The Complexation of Amino Acids by Crown Ethers and Cryptands in Methanol

Complex formation between several crown ethers and the cryptand (222) and -amino acids in methanol was studied by calorimetric titration. The ligand structure and the donor atoms of the ligands play an important role in determining the measured values of the reaction enthalpies and entropies. However, with the exception of the diaza crown ether (22) all stability constants are of the same order of magnitude. The enthalpic and entropic contributions to the stabilities of the complexes formed compensate each other. In methanolic solution the amino acids exist in their zwitterionic form. This equilibrium can be influenced. Under acidic, neutral or basic conditions different values of the reaction enthalpies are measured for the complexation of some amino acids with 18-crown-6. These results demonstrate that the concentration of the zwitterionic form of the -amino acids can be influenced. Thus the reaction between macrocyclic and macrobicyclic ligands and amino acids should be described by at least two different reaction schemes.     

Complex Formation Between Crown Ethers and Urea and Some Guanidinium Derivatives in Methanol

The complexation of urea and some guanidinium derivatives by the ligands 15-crown-5, 18-crown-6, benzo-18-crown-6 and diaza-18-crown-6 in methanol has been studied by means of calorimetric titrations. The complex formation is mainly favored by entropic contributions. The number of solvent molecules released during the complex formation is responsible for the stability of the complexes formed.This revised version was published online in November 2005 with corrections to the Cover Date.     

Polyallylammonium Ferrocyanide Films for Trace Water Detection in Halogenated Solvents

Polyallylammonium films with electrostatically bound ferrocyanide were formed by electrochemically reducing ferricyanide ions in the presence of polyallylammonium chloride. These films could be deposited onto the surfaces of Pt, Au or SnO₂ electrodes. In anhydrous organic electrolyte solutions, these films are electroinactive but become electroactive after the addition of trace water. For concentrations of water from 0.0 to 0.12% in chlorinated solvents, the electroactivity is linear with water concentration. The linearity between concentration of water and electroactivity can be exploited to develop a subsaturation trace water sensor.     

丙酮-水混合溶剂中3-甲基吡啶的电氧化

在以质子交换膜为隔膜的电解槽内, 通过3-甲基吡啶在PbO2电极上的电氧化研究, 发现在丙酮-水混合溶剂中, 与纯水作溶剂相比, 不仅在相同阳极电位下电流密度大幅度上升, 3-甲基吡啶电氧化生成烟酸的选择性和电流效率也明显提高. 通过循环伏安、极化曲线和恒电位电解实验, 研究了在丙酮-水混合溶剂中3-甲基吡啶的电氧化条件, 并比较了不同条件下的选择性和电流效率.     

Interactions of Polyglycol Ethers with Anionic Surfactants in Water

In order to determine the thermodynamic properties of the aggregation process between sodiun dodecyl sulfate (SDS) and polyglycol ethers (PEG) with average molar mass 35000, 20000, and 10000, the temperature dependence of polymer-surfactant ?nteraction is used. Surface tension, ionic conductivity, and solubilization methods have been used to quantify the interactions.It was found that the transfer of SDS micelles from aqueous media to aqueous polymer media is more feasible than the reverse. In addition, the hydropholic interaction seems to be important, as opposed to the charge-nonpolar type interaction.     

Dielectric Constants of Water,Methanol, Ethanol,Butanol and Acetone: Measurement and Computational Study

The dielectric constants (relative permittivities) of water, methanol, ethanol, butanol and acetone were measured at 91.3 kPa and (283.15 and 293.15) K and are reported here. The dielectric constants were determined by using a new setup based on a low-pass filter. The obtained dielectric constant values are compared with those reported in the literature, and are consistent with those reported in the literature. The obtained dielectric constant data were also compared with those calculated by the Kirkwood model. The comparisons indicated that Kirkwood model can be successfully used for calculation of dielectric constants of the pure fluids.     

Conductance and Thermodynamic Study of the Complexation of Ammonium Ion with Different Crown Ethers in Binary Nonaqueous Solvents

A conductance study of the interaction between ammonium ion and 18‐Crown‐6 (18C6), dicyclohexano‐18‐crown‐6 (DC18C6), ditertbutyl‐dicyclohexano‐18‐crown‐6 (t‐bu)₂DC18C6, diaza‐15‐crown‐5 (DA15C5), dibenzo‐21‐crown‐7 (DB21C7) and N‐Phenylaza‐15‐crown‐5 (NPA15C5) in acetonitril‐di‐methylsulfoxide mixture was carried out at various temperatures. The formation constants of the resultant 1:1 complexes were determined from the molar conductance‐mole ratio data and found to vary in the order of DA15C5 > DC18C6 > 18C6 > (t‐bu)₂DC18C6 > DB21C7 > NPA15C5. The enthalpy and entropy of the complexation reactions were determined from the temperature dependence of the formation constants.     

Osmotic Coefficients and Activity Coefficients of Nonaqueous Electrolyte Solutions. Part 2. Lithium Perchlorate in the Aprotic Solvents Acetone, Acetonitrile, Dimethoxyethane, and Dimethylcarbonate

Vapor pressure lowering by the addition of lithium perchlorate to the aprotic solvents acetone (0.02–0.6 m), acetonitrile (0.05–1.2 m), dimethoxyethane (0.02–0.4 m), and dimethylcarbonate (0.03–1.8 m) was measured at 25°C with high precision. The experimental data for the corresponding osmotic coefficients are compared to those obtained from the Pitzer equations and chemical model calculations. Mean activity coefficients are derived from the osmotic coefficients.     

New Wine in Old Bottles: Prolonging Room-Temperature Phosphorescence of Crown Ethers by Supramolecular Interactions

Supramolecular macrocyclic hosts have long been used in smart materials. However, their triplet emission and regulation at crystal level is rarely studied. Herein, ultralong and universal room-temperature phosphorescence (RTP) is reported for traditional crown ethers. A supramolecular strategy involving chain length adjustment and morphological locking through complexation with K⁺ was explored as a general method to tune the phosphorescence lifetime in the solid state. A maximum 10-fold increase of lifetime after complex formation accompanied with by invisible to visible phosphorescence was achieved. A deep encryption based on this activated RTP strategy was also facilely fabricated. This work thus opens a new world for supramolecular macrocycles and their intrinsic guest responsiveness offers a new avenue for versatile smart luminescent materials.     

One-Pot Synthesis of Cage-Functionalized,Ketal-Containing Crown Ethers

Acid-catalyzed reaction of pentacyclo[5.4.0.0^2,6.0^3,10.0^5.9]undecane-8,11-dione (1) with penta(ethylene glycol) produced two cage-functionalized, ketal-containing crown ethers, i.e., 2 and 3, in low yield. The structure of 2 was established unequivocally by direct methods. Alkali metal picrate extraction data obtained for 2 and for a structurally related model compound, i.e., 18-crown-6,indicate that 2 is an inefficient alkali metal picrate extracting agent.     

Solubility of l-tartaric Acid in Ethanol, Propanol, Isopropanol, n-Butanol, Acetone and Acetonitrile

The solubility of l-tartaric acid was measured in ethanol, propanol, isopropanol, n-butanol, acetone and acetonitrile in the temperature range 281.15 and 324.25 K under atmospheric pressure by a gravimetric method. The solubility of l-tartaric acid in those selected solvents increases with increasing temperature. The apparent molar enthalpies of solution of l-tartaric acid in the selected solvents were estimated from the solubility data. The solubility results were correlated with the van’t Hoff equation, the modified Apelblat equation, and the λh equation. Agreement with the experimental data was very good in all cases. The experimental results could be useful for optimizing the purification process of l-tartaric acid in industry.     

Correlation of Kinetic and Thermodynamic Quantities of Tl(I)/Tl(Hg) Electroreduction with Parameters of Binary Mixtures of Water with Acetone, Acetonitrile, Methanol, and N,N-dimethylformamide

The diffusion coefficient of Tl⁺ ions, the standard potential, the size factor of the activated complex, and the standard rate constant of the overall reaction Tl(I)/Tl(Hg) in aqueous mixtures of acetone, methanol, acetonitrile, and dimethylformamide are related to parameters representing the composition, polarity, electron pair, and hydrogen-bond donor ability of these mixtures. The dependencies on mixture composition, and the linear and multilinear correlation with solvatochromic parameters are interpreted by assuming a heterosolvation effect in combination with a two-step ion transfer – ion adsorption mechanism.     

蔗糖、葡萄糖对水溶液中丙酮、乙醇和乙腈活度的影响（298.1K）

用液上气相色谱法测定了298.1K下蔗糖和葡萄糖水溶液中丙酮、乙醇和乙腈的活度系数。对实验规律和3个非水组分活度数（lnγ）随糖浓度（m）的变化，从糖分子平伏羟基（e-OH)水化和溶剂混溶序及溶质与糖分子间相互作用的角度作了初步解释。     

新型卤代羟基三苯醚的合成与抑菌活性研究

设计合成了对(间、邻)苯二酚二(4-氯-2-羟基苯基)醚(4a～4c)及对(间、邻)苯二酚二(4-氯-5-溴-2-羟基苯基)醚(5a～5c)共6个卤代羟基三苯醚类化合物,其结构均经1H NMR,IR,MS和元素分析证实,并且对其抑菌活性进行了初步测试.结果表明:此类化合物大多在低浓度下对大肠杆菌、金黄色葡萄球菌、白色念珠菌、白色葡萄球菌、变形杆菌、卡他双球菌、青枯假单胞菌等具有良好的抗菌活性.     

Thermochemistry of Benzene Solution in Alcohols, Aprotic Solvents, and Mixtures of Aprotic Solvents with Methanol

The standard enthalpies of solution of benzene at 25°C in alcohols (methanol, 1-propanol, 1-pentanol, 1-decanol), aprotic solvents (1,4-dioxane, acetone, acetonitrile, dimethyl sulfoxide, dimethylformamide, propylene carbonate), and mixtures of methanol with these aprotic solvents were determined. Multiple regression analysis revealed the role of specific and nonspecific interactions in solvation of benzene in these solvents.     

Molecular Complexes of Crown Ethers in Crystals and Solutions

A review of the experimental and theoretical studies of the crown ether complexes with polar molecules in their crystals, solutions, and in a gas phase is given. The type of the molecular bonds in the complexes, their stoichiometry, and the change in the macrocycle conformation during complex formation are considered, as well as the effect of the macrocycle structure and the nature of the medium on the efficiency of the molecular bonding. New data are given on the enthalpies of transfer of the crown ethers from tetrachloromethane into solvents capable of forming hydrogen bonds. The enthalpies of specific interactions of macrocycles with the molecules of the solvents in the medium of the same solvents are characterized. The conformations of the crown ethers in the media under study are discussed.     

Crown Ethers and Phase Transfer Catalysis in Polymer Chemistry

Abstract

This paper is the first half of a two part review on the applications of crown ethers, cryptands, glymes and various onium ion salts to polymer chemistry. Part 1 surveys the use of these phase transfer catalysts (PTC's) in the synthesis and modification of macromolecules. Applications to ring-opening and vinyl polymerizations generally have involved solubilization and activation by PTC's of organic and inorganic salts which serve as anionic initiators. Change in the polymerization rates, polymer yields and product microstructure often resulted from association of the PTC with the active chain end.

Polymer modification and functionalization reactions have been enhanced by the use of PTC's. Macromolecular substrates have included both soluble and insoluble polymers, although the most popular have been the readily-available Merrifield resins. Generally these two-phase reactions have involved polymer solutions interacting with insoluble reagents or insoluble polymers reacting with the reagent solution. Some of the groups incorporated have been thiols, nitriles, carboxylic acids, esters, and crown ether analogs themselves. Most of this work has aimed at synthesis of polymer derivatives which can serve as chelating agents, catalysts and reagents in subsequent reactions. In almost all cases described, phase transfer catalysis offers definate advantages in selectivity and yield over conventional methods. The outline below gives the general subject areas of both Part 1 and Part 2; the latter will be published shortly.     

Synthesis and Enantiomeric Selectivity of Chiral Crown Ethers

Condensation of (4S,5S)-4,5-dihydroxymethyl-2-substituted dioxolanes with polyethylene glycols ditosylates yielded new chiral crown ethers. By potentiometry the enantioselectivity of complexing between the compounds obtained and L- and D-valine methyl ester hydrochlorides was evaluated.