Richard A. Sachleben

SURVEYING THE EXTRACTION OF CESIUM NITRATE BY 1,3-ALTERNATECALIX[4]ARENE CROWN-6 ETHERS IN 1,2-DICHLOROETHANE

ABSTRACT The extraction of cesium nitrate from a mixture of alkali metal nitrates by calix7lsqb;4]arene crown-6 ethers in 1,2-dichloroethane diluent has been surveyed at 25 °C. The results reveal that smaller substituents (but larger than C2,) at the phenolic positions of the calixarene opposite the crown ether increase both the extraction efficiency and the cesium selectivity. Benzo substituents on the crown ether tend to decrease extraction strength while increasing cesium-to-sodium selectivity. Conversely, a cyclohexano group on the crown ether has a negative impact on both extraction strength and selectivity.

Analysis of Equilibria in the Extraction of Cesium Nitrate by Calix[4]arene-bis(t-Octylbenzo- Crown-6) in 1,2-Dichloroethane

The extraction of CsNO3 by the highly lipophilic calixarene-crown ether calix[4]arene-bis(t-octylbenzo-crown-6) (CABOBC6) in 1,2-dichloroethane (1,2-DCE) at 25 °C has been shown to be consistent with the formation of both 1 : 1 and 2 : 1 metal : ligand species. Variation of the aqueous-phase CsNO concentration up to 1.0 M and variation of the organic-phase calixarene concentration up to 0.10∼M was modeled by the program SXLSQI. Formation of the organic-phase species CsBNO3 (B = calixarene) was confirmed as well as the organic-phase dissociation products CsB+ and NO3-. Good evidence for the 2 : 1 metal : ligand organic-phase species Cs2B(NO3)2 was also found, although the dissociation of nitrate from this complex was not observed. Binding of the second Cs+ cation by the ligand is approximately two orders of magnitude weaker than binding of the first Cs+ cation. The logarithm of the apparent partition ratio (log PB) of the calixarene between water and 1,2-DCE was found by 1H-NMR techniques to be > 5.1.

FUNDAMENTAL INVESTIGATIONS OF SEPARATIONS SCIENCE FOR RADIOACTIVE MATERIALS

ABSTRACT Fundamental investigations of solvent extraction and ion exchange separations of radioactive materials have been conducted within the National Laboratory system of the U. S. Department of Energy (and its predecessor agencies) for the past 50 years. Basic research conducted at Oak Ridge and Argonne National Laboratories has produced both high quality new science and important applications in nuclear technology. The present contribution is an attempt to summarize the most important scientific results arising from this research during the past 10 years, a time of great change in the nuclear separations field, and to suggest possible directions for the next stage of research and development in this field.

Dideoxygenated calix[4]arene crown-6 ethers enhanced selectivity for caesium over potassium and rubidium

Calix[4]arene crown-6 ethers derived from dideoxygenated calix[4]arene exhibit enhanced extraction selectivity for caesium over potassium; the crystal stucture of the uncomplexed calix[4]arene monobenzocrown-6 ether exists in the 1,3-alt conformation in the solid state.

Equilibrium aspects of the extraction of caesium nitrate by dicyclohexano-21-crown-7, dibenzo-21-crown-7 and bis-[tert-alkylbenzo]-21-crown-7 in 1,2-dichloroethane

The extraction of caesium nitrate has been measured for the crown ethers dibenzo-21-crown-7 (DB21C7), bis-[4(5),4′(5′)-tert-butylbenzo]-21-crown-7 [B(tBB)21C7], bis-[4,4′-tert-octylbenzo]-21-crown-7 [B(tOB)21C7] and dicyclohexano-21-crown-7 (DC21C7) in 1,2-dichloroethane at 25 °C. Variation of the aqueous caesium nitrate concentration up to 0.4 mol dm–3 and organic-phase crown ether concentration up to 0.025 mol dm–3 was modelled by the program SXLSQI. Formation of the species CsBNO3(B = crown ether) and partial dissociation to the ions CsB+ and NO3– in the organic phase satisfactorily account for the observed behaviour of the benzo crown ethers. However, evidence for both 1 : 1 and 1 : 2 metal : crown complexes was obtained for DC21C7. Differences in alkylation of the benzo groups did not produce substantial differences in the extraction behaviour of the three benzo crowns. By contrast, DC21C7 extracts CsNO3 much more strongly than the benzo crowns. Extraction constants are compared with constants available from previous studies of caesium extraction by related polyoxyethylene compounds.

Ring-size and substituent effects in the solvent extraction of alkali metal nitrates by crown ethers in 1,2-dichloroethane and 1-octanol

ABSTRACT The extraction of alkali metal nitrate salts by solutions of crown ethers in each of the two diluents 1,2-dichlorethane and 1-octanol has been surveyed. The crown ethers include 18-crown-6, 21-crown-7, and 24-crown-8 ethers bearing cyclohexano, benzo, t-alkylbenzo, and/or furano substitutents. The extraction efficiencies of the different crown ethers are examined in terms of ring-size, substituent, and solvent effects. Partition ratios for the crown ethers between water and either 1,2-dichloroethane or 1-octanol are discussed. The extraction selectivities, expressed as the separation factor for cesium over sodium, are examined in relation to crown ether structure.

Scanning tunneling microscopy of DNA : the chemical modification of gold surfaces for immobilization of DNA

We have investigated the coulostatic immobilization of DNA to a chemically modified gold surface. The chemical modification involves the covalent attachment of chemically polarizable groups by reaction of thiols and disulfides with clean gold surfaces. We have determined that chemically modified surfaces possessing pendant cationic groups bind DNA. In this paper we report the reliable and reproducible scanning tunneling microscopy (STM) imaging of DNA using a gold surface chemically modified with N,N,‐dimethyl‐2‐mercaptoethylamine and present the first STM images of an entire genetically functional DNA molecule, the circular plasmid pBS+.

A new highly selective calix[4]crown-6 fluorescent caesium probe

We have synthesized 1,3-alternate di-deoxygenated calix[4](9-cyano-10-anthrylmethyl)benzocrown-6, 1 and 1,3-alternate calix[4](9-cyano-10-anthrylmethyl)benzocrown-6, 2 as the second generation of caesium selective fluorescent probes; probe 1 shows 54-fold fluorescence enhancement upon caesium complexation while 2 exhibits only 8-fold enhancement; the selectivity ratios for 1 to complex caesium ion over potassium and rubidium (KCs/KK and KCs/KRb) are ca. 10 fold higher than those of 2 for the same ions; the observed selectivity ratios are consistent with data reported for other 1,3-alternate calix[4]crown-6 derivatives.

Prediction of Complexation Properties of Crown Ethers Using Computational Neural Networks

A computational neural network method was used for the prediction of stability constants of simple crown ether complexes. The essence of the method lies in the ability of a computer neural network to recognize the structure-property relationships in these host-guest systems. Testing of the computational method has demonstrated that stability constants of alkali metal cation (Na+, K+, Cs+)-crown ether complexes in methanol at 25 °C can be predicted with an average error of ±0.3 log K units based on the chemical structure of the crown ethers alone. The computer model was then used for the preliminary analysis of trends in the stabilities of the above complexes.

An efficient synthesis of lithium-selective extractants: Tertiary-alkyl-14-crown-4 ethers

Abstract Highly-substituted crown ethers can he synthesized efficiently from tertiary and neopentyl diols. Nonamethyl-14-crown-4 and methyl-didecalino-14-crown-4 ethers are lipophilic and highly soluble in organic solvents and function as efficient, lithium-selective extractants.