Metal Cations In Water Research Articles

MOLECULAR DYNAMICS STUDIES ON Fe2+, Co2+, AND Ni2+ AQUEOUS SOLUTIONS BASED ON ABEEM/MM FLUCTUATING CHARGE MODEL

Based on atom-bond electronegativity equalization method fused into molecular mechanics (ABEEM/MM), the intermolecular potential for transition metal ion Fe 2+, Co 2+, and Ni 2+ cations in water has been derived. Parameters for the effective interaction between a cation and a water molecule were determined by reproducing the ab initio results. Many structural and dynamic properties of Fe 2+(aq.), Co 2+(aq.), and Ni 2+(aq.) were studied using these potential parameters. Strong influences of the twofold charged cations on the structures of the hydration shells and some other properties of aqueous ionic solutions are discussed and compared with the results of a previous study of alkali metal and alkaline-earth metal cations in water. At the same time, comparative study of the hydration properties of each cation is also discussed. This work demonstrates that ABEEM/MM provides a useful tool in the exploration of the hydration of transition metal cations in water.

In Situ Synthesis of Metal Nanoparticles and Selective Naked-Eye Detection of Lead Ions from Aqueous Media

A novel one step synthesis of water soluble Au and Ag nanoparticles has been reported at room temperature using a naturally occurring bifunctional molecule, namely, gallic acid. The mechanistic details of nanoparticle formation were elucidated by carrying out control experiments using a variety of model compounds. The newly synthesized nanoparticles are extremely stable in the pH range of 4.5−5.0, due to (i) the strong electrostatic interaction of the carboxylate anion of the capping agent with the surface of the nanoparticle and (ii) a very high ζ potential (−45 mV). Under these pH conditions, it is difficult to bring nanoparticles in proximity due to strong interparticle electrostatic repulsion. However, the unique coordination behavior of Pb2+ ions (coordination number up to 12, flexible bond length and geometry) allows the formation of a stable supramolecular complex resulting in plasmon coupling and a visual color change. Because of the rigid coordination geometry, other metal cations (Ca2+, Cu2+, Cd2+, Hg2+, Mg2+, Ni2+, and Zn2+) interact only with lesser numbers of ligands, leaving the nanoparticles isolated; hence, no spectral change was observed under the experimental conditions. The ratiometric plots of the aggregated to the isolated forms indicate a high sensitivity as well as selectivity of Au and Ag nanoparticles toward Pb2+ ions. One of the significant features of the present system is its ability to detect micromolar quantities (ppm level) of Pb2+ ions in the presence of other metal cations in water. Further, we have theoretically modeled the interaction between the newly synthesized nanoparticles and the Pb2+ ion, and various optimized geometries are evaluated. On the basis of the experimental and theoretical studies, a tentative structure of the supramolecular complex leading to a strong interparticle interaction is provided.

Sequestration of Metal Cations with Zerovalent Iron NanoparticlesA Study with High Resolution X-ray Photoelectron Spectroscopy (HR-XPS)

Applications of nanoscale zerovalent iron (nZVI) for removal of metal cations in water are investigated with the result that nZVI has much larger capacity than conventional materials for the sequestration of Zn(II), Cd(II), Pb(II), Ni(II), Cu(II), and Ag(I). Characterizations with high-resolution X-ray photoelectron spectroscopy (HR-XPS) confirm that the iron nanoparticles have a core−shell structure, which leads to exceptional properties for concurrent sorption and reductive precipitation of metal ions. For metal ions such as Zn(II) and Cd(II) with standard potential E0 very close to or more negative than that of iron (−0.41 V), the removal mechanism is sorption/ surface complex formation. For metals with E0 greatly more positive than iron, for instance Cu(II), Ag(I), and Hg(II), the removal mechanism is predominantly reduction. Meanwhile, metals with E0 slightly more positive than iron for example Ni(II) and Pb(II) can be immobilized at the nanoparticle surface by both sorption and reduction. The dual sorption and reduction mechanisms on top of the large surface of nanosized particles produce rapid reaction and high removal efficiency, and offer nZVI as an efficient material for treatment and immobilization of toxic heavy metals.

Empirical Force Fields for Biologically Active Divalent Metal Cations in Water

We have presented a strategy for deriving ion-water van der Waals (vdW) parameters that implicitly include the microscopic solvent molecular effects around the ion. The strategy can be used to obtain vdW parameters for metal cations of the same formal charge and known experimental hydration free energies. In this work, it was applied to derive the vdW parameters for 24 divalent metal ions with measured hydration free energies ranging from -300 to -572 kcal/mol, coordination numbers (CNs) from 4 to 15, and ion-O (water) distances from 1.67 to 2.90 angstroms. The strategy used to derive the vdW parameters employs (1) a numerical procedure that links the coupling parameter used in free energy simulations with the experimental hydration free energies and (2) the first-shell CNs and structure for the entire series of divalent cations. One of the parameter sets obtained (referred to as MWc) simultaneously reproduces the observed (i) relative hydration free energies, (ii) first-shell CNs, and (iii) average ion-water distances of all the dications studied. In particular, the MWc parameters reproduce the observed (i) decrease in the CN from 6 for Cu2+ to 4 for Be2+, (ii) no change in the CN of 6 for dications with hydration free energies between those of Cu2+ and Cd2+, and (iii) an expansion of the CN from 6 for Cd2+ to 9.5 for Ba2+. The ion-water parameters derived herein represent a first step in the simulations of metalloproteins, which will also require potential energy functions incorporating polarizability, charge transfer, and other electronic effects to accurately model the protein-metal interactions in aqueous solution.

Molecular-dynamics simulations of alkaline-earth metal cations in water by atom-bond electronegativity equalization method fused into molecular mechanics

Intermolecular potential for alkaline-earth metal (Be(2+), Mg(2+), and Ca(2+)) cations in water has been derived using the atom-bond electronegativity equalization method fused into molecular mechanics (ABEEM/MM), and it is consistent with what was previously applied to the hydration study of the monovalent cations. Parameters for the effective interaction between a cation and a water molecule were determined, reproducing the ab initio results. The static, dynamic, and thermodynamic properties of Be(2+)(aq), Mg(2+)(aq), and Ca(2+)(aq) were studied using these potential parameters. Be(2+) requires a more complicated form of the potential function than Mg(2+) and Ca(2+) in order to obtain better fits. Strong influences of the twofold charged cations on the structures of the hydration shells and some other properties of aqueous ionic solutions are discussed and compared with the results of a previous study of monovalent cations in water. At the same time, comparative study of the hydration properties of each cation is also discussed. This work demonstrates that ABEEM/MM provides a useful tool in the exploration of the hydration of double-charged cations in water.

Fluorometric sensing of alkali metal and alkaline earth metal cations by novel photosensitive monoazacryptand derivatives in aqueous micellar solutions

Novel monoazacryptand-type fluorescent chemosensors, (derived from an 18-crown-6) and (derived from a 15-crown-5) both with a pyrene ring as their photoresponsive moiety, were synthesized. Their fluorescence properties for alkali metal and alkaline earth metal cations in water were then examined. The detection of metal cations was accomplished by a change in the fluorescence intensity of the host compounds, based on a photoinduced electron transfer (PET) mechanism. In aqueous solution, showed little fluorescence upon the addition of Ba2+ because of the very weak complexation with Ba2+, but the presence of micelles of polyoxyethylene(10) isooctylphenyl ether (Triton X-100) enabled to show highly sensitive and selective Ba2+ detection among alkali metal and alkaline earth metal cations. With respect to the selective fluorescent detection of important metal cations (Na+, K+, Mg2+, Ca2+) relevant to living organisms, was found to detect K+ with high selectivity in aqueous micellar solutions of polyoxyethylene(20) sorbitan monostearate (Tween-60). The selectivity for metal cations was mainly dependent on the goodness of fit of the host cavity and the metal cation size. In the presence of anionic surfactants, detected alkaline earth metal cations more effectively than alkali metal cations.

First Observation of Electron Paired with Divalent and Trivalent Nonreactive Metal Cations in Water

The effects of several chloride and perchlorate salts (NH4+, Na+, Mg2+, Tb3+) at high concentration in water on the optical absorption spectrum of the hydrated electron are studied. For a given salt, the hydrated electron spectrum shifts toward high energy as the salt concentration is increased. For the same chloride salt concentration, the blue shift of the hydrated electron spectrum increases with the charge of the cation, the largest corresponding to the pair formed with Tb3+, studied for the first time.

Al 3+-stabilized c-ZrO 2 nanoparticles at low temperature by forced hydrolysis of dispersed metal cations in water

A mixed aqueous solution (0.2–0.5 M) of ZrOCl 2·8H 2O and AlCl 3·6H 2O has a controlled forced hydrolysis to form an amorphous Zr 1−2 x Al 2 x O(OH) 2−2 x · αH 2O precursor on adding NH 4OH (in water) dropwise in a controlled manner at room temperature or preferably lower. X-ray diffraction of four halos at 19.2, 28.5, 39.2, and 57.0 nm −1 wavevectors ( x=0.05) characterizes the amorphous structure of the precursor. It undergoes a self-controlled reconstructive thermal decomposition into stabilized c-ZrO 2 of nanoparticles in Fm3 m cubic crystal structure at temperature as low as 200 °C. The process involves a predominant endothermic signal with a total of ∼60% loss in the precursor mass. It controls the local temperature and in turn governs moderate nucleation and grain growth in nanocrystals. The x=0.02–0.10 Al 3+additives cultivate stabilized c-ZrO 2 crystallites in 6–12 nm confined size ( d) on heating the precursor at 200–800 °C for 2–5 h. A reconstructive c→t/m-ZrO 2 phase transformation appears at extended temperature as 1000 °C as per the Al 3+additives. A pure m-phase, d∼26 nm, results at 1200 °C (800 °C otherwise at x=0). The lattice parameters vary as the x-value. The results of c-ZrO 2 formation and its stability and phase transformation are studied with X-ray diffraction, microstructure and thermal analysis of representative specimens.

Photonic crystal aqueous metal cation sensing materials.

We developed a polymerized crystalline colloidal array photonic material that senses metal cations in water at low concentrations (PCCACS). Metal cations such as Cu2+, Co2+, Ni2+, and Zn2+ bind to 8-hydroxyquinoline groups covalently attached to the PCCACS. At low metal concentrations (<microM), the cations form bisliganded complexes with two 8-hydroxyquinolines that cross-link the hydrogel and cause it to shrink, which blue shifts the photonic crystal diffraction. These bisliganded cross-links break at higher cation concentrations due to the formation of monoliganded cation complexes. This red shifts the diffraction. We have extended hydrogel volume phase transition theory in order to quantitatively model the diffraction dependence upon metal concentration. These materials can be used as a dosimeter to sense extremely low metal cation concentrations or as a sensor material for concentrations greater than 1 microM. Metal cation concentrations can be determined visually from the color of the diffracted light or can be determined by reflectance measurements using a spectrophotometer. This sensing material could be used in the field to visually determine metal cation concentrations in drinking water. A color chart would be used to relate the diffracted color to the metal cation concentration.

Study of the inhibition of certain trophic levels by the presence of metal cations in water

Bioassays and biological tools have been developed for the evaluation of the toxicity of water. A protocol of short-term tests allowed the examination of the influence of temperature, salinity, hardness and effect of complexation on the toxicity of Cd 2+, Cu 2+, Ni 2+ and Zn 2+ by means of a test daphnia ( Daphnia magna). The development of an experimental installation functioning continuously, where the trophic level is represented by the daphnia, led to the development of a system of bio-indication. The survival of the daphnia is examined under conditions of disturbances produced by Cd 2+, Cu 2+, Ni 2+ and Zn 2+. The application of the chronic test (21 d) allowed the folow-up of the inhibition of the survival and the reproduction of D. magna by Cd 2+, Cu 2+ and Ni 2+. A methodology with the help of the phototactic effect of D. magna was proposed. This one aims at developing a phototactic biosensor subjected to the toxicity of cadmium. Bioassays, using the purifying activity of the activated sludge, were considered and enabled understanding of the phenomena of inhibition and adaptation of these muds in the presence of trivalent chromium. In addition, two watery freshwater plants, Lemna minor and Salvinia natans, were exposed to Cd 2+, Cu 2+ and Zn 2+ in order to test their sensitivity. We consequently carried out a histological study on leaves of S. natans contaminated by metal toxicity independently of the test.

Controlled phase transformations in Al 3+ stabilized ZrO 2 nanoparticles via forced hydrolysis of metal cations in water

Al 3+ stabilized nanoparticles are obtained in a metastable c-ZrO 2 phase by a reconstructive thermal decomposition of an amorphous hydroxyl gel in air at moderate temperature as low as 200 °C. Average crystallite size ( d) lies in the 5–8 nm range as per the Al 3+ content. A transparent colorless Zr 1−2 x Al 2 x O(OH) 2−2 x · αH 2O gel, synthesized by a forced hydrolysis of a mixed aqueous solution of aluminum chloride and zirconium oxychloride with an ammonia solution at ∼5 °C, has been used. The phase formation and improved thermal stability in Al 3+ modified c-ZrO 2 nanoparticles are studied with X-ray diffraction of the specimen before and after selected annealing at subsequent temperatures as high as 1200 °C. A small x=0.02–0.20 Al 3+ content is found to inhibit a promptly controlled growth during the processing in nanoparticles, d≤36 nm. Practically no grain growth occurs in d above 36 nm as long as the temperature lies below 1200 °C. A reconstructive c-ZrO 2→t- or m-ZrO 2 phase transformation appears at 1000 or 1200 °C extended temperature in successive steps. No independent Al 2O 3 recrystallizes in a perfect Al 3+:ZrO 2 solid solution. Virgin c-ZrO 2 grows rapidly and appears in m-ZrO 2 directly as early as at 800 °C.

Analysis of the Opposite Solvent Effects Caused by Different Solute Cavities on the Metal−Water Distance of Monoatomic Cation Hydrates

Theoretical studies on metal cations in water have lead to a controversy regarding the distance between the cation and the oxygen nuclei of the first solvation shell. Apparently this is due to the differences in the description of solvent effects which can lead to opposite conclusions: a shortening or a lengthening of this distance in the bulk solution with respect to that found in the hydrated cation in a vacuum. This discrepancy has been attributed to the difference between discrete and continuum solvation models. Likewise, within the continuum model, two widely used methods, those of the multipole expansion (MPE), from the Nancy group (using a spherical cavity), and the polarized continuum model (PCM) from the Pisa group (using a molecularly shaped cavity), have given different results. This work reconsiders the solvent effects on the geometry of a set of hydrated cations ([M(H2O)m]n+, where M = Be2+, Mg2+, Ca2+, Zn2+, and Al3+) by comparing results derived from a previous work [J. Phys. Chem. 1991, 9...

Computer simulation studies of the structure and dynamics of ions and non–polar solutes in water

The mobility of simple ions such as alkali–metal and halide ions at room temperature shows two anomalies. Firstly, there are maxima in mobilities as a function of ion size for both positive and negative ions and, secondly, the maximum for negative ions occurs at a larger ionic radius than the maximum for positive ions. Theoretical treatments of this problem are reviewed and it is concluded that a molecular treatment of the system is needed to understand the results. Computer simulation using the simple point charge model (SPC/E) for water reproduced the observations and is used to discuss the application of theories. In particular, the nature of the first solvation shell is correlated with ion mobility. Simulation reveals a further anomaly, namely that if the charge is removed from a large ion, then it moves more slowly. This is interpreted as the result of formation of a solvent cage around the hydrophobic solute. The changes in local structure resulting from changes in charge and size also affect the solvation thermodynamics. Simulations show that the solvation entropy has a double maximum when viewed as a function of charge. The local minimum near zero charge is interpreted as being due to hydrophobic order, and the maxima as the result of structure breaking. This double maximum in the entropy of solvation is a signature of the hydrophobic cage effect. Comparisons are made between ion mobilities in liquid water at ambient and supercritical conditions.

NewN-substituted 1-hydroxy-3-aminopropylidenediphosphonic acids

N-Substituted 1-hydroxy-3-aminopropylidenediphosphonic acids were synthesized. Their acid-base and complexation properties toward a wide series of metal cations in water were investigated.

Thermodynamics of protonation and complexation of EDTA derivatives and metal cations in water

Two EDTA derivatives, ethylenedinitrilo-N,N′-diacetic-N,N′-bis(1-phenylethylacetamido) acid (EDTAMBA) and ethylenedinitrilo-N,N′-diacetic-N,N′-bis(2-pyridylacetamido) acid (EDTAPA) have been synthesised and characterised by IR anH NMR spectroscopy. The pKa values for the dissociation of the tertiary amino groups are lower by about three units relative to EDTA. Enthalpies of protonation of EDTAMBA and EDTAPA in water have been determined by titration calorimetry. Thermodynamic parameters of protonation show that the differences observed between the first protonation constants of these derivatives in water is of entropic origin. For EDTAPA, the enthalpy term is dominant in the differences found between the first and second protonation constants of this ligand. Stability constants (determined by potentiometry) and derived Gibbs energies, enthalpy (derived from calorimetry) and entropy data for these ligands and metal cations in water are reported. These data show that, unlike EDTA, there is hardly any variation in the Gibbs energies of complexation (or stability constants) of EDTAMBA and EDTAPA with metal cations in water, as a result of an almost complete compensation between enthalpy and entropy.

Molecular dynamics simulation of ionic mobility. I. Alkali metal cations in water at 25 °C

We describe a series of molecular dynamics simulations performed on model cation-water systems at 25 °C representing the behavior of Li+, Na+, K+, Rb+, and Cs+ in an electric field of 1.0 V/nm and in its absence. The TIP4P model was used for water and TIPS potentials were adapted for the ion-water interactions. The structure of the surrounding water molecules around the cations was found to be independent of the applied electric field. Some of the dynamic properties, such as the velocity and force autocorrelation functions of the cations, are also field independent. However, the mean-square displacements of the cations, their average drift velocities, and the distances traveled by them are field dependent. The mobilities of the cations calculated directly from the drift velocity or the distance traveled by the ion are in good agreement with each other and they are in satisfactory agreement with the mobilities determined from the mean-square displacement and the velocity autocorrelation function in the absence of the field. They also show the same trends with ionic radii that are observed experimentally; the magnitudes are, however, smaller than the experimental values in real water by almost a factor of 2. It is found that the water molecules in the first solvation shell around the small Li+ ion are stuck to the ion and move with it as an entity for about 190 ps, while the water molecules around the Na+ ion remain for 35 ps, and those around the large cations stay for 8–11 ps before significant exchange with the surroundings occurs. The picture emerging from this analysis is that of a solvated cation whose mobility is determined by its size as well as the static and dynamic properties of its solvation sheath and the surrounding water. The classical solventberg model describes the mobility of Li+ ions in water adequately but not those of the other ions.

Application of a Cation‐Exchange Membrane to Determine Cations of Trace Metals in River Water

AbstractDonnan‐membrane‐equilibrium graphite‐furnace atomic‐absorption spectrophotometry (DME‐GFAAS) has been developed to determine cations of trace metals in river water. The method employs a cation‐exchange membrane to separate metal cations from their complexes; both total and cationic forms of metals were determined by means of GFAAS. The sensitivity of the method for the measurement of trace metal cations is determined by the detection limits of GFAAS for the metals of interest. Comparable concentrations of metal cations in water from NBS and from the Erhjen river were obtained between the DME‐GFAAS and calculated (WATEQ4F) methods, indicating that the developed method is promising for natural fresh waters. The effect of pH on the distribution of metal cation in the NBS river water is significant for Cu and Pb; concentrations of these cations increase with decreasing pH. However, the concentrations of Cd and Zn cations do not vary with pH except that the concentration of the Zn cation decreases significantly as the pH value increases beyond 9. The method was applied to measure the capacity of complexing Cu in Chung‐Lu river water, which was estimated to be 2.3 μM.

Variation in stability of monohalide complexes and some properties of the solvated cations within the Mn 2+-Zn 2+ series

The stability of the monohalide complexes of the divalent first-row transition metal cations in water as well as in other donor solvents follows the sequence: MnX + > FeX + > CoX + > NiX + < CuX + > ZnX +. Moreover, some of the properties of the M(solvent) 6 2+ solvo-cations may be rationalized in terms of the same series. The observed sequence is opposite to that known as the Irving—Williams series.

The effect of the dielectric constant of proteins on the ionic transport processes in biomembranes

It has been shown that high efficiency of the ionic transport processes in biomembranes modified by protein ionic channels or carriers of peptide structure is determined by a high polarizability of these molecular systems, which is expressed by their large dielectric constant ϵ. According to our estimates, the minimal value of ϵ for proteins is equal to 20, i.e. it is closer to ϵ water, = 80 than to ϵ lipid = 2. In this connection we have considered in detail the effect of the dielectric constant of protein ion-transporting systems on the potential-dependent characteristics of ionic transport processes, on the processes of complex formation between permeant ions and anionic groups of the ionic channel, and cationic repulsion in the channel. In the framework of the concept developed the enthalpy of solvation of alkaline metal cations in water and proteins were calculated. The difference between these values is equal to 8–10 kcal/Mole, which is quite close to the value of the enthalpy of activation for ionic transport processes in biomembranes. This fact shows that only proteins (due to their high polarizability) appear to provide a high performance of the ionic transport systems in biomembranes.

The effect of the dielectric constant of proteins on the ionic transport processes in biomembranes

It has been shown that high efficiency of the ionic transport processes in biomembranes modified by protein ionic channels or carriers of peptide structure is determined by a high polarizability of these molecular systems, which is expressed by their large dielectric constant ∈. According to our estimates, the minimal value of ∈ for proteins is equal to 20, i.e. it is closer to ∈ water =80 than to ∈ lipid =2. In this connection we have considered in detail the effect of the dielectric constant of protein ion-transporting systems on the potential-dependent characteristics of ionic transport processes, on the processes of complex formation between permeant ions and anionic groups of the ionic channel, and cationic repulsion in the channel. In the framework of the concept developed the enthalpy of solvation of alkaline metal cations in water and proteins were calculated. The difference between these values is equal to 8–10 kcal/Mole, which is quite close to the value of the enthalpy of activation for ionic transport processes in biomembranes. This fact shows that only proteins (due to their high polarizability) appear to provide a high performance of the ionic transport systems in biomembranes.