Ionic Strength NaCl Research Articles

Effects of inorganic ions and natural organic matter on the aggregation of nanoplastics

The aggregation of nanoplastics (NPs) is a key issue in understanding the dynamic nature of NPs in the environment. The aggregation of NPs under various environmental conditions has not yet been studied. We investigated the influences of inorganic ions and natural organic matter (NOM) on polystyrene (PS) NPs aggregation in solutions. Results showed that PS NPs remained stable in wide ionic strength solutions of NaCl (1–100 mM) and CaCl2 (0.1–15 mM), and only in low ionic strength FeCl3 solutions (0.01 mM). However, obvious PS NPs aggregation was observed in FeCl3 solutions with an increase in ionic strength (0.1 and 1 mM). Moreover, NOM had a negligible effect on PS NPs aggregation in all ionic strengths of NaCl and CaCl2 solutions and in low ionic strength FeCl3 solutions (0.01 mM). However, NOM reduced PS NPs aggregation in an intermediate ionic strength FeCl3 (0.1 mM) solution and increased aggregation in a high ionic strength FeCl3 (1 mM) solution. Based on the theoretical analysis of interaction forces among PS NPs, the Derjaguin–Landau–Verwey–Overbeek force was a contributor governing PS NPs aggregation either in the absence or presence of NOM. In addition, other factors, including electrostatic heterogeneity of PS NPs surfaces, steric repulsion induced by NOM, and clusters formed via bridging effect in the presence of NOM also contributed to altered PS NPs aggregation under selected conditions. The PS NPs-NOM clusters were directly observed using a cryogenic scanning electron microscope.

Investigation of the effect of water chemistry on biologically mediated flocculation in the aquatic environment

Extracellular Polymeric Substances (EPS) in the water environment assemble fine, colloidal particles, such as clays, microorganisms and biomass, in large flocs, which are eventually subject to sedimentation and deposition and determine water/sediment quality and quantity. This study hence aimed to investigate the way that water and colloidal chemistry affects EPS-mediated flocculation of colloidal particles, using a jar-test experiment. Especially, ionic strength, divalent cation and humic substances concentrations were selected as experimental variables in the jar-test experiments, to elucidate their effects on EPS-mediated flocculation. A higher ionic strength increased flocculation capability, reducing electrostatic repulsion between EPS-attached colloidal particles and enhancing particle aggregation. 0.1 M NaCl ionic strength had higher flocculation capability, with 3 times larger floc size and 2.5 times lower suspended solid concentration, than 0.001 M NaCl. Divalent cations, such as Ca2+, built divalent cationic bridges between colloidal particles and EPS (i.e., colloid-Ca2+-EPS or EPS-Ca2+-EPS) and hence made colloidal particles to build into large, settelable flocs. A small Ca2+ concentration enhanced flocculation capability, reducing suspended solid concentration 20 times lower than the initial dosed concentration. However, humic substances, adsorbed on colloidal particles, reduced flocculation, because they blocked EPS adsorption on colloidal particles and increased negative charges and electrostatic repulsion of colloidal particles. Suspended solid concentration in the tests with humic substances remained as high as the initial dosed concentration, indicating stabilization rather than flocculation. Findings about EPS-mediated flocculation in this research will be used for better understanding the fate and transport of colloidal particles in the water environment and for developing the best management practices for water/sediment quality.

Thermostability of DNA Complexes with Mitoxantrone at Small Fillings

Thermostability of DNA complexes with anti-tumorous compound — mitoxantrone — at 0.011[Formula: see text]M and 0.11 M NaCl ionic strengths of solution by spectrophotometric and microcalorimetric methods has been studied. It was shown that at small fillings when one molecule of mitoxantrone corresponds to 250 or more base pairs of DNA, the thermostability of complexes strongly depends on the solution’s ionic strength; moreover, at an ionic strength of 0.011 M NaCl the melting temperature dependence on mitoxantrone concentration passes through a minimum. In the mentioned region of mitoxantrone concentration the melting enthalpy of the complexes increases linearly with mitoxantrone concentration enhancement. The observed phenomenon, which is not observed for ethidium bromide complexes with DNA, is qualitatively explained by the increasing of coil-shaped state of DNA–mitoxantrone complex due to additional freedom of rotation of mitoxantrone side groups.

Synthesis and Determination of Acid Dissociation Constants in Dimethyl Sulfoxide–Water Hydroorganic Solvent of 5,5-Diphenylpyrrolidine N-Aroylthiourea Derivatives

Novel 5,5-diphenylpyrrolidine N -aroylthioureas, containing 4-methylbenzoyl, 2-chlorobenzoyl,2,4-dichlorobenzoyl, and2-naphthoyl, were synthesized and their structural analysis was performed using 1 H nuclear magnetic resonance (NMR), 13 C NMR, Fourier transform infrared spectroscopy, mass spectrometry (MS), and high-resolution MS (HRMS) techniques. The acid dissociation constants of the 5,5-diphenylpyrrolidine N -aroylthiourea derivative compounds were determined using Hyperquad computer program for data obtained using potentiometric titration method in 25% (v/v) dimethyl sulfoxide–water hydroorganic solvent in the presence of 0.1 mol × L - 1 ionic strength of NaCl and in the acidic medium at 25±0.1°C, using sodium hydroxide base as a titrant. Two acid dissociation constants were obtained for 3a , 3b, and 3d, and it was suggested that they were related to N-H and enol groups. Furthermore, three acid dissociation constants obtained for 3a indicated that they were related to N-H, enthiol, and enol groups, and four acid dissociation constants obtained for 3c suggested that they were related to N-H, enthiol, enol, and carboxyl groups.

Ca2+ detection utilising AlGaN/GaN transistors with ion-selective polymer membranes

We demonstrate highly selective and sensitive potentiometric ion sensors for calcium ion detection, operated without the use of a reference electrode. The sensors consist of AlGaN/GaN heterostructure-based transistor devices with chemical functionalisation of the gate area using poly (vinylchloride)-based (PVC) membranes having high selectivity towards calcium ions, Ca2+. The sensors exhibited stable and rapid responses when introduced to various concentrations of Ca2+. In both 0.01 M KCl and 0.01 M NaCl ionic strength buffer solutions, the sensors exhibited near Nernstian responses with detection limits of less than 10−7 M, and a linear response range between 10−7–10−2 M. Also, detection limits of less than 10−6 M were achieved for the sensors in both 0.01 M MgCl2 and 0.01 M LiCl buffer solutions. AlGaN/GaN-based devices for Ca2+ detection demonstrate excellent selectivity and response range for a wide variety of applications. This work represents an important step towards multi-ion sensing using arrays of ion-selective field effect transistor (ISFET) devices.

Biophysical characterization of the association of histones with single-stranded DNA

BackgroundDespite the profound current knowledge of the architecture and dynamics of nucleosomes, little is known about the structures generated by the interaction of histones with single-stranded DNA (ssDNA), which is widely present during replication and transcription. MethodsNon-denaturing gel electrophoresis, transmission electron microscopy, atomic force microscopy, magnetic tweezers. ResultsHistones have a high affinity for ssDNA in 0.15M NaCl ionic strength, with an apparent binding constant similar to that calculated for their association with double-stranded DNA (dsDNA). The length of DNA (number of nucleotides in ssDNA or base pairs in dsDNA) associated with a fixed core histone mass is the same for both ssDNA and dsDNA. Although histone-ssDNA complexes show a high tendency to aggregate, nucleosome-like structures are formed at physiological salt concentrations. Core histones are able to protect ssDNA from digestion by micrococcal nuclease, and a shortening of ssDNA occurs upon its interaction with histones. The purified (+) strand of a cloned DNA fragment of nucleosomal origin has a higher affinity for histones than the purified complementary (−) strand. ConclusionsAt physiological ionic strength histones have high affinity for ssDNA, possibly associating with it into nucleosome-like structures. General significanceIn the cell nucleus histones may spontaneously interact with ssDNA to facilitate their participation in the replication and transcription of chromatin.

Ionic strength dependence of aggregate size and morphology on polymer-clay flocculation

Polymer-driven flocculation of suspended particles is a critical process for many applications, including composite materials synthesis, paper manufacturing, and water treatment. However, the role of solution physicochemical properties on the polymer-particle assembly dynamics is nontrivial, particularly for non-spherical, polydisperse particulates such as natural clays. In this work, we study the effects of ionic strength and aggregate size and structure on the polymer behavior and flocculation performance with anisotropic bentonite clay particles. Using jar tests, laser diffraction, confocal microscopy, and X-ray diffraction, we demonstrate that for smectite clay particles, the final floc structure is largely informed by ionic-strength driven changes to the initial clay aggregate size and surface structure. With increasing bentonite aggregate size, a transition from a networked to a patched polymer − aggregate floc structure is observed, independent of ionic strength during flocculation. Solutions were studied over four orders of magnitude of NaCl ionic strength. Initial, pre-flocculated bentonite aggregate sizes ranging from 0.015μm to 15μm were used, produced by tuning the initial solution ionic strength. Bentonite aggregate size and structure were measured with laser and X-ray diffraction, internal floc structure was visualized using confocal microscopy, and macro floc structure (fractal dimension) was measured with optical imaging. These results shed new light on the fundamental complexity of ionic strength dependence and the importance of the aggregate size and structure of the initial dispersion, in determining optimal reagent dosing and structure control for flocculation of anisotropic clays.

Stability of nickel(II) binary and ternary complexes with dipicolinic acid and the amino acids serine, threonine, methionine and phenylalanine

Abstract Binary and ternary complexes of nickel(II) with dipicolinic acid (H 2 dipic) and the amino acids serine (Hser), threonine (Hthr), methionine (Hmet) and phenylalanine (Hphe), have been investigated in aqueous solutions at a 1.0 mol·dm − 3 NaCl ionic strength and 25 °C. The types of complexes formed and their overall stability constants were established on the basis of computer analysis of potentiometric results using the least-squared program LETAGROP. In the Ni(II)-amino acid (HL) systems the complexes [NiL] + , NiL 2 and [NiL 3 ] − were detected. In the ternary systems only the heteroligand complexes Ni(dipic)(HL), [Ni(dipic)(L)] − and [Ni(dipic)(L)(OH)] 2 − were observed. The species distribution diagrams as functions of pH are briefly discussed.

Calcium l-tartrate complex formation in neutral and in hyperalkaline aqueous solutions.

The complex formation reaction between the l-tartrate (Tar2-) and calcium ions taking place in neutral and in hyperalkaline (pH > 13) aqueous solutions has been investigated. It was demonstrated that upon NaOH addition the solubility of the CaTar(s) precipitate significantly increases. Conductometric and freezing point depression measurements further confirmed that in this process water soluble species are formed as a result of a reaction between the CaTar(s) and the hydroxide ion (or, conversely, between Ca(OH)2(s) and the Tar2- ion). 13C NMR spectroscopic measurements yielded the value of pK3 = 15.4 ± 0.2 for the proton dissociation of one of the alcoholic OH groups of Tar2- (at 25.0 °C and 4 M Na(Cl) ionic strength). Upon addition of calcium ions to an alkaline Tar2- solution, the 1H NMR signal gradually broadened and the 13C-satellite peaks split to two components, which also indicate complexation. From H2/Pt potentiometric titrations performed with solutions in the 13.6 ≤ pH ≤ 14.4 range, it was observed, that this complex formation is accompanied by a hydroxide ion consuming process. The titration curves can be best described via assuming the formation of the CaTarH-1-(aq) (lg β11-1 = -11.2 ± 0.1) and CaTarH-22-(aq) (lg β11-2 = -25.3 ± 0.1) complexes. In hyperalkaline solutions, these two species account for more than 90-99% of the calcium ions present and the contribution of the other reasonable and well-established calcium-containing solution species is rather small. The possible structures of the above complexes have been modeled via ab initio calculations. The stoichiometries are consistent both with species containing coordinated alcoholate group(s) and with mixed Ca(ii)-hydroxo-tartrato complexes. From the data available at present, both types of structures can be considered as chemically reasonable.

Flotation behaviour of malachite in mono- and di-valent salt solutions using sodium oleate as a collector

We investigated the influence of a salt solution on the flotation behaviour of synthetic malachite using a sodium oleate as a collector. We found that the floatability of oleate ions-adsorbed synthetic malachite monotonically increases with an increase in the overall ionic strength (IS) range (1–1000mM) of the monovalent cation (Na+), while the floatability sharply increases only up to a level of 30mM of the divalent cation (Ca2+), followed by decreased floatability with further increases in the IS. For a monovalent salt, Na+ ions effectively screen a negatively charged bubble surface, reducing the energy barrier for attachment and thus increasing floatability. Moreover, electrophoretic mobility measurements revealed that oleate ions-adsorbed synthetic malachite is negatively charged in a NaCl solution while it is positively charged in a CaCl2 solution over the entire IS, indicating the specific adsorption of Ca2+ ions onto the surface of oleate ions-adsorbed synthetic malachite in a CaCl2 solution. This surface charge reversal in the CaCl2 solution suggests that electrostatic interaction between positively charged oleate ions-adsorbed synthetic malachite and a negatively charged bubble is attractive, yielding high flotation efficiency. The increased floatability of both the entire IS of NaCl and a low IS of CaCl2 can be well explained by the extended DLVO theory. At a high IS (100–1000mM) of CaCl2, however, the decreased floatability did not follow the extended DLVO prediction, implying that additional non-DLVO type interactions are likely to be involved. Direct contact angle measurements and an inductively coupled plasma (ICP) analysis with the electrophoretic mobility measurements revealed that this unusual flotation behaviour is likely due to the hydration layer by the hydrated Ca2+ adsorption onto oleate ions-adsorbed synthetic malachite.

Dissociation Constants and Octanol–Water Partition Equilibria for Several Fluoroquinolones

The octanol/water partition and acid–base dissociation equilibria for a set of six fluoroquinolones have been studied by the shake-flask method at 25 °C and at 0.15 M NaCl ionic strength, determining the partition coefficient (logD) in the pH range 3 to 9. The substances studied are ciprofloxacin (CIP), danofloxacin (DAN), difloxacin (DIF), enrofloxacin (ENR), marbofloxacin (MAR), and sarafloxacin (SAR). After the partition equilibrium, the remaining fluoroquinolone concentration is determined in aqueous phase by liquid chromatography with fluorescence detection. The pKa values obtained are in accordance with the previously published data, ranging between 5.59 and 6.50 for pKa1 and between 7.99 and 8.96 for pKa2. The lipophilicity of the substances is low, with logKOW ranging between −1.09 to 0.68. Additionally, we have determined the octanol/water partition coefficient for the cationic species in all cases.

Determination of binding capacity and adsorption enthalpy between Human Glutamate Receptor (GluR1) peptide fragments and kynurenic acid by surface plasmon resonance experiments

The interaction between kynurenic acid (KYNA) and two peptide fragments (ca. 30 residues) of Human Glutamate Receptor 201–300 (GluR1) using surface plasmon resonance (SPR) spectroscopy was investigated. Because of the medical interest in the neuroscience, GluR1 is one of the important subunits of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAR). AMPARs are ionotoropic glutamate receptors, which are mediating fast synaptic transmission and are crucial for plasticity in the brain. On the other hand, KYNA has been suggested to have neuroprotective activity and it has been considered for apply in therapy in certain neurobiological disorders. In this article the adsorption of the GluR1201–230 and GluR1231–259 peptides were studied on gold biosensor chip. The peptides were chemically bonded onto the gold surface via thiol group of l-cysteine resulted in the formation of peptide monolayer on the SPR chip surface. Because the GluR1231–259 peptide does not contain l-cysteine the Val256 was replaced by Cys256. The cross sectional area and the surface orientation of the studied peptides were determined by SPR and theoretical calculations (LOMETS) as well. The binding capability of KYNA on the peptide monolayer was studied in the concentration range of 0.1–5.0mM using 150mM NaCl ionic strength at pH 7.4 (±0.02) in phosphate buffer solutions. In order to determine the binding enthalpy the experiments were carried out between +10°C and +40°C. The heat of adsorption was calculated by using adsorption isotherms at different surface loading of KYNA on the SPR chip.

Selective and fast recovery of neodymium from seawater by magnetic iron oxide Fe3O4

Neodymium (Nd) is a key element that widely applied in high-tech industries; therefore, to recover it efficiently from aqueous solutions is rather important. This work examines the recovery of spiked Nd from seawater media by magnetic iron oxide (Fe3O4). A rapid increase of Nd recovery from 0.04 to 22.27mgg−1 was observed when the solution pH adjusted from 1.98 to 8.22 at 298K. A maxima Nd adsorption capacity was estimated to be 24.88mgg−1 at 308K and 8.22 pH. A negative change in standard free energy (ΔG°=−5.87, −6.69, −7.68kJmol−1 at 288, 298, and 308K, respectively) suggests that Nd adsorption is spontaneous. The positive ΔH° value (2.42kJmol−1) supports its endothermic nature of the adsorption and agrees with the observed enhanced Nd adsorption at high temperatures. Besides, the positive ΔS° (10.84Jmol−1K−1) displays that the randomness increase at the solid-solution interface during Nd adsorption. More importantly, we observed that the Nd adsorption only decreased slightly while the NaCl ionic strength increased from 0.001 to 1.0N, implying the involvement of inner-sphere mechanism. These data indicated that the adsorbent of ferrite has a great potential in selective and fast recovery of spiked Nd from seawater matrix.

Toxicity of TiO2 nanoparticles to Escherichia coli: effects of particle size, crystal phase and water chemistry.

Controversial and inconsistent results on the eco-toxicity of TiO2 nanoparticles (NPs) are commonly found in recorded studies and more experimental works are therefore warranted to elucidate the nanotoxicity and its underlying precise mechanisms. Toxicities of five types of TiO2 NPs with different particle sizes (10∼50 nm) and crystal phases were investigated using Escherichia coli as a test organism. The effect of water chemistry on the nanotoxicity was also examined. The antibacterial effects of TiO2 NPs as revealed by dose-effect experiments decreased with increasing particle size and rutile content of the TiO2 NPs. More bacteria could survive at higher solution pH (5.0–10.0) and ionic strength (50–200 mg L−1 NaCl) as affected by the anatase TiO2 NPs. The TiO2 NPs with anatase crystal structure and smaller particle size produced higher content of intracellular reactive oxygen species and malondialdehyde, in line with their greater antibacterial effect. Transmission electron microscopic observations showed the concentration buildup of the anatase TiO2 NPs especially those with smaller particle sizes on the cell surfaces, leading to membrane damage and internalization. These research results will shed new light on the understanding of ecological effects of TiO2 NPs.

Effect of pH, ionic strength, and background electrolytes on Cr(VI) and total chromium removal by acorn shell of Quercus crassipes Humb. & Bonpl.

The ability of Quercus crassipes acorn shells (QCS) to remove Cr(VI) and total chromium from aqueous solutions was investigated as a function of the solution pH, ionic strength, and background electrolytes. It was found that Cr(VI) and total chromium removal by QCS depended strongly on the pH of the solution. Cr(VI) removal rate increased as the solution pH decreased. The optimum pH for total chromium removal varied depending on contact time. NaCl ionic strengths lower than 200 mM did not affect chromium removal. The presence of 20 mM monovalent cations and anions, and of divalent cations, slightly decreased the removal of Cr(VI) and total chromium by QCS; in contrast, divalent anions (SO₄(2-), PO₄(2-), CO₃(2-)) significantly affected the removal of Cr(VI) and total chromium. The biosorption kinetics of chromium ions followed the pseudo-second-order model at all solution pH levels, NaCl ionic strengths and background electrolytes tested. Results suggest that QCS may be a potential low-cost biosorbent for the removal of Cr(VI) and total chromium from aqueous solutions containing various impurities.

Polyelectrolyte complexation between cationic and anionic polyelectrolytes with complementary polymer-bound reactive groups of amine and acetoacetate: effect of mono- and divalent salts

The copolymers of methacrylic acid with 0–50 % of 2-(methacryloyloxy)ethyl acetoacetate, and the copolymers of 2-(methacryloyloxy)ethyl trimethyl ammonium chloride with 0–50 % of 2-aminoethyl methacrylate were prepared by free radical polymerization in various solvents. The polyelectrolytes were characterized by potentiometric titration, NMR, viscometry and size exclusion chromatographic techniques. Polyelectrolyte complex formation between oppositely charged polyelectrolytes with polymer-bound (non)reactive polyelectrolytes was studied in the presence of NaCl and CaCl2 as a function of ionic strength. The physical nature and efficiency of polyelectrolyte complexes that form gels, liquid coacervates, or soluble complexes depend on variables such as ionic strength and charge ratio. The highest complexation efficiency was obtained when a 1:1 charge ratio was used. Liquid coacervates were obtained with high ionic strength NaCl. The inclusion of small amounts of CaCl2 led to drastic property changes in the polyelectrolyte complexes. The divalent calcium ion (Ca2+) displaced the poly[2-(methacryloyloxyethyl) trimethyl ammonium chloride] from the complexes and appeared as a new form of liquid coacervate in a range of ionic strength (50–200 mM CaCl2). The reactivity of the polyelectrolyte system was demonstrated by studying the formation of coacervate complexes. Herein, the feasibility of cross-linking of the resulting coacervate via complementary poly(methacrylic acid-co-2-(methacryloyloxy)ethyl acetoacetate)-bound acetoacetate groups with poly(2-(methacryloyloxy)ethyl trimethyl ammonium chloride-co-2-aminoethyl methacrylate)-bound amine groups is discussed in detail.

Estradiol Solubility in Aqueous Systems: Effect of Ionic Concentrations, pH, and Organic Solvents

This study examined the effects of ionic strengths of NaCl (0.1, 0.3, and 1.0 M), pH (3, 7, and 11), and organic solvents (dichloromethane, diethyl ether, and methanol) on the extraction of estradiol at concentrations of 5.0 pg/mL in human serum. Methanol extracted almost 100% of the estradiol at a 5.0 pg/mL concentration, while ether and dichloromethane extracted only 73% or 70%, respectively, of the estradiol. The methanol extracted material was subjected to reverse phase high-performance liquid chromatography (HPLC) using 60% methanol and was found to elute at the same position as estradiol standard. These results suggest that methanol extraction of estradiol may prove useful in situations where estradiol occurs at concentration levels of ≥5.0 pg/mL, concentrations of great clinical significance in the detection and treatment of breast cancer.

A high salt tolerant neutral protease from Aspergillus Oryzae: Purification, characterization and kinetic properties

A neutral high salt tolerant protease from Aspergillus oryzae CICIM F0899 which could be used for soy sauce production and other relevant applications under high-salt conditions was purified to homogeneity through ammonium sulfate precipitation, ion-exchange chromatography and gel filtration chromatography with overall recovery of 2%. Its molecular weight was estimated to be 50 kDa by SDS-PAGE. The optimum pH and temperature for activity of the extracellular protease of A. oryzae CICIM F0899 were shown to be between 7.0–9.0, and 50°C, respectively. The protease behaved high salt tolerance in 18% NaCl and retained 72% of initial activity after 14 days, indicating the high stability. The enzyme activity was inhibited by metal ions such as Al3+ and Ag+, and slightly activated by Mn2+ and Cu2+. A kinetic model incorporating the Debye-Huckel limiting law was proposed for A. oryzae CICIM F0899 protease hydrolysis of casein at ionic strength NaCl from 0.10 to 3.18 M. It was found that, with the higher ionic strength, the Michaelis constant Km of the protease monotonically increased while the turnover number kcat decreased in accordance with first order kinetic model. The high-salt tolerant protease has been demonstrated to be promising for the soy sauce production process.

Binding mechanism of Cu(II) at the clay–water interface by powder and polarized EXAFS spectroscopy

The sorption mechanism of Cu(II) on the 2:1 magnesian clay hectorite, the 2:1 aluminous clay montmorillonite, and the 1:1 aluminous clay kaolinite was investigated at pH 5.4–6.0 and 0.5M NaCl ionic strength by solution chemistry and powder and polarized XANES and EXAFS spectroscopy. Divalent copper was not photoreduced under the intense synchrotron X-ray beam and retained its usual square (bi)pyramidal coordination with four equatorial oxygens (Oeq) at 1.93–1.96Å and one to two axial oxygens (Oax) at 2.56–2.58Å. The angular dependence of XANES spectra, the measured angle of 57–58° between the Cu–Oeq atomic pair and the direction perpendicular to the clay layer plane ([001]∗), and the detection and polarization dependence of neighboring Al/Mg and Si cationic shells, together indicate that Cu(II) is bonded to the edges of the clay layers as an inner-sphere complex. Based on the number of Mg/Al and Si nearest neighbors, the Cu(Oeq)4(Oax)1–2 polyhedron is attached to the clay surface by sharing one to three edges with the structural Al/Mg octahedra and zero to three corners with the Si/Al tetrahedra. Copper has an unusually high coordination on the two dioctahedral aluminous clays, explained by the presence at their surface of distorted empty cavities which can accommodate irregular coordination polyhedra. The steric match between the distorted empty octahedral cavities and the Jahn–Teller distorted Cu polyhedra provides a rationale to explain the higher affinity of Cu(II) for Al octahedral sheets, including the hydrargillite sheet of lithiophorite ([Al,Li][MnO2]O2[OH]2) as observed in nature.

Configurational, LFDFT and NBO analysis of chromium(III) complexes of edta-type ligands

A new hexadentate chromium(III) complex, Na[Cr(l,3-pd3ap)]·3H2O, containing an unsymmetrical edta-type ligand, the 1,3-propanediamine-N,N,N′-triacetate-N′-3-propionate ion (1,3-pd3ap), has been prepared, chromatographically separated and characterized. Only one [trans(O5)] of the two possible geometrical isomers was isolated. In this isomer the two five-membered glycinate rings (R rings) occupy trans-axial sites, while the one glycinate ring and one β-alaninate ring lie in the equatorial plane with the two diamine nitrogens (G rings). This result confirms the assignment made on the basis of Density Functional Theory (DFT), IR and UV–Vis spectral data analyses. The spectral data and electronic transition assignment, DFT–NBO, Ligand Field DFT and extensive strain analysis are discussed by a comparison with those of other [Cr(edta-type)]− complexes of known configurations. The stoichiometry and stability of the complexes formed between the chromium(III) ion and 1,3-propanediamine-N,N,N′-triacetic-N′-propionic acid (H41,3-pd3ap) were determined in aqueous solution by potentiometry at 25°C and 0.1M NaCl ionic strength. The existence of Cr(HnL), n=0, 1, 2 and 3 type complexes were verified. The formation of the Cr(OH)L complex was observed at higher pH values. The concentration distribution diagrams of the complexes were evaluated.