Thermodynamic characterization of the amphotericity of oxides and hydroxides of group-IIIA elements in aqueous media

Dependences of the molar solubility of M₂O₃ solid oxides on the pH of aqueous media at 25°C and also the constants of acid-base equilibria in aqueous media for stable crystalline M₂O₃ oxides and for crystalline and dissolved M(OH)₃ hydroxides (M = In, Al, Ga, In, and Tl) were calculated by the thermodynamic method with account of the formation of hydroxo complexes.     

Thermodynamic calculation of the solubility of solid hydroxides M(OH)<Subscript>2</Subscript> in water and alkaline media

The influence exerted by the pH value on the molar solubility of a number of amorphous and crystalline hydroxides of Group-II elements in an aqueous alkaline medium was calculated thermodynamically with account of the formation of hydroxo complexes.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 8, 2004, pp. 1271–1274.Original Russian Text Copyright © 2004 by Shkolnikov.     

Thermodynamic characterization of the amphoterism of hydroxides and oxides of scandium subgroup elements in aqueous media

Effect of the pH value on the molar solubility of solid hydroxides M(OH)₃ and oxides M₂O₃ at 25°C and the constants of acid-base equilibria in aqueous media for crystalline hydroxides and oxides and dissolved hydroxides M(OH)₃ (M = Sc, Y, La) were calculated using the thermodynamic method, with the formation of hydroxo complexes taken into account.     

Thermodynamic characterization of the amphoterism of solid oxides MO in aqueous media

Thermodynamic method was used to calculate, with account of the formation of hydroxo complexes, the molar solubilities of crystalline and amphoteric oxides MO as functions of the pH value of an aqueous-alkaline nonoxidizing medium at 25°C and constants of heterogeneous equilibria in water and alkaline and acid media for amphoteric metal MO, where M is Be, Mn-Zn, Cd, Hg, Sn, or Pb.     

Structures of IV group elements and solid phases of water

The structures of solid phases of water and IV(b) group elements of the periodic table (carbon, silicon, germanium, and tin) are compared. Both water and mentioned elements are characterized by high polymorphism. All mentioned elements and ice have a modification with a diamond structure. For all substances considered, except tin, modifications with the structure of a hexagonal analogue of diamond (lonsdaleite) have been known. The modification with the β-Sn structure has not been known only for ice and carbon. One of the germanium modifications is isostructural to ice III. Tin has a modification with the α-Fe structure. The same structure is observed for ices VII, VIII, and X. Both water and IVb group elements can form clathrate compounds with cavities in the form of Allen’s polyhedra. In water clathrates these cavities contain noble gas atoms (Ar, Kr, Xe) and various molecules. Clathrates of IVb group elements contain metal atoms as well as noble gas atoms.     

Internet software for the calculation of the lipophilicity and aqueous solubility of chemical compounds

In this paper we describe an Internet Java-based technology that allows scientists to make their analytical software available worldwide. The implementation of this technology is exemplified by programs for the calculation of the lipophilicity and water solubility of chemical compounds available at http://www.lnh.unil.ch/~itetko/logp. Both these molecular properties are key parameters in quantitative structure-activity relationship studies and are used to provide invaluable information for the overall understanding of the uptake distribution, biotransformation, and elimination of a wide variety of chemicals. The compounds can be analyzed in batch or single-compound mode. The single-compound analysis offers the possibility to compare our results with several popular lipophilicity calculation methods, including CLOGP, KOWWIN, and XLOGP. The chemical compounds are analyzed according to SMILES line notation that can be prepared with the JME molecular editor of Peter Ertl. Conversion to SMILES from 56 formats is also available using the molecular structure information interchange hub developed by Pat Walters and Matt Stahl.     

Structure of aqueous solutions of group IIIA metals perchlorates by near infrared spectroscopy

The state of water in aqueous solutions of group IIIA metal perchlorates at 25°C was studied by the IR spectroscopy in the range of 5400–7500 cm^?1. The optical density values of the solution measured at different wavelengths were combined in a matrix of experimental data of the uniform dimension. The matrices were chemometrically analyzed. A number, spectra, and concentration profiles of the spectral forms existing in the solution were determined. By the principal component method, the IR spectra of the studied systems are grouped into the mathematical clusters according to the nature of the cation-water interaction in the solution. The combined use of the infrared spectroscopy and chemometric analysis showed that the structural changes in the solution predicted by the generalized phenomenological model are due to the existence and interconversion of the spectral forms.     

Estimation of the aqueous solubility of organic molecules by the group contribution approach

Several group contribution methods to estimate the aqueous solubility of organic molecules are proposed and evaluated for their ability to predict the water solubility of new molecules. The learning set consisted of 1168 organic compounds with experimental data taken from the literature after critical evaluation. The best method, based on a new fragment atom scheme, leads to a squared correlation coefficient of 0.95 and an average absolute calculation error of 0.50 log unit, which is superior to other group contribution methods currently available. One of the advantages of this model is that it has upper and lower limits so that the predicted solubilities cannot be unrealistily high or low.     

Catalytic activity of iron hydroxides and manganese hydroxides in the deoxygenation of water

Catalysts prepared by the modification of FIBAN K-4 and FIBAN X-1 fibrous ion exchangers with the hydroxides of iron and manganese were developed and tested in a water deoxygenation process. It was established that the samples obtained by the supporting of Fe(III) hydroxide onto the FIBAN X-1 ampholyte were most effective. The conclusion that the high activity of the catalytic system is caused by the formation of a mixed phase of Fe(II) and Fe(III) hydroxides of the spinel type containing mobile (weakly bound) lattice oxygen was made. A reaction scheme was proposed to explain the reaction mechanism.     

New insights on the doping of ZnO films with elements from group IIIA through electrochemical deposition

This study was focused in the electrodeposition of both compact and nanostructured extrinsic n-type doped ZnO films, which was achieved with aluminum, gallium, and indium. These elements were directly added into a Zn(II) rich electrolyte with molecular oxygen acting as an oxide precursor in aqueous perchlorate media. This way, the use of nitrate ions, whose by-products are accumulated in the aqueous electrolyte, and chloride ions, an electrically active element in ZnO, was therefore avoided. Speciation diagrams, conditional solubility diagrams and a potentiodynamic study were used to explain the way in which extrinsic n-type ZnO can be prepared by electrochemical deposition. Relatively compact films with a highly preferred orientation along the c-axis were suitable for impedance measurements, thus allowing the measurement of their doping levels. Al- and Ga-doped lamellar nanostructures were successfully prepared when the nature of the anion was changed from perchlorate to sulfate. Under specific conditions, the structure of these films changed from opened and isolated nanosheets to interconnected ones. Morphological, optical, and crystallographic properties of these films were also analyzed. Results and discussion presented here should provide a better understanding toward the study of alternative materials in fields such as photovoltaics and photocatalysis.     

Quotients of group algebrae in the calculation of intermediate ligand field matrix elements

The structure of the classes of symmetry elements excluded during the subduction of the representations of SU(2) onto the finite group 0* is shown to quantitatively define the relationship of the coupling algebrae of these two groups. This relationship is formalized as a quotient algebra. This quotient algebra is realized as 3-like symbols which exist whether or not the quotient can be defined as a group. These symbols distribute the value of a reduced matrix element of SU(2) onto the subduced reduced matrix elements of O* and are termed Partition Coefficients. Since the structure of the excluded symmetry classes is independent of the quantization of O*, these Partition Coefficients can be used to define the values of the matrix elements of O* without reference to the form of its basis set. Thus, the choice of physical interpretation of the ligand field is unimportant. The strong field, weak field, Russell-Saunders and j-j coupling models are all unified in terms of the Partition Coefficients and the 3 symbols which are appropriate to the quantization.     

A salt-free zero-charged aqueous onion-phase enhances the solubility of fullerene C60 in water

An onion-phase (multilamellar vesicular phase or Lalpha-phase) was prepared from salt-free zero-charged cationic and anionic (catanionic) surfactant mixtures of tetradecyltrimethylammonium hydroxide (TTAOH)/lauric acid (LA)/H2O. The H+ and OH- counterions form water (TTAOH + LA --> TTAL + H2O), leaving the solution salt free. The onion-phase solution has novel properties including low conductivity, low osmotic pressure and unscreened electrostatic repulsions between cationic and anionic surfactants because of the absence of salt. The spherical multilamellar vesicles have an average 250 nm radius as measured by freeze-fracture transmission electron microscopy (FF-TEM) and the maximum interlayer distance, i.e., the thickness of the hydrophobic bilayer and the water layer, was calculated to be around 52 nm by small-angle X-ray scattering (SAXS). Extremely hydrophobic C60 fullerene can be solubilized in this salt-free zero-charged aqueous onion-phase. As a typical result, 0.588 mg.mL(-1) (approximately 0.82 mmol.L(-1)) C60 has been successfully solubilized into a 50 mmol.L(-1) catanionic surfactant onion-phase aqueous solution. The weight ratio of fullerene to TTAL is calculated to be around 1:40. Solubilization of C60 in the salt-free catanionic onion-phase solution was investigated by using different sample preparation routes, and a variety of techniques were used to characterize these vesicular systems with or without encapsulated C60. The onion-phase solution changed color from slightly bluish to yellow or brown after C60 was solubilized. 1H and 13C NMR measurements indicated that the C60 molecules are located in the hydrophobic layers, i.e., in the central positions [omega-CH3 and delta-(CH2)x] of the hydrophobic layers of the TTAL onion-phase. Salt-free zero-charged catanionic vesicular aqueous solutions are good candidates for enhancing the solubility of C60 in aqueous solutions and may broaden the functionality of fullerenes to new potential applications in biology, medicine, and materials. Hopefully, our method can also be extended to solubilize functionalized carbon nanotubes in aqueous solutions.     

Lyoluminescence of luminol in aqueous alkaline metal hydroxides

The lyoluminescence emission spectra of luminol, induced by -irradiated NaCl in aqueous alkaline earth metal hydroxides, are recorded. Continuous emission bands are observed in the visible region from 390 to 535 nm. These emission bands on resolution showed two peaks at 430 and 460 nm, respectively in all hydroxides. An additional band of 490 appears in the case of calcium hydroxide. The colour centres released during disintegration of irradiated NaCl crystals in aqueous solution react with luminol to produce various excited molecular species, which are responsible for observed lyoluminescence of luminol.     

Synthesis of layered hydroxides stable in redox media

The introduction of hydrogen peroxide into the synthesis of iron-containing hydrotalcite-like layered hydroxides enhances the resistance of these materials to the postsynthesis action of H₂O₂. Hydrogen peroxide raises the relative magnesium content of the resulting hydroxides without causing any significant changes in their structure, morphology, or texture.     

Thermodynamic cycles and the calculation of pKa

A theoretical equation for the calculation of pK_a based on a proton transfer reaction between the acid and one water molecule is derived using the general chemical equilibrium relationship. The present result is compared with two equations recently used that were based on thermodynamic cycles, but predict different pK_a’s. It is shown that one thermodynamic cycle is wrong, and its better performance when compared with the correct cycle is due to an erroneous value used for the solvation free energy of the H₃O⁺ ion. In addition, this analysis indicates that the PCM-UAHF solvation model is inconsistently parametrized.     

Cation-exchange behaviour of the platinum group and some other rare elements in hydrobromic acid-thiourea-acetone media

Ion-exchange distribution coefficients and elution curves are presented for copper(I), silver, gold(I), palladium, platinum(II), rhodium(III), iridium(III), ruthenium(III), osmium(III), mercury(II), thallium(I), tellurium(II), lead and bismuth in mixtures of thiourea, hydrobromic acid, acetone and water, with the cation-exchange resin AGW50W-X4. The system affords excellent separations of rhodium, mercury, silver (or copper), tellurium, gold, and palladium (or platinum) from each other.     

Thermodynamic quantities relative to solution processes of Naproxen in aqueous media at pH 1.2 and 7.4

Based on van’t Hoff and Gibbs equations, the thermodynamic functions Gibbs free energy, enthalpy, and entropy of solution, mixing and solvation of naproxen (NAP) in water at pH 1.2 and 7.4, were evaluated from solubility values determined at several temperatures. The solubility at pH 7.4 and 25.0°C was almost 150 times higher with respect to pH 1.2. The enthalpies of solution were positive and greater for pH 1.2, while the entropies of solution were both negative, thereby implying a greater molecular organization at pH 7.4. The results were discussed in terms of solute–solvent interactions.