Water cation complexes with

Scheme 1). In addition to the determination of molar conductivity, magnetic moment, and IR spectra, the complex was characterized by X-ray structural analysis (4). This indicates that the cationic complex with neutral H2dapsox is symmetrically coordinated as a pentadentate ligand. Co(II) occurs in a PBP environment with water and methanol molecules in apical positions (Fig. 1). Although the side chains are symmetrically coordinated, Co-O(eq) bond lengths differ significantly. 

Neutral N-derivatized octadentate ligands based on cyclen (1,4,7,10-tetraazacy-clododecane) form tripositive cationic complexes with the trivalent lanthanides [116-124]. The N-substituted tetraamide derivatives have proven useful in understanding the relationship between the solution structure of the Ln3+ complex and its water exchange rate, a critical issue in attaining optimal relaxation efficiency of CA s [125-131]. 

Sodium and potassium cations are often encountered in the same biological environment and the transmembrane movements of both are required as part of an enzymatic pathway as in Na+, K+-ATPase. Under these circumstances it is essential that cation-specific channels are formed. What features of the channels contribute to the selectivity Earlier the preferred geometries of Na+and K+, sixfold octahedral and eightfold cubic respectively, were proposed as the main discriminatory factors. A computational analysis by Dudev and Lim [35] has considered the effect of coordinated water, number of available coordination sites in the channel walls, and the dipoles of the coordinating groups. The researchers investigated cation complexes with valinomycin and the protein KcsA, both K+-selective, and compared these with a non-selective NaK channel. 

A shallow layer of the cuprammonium form resin is placed in the filter crucible connected to a Buchner vacuum filtration assembly. Fhe resin is briefly contacted with a small quantity of 2.5 M (5 N) sulfuric acid which initiates elution of the cuprammonium ion. I he acid is filtered otf and the resin immediately rinsed with excess deionized water to remove all traces of acid. A sample of wetted beads are viewed under a microscope using transmitted light whereupon an inner unreacted blue core is seen to be surrounded by a transparent outer zone. This experiment is also a demonstration of a cation (Cu ) being sorbed emto a resin as a cationic complex with the ion originally present on the resin (NH4 ). 

Pickard, F.C., Dunn, M.E., Shields, G.C. Comparison of model chemistry and density functional theory thermochemical predictions with experiment for formation of ionic clusters of the ammonium cation complexed with water and ammonia atmospheric implications. J. Phys. Chem. A 2005,109(22), 4905-10. 

Finally, a few uptake curves with a minimum have been reported (cf. Fig, 4,7 (C)), chiefly for sorption of cations in the presence of anions that form very stable water soluble complexes with these cations. 

Adsorption of metal cations that form stable water soluble complexes with anions present in solution has been often interpreted in terms of formation of multiple surface species that differ in the number of anions coadsorbed with one adsorbed cation. When this number is greater than zero these species are termed ternary surface complexes. This can be interpreted as complexation of the adsorbed cation. This type of multiple surface species can be combined with the discussed above species that differ in the number of protons released per one specifically adsorbed cation. Less common (but also physically reasonable for ions that tend to form polymeric species in solution) is the idea of multiple polymeric surface species. For example, adsorption of cobalt on alumina was modeled in terms of formation of =A10Co2(OH)2 and =A10Co4(OH)5 surface species [106],... 

Use of an NH4OH solution can be effective If the contaminant has a tendency to form amino complexes, such as Cu (NH3)4 2, However, some cations such as Mg , Al and Pe+B will form Insoluble hydroxide complexes In basic solutions. Because of this, metals need to be removed by acidic solutions. Chelating agents are capable of forming water soluble complexes with many metal Ions. 

The group 2 metal ions are hard acids and are preferentially coordinated by hard bases (see Table 7.9). In this section we consider complexes formed in aqueous solution in which the metal centre is coordinated by O- and A -donor ligands to give cationic species. Two important ligands are [EDTA]" (see eq. 7.75) and [PsOjo] (see Fig. 15.19). Both form water-soluble complexes with Mg and the heavier metal ions, and are sequestering agents used in water-softening to remove Mg + and Ca ions. 

The aliphatic amino acids present more complicated structure changes upon hydration of the deprotonated complexes. [Pb (Pro-H) H20] is assigned a carboxylate structure with a proton transferred from the water, which can be viewed as a PbOH-l- complexed to a Pro carboxylate zwitterion (Scheme 7a) [83]. For the hydrated Pb " complexes of the other aliphatic amino acids (Ala, Val, Leu, and lieu), it was suggested that a structure type with intact carboxylate was most consistent with experiment, although not the lowest in energy. They suggest the structure shown in Scheme 7b, which, interestingly, amounts to a PbOH cation complexed with the intact (un-deprotonated) amino acid [83]. 

In addition, cationics are known for their formation of water-insoluble complexes with anionics. These complexes, which remain generally soluble in organic solvent, can be exploited in a variety of applications such as surface beneficiation or protection. 

The concentration of the surfactant were determined by titration with cetylbenzyldimethylammonium chloride, which forms water-insoluble complexes with the anionic surfactant. Potentiometric titrations were carried out with a Titroprocessor 672 (Metrohm, Switzerland) using a surfactant-sensitive electrode [7]. The cationic polymer was analyzed by polyelectrolyte titration with poly-(ethylensulfonate) (PES). The equivalence point of the polyelectrolyte complexation reaction was indicated either by streaming potential (PCD 2, Mutek GmbH, FRG) [8] or, for lower concentrations of the cationic polymer, by a color change due to the cooperative binding of a metachromic dye on the excess chromotrope titrant [9, 10]. Brilliant Yellow was used as dye indicator. 

Salts that are most effective in lowering the consolute temperature of polyoxyethylene in water have cations that tend to form strong crown-ether-like complexes with the polyoxyethylene and anions that are of low lyotropic number. Salts that tend to form cation complexes with polyoxyethylene and have anions with high lyotropic number show high ionic conductivity (24, 25) in the solid phase with poly(ethylene oxide). 

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