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131.
Ab initio molecular orbital calculations using the STO3-21G basis set has been carried out for the cluster series Na
n
+
, Na
n
, and Na
n
–
(wheren=2–7). The basis set is shown to be reliable compared with more extensive basis sets at the Hartree-Fock level. Thirty-one optimized structures are reported and discussed, many of which (especially for the anions) have not been considered. The STO3-21G//STO3-21G calculations suggest that for most of the species the optimum geometries are planar. In particular, the optimized structures for the anionic species should provide a starting point for more sophisticated configuration interaction calculations. 相似文献
132.
The paper presents a comparative analysis of the possibilities and characteristic features of the application of various polyhedral boron compounds, viz., the closo-decaborate anion [B10H10]2–, the closo-dodecaborate anion [B12H12]2–, the carba-closo-dodecaborate anion [CB11H12]–, carboranes C2B10H12, and the bis(dicarbollide) complexes [M(C2B9H11)2]– (M = Fe, Co, or Ni), in boron neutron capture therapy (BNCT) for cancer. The requirements on compounds used in BNCT are formulated and the advantages of the application of the closo-dodecaborate anion are considered. The data on the synthesis of various derivatives of the closo-dodecaborate anion, which either already found use in BNCT or are most promising in this field, are summarized. The possibilities of the application of agents derived from the closo-dodecaborate anion in medical diagnostics are discussed. 相似文献
133.
Rodion V. Panin Nellie R. Khasanova Evgeny V. Antipov Walter Schnelle 《Journal of solid state chemistry》2007,180(5):1566-1574
NaPd3O4, Na2PdO3 and K3Pd2O4 have been prepared by solid-state reaction of Na2O2 or KO2 and PdO in sealed silica tubes. Crystal structures of the synthesized phases were refined by the Rietveld method from X-ray powder diffraction data. NaPd3O4 (space group Pm3¯n, a=5.64979(6) Å, Z=2) is isostructural to NaPt3O4. It consists of NaO8 cubes and PdO4 squares, corner linked into a three-dimensional framework where the planes of neighboring PdO4 squares are perpendicular to each other. Na2PdO3 (space group C2/c, a=5.3857(1) Å, b=9.3297(1) Å, c=10.8136(2) Å, β=99.437(2)°, Z=8) belongs to the Li2RuO3-structure type, being the layered variant of the NaCl structure, where the layers of octahedral interstices filled with Na+ and Pd4+ cations alternate with Na3 layers along the c-axis. Na2PdO3 exhibits a stacking disorder, detected by electron diffraction and Rietveld refinement. K3Pd2O4, prepared for the first time, crystallizes in the orthorhombic space group Cmcm (a=6.1751(6) Å, b=9.1772(12) Å, c=11.3402(12) Å, Z=4). Its structure is composed of planar PdO4 units connected via common edges to form parallel staggered PdO2 strips, where potassium atoms are located between them. Magnetic susceptibility measurements of K3Pd2O4 reveal a Curie-Weiss behavior in the temperature range above 80 K. 相似文献
134.
Paula Messina Marcela A. Morini Pablo C. Schulz Gerardo Ferrat 《Colloid and polymer science》2002,280(4):328-335
We used a battery of different methods to study the association in aqueous sodium dehydrocholate (NaDHC) solutions. This
salt associates by a stepwise mechanism. Below (9.6 ± 4.2) × 10−4 mol dm−3 there is a molecular solution with some strongly insoluble dehydrocholic acid produced by hydrolysis. Between (9.6 ± 4.2) × 10−4 and (5.2 ± 2.2) × 10−3 mol dm−3, an aggregate similar to acid soap (NaDHC.HDHC) appears and its amount and the aggregate's size increase with concentration.
At =(2.20 ± 0.85) × 10−2 mol dm−3 the aggregates formed have properties usually associated with true micelles, such as solubilisation of water-insoluble dyes.
These aggregates increase in size with concentration and change their shape at 8 × 10−2 mol dm−3, giving nonsymmetrical aggregates. The changes in the solution physicochemical properties at these concentrations may be
misinterpreted and this explains the different values of the critical micelle concentration reported in the literature for
substances with similar structure, such as bile salts.
Received: 14 May 2001 Accepted: 10 August 2001 相似文献
135.
Entrapment and release of sodium polystyrene sulfonate (SPS) from calcium alginate gel beads 总被引:3,自引:0,他引:3
I. Rousseau D. Le Cerf L. Picton J.F. Argillier G. Muller 《European Polymer Journal》2004,40(12):2709-2715
The release of sodium polystyrene sulfonate (SPS) from calcium alginate hydrogel beads has been studied. It has been shown that the structure of the cross-linked calcium alginate network is of primary importance in the retention and/or release of the SPS. This has been evidenced by studying the influence of Ca2+ concentration, molar masses (Mn) and the ratio of mannuronic acid/guluronic acid components. A minimum in the SPS release is observed in relation with the organization of the network structure. Conditions inducing the organization of a strong gel (e.g. high Ca2+ concentration for example) are not always related to a low release. A good control of release is found when a compromise between a well-structured hydrogel and sterical consideration of SPS is reached. 相似文献
136.
The separation and selectivity of eight aromatic compounds ranging from hydrophilic to hydrophobic properties in micellar electrokinetic chromatography (MEKC) using sodium dodecyl sulfate (SDS) micelles or Tween 20-modified mixed micelles were investigated. The effect of different operation conditions such as SDS and Tween 20 modifier surfactant concentration, buffer pH, and applied voltage was studied. The resolution and selectivity of analytes could be markedly affected by changing the SDS micelle concentration or Tween 20 content in the mixed micelles. Applied voltage and pH of running buffers were used mainly to shorten the separation time. Complete separation of eight analytes could be achieved with an appropriate choice of the concentration of SDS micelles or Tween 20-modified mixed micelles. Quicker elution and better precision could be obtained with SDS-Tween 20 mixed micelles than with SDS micelles. The mechanisms that migration order of those analytes was mainly based on their structures and solute-micelle interactions, including hydrophobic, electrostatic, and hydrogen bonding interactions, were discussed. 相似文献
137.
研究了无水硫化钠与对二氯苯(以N-甲基吡咯烷酮为溶剂)合成聚苯硫醚反应的宏观动力学,该反应是一个小分子缩合串联自缩聚的过程,通过测定不同反应聚合体系中氯化钠的徨成率和硫化内的转化率,建立了该反应的宏观动力学方程:1/(1-PNaCl+PNa2s)=C0Kt+1;并计算得到220、250℃的表观反应速率为4.5×10^-4和3.0×10^-3kg/(mol.s),表观活化能为134kJ/mol。 相似文献
138.
增塑剂对1,1,1-三[1′-(2′-氧杂-4′-氧代-5′-氮杂-5′-甲基)十二烷基]丙烷PVC膜钠离子电极性能的影响 总被引:2,自引:0,他引:2
以1,1,1-三[1′-(2′-氧杂-4′-氧代-5′-氮杂-5′-甲基)十二烷基]丙烷(即ETH 227,Fluka No.71732)为中性载体的钠离子选择电极由于具有较强的抗钾离子干扰的能力,因而颇受注意。Guggi等首先用邻硝基苯辛醚和癸二酸二丁酯增塑,以合成的ETH227制成了K_((Na)~+,K~+)~(pot),<<10~(-2)的PVC膜钠离子电极.Jenny等以癸二酸二异辛酯为增塑剂, 相似文献
139.
Investigation of the root extract of Antidesma pentandrum var. barbatum led to the isolation of seven new compounds, antidesmol ( 1 ), antidesmanins E ( 2 ) and F ( 3 ), antidesnone ( 4 ), antidesnol ( 5 ), barbatumols A ( 6 ) and B ( 7 ), together with 14 known compounds including sodium aristolochate‐I ( 10 ) and aristolochic acid‐I methyl ester ( 11 ). 相似文献
140.
Otto Vogl Jan Bartus Joseph R. Murdoch 《Monatshefte für Chemie / Chemical Monthly》1990,121(4):311-316
Summary We report techniques for measuring optical rotation of suspended solids, including dissymmetric molecular crystals (e.g. sodium chlorate and bromate), synthetic polymers, polypeptides and biopolymers. Examples include poly(triphenylmethyl methacrylate), poly-S-lactide, poly-L-hydroxyproline, hemocyanine, cellulose acetate andRNA. The results indicate that optical rotation measurements are sensitive to differences in secondary structure and can serve as a probe for structural differences between solid-state and solution.
Messung der optischen Rotation von Makromolekülen im Festzustand unter Verwendung von Pulversuspensionen
Zusammenfassung Es wird über eine Methode zur Messung der optischen Rotation von Festkörpern in Suspensionen berichtet, wobei dissymetrische Kristalle (z. B. Natriumchlorat und -bromat), synthetische Polymere, Polypeptide und Biopolymere behandelt werden. Die Beispiele umfassen Poly(triphenylmethylmethacrylat), Poly-S-lactid, Poly-L-hydroxyprolin, Hemocyanin, Celluloseacetat undRNA. Die Ergebnisse zeigen, daß die optischen Rotationen bezüglich Unterschiede in der Sekundärstruktur empfindlich sind und daß diese Messungen als ein Maß für Strukturunterschiede zwischen Festzustand und Lösung herangezogen werden können.相似文献