Structural assignment of organotin hydrides containing the oxazoline ligand

A series of triorganotin hydrides and diorganotin dihydrides containing the optically active 2-(4-isopropyl-2-oxazolinyl)-5-phenyl ligand have been characterized by means of the multinuclear low-temperature NMR investigations, the results of which are discussed. In the corresponding organotin hydrides values of the ¹J(¹H-^117/119Sn) couplings appeared to be temperature dependent, supporting an axial/equatorial position of the hydrogen attached to the tin.     

Influence of Water Vapor on CCl4 and CHCl3 Conversion in Gliding Discharge

The effect of initial concentration of tetrachloromethane and trichloromethane on their conversion in gliding discharge was determined. The conversion of CCl₄ and CHCl₃ was carried out in air containing 20 or 8000 ppm of water vapor. The flow rate of the air containing 1.2, 2.5, or 6.0 vol% of CCl₄ or CHCl₃ was 200 Nl/h. The amount of tetrachloromethane and trichloromethane reacted was determined for a constant value of specific energy which was varied with 2.0 and 4.0 VAh/Nl. The amounts of CCl₄ and CHCl₃ reacted were a linear function of the initial concentration of these compounds in the inlet gas. The results obtained have shown that water vapor present in the air has a favorable effect on the conversion of tetrachloromethane and trichloromethane in gliding discharge.     

A SPIN TRAPPING STUDY OF THE PHOTOCHEMISTRY OF 5,5-DIMETHYL-1-PYRROLINE N-OXIDE (DMPO)

The photochemistry of 5,5-dimethyl-l-pyrroline N -oxide (DMPO) has been studied in benzene, cyclohexane and aqueous buffer solutions (pH 7.4) by means of electron paramagnetic resonance (EPR) and the spin trapping technique. Ultraviolet irradiation of DMPO in aqueous buffer with unfiltered UV radiation from a Xe arc lamp results in photoionization of the spin trap and the generation of the DMPO cation radical, DMPO⁺. The aqueous electron, e_aq⁻, was trapped by DMPO and detected as the DMPO/H adduct. The DMPO⁺- reacted with the water to yield the DMPO/OH adduct. Ultraviolet irradiation of DMPO in nitrogen-saturated benzene gave an unidentified carbon-centered DMPO adduct that was replaced by hydroperoxyl and alkoxyl adducts of DMPO when oxygen was present. Experiments employing ¹⁷O₂ gas indicated that the oxygen in the DMPO alkoxyl adduct was derived from molecular oxygen. However, UV irradiation of DMPO in cyclohexane yielded the cyclohexyl and cyclohexyloxyl adducts of DMPO in nitrogen-saturated and air-saturated solutions, respectively. These observations suggest that in aprotic solvents UV irradiation of DMPO generates a carbon-centered radical (R⁻), derived from the trap itself, which in benzene reacts with oxygen to yield an alkoxyl radical (RO⁻), possibly via a peroxyl radical (ROO⁻) intermediate. In cyclohexane R⁻ abstracts a hydrogen atom from the solvent to yield the cyclohexyl radical in the absence of oxygen and the cyclohexyloxyl radical in the presence of oxygen. These findings indicate that when DMPO is used as a spin trap in studies employing short-wavelength UV radiation (λ < 300 nm) the photochemistry of DMPO cannot be ignored.     

Influence of particle diameter distribution on protein recovery in the expanded bed adsorption process

The General Rate model has been developed and solved to describe protein adsorption in an expanded bed. The model takes into account axial and local variation of particle size distribution (PSD), external and intra-particle mass transfer resistances, and dispersion in liquid phase. The influence of PSD on breakthrough profiles has been analysed. The simulation results show that for a significantly high expanded bed the lower part of the breakthrough curve profiles, calculated for local particle size distribution (LPSD) and for axial average particle size distribution (APSD) are very similar. However, the upper part of breakthrough profiles calculated for LPSD approaches inlet concentration much more slowly than those calculated for APSD. The retention times of the lower part of uptake curves calculated with average particle diameter are constantly shorter than those obtained from LPSD. For the calculation of the dynamic capacity (DC), the LPSD can be replaced by APSD for large expanded bed heights. Using breakthrough profiles calculated for average particle size, DC values are constantly underestimated.     

Ortho effect in the mass spectrometric behaviour of N(pyrimidin-4-yl)aminobenzoic acids and their methyl esters

Ortho-. meta- and para-isomers of N-(pyrimidin-4-yl)aminobenzoic acid and their methyl esters were investigated by electron impact mass Spectrometry. Their fragmentation was found to be strongly dependent on the position of the substituent in the aminobenzoic moiety. Two different kinds of ortho effect were studied and confirmed with the aid of deuterium-labelled derivatives.     

Synthesis and anticonvulsant activity of new fluorinated N-phenyl- and N-benzyl-2-azaspiro[4.4]nonane- and [4.5]decane-1,3-dione derivatives: Part III

A series of N-phenyl- and N-benzyl-2-azaspiro[4.4]nonane- and [4.5]decane-1,3-diones containing a fluoro or trifluoromethyl substituents at the aryl ring was synthesized and tested for their anticonvulsant activity in the maximal electroshock (MES) and subcutaneous metrazole (sc.Met) tests. Among them, the most active were N-benzyl derivatives with fluoro and trifluoromethyl substituents especially at position-2 of the aryl moiety. The introduction of the phenyl ring at the imide nitrogen atom resulted in less active compounds. The results obtained showed that incorporation of fluoro or trifluoromethyl substituents increased the anticonvulsant activity in comparison to respective chloro, methoxy or methyl analogues. Crystallographically obtained conformation for one active and two inactive derivatives with trifluoromethyl substituents at position-2 or -3 of phenyl ring were initially used for molecular electrostatic potentials (MEP) calculation. The MEP distribution at carbonyl oxygen atoms was different for active and inactive molecules.     

Characterization of low-energy chlorophylls in the PSI-LHCI supercomplex from Chlamydomonas reinhardtii. A site-selective fluorescence study

Almost all photosystem I (PSI) complexes from oxygenic photosynthetic organisms contain chlorophylls that absorb at longer wavelength than that of the primary electron donor P700. We demonstrate here that the low-energy pool of chlorophylls in the PSI-LHCI complex from the green alga Chlamydomonas reinhardtii, containing five to six pigments, is significantly blue-shifted (A(max) at 700 nm at 4 K) compared to that in the PSI core preparations from several species of cyanobacteria and in PSI-LHCI particles from higher plants. This makes them almost isoenergetic with the primary donor. However, they keep the other characteristic features of "red" chlorophylls: clear spectral separation from the bulk chlorophylls, big Stokes shift revealing pronounced electron-phonon coupling, and large homogeneous and inhomogeneous broadening of approximately 170 and approximately 310 cm(-1), respectively.     

Orthogonality and similarity within silica-based reversed-phased chromatographic systems

The starting point of this study was a current set of 32 chromatographic systems used to select initial conditions for method development to determine the impurity profile of a drug. The system exhibiting the best selectivity is then selected for further method development. In this current set eight silica-based phases are applied in conjunction with four mobile phases at different pH. In order to save time and resources, the possibilities for a meaningful subset selection were investigated. The most differing systems in terms of selectivity, in other words only the most orthogonal systems, need to be selected. Since the stationary phases are all silica-based, the selectivity differences are examined within a more homogeneous group than if, for instance, also zirconia- or polymer-based columns would be involved. To select the subset of systems also the best overall separation performances are taken into account. The selection is based both on the HPLC-DAD data of a generic set of 68 drugs, and on the LC-MS-DAD results for a mixture of 15 drugs, less different in structure. The orthogonality is evaluated using weighted-average-linkage dendrograms and color maps, both created from the Pearson-correlation coefficients r between normalized retention times r. The Derringer's desirability functions are applied to define the systems with the best overall separation performances. Proposals for different representative subsets of the initial 32 systems are made.     

X-ray diffraction and solid-state NMR studies of a germanium binuclear complex

A compound formulated as (C4H12N2)[Ge2(pmida)2(OH)2] x 4 H2O (where pmida(4-) = N-(phosphonomethyl)iminodiacetate and C4H12N2(2+) = piperazinedium cation), containing the anionic [Ge2(pmida)2(OH)2]2- complex, has been synthesised by the hydrothermal approach and its structure determined by single-crystal X-ray diffraction analysis. Several high-resolution solid-state magic-angle spinning (MAS) NMR techniques, in particular two-dimensional 1H-X(13C,31P) heteronuclear correlation (HETCOR) and 1H-1H homonuclear correlation (HOMCOR) experiments incorporating a frequency-switched Lee-Goldburg (FS-LG) decoupling scheme, have been employed for the first time in such a material. Using these tools in tandem affords an excellent general approach to study the structure of other inorganic-organic hybrids. We assigned the NMR resonances with the help of C...H and P...H internuclear distances obtained through systematic statistical analyses of the crystallographic data. The compound was further characterised by powder X-ray diffraction techniques, IR and Raman spectroscopy, and by elemental and thermal analyses (thermogravimetric analysis and differential scanning calorimetry).