Crystallographic report: The [bis(η5‐cyclopentadienyl)titanium(IV)‐bis(L‐methionine)] dichloride

The structure of ionic complex [Cp₂Ti(L -Met)₂]²⁺[Cl⁻]₂ (where Cp = η⁵-C₅H₅) possessing C₂ symmetry is presented. Discrete cationic units with distorted tetrahedral geometry around the central titanium atom are connected through intermolecular H···Cl bonds between ammonium group protons of α-amino acid ligands and chloride anions. Copyright © 2004 John Wiley & Sons, Ltd.     

Electron affinities of small uracil-water complexes: a comparison of benchmark CCSD(T) calculations with DFT

We present benchmark CCSD(T) calculations of the adiabatic electron affinities (AEA) and the vertical detachment energies (VDE) of the uracil molecule interacting with one to three water molecules. Calculations with rather large aug-cc-pVTZ basis set were only tractable when the space of virtual orbitals was reduced to about 60% of the full space employing the OVOS (Optimized Virtual Orbital Space) technique. Because of the microhydration, the valence-bound uracil anion is stabilized leading to gradually more positive values of both AEA and VDE with increasing number of participating water molecules. This agrees with experimental findings. Upon hydration by three water molecules, the electron affinity of uracil increased in comparison with AEA of the isolated molecule by about 250 up to 570 meV, depending on the geometry of the complex. CCSD(T) results confirm trends determined by DFT calculations of the microhydrated uracil and its anion, even if electron affinities of the free and hydrated uracil molecule are overestimated by DFT by up to 300 meV.     

Anthraquinone as a redox label for DNA: synthesis, enzymatic incorporation, and electrochemistry of anthraquinone-modified nucleosides, nucleotides, and DNA

Modified 2'-deoxynucleosides and deoxynucleoside triphosphates (dNTPs) bearing anthraquinone (AQ) attached through an acetylene or propargylcarbamoyl linker at the 5-position of pyrimidine (C) or at the 7-position of 7-deazaadenine were prepared by Sonogashira cross-coupling of halogenated dNTPs with 2-ethynylanthraquinone or 2-(2-propynylcarbamoyl)anthraquinone. Polymerase incorporations of the AQ-labeled dNTPs into DNA by primer extension with KOD XL polymerase have been successfully developed. The electrochemical properties of the AQ-labeled nucleosides, nucleotides, and DNA were studied by cyclic and square-wave voltammetry, which show a distinct reversible couple of peaks around -0.4 V that make the AQ a suitable redox label for DNA.     

Effect of process parameters and methylcellulose supplementation on the properties of n-undecane emulsions

Study was made on the influence of processing parameters on droplet size during emulsification with an Ultra-Turrax homogenizer. Emulsions of undecane in water, stabilized with nonionic Igepals, were prepared at the optimum hydrophilic-lipophilic balance (HLB) of 11.5 and oil-to-water (O/W) ratio of 5/95; the sizes of emulsion droplets were measured at intervals from the commencement of emulsification. Results showed that the optimum emulsification conditions, as pertaining to minimum particle size, arose at 13 400 rpm and 20 minutes of Ultra-Turrax treatment. Additionally, effects exerted by the presence of methylcellulose, time and storage temperature on the emulsions were determined. Emulsions prepared at the optimal processing parameters revealed that the smallest particle sizes (lower than 200 nm) and the best emulsion stability were demonstrated at the oil/water ratios of 3/97 and 5/95, with 3% surfactant content, an HLB value of 10 to 11 and the storage temperature of 25°C, irrespective of the content of methylcellulose.     

An accurate equation of state of a hard convex body fluid mixture

A method enabling to calculate the contact-point values of the pair correlation function of convex body fluids from a semi-empirical equation of state is presented and the accurate Nezbeda equation of the pure hard convex body fluid is extended to mixtures. Comparison of results for one- and two-component systems with Monte Carlo simulation data shows excellent agreement.     

Thermal properties of oxide glasses

Glasses with the composition Li₂O·2SiO₂·nTiO₂ and Li₂O·2SiO₂·nZrO₂, where n=0, 0.03, 0.062, 0.1, were prepared and the onset and peak temperatures have been determined by DTA. From these characteristic temperatures, the kinetic parameters describing the nucleation and crystal growth have been obtained by isoconversional methods. The kinetic parameters have been used for the calculation of nucleation and crystal growth times for individual glasses so determining the order of glass stability at reheating. The stability of glasses increases with the content of TiO₂ or ZrO₂ where the increase is higher for ZrO₂. Within the concentration range under study, the increase of both times with the metal oxide concentration is quadratic. It has been discussed that the crystallization kinetics does not obey the Arrhenius law and, therefore, when using the evaluation methods based on this law, the results should not be extrapolated outside the temperature range of the measurements.     

Conductivity of flowing polyaniline suspensions in electric field

The formation of chain structures by polarized polyaniline (PANI) particles suspended in silicone oil in the electric field has been monitored by recording suspension conductivity in the course of time. For that purpose, three types of PANI particles differing in the conductivity (3.1 × 10⁻³, 1.7 × 10⁻¹, and 2.0 × 10⁻¹ S cm⁻¹) have been chosen out of a series of nine samples prepared by controlled protonation of PANI base in orthophosphoric acid solutions. Relaxation times reflecting this process and characterizing the rate of the response to the electric field decreased with particle conductivity, indicating a higher polarizability of particles. At the same time, the maximum conductivity of suspension increased as a consequence of the electric and shear forces acting on the particles. In the shear fields, shorter relaxation times appeared than at rest. The simultaneous measurement of the shear stress confirmed that the conductivity investigation can reliably characterize the development of electrorheological structures.     

Chromatic monitoring of downstream microwave plasma source

The application of the chromatic sensing for monitoring of a microwave plasma source is described. The emitted radiation from the plasma excited in the argon, oxygen and CF₄ mixture was measured with three PIN-diodes with integrated optical filters. The response of the chromatic signals on variation of power and gas composition was investigated. Whereas a good sensitivity of the integrated optical signal to the power was confirmed, only a limited sensitivity to the working gas mixture was found.