The phonon-assisted proton transfer between hydrazinium cations in (N2H5)2HMF6·2H2O (M∈{Ga, Al, Fe}) type compounds. FT IR and quantum theoretical study

FT IR spectra of a series of compounds with a general formula (N₂H₅)₂HMF₆·2H₂O (where M∈{Ga, Al, Fe}) were recorded at variable temperatures (from ∼100 to 300 K, at 10 K intervals). The appearance of the spectral region of ν(N-N) modes due to hydrazinium cations further supports the conclusions regarding the N₂H₅⁺?H⁺?N₂H₅⁺ hydrogen bond potential well based on Raman spectroscopic data [J. Raman Spectrosc. 28 (1997) 315]. The appearance of two bands corresponding to the ν(N-N) modes in the low temperature FT IR spectra that merge into one upon heating is a clear evidence of a symmetric potential well through which a phonon-assisted proton transfer (PAPT) occurs at higher temperatures. Ab initio MP2/6-311++G(2d,p) quantum chemical study of the proton transfer potential within the N₂H₅⁺?H⁺?N₂H₅⁺ cluster confirmed its double-minimum character. The first-order saddle point found on the MP2/6-311++G(2d,p) potential energy hypersurface corresponds to a centrosymmetric structure (C_2h symmetry), with the proton placed at the inversion center. The potential energy curve along the tunnelling coordinate was calculated by the intrinsic reaction coordinate (IRC) methodology, leading to an adiabatic PT barrier height of 3.94 kcal mol⁻¹ and a tunneling rate of 1.98 s⁻¹. The corresponding MP4(SDTQ)/6-311++G(2d,p)//MP2/6-311++G(2d,p) value of the adiabatic PT barrier height is 4.26 kcal mol⁻¹.     

Some aspects of quality assessment of the k0-based method of NAA

Neutron activation analysis is one of the analytical techniques often used for certification of reference materials. The k₀-based method of instrumental neutron activation analysis can also be applied in intercomparison runs in the certification process and therefore it is desirable to know its accuracy in advance. Possible systematic errors related to the application of nuclear data at given neutron flux rate parameters, that can affect the uncertainties of the results obtained by this specific method, are elucidated and error propagation factors calculated for a typical irradiation position in the TRIGA Mark II reactor of the Jozef Stefan Institute. It was found that these uncertainties are at the level of 1–2% on the average.     

Simultaneous determination of trace uranium and thorium by radiochemical neutron activation analysis

A method for the simultaneous, radiochemical neutron activation analysis of uranium and thorium at trace levels in biological materials is described, based on a technique known as LICSIR, in which a double neutron irradiation is employed. In the first, long irradiation²³³Pa (27.0 d) is induced by neutron capture on²³²Th and then the sample is cooled for several weeks. A second short irradiation to induce²³⁹U (23.5 m) is followed by a rapid sequential radiochemical separation by solvent extraction of²³⁹U with TBP and²³³Pa with TOPO. Chemical yields of²³⁹U and²³³Pa were measured for each sample aliquot using added²³⁵U and²³¹Pa tracers from the -spectra of the separated fractions. The technique was validated by quality control analyses.     

The influence of chitosan on in vitro properties of Eudragit RS microspheres

Eudragit RS microspheres containing chitosan hydrochloride were prepared by the solvent evaporation method using acetone/liquid paraffin solvent system and their properties were compared with Eudragit RS microspheres without chitosan, prepared in our previous study. Different stirring rates were applied (400-1200 rpm) and drug content, Higuchi dissolution rate constant, surface and structure characteristics of the microspheres were determined for each size fraction. An increase in average particle size with a reduction of stirring rate appeared in limited interval in both series. The average particle size of microspheres without chitosan, prepared at the same stirring rate, was smaller. Pipemidic acid content increased with increasing fraction particle size, but not with increasing stirring rate as it was observed for microspheres without chitosan. We presume that high pipemidic acid content in larger microspheres is a consequence of cumulation of undissolved pipemidic acid particles in larger droplets during microspheres preparation procedure. Pipemidic acid release was faster from microspheres with chitosan and no correlation between Higuchi dissolution rate constant and stirring rate or fraction particle size was found, though it existed in the system without chitosan. Structure and surface characteristics of microspheres observed by scanning electron microscope (SEM) were not changed significantly by incorporation of chitosan. But in contrast with microspheres without chitosan, the surface of chitosan microspheres was more porous after three hours of dissolution. It is supposed that the influence of particle size fraction and stirring rate on release characteristics is expressed to a great extent through porosity and indirectly through total effective surface area, but the incorporation of highly soluble component i.e. chitosan salt hides these effects on drug release. In conclusion, changes in biopharmaceutical properties due to varying stirring rate and fraction particle size exhibited the same direction as those reported for the microspheres without chitosan, although they are less expressed because of increased experimental variability, likely caused by chitosan.     

ETAAS determination of aluminium and copper in dialysis concentrates after microcolumn chelating ion-exchange preconcentration

A procedure was developed for the preconcentration and determination of aluminium and copper in dialysis concentrates at the ng cm^–3 level. The preconcentration was achieved on microcolumns filled with Chelex-100 resin adjusted to a pH of 4.0. Five repetitive cycles of the sample through the column ensured a sufficient contact time for quantitative retention of aluminium and copper ions. The retained ions were eluted with HNO₃ (0.5 mol dm^–3). Aluminium and copper were determined in the eluate by Zeeman ETAAS using the standard addition technique. The procedure was performed under clean room conditions (class 10,000), The reliability of the results was evaluated by recovery tests, using dialysis concentrates spiked with aluminium and copper. The recoveries obtained ranged from 86 to 106% for aluminium and from 92 to 97% for copper. Using the recommended procedure, the LOD of aluminium and copper in dialysis concentrates (preconcentration factor 2) was found to be 0.5 ng cm^–3 and 0.2 ng cm^–3, respectively. Received: 19 December 1997 / Revised: 10 March 1998 / Accepted: 28 March 1998     

New class of coordination compounds with noble gas fluorides as ligands to metal ions

A new class of coordination compounds of the type [Mⁿ⁺(L)_p](AF₆⁻)_n and [Mⁿ⁺(L)_r](BF₄⁻)_n, where M is Mg, Ca, Sr, Ba, Cd, Pb, lanthanides, A is P, As, Sb, Bi and L is XeF₂, XeF₄, XeF₆, KrF₂, was studied. A review of all known coordination compounds with L is XeF₂ is given: (a) synthetic routes for the preparation of these compounds; (b) analysis of their crystal structures (molecular, dimer, chain, double chain, layer, strongly interconnected double layers and three-dimensional network); (c) the influence of the ligand XeF₂ (small formula volume, linear, semi-ionic, charge of −0.5e on each F ligand); (d) the influence of the central metal ion; (e) the influence of the anions: AF₆⁻ and BF₄⁻ (the formula volume, Lewis basicity). On the basis of all properties of the metal ions, ligand and anions the obtained variety of the structures is analyzed.     

Characterization of a convection-based support microstructure through a flow resistance parameter

Modern convection-based supports differ substantially in pore size, porosity, and microstructure topology. Due to such variability, it is challenging to evaluate the contribution of a particular microstructure topology on flow resistance. We demonstrated that the flow resistance parameter ($\varphi$) introduced decades ago can be used as a criterion to evaluate the effect of microstructure topology on a pressure drop when the pore size is used as a characteristic support dimension. Furthermore, the $\varphi$ value of simple cubic packing was calculated over the entire range of open porosity and compared to the $\varphi$ values determined for pressure drop models derived for particular convection-based supports and experimental values of various convection-based supports from the literature. It was shown that different convection-based supports become clustered into distinct groups when plotted according to their $\varphi$ and open porosity values, allowing their discrimination.     

endo/exo isomerism in norcarane and 2-norcaranol hydrotrioxides (ROOOH)

Ozonation of norcarane (1) yielded endo and exo norcarane hydrotrioxides (2a, 2b), as characterized by (1)H and (13)C NMR spectroscopy. Further ozonation of the primary decomposition products of these hydrotrioxides, i.e., 2-norcaranols (3), produced the corresponding isomeric 2-norcaranol hydrotrioxides (4a, 4b), and hydrogen trioxide (HOOOH).     

Radon in the spa of Bizovac

The radon concentration in the air and water of the Bizovac spa was measured by the Radhome silicon detector and the average values were obtained as 70 Bq/m³ in the indoor pool, 40 Bq/m³ in the hotel room, 135 Bq/m³ in the closed therapeutic bathroom, but the geothermal water had a Rn concentration of 25.3 kBq/m³ and the potable one 2.7 kBq/m³. The Rn transfer factor (f) from water to air in the indoor pool and therapeutic bathroom was 10 and 40 times higher than for normal dwellings (f _n=10^–4), respectively. The effective equivalent dose of inhaled radon for permanent personnel under the worst conditions in the spa was 5.4 mSv/y, but visitors spending two weeks in the spa could receive the dose of 77 Sv.     

Real-time polymerase chain reaction detection of cauliflower mosaic virus to complement the 35S screening assay for genetically modified organisms

Labeling of genetically modified organisms (GMOs) is now in place in many countries, including the European Union, in order to guarantee the consumer's choice between GM and non-GM products. Screening of samples is performed by polymerase chain reaction (PCR) amplification of regulatory sequences frequently introduced into genetically modified plants. Primers for the 35S promoter from Cauliflower mosaic virus (CaMV) are those most frequently used. In virus-infected plants or in samples contaminated with plant material carrying the virus, false-positive results can consequently occur. A system for real-time PCR using a TaqMan minor groove binder probe was designed that allows recognition of virus coat protein in the sample, thus allowing differentiation between transgenic and virus-infected samples. We measured the efficiency of PCR amplification, limits of detection and quantification, range of linearity, and repeatability of the assay in order to assess the applicability of the assay for routine analysis. The specificity of the detection system was tested on various virus isolates and plant species. All 8 CaMV isolates were successfully amplified using the designed system. No cross-reactivity was detected with DNA from 3 isolates of the closely related Carnation etched ring virus. Primers do not amplify plant DNA from available genetically modified maize and soybean lines or from different species of Brassicaceae or Solanaceae that are natural hosts for CaMV. We evaluated the assay for different food matrixes by spiking CaMV DNA into DNA from food samples and have successfully amplified CaMV from all samples. The assay was tested on rapeseed samples from routine GMO testing that were positive in the 35S screening assay, and the presence of the virus was confirmed.