Concentration Of Trivalent Cations Research Articles

Regulation Mechanism of Trivalent Cations on Friction Coefficient of a Poly(Vinylphosphonic Acid) (PVPA) Superlubricity System

The application range of superlubricity systems can be extended effectively by realizing an adjustable friction coefficient. In this study, a stable poly(vinylphosphonic acid) (PVPA) superlubricity system was developed using sodium chloride (NaCl) solution as the lubricant. A sudden increase in the friction coefficient occurred when a trivalent salt solution was introduced to the base lubricant during the friction process. The changes in surface microstructure and interfacial molecular behavior induced by trivalent cations were studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and molecular dynamics simulation. The regulation mechanism of trivalent cations with respect to the friction coefficient of the PVPA superlubricity system was explored. Although La3+ and Fe3+ in solutions exist in two forms (La3+ and Fe(OH)3), both can destroy the stable coating structure through a bridging effect, resulting in a sudden increase in the friction coefficient. The ability of various cations to attract the surrounding water molecules is an important reason for the varying degree of change of the friction coefficient. In addition, the degree of sudden increase in the friction coefficient is dependent on the concentration of trivalent cations. There is an extreme concentration at which the maximum sudden increase degree in friction coefficient can be obtained. This study provides insights into the realization of oil-based superlubricity through interface regulation.

Nucleic Acid Identity, Structure, and Flexibility Affect the Electrochemical Signal of Tethered Redox Molecules upon Biopolymer Collapse.

We demonstrate that cation condensation can induce the collapse of surface-bound nucleic acids and that the electrochemical signal from a tethered redox molecule (methylene blue) upon collapse reports on nucleic acid identity, structure, and flexibility. Furthermore, the correlation of the electrochemical signal and structure is consistent with theoretical considerations of nucleic acid collapse. Changes in solution dielectric permittivity or the concentration of trivalent cations cause the structure of nucleic acids to become more compact due to an increase in attractive electrostatic interactions between the charged biopolymer backbone and multivalent ions in the solution. Consequently, the compaction of nucleic acids results in a change in the dynamics and location of the terminally appended redox marker, which is reflected in the faradaic current measured using cyclic voltammetry. In comparison to ssDNA, nucleic acid duplexes (dsDNA, DNA/peptide nucleic acid, and dsRNA) require nucleic-acid-composition-specific solution conditions for the collapse to occur. Moreover, the magnitude of current increase observed after the collapse is different for each nucleic structure, and we find here that these changes are dictated by physical parameters of the nucleic acids including the axial charge spacing and the periodicity of the helix. The work here aims to provide quantitative and predicative measures of the effects of the nucleic acid structure on the electrochemical signal produced from distal-end appended redox markers. This architecture is commonly employed in functional nucleic acid sensors and a better understanding of structure-to-signal correlations will enable the rational design of sensitive sensing architectures.

Role of Environmental Variables in the Transport of Microbes in Stormwater

Microbial pathogens present in stormwater, which originate from human sewage and animal faecal matters, are one of the major impediments in stormwater reuse. The transport of microbes in stormwater is more than just a physical process. The mobility of microbes in stormwater is governed by many factors, such as dissolved organic matter, cations, pH, temperature and water flow. This paper examined the roles of three environmental variables, namely: dissolved organic matter, positive cations and stormwater flow on the transport of two faecal indicator bacteria (FIB), Enterococcus spp. and Escherichia coli. Stormwater runoff samples were collected during twelve wet weather events and one dry weather event from a medium density residential urban catchment in Brisbane. Enterococcus spp. numbers as high as 3 × 104 cfu/100 mL were detected in the stormwater runoff, while Escherichia coli numbers up to 3.6 × 103 cfu/100 mL were observed. The dissolved organic carbon (DOC) in the stormwater samples was in the range of 2.2–5.9 mg/L with an average concentration of 4.5 mg/L in which the hydrophilic carbon constituted the highest mass fraction of 60–80%. The results also showed that the transport of FIB in stormwater was reduced with an increasing concentration of the hydrophilic organic fraction, especially the humic fraction. On the contrary, the concentration of trivalent cations and stormwater flow rate showed a positive correlation with the FIB numbers. These findings indicated the potentiality to make a good use and measurement of simple environmental variables to reflect the degree of microbe transport in stormwater from residential/suburban catchments.

Effect of MCl3 (M=La, U or Sc) component on the local structures and transport properties of LiCl–KCl–MCl3 eutectic: A molecular dynamics study

LiCl–KCl eutectic material is a crucial waste reprocessing candidate for use in molten salt reactors and the major component of spent nuclear fuel. Investigating the structure and thermodynamic transport properties of this eutectic mixed with fission waste cations will provide a better understanding of the reprocessing progress. In this study, molecular dynamic simulations were performed on the molten salts of a LiCl–KCl eutectic mixed with La3+, U3+, or Sc3+ cations, and the mole fractions of the trivalent cations ranged from 0% to 50% at 773 K, 873 K, and 973 K. The local structures (in nearest neighbor distance and coordination numbers) and macroscopic transport properties (self-diffusion, electrical conductivity, and viscosity coefficients) of the three systems have been studied. When the trivalent cation concentration varied from 0 mol% to 50 mol%, the mean nearest neighbor distance of La3+–Cl- and U3+–Cl- increased and the mean nearest neighbor distance of Sc3+–Cl- decreased, and the coordination numbers of La3+ and U3+ increased while the coordination numbers of Sc3+ decreased as the trivalent cation concentrations increased. The trivalent cations were primarily present in the form of [MClx]3−x in diluted mixtures, and they linked to form a network in the viscous regions. The viscosity was primarily affected by the network and followed by a nearly linear increase with the degree of the network in the arbitrary trivalent mixtures. Additional investigation predicted the electrical conductivity and self-diffusion over a broader range; the results indicated that the electrical conductivities were hardly affected by the radius of the given trivalent cation.

Rhodamine based chemosensor for trivalent cations: Synthesis, spectral properties, secondary complex as sensor for arsenate and molecular logic gates

A rhodamine based chemosensor, 2-(2-(5-bromo-2-hydroxybenzylideneamino)ethyl)-3’,6’-bis(diethylamino)spiro[isoindoline-1,9′-xanthen]-3-one (HL), has been explored for detection of trivalent cations, Al3+, Fe3+ and Cr3+. It has been synthesized by Schiff-base condensation and characterized by standard techniques including X-ray single crystal diffraction analysis. HL is colorless and non-fluorescent. In the presence of trivalent cations, colorless solution of HL turns pink. In UV–vis spectra, gradual addition of the cation produces gradual increment in absorption band at 528nm in HEPES buffer in methanol:water (7:3, v/v) (pH 7.2). No other monovalent and divalent cation except Cu2+ is able to cause color change. HL is almost non-fluorescent in HEPES buffer in methanol:water (7:3, v/v) (pH 7.2) when it is excited at 500nm. Emission intensity increases gradually at 552nm in the presence of increasing concentration of trivalent cations. Intensity increases by 98, 50 and 38 fold in the presence of one equivalent of Al3+, Cr3+ and Fe3+, respectively. No other metal ion can cause an enhancement in emission intensity of HL suggesting selectivity of the probe towards these trivalent cations. Quantum yield of HL complexes with M3+ increases significantly compared to that of free HL. Non-fluorescent HL is a closed ring compound whereas trivalent metal ions induce ring opening of spirolactam ring and complex formation enabling strong fluorescence. Limit of detection (LOD) values of HL have been determined to be 1.18, 1.80 and 4.04nM for Al3+, Cr3+ and Fe3+, respectively, suggesting very high sensitivity towards the cations. Job's plot analysis and mass spectral analysis shows 1:1 complex formation between HL and metal ion. AsO43− ion quenches emission intensity of HL–Al3+ complex as the anion snatches Al3+ from its complex thereby leading to the generation of non-fluorescent spirolactam unit. DFT and TD-DFT studies have been performed to investigate different optimized structures and various spectral transitions. Al3+ complex with HL acts as fluorescent sensor for arsenate ion as the anion snatches Al from Al-HL complex and it returns back to its ring closed spirolactam form. Advanced level molecular logic devices e.g. different 3 and 5 input advanced level logic gates, molecular keypad lock and memory device have been constructed using these properties and interpreted.

Effect of Surface and Salt Properties on the Ion Distribution around Spherical Nanoparticles: Monte Carlo Simulations.

Nanoparticle surface charge properties represent key parameters to predict their fate, reactivity, and complexation in natural, biological, and industrial dispersions. In this context, we present here an original approach to better understand the surface charge electrostatic properties of spherical nanoparticles (NPs). The ion distribution around one nanoparticle is investigated using Monte Carlo simulations and by adjusting a wide range of parameters including NP properties (surface charge density and site distribution), salt concentration (ionic strength and cation concentration), and salt valency (mono-, di-, and trivalent salt). A canonical Metropolis Monte Carlo method is used to reach equilibrium states and a primitive Coulomb model is applied to describe the electrostatic interactions between explicit discrete sites, counterions, and salt particles. Our results show that the presence of explicit surface charges on the NP and in solution has a strong influence on the local ion distribution and on the effective surface charge of the nanoparticles. The increase of surface charge density reduces the NP effective charge by the formation of a condensation layer around the nanoparticle. However, a limit of condensation is achieved due to steric effects and electrostatic repulsions. The presence of di- and trivalent cations is also found to strongly modify the effective charge and improve condensation state as long as electrostatic repulsion between the cations close to the surface are not so strong. At high trivalent cation concentration, the NP effective charge is greatly reduced and the local environment around the nanoparticle becomes more structured with the formation of a multi layer structure composed by anions and cations.

Effect of Cation Size and Charge on the Interaction between Silica Surfaces in 1:1, 2:1, and 3:1 Aqueous Electrolytes

Application of two complementary AFM measurements, force vs separation and adhesion force, reveals the combined effects of cation size and charge (valency) on the interaction between silica surfaces in three 1:1, three 2:1, and three 3:1 metal chloride aqueous solutions of different concentrations. The interaction between the silica surfaces in 1:1 and 2:1 salt solutions is fully accounted for by ion-independent van der Waals (vdW) attraction and electric double-layer repulsion modified by cation specific adsorption to the silica surfaces. The deduced ranking of mono- and divalent cation adsorption capacity (adsorbability) to silica, Mg(2+) < Ca(2+) < Na(+) < Sr(2+) < K(+) < Cs(+), follows cation bare size as well as cation solvation energy but does not correlate with hydrated ionic radius or with volume or surface ionic charge density. In the presence of 3:1 salts, the coarse phenomenology of the force between the silica surfaces as a function of salt concentration resembles that in 1:1 and 2:1 electrolytes. Nevertheless, two fundamental differences should be noticed. First, the attraction between the silica surfaces is too large to be attributed solely to vdW force, hence implying an additional attraction mechanism or gross modification of the conventional vdW attraction. Second, neutralization of the silica surfaces occurs at trivalent cation concentrations that are 3 orders of magnitude smaller than those characterizing surface neutralization by mono- and divalent cations. Consequently, when trivalent cations are added to our cation adsorbability series the correlation with bare ion size breaks down abruptly. The strong adsorbability of trivalent cations to silica contrasts straightforward expectations based on ranking of the cationic solvation energies, thus suggesting a different adsorption mechanism which is inoperative or weak for mono- and divalent cations.

Ab initiostudy of point defects in the strongly correlated system CoO

Density functional theory is applied to study the effect of substitutional Fe, Al, and In impurities on the structural, electronic, and magnetic properties of stoichiometric and nonstoichiometric CoO. Ab initiocalculated hyperfine interactions at the Fe impurity are used to determine aliovalent states of iron dopant in CoO and Co${}_{1\ensuremath{-}x}$O systems as well as to characterize the local structure around the impurity. Various Hubbard potentials describing the on-site Coulomb interactions at the Fe impurity are considered, and their influence on the calculated hyperfine parameters and electronic structure of Fe-doped CoO is analyzed. Different vacancy-impurity configurations within the Co-deficient matrix are taken into account to find the site preferences for Fe, Al, and In dopants. The hyperfine parameters at the Fe impurity in Co${}_{1\ensuremath{-}x}$O are also investigated as a function of the distance between vacancy and impurity. This study shows that divalent Fe cations are created inside the almost perfect host lattice, while the trivalent Fe cations are stabilized in the system containing cobalt vacancies. Trivalent Co ions are induced in the cobalt sublattice defected by vacancies and impurities. The overall concentration of trivalent cations in Co${}_{1\ensuremath{-}x}$O is twice as large as the concentration of cation vacancies. Trivalent cations of different ionic radii prefer residing in the second-neighbor sites of a cationic sublattice with respect to the cobalt vacancy. The energy gap of CoO with Fe${}^{2+}$ ions is comparable to that calculated for the defect-free system. The band gap of Co${}_{1\ensuremath{-}x}$O with Fe${}^{3+}$ and Co${}^{3+}$ ions is reduced due to the acceptor states introduced by both trivalent cations. Band-gap reduction arising from acceptor levels created by Co${}^{3+}$ cations is also observed for Co${}_{1\ensuremath{-}x}$O defected by nonmagnetic trivalent impurities. The present first-principles studies support and supplement results of several M\ossbauer spectroscopy experiments.

The incorporation of hydroxyl into zircon

We investigated the incorporation of hydrogen into zircon at 1650 and 1550 °C, and pressures of 2.5 and 1.5 GPa under water-saturated conditions in a piston-cylinder apparatus. Concentrations were determined by polarized Fourier transform infrared spectroscopy using the zircon absorption coefficient e i = 36 241 cm−2 per mol H2O/L and range from ~90 to 200 ppm H2O by weight. Crystals grown in the presence of Ti4+ or Th4+ do not differ significantly in their H2O content. We also synthesized zircons with various concentrations of Lu2O3 and Al2O3 to characterize changes in band positions and hydrogen concentrations related to coupled substitutions in zircon. Trivalent cations correlate in a nearly 1:1 molar fashion with hydrogen highlighting a potentially important coupled substitution in high water activity environments. Bands from undoped and doped zircons in the OH stretching region of the infrared spectrum show broad agreement when compared to spectra from natural samples. Heating experiments at 1 atm and 1000 °C produce a decrease in the integrated area; while some bands disappeared entirely, others are particularly stable with little decrease in integrated area after 128 h at 1000 °C. Results presented here help eliminate uncertainties that arose from Fourier transform infrared studies of natural zircons and provide further clarification for the origin of band positions in natural samples. In addition to the water activity of the crystallizing medium, the H2O content of natural grains will likely be significantly influenced by trivalent cation concentrations. In crustal zircons especially, trivalent atomic contents generally exceed those of phosphorus, meaning that hydrogen may be particularly important for trivalent cation charge compensation. An unanticipated result of this study was the development of a reasonably effective technique that produces relatively homogenous zircons doped with minor impurities. This technique could potentially be utilized in studies aimed at developing zircon standards, because it yields crystals that appear to be more homogenous than those produced by the flux method, and are generally free of inclusions.

Simulations of calcium channel block by trivalent cations: Gd 3+ competes with permeant ions for the selectivity filter

Current through L-type calcium channels (Ca V1.2 or dihydropyridine receptor) can be blocked by micromolar concentrations of trivalent cations like the lanthanide gadolinium (Gd 3+). It has been proposed that trivalent block is due to ions competing for a binding site in both the open and closed configuration, but possibly with different trivalent affinities. Here, we corroborate this general view of trivalent block by computing conductance of a model L-type calcium channel. The model qualitatively reproduces the Gd 3+ concentration dependence and the effect that substantially more Gd 3+ is required to produce similar block in the presence of Sr 2+ (compared to Ba 2+) and even more in the presence of Ca 2+. Trivalent block is explained in this model by cations binding in the selectivity filter with the charge/space competition mechanism. This is the same mechanism that in the model channel governs other selectivity properties. Specifically, selectivity is determined by the combination of ions that most effectively screen the negative glutamates of the protein while finding space in the midst of the closely packed carboxylate groups of the glutamate residues.

Positron depth profiling in ion-implanted zirconia stabilized with trivalent cations

Slow positron implantation spectroscopy has been performed on a series of (ZrO 2) 1− x (M 2O 3) x solid solutions, either stabilized in the cubic phase (with M:Y, Dy or Er and x = 0.095 , 0.16 or 0.16, respectively) or in the tetragonal metastable phase (M:Y and x = 0.03 ). Stabilization induces native oxygen-vacancy complexes, which lead to saturation trapping of positrons in the cubic crystals, regardless of the cation type. The positron diffusion length in the tetragonal phase ( L +≈60 nm, vs.≈2.5 nm in the cubic phase) suggests that Y atoms segregate around antiphase boundaries formed in the lattice. Implantations of helium and oxygen ions induce new defects, more trapping effective than the native defects. However, their production rate and temperature stability seem primarily dependent on the crystal structure, hence on the concentration of trivalent cations, irrespective of their chemical nature.

Use of polyvalent cations to improve the adsorption strength between adsorbed enzymes and supports coated with dextran sulfate

In this paper, we have shown that the presence of low concentrations of trivalent cations during the adsorption of proteins on supports coated with dextran sulfate strongly reinforces the adsorption strength of the proteins, without altering the enzyme activity. This makes much more difficult its desorption (in some cases, the protein remained fully adsorbed under conditions where the conventional immobilized enzymes have been fully desorbed), and in this way, enabling their use in a wider range of conditions. This may be explained if the trivalent cation forms an ionic bridge between the two charges of the sulfate group and the charge of aspartic or glutamic residues. The presence of moderate (e.g., 5–10 mM) of these cations during use may further reinforce the adsorption of the proteins, increasing by a 20–40%, the concentration of NaCl necessary to desorb 50% of the adsorbed proteins. Moreover, the enzymes immobilized under these conditions exhibited an improved stability in thermal and organic solvent inactivations (e.g., penicillin acylase improved its thermal stability by a six-fold factor).

Influence of Fe, Cr and Al on hydrogen incorporation in orthopyroxene

Three series of enstatite crystals doped with different amounts of Fe, Cr or Al were synthesized under water-saturated conditions at 25 kbar. The OH-incorporation was studied by FTIR-spectroscopy on oriented crystal sections. Strongest absorptions (approximately 65 % of total absortion) occurred in all cases when n γ was parallel to the electric field vector E of the incident light, weakest absorptions were observed when n β was parallel to E. In addition to the O-H absortion bands of pure enstatite (at 3070 and 3361 cm −1 , respectively), IR spectra on orthopyroxenes containing trivalent cations reveal additional peaks between 3250 and 3350 cm −1 as well as above 3400 cm −1 , consistent with the generation of new hydrogen sites and a distortion of the polyhedral chains and cationic effects influencing the local electric field around the H bond. The amount of the incorporated OH correlates well with the concentration of trivalent cations in the crystal, consistent to the exchange mechanisms Fe 3+ + H + ⇔ 2 Mg 2+ and Cr 3+ + H + ⇔ 2 Mg 2+ . Comparison to natural samples from the Earth9s upper mantle strongly suggests that coupled substitutions involving Al 3+ dominate the H + incorporation.

Trace elements in quartz - a combined electron microprobe, secondary ion mass spectrometry, laser-ablation ICP-MS, and cathodoluminescence study

We present electron microprobe, secondary ion mass spectrometry, and laser ablation inductively coupled mass spectrometry data for common trace elements (Li, Al, Ti, Na, K, Fe) in quartz. Our samples from both magmatic and hydrothermal environments all show heterogeneity at the single grain scale. ConcentrationsofAlandTi determinedbyEPMA,SIMS,andLA-ICP-MSareinroughagreementandconfirmtherobustnessof these analytical methods. The highest precision data were obtained from SIMS, but this is outweighed by the lack of a high quality quartz reference sample for calibrating this technique. Due to its large sampling volume, laser ablation analyses gave only average values for trace elements in zoned quartz. Because of its better spatial resolution in conjunction with the ability to combine spot analyseswithcathodoluminescenceimaging EPMAprovedthemost reliable insitu methodfor obtainingquantitativetraceelement dataofquartzatconcentrationsinexcessof afew10' sofppmandatthe<10µ mscale.However,oursamplecontainedfewelements at such high concentration levels. We found in our samples a positive correlation between CL signature and the observed Ti contents for the samples investigated. In particular, blue luminescing zones were found to have elevated Ti concentrations as compared to other nearby domains. Using a mathematical spectral deconvolution weshow thehighlycomplex natureof CL emission- it appearsthat other trace elementmight play a less pronounced role in this process. Our examples demonstrate the value of CL for documenting multi-phase alteration in quartz. In agreement with previously proposed models, we confirm a significant correlation between mono- and tri-valent cation concentrations in quartz. A very strong correlation in alkali metal contents is particularly obvious. Ti was found to be universally present in magmatic quartz, but at much lower abundance in hydrothermal quartz.

Application of electrokinetic data to test the adsorption models

The effect of adsorption of Gd(III) on the electrokinetic potential of silica (Aerosil, 390 m2/g) was studied at various Gd(III) concentrations (ranging from 10-6to 10-2mol dm-3) and at four different solid to liquid ratios (ranging from 0.05 to 8% of silica by weight). Up to some critical concentration of trivalent cations, their effect on the electrokinetic potential of silica is negligible and the sign is negative over the entire studied pH range. This critical concentration increases when the solid to liquid ratio increases. When Gd(III) concentration exceeds the critical value, the magnitude of the negative electrokinetic potential of silica is reduced. This effect is substantial at pH 6 but it is rather insignificant when the pH is very high (pH &gt; 8) or very low (pH &lt; 4). When the Gd(III) concentration is even higher, the sign of the electrokinetic potential is reversed to positive over certain pH range, which depends on the solid to liquid ratio and Gd(III) concentration. The shape of experimental electrokinetic curves of silica in the presence of trivalent cations often shows maximums and double isoelectric points, thus, it is very complex in comparison with the shape of the percentage of uptake vs. pH curves. Therefore, a test of an adsorption model based on electrokinetic curves is much more demanding than a test based merely on uptake vs. pH curves. The parameters of surface complexation model (SCM) derived from analysis of a large set of uptake curves were used to predict the course of electrokinetic curves. The calculated and experimentally observed maximums and isoelectric points do not exactly match (a difference up to one pH unit), but the model curves qualitatively reflect the trends observed in electokinetic experiments.

Stretching of Single Collapsed DNA Molecules

The elastic response of single plasmid and lambda phage DNA molecules was probed using optical tweezers at concentrations of trivalent cations that provoked DNA condensation in bulk. For uncondensed plasmids, the persistence length, P, decreased with increasing spermidine concentration before reaching a limiting value 40 nm. When condensed plasmids were stretched, two types of behavior were observed: a stick-release pattern and a plateau at ∼20 pN. These behaviors are attributed to unpacking from a condensed structure, such as coiled DNA. Similarly, condensing concentrations of hexaammine cobalt(III) (CoHex) and spermidine induced extensive changes in the low and high force elasticity of lambda DNA. The high force (5–15 pN) entropic elasticity showed worm-like chain (WLC) behavior, with P two- to fivefold lower than in low monovalent salt. At lower forces, a 14-pN plateau abruptly appeared. This corresponds to an intramolecular attraction of 0.083–0.33 kT/bp, consistent with osmotic stress measurements in bulk condensed DNA. The intramolecular attractive force with CoHex is larger than with spermidine, consistent with the greater efficiency with which CoHex condenses DNA in bulk. The transition from WLC behavior to condensation occurs at an extension about 85% of the contour length, permitting looping and nucleation of condensation. Approximately half as many base pairs are required to nucleate collapse in a stretched chain when CoHex is the condensing agent.

Solubility of highly charged anionic polyelectrolytes in presence of multivalent cations: Specific interaction effect

Studies performed on strong polyelectrolytes and on a weak polyelectrolyte, sodium poly(acrylate), show that their stability in presence of multivalent cations depends on the chemical nature of the charged side groups of the polymer. For sulfonate groups (SO3-) or sulfate groups (OSO3-) phase separation generally occurs in presence of inorganic cations of valency 3 (as La3+) or larger and a resolubilization takes place at high salt concentration. The interactions of the polyelectrolyte with multivalent cations are of electrostatic origin and the phase diagrams are weakly dependent on the chemical nature of the polymer backbone and on the specificity of the counterions. For acrylate groups, (COO-), the phase separation was observed with inorganic cations of valency 2 (as Ca2+) or larger without resolubilization at high salt concentration. The phase separation is due to a chemical association between cations and acrylate groups of two neighboring monomers of the same chain. This chemical association creates a hydrophobic complex by dehydrating both monomer and cation. With organic trivalent cation, as spermidine +H3N(CH2)4NH2+(CH2)3NH3+, where no chemical association occurs with the charged side groups COO- or SO3- of the polyelectrolyte, similar phase diagrams were observed whatever was the polyelectrolyte with a resolubilization at high trivalent cation concentration.

Aluminium Effects on Pollen Germination and Tube Growth of Chamelaucium uncinatum. A Comparison with Other Ca2+Antagonists

An interaction between aluminium (Al) and calcium (Ca) may be a cause of Al toxicity in plants. The pollen tube is a suitable system to test the interaction between Al and Ca since Ca ions play a pivotal role in pollen germination and tube growth. We investigated how Al and other known blockers of Ca2+-permeable channels (trivalent cations, ruthenium red, verapamil and nifedipine) influence pollen of an Australian native species Geraldton waxflower (Chamelaucium uncinatum). Pollen germination was inhibited by micromolar concentrations of trivalent cations (La3+>Al3+>Gd3+) and ruthenium red, but it was relatively insensitive to a micromolar concentration of verapamil. Exposure of the growing pollen tubes to micromolar concentrations of Al3+and La3+, and a millimolar concentration of Ca2+chelator ethyleneglycol-bis(β-aminoethyl ether)-N,N′-tetraacetic acid (EGTA) led to rapid tip bursting. In contrast, exposure to Gd3+, nifedipine, ruthenium red, verapamil and the organic trivalent cation tris (ethylenediamine)cobalt (TEC3+) caused only inhibition of pollen tube growth. The Al3+-related pollen tube bursting was reduced significantly by increasing either solution pH from 4.5 to 6 or activity of Ca2+from 0.25 to 5 m m. In contrast, La3+-related pollen tube bursting was insensitive to changes in Ca2+activity. The results are discussed in terms of Al interactions with cell wall Ca2+and the plasma membrane Ca2+-permeable channels.

Cobalt Phosphate Based Zeolite Structures with the Edingtonite Framework Topology

Hydrothermal syntheses and crystal structures of five zeolite edingtonite analogues are presented. For the first time, the edingtonite framework topology is assembled using an amine-assisted synthesis approach with either 1,2-diaminopropane or 1,2-diamino-2-methylpropane. These materials are created in the cobalt phosphate system with a small concentration of trivalent cations (Al3+ and Ga3+) incorporated into the framework for the host−guest charge matching. ACP-EDI1 and GCP-EDI1 are monoclinic, whereas ACP-EDI2, ACP-EDI3, and GCP-EDI2 are tetragonal (ACP = aluminum cobalt phosphate; GCP = gallium cobalt phosphate). The difference in lattice symmetries between ACP-EDI1 and ACP-EDI2 (or GCP-EDI1 and GCP-EDI2) is related to the synthesis conditions. All five structures have three-dimensional 8-ring channels along the crystallographic [001], [110], and [110] directions, regardless of the difference in symmetry. Amine molecules are more ordered in the monoclinic phases than in the tetragonal phases, and the...

Flocculation of melanoidins induced by inorganic ions

Natural melanoidin in alcohol distillery effluent and synthetic melanoidin, which was prepared from glucose and glycine, showed similar elemental (CHON) compositions, spectroscopic properties and electrophoretic mobilities at various pH values. Optimal flocculation induced by FeCl 3, AlCl 3 or polyferric hydroxysulfate was obtained at a trivalent cation concentration of 0.04 M; excess flocculant caused color intensification of distillery effluents. Based on the electrical charge properties of melanoidins, a model is proposed for their flocculation and deflocculation induced by inorganic ions.