Chelation ionic adsorption

The precise nature of the adhesion of the polyelectrolyte cements to untreated dental enamel and dentine has yet to be established. The earliest theory was due to Smith (1968) who speculated that the polyacrylate chains of the cement formed a chelate with calcium ions contained in the hydroxyapatite-like mineral in enamel and dentine. Beech (1973) considered this unhkely since it involved the formation of an eight-membered ring. Beech studied the interaction between PAA and hydroxyapatite, identified the formation of polyacrylate and so considered that adsorption was due to ionic attraction. 

Sasagawa, M. Nosaka, Y. 2001. Studies on the effects of Cd ion sources and chelating reagents on atomic layer CdS deposition by successive ionic layer adsorption and reaction (SILAR) method. Phys. Chem. Chem. Phys. 3 3371-3376. 

It is generally accepted that free ionic forms of heavy metals are generally more toxic to biota than chelated or precipitated forms. Several factors control metal bioavailability and, thus, toxicity in environmental samples. These factors include pH, redox potential, alkalinity, hardness, adsorption to suspended solids, cations and anions, as well as interaction with organic compounds (Kong et al., 1995). 

To address a diverse but related concern, the effect of chelation of adsorbed copper and iron species on the catalytic degradation of paper was investigated. The stability of paper containing copper and iron species adsorbed from ionic solutions was compared with that of paper containing the acetylacetonate chelates of these metals. Nonpolar acetylacetonate complexes of metals have no affinity for adsorption on paper. These copper and iron chelates are neither adsorbed nor chemically bonded to the paper matrix. 

Characteristic Physical adsorption Ionic binding Chelation Covalent bonding Cross-linking Physical entrapment Membrane entrapment Whole cells... 

Both chemical and physical methods may be used to immobilize biocatalysts while retaining or modifying their activity, selectivity, or stability. Among the techniques used for immobilization of enzymes are physical adsorption, covalent bonding, ionic binding, chelation, cross-linking, physical entrapment, microencapsulation, and retention in permselective membrane reactors. The mode of immobilization employed for a particular application depends not only on the specific choice of enzyme and support, but also on the constraints imposed by the microenvironment associated with the application. 

The extent of PHP adsorption is too low to be measured by loss from bulk solution. The catalysis of PHP hydrolysis by various metal oxides must come from their ability to chelate the ester and polarize the carbonyl C-O bond. Apparently Ti oxides and Fe oxides are capable of doing this, while Al oxides are not. Ionic strength effects on PHP surface-catalyzed hydrolysis are small electrostatics apparently have a minor role in ester chelation and subsequent attack by OH (Torrents and Stone, 1991). 

The mechanisms of sorption and/or the interaction of the solute with the mobile phase can be summarized as follows u, physical dissolution in the phase b, physical adsorption on the surface of the phase c, chemical reaction in the bulk phase or on its surface (acido-basic equilibrium, formation of coordination complexes or chelates, association of ionic pairs, exchange of ions, precipitation) d, steric exclusion (molecular sieving effect, gel permeation) e, bioaffinity association. 

The mechanism of complex formation of metals with chitosan is manifold and is probably dominated by different processes such as adsorption, ion exchange, and chelation under different conditions. In Fig. 15.6, it can be seen that the sorption capacity of chromium and cadmium is similar, while zinc has approximately double the affinity of these two metal ions for chitosan. Chitosan has almost three times the removal capacity for copper sorption than that for cadmium or chromium. These effects have proved complex to interpret but are a function of a number of parameters ionic radii ionic charge electron structure and possibly some hydration capacity of the metal ions solution pH and nature and availability of sites for chitosan. 

Oshita, K., Sabarudin, A., Takayanagi, T., Os-hima, M., and Motomizu, S. (2009.) Adsorption behavior of uranium(VI) and other ionic species on cross-linked chitosan resins modified with chelating moieties. Talanta. 79, 1031-1035. 

With this method of chromatography the actual process takes place on a thin layer of adsorbent fixed on a glass or aluminum plate, or on a plastic foil. The separation takes place on the basis of a partition mechanism, adsorption, or ion exchange, etc. Individual mechanisms are often combined or overlap, and it is not easy to determine the boundaries between individual processes. Basic forces playing a decisive role during the separation are ionic forces, further coordination forces, chelate formation, association of dipoles, hydrogen-bond formation, and dispersion (van der Waals forces). 

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