Thermodynamic properties of a liquid crystal carbosilane dendrimer

The temperature dependence of the heat capacity of a first-generation liquid crystal carbosilane dendrimer with methoxyphenyl benzoate end groups is studied for the first time in the region of 6–370 K by means of precision adiabatic vacuum calorimetry. Physical transformations are observed in this interval of temperatures, and their standard thermodynamic characteristics are determined and discussed. Standard thermodynamic functions C_p^°(T), H°(T) ? H°(0), S°(T) ? S°(0), and G°(T) ? H°(0) are calculated from the obtained experimental data for the region of Т → 0 to 370 K. The standard entropy of formation of the dendrimer in the partially crystalline state at Т = 298.15 K is calculated, and the standard entropy of the hypothetic reaction of its synthesis at this temperature is estimated. The thermodynamic properties of the studied dendrimer are compared to those of second- and fourth-generation liquid crystal carbosilane dendrimers with the same end groups studied earlier.     

Self-assembled liquid crystalline materials with fatty acids

Two new series of liquid crystalline materials with non-mesomorphic fatty acids, viz. nonanoic (C₉), capric (C₁₀), undecanoic (C₁₁), tridecanoic (C₁₃), myristic (C₁₄), palmitic (C₁₆) and stearic acids (C₁₈), are prepared with non-mesomorphic proton acceptors, viz. (4-pyridyl)-benzylidene-p-n-alkylanilines (PyBnA; n = 12 and 16). The smectic phase structures formed between the proton donor (fatty acid) and proton acceptor moieties are found due to the intermolecular hydrogen bonding (HB) and are monotropic. The presence of HB is confirmed by Fourier transform infrared spectroscopy in all the compounds. The characteristic optical textures of smectic phases are observed through polarizing optical microscope, provided with a hot stage and a camera. The phase transition temperatures and the enthalpy changes across the phase transitions are determined by differential scanning calorimetry. The smectic phase exhibited by the HB complexes is confirmed by miscibility studies as smectic-B. The π–π stacking interactions in layers are found to influence the mesomorphism in these HB complexes.     

Equilibrium and kinetics of calcium–uranyl–carbonate adsorption on silica nanoparticles

Solvent extraction studies on the purification of uranium from zirconium rich sodium diuranate (SDU) feed was carried out using n-tri butyl phosphate (TBP) as extractant and n-decanol as phase modifier. The presence of Zr in SDU leached solution leads to the formation of third phase during liquid–liquid extraction of uranium which was successfully prevented by addition of n-decanol in 30% (v/v) TBP/n-dodecane mixture. A seven stage counter current extraction of SDU feed solution followed by five stage stripping were carried out using optimum concentration of phase modifier 15% n-decanol-30% TBP in n-dodecane as solvent. Based on the findings a process flow-sheet has been developed for the purification of SDU to nuclear grade ammonium diuranate.     

Crystal structure as the basis for the lack of enantiotropic mesomorphism in 3-hydroxy-4-propionylphenyl-4′-<Emphasis Type="Italic">n</Emphasis>-alkyloxybenzoates

Features of the molecular structure and crystal packing of the mesogenic compounds 3-hydroxy-4-propionylphenyl esters of 4-n-amyloxy (1), 4-n-hexyloxy (2), 4-n-heptyloxy (3), and 4-n-octyloxybenzoic acid (4) have been analyzed on the basis of X-ray diffraction (XRD) data. Comparison of the results of XRD and DSC studies of these compounds has shown that the crystalline modification studied for each of the compounds is not a precursor to the mesophase. The possibility of mesophase formation from the melt is discussed.     

Description of the even-odd alternation of the clearing temperatures over homologous series of mesogens by second-order differential equations

It is shown for liquid crystals of various chemical classes that the nematic-isotropic transition temperatures in homologous series of compounds undergoing enantiotropic transitions are described by secondorder inhomogeneous recurrent equations with constant coefficients: T(n + 2) = aT(n + 1) + bT(n) + c (n is the number of alkyl carbon atoms). Solutions of the corresponding differential equations as T(n) functions allow reproduction of the even-odd alternation of the clearing temperatures.     

Radiation-Induced Heterogeneous Processes of Water Decomposition in the Presence of Mixtures of Silica and Zirconia Nanoparticles

The radiation-induced heterogeneous processes of water decomposition on mixtures of silicon dioxide (n-SiO₂) and zirconium dioxide (n-ZrO₂) nanoparticles have been studied. The kinetics of buildup of molecular hydrogen in the radiolytic processes of water decomposition in the test systems has been examined. The reaction rates and the radiation-chemical yield of hydrogen in the radiolysis of water in the presence of n-SiO₂–n-ZrO₂ mixtures with different ratios between the components have been determined. It has been found that the rates and radiation-chemical yields decreased on going from n-ZrO₂ to n-SiO₂. The individual components (n-SiO₂ and n-ZrO₂) and the mixtures of n-SiO₂–n-ZrO₂ and n-SiO₂–n-ZrO₂ + H₂O before and after γ-irradiation have been examined by Fourier-transform IR spectroscopy in order to reveal interactions between the components and to study the mechanism of radiolytic processes. It has been found that the adsorption of water in the test systems occurs via both molecular and dissociative mechanisms. It has been shown that there is no noticeable interaction between the components of the oxide nanoparticles under the conditions of the experiments.     

Synthesis,characterization, antimicrobial activity and ultrastructure of the affected bacteria of new quinoline compounds

The reaction on 8-hydroxy quinoline-7-aldehyde azo compounds (HL _n ) (where n = 1–5) with 4-amino-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one to obtain HL _n (where n = 6–10) have been characterized by means of TLC, melting point and spectral data, such as IR, ¹H NMR, mass spectra and thermal studies. The X-ray diffraction patterns of two starting materials 8-hydroxy quinoline-7-aldehyde (start 1), 4-amino-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one (start 2) and the ligands (HL_5,10) are investigated in powder form. All the ligands have been screened for their antimicrobial activity against four local bacterial species, two Gram-positive bacteria (Bacillus cereus and Staphylococcus aureus) and two Gram-negative bacteria (Escherichia coli and Klebsiella pneumoniae) as well as against four local fungi; Aspergillus niger, Alternaria alternata, Penicillium italicum and Fusarium oxysporium. The results show that the azo ligands (HL _n ) (where n = 1–5) have no antimicrobial activity against bacteria and fungi while most azomethine ligands (HL _n ) (where n = 6–10) are good antibacterial agents against E. coli and K. pneumoniae as well as antifungal agents against P. italicum and A. alternata. The results were compared to standard substances (start 1) and (start 2). Among the azomethine ligands, HL₁₀ was the most effective against the most microorganisms tested. The size of clear zone was ordered as p-(OCH₃ < CH₃ < H < Cl < NO₂) as expected from Hammett’s constant (σ ^R ). Also, the ultrastructure study of the affected bacteria confirmed that HL₈ is good antibacterial agent against E. coli and S. aureus.     

Simulation of copper(II) cations sorption on goethite from aqueous solutions of complexons

Effect of complexons of polyaminopolycarboxylic acid series (IDA, NTA, EDTA, and DTPA) and polyphosphonic acid series (HEDP, NTP, and EDTP) on Cu(II) cations sorption on goethite (α-FeOOH) from aqueous solutions has been studied. Obtained results have been considered in the context of complexation reactions in bulk solution and on sorbent surface. It has been found that all complexons (except for EDTA), depending on nature, produce on goethite surface (≡FeOH) triple complexes of type A (surface–metal–complexon) of composition ≡FeOCuLH _i ^1+i?n and ≡FeOCuL(OH) _j ^1?j?n or type B (surface–complexon–metal) of composition ≡FeLH _i Cu^3+i-n and ≡FeLCu(OH) _j ^3?j?n . pH-Ranges for complex existence and stability constants for the surface complexes have been determined. Factors affecting the character of complexon effect (immobilization/remobilization) on the sorbed metal have been analyzed.     

Optical Band Gap Energies in Quasi-Metal Carbon Nanotubes

The structure of carbon nanotubes is described by two positive integers (n₁, n₂). The π-electron model of the nanotube band structure predicts that when the difference n₁–n₂ is multiple of three, the energy gap between the valence and conduction bands vanishes so that such tubes should exhibit quasi-metal properties. The band structure of 50 chiral and achiral (n₁, n₂) nanotubes with 4 ≤ n₁ ≤ 18 and n₂ = n₁–3q has been calculated by the linearized augmented cylindrical wave method. Nanotubes have been identified for which the optical band gaps are in the terahertz range (1–40 meV) and which can be used for design of emitters, detectors, multipliers, antennas, transistors, and other nanoelements operating in the high-frequency range.     

Synthesis,thermal analysis,IR spectrum,and crystal structure of rubidium hexanitratothorate

Rubidium hexanitratothorate was synthesized, and its crystal structure was determined by X-ray diffraction analysis: space group P2₁/n; a = 8.347(1) Å, b = 6.890(1) Å, c = 13.069(1) Å, β = 91.88(1)°, Z = 2; 1812 independent reflections, R = 0.0165.     

Synthesis and crystal structures of the zinc(II) complexes with a tridentate Schiff base (1-pyridin-2-ylethylidene)pyridin-2-ylmethylamine

Two new isostructural zinc(II) complexes, [ZnCl₂(L)] (I) and [ZnBr₂(L)] (II), derived from the Schiff base ligand (1-pyridin-2-ylethylidene)pyridin-2-ylmethylamine (L), have been prepared and characterized by physicochemical methods and single-crystal X-ray crystallography. The crystal of I is monoclinic: space group P2₁/c, a = 11.699(3) Å, b = 8.460(2) Å, c = 14.766(3) Å, β = 99.686(3)°, V = 1440.6(6) ų, Z = 4. The crystal of II is monoclinic: space group P2₁/n, a = 8.166(2) Å, b = 15.153(3) Å, c = 11.966(2) Å, β = 96.964(2)°, V = 1469.7(5) ų, Z = 4. The geometry of the pentacoordinated zinc atoms in both complexes is best described as a square pyramid.     

New polymorph of CaHPO<Subscript>4</Subscript> (monetite): synthesis and crystal structure

A novel form of anhydrous dicalcium phosphate CaHPO₄ (monetite) is synthesized hydrothermally and characterized by single crystal X-ray diffraction. It crystallizes in the orthorhombic space group Ccm2₁ with a = 6.242(1) Å, b = 6.994(2) Å, c = 7.003(3) Å, V = 305.73(16) ų and it has four independent unit formulas in the unit cell (Z = 4). A three-dimensional crystal structure can be described by {HPO₄}_n infinite zigzag chains linked by Ca–O bonds. The comparison to the crystal structures of other polymorphs is given.     

Manganese Stereochemistry in the Structures of Oxygen-Containing Compounds

The Voronoi-Dirichlet polyhedra (VDP) and the method of intersecting spheres were used to carry out crystal chemical analysis of coordination of 1304 sorts of Mn atoms in the structure of 859 oxygen-containing compounds. The manganese atoms whose oxidation number varies from 2 to 7 were found to bind 4 to 8 oxygen atoms giving rise to the MnO _n coordination tetrahedra (n = 4), square pyramids (n = 5), octahedra or trigonal prisms (n = 6), pentagonal bipyramids or one-cap trigonal prisms (n = 7), trigonal dodecahedra, cubes, square antiprisms, or hexagonal bipyramids (n = 8). The effect of the valence state and the coordination number of manganese atoms on the parameters of their VDP was studied. The existence of a general linear correlation between the solid angles of the VDP faces corresponding to Mn-O bonds and the corresponding interatomic distances, which vary over a broad range (1.55–3.12 Å), was established. The VDP characteristics can be used to determine the valence state of Mn atoms in the crystal structures and in the crystal chemical analysis of manganites with giant magnetoresistance.     

The mutual influence of a liquid crystalline medium and chiral dopants of 1R,4R-<Emphasis Type="Italic">n</Emphasis>-mentane-3-one 2-arylidene derivatives dissolved in it

Molecular dynamics computer simulation and quantum chemistry methods were used to study the influence of nematic liquid crystalline 4-n-pentyl-4′-cyanobiphenyl on the conformations of chiral dopant molecules of 1R,4R-n-menthane-3-one 2-arylidene derivatives and the influence of these chiral dopants on the conformation of the liquid crystal. The simulation results are compared with the available experimental data.     

Heat capacities and thermal diffusivities of <Emphasis Type="Italic">n</Emphasis>-alkane acid ethyl esters—biodiesel fuel components

The heat capacities and thermal diffusivities of ethyl esters of liquid n-alkane acids C _n H_2n–1O₂C₂H₅ with the number of carbon atoms in the parent acid n = 10, 11, 12, 14, and 16 are measured. The heat capacities are measured using a DSC 204 F1 Phoenix heat flux differential scanning calorimeter (Netzsch, Germany) in the temperature range of 305–375 K. Thermal diffusivities are measured by means of laser flash method on an LFA-457 instrument (Netzsch, Germany) at temperatures of 305–400 K. An equation is derived for the dependence of the molar heat capacities of the investigated esters on temperature. It is shown that the dependence of molar heat capacity C _p,m (298.15 K) on n (n = 1–6) is close to linear. The dependence of thermal diffusivity on temperature in the investigated temperature range is described by a first-degree polynomial, but thermal diffusivity a (298.15 K) as a function of n has a minimum at n = 5.     

Synthesis,crystal structures,and catalytic property of dioxomolybdenum(VI) complexes with hydrazone ligands derived from 3,5-Di-<Emphasis Type="Italic">tert</Emphasis>-butylsalicylaldehyde

Two new dioxomolybdenum(VI) complexes, [MoO₂L¹(MeOH)] (I) and [MoO₂L²] (II), where L¹ and L² are the anionic forms of N'-(2-hydroxy-3,5-di-tert-butylbenzylidene)-4-methoxybenzohydrazide and 2-amino-N'-(2-hydroxy-3,5-di-tert-butylbenzylidene)benzohydrazide, respectively, have been synthesized and characterized by elemental analysis, FT-IR spectra, and single crystal X-ray determination (CF files CCDC nos. 1448089 (I), 1487063 (II)). The crystal of I is monoclinic: space group P21/n, a = 7.353(1), b = 24.758(3), c = 13.891(2) Å, β = 101.013(2)°, V = 2482.3(6) Å3, Z = 4, R ₁ = 0.0848, wR ₂ = 0.2050. The crystal of II is monoclinic: space group P2₁/c, a = 6.752(1), b = 16.947(1), c = 19.510(1) Å, β = 96.891(2)°, V = 2216.5(4) Å3, Z = 4, R ₁ = 0.0670, wR ₂ = 0.1638. The Mo atom in complex I is in octahedral coordination, with three donor atoms of the hydrazone ligand, two oxo groups, and one methanol O atom. The Mo atom in complex II is in square pyramidal coordination, with three donor atoms of the hydrazone ligand, and two oxo groups. The complexes have interesting catalytic properties for sulfoxidation reactions.     

Phase transitions in paraffins, <Emphasis Type="Italic">n</Emphasis>-alkane alcohols,and <Emphasis Type="Italic">α,ω</Emphasis>-alkane diols with different chain lengths

A comparative analysis of phase transitions in paraffins (C _n H_2n+2), n-alkane alcohols (C _n H_2n+1OH), and α,ω-alkane diols ?ubC _n H_2n (OH)₂?ub; has been performed via differential scanning calorimetry. The elimination of methodical errors makes it possible to calculate the true values of thermodynamic parameters of phase transitions and to gain insight into their nature. Methods of finding true heat capacity jumps in the region of low-temperature solid-phase transitions of the first order and high-temperature order-disorder transitions of the second-order have been proposed. The quantitative analysis of heat capacity jump profiles has been performed within the framework of the first-order diffuse transition theory and Landau’s theory of order-disorder transitions.     

Synthesis,crystal structure,and antibacterial activity of oxovanadium(V) complexes derived from <Emphasis Type="Italic">N</Emphasis>'-[1-(5-fluoro-2-hydroxyphenyl)methylidene]nicotinohydrazide and <Emphasis Type="Italic">N</Emphasis>'-(5-fluoro-2-hydroxybenzylidene)-2-hydroxynaphthylhydrazide

Two new oxovanadium(V) complexes, [VOL¹(OCH₃)(CH₃OH)] (I) and [VOL²(OCH₃)] (II), where L¹ and L² are the di-anionic form of N'-[1-(5-fluoro-2-hydroxyphenyl)methylidene]nicotinohydrazide and N'-(5-fluoro-2-hydroxybenzylidene)-2-hydroxynaphthylhydrazide, respectively, have been synthesized and characterized by elemental analysis, FT-IR spectra, and single crystal X-ray determination (CIF files CCDC nos. 891852 (I), 891853 (II)). The crystal of I is monoclinic: space group P2₁/c, a = 8.061(1), b = 15.293(2), c = 13.471(2) Å, ß = 92.595(2)°, V = 1658.8(4) ų, Z = 4. The crystal of II is monoclinic: space group P2₁/n, a = 7.4454(9), b = 8.0833(9), c = 28.906(2) Å, ß = 92.644(2)°, V = 1737.8(3) ų, Z = 4. The V atom in I is in an octahedral coordination, and that in II is in a square-pyramidal coordination. The antibacterial activity of the compounds against various bacteria was assayed.     

Computational Studies on the Mo-Doped Gold Nanoclusters Au<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>Mo(<Emphasis Type="Italic">n</Emphasis> = 1–10): Structures,Stabilities and Magnetic Properties

The geometric structures, relative stabilities, magnetic properties of Mo-doped gold clusters Au _n Mo(n = 1–10) have been investigated at the PBE1PBE/def2TZVP level of theory. The results show that molybdenum doping has a significant effect on the geometric structures and electronic properties of Au _n Mo(n = 1–10) clusters. For the lowest energy structures of Au _n Mo(n = 1–10), the two dimensional to three dimensional transition occurs at cluster size n ≥ 8, and their relative stabilities exhibit odd–even oscillation with the change of Au atom number. It is found that charge in corresponding Au _n Mo clusters transfers from Mo atom to Au _n host in the size range n = 1–7, whereas the charge in opposition direction in the size range n = 8–10. In addition, the magnetic properties of Au _n Mo clusters are enhanced after doping single Mo atom into the corresponding gold clusters. Our results are valuable for the design of magnetic material.     

Synthesis of urethane—acrylic multi-block copolymers via electrochemically mediated ATRP

The electrochemically mediated atom transfer radical polymerisation (eATRP) of n-butyl acrylate was investigated under a variety of catalyst concentrations. Poly(n-butyl acrylate)-block-polyurethane-block-poly(n-butyl acrylate) copolymers were prepared via electrochemically mediated atom transfer radical polymerisation (eATRP) using only 7 × 10^?6 mole % of Cu^II complex. The successful chain extension and formation of penta-block copolymers confirmed the living nature of the poly(alkyl acrylates) prepared by eATRP. In this work, the tri-block and penta-block urethane-acrylate copolymers were synthesised for the first time by using tertiary bromine-terminated polyurethane macro-initiators as transitional products reacting with n-butyl acrylate, and subsequently with tert-butyl acrylate in the presence of the Cu^IIBr₂/TPMA catalyst complex. The results of ¹H NMR spectral studies support the formation of tri-block poly(n-butyl acrylate)-block-polyurethane-block-poly(n-butyl acrylate) copolymers, and penta-block poly(tert-butyl acrylate)-block-poly(n-butyl acrylate)-block-polyurethane-block-poly(n-butyl acrylate)-block-poly(tert-butyl acrylate) copolymers.