Jong Chan Lee

Highly selective recognition of lead ion in water by a podand fluoroionophore/γ-cyclodextrin complex sensor

We report herein a novel podand fluoroionophore/gamma-cyclodextrin (gamma-CyD) complex sensor that shows markedly high selectivity for lead (Pb2+) ion in water.

Influence of medium polarity upon selectivity and efficiency of alkali metal cation sorption by polyether carboxylic acid resins

The influence of medium polarity upon competitive sorption of alkali-metal cations from aqueous and aqueous methanolic solutions by the polymethacrylic acid resin Amberlite CG-50, two acyclic polyether carboxylic acid resins, and six sym-(alkyl)dibenzo-16-crown-5-oxyacetic acid resins has been investigated. Addition of methanol was found to strongly depress the selective Li(+) sorption of CG-50 and one of the acyclic polyether carboxylic acid resins. Enhancement of metal ion-crown ether interactions as the percentage of methanol in the medium was increased accentuates the Na(+) sorption selectivity for the lariat ether carboxylic acid resins. The highest Na(+) sorption selectivity was obtained for sym-(alkyl)-dibenzo-16-crown-5-oxyacetic acid resins with ethyl and propyl groups in 80% methanol-20% water.

Effect of Ring-Size Variation within Dibenzocrown Ether Resins upon Ion-Pair Sorption of Alkali-Metal Cations from Aqueous and Aqueous Methanol Solutions

Abstract A batch analysis method has been developed for evaluation of metal salt sorption by crown ether polymers. Selectivity in competitive alkali-metal chloride sorption by a series of formaldehyde condensation polymers of dibenzocrown ethers is influenced by the relationship between the crown ether cavity size and metal ion diameter, as well as the degree of hydration of the metal salt. Effective and selective sorption of KCl from the other alkali-metal chlorides was obtained with a dibenzo-18-crown-6 resin. Excellent sorption selectivity for the monovalent metal chlorides was noted for competitive ion-pair sorption of NaCl, KCl, MgCl2, and CaCl2 by this resin. This resin was examined as a stationary phase for selective column separation of KCl from alkali-metal chlorides and of KCl and NaCl from alkali-metal and alkaline-earth chloride mixtures in 80% methanol—20% water.

Transport of alkali metal cations through monoazacrown ether-modified NafionTM 117 membrane

Abstract Conditions have been developed for the surface modification of Nafion TM 117 cation-exchange membrane by conversion to the sulfonyl chloride form and coupling with secondary amines to form sulfonamide groups. Nafion 117 membranes modified with diethylamine ( 13 ), dibutylamine ( 14 ), morpholine ( 15 ), bis(2-methoxyethyl)amine ( 16 ), and 8-aza-2,5,11, 14-tetraoxapentadecane ( 17 ), monoaza-12-crown-5 ( 18 ), monoaza-15-crown-5 ( 19 ), and monoaza-18-crown-6 ( 20 ) were prepared and their competitive, proton-coupled transport of alkali metal cations was compared with that of unmodified Nafion 117 membrane. Alkali metal cation permeation of membranes 13–16 was found to be poor. However, membranes 17–19 which were produced by coupling with an acyclic or cyclic polyether amine having more than three oxygen atoms gave efficient alkali metal cation permeation which was comparable with that for unmodified Nafion 117 membrane. The permeation selectivity order for these surface-modified Nafion 117 membranes was Cs + > Rb + > K + > Na + > Li + which differs from the ordering of K + > Rb + > Cs + > Na + > Li + observed for unmodified Nafion 117 membrane.

A dibenzo-16-crown-5 fluoroionophore for selective emission ratio sensing of Na+ in basic aqueous dioxane solution

For alkali metal cation sensing in aqueous dioxane solution, a novel dibenzo-16-crown-5 (DB16C5) fluoroionophore 1, N-(pyren-1-yl)-sym-(propyl)dibenzo-16-crown-5-oxyacetamide, has been synthesized. Examination of fluorescent behavior for 1 in 4∶1 1,4-dioxane–water (v/v) containing tetramethylammonium hydroxide (TMAOH) reveals that proton dissociation of the carboxamido moiety is promoted by Na+ binding, which results in an emission ratio response due to internal charge transfer (ICT) from the donor carboxamido anion to the pyrene acceptor. The emission intensity ratio (I459/I387) increases with enhancement of the Na+ concentration. No fluorescent response is induced by the presence of Li+, K+, or Cs+. This high Na+ selectivity is attributed to a preorganized structure of DB16C5 lariat ether binding site in which Na+ binds tightly to the carbonyl oxygen of the side arm to induce selective proton dissociation. Thus a ratiometric emission response with high Na+ selectivity has been obtained for 1 in 4∶1 1,4-dioxane–water (v/v) containing TMAOH.

Crystal Structures of Dibenzo-13-crown-4 and sym-(2-Picolyloxy)dibenzo-13-crown-4

Solid-state structures are determined for two compounds which containdibenzo-13-crown-4 rings. These include the parent crown etherdibenzo-13-crown-4 and its lariat ether derivativesym-(2-picolyloxy)dibenzo-13-crown-4. The solid-state structure ofdibenzo-13-crown-4 is complicated by disorder of the carbon atoms in theethylene and propylene bridges. The asymmetric unit of the crystal for thelariat ether derivative consists of two chemically identical, butcrystallographically different, molecules.

Structural and conformational studies of alcohol, diol and methyl ether derivatives of dibenzo-14-crown-4. Implications for ligand and tecton design

Molecular structures are determined for six dibenzo-14-crown-4 derivatives that have one or two substituents on the central carbon(s) of the three-carbon bridge(s). The series of compounds includes three crown ether alcohols, one crown ether trans-diol, and two methoxy crown ether compounds. The crystal structures for these six crown ethers reveal that due to hydrogen-bonding and steric interactions, a hydroxy substituent is directed, at least partially, toward the crown ether cavity and an unusual intra- and intermolecular hydrogen bond network is formed between the hydroxy group protons and the ether oxygens of the crown ether ring. On the other hand, an ether group or a substituent with carbon as the first atom is oriented away from the polyether ring. The structure of sym-(methoxy)(methyl)dibenzo-14-crown-4 is markedly different from that of sym-(hydroxy)(methyl)dibenzo-14-crown-4 both in terms of the substituent orientation and very significant distortion from planarity of the four crown ether oxygens in the former. Support for an unusual conformation for sym-(methoxy)(methyl)dibenzo-14-crown-4 in solution is derived from 13C NMR measurements. Crown ether alcohols are hydrogen-bonding “tectons” that participate in strong, specific and directional intermolecular interactions.