Liquid crystal proton N.M.R. spectral analysis by numerical calculation

We offer an approximate method with which to calculate proton N.M.R. spectra generally caused by dipole-dipole interactions. The method consists of subdividing the spin system of the liquid crystal molecule into interacting blocks. The spectrum of each block is calculated exactly. The interaction between spins of different blocks is calculated approximately. The method is compared with the known methods using 4-n-pentyl-d₁₁-4'-cyanobiphenyl (5CB-d₁₁) and 4,4'-dimeth-oxyazoxybenzene (PAA) as examples.     

Substitution behavior of square-planar and square-pyramidal Cu(II) complexes with bio-relevant nucleophiles

Substitution reactions of [CuCl₂(en)] and [CuCl₂(terpy)] complexes (where en = 1,2-diaminoethane and terpy = 2,2′:6′,2″-terpyridine) with bio-relevant nucleophiles such as inosine-5′-monophosphate (5′-IMP), guanosine-5′-monophosphate (5′-GMP), L-methionine (L-Met), glutathione (GSH) and DL-aspartic acid (DL-Asp) have been investigated at pH 7.4 in the presence of 0.010 M NaCl. Mechanism of substitution was probed via mole-ratio, kinetic, mass spectroscopic and EPR studies at pH 7.4. In the presence of an excess of chloride, the octahedral complex anion [CuCl₄(en)]^2? is formed rapidly while equilibrium reaction was observed for [CuCl₂(terpy)]. Different order of reactivity of bio-molecules toward Cu(II) complexes was observed. Mass spectrum of [CuCl₂(terpy)] in Hepes buffer has shown two new signals at m/z = 477.150 and m/z = 521.00, assigned to [CuCl(terpy)]⁺-Hepes fragments of coordinated Hepes buffer. These signals also appear in the mass spectra of ligand substitution reactions between [CuCl₂(terpy)] and bio-molecules in molar ratio 1:1 and 1:2. According to EPR data, L-Met forms the most stable complex with [CuCl₂(en)] among the ligands considered, while [CuCl₂(terpy)] complex did not show significant changes in its square-pyramidal geometry in the presence of the buffer or bio-ligands.     

The equilibrium and kinetic rigidity of additive poly(trimethylsilyltricyclononenes) with one and two Si(CH<Subscript>3</Subscript>)<Subscript>3</Subscript> groups in monomer unit

The homologous series of additive poly[3-(trimethylsilyl)tricyclononene-7] with two heminal substituents Si(CH₃)₃ in the side cycle of the monomer unit is studied for the first time via the methods of viscometry and static and dynamic light scattering in the range of molecular masses of (29–770) × 10³. The scaling ratios for the intrinsic viscosity and the coefficient of translational diffusion of macromolecules in toluene at 298 K are obtained, and the equilibrium rigidity of the polymer chain is determined. The hydrodynamic and conformation properties of the polymer are compared to an analog with only one Si(CH₃)₃ substituent in the monomer unit. It is found that the introduction of the second side substituent in the heminal position increases the equilibrium rigidity of the additive poly[3-(trimethylsilyl)tricyclononene-7] by 1.4 times and has a far stronger effect on the kinetic rigidity of the polymer. With the use of the ¹Н NMR relaxation method, it is shown that the mobility of side groups of the polymer with two substituents decreases significantly and the correlation times of hydrogen atoms of Si(CH₃)₃ groups exceed some 20 times the corresponding values for the analog with one Si(CH₃)₃ group in the monomer unit cycle.     

Electrical transport and magnetic ordering in R 2Ti3Ge4 (R=Dy, Ho and Er) compounds

New R ₂Ti₃Ge₄ (R=Dy, Ho and Er) intermetallic compounds have been synthesized and characterized by X-ray diffraction and low temperature ac magnetic susceptibility, electrical resistivity and thermoelectric power measurements were carried out. The compounds crystallize in the parent, Sm₅Ge₄-type orthorhombic structure (space group Pnma) and lanthanide contraction is observed as one moves along the rare-earth series. The changeover from paramagnetic to antiferromagnetic phase happens at low temperatures and the ordering temperature scales with the de Gennes factor. The electrical resistivity is metallic with a negative curvature above 100 K. Thermopower displays a weak maximum at temperatures less than 50 K signifying the possible phonon and magnon drag effects.     

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.     

A study of the structural and thermodynamic properties of water by the molecular dynamics method

The thermodynamic and structural properties of four rigid water models were studied by the molecular dynamics method over a wide temperature range. Two three-center (SPC/E and TIP3P) and two five-center (ST4 and TIP5P) models were considered. The results discussed include the boiling and condensation temperatures, VT phase transition diagrams, three-dimensional spatial distributions of atoms, the temperature dependences of the total energy, density, heat capacity, the number of H-bonds per molecule, the distribution of H-bonds over the ∠HOO angle, the self-diffusion coefficient, and the radial distribution functions. The boiling points of all the models did not correspond to 100°C and were noticeably different from each other. The condensation points were also different. The data on the structural parameters led us to conclude that the TIP5P model reproduced the local structure of water most correctly. However, if the reproduction of the local structure is not a necessary condition, less resource consuming three-center models can be used.     

Elastic properties of the Ta–V system: bcc Ta0.33V0.67 and C15 TaV2

Resonant ultrasound spectroscopy was used to measure the elastic constants of bcc Ta_0.33V_0.67 over the temperature range 3.5–300?K; the results were compared to earlier measurements on C15 TaV₂. The temperature dependence of the polycrystalline shear modulus is completely different in the two phases; that of the bcc phase decreases with temperature whereas that of the C15 phases increases in an anomalous fashion. This difference is consistent with a model involving doubly-degenerate levels at the X point of the Brillouin zone in the C15 phase with the Fermi level lying near the doubly degenerate level. This model accounted for the unusual behaviour of the C15 phase. Debye temperatures were determined from the ultrasonic measurements: 295?K for the C15 phase and 315?K for the bcc phase.     

Computer simulation of a real liquid crystal

We carried out a computer simulation study of a liquid crystal using semi-empirical atom-atom potentials (the Lennard-Jones 6-12 modification) with nematic 4-ethoxybenzylidene-4-n-butylaniline as an example. The two stages of the calculations were (1) simulation of the structure of an isolated molecule and (2) Monte Carlo simulation of liquid crystal phase. The energy of the system was calculated as the sum over all atomic pair interactions. The molecular structure preferred in the nematic phase is discussed.     

First and Second Hydration Shell of Ni2+ Studied by Molecular Dynamics Simulations

Molecular dynamics simulations of a Ni²⁺ ion in water have been carried out to investigate the structure and dynamics of water molecules around the nickel, extending the analysis to the second hydration shell. The structural parameters as well as the motions of water molecules in various sub-structures of the solution have been evaluated giving a detailed picture of the motional modes of water molecules