Isolated and solvated thioxanthone: a photophysical study

Quantum chemical methods have been employed to study the photophysics of thioxanthone in vacuum and various solvents. Structurally, the solvation leads to a lengthening of the carbonyl bond, whereas the benzene skeleton is mostly unaffected. This is mirrored by the larger blue shift of the (n(O)π*) states as compared to the red shift which the (ππ*) states undergo. For a proper understanding of the radiative and radiationless processes occurring, the excitation energy profile along a linearly interpolated path has been determined in various cases. The interesting interplay of excited states thus revealed, has been investigated to qualitatively suggest the relaxation pathways available (or dominant) in the cases under study. Rates for these processes have also been computed wherever possible.     

Four-Body Bound-States Systems in Relativistic Scalar Quantum Field Theory: Variational Basis-State Approach

The variational method within the Hamiltonian formalism of quantum field theory has been used in order to investigate the effect of virtual pairs for four-body scalar systems consisting of two particles and two antiparticles of the same mass. The scalar particles and antiparticles interact via a massive or massless mediating scalar field. The ground state energy solutions of Fock-space variational trial states (\(|N{\bar {N}}N{\bar {N}}{ \rangle }+|N{\bar {N}}N{\bar {N}}N{\bar {N}\rangle }\)) of the relativistic wave equations have been studied. We have compared these results with the previous work of four-body system (variational trial states of the form \(|N{ \bar {N}}N{\bar {N}}{\rangle }\)) and we have shown that the inclusion of virtual pairs has a noticeable effect at low coupling and at high coupling the energy of the system is changed by an important amount. In other words, the calculations show that the inclusion of virtual pairs augments the binding energy of the four-body system by a substantial amount at strong coupling. This study can pave the way for some new ideas in order to investigate the effect of virtual pairs, for example, for a bound-states quark-antiquark or tetraquark systems in future.     

A Study of PbTiO3 Crystallization in Pure and Composite Nanopowders Prepared by the Sol-Gel Technique

Summary.  In this investigation the crystallization of PbTiO₃ upon annealing of pure nanopowders and PbTiO₃–SiO₂ (1:1 v/v) nanocomposite powders prepared by the sol-gel technique was studied. Using X-ray diffraction phase analysis, the start of PbTiO₃ crystallization in pure PbTiO₃ powders was detected at 400°C. Distinct crystallization of PbTiO₃ in PbTiO₃–SiO₂ nanocomposites starts at 700°C, whereas SiO₂ remains amorphous. There are indications that an interface interaction between the PbTiO₃ and the SiO₂ phase plays an important role in hindering the crystallization of PbTiO₃. The particle size (size of coherently scattering regions) was estimated from the broadening of the X-ray diffraction line profiles. The average size of PbTiO₃ nanocrystallites increases with temperature and time of annealing, the influence of temperature being more significant than that of the annealing time. Differential scanning calorimetry confirmed the results of the X-ray diffraction with respect to the start of the crystallization. Laser beam scattering and scanning electron microscopy provided the statistical distribution of the grain size and the morphology of the powder grains, showing that each grain of the powders contains several nanocrystallites (coherently scattering regions). Received October 4, 2001. Accepted (revised) December 14, 2001     

Palladium complexes of a chiral P,C-chelating phosphino-(sulfinylmethyl)phosphonium ylide ligand

A new type of phosphino-phosphonium ylide ligand bearing a chiral sulfinyl center affords a P,C-chelated palladium(II) complex with a resolved asymmetric ylidic carbon atom. According to ³¹P NMR analysis of the crude material, the diastereoselectivity of the complexation at room temperature is ca. 7:1. In the crystal state, an X-ray diffraction analysis of one epimer reveals a quasi C₂-symmetric chloro-bridged dinuclear structure, where the (S) configuration of the sulfur atom induces a (S) configuration of the ylidic carbon atom. A in situ Pd(0) catalyst generated from the phosphino-ylide and Pd(PPh₃)₄ promotes allylic substitution of 3-acetoxy-1,3-diphenylpropene by sodium malonate in 70% yield and 5% e.e.     

Synthesis,Spectral and Magnetic Properties,and Crystal Structures of Copper(II) Pyridinecarboxylate Adducts with N‐Heterocyclic Ligands

Synthesis and characterization of seven new complexes [Cu(2‐MeSnic)₂(CH₃OH)]₂ (where 2‐MeSnic is 2‐methylthionicotinate), [Cu(2‐MeSnic)₂L₂]₂ (where L is pyridine — py, ethylnicotinate — Etnic and butylnicotinate — Bunic), [Cu(2‐MeSnic)₂L₂(H₂O)₂] (where L is py and nicotinamide — nia) and [Cu(2‐MeSnic)₂(N‐Menia)₂(H₂O)₂]·2H₂O (where N‐Menia is N‐methylnicotinamide) are reported. The characterization were based on elemental analysis, infrared, electronic and EPR spectra, and magnetic susceptibility measurements over a temperature range of 1.8 — 300 K or 70 — 300 K. Three complexes of different type were studied by X‐ray analysis. The molecule of [Cu(2‐MeSnic)₂(CH₃OH)]₂ has dimeric paddle‐wheel cage structure with a tetragonal pyramidal arrangement around Cu^II. The dimer results from the fact that carboxyl groups of four 2‐MeSnic anions function as bridging in a syn‐syn arrangement. On the other hand [Cu(2‐MeSnic)₂(py)₂]₂ forms dimers with hexacoordinated Cu^II atoms in highly distorted coordination octahedra, each with two oxygen atoms of bridging carboxyl groups in an anti‐anti arrangement of two 2‐MeSnic anions, with two oxygen atoms of one asymmetrically chelating 2‐MeSnic anion and with two nitrogen atoms of two pyridine ligands. The temperature independent EPR spectrum for this complex exhibits an axial signal which corresponds to almost isolated S = ¹/₂ magnetic ions. Magnetic data for the dimer show a weak antiferromagnetic interaction between the two metal ions with J = —0.65 cm^—1. The Cu^II atom in complex [Cu(2‐MeSnic)₂(py)₂(H₂O)₂] is hexacoordinated in an elongated centrosymmetrical tetragonal‐bipyramidal arrangement (4 + 2). Based on the molecular structure the electronic, infrared, electron paramagnetic resonance spectra and magnetic properties are discussed and stereochemistry as well as the mode of ligand coordination in new solid complexes under study have been determined.     

Spectroelectrochemical Study of 9‐Substituted Acridines with Potential Antitumor Activity

The electrochemical and spectroelectrochemical behavior of 9‐substituted with ? CN and ? COOH acridine N‐oxides with potential antitumor activity was investigated. In SER spectra of the investigated compounds, the ring stretching vibration at 1568 cm^?1 for 9‐CN‐substituted compound respectively 1639 cm^?1 for 9‐COOH‐substituted compound was analyzed. Cyclic voltammograms indicates that the reduction potential ?0.766 V for ? CN substituted compound increase towards ?0.745 V for ? COOH substituted compound. The proposed theoretical method in the electrochemical impedance spectroscopy uses a reference redox dielectrode and a multielectrode containing the compound. To account for the change of electrochemical impedance we have considered two theoretical quantities: a pseudocapacitance and a pseudo inductance. Two possible arrangements of them: in series, respective in parallel can be used like criteria of drug classification.     

QM/MM calculation of solvent effects on absorption spectra of guanine

Electronic spectra of guanine in the gas phase and in water were studied by quantum mechanical/molecular mechanical (QM/MM) methods. Geometries for the excited‐state calculations were extracted from ground‐state molecular dynamics (MD) simulations using the self‐consistent‐charge density functional tight binding (SCC‐DFTB) method for the QM region and the TIP3P force field for the water environment. Theoretical absorption spectra were generated from excitation energies and oscillator strengths calculated for 50 to 500 MD snapshots of guanine in the gas phase (QM) and in solution (QM/MM). The excited‐state calculations used time‐dependent density functional theory (TDDFT) and the DFT‐based multireference configuration interaction (DFT/MRCI) method of Grimme and Waletzke, in combination with two basis sets. Our investigation covered keto‐N7H and keto‐N9H guanine, with particular focus on solvent effects in the low‐energy spectrum of the keto‐N9H tautomer. When compared with the vertical excitation energies of gas‐phase guanine at the optimized DFT (B3LYP/TZVP) geometry, the maxima in the computed solution spectra are shifted by several tenths of an eV. Three effects contribute: the use of SCC‐DFTB‐based rather than B3LYP‐based geometries in the MD snapshots (red shift of ca. 0.1 eV), explicit inclusion of nuclear motion through the MD snapshots (red shift of ca. 0.1 eV), and intrinsic solvent effects (differences in the absorption maxima in the computed gas‐phase and solution spectra, typically ca. 0.1–0.3 eV). A detailed analysis of the results indicates that the intrinsic solvent effects arise both from solvent‐induced structural changes and from electrostatic solute–solvent interactions, the latter being dominant. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

SAW hydrogen gas sensor based on WO3 and Pd nanostructures

Bi-layer nanostructures of WO₃ (～100 nm and 150 nm) with a very thin film of palladium (Pd～10 nm) on the top, have been studied for hydrogen gas-sensing application at ～700C and medium hydrogen concentrations (1 – 4%) in air. The structures were obtained by vacuum deposition (first the WO₃ and then the Pd film) onto a LiNbO₃ Y- cut Z-propagating substrate and were tested by means of Surface Acoustic Wave method in a three channel delay line configuration. Very repeatable results have been observed for these two nanostructures with changes in frequency on the level of 500 to 1800 Hz for hydrogen concentration from 1 to 4 % in air. The absolute response value depends on the WO₃ film thickness and hydrogen gas concentration and is greater for the nanostructure with a thicker WO₃ film.     

Mutual Solubilities of Water and Alkanes

Summary.  The evaluation of mutual solubility data for systems water with n-alkanes, isoalkanes, and cycloalkanes along the three phase line is reported and a formula for the prediction of solubility of alkanes in water is developed. Then a cubic equation of state with an added term, which accounts for hydrogen bonding is used for correlation of liquid–liquid equilibrium data and for prediction of solubility of water in hydrocarbons using alkane in water solubility data. Comparison of the predicted and experimental solubilities is performed using all accessible experimental data. With this approach it is possible to predict the solubilities of water in alkanes with good accuracy over the temperature range up to about 20 K below critical temperature. Solubility of alkanes in water can also be calculated using experimental data for solubility of water in alkanes but results of these calculations are more sensitive to experimental errors of the data. Corresponding author: E-mail: macz@ichf.edu.pl Received August 5, 2002; accepted (revised) September 13, 2002 Published online March 13, 2003 RID="a" ID="a" Dedicated to Prof. Dr. H. Gamsj?ger on the occasion of his 70^th birthday anniversary     

Optimized conditions for hydrocarbon group type analysis of base oils by thin-layer chromatography-flame ionisation detection

The results of research on the optimization of the thin-layer chromatography-flame ionisation detection for the determination of group composition of natural base oils, including separation of the aromatics into subgroups, are presented. Neutral base oils obtained in several steps of refining from vacuum distillation petroleum fractions are the most difficult to analyze by hydrocarbon group type analysis (HGTA) because of the high content of aliphatic fragments in their molecules. Factors affecting the accuracy and precision of the results were identified. The paper presents the analytical procedure, including two different calibration methods, as well as the results of studies on the reproducibility of HGTA of typical base oils of different viscosity classes under the optimized conditions. The same conditions were found suitable for HGTA of other high-boiling petroleum fractions by TLC with flame ionisation detection. The paper also introduces a new procedure for reproducible determination of polar fractions in base oils utilizing solid-phase extraction columns, and presents a corrected procedure for the determination of saturated compounds and aromatics (mono-, bi- and polycyclic) in base oils by column liquid chromatography.