Dynamic chirality: keen selection in the face of stereochemical diversity in mechanically bonded compounds

The template-directed syntheses, employing bisparaphenylene-[34]crown-10 (BPP34C10), 1,5-dinaphthoparaphenylene-[36]crown-10 (1/5NPPP36C10), and 1,5-dinaphtho-[38]crown-10 (1/5DNP38C10) as templates, of three [2]catenanes, whereby one of the two bipyridinium units in cyclobis(paraquat-p-phenylene) is replaced by a bipicolinium unit, are described. The crude reaction mixtures comprising the [2]catenanes all contain slightly more of the homologous [3]catenanes, wherein a "dimeric" octacationic cyclophane has the crown ether macrocycles encircling the alternating bipyridinium units with the bipicolinium units completely unfettered. X-ray crystallography, performed on all three [2]catenanes and two of the three [3]catenanes reveals co-conformational and stereochemical preferences that are stark and pronounced. Both the [3]catenanes crystallize as mixtures of diastereoisomers on account of the axial chirality associated with the picolinium units in the solid state. Dynamic (1)H NMR spectroscopy is employed to probe in solution the relative energy barriers for rotations by the phenylene and pyridinium rings in the tetracationic cyclophane component of the [2]catenanes. Where there are co-conformational changes that are stereochemically "allowed", crown ether circumrotation and rocking processes are also investigated for the relative rates of their occurrence. The outcome is one whereby the three [2]catenanes containing BPP34C10, 1/5NPPP36C10, and 1/5DNP38C10 exist as one major enantiomeric pair of diastereoisomers amongst two, four, and eight diastereoisomeric pairs of enantiomers, respectively. The diastereoisomerism is a consequence of the presence of axial chirality together with helical and/or planar chirality in the same interlocked molecule. These [2]catenanes constitute a rich reserve of new stereochemical types that might be tapped for their switching and mechanical properties.     

Rice Bran as an Excellent Sorbent for Heavy Metals from Aqueous Media, 1. Optimization of Conditions

In this two‐part report, the efficiency of rice bran in removal of heavy metals such as cadmium, lead, zinc, nickel, copper and iron(III) from aqueous solution is investigated. The different experimental conditions such as pH, temperature, volume of solution, bran amount, particle size, exchange time, stirring speed, etc. are studied, and the optimum conditions are selected in part 1 of this series of reports. The efficiency of bran in removal of heavy metals is presented with and without treatments. For treatment, heat or acid, alkali and salt solutions were used. The results obtained show that after treating with saturated sodium chloride solution, its efficiency for Ni²⁺ and Zn²⁺ improves. At pH 5, all studied cations have recoveries more than 93% (lead and cadmium 100%). The exchange speed is very high and has preference over the classical ion exchangers.     

Titanium as a chemical modifier for the determination of cobalt in marine sediments

The determination of cobalt in marine sediments by electrothermal atomic absorption spectrometry was studied using no modifier and magnesium and titanium as modifiers. Titanium is one of the major sediment constituents, which widely affects the cobalt determination and it was studied as a chemical modifier since it was the only concomitant that increased the cobalt signal in the concentration range usually found in sediments. The performance of Mg and Ti as chemical modifiers was compared relative to maximum pyrolysis and atomization temperatures, linear calibration range, sensitivity and matrix effects. The pyrolysis curves showed that the analyte could be stabilized up to 1400 °C when either Ti or Mg(NO₃)₂ was present, while only 1000 °C could be used in the absence of a modifier. The optimum atomization temperature was 2500 °C in all cases. Analytical curves were compared using no modifier, 5 μg Ti and 100 μg Mg(NO₃)₂ as modifiers, and the linear range found was up to approximately 4 ng Co whether a modifier was used or not. With Ti as a chemical modifier, analytical curves for cobalt in aqueous solution and in a synthetic matrix resulted in the same sensitivity (m₀=55 pg), whereas the use of Mg led to characteristic mass values of 59 and 72 pg in aqueous solution and in a synthetic matrix, respectively, showing some matrix effect. The detection limits (3σ, n=10) were 0.4 μg g⁻¹ using no modifier and 0.3 μg g⁻¹ with Ti as a modifier in the original matrix. A reference estuarine sediment NIST 1646 with a non-certified content of 10.5 μg g⁻¹ Co was analyzed and the found value of 10.9±2.4 μg g⁻¹, (n=3), using Ti as chemical modifier and calibration against aqueous standards, was in good agreement with the recommended value.     

Synthesis, Crystal Structure, and IR Spectroscopic Characterization of 1,6-Hexanediammonium Dihydrogendecavanadate

Summary.  Anhydrous 1,6-hexanediammonium dihydrogendecavanadate ((HdaH₂)₂H₂V₁₀O₂₈, 1) was prepared by reaction of V₂O₅ with 1,6-hexanediamine in aqueous solution. The crystal structure of 1 was determined, and the proton positions in the H₂V₁₀O₂₈ ⁴⁻ anion were calculated by the bond length/bond number method. The protons are bound to the centrosymmetrically oriented μ–OV₃ groups of the decavanadate anion. Based on the analysis of IR spectra of 1 prepared from H₂O and D₂O, the absorption band at 871 cm⁻¹ can be attributed to δ(V–O_b–H) vibrations. Received August 3, 2001. Accepted (revised) October 8, 2001     

Chromium ion incorporation in the crystal structure of BGO

Comprehensive investigations have been performed by EPR and optical spectroscopy for Bi₃GeO₄ crystals doped with chromium ions. It is demonstrated that the known optical absorption spectrum for chromium ions, specifically, the triplet in the region 600–900 nm has an analog in the EPR spectra — the center with electron spin S = 1. The spectrum is described by the spin-Hamiltonian with the parameters D = 550 G, E = 10 G, g _xx = g _yy = 1.915, g _zz = 1.932. The EPR spectrum is dictated by Cr⁴⁺ incorporation at the germanium sites. Luminescence observed in the region 1.2–1.7 μm is also caused by transitions of Cr⁴⁺ with tetrahedral surroundings to germanium sites. Original Russian Text Copyright ? 2005 N. V. Chernei, V. A. Nadolinnyi, N. V. Ivannikova, V. A. Gusev, I. N. Kupriyanov, V. N. Shlegel, and Ya. V. Vasiliev __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 3, pp. 444–450, May–June, 2005.     

Darstellung und Kristallstruktur von Cadmiumazid Cd(N3)2

Preparation and Crystal Structure of Cadmium Azide Cd(N₃)₂ Solvent free, binary cadmium azide was synthesized by the reaction of cadmium carbonate and a 24 weight% solution of HN₃ in water. Cadmium azide is a colorless, crystalline powder which is highly sensitive to percussion and heat. Caution, the manipulation of Cd(N₃)₂ is very dangerous! The crystal structure was solved by single‐crystal methods and the phase purity was verified by a Rietveld refinement (Cd(N₃)₂, Pbca, no. 61; a = 7.820(2), b = 6.440(2), c = 16.073(3) Å; Z = 8, 1174 independent reflections, 64 parameters, R1 = 0.022). Cadmium azide crystallizes in a new structure type. In the crystal there are edge‐sharing Cd₂(N₃)₁₀ double octahedrons which are further connected to other units by azide bridges. Vibrational spectroscopic investigations (Raman an IR) are discussed with respect to the crystal structure data.     

牛血清白蛋白与十二烷基硫酸钠作用的机理

利用电动势法得到了牛血清白蛋白(BSA)与十二烷基硫酸钠(SDS)相互作用的结合等温线. 通过四阶导数紫外光谱法和荧光光谱法研究了相互作用过程中芳香族氨基酸残基微环境极性的变化. 通过研究发现, 随着SDS浓度的逐渐增大, SDS在BSA上的平均结合数(v)逐渐增大, 色氨酸(Trp)残基所处微环境的极性在减弱后保持基本不变, 酪氨酸残基所处微环境的极性在明显增强后稍有减弱, 苯丙氨酸残基所处微环境的极性略有增强. 结果表明, 当v由0增大到14时, SDS主要结合在BSA的Trp-213附近并逐渐形成聚集体, 从而诱导BSA由结构域ⅡA 开始逐渐展开. 此后, SDS呈正协同作用的特点与BSA 结合, v急剧增大. 当v约为302 时, SDS在BSA上的结合基本达到饱和, BSA的构象趋于稳定.     

Electron traps on oxide surfaces: (H+)(e-) pairs stabilized on the surface of 17O enriched CaO.

(H+)(e-) pairs generated at the surface of polycrystalline CaO are analyzed for the first time in terms of the interaction of the unpaired electron spin with the nuclear spin of the 17O anions of the surface. CaO crystals enriched in the 17O isotope are prepared and the corresponding hyperfine coupling constants are measured in electron paramagentic resonance (EPR) spectra. The results are analyzed on the basis of cluster model density functional theory calculations. The computed hyperfine coupling constants for (H+)(e-) pairs formed on the edge, corner, and reverse corner sites of the CaO surface allow a tentative assignment of two observed spectral features to specific morphological surface sites.     

牛血清白蛋白与十二烷基硫酸钠作用的机理

利用电动势法得到了牛血清白蛋白(BSA)与十二烷基硫酸钠(SDS)相互作用的结合等温线. 通过四阶导数紫外光谱法和荧光光谱法研究了相互作用过程中芳香族氨基酸残基微环境极性的变化. 通过研究发现, 随着SDS浓度的逐渐增大, SDS在BSA上的平均结合数(v)逐渐增大, 色氨酸(Trp)残基所处微环境的极性在减弱后保持基本不变, 酪氨酸残基所处微环境的极性在明显增强后稍有减弱, 苯丙氨酸残基所处微环境的极性略有增强. 结果表明, 当v由0增大到14时, SDS主要结合在BSA的Trp-213附近并逐渐形成聚集体, 从而诱导BSA由结构域ⅡA 开始逐渐展开. 此后, SDS呈正协同作用的特点与BSA 结合, v急剧增大. 当v约为302 时, SDS在BSA上的结合基本达到饱和, BSA的构象趋于稳定.     

Untersuchungen im System LaI2/H2: Phasenverhältnisse und Fehlordnung

Investigation of the LaI₂/H₂ System: Phase Relations and Stacking Disorder Heating of LaI₂ under 1 bar hydrogen pressure to 650 °C leads to light gray LaI₂H_0.95(3), accompanied by a structural change from tetragonal to hexagonal. Sharp reflections in the XRD pattern can be indexed in P6₃/mmc with a = 4.2158(7)Å and c = 15.508(3)Å, however, diffuse reflections indicate the presence of stacking faults in the structure, which correspond to a polytypic intergrowth of MoS₂ and NbS₂ type structural fragments. Increasing the reaction temperature to 730 °C results in a better defined diffraction pattern with the peak positions close to those of the 2H‐NbS₂ structure type. An X‐ray powder study of the samples LaI₂H_n proved the miscibility gap between LaI₂ and LaI₂H_n (0 ≤ n ≤ 0.5) in agreement with previous results. With decreasing H‐content of the homogeneous phase the lattice parameters change in opposite direction, a increasing to 4.236(1)Å and c decreasing to 15.39(2)Å for the lower limit.