Coordination around thorium(IV) in aqueous perchlorate,chloride and nitrate solutions

The coordination around the thorium(IV) ion in aqueous perchlorate, chloride and nitrate solutions has been determined from large angle X-ray scattering measurements. In perchlorate solutions, where inner-sphere complexes are not formed, the first coordination sphere contains 8.0±0.5 water molecules with Th-H₂O bond lengths of 2.48₅ Å. In chloride solutions inner-sphere complexes are formed, which lead to an increase in the coordination number. In nitrate solutions the nitrate ions are bonded as bidentate ligands to the thorium ion. The bond lengths are similar to those found in crystalline hydrates of thorium nitrate. The coordination numbers found for thorium(IV) in solution are compared with previously reported values for lower charged ions of similar size.On leave from Department of Inorganic Chemistry Royal Institute of Technology S-10044 Stockholm Sweden     

Structure determination of zinc iodide complexes formed in aqueous solution

Structures of the complexes formed in aqueous solutions between zinc(II) and iodide ions have been determined from large-angle X-ray scattering, Raman and far-IR measurements. The coordination in the hydrated Zn²⁺ hexaaqua ion and the first iodide complex, [ZnI]⁺, is octahedral, but is changed into tetrahedral in the higher complexes, [ZnI₂(H₂O)₂], [ZnI₃(H₂O)]^– and [ZnI₄]^2–. The Zn-I bond length is 2.635(4)Å in the [ZnI₄]^2– ion and slightly shorter, 2.592(6)Å, in the two lower tetrahedral complexes. In the octahedral [ZnI(H₂O)₅]⁺ complex the Zn-I bond length is 2.90(1)Å. The Zn-O bonding distances in the complexes are approximately the same as that in the hydrated Zn²⁺ ion, 2.10(1)Å.     

Interaction between the antibacterial compound,oleuropein, and model membranes

Oleuropein, a secoiridoid glycoside extracted from the olive tree, Olea europaea L., has been described as showing antibacterial properties. However, the exact mechanism of these antimicrobial properties is not yet well understood. In the present study, we have studied the interaction of oleuropein with phosphatidylglycerol (PG) as a model membrane for Staphylococcus aureus (S. aureus) (Gram-positive bacteria) and phosphatidylethanolamine and Escherichia coli (E. coli) lipid extract as a model membrane for E. coli (Gram-negative bacteria). The study has been carried out using monolayers as model membranes and using kinetics at constant area and compression isotherms with Brewster angle microscopy (BAM) observations. The results show that oleuropein interacts in higher extent with PG monolayers, which is related with its stronger antibacterial effect against Gram-positive bacteria. The effects on the membrane are probably produced at the cell surface because oleuropein did not form stable mixed monolayers with the lipids assayed at the air/water interface.     

Strukturuntersuchungen an naßersponnenen Polyacrylnitrilfasern nach der Gefriertrocknung

Zusammenfassung An unterschiedlich verstreckten und hydrothermisch nachbehandelten, danach gefriergetrockneten Polyacrylnitril-Gelfasern (PAN) wurden Messungen der Röntgenkleinwinkelstreuung (RKWS), Röntgenweitwinkelstreuung (RWWS) und Tieftemperatur-Gassorption (TTGA) durchgeführt. Die RKWS-Messungen zeigen, daß sowohl in den isotropen als auch in den orientierten Proben eine exponentialstatistische Verteilung der Form und Größe der Inhomogenitäten (Hohlräume, Cluster) vorliegt, welche durch die Kohärenzlängel _c bestimmt wird. Eine erhöhte Röntgenabsorption wurde bei den verstreckten Proben festgestellt. Die Analyse der aus der Kohärenzlänge und den Volumsanteilen der Phasen berechneten charakteristischen RK WS-Parameter (z.B. innere Oberfläche, Durchschußlänge) ergibt, daß jede Behandlung der Gelfasern eine Zu- oder Abnahme der etwa gleich großen Hohlräume verursacht (nucleotic change). Das relative Ausmaß dieser Veränderungen wird besprochen.Der Vergleich mit den Ergebnissen der TTGA an den gleichen Fasern zeigt, daß die Tendenzen bei der spezifischen Oberfläche und dem Porenvolumen (Zu- bzw. Abnahme) bei beiden Methoden annähernd gleich sind. Die Absolutwerte des Hohlraumvolumens unterscheiden sich aber z.T. um den Faktor 40. Dies führt zur Schlußfolgerung, daß mit der RK WS Faserbereiche als Hohlräume erfaßt werden, die bei der TTGA nicht angezeigt werden, weil sie für das Meßgas unzugänglich sind.

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Structural studies on wet-spun freeze-dried polyacrylonitrile fibers

Summary Polyacrylonitrile fibers (PAN) were drawn to different extents, hydrothermally aftertreated, and at last freeze-dried. The products were studied by small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS), and low temperature gassorption (LTGS). The SAXS data show that the shape and the size of the inhomogeneities (voids, clusters) have an exponential statistical distribution determined by the correlation lengthl _c, both in the isotropic fibers and in the fiber-oriented ones. It has also been observed that stretching always causes a higher X-ray absorption. An analysis of the characteristic SAXS parameters (e.g., internal surface, mean chord length), which were calculated from the correlation length and the volume fractions of the phases, evidences that in all samples an augmentation or diminution of the number of the voids with nearly the same shape and size takes place (nucleotic change). Its relative number has been pointed out.Comparison with the results of the LTGS investigations at the same fibers shows that the tendencies of the specific surface and porosity (increase, decrease) are approximately the same with both methods. However, the absolute values of void volume differ in some cases by the factor 40. This leads to the conclusion that the SAXS method records domains of these fibers as voids which are not registered by LTGS (voids not accessible for the gas).

Herrn em.o.Univ. Prof. Dr.Josef Schurz zum 70. Geburtstag gewidmet     

HYDROPHOBICITY OF CONTAMINATED SILICONE RUBBER SURFACES

Silicone rubber (SIR) shows superior performance when used outdoors, but its surface can be transformed frominherently hydrophobic to hydrophilic by the adsorption of contaminants. Al(OH)_3, Al_2O_3, quartz powder and active carbonwere selected as authentic contaminants. Hydrophobicity of the surface was determined using contact angle measurement.The results indicate that the adsorbability of the contaminants can strongly affect the hydrophobicity of contaminated SIRsurface. The increasing rate of contact angle of specimens contaminated by Al(OH)_3 was much faster than that by Al_2O_3 andquartz due to the adsorption of migrated low molecular weight (LMW) polydimethylsiloxanes. Specimens contaminated byactive carbon could achieve sunde hydrophobicity within 15 min because active carbon has high adsorbability. Surfaces ofcontaminated ultrapure SIR, polytetrafluoroethylene (PTFE) and glass remain hydrophilic because they contain no mobileLMW components. The addition of oligomeric polydimethylsiloxanes has little effect on the hydrophobicity of contaminantscovered on SIR surface.     

High-resolution solid-state MAS 73Ge NMR spectra of some organogermanes

High-resolution solid-state magic angle spinning (73)Ge NMR spectra of some organogermanium compounds were measured. Most tetrasubstituted germanes with identical substituents exhibited signals except for one case. Tetrasubstituted germanes with two kinds of different but somewhat similar substituents exhibited broad peaks. Trisubstituted germanes failed to show signals, indicating the importance of symmetry around germanium.     

MEASUREMENTS OF CHAIN INTERPENETRATION OF POLYMER GLASSES

The concept of entanglement provides the basis of our current understanding of the flow behavior of polymer melts, Current techniques developed to investigate the degree of interpenetration of polymer chains only provide indirectly the information of the degree of entanglement in a relatively large scale （several to tens of nanometer）. In this article, we report ^1H-NMR spectroscopy with dipolar filters under fast magic angle spinning for probing chain interpenetration of polymer glasses at the molecular level.     

Study of geometrical parameters in N-H...N type of hydrogen bonds

Geometrical parameters associated with N-H ... N types of hydrogen bonds have been analysed using crystal structure data on nucleic acids, amino acids and related compounds. Histograms depicting the frequency distribution of N-H ... N length (l) and H-N ... N angle (θ) have been drawn and conclusions on the favoured geometry of such bonds have been arrived at. The distribution ofl shows a pronounced maximum in the range between 2.9? and 3.0? with an overall average of 2.98 ?. The θ distribution shows a pronounced maximum for the hydrogen bond angle in the range 0°-10°, with a rapid fall-off in frequency for nonlinear hydrogen bonds. The frequency shows a cos⁶θ dependence as compared to cos²θ dependence term used earlier to predict the angular dependence of hydrogen bond potential energy in proteins and polypeptides.     

溶致液晶中金属纳米粒子的掺杂及其作用机制研究

在用琥珀酸二异辛酯磺酸钠(AOT)构建的具有长程有序结构的层状溶致液晶内, 用不同方式导入预制的亲油或亲水贵金属纳米粒子, 可得到纳米粒子分布在不同介观空间内的无机/有机杂合体. 依据小角X射线散射和偏光显微镜结果, 通过分析掺杂纳米粒子与液晶模板的相互作用, 对掺杂前后体系结构的变化及制得杂合体的稳定性进行了表征. 结果表明, 除考虑掺杂粒子与层状模板空间的匹配外, 体系中静电斥力、范德华引力和Helfrich涨落力之间的平衡是维持液晶结构稳定的基本条件.     

直链醇链长对层状液晶结构与稳定性的影响

作为助表面活性剂,直链醇在层状溶致液晶的制备中是非常重要的。本文以层状液晶的相行为和小角度X射线衍射测量,研究了直链醇链长对层状液晶结构与稳定的影响。