On integral conditions in the mapping theory

Interconnections between various integral conditions that play an important role in the theory of space mappings and in the theory of degenerate Beltrami equations in the plane are established.     

On‐line separation of bacterial cells by carbon‐electrode dielectrophoresis

Dielectrophoresis (DEP) represents a powerful approach to manipulate and study living cells. Hitherto, several approaches have used 2‐D DEP chips. With the aim to increase sample volume, in this study we used a 3‐D carbon‐electrode DEP chip to trap and release bacterial cells. A continuous flow was used to plug an Escherichia coli cell suspension first, to retain cells by positive DEP, and thereafter to recover them by washing with peptone water washing solution. This approach allows one not only to analyze DEP behavior of living cells within the chip, but also to further recover fractions containing DEP‐trapped cells. Bacterial concentration and flow rate appeared as critical parameters influencing the separation capacity of the chip. Evidence is presented demonstrating that the setup developed in this study can be used to separate different types of bacterial cells.     

Ion-binding study by 17O solid-state NMR spectroscopy in the model peptide Gly-Gly-Gly at 19.6 T

Li(+) and Ca(2+) binding to the carbonyl oxygen sites of a model peptide system has been studied by (17)O solid-state NMR spectroscopy. (17)O chemical shift (CS) and quadrupole coupling (QC) tensors are determined in four Gly-(Gly-(17)O)-Gly polymorphs by a combination of stationary and fast magic-angle spinning (MAS) methods at high magnetic field, 19.6 T. In the crystal lattice, the carbonyl oxygen of the central glycyl residue in two gly-gly-gly polymorphs form intermolecular hydrogen bonds with amides, whereas the corresponding carbonyl oxygens of the other two polymorphs form interactions with Li(+) and Ca(2+) ions. This permits a comparison of perturbations on (17)O NMR properties by ion binding and intermolecular hydrogen bonding. High quality spectra are augmented by density functional theory (DFT) calculations on large molecular clusters to gain additional theoretical insights and to aid in the spectral simulations. Ion binding significantly decreases the two (17)O chemical shift tensor components in the peptide plane, delta(11) and delta(22), and, thus, a substantial change in the isotropic chemical shift. In addition, quadrupole coupling constants are decreased by up to 1 MHz. The effects of ion binding are found to be almost an order of magnitude greater than those induced by hydrogen bonding.     

Dimeric allylpalladium(II) complexes with pyrazolate bridges: Synthesis, characterization, structure and thermal behaviour

The synthesis, characterization and thermal behaviour of some new dimeric allylpalladium (II) complexes bridged by pyrazolate ligands are reported. The complexes ; R = H, R′ = C(CH₃)₃ (1b), R = H, R′ = CF₃ (1c); R = CH₃, R′ = CH(CH₃)₂ (2a); R = CH₃, R′ = C(CH₃)₃ (2b); and R = CH₃, R′ = CF₃ (2c)] have been prepared by the room temperature reaction of [Pd(η³-CH₂C(R)CH₂)(acac)](acac = acetylacetonate) with 3,5-disubstituted pyrazoles in acetonitrile solution. The complexes have been characterized by NMR (¹H, ¹³C{¹H}), FT-IR, and elemental analyses. The structure of a representative complex, viz. 2c, has been established by single-crystal X-ray diffraction. The dinuclear molecule features two formally square planar palladium centres which are bridged by two pyrazole ligands and the coordination of each metal centre is completed by allyl substituents. The molecule has non-crystallographic mirror symmetry. Thermogravimetric studies have been carried out to evaluate the thermal stability of these complexes. Most of the complexes thermally decompose in argon atmosphere to give nanocrystals of palladium, which have been characterized by XRD, SEM and TEM. However, complex 2c can be sublimed in vacuo at 2 mbar without decomposition. The equilibrium vapour pressure of 2c has been measured by the Knudsen effusion technique. The vapour pressure of the complex 2c could be expressed by the relation: ln (p/Pa)(±0.06) = −18047.3/T + 46.85. The enthalpy and entropy of vapourization are found to be 150.0 ± 3 kJ mol⁻¹ and 389.5 ± 8 J K⁻¹ mol⁻¹, respectively.     

(4R)-4-Hydroxy-1-nitroso-l-proline: synthesis, X-ray structure, ab initio and conformational calculations

4-Hydroxy-l-proline, an amino acid, an important component of collagen, was transformed into its N-nitroso-derivative, (4R)-4-hydroxy-1-nitroso-l-proline, 1 by butylnitrite in the acidic medium. The structure is a cyclic hydroxy-N-nitrosoacid with the carboxyl and hydroxyl groups trans to each other. The carboxyl group is in the syn-conformation. In the structure, the neutral molecules are connected via classical intermolecular O-H?O hydrogen bonds involving the hydroxyl and carboxyl groups [O?O=2.6251(14) Å], and form chains along the a-axis direction. The chains are linked into sheets via O-H?O hydrogen bond, [O?O=2.6813(15) Å] with participation of oxygen atom of nitroso group. Ab initio calculations based on density functional theory at the B3LYP/6-311++G(d, p) level of theory were performed to analyze the influence of 4-hydroxy-l-proline (Hyp) nitrosation on the conformation of the synthesized N-nitroso-compound. The geometry optimization of 1 and initial 4-hydroxy-l-proline was carried out in the gas phase and in solution using the polarizable continuum model. The single-point calculation was performed for the crystal structure of 1. The most stable conformer of 1 is observed in an aqueous solution. In this state, the pyrrolidine ring adopts an envelope conformation, which is also maintained in the gas phase. The twisted conformation of the pyrrolidine ring is present in all states of Hyp and in the crystal structure of 1. In 1 the interchange of five-membered ring conformation in solution and in the gas phase in comparison with the crystal is accompanied by an increase of the dipole moment of the molecule, which is maximal in solution.     

The electrochemical detection of Ru(II) in a methyl methacrylate solution

This article describes the voltammetric behaviour of RuCl₂(PPh₃)₃ in a methyl methacrylate (MMA) solution. Acquiring this type of information is only possible when the ohmic resistance can be kept sufficiently low. Therefore, the conductivity study of pure methyl methacrylate and a tetrabutylammonium tetrafluoroborate (TBABF₄) methyl methacrylate solution has been described as well. Impedance measurements show an increase in conductivity by adding TBABF₄, while a conductometric curve illustrates the presence of ion pairs, triple ions and quadrupoles depending on the TBABF₄ concentration. The conductivity of a 0.1 mol L⁻¹ TBABF₄-MMA solution (formation of charged triple ions) was high enough to perform electrochemical experiments and a calibration curve could be obtained. The ability of obtaining relevant electrochemical data in low conducting media opens up new perspectives, especially for electroanalytical purposes used to monitor polymer reactions, more specific atom transfer radical polymerization (ATRP) reactions. This method employs a redox process with transition metal complexes in which a halogen ion is transferred reversibly between the transition metal and the polymer chain end. The dynamic equilibrium can be monitored by measuring the ruthenium concentration.