Lithium-7 nuclear magnetic resonance and calorimetric study of lithium crown complexes in various solvents

Lithium-7 NMR studies have been carried out on lithium ion complexes with crown ethers 12C4, 15C5, and 18C6 in water and in several nonaqueous solvents. In all cases the exchange between the free and complexed lithium ion was fast on the NMR time scale, and a single, population average, resonance was observed. Both 1:1 and 2:1 (sandwich) complexes were observed between lithium ion and 12C4 in nitromethane solution. The stability of the complexes varied very significantly with the solvent. With the exception of pyridine, the stability varies inversely with the Gutmann donor number of the solvent. In general, the stability order of the complexes was found to be 15C5·Li⁺>12C4·Li⁺>18C6·Li⁺. Calorimetric studies on these complexes show that, in most cases, the complexes are both enthalpy and entropy stabilized.     

离子液体中NaHSO4催化芳香醛与1,3-环己二酮的缩合反应

以NaHSO₄为催化剂, 在离子液体1-丁基-3-甲基咪唑四氟硼酸盐([bmim]BF₄)介质中, 由芳香醛与1,3-环己二酮衍生物制备了9-芳基-2,3,4,5,6,7-六氢-2H-氧杂蒽-1,8-二酮衍生物. 在沸水浴中反应1～2 h, 产率达81.2%～93.0%. 该方法反应时间短, 产率高, 催化剂价廉易得, 而且对环境友好.     

The disordered cubic structure of Ca7Co3Ga5O18

The new mixed oxide having composition close to Ca₇Co₃Ga₅O₁₈ was synthesized from CaCO₃, Co₃O₄ and Ga₂O₃ at 1150 °C in air and studied by neutron and synchrotron X-ray powder diffraction, selected-area electron diffraction and high-resolution electron microscopy. The structure was refined, using time-of-flight (TOF) neutron powder diffraction data, in space group F432, with and Z=8, to R_F=0.7%. It is considerably disordered, with four different tetrahedral sites randomly occupied by Co and Ga atoms at a ratio of 1:2. The tetrahedra form a disordered (Co_1/3Ga_2/3)O₂ 3D-framework inside which isolated CoO₆ octahedra, surrounded by 8 Ca atoms, are located. The structure is related to the ordered structure of Ca₁₄Al₁₀Zn₆O₃₅. Electron diffraction patterns confirmed the symmetry and unit cell and revealed no diffuse scattering. High-resolution electron microscopy images showed the absence of extended structural defects.     

快离子导体系统中Li+运动的7Li NMR研究

Lil＋2。TiZ。Mg。P3012是一种具有较高离子导电车的快离子导体材料，其结晶化学和电导性能都已经进行了深入的研究，表明化合物具有规整的三维骨架结构，h离子位于骨架间隙中，并且其离子电导率随温度升高而增加＊．作者曾应用”P固体高分辨NMR技术对该固港体系统的微观晶体结构进行了研究，分析了Mg’“离子部分替代Ti‘“离子后，化合物骨架结构的特征＊．但对该体系的Li离子微观动态行为的研究还没有开展，在这里我们应用、i固体NMR技术研究了L计的状态及其动态行为，在此基J由上分析了Li离子可能的迁移机理．1实验部分’LiNMR…     

法呢基苯乙酮及其黄烷酮化合物的全合成

以2，4，6-三羟基苯乙酮和法呢基溴为原料，经一步反应以52．0％和6．5％的收率同时得到3-法呢基-2，4，6-三羟基苯乙酮（1）和4-法呢氧基-2，6-二羟基苯乙酮（2）；然后以化合物1和3，4-二羟基苯甲醛为原料，经羟基保护、缩合、环化和去保护基共6步反应，以19．8％的总收率全合成了（±）-6-法呢基-3'，4'，5，7-四羟基黄烷酮（3）．化合物1、2和3均是从澳大利亚植物Borroniaramosa中分离得到的新天然产物，此次为首次合成．     

Direct observation of a series of non-covalent complexes formed by phosphorylated flavonoid-protein interactions through electrospray ionization tandem mass spectroscopy

In the work described in this paper, 7-hydroxyflavone and chrysin were phosphoylated by a modified Atheron-Todd reaction. Three new phosphorylated flavonoids (PF) were obtained, and the structures of the target products were determined by X-ray and NMR data and electrospray ionization (ESI) tandem mass spectroscopy (MS). The mixed solutions of the phosphorylated flavonoids and different proteins such as insulin, lysozyme, and cytochrome c were injected in an ion trap mass spectrometer. The results show that all the phosphorylated flavonoids could form non-covalent complexes with the proteins mentioned above, while non-covalent complexes were not detected from the mixed solution of the chrysin or 7-hydroxyflavone with proteins. The research shows that the phosphorylated flavonoids could enhance the interaction with proteins. It may imply their important role in biological processes. The method described in this paper provides us additional information for studying such interactions for phosphorylated flavonoids in this important field.     

Effect of the crystalline environment upon the rotational conformation about the N-C and C-C′ bonds (Φ andΨ) in amides and peptides

SCFab initio and PCILO computations indicate the intrinsic preference of the torsion angle for 60 °. In the crystal structure of simple methylamides and peptides the observed values for this torsion angle lie between 0 °–30 °. Different procedures for computing lattice energies and total crystallographic conformational energies (lattice + torsional) utilized by other authors, failed to account for this situation. We show that the procedure developed recently in our laboratory for computing lattice energies indicates that the minima of these energies for in acetamide and N-methylacetamide correspond well to 0 °–30 °. Because of the low value of the barrier of the torsional potential for this angle, the total crystallographic conformational energy corresponds also to = 0 °–30 ° in agreement with the experimental data.     

The elimination of fast variables in complex chemical reactions. II. Mesoscopic level (reducible case)

The master equation for chemical reactions that proceed through a number of steps (complex reactions) is considered. Examples are studied in which the reaction constant of one of the steps is much larger than the others, and a reduced master equation is derived by means of a projection operator formalism. This reduction amounts to an elimination of intermediates. The consistency of the scheme is shown by means of the-expansion.     

Collapse of percolation clusters — A transfer matrix study

Exact calculations using transfer matrices on finite strips are performed to study the two-dimensional problem of site percolation clusters with an attractive nearest neighbor interaction. Thermodynamic quantities such as free energy per site and specific heat are calculated. Finite-size scaling with two strips of different widths yields very accurate approximations of the critical line and the correlation length exponent. The result shows clearly a site percolation fixed point at very high temperatures, a random animal fixed point at intermediate temperatures, a point for the collapse of lattice animals at lower temperatures, and a compact-cluster fixed point at the lowest temperatures.On leave from Institute of Theoretical Physcis, Chinese Academy of Sciences, Beijing, China.     

Synthesis and Crystal Structure of a Novel Supramolecular Compound [Mg(H_2O)_6](C_(16)H_(11)O_4SO_3)_2·10H_2O

IntroductionMolecularpolymerwithonedimensionalormultidimen sionalstructureassemblingthroughhydrogenbondsisanim portantresearchcontentinthesupramolecularchemistryandcrystalenginnering .1,2 Withthedevelopmentofnewtypefunctionalmaterialssuchasmolecularmagnetic ,selectedcatalysis ,reversiblecatalysis ,reversiblehost guestmolecular(ion)exchangeetc.,3themoleculardesignandsynthesishavealreadyattractedconsiderableattentioninsupramolecu larsystem .Thesupramolecularcomplexesandorganiccom poundscontainin…