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21.
Grell D. Grell E. Bugnon P. Dietrich B. Lehn J.-M. 《Journal of Thermal Analysis and Calorimetry》2004,77(2):483-495
The coordination of divalent and monovalent inorganic anions to synthetic polyammonium receptors is investigated in aqueous
solution around neutral pH by titration calorimetry and NMR spectroscopy. High-affinity 1:1 complexes are formed by a pyrrole
type cryptand (1) with sulfate and phosphate, characterized by association constants of almost 107 M-1. Affinities close to 105 M-1 are found for polyazacryptands (3 and 4) exhibiting F-/Cl- selectivity. The binding affinities and the anion selectivities are mainly caused by the charges of ligands and anions, which
is discussed on the basis of simple calculations of the electrostatic contribution to the anion/receptor interactions. The
binding of all investigated anions is exothermic at 298.2 K. The contribution of the large negative ΔH values to the free
energy of anion binding of the pyrrole type ligand is partially compensated by marked negative ΔS values. These unfavorable
entropic contributions are attributed to the additional inclusion of water molecules in the anion/receptor complexes.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
22.
H.-J. Buschmann L. Mutihac E. Schollmeyer 《Journal of inclusion phenomena and macrocyclic chemistry》2003,46(3-4):133-137
The stability constants (log K), the reaction enthalpy( H) and entropy ( S) of the complexesformed between some amino acids (glycine, L-alanine,L-valine, L-leucine, L-phenylalanine, L-tryptophan,L-threonine, and L-lysine) and peptides (glycyl-glycine,glycyl-L-alanine, glycyl-L-leucine, glycyl-L-phenylalanine,L-leucyl-glycine, L-leucyl-L-alanine, glycyl-L-valine,L-leucyl-glycyl-glycine, and glycyl-glycyl-glycine) withp-sulfonatocalix[4]arene and hexasodiump-sulfonatocalix[6]arene in aqueous solutions by meansof calorimetric titration have been investigated. The reportedresults demonstrate that the amino acids and peptides under studyform complexes with both p-sulfonatocalix[4]areneand hexasodium p-sulfonatocalix[6]arene. In the case of theamino acids and peptides the complexation with water-solublecalixarenes in aqueous solution is favored by enthalpiccontributions and disfavored by entropic contributions. However,no influence of the ring size of the calixarenes upon thecomplexation is observed. By comparison with the reaction ofthe sodium salt of phenol-4-sulfonic acid with amino acids amacrocyclic effect in case of the calixarenes is possible. 相似文献
23.
Heung-Jin Choi Dong-Hee Lee Yeon Sil Park In-Kyu Lee Young-Chul Kim 《Journal of inclusion phenomena and macrocyclic chemistry》2002,43(1-2):15-18
Octahedrally converging hexadentate macrocyclic receptors 1 and 2, based on L-tartaric acid and furanmoieties, were synthesized andtheir complexation properties studied. In this paper,magnesium ion selectivitiesdetermined by ISE experiments, chiroptical changes observedby circular dichroism(CD) on complexation, and association constants measuredby NMR titration arediscussed. 相似文献
24.
Labeling experiments using several deuterated lipids were pursued to study the biosynthesis of macrocyclic isoprenoidal lipids of thermophilic methanogenic archaea, Methanothermobacter thermautotrophicus. The isopropylidene terminal of geranylgeranyl group of monomeric precursor appeared to be important for the CC bond formation at the hydrophobic end in the macrocyclic lipids. A mechanism involving a radical trigger at the allylic methyl group is proposed for this CC bond formation. 相似文献
25.
过氧化氢氧化酸碱滴定法测定苯甲醛的含量 总被引:2,自引:1,他引:2
本文提出和建立了一种分析醛类化合物的方法,并用此方法测定了分析纯苯甲醛的含量为99.4%,相对标准偏差为0.21%,实验苯甲醛中所带的寻质苯甲醇以及乙醇,甲醇均不干扰测定,苯甲酸的干扰可以扣除,本法操作简单,终点易于掌握,推广应用方便。 相似文献
26.
季铵盐用于示波极谱滴定法测定培氟沙星和环丙沙星 总被引:4,自引:0,他引:4
介绍采用季铵盐 十六烷基三甲基溴化铵作滴定剂的示波极谱滴定法测定培氟沙星和环丙沙星含量的方法。在pH 4 .8HAc NaAc缓冲溶液中 ,培氟沙星和环丙沙星均能与四苯硼钠 (Na TPB)作用生成沉淀 ,干过滤后 ,用十六烷基三甲基溴化铵标准溶液代替在示波极谱滴定法中常用的有毒硫酸亚铊作为滴定剂 ,回滴滤液中过量的Na TPB ,由示波极谱图 [dE dt=f(E)曲线 ]上TPB的切口消失指示终点。本法终点直观、灵敏 ,操作简便、快速 ,应用于多批原料药样品的测定 ,均获得满意的结果 ,其回收率在 99.9%~ 10 0 .3%之间 ,最大相对误差 <± 0 .3% ,与非水滴定法测得结果基本吻合。 相似文献
27.
The bridged tri-imidazoliums 3.3X^--5.3X^-(X^-=PF6^-,Br^-,I^-)and bis-imidazoliums 6.2PF6^- were synthesized by N-quaternization of imidazole derivative 1 in acetonitrile under reflux.UV spectroscopic titration experiments showed that the halide salts and hexafluorophosphate salts of these imidazoliums exhibited good recognition toward anions in water and in acetonitrile,respectively. 相似文献
28.
Jia-you Shu Mo Zhu Yi Shu Qi-jun Liu Tong Li 《高分子科学》2006,(4):395-401
The new chelate resins, abbreviated as PNBMZs and PBBMZs based on epoxide polymer, were synthesized by polycondensation of N,N-diglycidyl-4-glycidyloxyaniline or 1,4-bis(2,3-epoxypropyl)benzene with the primary amine group of 1,3-bis(benzimidazol-2yl)propylamine (BBPAH). The ion exchangers contain 2.71-3.23 mmol of the ligand contents per gram of the resin. Batch extraction capacities were determined for the metal chloride salts in buffer solutions in the pH range from -1 to 6.0. The chelate resins were very selective for Cu^2+, Zn^2+, Cd^2+ in the presence of other divalent transition metal ions. The maximum uptake capacities of PNBMZ (synthetic molar ratio = 1:1.5) under non-competitive condition were found to be 0.94 mmol/g for Cu^2+ at pH = 2, 1.3 mmol/g for Cd^2+ at pH = 1 and 1.75 mmol/g for Zn^2+ at pH = -1 respectively. While in the case of PBBMZ, it was 1.39 mmol/g for Cd〉 at pH = 1. The metal-uptake behaviors for both of them showed strong pH dependence, and their extraction capacities increase with decreasing pH. The uptake of Cu^2+ by the resin PNBMZs at pH = 1 was found to be rather fast with t1/2 = 18 min. Metal-uptake experiments under competitive conditions also confirm that the chelate resins have a high selectivity for Cu^2+, Zn^2+, Cd^2+ and the contrary pH dependence. 相似文献
29.
库仑滴定法测定有机硅样品中的氮含量 总被引:3,自引:0,他引:3
本文利用库仑滴定法研究了高分子和低分子硅氮化合物及含氮有机硅样品中氮含量的测定,并研究和讨论了影响测定结果准确性的因素。 相似文献
30.
A model has been developed to describe the chemistry which occurs in CF4 plasmas and the etching of Si both in the plasma and downstream. One very important feature of this model is that for discharge residence times which vary by more than an order of magnitude, the amount of CF4 consumed is low and relatively constant. This is because the gas-phase combination reactions between F and both CF3 and CF2 lead to the rapid reforming of CF4. The model predicts that CF2 is a major species in the gas phase and that the [F] detected as a sample point downstream is a very sensitive function of [CF2]/[F] in the discharge. Even though the calculations show that [F] in the discharge varies only slightly over the wide range of experimental conditions considered, large variations in [F] at the sample point occur because the [CF2]/[F] ratio in the discharge changes. The concentrations of C2F6 and SiF4 are predicted to within a factor of 2 over a very wide range of experimental conditions. This confirms the importance of gas-phase free radical reactions in the etching of Si. 相似文献