Ion inclusion

Many synthetic water-soluble polymers are easily analyzed by GPC. These include polyacrylamide,130 sodium poly(styrenesulfonate),131 and poly (2-vinyl pyridine).132 An important issue in aqueous GPC of synthetic polymers is the effect of solvent conditions on hydrodynamic volume and therefore retention. Ion inclusion and ion exclusion effects may also be important. In one interesting case, samples of polyacrylamide in which the amide side chain was partially hydrolyzed to generate a random copolymer of acrylic acid and acrylamide exhibited pH-dependent GPC fractionation.130 At a pH so low that the side chain would be expected to be protonated, hydrolyzed samples eluted later than untreated samples, perhaps suggesting intramolecular hydrogen bonding. At neutral pH, the hydrolyzed samples eluted earlier than untreated samples, an effect that was ascribed to enlargement... 

There are a number of different enthalpic interactions that can occur between polymer and packing, and in many cases multiple interactions can exist depending on the chemical structure of the polymer. Enthalpic interactions that are related to water-soluble polymers include ion exchange, ion inclusion, ion exclusion, hydrophobic interactions, and hydrogen bonding (12)- Other types of interactions commonly encountered in SEC, as well as in all other chromatographic separations, are dispersion (London) forces, dipole interactions (Keeson and Debye forces), and electron-donor-acceptor interactions (20). 

A third ionic effect may also influence the separation behavior, namely, ion inclusion. In this instance, small, charged molecules from the sample become concentrated in the gel pores and thus are eluted at a lower rate than expected. The described ionic effects are usually diminished by the addition of an electrolyte to the solvent. 

The conformational isomers of a cahxarene with four phenol residues are shown in Fig. 2.17. The isomers vary in terms of the orientations of their phenol groups (a) has a cone structure with all of the phenols pointing to the same direction (b) has a partial cone structure with one phenol pointing in a different direction to the others (c) has a 1,3-alternate structure with neighboring phenols pointing in opposite directions. These isomeric hosts have different selectivities for metal ion inclusion in the upper cavity and the lower cavity. Of course, changing the number of phenol residues alters the guest size appropriate for effective inclusion. 

In many cases, the steps involved in the production of the polymerisable complex are given in the literature for the non-vinyl-substituted ligand analogues. There is a sizeable literature on metal-containing polymers. Metal ion inclusion can affect... 

Ion inclusion Crown ethers (15-crown-6, 18-crown-6, etc.) Cyclodextrins... 

Lee, M-Y. et al. (1996) Influence of metal ion inclusion on the morphology of Gibbsite. Chemical Engineering Research and Design, 74, 739-743. 

As notified, the pecrrlarities are only briefly mentioned of ionic interactions among segments of macromolectrles that induce exterrsive coil expartsiotts, as well as between macromolectrles and packing that may lead to ion-exchange, ion-inclusion, and ion-exclusion processes. 

Even if the ionic sample solutions are prepared from the eluant, when the mobile phase consists of a salt solution there is often a peak near total permeation caused by the salt. This is believed to be a result of ion inclusion (30), in which the porous packing acts as a semipermeable membrane and an equilibrium is established such that the ion of the same charge as the excluded sample is forced into the pores, giving rise to a permeated peak. This can be problematical it may interfere with sample components, and in this case column selection may have to be adjusted to give more resolution for very small molecules. 

Because of the greater flexibility imparted them by the lack of head-to-tail covalent linkage, the carboxylic ionophores respond much more strongly to environmental forces such as local polarity than do the neutral macrocyclic ionophores. Upon leaving a membrane interface during the course of a catalytic transport cycle, an ionophore does not experience an abrupt change from a polar aqueous environment to an apolar hydrocarbon-like environment. The polarity boundary is rather diffuse. In order to properly evaluate the factors affecting carboxylic ionophore mediated transport, it is necessary to determine the effects of each of the microenvironments encountered within the membrane on the conformation of the ionophore and the stability of the ionophore-ion inclusion complex. 

George Gokel (Miami) gave a vibrant presentation on the metal ion inclusion complexes of lariat ethers. These synthetic receptors are being designed to parallel the properties of natural hosts such as valinomycin. In addition, the investigation reveals the diverse potential of such systems. A brief resume of the properties of the simpler lariat ethers, copiously illustrated by crystal... 

The latter appears to be applicable for cations displaying relatively low positive secondary ion yields. As this is noted for the transition metal ions inclusive but not limited to Cu+, Ag+, and Au (see Figure 3.26), this has been argued to be... 

LLUCH - The nonadditivity of the pair potentials can be responsible for the failure of Monte-Carlo and Molecular Dynamics simulations to give correct results in some studies of solvated ions. Inclusion of the polarisation term of the three-body correction is nowadays possible, although too costly in many cases. However, the most important source of error is often the lack of the charge transfer part of the many-body correction, whose incorporation is generally not evident. This is the case of the solvated proton. 

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