentrations higher than 0.75 mol L–1. In the case of divalent cations, three different situations were observed: (i) at 0.01 mol L–1 the dispersions were very stable, (ii) in the concentration range of 0.1 to 0.5 mol L–1 the particles aggregated due to charge screening, and (iii) at 1.0 mol L–1 the stability was larger than at the inte...