Cations Anions Research Articles

A study on contaminant migration of sugarcane effluent through porous soil medium

A significantly large volume of effluent is generated during the manufacture of sugar and contains high amount of pollution load. The effluent from sugarcane industry is disposed off on land moves into the wider environment through a number of routes and the soil itself retains the various contaminants in the effluent to a greater or lesser extent depending on the physical nature of the soil. The analysis of contaminant transport through soil used to design of industrial wastewater treatments and disposal systems. This paper discussed the adsorption and diffusion of cations calcium, magnesium, sodium and anions chloride and sulphate by the sorption diffusion permeameter under different hydraulic retentions time of 3 min, 13 min, 27 min and 58 min with a constant diffusion flow rate of 3.6 L/h. In this study, less percentage error found between observed adsorption and diffusion coefficients from the experiments at different hydraulic retentions time and optimum adsorption and diffusion coefficients from the experiments at optimum hydraulic retentions time of 30 min for calcium, magnesium, sodium, choloride and sulphate. The results of regression analysis implied that the adsorption and diffusion coefficients obtained from the equation for cations and anions were good recognizing with the experimental results.

ChemInform Abstract: Enthalpies of Cleavage for a Series of Radical Cations and Radical Anions: Comparison with Heats of Homolysis and Heterolysis of Their Neutral Precursors.

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Influence of temperature on the structure and dynamics of the [BMIM][PF6] ionic liquid/graphite interface

The influence of temperature on the structure and dynamics of the [BMIM][PF(6)] ionic liquid/graphite interface has been investigated by molecular dynamics simulations. The performed simulations cover a 100 K wide temperature interval, ranging from 300 K to 400 K. It was shown that the magnitudes of density peaks of anions in the vicinity of the surface decrease with increasing temperature while in the case of cations anomalous temperature behaviour of the density profile is observed: the magnitude of the second peak of cations increases with the increase of temperature. To characterize interface dynamics the local self-diffusion coefficients D(x) of ions in the normal direction to the surface and the residence time of ions in the first and second interfacial layer have been estimated. It was shown that the local self-diffusion coefficients in the vicinity of the surface correlate with the local ion density; the maxima of the function D(x)(x) for the cations (anions) coincide with the regions of reduced cation (anion) density and vice versa. Finally, the influence of temperature on the screening potential in the vicinity of a charged graphite surface has been studied. It was shown that the increase of temperature from 300 K to 400 K induces the decrease of the potential drop across the interface that implies the increase of the capacitance of the electrical double layer.

Effects of Alkali Cations and Halide Anions on the DOPC Lipid Membrane

By means of molecular dynamics simulations with an all-atom force field, we investigated the affinities of alkali cations and halide anions for the dioleoylphosphatidylcholine lipid membrane in aqueous salt solutions. In addition, changes in phospholipid lateral diffusion and in headgroup mobility upon adding NaCl were observed using fluorescence spectroscopy. The simulations revealed that sodium is attracted to the headgroup region with its concentration being maximal in the vicinity of the phosphate groups. Potassium and cesium, however, do not preferentially adsorb to the membrane. Similarly, halide anions do not exhibit a strong affinity for the lipid headgroups but merely compensate for the positive charge of the sodium countercations. Nevertheless, larger halides such as bromide and iodide penetrate deeper into the headgroup region toward the boundary with the hydrophobic alkyl chain, this effect being likely underestimated within the present nonpolarizable force field. Addition of alkali halide salts modifies physical properties of the bilayer including the electronic density profiles, the electrostatic potential, and the area per lipid headgroup.

Oxidation of Guanine in G, GG, and GGG Sequence Contexts by Aromatic Pyrenyl Radical Cations and Carbonate Radical Anions: Relationship between Kinetics and Distribution of Alkali-Labile Lesions

Oxidatively generated DNA damage induced by the aromatic radical cation of the pyrene derivative 7,8,9,10-tetrahydroxytetrahydrobenzo[a]pyrene (BPT), and by carbonate radicals anions, was monitored from the initial one-electron transfer, or hole injection step, to the formation of hot alkali-labile chemical end-products monitored by gel electrophoresis. The fractions of BPT molecules bound to double-stranded 20-35-mer oligonucleotides with noncontiguous guanines G and grouped as contiguous GG and GGG sequences were determined by a fluorescence quenching method. Utilizing intense nanosecond 355 nm Nd:YAG laser pulses, the DNA-bound BPT molecules were photoionized to BPT*+ radicals by a consecutive two-photon ionization mechanism. The BPT*+ radicals thus generated within the duplexes selectively oxidize guanine by intraduplex electron-transfer reactions, and the rate constants of these reactions follow the trend 5'-..GGG.. > 5'-..GG.. > 5'-..G... In the case of CO3*- radicals, the oxidation of guanine occurs by intermolecular collision pathways, and the bimolecular rate constants are independent of base sequence context. However, the distributions of the end-products generated by CO3*- radicals, as well as by BPT*+, are base sequence context-dependent and are greater than those in isolated guanines at the 5'-G in 5'-...GG... sequences, and the first two 5'- guanines in the 5'-..GGG sequences. These results help to clarify the conditions that lead to a similar or different base sequence dependence of the initial hole injection step and the final distribution of oxidized, alkali-labile guanine products. In the case of the intermolecular one-electron oxidant CO3*-, the rate constant of hole injection is similar for contiguous and isolated guanines, but the subsequent equilibration of holes by hopping favors trapping and product formation at contiguous guanines, and the sequence dependence of these two phenomena are not correlated. In contrast, in the case of the DNA-bound oxidant BPT*+, the hole injection rate constants, as well as hole equilibration, exhibit a similar dependence on base sequence context, and are thus correlated to one another.

Crystallization of magmatic sulfides: An empirical model and application to Sudbury ores

I present an empirical parameterization of low-pressure melting relations of monosulfide solid solution in the system Ni–Cu–Fe–S–O and use it to argue that sulfide ores at Sudbury are almost exclusively cumulate in origin. In the model the solid is considered to be composed of four components NiS, CuS, FeS, and S, where S represents substitution of a vacancy for a cation. The liquid solution is considered to be a mixture of cations Ni, Fe, and Cu and anions S and O. The exchange of metals and sulfur between solid and melt is treated as a series of reactions of the form M l + S l = MS s, where subscripts l and s denote liquid and solid, respectively, allowing the definition of an exchange coefficient K D = X s MS / ( X l M × X l S ) where X denotes mole fraction. I have fitted equations of the form log K D = a/ T + bX lS + c to the existing database for coexisting sulfide liquid–monosulfide solid solution for each of the liquid components Ni, Cu, and S. The fitted K D expressions have been implemented in a Matlab program to estimate the compositions of coexisting solid and liquid sulfide phases in the system Ni–Cu–Fe–S–O, using the liquidus temperature approximation of Fleet and Pan [Fleet M. E. and Pan Y. (1994) Fractional crystallization of anhydrous sulfide liquid in the system Fe–Ni–Cu–S, with application to magmatic sulfide deposits. Geochim. Cosmochim. Acta 58, 3369–3377], and using a crude approximation to the liquidus surface of magnetite. Ni is found to be incompatible with mss over most of the range of conditions of crystallization of natural sulfide magmas, becoming compatible only at the lowest temperatures and highest Ni and Cu contents attained. Comparison with compositions of sulfide ores from Sudbury demonstrates that many ore compositions are distributed along mixing lines between primary mss and intermediate solid solution (iss) or between high pentlandite (heazlewoodite solid solution; hzss) and iss. The mss–iss trend can be modeled as a mixing line between mss and residual sulfide liquid or between mss and iss cumulates. In the former case, the Ni-rich composition of the mss must reflect continuous equilibration of solids and liquids during cooling to low temperatures close to the sulfide solidus. In the latter case, a significant mass of highly Ni- and Cu-enriched residual sulfide liquid must be interpreted to have left the mss–iss cumulates behind during a late-stage migration process at temperatures well below the solidus temperature of the enclosing silicate rocks. Subsequent crystallization of hzss–iss cumulates from Ni- and Cu-rich residual sulfide liquids produced the second trend between the compositions of pentlandite and chalcopyrite. The balance of evidence favors the hypothesis that most sulfide ores represent cumulate mixtures of iss and mss or of iss and hzss rather than residual Cu-rich sulfide liquids.

Estrutura elétrica da contaminação hídrica provocada por fluidos provenientes dos depósitos de lixo urbano e de um curtume no município de Alagoinhas, Bahia

O atual aterro sanitário do município de Alagoinhas foi construído nas vizinhanças do antigo depósito de lixo da cidade e de uma grande indústria de couros. Tais fontes perigosas de poluição estão situadas sobre uma área de recarga do aqüífero São Sebastião, um dos mais importantes reservatórios de água doce do estado da Bahia, que é intensivamente explorado para suprimento das populações humanas e animais, irrigação e indústrias. Uma caracterização das alterações hidrológicas e ambientais geradas pela presença dos depósitos de lixo e da indústria de couros foi realizada por meio da aplicação de métodos geofísicos elétricos combinados com análises físico-químicas de amostras de águas. Os resultados interpretados de 49 sondagens elétricas verticais (SEVs) executadas na área mostraram a presença de uma anomalia condutiva tridimensional, que se estende desde a superfície até mais de 40 m de profundidade. Esta é interpretada como resultante da invasão de líquidos originados dos depósitos de lixo e da lagoa de rejeito do curtume. Uma investigação da qualidade das águas realizada a partir de coletas em poços e no rio Sauípe e seu afluente, onde são lançados os efluentes da indústria, confirma os resultados da investigação geoelétrica. Detectamos alterações nas concentrações de cromo trivalente, demandas química e bioquímica de oxigênio (DBO e DQO), amônia, nitrogênio total e fósforo, sólidos suspensos e dissolvidos, dos cátions sódio, potássio, magnésio e cálcio, dos ânions cloreto e sulfato, estando os valores obtidos muitas vezes acima dos limites fixados pela legislação.

Monte Carlo simulations of a charged dendrimer with explicit counterions and salt ions

Static properties of a dendrimer with generation g = 5 with positively charged terminal groups in an athermal solvent are studied by lattice Monte Carlo simulations using the cooperative motion algorithm as the tossing scheme. The calculations are performed both for a salt-free system with neutralizing counterions and for a small amount of added monovalent and divalent salt. The full Coulomb potential and the excluded volume interactions between ions and beads are taken explicitly into account with the reduced temperature tau, the number of salt cations (anions) n(s), and salt valence z(s) as the simulation parameters. The bahaviour of the systems is analyzed by the mean effective charge per end-bead <Q>, Coulomb mean energy <E>, mean-square radius of gyration <R(g)(2)>, pair correlation functions g(alphabeta), and charge density rho(ch). The simulations show that for n(s)> or = 0 and decreasing tau: (a) there is encapsulation in the dendrimer and condensation onto the terminal groups of anions accompanied by a monotonic decrease in <Q> and <E> and by subsequent swelling and shrinking of the molecule; (b) encapsulation, condensation and shrinking are the most significant and swelling weaker for |z(s)| = 2; (c) penetration of salt cations into the dendrimer is minor when compared to that of anions; (d) rho(ch) is reduced and becomes negative close to the center of mass of the dendrimer and on its periphery; (e) for the considered n(s) > 0, unlike divalent salt ions the monovalent ones cause slight effects when compared to the salt-free case.

Emission from Charge Recombination between Radical Cations and Radical Anions of 9‐Cyano‐10‐(p‐Substituted Phenyl)Anthracene Generated during Pulse Radiolysis

AbstractEmission from charge recombination between radical cations and anions of 9‐cyano‐10‐(p‐substituted phenyl)anthracenes (RA, where R is 10‐p‐substituted phenyl: R = Phenyl (PA), anisyl (OA), p‐N,N‐dimethylaminophenyl (NA), N, N‐di‐p‐anisylaminophenyl (DA)), as donor‐acceptor type molecules, generated during the pulse radiolysis in benzene was measured together with the transient absorption of RA radical cations (RA•+) and anions (RA•−). Based on the transient absorption and density functional theory (DFT‐B3LYP/6‐31G*) calculation, a twisted geometry is assumed for all RA in the ground state, RA•+, and RA•−. It is suggested that the positive charge of PA•+, OA•+, and NA•+ is delocalized on two moieties, and that of DA•+ is localized on the donor N,N‐di‐p‐anisylaminophenyl moiety, while the negative charge of all RA•− is mainly on the acceptor 9‐(10‐cyano)anthracenyl moiety. When both RA•+ and RA•− are generated with sufficiently high concentrations during the pulse radiolysis in benzene, the charge recombination between RA•+ and RA•− occurred to give RA in the singlet excited state (1RA*) as the emissive species, but not the excimers because of the twisted geometries of RA•+ and RA•− with the large torsional angles between the 9‐(10‐cyano)anthracenyl and p‐substituted phenyl moieties. Not only the fluorescence quantum yield of 1RA* but also the energy differences between the annihilation enthalpy change and the excitation energy of 1RA* are important factors for the radiolysis induced emission intensity of RA in benzene.

Monte Carlo simulations of a polyelectrolyte chain with added salt: Effect of temperature and salt valence

Using the cooperative motion algorithm, the effect of salt valence z(s) and of the reduced temperature T* on a single polyelectrolyte chain as well as on counterions and salt ions themselves is studied. The calculations show that both parameters strongly influence the polymer, causing it to undergo conformational changes. For a given number of the added salt cations (anions) n(s) and temperature T*, the chain takes more and more compact forms as z(s) increases (z(s) > 0). For fixed z(s), in turn, the polymer size reduces sharply as T* drops down from intermediate to low. For high T* configurational the entropy dominates the chain statistics and the mean-square radius of gyration (s2)1/2(T*,n(s),z(s)) approaches its athermal value. The low-temperature polymer collapse is also accompanied by a drop in the effective mean charge per monomer q*(T*,n(s),z(s)) (condensation of ions onto the chain) and the total inner energy e*(T*,n(s),z(s)). Furthermore, the local structure of the system is analyzed by means of pair-correlation functions g(ab)(r,T*,n(s),z(s)). At lower T* they possess sharp local maxima at small interparticle distances r that disappear as T* grows. The former observation indicates that at lower T* the ions tend to group themselves close to each other. In particular, it is concluded that the condensation is dominated by the multivalent salt ions carrying charges of opposite sign to that of monomers.

Coadsorption of Tetraalkylammonium Cations and Halide Anions on the Uncharged Surface of Mercury Electrode

The data on coadsorption of tetraethylammonium (Et4N+), tetrapropylammonium (Pr4N+), and tetrabutylammonium (Bu4N+) cations with Cl–, Br–, and I– anions on an uncharged mercury electrode are compared with the models of coadsorption in a common monolayer and two parallel layers. The second model is shown to be in best agreement with experimental isotherms. However, the least discrepancy between calculations and experimental results is obtained when coadsorption of mentioned cations and anions is described by the Frumkin isotherm for neutral molecules with certain effective adsorption parameters.

Simulation study of nutrient uptake by plants from soilless cultures as affected by salinity buildup and transpiration

Soilless plant growth systems are widely used as a means to save irrigation water and to reduce groundwater contamination. While nutrient concentrations in the growth medium are depleted due to uptake by the plants, salinity and toxic substances accumulate due to transpiration. A theoretical model is suggested, to simulate nutrient uptake by plants grown in soilless cultures with recycled solutions. The model accounts for salinity accumulation with time and plant growth, and its effects on uptake of the different nutrients by means of interaction with Na and Cl ions. The sink term occurs due to uptake by a growing root system. Influx as a function of the ion concentration is according to Michaelis–Menten active mechanisms for K+, NO3 −-N, NH4 +-N, PO4-P, Ca2+, Mg2+ and SO4 2-, whose influx parameters are affected by Na and Cl−, but not with time (age). Sodium influx is passive above a critical concentration. Sum of cations–anions concentrations is balanced by Cl− to maintain electro-neutrality of the growth solution. Salinity (by means of Na concentration) suppresses root and leaf growth, which further effect uptake and transpiration. The model accounts for instantaneous transpiration losses, during daytime only and its effect on uptake of nutrients and plant development due to salt accumulation. The model was tested against NO3 − and K+ uptake by plants associated with cumulative transpiration and with different NaCl salinity levels. Deviations from observed K+ uptake should be attributed to the salinity tolerance of the plants. In a study with data obtained from published literature, the model indicated that nutrient depletion and salinity buildup might be completely different with fully grown-up plants (that do not grow) and plants that grow with time. Depletion of different nutrients are according to their initial concentration and plant uptake rate, but also affected by their interactions with Na and Cl ions.

Supramolecular assemblies of quaternary ammonium cations and halide anions in the gas phase: ESMS-FTICR data and computer modelling

Supramolecular aggregates of tetraalkylammonium halides (R4NX) are formed by electrospray out of acetonitrile solution. Mass spectrometry reveals 88 charged aggregates for R= Me, Et, Bu; X= Br, I, ranging up to [(Bu4N)39Br42]3- in size. With the objective of improving calculations of intermolecular energies for supramolecular aggregates of ions, calibrated semi-empirical potentials for inter-ion interactions have been developed and applied to these aggregates. The accuracy of the calculated energies is supported by the measured collisional dissociation energy of (Et4N+)4 (I-)5. Energy optimisations indicate that the probable structures have the halide ions dispersed in a matrix of cations, which, for Bu4N+, can be mutually attractive. The aggregates are structurally fluid, with multiple structures separated by 4-8 kJmol(-1). The energy calculations are entirely consistent with the observed formation of large aggregates, and of multiply charged anions. It is estimated that the cohesive energies of supramolecular assemblies of ions such as these reach about 40 kJmol(-1) per constituent ion.

A Consistance Model for Anion Exclusion and Surface Diffusion

AbstractA decomposition of the diffusion flux equation for an electrostatically bound and mobile hydrated ion into two components is proposed. The first component includes the effects arising solely from the irregular pore shape and increase in solvent viscosity in the proximity of negatively charged pore walls. Apart from these effects, the second flux component includes an additional contribution from an increased (decreased) concentration for cations (anions) close to the pore walls. Defining the distribution coefficient, Kd, in a fashion that allows negative values for co-ions readily accounts for their exclusion without the need to introduce somewhat artificial quantities like the “effective co-ion porosity”. In this study, it is thus possible to retain the purely volumetric meaning of the porosity and to maintain consistency throughout the conceptualization for anions, cations and electrically neutral species. Furthermore, the decomposition of the flux equation provides support for surface diffusion, a subject of great controversy and lively debate in the literature. In this connection, the role of concentration to regulate the diffusive flux for ions in relation to neutral species is emphasized. Implications for the theoretical apparent and effective diffusivities in compacted montmorillonite clay are also discussed and a modified form of the macroscopic theory is proposed.

Discontinuities of pH at zone boundaries in isotachophoretic systems with poorly buffering leading electrolytes

Discontinuities of pH at zone boundaries of strong ion sample zones in isotachophoretic systems with poorly buffering leading electrolytes have been discovered by dynamic computer simulations of isotachophoretic separations with uncommon electrolyte systems. When using a salt solution containing a strong cation (anion) as leading ion and a weak anion (cation) as counterion for the isotachophoretic separation of strong cations (anions), severe pH discontinuities are present at zone boundaries of these cations (anions). The magnitude of these pH discontinuities has been investigated as a function of several parameters, namely counter ion/leading ion concentration ratio of the leading electrolyte, pK values, and mobilities of sample ions and counterion.

Interaction theory for double electric layers of dissimilar particles for equilibrium regime of surface ionization Low surface potentials

The solution to the problem of the interaction of double electric layers formed by dissimilar particles is obtained on the basis of the linearized Poisson-Boltzmann equation assuming the equilibrium regime of particle surface charging. Three types of particle surface ionization by the ions of the electrolyte whose concentration corresponds to the Henry law region are considered: (a) cations (anions) adsorption on an initially uncharged surface which does not possess any non-compensated charge before the adsorption of ions takes place; (b) ions adsorption (ion exchange) on an initially charged particle surface that possesses this charge; (c) ions adsorption (ion exchange) on amphoteric surfaces. The three cases can be reduced to the case (c) with unequal Nernst potentials of the surfaces. The dependencies of potentials, densities of plate charges, and electrostatic component of the Gibbs free energy of the particle interactions on the nearest distance between the particles are studied qualitatively, and the corresponding analytical expressions are derived.

Structure and Ferromagnetic Interactions in Open-Shell Supramolecular Assemblies Constructed from Radical Cations and Hexacyanometallate Anions

The goal of our work was to design in a controlled manner open-shell supramolecular assemblies with dominant intermolecular ferromagnetic interactions. Along this line, the compounds of formula rad6M(CN)6I3· 2H2O with M = Cr, Fe, and Co have been synthesized; rad+ stands for the 2-(3-N-methylpyridinium)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazo-1-oxyl 3-N-oxide radical cation. The crystal structures have been solved. The three compounds are isomorphous. They crystallize in the trigonal space group P3 (a = 13.178(3) Å, c = 10.763(6) Å for M = Fe). The structure may be viewed as a two-dimensional honeycomb lattice, with three kinds of hexagons and three kinds of rad- - -rad magnetic interactions. In addition, for M = Cr and Fe, there is a fourth kind of magnetic interaction, occurring between the M(CN)63- anion and the radical core. The magnetic properties of the three compounds have been investigated. They are characteristic of dominant ferromagnetic interactions to which weak antiferromagnetic interactions are superimposed. A quantitative interpretation of the magnetic data has been developed. In particular, for the chromium derivative, three out of four interactions have been found to be ferromagnetic, including the rad- - -Cr(CN)6 interaction. The spin topologies of our supramolecular assemblies have been discussed in the context of the spin frustration phenomenon. The potentialities of the supramolecular chemistry of open-shell units have been emphasized.

Thermodynamic calculation of phase diagrams of the 60 common-ion ternary systems containing cations Li, Na, K, Rb, Cs and anions F, Cl, Br, I

The phase diagrams of all 60 possible common-ion ternary alkali halide systems were calculated thermodynamically. The thermodynamic properties of the ternary phases were calculated from the optimized properties of the binary subsystems, which were obtained from previously reported critical evaluations of binary data. Calculated ternary phase diagrams are compared with experimental diagrams in those 47 systems for which the latter are available. In most cases, agreement is within experimental error limits. For five systems, a small empirical correction term was added to the Gibbs energy expression in order to bring the calculated and reported diagrams into coincidence. The calculated ternary diagrams are considered to be the best evaluated diagrams that can be deduced from currently available data. A probable maximum inaccuracy was estimated for each system.

Corn Responses to Post‐tasseling Nitrogen Deprivation and to Various Ammonium/Nitrate Ratios

AbstractCorn (Zea mays L.) takes up more than half of its total N after tasseling. An experiment was conducted to determine how the availability of N and the N form, NH4 or NO3, during the post‐tasseling period affect corn plant growth, ear development, and nutrient composition. In this experiment, corn hybrid ‘Pioneer 3343’ plants were grown hydroponically in pots outdoors with 50:50 NH4:NO3 up to the emergence of tassels and then the plants were either deprived of N or changed to various ratios of NH4:NO3 nutrition and grown to maturity. Nitrogen deprivation reduced both vegetative (stalk and leaf) and reproductive (cob, total kernel, and individual kernel) dry matter accumulation. Continuous supply of 50:50 ratio of NH4:NO3 produced greater vegetative dry matter than changing to either higher or lower ratios of NH4:NO3. The ratio of NH4:NO3 did not affect the ear dry matter production. Nitrogen deprivation decreased both leaf and kernel N concentration. While 50:50 NH4:NO3 ratio increased the leaf N concentration, all NH4 increased the kernel N concentration compared to other ratios. Nitrogen deprivation also reduced the concentrations of Mg, Fe, Mn, Zn, and B in the leaves but had no effect on the kernel nutrient composition. The cation and anion concentrations in the leaves and kernels were not according to the NH4 and NO3 effects (viz., uptake of cations greater and anions lower with NH4 than with NO3 nutrition), which were previously observed before tasseling. This difference may be due to a change in the uptake capacity for these nutrients after tasseling.

ChemInform Abstract: Origin of Methyl Conformational Preferences and Rotational Barriers in the Ground States, Excited Triplet States, Radical Cations, and Radical Anions of Molecules Having CH3‐C=X Functionalities

ChemInform Abstract: Origin of Methyl Conformational Preferences and Rotational Barriers in the Ground States, Excited Triplet States, Radical Cations, and Radical Anions of Molecules Having CH3‐C=X Functionalities