Conformations of the 10-membered Ring in 5, 10-Secosteroids. II. (E)-3α-Acetoxy-5, 10-seco-1 (10)-cholesten-5-one and (E)-5, 10-seco-1 (10)-cholestene-3, 5-dione

(E)-3α-Acetoxy-5, 10-seco-1(10)-cholesten-5-one ( 3 ) was synthesized by fragmentation of 3α-acetoxy-5α-cholestan-5-ol ( 1 ) using the photochemical version [3] of the lead tetraacetate reaction [4], and transformed into the corresponding 3-oxo-compound ( 5 ). Two conformations ( A and B ) were deduced for the 10-membered ring of 3 by analysis of the ¹H- and ¹³C-NMR. spectra in toluene. The major conformation ( A ) corresponds to that found in the solid state by X-ray analysis. According to its NMR. spectra in toluene, the medium-sized ring of the diketone 5 exists also predominantly in two conformations, the major one being analogous to A (the solid-state conformation of the 3β-acetoxy isomer ( 9 ) [1]) and the minor one to A (see above). The stereochemistry of the acidcatalyzed and thermal cyclisations of 3 as well as of the corresponding 5-oxime is discussed in terms of conformational factors.     

Determination of phenols with ICN and BrCN in nonaqueous media

Phenol, cresols, ethylphenols, thymol, catechol, resorcinol, hydroquinone, phloroglucinol and β-naphthol have been titrimetrically determined with ICN and BrCN in 10–100% acetic acid and 1:1 glacial acetic acid-acetic anhydride mixture. The phenols undergo substitution; the extent of which depends upon the entire system involved. As little as 0.5 mg of the phenol can be determined with ±0.25% error in these nonaqueous media.     

Reaktionen von Steroiden mit Dialkylaminoschwefeltrifluoriden. I. 11β-Hydroxysteroide. Über STeroide, 233. Mitteilung

Reactions of Steroids with Dialkylaminosulfur Trifluorides. I. 11β-Hydroxysteroids. Reactions of three types of 11β-hydroxy steroids with dialkylaminosulfur trifluorides (DAST) have been studied. 9Δ-unsubstituted 11-alcohols are dehydrated with DAST to Δ⁹⁽¹¹⁾-unsaturated compounds under very mild conditions. 9α-Chloro-11β-hydroxy steroids are quantitatively fluorinated in position 11 yielding the known 9α-chloro-11β-fluoro derivatives. Finally, 9α, 11Δ-fluorohydrins at 0–25° are selectively transformed with DAST into Δ¹¹-9α-fluorides. When the latter reaction is run at lower temperature, the corresponding 11-piperidinesulfinates, products of partial hydrolysis of the alkoxy-dialkylaminosulfur difluoride intermediates postulated by Middleton, can be isolated in high yields. A rational explanation of the results is presented.     

(1)H NMR and small-angle neutron scattering investigation of the structure and solubilization behavior of three-layer nanoparticles

Three-layer nanoparticles were prepared by radiation-induced polymerization of 1-10 g/L of methyl methacrylate dissolved in a 0.1 wt % D(2)O solution of polystyrene-poly(methacrylic acid) (PS-PMA) micelles. According to NMR and small-angle neutron scattering (SANS), most of the poly(methyl methacrylate) (PMMA) is adsorbed at the core-shell interface of the particles. A small fraction of shorter PMMA probably sticks to outer parts of the PMA chains. The absorption kinetics and equilibria of benzene and chloroform were studied by NMR and SANS time-resolved experiments. The diffusion front in the PS core is very narrow but quite broad in the PMMA sheet suggesting, thus, a less compact state of PMMA. According to SANS, the diffusion kinetics is almost independent of the PMMA sheet thickness. In contrast to it, the absorption capacity, reflected by both SANS and NMR, increases markedly with the PMMA content in the particle. The maximum amount of solubilized compound depends on its positive interaction with PMMA (expressed by the chi parameter) but is restricted by the growing interface tension between swollen PMMA and D(2)O. In accordance with this conclusion, a particle saturated with benzene can absorb chloroform only at the expense of a part of benzene expelled into the surrounding medium and vice versa. Starting with 10 g PMMA/L (10 times the weight of the original micelles), the particles become unstable when being swollen with a good solvent.     

Chemie der Seltenerdmetalle, 7. Mitt.: Tartratkomplexe des dreiwertigen Cers

Zusammenfassung Es wurde die systematische Untersuchung des Systems im sauren Bereich durchgeführt. Es wurden Stoffe der Zusammensetzung Ce₂(H₂ T)₃·6H₂O, Ce₂(H₂ T)₃·2H₂O, H[Ce(H₂ T)₂]·2H₂O isoliert^***. Diese wurden röntgenographisch untersucht und es wurde ihre thermische Analyse durchgeführt. Auf Grund von pH-Messungen wurden die Dissoziationskonstanten bestimmt.

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The systems were investigated in the acidic range. The compounds Ce₂(H₂ T)₃·6 H₂O, Ce₂(H₂ T)₃·2 H₂O and H[Ce(H₂ T)₂]·2 H₂O^*** were isolated. X-ray powder diagrams were taken, and a thermal analysis performed. The dissociation constants were determined, based upon pH-measurements.

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Mit 2 Abbildungen

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6. Mitt.:F. Bezina, J. Rosický undR. Pastorek, Acta Univ. Palack., im Druck.     

Axisymmetric free surface seepage

Summary Seepage through porous media in most instances is not a two-dimensional flow phenomenon. One such situation which is investigated herein is the flow from a pond with a bottom formed by the rotation of a curve consisting of a small segment being horizontal and the remainder being an arbitrary convex shaped curve. The approach used to solve this free surface axisymmetric seepage problem is an alternating iteration scheme in conjunction with the Baiocchi transformation and method. The problem is split into two overlapping regions, one in which the free surface is treated and the other in which the singularity is treated. This approach does not require moving meshes and allows a very general prescribed shape for the pond boundary. The numerical approach to the reformulated seepage problem is presented along with several numerical results and comparisons. Also presented is a proof of uniqueness of the solution for such problems provided we make a certain smoothness assumption for the free surface.The alternating iteration scheme is proved to converge provided existence and certain smoothness for the iterates and for their free surfaces are assumed. The iterates involved are solutions of certain complementarity systems. The existence and regularity of these solutions is not investigated in this paper.     

Evaluation of DNA bending models in their capacity to predict electrophoretic migration anomalies of satellite DNA sequences

DNA containing a sequence that generates a local curvature exhibits a pronounced retardation in electrophoretic mobility. Various theoretical models have been proposed to explain relationship between DNA structural features and migration anomaly. Here, we studied the capacity of 15 static wedge‐bending models to predict electrophoretic behavior of 69 satellite monomers derived from four divergent families. All monomers exhibited retarded mobility in PAGE corresponding to retardation factors ranging 1.02–1.54. The curvature varied both within and across the groups and correlated with the number, position, and lengths of A‐tracts. Two dinucleotide models provided strong correlation between gel mobility and curvature prediction; two trinucleotide models were satisfactory while remaining dinucleotide models provided intermediate results with reliable prediction for subsets of sequences only. In some cases, similarly shaped molecules exhibited relatively large differences in mobility and vice versa. Generally less accurate predictions were obtained in groups containing less homogeneous sequences possessing distinct structural features. In conclusion, relatively universal theoretical models were identified suitable for the analysis of natural sequences known to harbor relatively moderate curvature. These models could be potentially applied to genome wide studies. However, in silico predictions should be viewed in context of experimental measurement of intrinsic DNA curvature.     

The oxidative polymerization of p‐phenylenediamine with silver nitrate: Toward highly conducting micro/nanostructured silver/conjugated polymer composites

The oxidative polymerization of p‐phenylenediamine with silver nitrate by using various oxidant/monomer mole ratios in aqueous solutions of both acetic and nitric acid was studied experimentally and computationally. The produced micro/nanostructured conducting poly(p‐phenylenediamine)–silver composites, reaching the conductivities >10⁴ S/cm, were characterized by conductivity and density measurements, gel permeation chromatography, transmission electron microscopy, UV–visible, FTIR, and Raman spectroscopies. The highest conductivity was 31,700 S/cm for poly(p‐phenylenediamine) base–silver (81.4 wt % Ag). The unexpected increase of conductivity after deprotonation of polymer component is discussed on the basis of interfacial electrical barriers and their removal. Theoretical study of the mechanism of p‐phenylenediamine oxidation has been based on the AM1 semi‐empirical quantum chemical computations of the heat of formation of the reaction intermediates, taking into account the influence of pH and solvation effects. Quantum chemical predictions of molecular structure of poly(p‐phenylenediamine) were correlated with spectroscopic findings. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011