Polyvalent cation interactions

Ghelants and Precipitation Inhibitors vs Dispersants. Dispersants can inhibit crystal growth, but chelants, such as ethylenediaminetetraacetic acid [60-00-4] (EDTA), and pure precipitation inhibitors such as nitrilotris(methylene)tris-phosphonic acid [6419-19-8], commonly known as amino trismethylene phosphonic acid (ATMP), can be more effective under certain circumstances. Chelants can prevent scale by forming stoichiometric ring stmctures with polyvalent cations (such as calcium) to prevent interaction with anions (such as carbonate). Chelants interact... 

The nature of chemical coagulants are such that the macrofloc may possess certain charges for example lime (CaO), alum (A1203) and flocculating polyvalent cations cany positive charges, which interact with proteins. The interactions are simply illustrated in Figure 7.6. 

The strong interaction of polyvalent cations with polyions is well known to strongly alter the rheological properties of hydrolyzed polyacrylamide used in the tertiairy oil recovery process (1-4). The influence of divalent cations have already been studied(5-7) but the role played by the presence of small quantities of aluminium ions has never been investigated. 

Without considering the aomplexity of additional interactions of phytate and Ca2+ with other polyvalent cations, proteins, and fiber, Figures 3 and 4 predict that the progressive elimination of bran in Table II lowers the concentration of soluble Ca2+. This effect is especially pronounced in the bread, where part of the remaining phytate was hydrolyzed by yeast phytase during leavening (Table II). These conclusions and their implications... 

Formation of a complex between DNA and polycationic compounds appears to be the initial and quite possibly a critical parameter for nonviral gene delivery. Several synthetic vector systems, which are generally cationic in nature, including poly(lysines), cationic liposomes or various types of block copolymers and recently dendrimers, have been shown to self-assemble with plasmid DNA [13-15] [16]. Specific physicochemical properties manifested by these DNA complexes depend on the type of cationic agent used however, interesting patterns for such interactions are beginning to evolve [17, 18]. Under certain conditions, the interaction of DNA with polyvalent cations results in... 

Ion bridging is a specific type of Coulombic interaction involving the simultaneous binding of polyvalent cations (e.g., Ca, Fe, Cu ) to two different anionic functional groups on biopolymer molecules. This type of ionic interaction is commonly involved in associative self-assembly of biopolymers. As a consequence it is also an important contributory factor in the flocculation (via bridging or depletion) of colloidal particles or emulsion droplets in aqueous media containing adsorbed or non-adsorbed biopolymers (Dickinson and McClements, 1995). 

Alcoholates formed from polyvalent cations are more stable than those from monovalent cations. Charley and co-workers (12) have presented evidence that sugars and polyols interact with Fe3+ in mildly alkaline, aqueous solution to form somewhat stable, soluble chelates. Under similar conditions, D-fructose was shown to react with various polyvalent cations Fe3+, Fe2+, Mn2+, Co2+, Ni2+, Zn2+, Ca2+, Sr2+, and Ba2+. 

Rowatt and Williams [86] used an ion-exchange membrane (Bio-Rex) to remove polyvalent cations from phosvitin, a phosphorylated protein, before studying its interaction with aluminum in the presence of silicic acid. 

The interaction between A104-sites is weak indeed providing that the AIO4- sites are randomly distributed throughout the structure. It is also difficult to describe the coordination of a polyvalent cation to such widely spaced negative sites. 

All of the fluoroquinolones interact with polyvalent cations, and their systematic availability is reduced by 50% when they are co-administered with iron compounds ciprofloxacin and moxifloxacin (16) are more affected than gemifloxacin or levofloxacin (139). 

The interaction between NaY and Nb205 at 975K most probably does not lead to an exchange of Na cations by niobium cations in agreement with earlier studies concerning the solid-state exchange of other polyvalent cations [5,16]. However, in contrast to... 

The rheological properties of suspensions of montmorillonite depend on the presence of electrolytes and polyelectrolytes. " The face-to-face interactions (coagulation) occur in the presence of polyvalent cations. The edge-to-face interactions are strongest at low pH and in the presence of high concentrations of electrolytes. 

The mechanism responsible for these changes is not at present clear, but it does indicate some interaction of the cations with the ether oxygens, particularly for Na, Li, and polyvalent cations. One may conclude that in hydrated Nafion some portions of the side-chains are exposed to the electrostatic field of the cations, and hence that the side-chains penetrate to some extent into the ion clusters. 

A1r Separation Properties. Self-bound LSX adsorbents have an enhanced ability to selectively adsorb nitrogen from air. For thermodynamically driven adsorption processes, the quantity of a gas adsorbed by a zeolite at a given pressure and temperature Is a function of Its the affinity for the cationic adsorption sites as well as the quantity of sites available for Interaction. Electronic charge balance dictates that the LSX will have the maximum number of cationic sites available for direct Interaction with weakly Interacting adsorbates. The electric field within the zeolite cavity 1s dependent on both structure and the charge density of the extra-framework cation. Small polyvalent cations 1n the dehydrated/dehydroxylated state, especially calcium, show high selectivity for N2 from a1r.(l2)... 

Khodakov A Yu, Kustov L M, Kazansky V B and Williams C (1992), Infrared spectroscopic study of the interaction of cations in zeolites with simple molecular probes. Part 2. Adsorption and polarization of molecular hydrogen on zeolites containing polyvalent cations , J Chem Soc, Faraday Trans, 88, 3251. 

The first 4 structures of Table V show a remarkable identity of electron density peaks in the sodalite unit of polyvalent cation forms of faujasite. The authors have assigned the electron density to various atoms or water molecules, but if the data are transformed back into the number of electrons, they are consistent with 32 H20 in II and about 20-25 H20 in I, irrespective of the type of exchangeable polyvalent cation. From the strict viewpoint of the crystal structure, the only obvious argument against such an assignment of water molecules is that the I —03 distances of 2.5A are rather short. However, it is possible that extremely strong electrostatic interactions might permit such short distances. 

Microbial availability of organic matter for decomposition can be limited by organomineral interactions such as adsorption onto clay particles or complexation with polyvalent cations (Oades et al, 1988 Sollins et al, 1996). The incorporation of cationic amides into interlayers of clay minerals (Huang and Schnitzer,... 

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