Divalent Cation Salts Research Articles

Effect of counterions on the structure and dynamics of water near a negatively charged surfactant: a theoretical vibrational sum frequency generation study.

Charged aqueous interfaces are of paramount importance in electrochemical, biological and environmental sciences. The properties of aqueous interfaces with ionic surfactants can be influenced by the presence of counterions. Earlier experiments involving vibrational sum frequency generation (VSFG) spectroscopy of aqueous interfaces with negatively charged sodium dodecyl sulfate (Na+DS- or SDS) surfactants revealed that the hydrogen bonding strength of the interfacial water molecules follows a certain order when salts of monovalent and divalent cations are added. It is known that cations do not directly participate in hydrogen bonding with water molecules, rather they only influence the hydrogen bonded network through their electrostatic fields. In the current work, we have simulated the aqueous interfacial systems of sodium dodecyl sulfate in the presence of chloride salts of mono and divalent countercations. The electronic polarization effects on the ions are considered at a mean-field level within the electronic continuum correction model. Our calculations of the VSFG spectra show a blue shift in the presence of added countercations whose origin is traced to different relative contributions of water molecules from the solvation shells of the surfactant headgroups and the remaining water molecules in the presence of countercations. Furthermore, the cations shield the electric fields of the surfactant headgroups, which in turn influences the contributions of water molecules to the total VSFG spectrum. This shielding effect becomes more significant when divalent countercations are present. The dynamics of water molecules is found to be slower at the interface in comparison to the bulk. The interfacial depth dependence of various dynamical quantities shows that the interface is structurally and dynamically more heterogeneous at the microscopic level.

Dually charged polyamide nanofiltration membrane incorporated UiO-66-(NH2)2: Synergistic rejection of divalent cations and anions

Traditional polyamide nanofiltration membranes suffer from permeability-selectivity trade-off limitation and unsatisfactory rejection for divalent cations. Herein, a novel dually charged membrane was constructed by incorporating positively charged UiO-66-(NH2)2 into the negatively charged polyamide layer. Thanks to the customizable nanochannels of metal-organic frameworks, the amino-rich nanochannels of UiO-66-(NH2)2 could be fabricated through a ligand replacement strategy. UiO-66-(NH2)2 played a crucial role in the enhanced rejection of divalent cations, meanwhile negatively charged polyamide surface guaranteed the efficient Na2SO4 rejection. Satisfactory rejections of CaCl2 (96.07 %) and Na2SO4 (90.62 %) were achieved simultaneously by optimal TFN-D5. Meanwhile, TFN-D5 owned the greatly-improved water permeance of 19.44 LMH/bar, which was about 1.5 times better than that of the TFC-control. Calculations based on density functional theory further confirmed UiO-66-(NH2)2 rejected Ca2+ efficiently since the migration energy barrier across UiO-66-(NH2)2 was an order of magnitude higher than that of UiO-66-NH2 and UiO-66. Moreover, the desirable rejections were beyond 94 % towards many divalent cation salts including MgCl2, NiCl2, PbCl2, MnCl2, CdCl2 and ZnCl2. Thus, this work provided an efficient way to realize the synergistic removal of both divalent cations and anions.

N-Oxide Zwitterion Functionalized Positively Charged Polyamide Composite Membranes for Nanofiltration.

N-Oxide zwitterionic polyethyleneimine (ZPEI), a new kind of aqueous phase monomer synthesized by commercially branched polyethyleneimine (PEI) via oxidation reaction, was prepared for fabrication of thin-film composite (TFC) polyamide membranes via interfacial polymerization. The main factors, including the monomer concentration and immersion time of the aqueous phase and organic phase, were investigated. Compared with PEI-TFC membranes, the obtained optimal defect-free ZPEI-TFC membranes exhibited a lower roughness (3.3 ± 0.3 nm), a better surface hydrophilicity, and a smaller pore size (238 Da of MWCO). The positively charged ZPEI-TFC membranes (isoelectric point at pH 8.05) showed higher rejections toward both divalent cationic (MgCl2, 93.0%) and anionic (Na2SO4, 96.1%) salts with a water permeation flux of up to 81.0 L·m-2·h-1 at 6 bar, which surpassed currently reported membranes. More importantly, mainly owing to N-oxide zwitterion with strong hydration capability, ZPEI-TFC membranes displayed a high flux recovery ratio (97.0%) toward a model protein contaminant (bovine serum albumin), indicating good anti-fouling properties. Therefore, the novel N-oxide zwitterion functionalized positively charged nanofiltration membranes provide an alternative for water desalination and sewage reclamation.

Manipulating polydispersity of lens β-crystallins using divalent cations demonstrates evidence of calcium regulation

Crystallins comprise the protein-rich tissue of the eye lens. Of the three most common vertebrate subtypes, β-crystallins exhibit the widest degree of polydispersity due to their complex multimerization properties in situ. While polydispersity enables precise packing densities across the concentration gradient of the lens for vision, it is unclear why there is such a high degree of structural complexity within the β-crystallin subtype and what the role of this feature is in the lens. To investigate this, we first characterized β-crystallin polydispersity and then established a method to dynamically disrupt it in a process that is dependent on isoform composition and the presence of divalent cationic salts (CaCl2 or MgCl2). We used size-exclusion chromatography together with dynamic light scattering and mass spectrometry to show how high concentrations of divalent cations dissociate β-crystallin oligomers, reduce polydispersity, and shift the overall protein surface charge-properties that can be reversed when salts are removed. While the direct, physiological relevance of these divalent cations in the lens is still under investigation, our results support that specific isoforms of β-crystallin modulate polydispersity through multiple chemical equilibria and that this native state is disrupted by cation binding. This dynamic process may be essential to facilitating the molecular packing and optical function of the lens.

Calcium decreases cell wall swelling in sweet cherry fruit

Swelling of epidermal cell walls decreases cell-to-cell adhesion and increases cracking susceptibility in sweet cherry. Ca is suggested to decrease cracking susceptibility by crosslinking of cell wall components and, possibly, by decreasing swelling. The objective is to test this hypothesis. The effect of Ca on swelling of anticlinal epidermal cell walls was quantified microscopically in vivo using excised skin sections and in vitro using extracted cell walls. After removal of turgor, cell wall thickness increased. Incubation in CaCl2 decreased cell wall thickness up to 3 mM CaCl2. At higher concentrations thickness remained constant. Decreased cell wall swelling in vivo also occurred with other salts of divalent and trivalent cations, but not with those of monovalent cations. Decreased swelling was due to the Ca cation, the anions had no effect. Ca also decreased swelling of cell walls that were already swollen. CaCl2 also decreased swelling of extracted cell walls in vitro. There was no effect on swelling pressure. The effect on swelling increased as the CaCl2 concentration increased. Chlorides of divalent and trivalent cations, but not those of monovalent cations decreased swelling in vitro. The decrease in swelling among the divalent cations was linearly related to the radius of the cation. The results indicate that Ca decreases cracking susceptibility by decreasing swelling.

Divalent nitrogen-rich cationic salts with great gas production capacities

Monocyclic nitrogen-rich 3-(aminomethyl)-4,5-diamine-1,2,4-triazole (1) and fused cyclic 3,7-diamine-6-(aminomethyl)-[1,2,4] triazolo [4,3-b] [1,2,4] triazole (9) were synthesized through the convenient cyclization reaction from the readily available reactant. Their energetic salts with high nitrogen content were proved to be rare examples of divalent monocyclic/fused cyclic cationic salts according to the single crystal analyses. The structure of intermediate B was also identified and verified by its trivalent cation crystal 17.5H2O indirectly. Energetic compounds 2–8 and 10–17 were fully characterized by NMR spectroscopy, infrared spectroscopy, differential scanning calorimetry, elemental analysis. These energetic salts exhibit good thermal stability with decomposition temperatures ranged from 182 °C to 245 °C. The sensitivity of compounds 2, 6, 10 and 14 is similar or superior to that of RDX while the others were much more insensitive to mechanical stimulate. Furthermore, detonation velocity of 10 (8843 m/s) surpass that of RDX (D = 8795 m/s). Considering the high gas production volume (≥808 L/kg) of 2, 4, 10 and 12, constant-volume combustion experiments were conduct to evaluate their gas production capacities specifically. These compounds possess much higher maximum gas-production pressures (Pmax: 7.88–10.08 MPa) than the commonly used reagent guanidine nitrate (GN: Pmax = 4.20 MPa), which indicate their strong gas production capacity.

Towards purely inorganic clusters in medicine: Biocompatible divalent cations as counterions of cobaltabis(dicarbollide) and its iodinated derivatives

Monovalent cations, Cs+, and alkylammonium ([NR4]+) salts have traditionally been used to precipitate the anions of boranes, carborane and metallocarborane clusters. In contrast, in the body and in living organisms in general, divalent cations have a special relevance. In this work, we isolate for the first time the cobaltabis(dicarbollide) salts of the biocompatible divalent cations of biological importance that can have application both in biology and in materials science. The preparation of Ca2+, Mg2+ and Fe2+ salts of anionic iodinated nido-[C2B9H12]− and cobaltabis(dicarbollide) as well as its di-, tetra- and octa-iodinated derivatives are reported. Ca2+ and Mg2+ are hard Lewis acids and thus forms aqua ions if water is present in the synthetic process. All solid Ca2+ and Mg2+ salts studied in this work contained water molecules coordinated that have been detected by IR and TGA/DSC. Fe2+ is a medium hard Lewis acid and Fe3+ is a hard one. In acetone they do not coordinate to cobaltabis(dicarbollide) anion, but are solvated by acetone. The studied Ca2+ salts of iodinated cobaltabis(dicarbollide) are basically inorganic small molecules that provide at once the biocompatible divalent Ca2+ cation and and iodinated anions thus simultaneously providing an X-ray contrast agent and/or bone defect repairing agent in regenerative medicine.

The System CaCl2–H2O: Thermodynamic Modeling and Flow Calorimetry Experiments at Elevated Temperatures and Pressures

Produced water from oil and natural gas production is challenging to treat due to its high salinity. Such brines are often a mixture of various mono- and divalent-cation salts, and elevated pressur...

Incorporation of lysine-modified UiO-66 for the construction of thin-film nanocomposite nanofiltration membrane with enhanced water flux and salt selectivity

The utilization of metal-organic frameworks (MOFs) has been proved to be promising in the attainment of high-performance membranes. In this work, lysine-decorated UiO-66 (Lys@UiO-66) is prepared via post-synthetic modification. Then, the controlled positioning of Lys@UiO-66 on a polyethersulfone (PES) substrate membrane is achieved by a pressure-assisted method, followed by interfacial polymerization to fabricate the Lys@UiO-66-based thin-film nanocomposite membrane (TFN-LDU). An even distribution of hydrophilic MOFs atop the substrate induces the formation of regular tent-like and mesh-topology polyamide structures, which enhance the effective membrane surface area and provide additional water transport channels. The optimal membrane with a Lys@UiO-66 loading density of 17.13 μg cm−2, TFN-LDU8, achieves a 55% enhancement in water permeability (18.27 L m−2 h−1 bar−1) without compromising the solute selectivity. Importantly, the TFN-LDU8 membrane exhibits high rejections of divalent cation salts (97.81% for MgCl2 and 92.81% for CaCl2) and improved mono-/divalent cation selectivity due to the pore hindrance and electrostatic exclusion of the Lys@UiO-66. Furthermore, the TFN-LDU8 membrane evinces a stable nanofiltration performance during the long-term nanofiltration experiment and displays a good antifouling ability in the fouling tests. This research provides a promising strategy for the design of nanofiltration membranes with special functions by using modified MOFs.

Molecular Dynamics Simulation Study of Ion Transport, Structural and Mechanical Properties of Li2CO3 and Mn-Li-CO3

In this study, we focus on understanding properties of the Solid Electrolyte Interphase (SEI), which plays an important role in the performance of Li-ion batteries. SEI has a complex structure including domains and blends of different organic (such as LEC, LMC, Li2EDC, etc.) and inorganic compounds (such as LiF, Li2O, etc.) which are byproducts of single and double electron reduction processes of electrolyte solvent and ions. Because of this complexity, the detailed structure and characteristics of SEI are still not well understood. Dilithium carbonate, Li2CO3, is known to be one of the important and stable compounds in the SEI structure. While there were some studies considering crystal phase of Li2CO3, the properties of amorphous glassy phase that can form at the domain boundaries within SEI or under fast rates of electrolyte reduction has not been investigated. In addition to SEI, amorphous blends of Li2CO3 with other oxides have been considered as potential materials for solid electrolytes. To the best of our knowledge, we present the first study considering the amorphous phase from theoretical point of view. Using atomistic MD simulations and a polarizable force field, we investigated properties of amorphous Li2CO3 phase and predict structural, dynamical, and mechanical properties of Li2CO3 as a function of temperature as well as the content of Mn2+ in the SEI. The latter investigates the influence of SEI “contamination” by divalent cations dissolved from high-voltage cathods or intentional introduction of sacrificial divalent cation salts to promote formation of denser and stronger SEI. According to our study, Mn0.2Li1.6CO3 forms the glassy state below 600 K, which is a 150 K increase compared to Li2CO3 system. Besides, Mn0.2Li1.6CO3 shows 15% higher density. From mechanical property calculations, shear modulus value for Li2CO3 is around 8 GPa, while it increases significantly with the addition of Mn2+.

Investigation of the effect of gel properties on supercritical drying kinetics of ionotropic alginate gel particles

A series of spherical ionotropic alginate gel particles with different diameters ranging from 2.8 mm to 5.0 mm and porosities ranging from 0.899 to 0.976 were prepared by dripping a Na-alginate solution into a solution of salts of divalent cations (Ca2+, Mn2+, Ni2+, Co2+, Cu2+ and Zn2+). After solvent exchange with ethanol, kinetics of supercritical drying of these ionotropic alginate gel particles in a packed bed was investigated at 308–338 K and 100–120 bar. Experimental data were compared with predictions of a model which considers diffusive transport inside the pores and convection in the flowing fluid stream. The model predicted drying profiles by taking into account only the changes in porosity and diameter of the gel particles. A convective mass transfer coefficient correlation that was originally developed for supercritical drying of Ca-alginate gel particles was found to be suitable for M-alginate gel particles.

Phosphate and sulphate-mediated structure and stability of bone morphogenetic protein - 2 (BMP - 2): A spectroscopy enabled investigation

Impact of different monovalent and divalent cationic salts of sulphates and phosphates on conformation and stability of BMP - 2 was unraveled by absorbance, fluorescence and circular dichroism (CD) spectroscopy. Increase in absorbance of protein confirms the ground-state complexation between salt and BMP - 2. Phosphate salts, with the exception of sodium phosphate quenched the fluorescence intensity. The nature of quenching was static, as revealed by temperature-dependent fluorescence studies (Stern-Volmer constant (KSV) decreased with rise in temperature). Moreover, kq (bimolecular quenching constant) was in the range of 1012 M−1 s−1, confirming binding of phosphate salts with the protein. Contrary to this, sulphate salts increased the fluorescence intensity and excited-state lifetime of BMP - 2 (2.668 ns), with the maximum calculated for 300 mM sodium sulphate (3.216 ns). Phosphates reduced the lifetime of protein, with the least observed in presence of 300 mM magnesium phosphate (1.480 ns). Thermal stability of the protein (Tm = 70.66 °C) was altered significantly upon interaction with phosphate salts; however, it did not vary significantly in case of sulphates (exception - magnesium sulphate). Experimental evidences confirm the role played by anionic group on protein conformation and stability and identifies monovalent and divalent cations as insignificant contributor.

Interaction of divalent cations with carboxylate group in TEMPO-oxidized microfibrillated cellulose systems

Cellulose-based films can potentially replace non-biodegradable plastic films in various applications such as food packaging. In this work we produced and studied films made of mixtures of chemical pulps and catalytically oxidized microfibrillated cellulose. The films were prepared on a support which was then soaked in solutions of CaCl2 and MgCl2 to exchange the sodium ions originally present in the film to divalent metal cations. We assumed that the electrostatic interaction of the anionic pulp fibers and the fibrils with Ca2+ and Mg2+ would promote internal bonding of the fiber-fibril network that would then reflect positively on the film properties. The immersion of the wet film into aqueous CaCl2 or MgCl2 solidified the film with time. When the solidified films were dried with an excess of the salt, elastic, skin-like materials were formed. Rewetting in water and redrying the materials produced paper-like films with improved mechanical properties in comparison with films prepared without the divalent cation salts. SEM imaging of the fracture surfaces provided support for the increased internal film strength by the divalent cations. The new knowledge on their role could be utilized in tailoring cellulosic film properties for specific uses.

Interactions between colliding oil drops coated with non-ionic surfactant determined using optical tweezers

Non-ionic surfactants are widely used in many industrial applications such as detergents, oil recovery, and mineral flotation techniques. Non-ionic surfactants readily adsorb onto the oil-water interface, although they cannot dissociate in solutions like ionic surfactants can. Nonetheless, the electrostatic double-layer (EDL) repulsive force between oil drops coated with the non-ionic surfactant can still provide stability against coalescence. In this work, the interaction forces between two tetradecane drops with diameter of 6.5 µm were measured in the presence of the non-ionic fluorocarbon-based surfactant FS-30 in various salt solutions using optical tweezers. The measured force curves were consistent with the presence of a surface charge, even though the surfactant was non-ionic in nature. The results clearly show that the EDL repulsive force is gradually screened with increasing salt concentration. It was also found that the EDL repulsive force was significantly screened in the divalent cation salt solutions (Ca2+, Ba2+) in comparison to in the monovalent cation salt solutions (Na+). In addition, the absolute value of the measured zeta potential (−ξ) of emulsified tetradecane drops gradually decreased with increasing FS-30 concentration. In all experimental processes, the emulsified tetradecane drops coated with FS-30 were stable against coalescence. These findings have significant implications for the stability of emulsions used in the food, cosmetic, and detergent industries.

Fortification of Concentrated Milk Protein Beverages with Soy Proteins: Impact of Divalent Cations and Heating Treatment on the Physical Stability

This study investigated the effects of adding calcium and magnesium chloride on heat and storage stability of milk protein concentrate-soy protein isolate (8:2 respectively) mixtures containing 10% w/w total protein subjected to the in-container sterilization (115oC x 15 min). The particle size does not change when emulsions are heated at pH between 6.7 and 7.3 irrespective of the mixed protein ratio. Increasing concentration of divalent cation salts resulted in an increase in protein particle size, dry sediment formation and sediment height and a decrease in pH, heat stability and hydration in milk protein concentrate-soy protein isolate mixtures solutions on sterilization at 115oC. Fortification of divalent cation salts in milk protein concentrate-soy protein isolate mixture solutions resulted in an accelerated protein sedimentation and two unique sediment regions during accelerated storage stability testing. Moreover, the heat stability decreased upon sterilization at 115oC, with addition of MgCl2 causing a greater increase in sedimentation velocity and compressibility than CaCl2. Increasing pH value of protein milk concentrate-soy protein isolate mixtures solutions from 6.7 to 7.2 resulted in an increase in viscosity following the heat treatment. The study demonstrated that the type and concentration of divalent cation salts used strongly impacts heat and storage stability of milk protein concentrate-soy protein isolate mixture nutritional beverages.

Effects of Common Inorganic Salts on Glycine Polymorphic Transformation: An Insight into Salt-Dependent Polymorphic Selectivity

The effects of typical inorganic salts on solution-mediated polymorphic transformation from metastable α-glycine to stable γ-glycine were investigated, with the measurement of induction times of γ-glycine nucleation being the key objective. Interestingly, it was observed that all the inorganic salts examined in this study considerably shorten induction time, showing that they accelerate γ-glycine secondary nucleation to a great extent. Surprisingly, it was found that the divalent cation salts (Ca(NO3)2 and MgSO4) exert a peculiar effect in that they greatly promote γ-glycine secondary nucleation despite their significant inhibition to γ-glycine growth. Furthermore, it was revealed that the monovalent cation salts (NaCl, KNO3, and (NH4)2SO4) enhance γ-glycine nucleation far more than the divalent cation salts. These obtained results provide an insight into the general observation that the polymorphic selectivity of glycine from unseeded solution crystallization is salt-dependent. All the experimental obser...

Cold-set hydrogels made of whey protein nanofibrils with different divalent cations

Whey protein nanofibrils are gaining interest to fabricate cold-set hydrogels due to their ability to gel at lower concentrations than parent proteins. In the present research, fibrillated protein solution was gelled with three different divalent cation salts including CaCl2, MnCl2 and ZnCl2 and the textural and functional characteristics of the resulting hydrogel samples were studied. Atomic force microscopy indicated that the flexible micron-scaled fibrils with nanometric thickness (up to 8.0nm) that formed at pH 2.0 underwent breaking in length upon post-formation pH rise to 7.5. Whilst heat-denatured protein solution failed to form self-supporting gel at pH 7.5, fibrillated protein solution gelled by all three types of cations. Fibrillation increased the protein solution consistency coefficient (K) much more than heat denaturation. It was suggested based on Fourier-transform infra-red (FT-IR) spectra that some hydrogen bonds were disrupted by fibrillation. Zn2+-induced gel was firmer, had a higher water holding capacity and a more compact microstructure, as well, required a higher compressive stress to fracture than its counterparts. Nonetheless, the Mn2+- and Ca2+-induced gels disintegrated to a much lesser extent in both pepsin-free and pepsin-present simulated gastric juice than Zn2+-induced sample. Chitosan coating approximately halved the simulated degradability of all gel samples.

Complex Formation of Divalent Cations with Carboxylic Acid Resins as a Factor Determining Different Stationary States of Their Swelling

ABSTRACTThree samples of carboxylic acid gel-type cross-linked polyelectrolytes were examined by registering the extent and kinetics of their volume change depending on the temperature, concentration, and nature of external electrolyte solutions, as well as the initial state (ionic form, water content) of the bead. It is found that in some systems the swelling of the bead (as a result of lowering the temperature) proceeds much more slowly than the preceding shrinking (as a result of the increase of temperature). Moreover, the initial volume of the bead is not restored, and a new stationary state of swelling is established. By means of optical dilatometry, it is found that in the systems in which the differences in the stationary states of swelling are found, the beads display plasto-elastic properties, whereas in the absence of such differences the beads show elastic properties. It is found that different stationary states of swelling are also established when the beads of copolymer of methacrylic acid cross-linked with divinylbenzene in Na+ form in the dry state and in the NaCl solution-swollen state are placed into a solution of a divalent cation salt. The difference in the stationary states of swelling reaches 12% in 4 N NiCl2 solution. The substantial differences in the swelling behavior and viscoelastic properties of the resins in their Na+, Mg2+, Ca2+, and Ni2+ forms are interpreted in terms of formation of different kinds of complexes of functional groups of the polymer with Ca2+ and Ni2+ ions.

Salt-dependent growth kinetics in glycine polymorphic crystallization

Divalent cation salts inhibit the growth of α-glycine far less severely than that of γ-glycine, causing α-glycine to have a greater competitive advantage over γ-glycine, thus further reinforcing the preferential formation of α-glycine on a relative basis.

Excess white noise to probe transport mechanisms in a membrane channel.

Current fluctuation analysis has been successfully used over the years to investigate the physical properties of different systems. Here, we perform single-channel time-resolved current experiments in a protein channel to evaluate the different transport mechanisms governing the channel function. Using different salts of monovalent and divalent cations in a wide range of concentrations and applied potentials, we analyze current fluctuations focusing on the voltage dependence of the additional white noise that appears in the low-frequency range of the spectra. We demonstrate that the channel displays two characteristic transport regimes: at low salt concentrations (10 mM to 1 M) ion permeation is controlled by the protein fixed charges that induce accumulation or exclusion of ions to preserve local electroneutrality. At high salt concentrations (>1M) adsorption processes associated to the binding of cations to the channel charges regulate the transport properties.