Synthesis and Use of 6-, 7-and 8-Membered P-Heterocycles

The synthesis of new families of P-heterocycles by reductive modifications, ring enlargement and Diels-Alder cycloaddition is described.     

Evaluation of the novel passive sampler for cyanobacterial toxins microcystins under various conditions including field sampling

In the present study, we have evaluated the effectiveness of a passive sampler for polar organic chemicals to accumulate a group of widespread and hazardous tumor-promoting toxins produced in cyanobacterial water blooms—microcystins (MC). The previously optimized configuration of the sampler based on polycarbonate membrane and Oasis HLB sorbent (2.75 mg/cm²) was validated under various exposure scenarios in laboratory and field. Calibration of the passive sampler conducted under variable conditions and concentrations of MC revealed linearity of the sampling up to 4 weeks. The sampling rates of microcystins for two different exposure scenarios were derived (e.g., MC-LR: R _s = 0.017 L/day under static and 0.087 L/d under turbulent conditions). R _s values were further used for calculations of time-weighted average concentrations in natural water. Improved sensitivity and selectivity of the in-house-made sampler was observed in comparison with the commercially available Polar Organic Compound Integrative Sampler (POCIS). Comparisons of grab and passive sampling methods were performed during cyanobacterial water bloom season in the Brno reservoir, Czech Republic in 2008. Data obtained by passive sampling provided a more relevant picture of the situation and enabled better assessment of potential risks. The present study demonstrated that the modification of POCIS is suitable for monitoring of occurrence and retrospective estimations of microcystin water concentrations, especially with respect to the control of drinking water quality.     

Acid-base behaviour of sanguinarine and dihydrosanguinarine

Acid-base and optical properties of sanguinarine and dihydrosanguinarine were studied in the presence of HCl, HNO₃, H₂SO₄, H₃PO₄, CAPSO and acetic acid (HAc) of different concentrations and their mixtures. The equilibrium constants pK_R+ of the transition reaction between an iminium cation Q⁺ of sanguinarine and its uncharged QOH (pseudo-base, 6-hydroxy-dihydroderivative) form were calculated. A numerical interpretation of the A-pH curves by a SQUAD-G computer program was used. Remarkable shifts of formation parts of absorbance-pH (A-pH) curves to alkaline medium were observed. The shifts depend on the type and concentration of inert electrolyte (the most remarkable for HNO₃ and HCl). The corresponding pK_R+ values ranged from 7.21 to 8.16 in the same manner (ΔpK_R+ = 0.81 and 0.73 for HNO₃ and HCl, respectively). The priority effect of ionic species and ionic strength was confirmed in the presence of NaCl and KCl. The strength of interaction of SA with bioactive compounds (i.e. receptors, transport proteins, nucleic acids etc.) may be affected because of the observed influence of both cations and anions of the inert electrolytes.      

Deposition of NiO onto MoO3/γ-Al2O3 extrudates by slurry impregnation method

NiO-MoO₃/γ-Al₂O₃ catalysts were prepared by the reaction of γ-Al₂O₃ extrudates with an aqueous slurry of MoO₃, followed by the reaction of the MoO₃/γ-Al₂O₃ catalyst with an aqueous slurry of NiO, Ni(OH)₂, NiCO₃·2Ni(OH)₂·xH₂O, or 2NiCO₃·3Ni(OH)₂·4H₂O and by subsequent drying. The NiO deposition was examined with electron probe microanalysis. The deposited Ni efficiently increased the activity in benzothiophene hydrodesulfurization.     

Experimental verification of the theory of the successive production of striations in a glow discharge

The properties of the wave of stratification in the plasma of the positive column in a glow discharge in neon are measured. The measurements are compared with the results of the theory of the successive production of striations and good agreement is found.

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In conclusion the author thanks M. Novák for help in measuring and evaluating the experimental results, and F. Kroupa and V. Krejí for carefully reading this paper and for valuable remarks.     

Use of cathode lens in scanning electron microscope for low voltage applications

At a landing energy of 10 eV it is possible to achieve spatial resolution of the same order as at the nominal energy, which is usually 15 keV in the classical scanning electron microscope, by taking advantages of the optical properties of the cathode lens. Two different types of the detection system were designed and tested to learn as much about the optical properties of this system as possible and to start to understand the contrast mechanisms at very low energies. Great changes in the contrast take place when the landing energy is changed from 10 eV to an energy of about 2 keV.     

A theory of the successive production of moving striations in the plasma of inert gases

On the basis of results already published of experiments carried out by the method of excitation of transient processes with small perturbation, a theory is elaborated on the successive production of moving striations (waves of stratification) in an inert gas. The stratification of the plasma is interpreted as the successive production of regions with an alternately positive and negative space charge, i. e. as the producti n of a characteristic macroscopic periodic polarization of the plasma. The basic assumption of the theory is the relative independence of the chain of processes in each dark or light region of the striations, so that interaction between the regions occurs as a result of the electric field of the space charge in the neighbouring region.Equations are derived expressing the chronological order of the processes leading to the production of a space charge in each individual region and the interaction of the regions. The solution of the equations leads to functions, some of which are in agreement with experimental data while others cannot be verified on the basis of the experimental material at present at our disposal and require the carrying out of new experiments.The main results contained in this paper were reported on at the Conference on the Physics of Plasma in Leipzig on October 8th, 1956.     

A study of oxidation of benzidine, o,o′-tolidine,and o,o′-dianisidine

The oxidation of benzidine, o,o′-tolidine, and o,o′-dianisidine by the acetate complex of trivalent cobalt was studied chiefly in glacial acetic acid medium, considering the possible formation of semiquinone and quinonediimine compounds. The effect of uv light on the solutions of these compounds in glacial acetic acid and in benzene was followed spectrophotometrically and chromatographically and compared with the effect of Co(III) acetate. Certain possibilities explaining the course of the studied reactions are discussed.     

Hydrophobic and Hofmeister effects on the adhesion of spider silk proteins onto solid substrates: an AFM-based single-molecule study

AFM-based single-molecule force spectroscopy has been used to study the effect of Hofmeister salts and protein hydrophobicity on the adhesion of recombinant spider silk proteins onto solid substrates. Therefore, a molecular probe consisting of a spider silk protein and an AFM tip has been developed, which (i) is a well-defined, small system that can be simulated by molecular dynamics simulations, (ii) allows access to the whole soluble concentration range for ions, and (iii) provides the distribution of desorption forces rather than just ensemble-averaged mean values. The measured desorption forces follow the Hofmeister series for anions (H2PO4-, Cl-, I-) with a stabilizing energy of more than 15 kBT for 5 M NaH2PO4. Moreover, this effect is influenced by the hydrophobicity of the spider silk protein, indicating that hydrophobic and Hofmeister effects are closely related.