Classification of hydrated oxygen compounds of boron

The known structural classifications of borates are based on the analysis of boron-oxygen radicals consisting of B-triangles and B-tetrahedra sharing O atoms to form more complicated structures. Such classifications ignore the possible presence and the role of hydrogen bonds, which may be the only bonds or additional bonds linking the [BO₃]-and [BO₄]-groups. A new detailed classification of hydrated boron compounds taking into account hydrogen bonds between the B-polyhedra is proposed.     

Mechanical properties and adhesion of hydrated glass surface layers

This paper reviews results for interfacial adhesion and fracture of silicate glasses that demonstrate the effect of hydrated glass surface layers on the mechanical properties of glass. First, it is shown how the generation of hydrated surface layers formed on alkali borosilicate glasses can control crack propagation rates. Crack growth data, solution analysis and surface stress measurements are used to support a fracture model that involves the generation of surface stress on the crack walls behind the crack tip. A fracture mechanics based model is used to show that stressed layers can contribute to the crack tip stress intensity in a way that either increases or decreases the rate of crack propagation. In the case of alkali containing silicate glasses, tensile stresses formed on the crack walls increase the crack tip stress and contribute to the formation of a low velocity plateau in the stress intensity vs. crack velocity curve. Second, fracture mechanics test techniques are used to examine the adhesive bond formed between hydrated surface layers and bulk silicate glass. The adhesive bonds formed by sol-gel precursors composed of colloidal silica, hydrolyzed organosilanes and alkali silicate solutions are compared to determine the mechanism of interfacial bonding to dense silica substrates. The formation of siloxane bonds across the interface depends upon the nature of the silicate polyanions in solution. For the case of soluble alkali silicate derived films, heat treatments at temperatures as low as 200°C can result interferfacial adhesion energies as large as the fracture energy of silica glass. These results have important implications to the aging and repair of surface damage in glass as well as the adhesion of sol-gel derived thin films.     

Water-network percolation transition in hydrated blue-green algae in vivo

We found that dc conductivity percolation process typical for low hydrated porous materials shows up in bulk viable blue-green algae, Arthrospira (Spirulina) platensis (strain Laporte 1963/M-132/2b) at unusually low hydrations, more than an order of magnitude lower than in, e.g., hydrated yeast [D. Sokolowska, A. Krol-Otwinowska, J.K. Moscicki, Phys. Rev. E 70 (2004) 052901]. The critical exponent is characteristic for two-dimensional network. Comparison with results for yeast and other similar materials shows that the hydration percolation threshold is a sensitive indicator of wettability of water accessible surface in porous bio- and abiotic materials.     

Electrical relaxation from hydrated surface layers in alkali silicate glasses

Complex impedance plots for a 25 Na₂O?75 SiO₂ glass exposed to the ambient atmosphere indicate the presence of a relaxation at frequencies well below those for the electrical relaxation of the bulk material, but above the frequencies where electrode polarization takes place. This low frequency relaxation is shown to occur in a high resistivity surface layer having a thickness a few times 0.1 μm and formed by the action of atmospheric water vapor. The rate of growth of the surface layer could be monitored by means of the impedance measurements and was found to decrease with the duration of exposure of the glass to the laboratory atmosphere. Complex impedance plots for a chemically durable lithium aluminosilicate glass indicate that the hydrated surface layer thickness is much smaller than in the 25 Na₂O?75 SiO₂ glass.     

REDOR NMR: approaching structural elucidation of hydrated layers in silicate electrode glasses

Rotational echo double resonance (REDOR) is proposed as an alternative method for the structural determination of hydrated glasses, in particular of the incorporation of protons into the structure. First ²³N---¹H and ²⁷Al---¹H REDOR nuclear magnetic resonance data are presented for hydrated layers of electrode glasses of the system Na₂O---Al₂O₃---SiO₂ showing distinct differences of both the equilibrium amplitudes of the REDOR signals and the heteronuclear dipole couplings. The potential of this approach is demonstrated for kaolinite in terms of quantitative results.     

Thermal behaviour of hydrated lysozyme in the presence of sucrose and trehalose by EINS

The main aim of the present work is to investigate the dynamical effects of the addition of disaccharides to hydrated lysozyme. The Self-Distribution-Function procedure is at first applied on Elastic Incoherent Neutron Scattering data obtained by the IN13 spectrometer on trehalose/H₂O and sucrose/H₂O where it highlights a different Q-dependence for the two disaccharides. Then a quantitative analysis of the Mean Square Displacement of lysozyme/trehalose/H₂O and of lysozyme/sucrose/H₂O from Elastic Incoherent Neutron Scattering data obtained by the IN10 spectrometer is presented. It is shown how the resolution function gives rise to a time integration of a given time-dependent Mean Square Displacement function. Furthermore the analysis shows that the protein dynamical transition, registered at a temperature value of about T = 200-220 K in the H₂O hydrated lysozyme sample, is inhibited by the addition of the disaccharides.     

Modular structure of highly ordered eudialyte and its place among hydrated minerals of rastsvetaevite family

The crystal structure of a representative of eudialyte group, which was found by A.P. Khomyakov at the Rasvumchorr mountain of the Khibiny alkaline massif (Kola Peninsula), has been studied by X-ray diffraction. The trigonal unit-cell parameters are found to be a = 14.2328(5) Å, c = 60.217(2) Å, V = 10564.08(3) Å3, sp. gr. R3m. The structure has been refined with the isotropic and anisotropic approximation displacement parameters to the total reliability factor R = 5.6%, based on 2989 reflections with |F| > 4σ(F). The idealized formula (Z = 3) is determined as [(H₃O)₁₁Na₁₀K5]Cа₁₂(Na₃Fe₂Mn)Si₄Zr₆(Si₄₈O₁₄₄)(OH,Cl)₅(H₂O)₅. The unit cell of the mineral is doubled due to the presence of two modules of different composition and structure in it (alluaivite-and kentbrooksite-like ones) and the formation of a polyhedral cluster in the kentbrooksite module. A comparison with two hydrated minerals having a modular structure shows that these minerals, being similar in their chemical composition, differ in the cation ordering over the sites of the two modules. The sample under study contains potassium in only one module, while oxonium groups are distributed in both modules but over different sites.     

Crystal structures of the hydrated disodium and paraquat salts of 1,8-disulfonato-3,4,5,6-acridinetetracarboxylic acid

Two hydrated salts of 1,8-disulfonato-3,4,5,6-acridinetetracarboxylic acid, H₂L, have been characterized by single-crystal X-ray analysis. Compound 1, Na₂L·9 H₂O, crystallizes in the monoclinic space group C2/c with a = 42.005(1), b = 6.838(1), c = 23.807 (1) Å, = 122.71 (1)°, and Z = 8. Compound 2, (paraquat)L·2H₂O, belongs to the triclinic space group with a = 9.940(1), b = 11.543(1), c = 14.033(1) Å, = 105.45(1), = 95.82(1), = 100.14(1)° and and Z = 2. All four carboxyl groups in the 3,4,5,6-tetracarboxyacridine-1,8-disulfonate dianion L^2– are un-ionized. In 1 the distorted octahedrally coordinated sodium cations, the anions, and the lattice water molecules are joined together by hydrogen bonds to generate a three-dimensional network. In the crystal structure of 2, a host framework composed of L^2– ions and water molecules accommodate the paraquat dications within two channel systems running parallel to the a and b axes.     

Electrical conductivity and thermal dehydration studies of hydrated barium oxalate and barium cadmium oxalate crystals

The measurement of electrical conductivity for the investigation of the number of water molecules present in the hydrated barium oxalate, and barium cadmium oxalate lattice have been carried out in the temperature range 30 to 415 °C. The dehydration temperature and the number of water molecules jettisoned out of the structure at a particular temperature is estimated from the sharp increase in conductivity at these points. The almost abrupt increase of conductivity is attributed to the increase in the number of mobile charge carriers viz., H⁺ and OH⁻ ions generated from the escaping water molecules. Samples in the form of pellets with and without silver paste applied, showed different behaviour with respect to conductivity of the material upto the completion of dehydration. The study of electrical conductivity in association with the thermal behaviour has been used to understand the mechanism of conduction.     

The role of primitive relaxation in the dynamics of aqueous mixtures, nano-confined water and hydrated proteins

The relaxation scenario in aqueous systems, such as mixtures of water with hydrophilic solutes, nano-confined water and hydrated biomolecules, has been shown to exhibit general features, in spite of the huge differences in structure, chemical composition and complexity. Dynamics, in all these systems, invariably shows at least two relaxations: (i) a slower process, related to cooperative and structural motions of water and solute molecules (in the case of mixtures) or related to interfacial processes in the case of confined water and (ii) a faster process, with non-cooperative character originating from water. The latter has properties including timescale and temperature dependence similar or related in all the aqueous systems. This water-specific relaxation can be identified as the primitive relaxation, or the Johari-Goldstein β-relaxation. The primitive process is the precursor of the many-body relaxation process which increases in length-scale with time until the terminal α-relaxation is reached.Using new experimental data (at atmospheric and high pressure) along with a revision of most of the recent literature on the dynamics of confined water and aqueous mixtures, we show that the two abovementioned relaxation processes are inter-related as evidenced by correlations in their properties. For instance, both relaxation time and dielectric strength of the water-specific relaxation exhibit a crossover from a stronger to a weaker dependence with decreasing T, at the temperature where the slow process attains a very long timescale (> 1 ks) and becomes structurally arrested, exactly analogous to that found for β-relaxation in van der Waals liquids. Moreover, the primitive relaxation of water is shown to play a pivotal role in determining the dynamics of hydrated biomolecules in general, including the “dynamic transition” observed by neutron scattering and Mössbauer spectroscopy. We show that the primitive relaxation of the solvent is responsible for the dynamic transition, even in the case that the solvent is not pure water or an aqueous mixture.     

Binding of alkaline earth metal ions to nucleotides: crystal structure of a hydrated strontium salt of inosine-5′-monophosphate

Crystals of Sr²⁺ (C₁₀H₁₁PN₄O₈)^2– · 6.5H₂O are orthorhombic, space groupP2₁2₁2₁, witha = 21.925(1),b = 21.503(1),c = 8.600(1) Å, and eight formula weights per unit cell. A trial structure was obtained by Patterson, superposition, and Fourier techniques and was refined by full-matrix least-squares calculations using absorption-corrected, CuK, diffractometer data. The finalR index is 0.032. A strontium ion is coordinated to N(7), the site that is often involved in the binding of transition metals to purine nucleotides. Strontium ions are also directly coordinated to a phosphate-oxygen atom and to ribose-hydroxyl groups. These direct interactions are accompanied by a number of outer-sphere, water-mediated contacts of strontium ions with various acceptor sites on the nucleotides.     

Synthesis and crystallographic characterization of a chiral complex of (R)‐2‐(pyridin‐2‐ylmethylene)amino‐2′‐hydroxy‐1,1′‐binaphthyl(L) with hydrated nickel(II) acetate

A chiral complex of (R)‐2‐((pyridin‐2‐ylmethylene)amino)‐2′‐hydroxy‐1,1′‐binaphthyl ( L ) with hydrated nickel (II) acetate has been synthesized and spectroscopically characterized. The crystal structure of [NiL₂(CH₃OH)(CH₃COO)]CH₃COO·CH₃OH has been determined by single‐crystal X‐ray diffraction. The complex crystallizes in the orthorhombic space group P 2(1) 2(1) 2(1) with cell constants a = 15.1035 (19), b = 17.836 (2), c = 18.730 (2)Å, α = β = γ = 90.00°, Z = 4. The structure was solved by direct methods and refined to R = 0.0346 (wR₂ = 0.0863). The analytical result of the crystal structure indicates that a pair of L ligands chelate to a Ni (II) atom in an asymmetric fashion with one Ni‐N bond being longer than the other, the Ni (II) atom is further coordinated by one methanol molecule and one acetate anion to form a distorted octahedral geometry. In the crystal of the complex, the coordination cation [NiL₂(CH₃OH)(CH₃COO)]⁺, the uncoordinated methanol molecule and uncoordinated acetate anion are further assembled into one‐dimensional chain structure via intermolecular hydrogen bonds along the a‐axis. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Very strong hydrogen bonds in hydrated 1:1 adducts of an olefinic double betaine with perchloric and nitric acids: L·HClO4·H2O and L·HNO3·H2O [L=cis-(p-Me2N+C5H4N)2C2(COO−)2]

The hydrated 1:1 adducts of an olefinic double betaine with perchloric and nitric acids, L·HClO₄·H₂O I and L·HNO₃·N₂O2 [L=cis-(p-Me₂N⁺C₅H₄N)₂C₂(COO^–)₂], have been shown to be nearly isostructural by X-ray crystallography and infrared spectroscopy. The common cationic unit HL⁺ of both compounds exhibits significant semi-quinonoid character and possesses symmetrym, ist two coplanar carboxylate groups being linked by a very strong, nearly linear intramolecular O–H–O hydrogen bond [O...O 2.397(9)Å and O–H–O 167.1° for1; 2.388(7)Å and 167.4° for2]. The HL⁺ units are further connected by intermolecular O–H...O hydrogen bonds between the exocyclic carboxyl oxygen atoms and the water molecules to generate polymeric zigzag chains running parallel to thec axis, and the disordered ClO₄ or NO ₃ ^– anions occupy channels running parallel to thea axis in the resulting host lattice.     

Crystal structure of Rb<Subscript>2</Subscript>Mn<Subscript>3</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>[P<Subscript>2</Subscript>O<Subscript>7</Subscript>]<Subscript>2</Subscript>, a new representative of the family of hydrated diphosphates

The crystal structure of Rb₂Mn₃(H₂O)₂[P₂O₇]₂, a new phase obtained in the form of single crystals under hydrothermal conditions in the MnCl₂–Rb₃PO₄–H₂O system, is determined by X-ray diffraction (Xcalibur-S-CCD diffractometer, R = 0.0270): a = 9.374(2), b = 8.367(2), c = 9.437(2) Å, ß = 99.12(2)°, space group P2₁/c, Z = 2, D_x = 3.27 g/cm³. A correlation between the unit-cell parameters and the size of cations forming the crystal structures of isostructural A₂M₃(H₂O)₂[P₂O₇]₂ diphosphates (A = K, NH₄, Rb, or Na; _M = Mn, Fe, Co, or Ni) is revealed. It is shown that, due to the topological similarity, the structures of diphosphates and orthophosphates of the farringtonite structural type can undergo mutual transformations.     

Modelling of mechanism of agglomeration of KCl crystallization

The article presents an analysis into agglomeration during KCl vacuum crystallization. The theoretical and experimental investigations into the mechanism of agglomeration during mass crystallization result in an extension of the growth phenomena within the known model equations. The basis for this is essentially constituted by the collision model concepts of the theory of floculation in disperse systems. The parameters derived from the microprocess analysis (energy dissipation, content of solids, growth rate of individual grains) lead to model equations which are confirmed by laboratory and test trials.     

Relationship of Morphological Types of Dynamic Forms of Crystals

Crystallography Reports - The relationship of morphological spectra (sets of data on the morphological types of real polyhedral crystals and their probabilities under current physicochemical...     

Velocities of Disappearance and Lifetime of Faces of Growing Crystals

The formulae for absolute R_disap and relative R velocities of disappearance and lifetime τ of faces of growing crystals have been derived for stationary growth. It was shown that the quantities are determined by the relative growth velocity R_A/R_critA of the vanishing face A with respect to the critical growth velocity R_critA and by the geometry of a crystal expressed by the trigonometric functions of interfacial angles β and γ formed between face A and the adjacent faces. R increases and τ decreases with the increase in R_A/R_critA to certain limiting values. The calculations have been verified and illustrated by the experimental results for triclinic potassium bichromate (KBC) crystals. Results enable ones to predict values of velocities of disappearance and lifetimes of undesirable, supplementary faces of any real crystal.     

Development of Pauling's concepts of geometric characteristics of atoms

The evolution of the geometric characteristics introduced by Pauling and their dependence on the specific features of the structure and chemical bonds have been considered. The values of the covalent and van der Waals radii are given as well as their relationships and mutual transitions.     

Dependence of the parameters of equations of viscous flow on chemical composition of silicate melts

The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts x_i of all oxides dissolved in SiO₂, the molar fraction of the latter being 1 ? x. It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature T_r , at which viscosity is η_r = 10¹³ [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, l_i is a product of molar part x_i and a specific dimensionless coefficient 0 ≤ k_i ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0, the reference temperature is related to the “lubricant fraction” l through the reference temperature T_r,SiO2 of pure SiO₂.