Capillary zone electrophoresis in methanol: migration behavior and background electrolytes

Nonaqueous (NA) solutions are often used as background electrolytes (BGEs) and NA solvents are added to aqueous BGEs as organic modifiers in capillary zone electrophoresis (CZE), in order to optimize the separations. This can be tricky, however, because the pH* and pK* concepts may be totally different in NA solvents, whereas often less knowledge is available concerning phenomena, such as system zones, applying NA solvents. In this paper, the concepts of pH* and pK* are considered for methanol as a solvent and pK* values are determined for several components in mixtures of water and methanol. With a mathematical model, adapted for calculations in methanol, parameters are calculated describing the fronting or tailing character of peaks and the question of peaks or dips, and the existence of system zones is discussed for pure methanol as a solvent. These aspects are experimentally verified, applying BGEs useful for the separation of cationic species in the indirect UV mode. It can be concluded that the mathematical model developed for aqueous BGEs is applicable to BGEs in methanol, too, and that the behavior of BGEs in methanol is comparable with that in water concerning the fronting or tailing character of peaks and the question of peaks and dips, although the mobilities and pK values can change significantly.     

Theoretical modeling of the relationship between Young's modulus and formulation variables for segmented polyurethanes

We describe a new modeling approach to prediction of Young's modulus of segmented polyurethanes. This approach combines micromechanical models with thermodynamic considerations based on the theory of block copolymers. The resulting model predicts both the equilibrium morphology and the “ideal” Young's modulus of a segmented polyurethane polymer as a function of its formulation (hard segment chemical structure, hard segment weight fraction, soft segment equivalent weight) and temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2123–2135, 2007     

Cardinality of retracts of monounary algebras

For an uncountable monounary algebra (A, f) with cardinality κ it is proved that (A, f) has exactly 2_κ retracts. The case when (A, f) is countable is also dealt with. This work was suported by the the Slovak VEGA Grant No. 1/3003/06. This work was supported by Science and Technology Assistance Agency under the contract No. APVT-20-004104.     

Magnetic behavior of a spin-1 dimer: model system for homodinuclear nickel(II) complexes

Magnetic behavior of a spin-1 Heisenberg dimer is analysed in dependence on the both uniaxial single-ion anisotropy and XXZ exchange anisotropy in a zero- as well as non-zero longitudinal magnetic field. A complete set of eigenfunctions and eigenvalues of the total Hamiltonian is presented together with an exact analytical expression for the Gibbs free energy, longitudinal magnetization, longitudinal and transverse susceptibility. The obtained theoretical results are compared with the relevant experimental data of [Ni₂(Medpt)₂(μ-ox)(H₂O)₂](ClO₄)₂·2H₂O (Medpt=methyl-bis(3-aminopropyl)amine).     

Pseudo‐merohedrally twinned tetra­kis­(1H‐imidazole‐κN3)bis­(N‐nitro­cyanamidato‐κN)copper(II)

Crystals of the title complex, [Cu(CN₃O₂)₂(C₃H₄N₂)₄], the structure of which has been determined by single‐crystal X‐ray diffraction at 304 K, appear to be pseudo‐merohedrally twinned. Transformation to a monoclinic C‐centred cell was necessary in order to derive the twin law. Twin refinement in a triclinic unit cell significantly reduced the R value. The asymmetric unit of the triclinic cell consists of one mol­ecule in a general position and two half entities with the Cu atom on a centre of inversion. The coordination of the Cu atom is quasi‐octa­hedral, with four imidazole N‐atom donors in the equatorial plane and two cyano N atoms from the N‐nitro­cyanamidate anion in axial positions. Owing to symmetry in the centrosymmetric mol­ecules, the trans imidazole ligands are parallel, while those in the non‐centrosymmetric mol­ecule make angles of 22.8 (2) and 77.9 (2)°.     

3‐Butyl‐1‐(5‐nitro­benzo­[c][1,2]­thia­zol‐3‐yl)‐3‐phenyl­triazene

The mol­ecule of the title compound, C₁₇H₁₇N₅O₂S, consists of three π systems, viz. two aromatic rings and the triazene moiety, which are mutually deconjugated although coplanar. The n‐butyl chain is roughly perpendicular to the molecular plane, with the terminal methyl­ene and methyl groups disordered between two equally populated positions. The mol­ecules in the crystal associate in an antiparallel fashion, forming dimers across the centre of symmetry, the principal intradimer interaction being stacking of the π‐electron portions of the mol­ecules.     

Three isomeric forms of hydroxyphenyl‐2‐oxazoline: 2‐(2‐hydroxyphenyl)‐2‐oxazoline, 2‐(3‐hydroxyphenyl)‐2‐oxazoline and 2‐(4‐hydroxyphenyl)‐2‐oxazoline

Crystal structures are reported for three isomeric compounds, namely 2‐(2‐hydroxy­phenyl)‐2‐oxazoline, (I), 2‐(3‐hydroxy­phenyl)‐2‐oxazoline, (II), and 2‐(4‐hydroxy­phenyl)‐2‐oxazoline, (III), all C₉H₉NO₂ [systematic names: 2‐(4,5‐dihydro‐1,3‐oxazol‐2‐yl)phenol, (I), 3‐(4,5‐dihydro‐1,3‐oxazol‐2‐yl)phenol, (II), and 4‐(4,5‐dihydro‐1,3‐oxazol‐2‐yl)phenol, (III)]. In these compounds, the deviation from coplanarity of the oxazoline and benzene rings is dependent on the position of the hydroxy group on the benzene ring. The coplanar arrangement in (I) is stabilized by a strong intra­molecular O—H⋯N hydrogen bond. Surprisingly, the 2‐oxazoline ring in mol­ecule B of (II) adopts a ³T₄ (^C2T_C3) conformation, while the 2‐oxazoline ring in mol­ecule A, as well as that in (I) and (III), is nearly planar, as expected. Tetra­mers of mol­ecules of (II) are formed and they are bound together via weak C—H⋯N hydrogen bonds. In (III), strong inter­molecular O—H⋯N hydrogen bonds and weak intra­molecular C—H⋯O hydrogen bonds lead to the formation of an infinite chain of mol­ecules perpendicular to the b direction. This paper also reports a theoretical investigation of hydrogen bonds, based on density functional theory (DFT) employing periodic boundary conditions.