Home – Home – Jornals – 2011 number 6

Within density functional theory by an ab initio molecular dynamics method (SIESTA code) the features of structural, electronic properties and chemical bonding in lithium metallates Li₂MO₃ (M = Ti, Zr, Sn) are studied, as well as of their protonated forms Li_2-xH_xMO₃ at all possible H⁺ → Li⁺ substitutions. With the use of the calculated crystal orbital overlap populations and the formation energies of Li_2-xH_xMO₃ the most preferred H⁺ → Li⁺ substitutions in Li₂MO₃ metallates are discussed.

A quantum chemical DFT method with the hybrid B3LYP functional in the 6-31G(d) basis set is employed to calculate the equilibrium geometric parameters of the ground and excited states of cationic symmetric indopolycarbocyanine dyes. Based on the Bader topological analysis of the electron density distribution function, it is found that there are hydrogen-hydrogen bonding interactions in the ground, first singlet, and first triplet states of the studied compounds. These interactions are assumed to have the dispersion character. The effect of the stabilization of the conformational position of methyl groups due to hydrogen-hydrogen interatomic interactions on fluorescence deactivation processes is shown. The total stabilization energy of hydrogen-hydrogen interatomic interactions in dye cations is found, which is ≈9 kcal/mol.

The CH₃XC=S…S (X = H, HO, HS, PH₂, CH₃) bonding types are investigated using the second order Møller-Plesset perturbation approximation with the cc-pVDZ basis set. Electrostatic density potential maps of CH₃XC=S (X = H, HO, HS, PH₂, CH₃) are generated at the MP2/cc-pVDZ level of theory. The interaction energy and topological property are theoretically encompassed for the five complexes. Electrostatic density potential maps of five monomers are generated for the determination of attractive interaction sites. There are different misshaped electron clouds. The red-shifting character is obtained for the CH₃XC=S…S (X = H, HO, HS, PH₂) interaction. For all complexes the S…S bonds are typical closed-shell interactions, and the topological properties of the S…S bond fall short of three criteria for the existence of the hydrogen bond. Theoretical values are in very good agreement with the experimental results.

A subsolidus triangulation of Li₂MoO₄-Rb₂MoO₄-MMoO₄ (M = Ca, Sr, Pb, Ba) systems is performed. The RbLiMoO₄-Rb₂M(MoO₄)₂ (M = Pb, Ba) joins, where 11 mol.% long Rb₂M(MoO₄)₂-based solid solutions are found, are studied in most detail. Ternary molybdates do not form in the systems, which is confirmed by spontaneous flux crystallization. The α-Rb₂Pb(MoO₄)₂ crystals are obtained and their crystal structure is solved (а = 20.9724(15) Å, b = 12.1261(8) Å, с = 16.1171(10) Å, β = 115.728(13)°, С2/m space group, R = 0.0695, Z = 16), which is a monoclinic superstructure of the palmierite type and has the largest cell volume and the most complex structure among lead-containing palmierites. One of the MoO₆ tetrahedra is orientationally disordered over two sites; lead atoms are shifted from the centers of their coordination polyhedra to one of their faces and have cn = 6-8; for rubidium cations cn = 10-12.

The structures of tris-hexafluoroacetylacetonates Al(hfa)₃ and Sc(hfa)₃·H₂O are determined by single crystal X-ray crystallography (Bruker-Nonius X8 Apex diffractometer, MoK_α radiation, T = 150(2) K). The Al(hfa)₃ complex is trigonal, a = 17.8944(11) Å, c = 12.4061(11) Å, P-3с1 space group, V = 3440.3(4) ų, Z = 6, R = 0.076. The Sc(hfa)₃·H₂O complex is monoclinic, a = 16.0926(4) Å, b = 14.7980(3) Å, c = 24.4020(5) Å, β = 125.641(1)°, P2₁/c space group, V = 4722.54(18) ų, Z = 8, R = 0.060. The structures of the complexes are formed by neutral molecules; the coordination environment of the metal atom involves six oxygen atoms of three β-diketone ligands (Al(hfa)₃) and, additionally, a water oxygen atom (Sc(hfa)₃·H₂O). The shortest Al…Al distance is 6.203(6) Å. The Sc(hfa)₃·H₂O molecules are joined in dimers by hydrogen bonds with Sc…Sc separations of 5.6992(8) Å and 5.6853(8) Å. In the crystals, the molecules are joined by van der Waals interactions, moreover, there are intermolecular contacts F…H ~ 2.5 Å in the structure of Sc(hfa)₃·H₂O.

Structure formation processes in polytetrafluoroethylene under the action of liquid lubricant components and zeolite particles are considered. Based on the results of single crystal X-ray diffraction, electron and atomic force microscopic, chromato mass spectroscopic studies, the formation mechanisms of polymer composites, which were obtained by liquid phase filling with motor oils, are proposed.

The title compound 2-[({[(4-methylphenyl)sulfonyl]methyl}amino)carbonyl]-1,3-dioxo-2,3-dihydro-1H-inden-2-yl 2-thiophenecarboxylate is synthesized and studied by the single crystal X-ray diffraction method. The structure of the product is confirmed by IR, ¹H and ¹³C NMR spectroscopy, and mass spectrometry. The structure is solved in the C2/c monoclinic space group with a = 16.739(3), b = 11.087(3), c = 23.194(4) Å, β = 93.32(3)°, V = 4297.2(16) ų, Z = 8, R1 = 0.033 and wR2 = 0.088.

Density functional theory in the plane wave basis set is used to study As adsorption on the Pd(111) surface in order to determine the action of a palladium chemical modifier used in electrothermal atomic absorption spectrometry (ETAAS). The calculated heat of desorption of the arsenic atom is 435 kJ/mole, which corresponds to the activation energy of arsenic atomization of 439 kJ/mole (in the range of high temperatures T > 1828 K), obtained by ETAAS. Based on the calculated data, the action of the palladium modifier for the determination of As is assumed to be controlled by the process of chemisorption.

¹⁹F NMR, IR, Raman and impedance spectroscopy are used to study the ionic mobility, structure, and conductivity of 45ZrF₄-35BiF₃-20CsF bismuth fluorozirconate glass. With the increase in temperature from 150 K to 500 K the fluorine-containing groups pass from the rigid lattice to local movements (reorientations), and then to diffusion. According to the results of IR and Raman spectroscopy, the lattice of this glass consists of ZrF₈ polyhedra linked by their vertices into chains. The glass has high ionic conductivity: σ ≈ 1.8×10^-4 S/cm in a temperature range of 480-485 K.

An analysis of the literature data on the partial molar volume of glycine in an aqueous urea solution at 298 K is performed. The mentioned value linearly increases with the increase in the urea concentration (wt.%). The hydration number of glycine decreases by a factor of 2 when passing from water to the saturated (20m) urea solution.

The new co-crystal copper(II) melamine complex poly[bis(μ-methacrylato)μ-(1,3,5-triazine-2,4,6-triamine)], C₁₉H₂₆Cu₂N₆O₈ (1) crystallizes in the triclinic P-1 space group with a = 8.9670(2) Å, b = 9.4108(2) Å, c = 15.4476(3) Å, α = 96.6090(10)°, β = 100.6270(9)°, γ = 95.5950(10)°. Each Cu(II) exhibits a pseudooctahedral geometry. Four coplanar carboxylate oxygen atoms coordinated to the Cu(II) ion define the basal plane, whereas the apical position is occupied by one nitrogen atom from the melamine ligand. Here, the carboxylato-bridged two dinuclear copper(II) complexes are linked through melamine giving a 1D alternating chain. The structure of 1 consists of a two-dimensional supramolecular layer constructed by intermolecular N-H…N hydrogen bonds of the melamine ligands from adjacent one-dimensional [Cu₂(C₄H₅O₂)₄(C₃H₆N₆)] chains.

The structure of a nickel(II) complex with 2-amino-4-iminopentane is determined by X-ray crystallography at 150 K. Crystal data for C₁₀H₁₈N₄Ni are: a = 10.9802(3) Å, b = 13.5780(4) Å, c = 8.0935(2) Å, β = 107.304(1)°, space group P2₁/c, V = 1152.04(5) ų, Z = 4, d_x = 1.459 g/cm³, R = 0.0283. The structure is molecular; the metal atom is coordinated by four nitrogen atoms of two β-diimine ligands. The Ni-N distances in Ni(NacNac)₂ fall within 1.8571-1.8623 Å. The molecules in the crystal are joined by only van der Waals interactions.

Counter-diffusion of the aqueous solution of Cs_2.75K_1.25[Re₆Se₈(CN)₄(OH)₂] and a water-ammonia solution of NiCl₂ afforded crystals of a rhenium cluster complex trans-{[Ni(NH₃)₅]₂[Re₆Se₈(CN)₄(OH)₂]}·6H₂O. The structure of the complex is determined by single crystal X-ray diffraction. In the structure, nickel atoms have an octahedral coordination environment involving nitrogen atoms of five NH₃ ligands and one CN ligand of the cluster anion. The anion has two bridging CN ligands in the trans-positions.

Reaction of zinc iodide, sodium azide and 2-[(3-dimethylaminopropylimino)methyl]-6-ethoxyphenol (HL) results in the formation of a trinuclear complex [Zn₃L₂(μ_1,1-N₃)₂I₂]. The complex is characterized by elemental analysis, IR spectroscopy, and X-ray crystallography. The complex possesses crystallographic two-fold rotation axis symmetry and crystallizes in the monoclinic system, C2/c space group, a = 23.241(2) Å, b = 10.849(1) Å, c = 17.384(2) Å, β = 120.868(1)°, V = 3762.4(6) ų, Z = 4. The molecule consists of two [ZnL(N₃)I] units connected together by a central Zn atom. The terminal Zn atom is five-coordinated in a trigonal-bipyramidal geometry, and the central Zn atom is six-coordinated in an octahedral geometry. The Zn⋯Zn separation between the terminal and the central Zn atoms is 3.257(2) Å.

The Schiff-base compound N,N′-Bis-(2,5-dimethoxybenzylidene)-1,3-diaminopropan, (2,5-MeO-ba)₂pn, is synthesized and characterized by elemental analysis, FT-IR and ¹H NMR spectroscopy. The crystal structure of (2,5-MeO-ba)₂pn is determined by X-ray single crystal diffraction analysis. The X-ray diffraction analysis at 120 K reveals that (2,5-MeO-ba)₂pn crystallizes in the orthorhombic system, Fdd2 space group with a = 29.339(9) Å, b = 29.4073(11) Å, c = 4.4524(2) Å, V = 3840.8(3) ų, μ = 0.72 mm^-1, and Z = 8.

Ultrasonic velocity and density values are measured for aqueous solutions containing 2.00 mol.%, 4.00 mol.%, and 5.00 mol.% glycine in a temperature range of 15-65°C, 5.50 mol.% glycine (20-65°C), and 6.00 mol.% glycine (25-65°C). Adiabatic compressibilities (κ_S) and molar adiabatic compressibilities (Κ_S) are calculated. The values of κ_S and Κ_S decrease monotonically with an increase in glycine concentrations up to saturation at all the temperatures. The temperature dependences of κ_S and Κ_S have minima that are typical of water and aqueous solutions; the positions of the minima depend on the glycine concentration. The temperature coefficients of the molar compressibility, ∂Κ_S/∂T, change their signs from negative to positive at lower temperatures (by approximately 10 deg) than ∂κ_S/∂T.

The Monte Carlo method is used to calculate the radial distribution functions (RDFs) of Na⁺Cl⁻, Na⁺Na⁺ , and Cl⁻Cl⁻ ion pairs in water clusters that differ both in composition and size. An analysis of the RDFs shows that like-charged ions can approach one another at extremely small distances (direct ion contact) without the participation of a third ion of the opposite sign. The Na⁺Na⁺ (interionic distance 3.5 Å) and Cl⁻Cl⁻ (interionic distance 5.25 Å) ion pairs are most likely to form in very dilute solutions. The composition of ionic associates changes with increasing concentration of ions in the solution (it is indicated by the emergence of the RDF peak at 4.25 Å and its further growth with concentration and by a selective visual analysis of instantaneous cluster configurations) so that groups of three, five, etc. ions of the opposite sign bearing a net charge of 1+ or 1- appear.

The dielectric relaxation spectra (DRS) of 1,2-ethanediol, 1,2-propanediol, and 1,2,6-gexanetriol are analyzed in terms of the Dissado-Hill (DH) model in a wide range of temperatures, with all parameters required for calculating the cluster dipole moments being determined within the DH molecular model itself. The dependence of the equilibrium and relaxation properties of DRS on the hydrocarbon radical length and the number of OH groups is studied. The dipole moments of the clusters are calculated. It is shown how the roles of the processes of intracluster rearrangement are redistributed due to the break of hydrogen bonds and fluctuation processes of synchronous exchange of molecules between the clusters.

Chemical modification of polyethylene glycols by antioxidants belonging to the class of sterically hindered phenols is used to obtain water-soluble conjugates differing in the structure of the joined antioxidant and molecular weight. The inclusion of hydrophobic end groups in polyethylene glycol molecules leads to a decrease in the lower critical mixing point of the solution as compared to the original polymer. Dilute solution viscometry and light scattering are used to determine the molecular-mass characteristics of the polymers and the hydrodynamic radii of single conjugate molecules. The mass fraction of single molecules in aqueous solutions of the conjugates is greater than 95%. The aggregates are micellar-type particles whose core is formed by the hydrophobic moieties of sterically hindered phenols. It is shown that the antiradical activity of the antioxidants 3-(3-tert-butyl-4-hydroxy-5-methylphenyl)-propionic acid and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionic acid, which are used for the modification, differs only slightly, whereas the activity of the relevant conjugates increases significantly.

Electron microscopy and dynamic light scattering are used to investigate the structuring process of a supramolecular system based on the aqueous solutions of L-cysteine and silver nitrate diluted with liquid water-soluble nonelectrolytes. The gel formation mechanism is discussed.

The physicochemical characteristics of single and mixed zirconia and silica gels produced by the sol-gel technique at different synthesis pH and sequence of introducing the reagents in the mother liquid are presented. As a result of comparing the data obtained by different research methods, it is found that in the mixed gels, irrespective of the synthesis technique, Si-O-Zr bonds are present. The introduction of a zirconium salt in the mother liquid containing a silicate salt leads to the preferred formation of zirconia gel granules of 20-30 nm in diameter enclosed in the matrix of silica gel. The inverse sequence of introducing the gel-forming components in the reaction mixture promotes the formation of large gel aggregates containing the particles of less that 10 nm and having a high degree of polymerization. Mixed gels of zirconium oxyhydrate and silicic acid have an order higher sorptive capacity for yttrium (III) and calcium cations, as compared to single silica gels and zirconia gels.

By means of a variant of the Monte Carlo method (entropic sampling within the Wang-Landau algorithm) the models of the interaction of a neutral polymer with a flat surface are studied. The method yields distribution functions over the energy and the distance from the polymer to the surface. Based on these distributions, excess entropies of the systems and their thermal properties are calculated: internal energy, heat capacity, average radius of gyration, average chain end-to-end distance, and average distance from the polymer to the surface. Continuous and lattice models are considered.

The capacities of the wetting method for the characterization of the surface structure of polymers and surfactant adsorption layers on polymer surfaces and also the determination of the energy characteristics of polymer surfaces at different interfaces, which are used to optimize the choice of polymers in the solution of actual practical problems, are demonstrated.

A method to develop DNA fibrils with a length more than a few tens of micrometers, oriented in one direction on the n- and p-type silicon surface is described. A new simple and effective technique is proposed to produce silver nanowires by electrochemical reduction of silver ions bound to DNA using the obtained fibrils as a template, as a result of which DNA molecules fixed on the surface of the n-type silicon single crystal are uniformly covered by silver clusters with a size of about 30 nm. The proposed metallization procedure of DNA on the n-type silicon surface has an advantage in comparison with a similar one for macromolecules fixed on freshly cleaved mica, glass surface, and р-type silicon. n-Type silicon is not only a substrate, but also a source of electrons for silver reduction. The absence of an additional chemical component (reducer) principally distinguishes the proposed method from the others currently known. Atomic force microscopic images of fixed DNA molecules and prepared nanowires are obtained.

The methods of circular dichroism, ultraviolet spectrophotometry, dynamic light scattering, viscometry, dynamic birefringence, and atomic force microscopy are employed to study the conformational properties of the DNA molecule during its complexation with oligopeptides. Samples with с 2, 3, and 5 monomeric L-lysine residues are used. Experimental data evidence that in the diluted solutions (with a low ionic strength) of DNA with oligopeptides (with 3 and 5 monomeric units) the condensation of the macromolecule is observed at specific peptide concentrations. For the bipeptide the DNA condensation in the solution is not observed. In the DNA solutions with a high ionic strength (1 M NaCl), oligopeptides do not affect the macromolecule size.

The radioprotective action of caffeine upon γ irradiation of DNA solutions is demonstrated by means of low gradient viscometry, flow birefringence, atomic force microscopy and UV spectroscopy. In the presence of caffeine, a decrease in the radiation effect on the DNA coil size in the solution, in the number of double-stranded breaks and damaged nitrogen bases, and in the degree of radiation-induced denaturation is observed.

Methods of spectrophotometry, spectropolarimetry, and viscometry are used to study the self-organization in the solution of crown-containing actinocin derivative (I) exhibiting antitumor activity and the interaction of the formed aggregates with a DNA molecule. The presence of the 4′-benzo-15-crown-5 radical in the structure of the studied compound determines the observed differences in its complexation with Na⁺ and K⁺ ions. The process of aggregation in the presence of K⁺ ions is accompanied by a shift of the long-wave band in the absorption spectrum to short-wave (the formation of H type aggregates) or long-wave (the formation of J type aggregates) regions depending on the K⁺ ion concentration in the solution. In the presence of Na⁺ ions, regardless of their concentration in the solution, J type aggregates form. A scheme of complex formation and their mutual transformations with changes in the ionic composition of the medium is proposed. A study of the interaction of this compound with DNA shows that in the presence of K⁺ ions it binds to the DNA molecule in the form of monomers and/or dimers without producing large supramolecular aggregates. The H and J structures formed in K⁺-containing solutions of compound I are broken in the interaction with DNA. If a solution of compound I is added to a DNA solution containing Na⁺ ions, the J type aggregates are formed directly on the surface of the DNA molecule. At the same type, the J structures originally formed in the Na⁺-containing solution of compound I practically do not interact with DNA. A study of this system shows that the introduction of the crown group in the compound molecule with a heterocyclic chromophore provides the opportunity to affect its affinity and binding to the DNA molecule by means of the ionic composition of the medium.